Merge remote-tracking branch 'origin/main' into rebranch

2025-12-21 12:14:44 +01:00 · 2021-01-08 16:12:47 -08:00
parent 6ceca8cd70 7e6536d983
commit 0988129fe1
34 changed files with 3185 additions and 1077 deletions
--- a/include/swift-c/DependencyScan/DependencyScan.h
+++ b/include/swift-c/DependencyScan/DependencyScan.h
@@ -0,0 +1,332 @@
+//===--- DependencyScan.h - C API for Swift Dependency Scanning ---*- C -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// This C API is primarily intended to serve as the Swift Driver's
+// dependency scanning facility (https://github.com/apple/swift-driver).
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_C_DEPENDENCY_SCAN_H
+#define SWIFT_C_DEPENDENCY_SCAN_H
+
+#include "DependencyScanMacros.h"
+#include <stdbool.h>
+#include <stddef.h>
+#include <stdint.h>
+
+/// The version constants for the SwiftDependencyScan C API.
+/// SWIFTSCAN_VERSION_MINOR should increase when there are API additions.
+/// SWIFTSCAN_VERSION_MAJOR is intended for "major" source/ABI breaking changes.
+#define SWIFTSCAN_VERSION_MAJOR 0
+#define SWIFTSCAN_VERSION_MINOR 1
+
+SWIFTSCAN_BEGIN_DECLS
+
+//=== Public Scanner Data Types -------------------------------------------===//
+
+/**
+ * A character string used to pass around dependency scan result metadata.
+ * Lifetime of the string is strictly tied to the object whose field it
+ * represents. When the owning object is released, string memory is freed.
+ */
+typedef struct {
+  const void *data;
+  size_t length;
+} swiftscan_string_ref_t;
+
+typedef struct {
+  swiftscan_string_ref_t *strings;
+  size_t count;
+} swiftscan_string_set_t;
+
+typedef enum {
+  SWIFTSCAN_DEPENDENCY_INFO_SWIFT_TEXTUAL = 0,
+  SWIFTSCAN_DEPENDENCY_INFO_SWIFT_BINARY = 1,
+  SWIFTSCAN_DEPENDENCY_INFO_SWIFT_PLACEHOLDER = 2,
+  SWIFTSCAN_DEPENDENCY_INFO_CLANG = 3
+} swiftscan_dependency_info_kind_t;
+
+/// Opaque container of the details specific to a given module dependency.
+typedef struct swiftscan_module_details_s *swiftscan_module_details_t;
+
+/// Opaque container to a dependency info of a given module.
+typedef struct swiftscan_dependency_info_s *swiftscan_dependency_info_t;
+
+/// Opaque container to an overall result of a dependency scan.
+typedef struct swiftscan_dependency_graph_s *swiftscan_dependency_graph_t;
+
+/// Opaque container to contain the result of a dependency prescan.
+typedef struct swiftscan_import_set_s *swiftscan_import_set_t;
+
+/// Full Dependency Graph (Result)
+typedef struct {
+  swiftscan_dependency_info_t *modules;
+  size_t count;
+} swiftscan_dependency_set_t;
+
+//=== Batch Scan Input Specification --------------------------------------===//
+
+/// Opaque container to a container of batch scan entry information.
+typedef struct swiftscan_batch_scan_entry_s *swiftscan_batch_scan_entry_t;
+
+typedef struct {
+  swiftscan_batch_scan_entry_t *modules;
+  size_t count;
+} swiftscan_batch_scan_input_t;
+
+typedef struct {
+  swiftscan_dependency_graph_t *results;
+  size_t count;
+} swiftscan_batch_scan_result_t;
+
+//=== Scanner Invocation Specification ------------------------------------===//
+
+/// Opaque container of all relevant context required to launch a dependency
+/// scan (command line arguments, working directory, etc.)
+typedef struct swiftscan_scan_invocation_s *swiftscan_scan_invocation_t;
+
+//=== Dependency Result Functions -----------------------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_dependency_graph_get_main_module_name(
+    swiftscan_dependency_graph_t result);
+
+SWIFTSCAN_PUBLIC swiftscan_dependency_set_t *
+swiftscan_dependency_graph_get_dependencies(
+    swiftscan_dependency_graph_t result);
+
+//=== Dependency Module Info Functions ------------------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_module_info_get_module_name(swiftscan_dependency_info_t info);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_module_info_get_module_path(swiftscan_dependency_info_t info);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_module_info_get_source_files(swiftscan_dependency_info_t info);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_module_info_get_direct_dependencies(swiftscan_dependency_info_t info);
+
+SWIFTSCAN_PUBLIC swiftscan_module_details_t
+swiftscan_module_info_get_details(swiftscan_dependency_info_t info);
+
+//=== Dependency Module Info Details Functions ----------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_dependency_info_kind_t
+swiftscan_module_detail_get_kind(swiftscan_module_details_t details);
+
+//=== Swift Textual Module Details query APIs -----------------------------===//
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_textual_detail_get_module_interface_path(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_compiled_module_candidates(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_textual_detail_get_bridging_header_path(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_bridging_source_files(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_bridging_module_dependencies(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_command_line(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_extra_pcm_args(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_textual_detail_get_context_hash(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC bool swiftscan_swift_textual_detail_get_is_framework(
+    swiftscan_module_details_t details);
+
+//=== Swift Binary Module Details query APIs ------------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_binary_detail_get_compiled_module_path(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_binary_detail_get_module_doc_path(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_binary_detail_get_module_source_info_path(
+    swiftscan_module_details_t details);
+
+//=== Swift Placeholder Module Details query APIs -------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_placeholder_detail_get_compiled_module_path(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_placeholder_detail_get_module_doc_path(
+    swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_swift_placeholder_detail_get_module_source_info_path(
+    swiftscan_module_details_t details);
+
+//=== Clang Module Details query APIs -------------------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_clang_detail_get_module_map_path(swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_clang_detail_get_context_hash(swiftscan_module_details_t details);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_clang_detail_get_command_line(swiftscan_module_details_t details);
+
+//=== Batch Scan Input Functions ------------------------------------------===//
+
+/// Create an \c swiftscan_batch_scan_input_t instance.
+/// The returned \c swiftscan_batch_scan_input_t is owned by the caller and must be disposed
+/// of using \c swiftscan_batch_scan_input_dispose .
+SWIFTSCAN_PUBLIC swiftscan_batch_scan_input_t *
+swiftscan_batch_scan_input_create();
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_input_set_modules(swiftscan_batch_scan_input_t *input,
+                                       int count,
+                                       swiftscan_batch_scan_entry_t *modules);
+
+//=== Batch Scan Entry Functions ------------------------------------------===//
+
+/// Create an \c swiftscan_batch_scan_entry_t instance.
+/// The returned \c swiftscan_batch_scan_entry_t is owned by the caller and must be disposed
+/// of using \c swiftscan_batch_scan_entry_dispose .
+SWIFTSCAN_PUBLIC swiftscan_batch_scan_entry_t
+swiftscan_batch_scan_entry_create();
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_entry_set_module_name(swiftscan_batch_scan_entry_t entry,
+                                           const char *name);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_entry_set_arguments(swiftscan_batch_scan_entry_t entry,
+                                         const char *arguments);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_entry_set_is_swift(swiftscan_batch_scan_entry_t entry,
+                                        bool is_swift);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_batch_scan_entry_get_module_name(swiftscan_batch_scan_entry_t entry);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_batch_scan_entry_get_arguments(swiftscan_batch_scan_entry_t entry);
+
+SWIFTSCAN_PUBLIC bool
+swiftscan_batch_scan_entry_get_is_swift(swiftscan_batch_scan_entry_t entry);
+
+//=== Prescan Result Functions --------------------------------------------===//
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_import_set_get_imports(swiftscan_import_set_t result);
+
+//=== Scanner Invocation Functions ----------------------------------------===//
+
+/// Create an \c swiftscan_scan_invocation_t instance.
+/// The returned \c swiftscan_scan_invocation_t is owned by the caller and must be disposed
+/// of using \c swiftscan_scan_invocation_dispose .
+SWIFTSCAN_PUBLIC swiftscan_scan_invocation_t swiftscan_scan_invocation_create();
+
+SWIFTSCAN_PUBLIC void swiftscan_scan_invocation_set_working_directory(
+    swiftscan_scan_invocation_t invocation, const char *working_directory);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_scan_invocation_set_argv(swiftscan_scan_invocation_t invocation,
+                                   int argc, const char **argv);
+
+SWIFTSCAN_PUBLIC swiftscan_string_ref_t
+swiftscan_scan_invocation_get_working_directory(
+    swiftscan_scan_invocation_t invocation);
+
+SWIFTSCAN_PUBLIC int
+swiftscan_scan_invocation_get_argc(swiftscan_scan_invocation_t invocation);
+
+SWIFTSCAN_PUBLIC swiftscan_string_set_t *
+swiftscan_scan_invocation_get_argv(swiftscan_scan_invocation_t invocation);
+
+//=== Cleanup Functions ---------------------------------------------------===//
+
+SWIFTSCAN_PUBLIC void
+swiftscan_dependency_graph_dispose(swiftscan_dependency_graph_t result);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_import_set_dispose(swiftscan_import_set_t result);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_entry_dispose(swiftscan_batch_scan_entry_t entry);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_input_dispose(swiftscan_batch_scan_input_t *input);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_batch_scan_result_dispose(swiftscan_batch_scan_result_t *result);
+
+SWIFTSCAN_PUBLIC void
+swiftscan_scan_invocation_dispose(swiftscan_scan_invocation_t invocation);
+
+//=== Scanner Functions ---------------------------------------------------===//
+
+/// Container of the configuration state and shared cache for dependency
+/// scanning.
+typedef void *swiftscan_scanner_t;
+
+/// Create an \c swiftscan_scanner_t instance.
+/// The returned \c swiftscan_scanner_t is owned by the caller and must be disposed
+/// of using \c swiftscan_scanner_dispose .
+SWIFTSCAN_PUBLIC swiftscan_scanner_t swiftscan_scanner_create(void);
+SWIFTSCAN_PUBLIC void swiftscan_scanner_dispose(swiftscan_scanner_t);
+
+/// Invoke a dependency scan using arguments specified in the \c
+/// swiftscan_scan_invocation_t argument. The returned \c
+/// swiftscan_dependency_graph_t is owned by the caller and must be disposed of
+/// using \c swiftscan_dependency_graph_dispose .
+SWIFTSCAN_PUBLIC swiftscan_dependency_graph_t swiftscan_dependency_graph_create(
+    swiftscan_scanner_t scanner, swiftscan_scan_invocation_t invocation);
+
+/// Invoke the scan for an input batch of modules specified in the
+/// \c swiftscan_batch_scan_input_t argument. The returned
+/// \c swiftscan_batch_scan_result_t is owned by the caller and must be disposed
+/// of using \c swiftscan_batch_scan_result_dispose .
+SWIFTSCAN_PUBLIC swiftscan_batch_scan_result_t *
+swiftscan_batch_scan_result_create(swiftscan_scanner_t scanner,
+                                   swiftscan_batch_scan_input_t *batch_input,
+                                   swiftscan_scan_invocation_t invocation);
+
+/// Invoke the import prescan using arguments specified in the \c
+/// swiftscan_scan_invocation_t argument. The returned \c swiftscan_import_set_t
+/// is owned by the caller and must be disposed of using \c
+/// swiftscan_import_set_dispose .
+SWIFTSCAN_PUBLIC swiftscan_import_set_t swiftscan_import_set_create(
+    swiftscan_scanner_t scanner, swiftscan_scan_invocation_t invocation);
+
+SWIFTSCAN_END_DECLS
+
+#endif // SWIFT_C_DEPENDENCY_SCAN_H
--- a/include/swift-c/DependencyScan/DependencyScanMacros.h
+++ b/include/swift-c/DependencyScan/DependencyScanMacros.h
@@ -0,0 +1,31 @@
+//===-- DependencyScanMacros.h - Swift Dependency Scanning Macros -*- C -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifdef  __cplusplus
+# define SWIFTSCAN_BEGIN_DECLS  extern "C" {
+# define SWIFTSCAN_END_DECLS    }
+#else
+# define SWIFTSCAN_BEGIN_DECLS
+# define SWIFTSCAN_END_DECLS
+#endif
+
+#ifndef SWIFTSCAN_PUBLIC
+# ifdef _WIN32
+#  ifdef libSwiftScan_EXPORTS
+#    define SWIFTSCAN_PUBLIC __declspec(dllexport)
+#  else
+#    define SWIFTSCAN_PUBLIC __declspec(dllimport)
+#  endif
+# else
+#  define SWIFTSCAN_PUBLIC
+# endif
+#endif
--- a/include/swift-c/DependencyScan/module.modulemap
+++ b/include/swift-c/DependencyScan/module.modulemap
@@ -0,0 +1,4 @@
+module _InternalSwiftScan {
+  header "DependencyScan.h"
+  link "_InternalSwiftScan"
+}
--- a/include/swift/DependencyScan/DependencyScanImpl.h
+++ b/include/swift/DependencyScan/DependencyScanImpl.h
@@ -0,0 +1,159 @@
+//===-------------- DependencyScanImpl.h - Swift Compiler -----------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Implementation details of the dependency scanning C API
+//
+//===----------------------------------------------------------------------===//
+#ifndef SWIFT_C_DEPENDENCY_SCAN_IMPL_H
+#define SWIFT_C_DEPENDENCY_SCAN_IMPL_H
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+
+namespace swift {
+namespace dependencies {
+class DependencyScanningTool;
+}
+} // namespace swift
+
+struct swiftscan_dependency_graph_s {
+  /// The name of the main module for this dependency graph (root node)
+  swiftscan_string_ref_t main_module_name;
+
+  /// The complete list of modules discovered
+  swiftscan_dependency_set_t *dependencies;
+};
+
+struct swiftscan_dependency_info_s {
+  /// The module's name
+  /// The format is:
+  /// `<module-kind>:<module-name>`
+  /// where `module-kind` is one of:
+  /// "swiftTextual"
+  /// "swiftBinary"
+  /// "swiftPlaceholder"
+  /// "clang""
+  swiftscan_string_ref_t module_name;
+
+  /// The path for the module.
+  swiftscan_string_ref_t module_path;
+
+  /// The source files used to build this module.
+  swiftscan_string_set_t *source_files;
+
+  /**
+   * The list of modules which this module direct depends on.
+   * The format is:
+   * `<module-kind>:<module-name>`
+   */
+  swiftscan_string_set_t *direct_dependencies;
+
+  /// Specific details of a particular kind of module.
+  swiftscan_module_details_t details;
+};
+
+/// Swift modules to be built from a module interface, may have a bridging
+/// header.
+typedef struct {
+  /// The module interface from which this module was built, if any.
+  swiftscan_string_ref_t module_interface_path;
+
+  /// The paths of potentially ready-to-use compiled modules for the interface.
+  swiftscan_string_set_t *compiled_module_candidates;
+
+  /// The bridging header, if any.
+  swiftscan_string_ref_t bridging_header_path;
+
+  /// The source files referenced by the bridging header.
+  swiftscan_string_set_t *bridging_source_files;
+
+  /// (Clang) modules on which the bridging header depends.
+  swiftscan_string_set_t *bridging_module_dependencies;
+
+  /// Options to the compile command required to build this module interface
+  swiftscan_string_set_t *command_line;
+
+  /// To build a PCM to be used by this Swift module, we need to append these
+  /// arguments to the generic PCM build arguments reported from the dependency
+  /// graph.
+  swiftscan_string_set_t *extra_pcm_args;
+
+  /// The hash value that will be used for the generated module
+  swiftscan_string_ref_t context_hash;
+
+  /// A flag to indicate whether or not this module is a framework.
+  bool is_framework;
+} swiftscan_swift_textual_details_t;
+
+/// Swift modules with only a binary module file.
+typedef struct {
+  /// The path to the pre-compiled binary module
+  swiftscan_string_ref_t compiled_module_path;
+
+  /// The path to the .swiftModuleDoc file.
+  swiftscan_string_ref_t module_doc_path;
+
+  /// The path to the .swiftSourceInfo file.
+  swiftscan_string_ref_t module_source_info_path;
+} swiftscan_swift_binary_details_t;
+
+/// Swift placeholder modules carry additional details that specify their
+/// module doc path and source info paths.
+typedef struct {
+  /// The path to the pre-compiled binary module
+  swiftscan_string_ref_t compiled_module_path;
+
+  /// The path to the .swiftModuleDoc file.
+  swiftscan_string_ref_t module_doc_path;
+
+  /// The path to the .swiftSourceInfo file.
+  swiftscan_string_ref_t module_source_info_path;
+} swiftscan_swift_placeholder_details_t;
+
+/// Clang modules are built from a module map file.
+typedef struct {
+  /// The path to the module map used to build this module.
+  swiftscan_string_ref_t module_map_path;
+
+  /// clang-generated context hash
+  swiftscan_string_ref_t context_hash;
+
+  /// Options to the compile command required to build this clang modulemap
+  swiftscan_string_set_t *command_line;
+} swiftscan_clang_details_t;
+
+struct swiftscan_module_details_s {
+  swiftscan_dependency_info_kind_t kind;
+  union {
+    swiftscan_swift_textual_details_t swift_textual_details;
+    swiftscan_swift_binary_details_t swift_binary_details;
+    swiftscan_swift_placeholder_details_t swift_placeholder_details;
+    swiftscan_clang_details_t clang_details;
+  };
+};
+
+struct swiftscan_batch_scan_entry_s {
+  swiftscan_string_ref_t module_name;
+  swiftscan_string_ref_t arguments;
+  bool is_swift;
+};
+
+struct swiftscan_import_set_s {
+  /// The complete list of imports discovered
+  swiftscan_string_set_t *imports;
+};
+
+struct swiftscan_scan_invocation_s {
+  swiftscan_string_ref_t working_directory;
+  swiftscan_string_set_t *argv;
+};
+
+#endif // SWIFT_C_DEPENDENCY_SCAN_IMPL_H
--- a/include/swift/DependencyScan/DependencyScanningTool.h
+++ b/include/swift/DependencyScan/DependencyScanningTool.h
@@ -0,0 +1,83 @@
+//===-------------- DependencyScanningTool.h - Swift Compiler -------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_DEPENDENCY_SCANNING_TOOL_H
+#define SWIFT_DEPENDENCY_SCANNING_TOOL_H
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+#include "swift/Frontend/Frontend.h"
+#include "swift/AST/ModuleDependencies.h"
+#include "swift/DependencyScan/ScanDependencies.h"
+#include "swift/Frontend/PrintingDiagnosticConsumer.h"
+#include "llvm/Support/Error.h"
+#include "llvm/Support/StringSaver.h"
+
+namespace swift {
+namespace dependencies {
+
+/// The high-level implementation of the dependency scanner that runs on
+/// an individual worker thread.
+class DependencyScanningTool {
+public:
+  /// Construct a dependency scanning tool.
+  DependencyScanningTool();
+
+  /// Collect the full module depenedency graph for the input, ignoring any
+  /// placeholder modules.
+  ///
+  /// \returns a \c StringError with the diagnostic output if errors
+  /// occurred, \c swiftscan_dependency_result_t otherwise.
+  llvm::ErrorOr<swiftscan_dependency_graph_t>
+  getDependencies(ArrayRef<const char *> Command,
+                  const llvm::StringSet<> &PlaceholderModules);
+
+  /// Collect the set of imports for the input module
+  ///
+  /// \returns a \c StringError with the diagnostic output if errors
+  /// occurred, \c swiftscan_prescan_result_t otherwise.
+  llvm::ErrorOr<swiftscan_import_set_t>
+  getImports(ArrayRef<const char *> Command);
+
+  /// Collect the full module depenedency graph for the input collection of
+  /// module names (batch inputs) and output them to the
+  /// BatchScanInput-specified output locations.
+  ///
+  /// \returns a \c std::error_code if errors occured during scan.
+  std::vector<llvm::ErrorOr<swiftscan_dependency_graph_t>>
+  getDependencies(ArrayRef<const char *> Command,
+                  const std::vector<BatchScanInput> &BatchInput,
+                  const llvm::StringSet<> &PlaceholderModules);
+
+private:
+  /// Using the specified invocation command, instantiate a CompilerInstance
+  /// that will be used for this scan.
+  llvm::ErrorOr<std::unique_ptr<CompilerInstance>>
+  initCompilerInstanceForScan(ArrayRef<const char *> Command);
+
+  /// Shared cache of module dependencies, re-used by individual full-scan queries
+  /// during the lifetime of this Tool.
+  std::unique_ptr<ModuleDependenciesCache> SharedCache;
+
+  /// Shared cache of compiler instances created during batch scanning, corresponding to
+  /// command-line options specified in the batch scan input entry.
+  std::unique_ptr<CompilerArgInstanceCacheMap> VersionedPCMInstanceCacheCache;
+
+  /// A shared consumer that, for now, just prints the encountered diagnostics.
+  PrintingDiagnosticConsumer PDC;
+  llvm::BumpPtrAllocator Alloc;
+  llvm::StringSaver Saver;
+};
+
+} // end namespace dependencies
+} // end namespace swift
+
+#endif // SWIFT_DEPENDENCY_SCANNING_TOOL_H
--- a/include/swift/DependencyScan/ScanDependencies.h
+++ b/include/swift/DependencyScan/ScanDependencies.h
@@ -0,0 +1,88 @@
+//===--- ScanDependencies.h -- Scans the dependencies of a module ------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef SWIFT_DEPENDENCY_SCANDEPENDENCIES_H
+#define SWIFT_DEPENDENCY_SCANDEPENDENCIES_H
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
+#include "llvm/Support/Error.h"
+
+namespace llvm {
+class StringSaver;
+}
+
+namespace swift {
+
+class CompilerInvocation;
+class CompilerInstance;
+class ModuleDependenciesCache;
+
+namespace dependencies {
+
+using CompilerArgInstanceCacheMap =
+    llvm::StringMap<std::pair<std::unique_ptr<CompilerInstance>,
+                              std::unique_ptr<ModuleDependenciesCache>>>;
+
+struct BatchScanInput {
+  llvm::StringRef moduleName;
+  llvm::StringRef arguments;
+  llvm::StringRef outputPath;
+  bool isSwift;
+};
+
+// MARK: FrontendTool dependency scanner entry points
+/// Scans the dependencies of the main module of \c instance and writes out
+/// the resulting JSON according to the instance's output parameters.
+bool scanDependencies(CompilerInstance &instance);
+
+/// Identify all imports in the translation unit's module.
+bool prescanDependencies(CompilerInstance &instance);
+
+/// Batch scan the dependencies for modules specified in \c batchInputFile.
+bool batchScanDependencies(CompilerInstance &instance,
+                           llvm::StringRef batchInputFile);
+
+/// Batch prescan the imports of modules specified in \c batchInputFile.
+bool batchPrescanDependencies(CompilerInstance &instance,
+                              llvm::StringRef batchInputFile);
+
+// MARK: Dependency scanning execution
+/// Scans the dependencies of the main module of \c instance.
+llvm::ErrorOr<swiftscan_dependency_graph_t>
+performModuleScan(CompilerInstance &instance,
+                  ModuleDependenciesCache &cache);
+
+/// Scans the main module of \c instance for all direct module imports
+llvm::ErrorOr<swiftscan_import_set_t>
+performModulePrescan(CompilerInstance &instance);
+
+/// Batch scan the dependencies for modules specified in \c batchInputFile.
+std::vector<llvm::ErrorOr<swiftscan_dependency_graph_t>>
+performBatchModuleScan(CompilerInstance &invocationInstance,
+                       ModuleDependenciesCache &invocationCache,
+                       CompilerArgInstanceCacheMap *versionedPCMInstanceCache,
+                       llvm::StringSaver &saver,
+                       const std::vector<BatchScanInput> &BatchInput);
+
+/// Batch prescan the imports of modules specified in \c batchInputFile.
+std::vector<llvm::ErrorOr<swiftscan_import_set_t>>
+performBatchModulePrescan(CompilerInstance &invocationInstance,
+                          ModuleDependenciesCache &cache,
+                          llvm::StringSaver &saver,
+                          const std::vector<BatchScanInput> &BatchInput);
+
+} // end namespace dependencies
+} // end namespace swift
+
+#endif
--- a/include/swift/DependencyScan/StringUtils.h
+++ b/include/swift/DependencyScan/StringUtils.h
@@ -0,0 +1,41 @@
+//===----- StringUtils.h - Managed C String Utility Functions -----*- C -*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+#include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/StringSet.h"
+#include <string>
+#include <vector>
+
+//=== Private Utility Functions--------------------------------------------===//
+namespace swift {
+namespace dependencies {
+
+/// Create null string
+swiftscan_string_ref_t create_null();
+
+/// Create a \c swiftscan_string_ref_t object from a nul-terminated C string.  New
+/// \c swiftscan_string_ref_t will contain a copy of \p string.
+swiftscan_string_ref_t create_clone(const char *string);
+
+/// Create an array of \c swiftscan_string_ref_t objects from a vector of C++ strings using the
+/// create_clone routine.
+swiftscan_string_set_t *create_set(const std::vector<std::string> &strings);
+
+/// Create an array of swiftscan_string_ref_t objects from an array of C strings using the
+/// create_clone routine.
+swiftscan_string_set_t *create_set(int count, const char **strings);
+
+/// Retrieve the character data associated with the given string.
+const char *get_C_string(swiftscan_string_ref_t string);
+}
+}
--- a/include/swift/Frontend/Frontend.h
+++ b/include/swift/Frontend/Frontend.h
@@ -491,8 +491,6 @@ public:
  DependencyTracker *getDependencyTracker() { return DepTracker.get(); }
  const DependencyTracker *getDependencyTracker() const { return DepTracker.get(); }

-  ModuleDependenciesCache *getModuleDependencyCache() { return ModDepCache.get(); }
-
  UnifiedStatsReporter *getStatsReporter() const { return Stats.get(); }

  /// Retrieve the main module containing the files being compiled.
@@ -558,7 +556,6 @@ private:
  bool setUpVirtualFileSystemOverlays();
  void setUpLLVMArguments();
  void setUpDiagnosticOptions();
-  void setUpModuleDependencyCacheIfNeeded();
  bool setUpModuleLoaders();
  bool setUpInputs();
  bool setUpASTContextIfNeeded();
--- a/include/swift/Frontend/FrontendOptions.h
+++ b/include/swift/Frontend/FrontendOptions.h
@@ -134,7 +134,6 @@ public:
    DumpPCM, ///< Dump information about a precompiled Clang module

    ScanDependencies,        ///< Scan dependencies of Swift source files
-    ScanClangDependencies,   ///< Scan dependencies of a Clang module
    PrintVersion,       ///< Print version information.
    PrintFeature,       ///< Print supported feature of this compiler
  };
--- a/include/swift/Option/Options.td
+++ b/include/swift/Option/Options.td
@@ -1121,10 +1121,6 @@ def scan_dependencies : Flag<["-"], "scan-dependencies">,
  HelpText<"Scan dependencies of the given Swift sources">, ModeOpt,
  Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;

-def scan_clang_dependencies : Flag<["-"], "scan-clang-dependencies">,
-  HelpText<"Scan dependencies of the given Clang module">, ModeOpt,
-  Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;
-
 def emit_supported_features : Flag<["-"], "emit-supported-features">,
  HelpText<"Emit a JSON file including all supported compiler features">, ModeOpt,
  Flags<[FrontendOption, NoInteractiveOption, DoesNotAffectIncrementalBuild]>;
--- a/lib/AST/ModuleLoader.cpp
+++ b/lib/AST/ModuleLoader.cpp
@@ -180,6 +180,7 @@ ModuleDependencies::collectCrossImportOverlayNames(ASTContext &ctx,
  llvm::StringMap<llvm::SmallSetVector<Identifier, 4>> result;
  // Mimic getModuleDefiningPath() for Swift and Clang module.
  if (auto *swiftDep = getAsSwiftTextualModule()) {
+    if (swiftDep->swiftInterfaceFile.hasValue()) {
      // Prefer interface path to binary module path if we have it.
      modulePath = swiftDep->swiftInterfaceFile;
      assert(modulePath.hasValue());
@@ -187,6 +188,11 @@ ModuleDependencies::collectCrossImportOverlayNames(ASTContext &ctx,
      if (llvm::sys::path::extension(parentDir) == ".swiftmodule") {
        modulePath = parentDir.str();
      }
+    } else {
+      // This must be a module compiled from source-code
+      assert(!swiftDep->sourceFiles.empty());
+      return result;
+    }
  } else if (auto *swiftBinaryDep = getAsSwiftBinaryModule()) {
    modulePath = swiftBinaryDep->compiledModulePath;
    assert(modulePath.hasValue());
--- a/lib/CMakeLists.txt
+++ b/lib/CMakeLists.txt
@@ -19,6 +19,7 @@ add_subdirectory(ASTSectionImporter)
 add_subdirectory(Basic)
 add_subdirectory(ClangImporter)
 add_subdirectory(Demangling)
+add_subdirectory(DependencyScan)
 add_subdirectory(Driver)
 add_subdirectory(Frontend)
 add_subdirectory(FrontendTool)
--- a/lib/DependencyScan/CMakeLists.txt
+++ b/lib/DependencyScan/CMakeLists.txt
@@ -0,0 +1,13 @@
+#set_swift_llvm_is_available()
+
+add_swift_host_library(swiftDependencyScan STATIC
+  DependencyScanningTool.cpp
+  ScanDependencies.cpp
+  StringUtils.cpp)
+
+target_link_libraries(swiftDependencyScan INTERFACE
+  clangBasic)
+
+target_link_libraries(swiftDependencyScan PRIVATE
+    swiftClangImporter
+    swiftFrontend)
--- a/lib/DependencyScan/DependencyScanningTool.cpp
+++ b/lib/DependencyScan/DependencyScanningTool.cpp
@@ -0,0 +1,124 @@
+//===------------ DependencyScanningTool.cpp - Swift Compiler -------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/DependencyScan/DependencyScanningTool.h"
+#include "swift/AST/DiagnosticEngine.h"
+#include "swift/AST/DiagnosticsFrontend.h"
+#include "swift/Basic/LLVMInitialize.h"
+#include "swift/DependencyScan/DependencyScanImpl.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/FileSystem.h"
+
+#include <sstream>
+
+namespace swift {
+namespace dependencies {
+
+DependencyScanningTool::DependencyScanningTool()
+    : SharedCache(std::make_unique<ModuleDependenciesCache>()),
+      VersionedPCMInstanceCacheCache(
+          std::make_unique<CompilerArgInstanceCacheMap>()),
+      PDC(), Alloc(), Saver(Alloc) {}
+
+llvm::ErrorOr<swiftscan_dependency_graph_t>
+DependencyScanningTool::getDependencies(
+    ArrayRef<const char *> Command,
+    const llvm::StringSet<> &PlaceholderModules) {
+  // The primary instance used to scan the query Swift source-code
+  auto InstanceOrErr = initCompilerInstanceForScan(Command);
+  if (std::error_code EC = InstanceOrErr.getError())
+    return EC;
+  auto Instance = std::move(*InstanceOrErr);
+
+  // Execute the scanning action, retreiving the in-memory result
+  auto DependenciesOrErr = performModuleScan(*Instance.get(), *SharedCache);
+  if (DependenciesOrErr.getError())
+    return std::make_error_code(std::errc::not_supported);
+  auto Dependencies = std::move(*DependenciesOrErr);
+
+  return Dependencies;
+}
+
+llvm::ErrorOr<swiftscan_import_set_t>
+DependencyScanningTool::getImports(ArrayRef<const char *> Command) {
+  // The primary instance used to scan the query Swift source-code
+  auto InstanceOrErr = initCompilerInstanceForScan(Command);
+  if (std::error_code EC = InstanceOrErr.getError())
+    return EC;
+  auto Instance = std::move(*InstanceOrErr);
+
+  // Execute the scanning action, retreiving the in-memory result
+  auto DependenciesOrErr = performModulePrescan(*Instance.get());
+  if (DependenciesOrErr.getError())
+    return std::make_error_code(std::errc::not_supported);
+  auto Dependencies = std::move(*DependenciesOrErr);
+
+  return Dependencies;
+}
+
+std::vector<llvm::ErrorOr<swiftscan_dependency_graph_t>>
+DependencyScanningTool::getDependencies(
+    ArrayRef<const char *> Command,
+    const std::vector<BatchScanInput> &BatchInput,
+    const llvm::StringSet<> &PlaceholderModules) {
+  // The primary instance used to scan Swift modules
+  auto InstanceOrErr = initCompilerInstanceForScan(Command);
+  if (std::error_code EC = InstanceOrErr.getError())
+    return std::vector<llvm::ErrorOr<swiftscan_dependency_graph_t>>(
+        BatchInput.size(), std::make_error_code(std::errc::invalid_argument));
+  auto Instance = std::move(*InstanceOrErr);
+
+  auto batchScanResults = performBatchModuleScan(
+      *Instance.get(), *SharedCache, VersionedPCMInstanceCacheCache.get(),
+      Saver, BatchInput);
+
+  return batchScanResults;
+}
+
+llvm::ErrorOr<std::unique_ptr<CompilerInstance>>
+DependencyScanningTool::initCompilerInstanceForScan(
+    ArrayRef<const char *> Command) {
+  // State unique to an individual scan
+  auto Instance = std::make_unique<CompilerInstance>();
+  Instance->addDiagnosticConsumer(&PDC);
+
+  // Basic error checking on the arguments
+  if (Command.empty()) {
+    Instance->getDiags().diagnose(SourceLoc(), diag::error_no_frontend_args);
+    return std::make_error_code(std::errc::invalid_argument);
+  }
+
+  CompilerInvocation Invocation;
+  SmallString<128> WorkingDirectory;
+  llvm::sys::fs::current_path(WorkingDirectory);
+
+  // Parse arguments.
+  std::string CommandString;
+  for (const auto *c : Command) {
+    CommandString.append(c);
+    CommandString.append(" ");
+  }
+  SmallVector<const char *, 4> Args;
+  llvm::cl::TokenizeGNUCommandLine(CommandString, Saver, Args);
+  if (Invocation.parseArgs(Args, Instance->getDiags())) {
+    return std::make_error_code(std::errc::invalid_argument);
+  }
+
+  // Setup the instance
+  Instance->setup(Invocation);
+  (void)Instance->getMainModule();
+
+  return Instance;
+}
+
+} // namespace dependencies
+} // namespace swift
--- a/lib/DependencyScan/ScanDependencies.cpp
+++ b/lib/DependencyScan/ScanDependencies.cpp
--- a/lib/DependencyScan/StringUtils.cpp
+++ b/lib/DependencyScan/StringUtils.cpp
@@ -0,0 +1,62 @@
+//===- StringUtils.cpp - Routines for manipulating swiftscan_string_ref_t -===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/DependencyScan/StringUtils.h"
+#include <string>
+#include <vector>
+
+namespace swift {
+namespace dependencies {
+
+swiftscan_string_ref_t create_null() {
+  swiftscan_string_ref_t str;
+  str.data = nullptr;
+  str.length = 0;
+  return str;
+}
+
+swiftscan_string_ref_t create_clone(const char *string) {
+  if (!string)
+    return create_null();
+
+  if (string[0] == '\0')
+    return create_null();
+
+  swiftscan_string_ref_t str;
+  str.data = strdup(string);
+  str.length = strlen(string);
+  return str;
+}
+
+swiftscan_string_set_t *create_set(const std::vector<std::string> &strings) {
+  swiftscan_string_set_t *set = new swiftscan_string_set_t;
+  set->count = strings.size();
+  set->strings = new swiftscan_string_ref_t[set->count];
+  for (unsigned SI = 0, SE = set->count; SI < SE; ++SI)
+    set->strings[SI] = create_clone(strings[SI].c_str());
+  return set;
+}
+
+swiftscan_string_set_t *create_set(int count, const char **strings) {
+  swiftscan_string_set_t *set = new swiftscan_string_set_t;
+  set->count = count;
+  set->strings = new swiftscan_string_ref_t[set->count];
+  for (unsigned SI = 0, SE = set->count; SI < SE; ++SI)
+    set->strings[SI] = create_clone(strings[SI]);
+  return set;
+}
+
+const char *get_C_string(swiftscan_string_ref_t string) {
+  return static_cast<const char *>(string.data);
+}
+} // namespace dependencies
+} // namespace swift
--- a/lib/Frontend/ArgsToFrontendOptionsConverter.cpp
+++ b/lib/Frontend/ArgsToFrontendOptionsConverter.cpp
@@ -379,8 +379,6 @@ ArgsToFrontendOptionsConverter::determineRequestedAction(const ArgList &args) {
    return FrontendOptions::ActionType::EmitImportedModules;
  if (Opt.matches(OPT_scan_dependencies))
    return FrontendOptions::ActionType::ScanDependencies;
-  if (Opt.matches(OPT_scan_clang_dependencies))
-    return FrontendOptions::ActionType::ScanClangDependencies;
  if (Opt.matches(OPT_parse))
    return FrontendOptions::ActionType::Parse;
  if (Opt.matches(OPT_resolve_imports))
--- a/lib/Frontend/Frontend.cpp
+++ b/lib/Frontend/Frontend.cpp
@@ -321,22 +321,11 @@ void CompilerInstance::setupDependencyTrackerIfNeeded() {
  DepTracker = std::make_unique<DependencyTracker>(*collectionMode);
 }

-void CompilerInstance::setUpModuleDependencyCacheIfNeeded() {
-  const auto &Invocation = getInvocation();
-  const auto &opts = Invocation.getFrontendOptions();
-  if (opts.RequestedAction == FrontendOptions::ActionType::ScanDependencies ||
-      opts.RequestedAction == FrontendOptions::ActionType::ScanClangDependencies) {
-    ModDepCache = std::make_unique<ModuleDependenciesCache>();
-  }
-}
-
 bool CompilerInstance::setup(const CompilerInvocation &Invok) {
  Invocation = Invok;

  setupDependencyTrackerIfNeeded();

-  setUpModuleDependencyCacheIfNeeded();
-
  // If initializing the overlay file system fails there's no sense in
  // continuing because the compiler will read the wrong files.
  if (setUpVirtualFileSystemOverlays())
--- a/lib/Frontend/FrontendOptions.cpp
+++ b/lib/Frontend/FrontendOptions.cpp
@@ -66,7 +66,6 @@ bool FrontendOptions::needsProperModuleName(ActionType action) {
  case ActionType::DumpTypeInfo:
  case ActionType::EmitPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
    return true;
  }
  llvm_unreachable("Unknown ActionType");
@@ -80,7 +79,6 @@ bool FrontendOptions::shouldActionOnlyParse(ActionType action) {
  case ActionType::DumpInterfaceHash:
  case ActionType::EmitImportedModules:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return true;
@@ -98,7 +96,6 @@ bool FrontendOptions::doesActionRequireSwiftStandardLibrary(ActionType action) {
  case ActionType::DumpInterfaceHash:
  case ActionType::EmitImportedModules:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::EmitPCH:
  case ActionType::EmitPCM:
@@ -146,7 +143,6 @@ bool FrontendOptions::doesActionRequireInputs(ActionType action) {
  case ActionType::DumpInterfaceHash:
  case ActionType::EmitImportedModules:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::EmitPCH:
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
@@ -191,7 +187,6 @@ bool FrontendOptions::doesActionPerformEndOfPipelineActions(ActionType action) {
  case ActionType::DumpInterfaceHash:
  case ActionType::EmitImportedModules:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::CompileModuleFromInterface:
  case ActionType::TypecheckModuleFromInterface:
  case ActionType::ResolveImports:
@@ -308,7 +303,6 @@ FrontendOptions::formatForPrincipalOutputFileForAction(ActionType action) {
    return TY_ClangModuleFile;

  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
    return TY_JSONDependencies;
  case ActionType::PrintFeature:
    return TY_JSONFeatures;
@@ -352,7 +346,6 @@ bool FrontendOptions::canActionEmitDependencies(ActionType action) {
  case ActionType::EmitImportedModules:
  case ActionType::EmitPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
    return true;
  }
  llvm_unreachable("unhandled action");
@@ -378,7 +371,6 @@ bool FrontendOptions::canActionEmitReferenceDependencies(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return false;
@@ -432,7 +424,6 @@ bool FrontendOptions::canActionEmitModuleSummary(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::Typecheck:
  case ActionType::MergeModules:
  case ActionType::EmitModuleOnly:
@@ -471,7 +462,6 @@ bool FrontendOptions::canActionEmitObjCHeader(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return false;
@@ -511,7 +501,6 @@ bool FrontendOptions::canActionEmitLoadedModuleTrace(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return false;
@@ -557,7 +546,6 @@ bool FrontendOptions::canActionEmitModule(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return false;
@@ -604,7 +592,6 @@ bool FrontendOptions::canActionEmitInterface(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintFeature:
    return false;
  case ActionType::Typecheck:
@@ -652,7 +639,6 @@ bool FrontendOptions::doesActionProduceOutput(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintFeature:
    return true;

@@ -700,7 +686,6 @@ bool FrontendOptions::doesActionProduceTextualOutput(ActionType action) {
  case ActionType::DumpTypeInfo:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return true;
@@ -728,7 +713,6 @@ bool FrontendOptions::doesActionGenerateSIL(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return false;
@@ -777,7 +761,6 @@ bool FrontendOptions::doesActionGenerateIR(ActionType action) {
  case ActionType::EmitPCM:
  case ActionType::DumpPCM:
  case ActionType::ScanDependencies:
-  case ActionType::ScanClangDependencies:
  case ActionType::PrintVersion:
  case ActionType::PrintFeature:
    return false;
--- a/lib/FrontendTool/CMakeLists.txt
+++ b/lib/FrontendTool/CMakeLists.txt
@@ -4,7 +4,6 @@ add_swift_host_library(swiftFrontendTool STATIC
  ImportedModules.cpp
  LoadedModuleTrace.cpp
  MakeStyleDependencies.cpp
-  ScanDependencies.cpp
  TBD.cpp)
 add_dependencies(swiftFrontendTool
  swift-syntax-generated-headers
@@ -15,6 +14,7 @@ target_link_libraries(swiftFrontendTool INTERFACE
 target_link_libraries(swiftFrontendTool PRIVATE
    swiftClangImporter
    swiftDemangling
+    swiftDependencyScan
    swiftFrontend
    swiftIDE
    swiftImmediate
--- a/lib/FrontendTool/FrontendTool.cpp
+++ b/lib/FrontendTool/FrontendTool.cpp
@@ -2,7 +2,7 @@
 //
 // This source file is part of the Swift.org open source project
 //
-// Copyright (c) 2014 - 2018 Apple Inc. and the Swift project authors
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
 // Licensed under Apache License v2.0 with Runtime Library Exception
 //
 // See https://swift.org/LICENSE.txt for license information
@@ -21,8 +21,8 @@
 //===----------------------------------------------------------------------===//

 #include "swift/FrontendTool/FrontendTool.h"
+#include "swift/DependencyScan/ScanDependencies.h"
 #include "Dependencies.h"
-#include "ScanDependencies.h"
 #include "TBD.h"
 #include "swift/Subsystems.h"
 #include "swift/AST/DiagnosticsFrontend.h"
@@ -1134,10 +1134,17 @@ withSemanticAnalysis(CompilerInstance &Instance, FrontendObserver *observer,
 static bool performScanDependencies(CompilerInstance &Instance) {
  auto batchScanInput =
      Instance.getASTContext().SearchPathOpts.BatchScanInputFilePath;
+  ModuleDependenciesCache SingleUseCache;
  if (batchScanInput.empty()) {
-    return scanDependencies(Instance);
+    if (Instance.getInvocation().getFrontendOptions().ImportPrescan)
+      return dependencies::prescanDependencies(Instance);
+    else
+      return dependencies::scanDependencies(Instance);
  } else {
-    return batchScanModuleDependencies(Instance, batchScanInput);
+    if (Instance.getInvocation().getFrontendOptions().ImportPrescan)
+      return dependencies::batchPrescanDependencies(Instance, batchScanInput);
+    else
+      return dependencies::batchScanDependencies(Instance, batchScanInput);
  }
 }

@@ -1224,8 +1231,6 @@ static bool performAction(CompilerInstance &Instance,
  // MARK: Dependency Scanning Actions
  case FrontendOptions::ActionType::ScanDependencies:
    return performScanDependencies(Instance);
-  case FrontendOptions::ActionType::ScanClangDependencies:
-    return scanClangDependencies(Instance);

  // MARK: General Compilation Actions
  case FrontendOptions::ActionType::Parse:
--- a/lib/FrontendTool/ScanDependencies.cpp
+++ b/lib/FrontendTool/ScanDependencies.cpp
@@ -1,969 +0,0 @@
-//===--- ScanDependencies.cpp -- Scans the dependencies of a module -------===//
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
-//
-//===----------------------------------------------------------------------===//
-
-#include "ScanDependencies.h"
-#include "swift/AST/ASTContext.h"
-#include "swift/AST/Decl.h"
-#include "swift/AST/DiagnosticEngine.h"
-#include "swift/AST/DiagnosticsFrontend.h"
-#include "swift/AST/Module.h"
-#include "swift/AST/ModuleDependencies.h"
-#include "swift/AST/ModuleLoader.h"
-#include "swift/AST/SourceFile.h"
-#include "swift/ClangImporter/ClangImporter.h"
-#include "swift/Basic/Defer.h"
-#include "swift/Basic/LLVM.h"
-#include "swift/Basic/STLExtras.h"
-#include "swift/Frontend/Frontend.h"
-#include "swift/Frontend/FrontendOptions.h"
-#include "swift/Frontend/ModuleInterfaceLoader.h"
-#include "swift/Strings.h"
-#include "clang/Basic/Module.h"
-#include "llvm/ADT/SetVector.h"
-#include "llvm/ADT/StringMap.h"
-#include "llvm/ADT/StringRef.h"
-#include "llvm/ADT/StringSet.h"
-#include "llvm/Support/CommandLine.h"
-#include "llvm/Support/FileSystem.h"
-#include "llvm/Support/StringSaver.h"
-#include "llvm/Support/YAMLTraits.h"
-#include "llvm/Support/YAMLParser.h"
-#include <set>
-
-using namespace swift;
-using namespace llvm::yaml;
-
-namespace {
-struct BatchScanInput {
-  StringRef moduleName;
-  StringRef arguments;
-  StringRef outputPath;
-  bool isSwift;
-};
-
-static std::string getScalaNodeText(Node *N) {
-  SmallString<32> Buffer;
-  return cast<ScalarNode>(N)->getValue(Buffer).str();
-}
-
-/// Parse an entry like this, where the "platforms" key-value pair is optional:
-///  {
-///     "swiftModuleName": "Foo",
-///     "arguments": "-target 10.15",
-///     "output": "../Foo.json"
-///  },
-static bool parseBatchInputEntries(ASTContext &Ctx, llvm::StringSaver &saver,
-                                   Node *Node, std::vector<BatchScanInput> &result) {
-  auto *SN = cast<SequenceNode>(Node);
-  if (!SN)
-    return true;
-  for (auto It = SN->begin(); It != SN->end(); ++It) {
-    auto *MN = cast<MappingNode>(&*It);
-    BatchScanInput entry;
-    Optional<std::set<int8_t>> Platforms;
-    for (auto &Pair: *MN) {
-      auto Key = getScalaNodeText(Pair.getKey());
-      auto* Value = Pair.getValue();
-      if (Key == "clangModuleName") {
-        entry.moduleName = saver.save(getScalaNodeText(Value));
-        entry.isSwift = false;
-      } else if (Key == "swiftModuleName") {
-        entry.moduleName = saver.save(getScalaNodeText(Value));
-        entry.isSwift = true;
-      } else if (Key == "arguments") {
-        entry.arguments = saver.save(getScalaNodeText(Value));
-      } else if (Key == "output") {
-        entry.outputPath = saver.save(getScalaNodeText(Value));
-      } else {
-        // Future proof.
-        continue;
-      }
-    }
-    if (entry.moduleName.empty())
-      return true;
-    if (entry.outputPath.empty())
-      return true;
-    result.emplace_back(std::move(entry));
-  }
-  return false;
-}
-
-static Optional<std::vector<BatchScanInput>>
-parseBatchScanInputFile(ASTContext &ctx, StringRef batchInputPath,
-                        llvm::StringSaver &saver) {
-  assert(!batchInputPath.empty());
-  namespace yaml = llvm::yaml;
-  std::vector<BatchScanInput> result;
-
-  // Load the input file.
-  llvm::ErrorOr<std::unique_ptr<llvm::MemoryBuffer>> FileBufOrErr =
-    llvm::MemoryBuffer::getFile(batchInputPath);
-  if (!FileBufOrErr) {
-    ctx.Diags.diagnose(SourceLoc(), diag::batch_scan_input_file_missing,
-                       batchInputPath);
-    return None;
-  }
-  StringRef Buffer = FileBufOrErr->get()->getBuffer();
-
-  // Use a new source manager instead of the one from ASTContext because we
-  // don't want the Json file to be persistent.
-  SourceManager SM;
-  yaml::Stream Stream(llvm::MemoryBufferRef(Buffer, batchInputPath),
-                      SM.getLLVMSourceMgr());
-  for (auto DI = Stream.begin(); DI != Stream.end(); ++ DI) {
-    assert(DI != Stream.end() && "Failed to read a document");
-    yaml::Node *N = DI->getRoot();
-    assert(N && "Failed to find a root");
-    if (parseBatchInputEntries(ctx, saver, N, result)) {
-      ctx.Diags.diagnose(SourceLoc(), diag::batch_scan_input_file_corrupted,
-                         batchInputPath);
-      return None;
-    }
-  }
-  return result;
-}
-}
-
-/// Find all of the imported Clang modules starting with the given module name.
-static void findAllImportedClangModules(ASTContext &ctx, StringRef moduleName,
-                                        ModuleDependenciesCache &cache,
-                                        std::vector<std::string> &allModules,
-                                        llvm::StringSet<> &knownModules) {
-  if (!knownModules.insert(moduleName).second)
-    return;
-  allModules.push_back(moduleName.str());
-
-  auto dependencies = cache.findDependencies(
-      moduleName, ModuleDependenciesKind::Clang);
-  if (!dependencies)
-    return;
-
-  for (const auto &dep : dependencies->getModuleDependencies()) {
-    findAllImportedClangModules(ctx, dep, cache, allModules, knownModules);
-  }
-}
-
-/// Resolve the direct dependencies of the given module.
-static std::vector<ModuleDependencyID> resolveDirectDependencies(
-    CompilerInstance &instance, ModuleDependencyID module,
-    ModuleDependenciesCache &cache,
-    InterfaceSubContextDelegate &ASTDelegate) {
-  auto &ctx = instance.getASTContext();
-  auto knownDependencies = *cache.findDependencies(module.first, module.second);
-  auto isSwift = knownDependencies.isSwiftTextualModule();
-
-  // Find the dependencies of every module this module directly depends on.
-  std::set<ModuleDependencyID> result;
-  for (auto dependsOn : knownDependencies.getModuleDependencies()) {
-    // Figure out what kind of module we need.
-    bool onlyClangModule = !isSwift || module.first == dependsOn;
-
-    // Retrieve the dependencies for this module.
-    if (auto found = ctx.getModuleDependencies(
-            dependsOn, onlyClangModule, cache, ASTDelegate)) {
-      result.insert({dependsOn, found->getKind()});
-    }
-  }
-
-  if (isSwift) {
-    // A record of all of the Clang modules referenced from this Swift module.
-    std::vector<std::string> allClangModules;
-    llvm::StringSet<> knownModules;
-
-    // If the Swift module has a bridging header, add those dependencies.
-    if (knownDependencies.getBridgingHeader()) {
-      auto clangImporter =
-          static_cast<ClangImporter *>(ctx.getClangModuleLoader());
-      if (!clangImporter->addBridgingHeaderDependencies(module.first, cache)) {
-        // Grab the updated module dependencies.
-        // FIXME: This is such a hack.
-        knownDependencies = *cache.findDependencies(module.first, module.second);
-
-        // Add the Clang modules referenced from the bridging header to the
-        // set of Clang modules we know about.
-        auto swiftDeps = knownDependencies.getAsSwiftTextualModule();
-        for (const auto &clangDep : swiftDeps->bridgingModuleDependencies) {
-          findAllImportedClangModules(ctx, clangDep, cache, allClangModules,
-                                      knownModules);
-        }
-      }
-    }
-
-    // Find all of the Clang modules this Swift module depends on.
-    for (const auto &dep : result) {
-      if (dep.second != ModuleDependenciesKind::Clang)
-        continue;
-
-      findAllImportedClangModules(ctx, dep.first, cache, allClangModules,
-                                  knownModules);
-    }
-
-    // Look for overlays for each of the Clang modules. The Swift module
-    // directly depends on these.
-    for (const auto &clangDep : allClangModules) {
-      if (auto found = ctx.getModuleDependencies(
-              clangDep, /*onlyClangModule=*/false, cache, ASTDelegate)) {
-        // ASTContext::getModuleDependencies returns dependencies for a module with a given name.
-        // This Clang module may have the same name as the Swift module we are resolving, so we
-        // need to make sure we don't add a dependency from a Swift module to itself.
-        if ((found->getKind() == ModuleDependenciesKind::SwiftTextual ||
-             found->getKind() == ModuleDependenciesKind::SwiftBinary ||
-             found->getKind() == ModuleDependenciesKind::SwiftPlaceholder) &&
-            clangDep != module.first) {
-          result.insert({clangDep, found->getKind()});
-        }
-      }
-    }
-  }
-  return std::vector<ModuleDependencyID>(result.begin(), result.end());
-}
-
-static void discoverCrosssImportOverlayDependencies(
-    CompilerInstance &instance, StringRef mainModuleName,
-    ArrayRef<ModuleDependencyID> allDependencies,
-    ModuleDependenciesCache &cache, InterfaceSubContextDelegate &ASTDelegate,
-    llvm::function_ref<void(ModuleDependencyID)> action) {
-  // Modules explicitly imported. Only these can be secondary module.
-  llvm::SetVector<Identifier> newOverlays;
-  for (auto dep: allDependencies) {
-    auto moduleName = dep.first;
-    auto dependencies = *cache.findDependencies(moduleName, dep.second);
-    // Collect a map from secondary module name to cross-import overlay names.
-    auto overlayMap = dependencies.collectCrossImportOverlayNames(
-      instance.getASTContext(), moduleName);
-    if (overlayMap.empty())
-      continue;
-    std::for_each(allDependencies.begin(), allDependencies.end(),
-                  [&](ModuleDependencyID Id) {
-      // check if any explicitly imported modules can serve as a secondary
-      // module, and add the overlay names to the dependencies list.
-      for (auto overlayName: overlayMap[Id.first]) {
-        if (std::find_if(allDependencies.begin(), allDependencies.end(),
-            [&](ModuleDependencyID Id) { return Id.first == overlayName.str(); })
-                == allDependencies.end()) {
-          newOverlays.insert(overlayName);
-        }
-      }
-    });
-  }
-  // No new cross-import overlays are found, return.
-  if (newOverlays.empty())
-    return;
-  // Construct a dummy main to resolve the newly discovered cross import overlays.
-  StringRef dummyMainName = "DummyMainModuleForResolvingCrossImportOverlays";
-  auto dummyMainDependencies = ModuleDependencies::forMainSwiftModule({});
-
-  // Update main module's dependencies to include these new overlays.
-  auto mainDep = *cache.findDependencies(mainModuleName,
-                                         ModuleDependenciesKind::SwiftTextual);
-  std::for_each(newOverlays.begin(), newOverlays.end(), [&](Identifier modName) {
-    dummyMainDependencies.addModuleDependency(modName.str());
-    mainDep.addModuleDependency(modName.str());
-  });
-  cache.updateDependencies({mainModuleName.str(),
-                            ModuleDependenciesKind::SwiftTextual}, mainDep);
-
-  // Record the dummy main module's direct dependencies. The dummy main module
-  // only directly depend on these newly discovered overlay modules.
-  cache.recordDependencies(dummyMainName, dummyMainDependencies);
-  llvm::SetVector<ModuleDependencyID, std::vector<ModuleDependencyID>,
-                  std::set<ModuleDependencyID>> allModules;
-
-  // Seed the all module list from the dummpy main module.
-  allModules.insert({dummyMainName.str(), dummyMainDependencies.getKind()});
-
-  // Explore the dependencies of every module.
-  for (unsigned currentModuleIdx = 0;
-       currentModuleIdx < allModules.size();
-       ++currentModuleIdx) {
-    auto module = allModules[currentModuleIdx];
-    auto discoveredModules = resolveDirectDependencies(instance, module,
-                                                       cache, ASTDelegate);
-    allModules.insert(discoveredModules.begin(), discoveredModules.end());
-  }
-  // Report any discovered modules to the clients, which include all overlays
-  // and their dependencies.
-  std::for_each(/* +1 to exclude dummy main*/allModules.begin() + 1,
-                allModules.end(), action);
-}
-
-/// Write a single JSON field.
-namespace {
-  template<typename T>
-  void writeJSONSingleField(llvm::raw_ostream &out,
-                            StringRef fieldName,
-                            const T &value,
-                            unsigned indentLevel,
-                            bool trailingComma);
-
-  /// Write a string value as JSON.
-  void writeJSONValue(llvm::raw_ostream &out,
-                      StringRef value,
-                      unsigned indentLevel) {
-    out << "\"";
-    out << value;
-    out << "\"";
-  }
-
-  /// Write a boolean value as JSON.
-  void writeJSONValue(llvm::raw_ostream &out,
-                      bool value,
-                      unsigned indentLevel) {
-    out.write_escaped(value ? "true" : "false");
-  }
-
-  /// Write a module identifier.
-  void writeJSONValue(llvm::raw_ostream &out,
-                      const ModuleDependencyID &module,
-                      unsigned indentLevel) {
-    out << "{\n";
-    std::string moduleKind;
-    if (module.second == ModuleDependenciesKind::SwiftTextual)
-      moduleKind = "swift";
-    else if (module.second == ModuleDependenciesKind::SwiftBinary)
-      // FIXME: rename to be consistent in the clients (swift-driver)
-      moduleKind = "swiftPrebuiltExternal";
-    else if (module.second == ModuleDependenciesKind::SwiftPlaceholder)
-      moduleKind = "swiftPlaceholder";
-    else
-      moduleKind = "clang";
-
-    writeJSONSingleField(
-        out,
-        moduleKind,
-        module.first,
-        indentLevel + 1,
-        /*trailingComma=*/false);
-
-    out.indent(indentLevel * 2);
-    out << "}";
-  }
-
-  /// Write a JSON array.
-  template<typename T>
-  void writeJSONValue(llvm::raw_ostream &out,
-                      ArrayRef<T> values,
-                      unsigned indentLevel) {
-    out << "[\n";
-
-    for (const auto &value: values) {
-
-      out.indent((indentLevel + 1) * 2);
-
-      writeJSONValue(out, value, indentLevel + 1);
-
-      if (&value != &values.back()) {
-        out << ",";
-      }
-      out << "\n";
-    }
-
-    out.indent(indentLevel * 2);
-    out << "]";
-  }
-
-  /// Write a JSON array.
-  template<typename T>
-  void writeJSONValue(llvm::raw_ostream &out,
-                      const std::vector<T> &values,
-                      unsigned indentLevel) {
-    writeJSONValue(out, llvm::makeArrayRef(values), indentLevel);
-  }
-
-  /// Write a single JSON field.
-  template<typename T>
-  void writeJSONSingleField(llvm::raw_ostream &out,
-                            StringRef fieldName,
-                            const T &value,
-                            unsigned indentLevel,
-                            bool trailingComma) {
-    out.indent(indentLevel * 2);
-    writeJSONValue(out, fieldName, indentLevel);
-    out << ": ";
-    writeJSONValue(out, value, indentLevel);
-    if (trailingComma)
-      out << ",";
-    out << "\n";
-  }
-}
-
-static void writePrescanJSON(llvm::raw_ostream &out,
-                             const ModuleDependencies &mainModuleDependencies) {
-  // Write out a JSON containing all main module imports.
-  out << "{\n";
-  SWIFT_DEFER {
-    out << "}\n";
-  };
-
-  writeJSONSingleField(out, "imports", mainModuleDependencies.getModuleDependencies(), 0, false);
-}
-
-static void writeJSON(llvm::raw_ostream &out,
-                      CompilerInstance &instance,
-                      ModuleDependenciesCache &cache,
-                      InterfaceSubContextDelegate &ASTDelegate,
-                      ArrayRef<ModuleDependencyID> allModules) {
-  // Write out a JSON description of all of the dependencies.
-  out << "{\n";
-  SWIFT_DEFER {
-    out << "}\n";
-  };
-
-  // Name of the main module.
-  writeJSONSingleField(out, "mainModuleName", allModules.front().first,
-                       /*indentLevel=*/1, /*trailingComma=*/true);
-
-  // Write out all of the modules.
-  out << "  \"modules\": [\n";
-  SWIFT_DEFER {
-    out << "  ]\n";
-  };
-  for (const auto &module : allModules) {
-    auto directDependencies = resolveDirectDependencies(
-      instance, ModuleDependencyID(module.first, module.second), cache,
-      ASTDelegate);
-
-    // Grab the completed module dependencies.
-    auto moduleDeps = *cache.findDependencies(module.first, module.second);
-
-    // The module we are describing.
-    out.indent(2 * 2);
-    writeJSONValue(out, module, 2);
-    out << ",\n";
-
-    out.indent(2 * 2);
-    out << "{\n";
-
-    auto swiftPlaceholderDeps = moduleDeps.getAsPlaceholderDependencyModule();
-    auto swiftTextualDeps = moduleDeps.getAsSwiftTextualModule();
-    auto swiftBinaryDeps = moduleDeps.getAsSwiftBinaryModule();
-    auto clangDeps = moduleDeps.getAsClangModule();
-
-    // Module path.
-    const char *modulePathSuffix =
-        moduleDeps.isSwiftModule() ? ".swiftmodule" : ".pcm";
-
-    std::string modulePath;
-    if (swiftPlaceholderDeps)
-      modulePath = swiftPlaceholderDeps->compiledModulePath;
-    else if (swiftBinaryDeps)
-      modulePath = swiftBinaryDeps->compiledModulePath;
-    else
-      modulePath = module.first + modulePathSuffix;
-
-    writeJSONSingleField(out, "modulePath", modulePath, /*indentLevel=*/3,
-                         /*trailingComma=*/true);
-
-    // Source files.
-    if (swiftTextualDeps) {
-      writeJSONSingleField(out, "sourceFiles", swiftTextualDeps->sourceFiles, 3,
-                           /*trailingComma=*/true);
-    } else if (clangDeps) {
-      writeJSONSingleField(out, "sourceFiles", clangDeps->fileDependencies, 3,
-                           /*trailingComma=*/true);
-    }
-
-    // Direct dependencies.
-    if (swiftTextualDeps || swiftBinaryDeps || clangDeps)
-      writeJSONSingleField(out, "directDependencies", directDependencies, 3,
-                           /*trailingComma=*/true);
-
-    // Swift and Clang-specific details.
-    out.indent(3 * 2);
-    out << "\"details\": {\n";
-    out.indent(4 * 2);
-    if (swiftTextualDeps) {
-      out << "\"swift\": {\n";
-
-      /// Swift interface file, if there is one. The main module, for example, will not have
-      /// an interface file.
-      if (swiftTextualDeps->swiftInterfaceFile) {
-        writeJSONSingleField(out, "moduleInterfacePath",
-                             *swiftTextualDeps->swiftInterfaceFile, 5,
-                             /*trailingComma=*/true);
-        writeJSONSingleField(out, "contextHash",
-                             swiftTextualDeps->contextHash, 5,
-                             /*trailingComma=*/true);
-        out.indent(5 * 2);
-        out << "\"commandLine\": [\n";
-        for (auto &arg :swiftTextualDeps->buildCommandLine) {
-
-          out.indent(6 * 2);
-          out << "\"" << arg << "\"";
-          if (&arg != &swiftTextualDeps->buildCommandLine.back())
-            out << ",";
-          out << "\n";
-        }
-        out.indent(5 * 2);
-        out << "],\n";
-        out.indent(5 * 2);
-        out << "\"compiledModuleCandidates\": [\n";
-        for (auto &candidate: swiftTextualDeps->compiledModuleCandidates) {
-          out.indent(6 * 2);
-          out << "\"" << candidate << "\"";
-          if (&candidate != &swiftTextualDeps->compiledModuleCandidates.back())
-            out << ",";
-          out << "\n";
-        }
-        out.indent(5 * 2);
-        out << "],\n";
-      }
-      writeJSONSingleField(
-          out, "isFramework",
-          swiftTextualDeps->isFramework, 5,
-          /*trailingComma=*/!swiftTextualDeps->extraPCMArgs.empty() ||
-                           swiftTextualDeps->bridgingHeaderFile.hasValue());
-      if (!swiftTextualDeps->extraPCMArgs.empty()) {
-        out.indent(5 * 2);
-        out << "\"extraPcmArgs\": [\n";
-        for (auto &arg : swiftTextualDeps->extraPCMArgs) {
-          out.indent(6 * 2);
-          out << "\"" << arg << "\"";
-          if (&arg != &swiftTextualDeps->extraPCMArgs.back())
-            out << ",";
-          out << "\n";
-        }
-        out.indent(5 * 2);
-        out << (swiftTextualDeps->bridgingHeaderFile.hasValue() ? "],\n" : "]\n");
-      }
-      /// Bridging header and its source file dependencies, if any.
-      if (swiftTextualDeps->bridgingHeaderFile) {
-        out.indent(5 * 2);
-        out << "\"bridgingHeader\": {\n";
-        writeJSONSingleField(out, "path", *swiftTextualDeps->bridgingHeaderFile, 6,
-                             /*trailingComma=*/true);
-        writeJSONSingleField(out, "sourceFiles", swiftTextualDeps->bridgingSourceFiles,
-                             6,
-                             /*trailingComma=*/true);
-        writeJSONSingleField(out, "moduleDependencies",
-                             swiftTextualDeps->bridgingModuleDependencies, 6,
-                             /*trailingComma=*/false);
-        out.indent(5 * 2);
-        out << "}\n";
-      }
-    } else if (swiftPlaceholderDeps) {
-      out << "\"swiftPlaceholder\": {\n";
-
-      // Module doc file
-      if (swiftPlaceholderDeps->moduleDocPath != "")
-        writeJSONSingleField(out, "moduleDocPath",
-                             swiftPlaceholderDeps->moduleDocPath,
-                             /*indentLevel=*/5,
-                             /*trailingComma=*/true);
-
-      // Module Source Info file
-      if (swiftPlaceholderDeps->moduleDocPath != "")
-        writeJSONSingleField(out, "moduleSourceInfoPath",
-                             swiftPlaceholderDeps->sourceInfoPath,
-                             /*indentLevel=*/5,
-                             /*trailingComma=*/false);
-    } else if (swiftBinaryDeps) {
-      out << "\"swiftPrebuiltExternal\": {\n";
-      assert(swiftBinaryDeps->compiledModulePath != "" &&
-             "Expected .swiftmodule for a Binary Swift Module Dependency.");
-      writeJSONSingleField(out, "compiledModulePath",
-                           swiftBinaryDeps->compiledModulePath,
-                           /*indentLevel=*/5,
-                           /*trailingComma=*/true);
-      // Module doc file
-      if (swiftBinaryDeps->moduleDocPath != "")
-        writeJSONSingleField(out, "moduleDocPath",
-                             swiftBinaryDeps->moduleDocPath,
-                             /*indentLevel=*/5,
-                             /*trailingComma=*/true);
-
-      // Module Source Info file
-      if (swiftBinaryDeps->moduleDocPath != "")
-        writeJSONSingleField(out, "moduleSourceInfoPath",
-                             swiftBinaryDeps->sourceInfoPath,
-                             /*indentLevel=*/5,
-                             /*trailingComma=*/false);
-    } else {
-      out << "\"clang\": {\n";
-
-      // Module map file.
-      writeJSONSingleField(out, "moduleMapPath", clangDeps->moduleMapFile, 5,
-                           /*trailingComma=*/true);
-
-      // Context hash.
-      writeJSONSingleField(out, "contextHash", clangDeps->contextHash, 5,
-                           /*trailingComma=*/true);
-
-      // Command line.
-      writeJSONSingleField(out, "commandLine", clangDeps->nonPathCommandLine, 5,
-                           /*trailingComma=*/false);
-    }
-
-    out.indent(4 * 2);
-    out << "}\n";
-    out.indent(3 * 2);
-    out << "}\n";
-    out.indent(2 * 2);
-    out << "}";
-
-    if (&module != &allModules.back())
-      out << ",";
-    out << "\n";
-  }
-}
-
-static bool diagnoseCycle(CompilerInstance &instance,
-                          ModuleDependenciesCache &cache,
-                          ModuleDependencyID mainId,
-                          InterfaceSubContextDelegate &astDelegate) {
-  llvm::SetVector<ModuleDependencyID, std::vector<ModuleDependencyID>,
-                  std::set<ModuleDependencyID>> openSet;
-  llvm::SetVector<ModuleDependencyID, std::vector<ModuleDependencyID>,
-                  std::set<ModuleDependencyID>> closeSet;
-  // Start from the main module.
-  openSet.insert(mainId);
-  while(!openSet.empty()) {
-    auto &lastOpen = openSet.back();
-    auto beforeSize = openSet.size();
-    for (auto dep: resolveDirectDependencies(instance, lastOpen, cache,
-                                             astDelegate)) {
-      if (closeSet.count(dep))
-        continue;
-      if (openSet.insert(dep)) {
-        break;
-      } else {
-        // Find a cycle, diagnose.
-        auto startIt = std::find(openSet.begin(), openSet.end(), dep);
-        assert(startIt != openSet.end());
-        llvm::SmallString<64> buffer;
-        for (auto it = startIt; it != openSet.end(); ++ it) {
-          buffer.append(it->first);
-          buffer.append((it->second == ModuleDependenciesKind::SwiftTextual ||
-                         it->second == ModuleDependenciesKind::SwiftBinary)?
-                        ".swiftmodule": ".pcm");
-          buffer.append(" -> ");
-        }
-        buffer.append(startIt->first);
-        buffer.append((startIt->second == ModuleDependenciesKind::SwiftTextual ||
-                       startIt->second == ModuleDependenciesKind::SwiftBinary)?
-                      ".swiftmodule": ".pcm");
-        instance.getASTContext().Diags.diagnose(SourceLoc(),
-                                                diag::scanner_find_cycle,
-                                                buffer.str());
-        return true;
-      }
-    }
-    // No new node added. We can close this node
-    if (openSet.size() == beforeSize) {
-      closeSet.insert(openSet.back());
-      openSet.pop_back();
-    } else {
-      assert(openSet.size() == beforeSize + 1);
-    }
-  }
-  assert(openSet.empty());
-  return false;
-}
-
-static bool scanModuleDependencies(CompilerInstance &instance,
-                                   StringRef moduleName,
-                                   bool isClang,
-                                   StringRef outputPath) {
-  ASTContext &ctx = instance.getASTContext();
-  auto &FEOpts = instance.getInvocation().getFrontendOptions();
-  ModuleInterfaceLoaderOptions LoaderOpts(FEOpts);
-  auto ModuleCachePath = getModuleCachePathFromClang(ctx
-    .getClangModuleLoader()->getClangInstance());
-
-  llvm::SetVector<ModuleDependencyID, std::vector<ModuleDependencyID>,
-                  std::set<ModuleDependencyID>> allModules;
-  // Retrieve the instance's module dependency cache.
-  ModuleDependenciesCache *cache = instance.getModuleDependencyCache();
-  assert(cache &&
-         "Dependency Scanner expected a ModuleDependenciesCache on a compiler instance.");
-  InterfaceSubContextDelegateImpl ASTDelegate(ctx.SourceMgr, ctx.Diags,
-                                              ctx.SearchPathOpts, ctx.LangOpts,
-                                              ctx.ClangImporterOpts,
-                                              LoaderOpts,
-                                              /*buildModuleCacheDirIfAbsent*/false,
-                                              ModuleCachePath,
-                                              FEOpts.PrebuiltModuleCachePath,
-                                              FEOpts.SerializeModuleInterfaceDependencyHashes,
-                                              FEOpts.shouldTrackSystemDependencies());
-  std::error_code EC;
-  llvm::raw_fd_ostream out(outputPath, EC, llvm::sys::fs::F_None);
-  Optional<ModuleDependencies> rootDeps;
-  if (isClang) {
-    // Loading the clang module using Clang importer.
-    // This action will populate the cache with the main module's dependencies.
-    rootDeps = ctx.getModuleDependencies(moduleName, /*IsClang*/true, *cache,
-                                         ASTDelegate);
-  } else {
-    // Loading the swift module's dependencies.
-    rootDeps = ctx.getSwiftModuleDependencies(moduleName, *cache, ASTDelegate);
-  }
-  if (!rootDeps.hasValue()) {
-    // We cannot find the clang module, abort.
-    return true;
-  }
-  // Add the main module.
-  allModules.insert({moduleName.str(), isClang ? ModuleDependenciesKind::Clang:
-                                        ModuleDependenciesKind::SwiftTextual});
-
-  // Output module prescan.
-  if (FEOpts.ImportPrescan) {
-    writePrescanJSON(out, rootDeps.getValue());
-    return false;
-  }
-
-  // Explore the dependencies of every module.
-  for (unsigned currentModuleIdx = 0;
-       currentModuleIdx < allModules.size();
-       ++currentModuleIdx) {
-    auto module = allModules[currentModuleIdx];
-    auto discoveredModules =
-        resolveDirectDependencies(instance, module, *cache, ASTDelegate);
-    allModules.insert(discoveredModules.begin(), discoveredModules.end());
-  }
-  // Write out the JSON description.
-  writeJSON(out, instance, *cache, ASTDelegate, allModules.getArrayRef());
-  return false;
-}
-
-bool swift::scanClangDependencies(CompilerInstance &instance) {
-  return scanModuleDependencies(instance,
-                                instance.getMainModule()->getNameStr(),
-                                /*isClang*/true,
-                                instance.getInvocation().getFrontendOptions()
-                                  .InputsAndOutputs.getSingleOutputFilename());
-}
-
-bool swift::batchScanModuleDependencies(CompilerInstance &instance,
-                                        llvm::StringRef batchInputFile) {
-  const CompilerInvocation &invok = instance.getInvocation();
-
-  (void)instance.getMainModule();
-  llvm::BumpPtrAllocator alloc;
-  llvm::StringSaver saver(alloc);
-  auto results = parseBatchScanInputFile(instance.getASTContext(),
-                                         batchInputFile, saver);
-  if (!results.hasValue())
-    return true;
-  auto &diags = instance.getDiags();
-  ForwardingDiagnosticConsumer FDC(diags);
-  // Keep track of all compiler instances we have created.
-  llvm::StringMap<std::unique_ptr<CompilerInstance>> subInstanceMap;
-  for (auto &entry: *results) {
-    CompilerInstance *pInstance = nullptr;
-    if (entry.arguments.empty()) {
-      // Use the compiler's instance if no arguments are specified.
-      pInstance = &instance;
-    } else if (subInstanceMap.count(entry.arguments)) {
-      // Use the previously created instance if we've seen the arguments before.
-      pInstance = subInstanceMap[entry.arguments].get();
-    } else {
-      // Create a new instance by the arguments and save it in the map.
-      pInstance = subInstanceMap.insert({entry.arguments,
-        std::make_unique<CompilerInstance>()}).first->getValue().get();
-      SmallVector<const char*, 4> args;
-      llvm::cl::TokenizeGNUCommandLine(entry.arguments, saver, args);
-      CompilerInvocation subInvok = invok;
-      pInstance->addDiagnosticConsumer(&FDC);
-      if (subInvok.parseArgs(args, diags)) {
-        instance.getDiags().diagnose(SourceLoc(), diag::scanner_arguments_invalid,
-                                     entry.arguments);
-        return true;
-      }
-      if (pInstance->setup(subInvok)) {
-        instance.getDiags().diagnose(SourceLoc(), diag::scanner_arguments_invalid,
-                                     entry.arguments);
-        return true;
-      }
-    }
-    assert(pInstance);
-    // Scan using the chosen compiler instance.
-    if (scanModuleDependencies(*pInstance, entry.moduleName, !entry.isSwift,
-                               entry.outputPath)) {
-      return true;
-    }
-  }
-  return false;
-}
-
-bool swift::scanDependencies(CompilerInstance &instance) {
-  ASTContext &Context = instance.getASTContext();
-  ModuleDecl *mainModule = instance.getMainModule();
-  const CompilerInvocation &invocation = instance.getInvocation();
-  const FrontendOptions &opts = invocation.getFrontendOptions();
-
-  std::string path = opts.InputsAndOutputs.getSingleOutputFilename();
-  std::error_code EC;
-  llvm::raw_fd_ostream out(path, EC, llvm::sys::fs::F_None);
-
-  if (out.has_error() || EC) {
-    Context.Diags.diagnose(SourceLoc(), diag::error_opening_output, path,
-                           EC.message());
-    out.clear_error();
-    return true;
-  }
-
-  // Main module file name.
-  auto newExt = file_types::getExtension(file_types::TY_SwiftModuleFile);
-  llvm::SmallString<32> mainModulePath = mainModule->getName().str();
-  llvm::sys::path::replace_extension(mainModulePath, newExt);
-
-  std::string apinotesVer = (llvm::Twine("-fapinotes-swift-version=")
-    + instance.getASTContext().LangOpts.EffectiveLanguageVersion
-      .asAPINotesVersionString()).str();
-  // Compute the dependencies of the main module.
-  auto mainDependencies =
-    ModuleDependencies::forMainSwiftModule({
-      // ExtraPCMArgs
-      "-Xcc", "-target", "-Xcc", instance.getASTContext().LangOpts.Target.str(),
-      "-Xcc", apinotesVer
-    });
-
-  // Compute Implicit dependencies of the main module
-  {
-    llvm::StringSet<> alreadyAddedModules;
-    for (auto fileUnit : mainModule->getFiles()) {
-      auto sf = dyn_cast<SourceFile>(fileUnit);
-      if (!sf)
-        continue;
-
-      mainDependencies.addModuleDependencies(*sf, alreadyAddedModules);
-    }
-
-    const auto &importInfo = mainModule->getImplicitImportInfo();
-
-    // Swift standard library.
-    switch (importInfo.StdlibKind) {
-    case ImplicitStdlibKind::None:
-    case ImplicitStdlibKind::Builtin:
-      break;
-
-    case ImplicitStdlibKind::Stdlib:
-      mainDependencies.addModuleDependency("Swift", &alreadyAddedModules);
-      break;
-    }
-
-    // Add any implicit module names.
-    for (const auto &import : importInfo.AdditionalUnloadedImports) {
-      mainDependencies.addModuleDependency(import.module.getModulePath(), &alreadyAddedModules);
-    }
-
-    // Already-loaded, implicitly imported module names.
-    for (const auto &import : importInfo.AdditionalImports) {
-      mainDependencies.addModuleDependency(import.module.importedModule->getNameStr(), &alreadyAddedModules);
-    }
-
-    // Add the bridging header.
-    if (!importInfo.BridgingHeaderPath.empty()) {
-      mainDependencies.addBridgingHeader(importInfo.BridgingHeaderPath);
-    }
-
-    // If we are to import the underlying Clang module of the same name,
-    // add a dependency with the same name to trigger the search.
-    if (importInfo.ShouldImportUnderlyingModule) {
-      mainDependencies.addModuleDependency(mainModule->getName().str(),
-                                           &alreadyAddedModules);
-    }
-  }
-
-  // If import-prescan is specified, discover and serialize main module dependencies only and exit.
-  if (opts.ImportPrescan) {
-    writePrescanJSON(out, mainDependencies);
-    // This process succeeds regardless of whether any errors occurred.
-    // FIXME: We shouldn't need this, but it's masking bugs in our scanning
-    // logic where we don't create a fresh context when scanning Swift interfaces
-    // that includes their own command-line flags.
-    Context.Diags.resetHadAnyError();
-    return false;
-  }
-
-  // Add the main module.
-  StringRef mainModuleName = mainModule->getNameStr();
-  llvm::SetVector<ModuleDependencyID, std::vector<ModuleDependencyID>,
-                  std::set<ModuleDependencyID>> allModules;
-  
-  allModules.insert({mainModuleName.str(), mainDependencies.getKind()});
-
-  // Retrieve the instance's module dependency cache.
-  ModuleDependenciesCache *cache = instance.getModuleDependencyCache();
-  assert(cache &&
-         "Dependency Scanner expected a ModuleDependenciesCache on a compiler instance.");
-  cache->recordDependencies(mainModuleName, std::move(mainDependencies));
-
-  auto &ctx = instance.getASTContext();
-  auto ModuleCachePath = getModuleCachePathFromClang(ctx
-    .getClangModuleLoader()->getClangInstance());
-  auto &FEOpts = instance.getInvocation().getFrontendOptions();
-  ModuleInterfaceLoaderOptions LoaderOpts(FEOpts);
-  InterfaceSubContextDelegateImpl ASTDelegate(ctx.SourceMgr, ctx.Diags,
-                                              ctx.SearchPathOpts, ctx.LangOpts,
-                                              ctx.ClangImporterOpts,
-                                              LoaderOpts,
-                                              /*buildModuleCacheDirIfAbsent*/false,
-                                              ModuleCachePath,
-                                              FEOpts.PrebuiltModuleCachePath,
-                                              FEOpts.SerializeModuleInterfaceDependencyHashes,
-                                              FEOpts.shouldTrackSystemDependencies());
-
-  // Explore the dependencies of every module.
-  for (unsigned currentModuleIdx = 0;
-       currentModuleIdx < allModules.size();
-       ++currentModuleIdx) {
-    auto module = allModules[currentModuleIdx];
-    auto discoveredModules =
-        resolveDirectDependencies(instance, module, *cache, ASTDelegate);
-    allModules.insert(discoveredModules.begin(), discoveredModules.end());
-  }
-
-  // We have all explicit imports now, resolve cross import overlays.
-  discoverCrosssImportOverlayDependencies(instance, mainModuleName,
-      /*All transitive dependencies*/allModules.getArrayRef().slice(1), *cache,
-      ASTDelegate, [&](ModuleDependencyID id) {
-    allModules.insert(id);
-  });
-
-  // Dignose cycle in dependency graph.
-  if (diagnoseCycle(instance, *cache, /*MainModule*/allModules.front(), ASTDelegate))
-    return true;
-
-  // Write out the JSON description.
-  writeJSON(out, instance, *cache, ASTDelegate, allModules.getArrayRef());
-
-  // Update the dependency tracker.
-  if (auto depTracker = instance.getDependencyTracker()) {
-    for (auto module : allModules) {
-      auto deps = cache->findDependencies(module.first, module.second);
-      if (!deps)
-        continue;
-
-      if (auto swiftDeps = deps->getAsSwiftTextualModule()) {
-        if (auto swiftInterfaceFile = swiftDeps->swiftInterfaceFile)
-          depTracker->addDependency(*swiftInterfaceFile, /*IsSystem=*/false);
-        for (const auto &sourceFile : swiftDeps->sourceFiles)
-          depTracker->addDependency(sourceFile, /*IsSystem=*/false);
-        for (const auto &bridgingSourceFile : swiftDeps->bridgingSourceFiles)
-          depTracker->addDependency(bridgingSourceFile, /*IsSystem=*/false);
-      } else if (auto clangDeps = deps->getAsClangModule()) {
-        if (!clangDeps->moduleMapFile.empty())
-          depTracker->addDependency(clangDeps->moduleMapFile, /*IsSystem=*/false);
-        for (const auto &sourceFile : clangDeps->fileDependencies)
-          depTracker->addDependency(sourceFile, /*IsSystem=*/false);
-      }
-    }
-  }
-
-  // This process succeeds regardless of whether any errors occurred.
-  // FIXME: We shouldn't need this, but it's masking bugs in our scanning
-  // logic where we don't create a fresh context when scanning Swift interfaces
-  // that includes their own command-line flags.
-  Context.Diags.resetHadAnyError();
-  return false;
-}
--- a/lib/FrontendTool/ScanDependencies.h
+++ b/lib/FrontendTool/ScanDependencies.h
@@ -1,36 +0,0 @@
-//===--- ScanDependencies.h -- Scans the dependencies of a module ------===//
-//
-// This source file is part of the Swift.org open source project
-//
-// Copyright (c) 2014 - 2017 Apple Inc. and the Swift project authors
-// Licensed under Apache License v2.0 with Runtime Library Exception
-//
-// See https://swift.org/LICENSE.txt for license information
-// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
-//
-//===----------------------------------------------------------------------===//
-
-#ifndef SWIFT_FRONTENDTOOL_SCANDEPENDENCIES_H
-#define SWIFT_FRONTENDTOOL_SCANDEPENDENCIES_H
-
-#include "llvm/ADT/StringRef.h"
-
-namespace swift {
-
-class CompilerInvocation;
-class CompilerInstance;
-
-/// Batch scan the dependencies for modules specified in \c batchInputFile.
-bool batchScanModuleDependencies(CompilerInstance &instance,
-                                 llvm::StringRef batchInputFile);
-
-/// Scans the dependencies of the main module of \c instance.
-bool scanDependencies(CompilerInstance &instance);
-
-/// Scans the dependencies of the underlying clang module of the main module
-/// of \c instance.
-bool scanClangDependencies(CompilerInstance &instance);
-
-} // end namespace swift
-
-#endif
--- a/test/ScanDependencies/module_deps_clang_only.swift
+++ b/test/ScanDependencies/module_deps_clang_only.swift
@@ -1,21 +0,0 @@
-// RUN: %empty-directory(%t)
-// RUN: mkdir -p %t/clang-module-cache
-// RUN: %target-swift-frontend -scan-clang-dependencies -module-cache-path %t/clang-module-cache %s -o %t/deps.json -I %S/Inputs/CHeaders -I %S/Inputs/Swift -emit-dependencies -emit-dependencies-path %t/deps.d -import-objc-header %S/Inputs/CHeaders/Bridging.h -swift-version 4 -disable-implicit-swift-modules -module-name C
-
-// Check the contents of the JSON output
-// RUN: %FileCheck %s < %t/deps.json
-
-// CHECK:  	    "mainModuleName": "C",
-// CHECK-NEXT:  "modules": [
-// CHECK-NEXT:  {
-// CHECK-NEXT:    "clang": "C"
-// CHECK-NEXT:  },
-// CHECK-NEXT:  {
-// CHECK-NEXT:    "modulePath": "C.pcm",
-// CHECK-NEXT:    "sourceFiles": [
-
-
-// CHECK:       "directDependencies": [
-// CHECK-NEXT:  {
-// CHECK-NEXT:    "clang": "B"
-// CHECK-NEXT:  }
--- a/tools/CMakeLists.txt
+++ b/tools/CMakeLists.txt
@@ -28,6 +28,7 @@ add_swift_tool_subdirectory(swift-llvm-opt)
 add_swift_tool_subdirectory(swift-api-digester)
 add_swift_tool_subdirectory(swift-ast-script)
 add_swift_tool_subdirectory(swift-refactor)
+add_swift_tool_subdirectory(libSwiftScan)
 if(SWIFT_BUILD_SYNTAXPARSERLIB)
  add_swift_tool_subdirectory(libSwiftSyntaxParser)
  if(SWIFT_INCLUDE_TESTS)
--- a/tools/libSwiftScan/CMakeLists.txt
+++ b/tools/libSwiftScan/CMakeLists.txt
@@ -0,0 +1,28 @@
+include(SwiftWindowsSupport)
+swift_swap_compiler_if_needed("libSwiftScan")
+
+# Use an 'internal' name, this is primarily intended for SwiftDriver to import.
+set(SWIFT_SCAN_LIB_NAME "_InternalSwiftScan")
+
+set(LLVM_EXPORTED_SYMBOL_FILE
+    ${CMAKE_CURRENT_SOURCE_DIR}/libSwiftScan.exports)
+
+add_swift_host_library(libSwiftScan SHARED
+  libSwiftScan.cpp
+  c-include-check.c)
+
+add_dependencies(libSwiftScan
+  clang
+  swiftDependencyScan)
+
+target_link_libraries(libSwiftScan PRIVATE
+    swiftDependencyScan)
+
+set_target_properties(libSwiftScan
+    PROPERTIES
+    OUTPUT_NAME ${SWIFT_SCAN_LIB_NAME})
+
+add_llvm_symbol_exports(libSwiftScan ${LLVM_EXPORTED_SYMBOL_FILE})
+
+# Adds -dead_strip option
+add_link_opts(libSwiftScan)
--- a/tools/libSwiftScan/c-include-check.c
+++ b/tools/libSwiftScan/c-include-check.c
@@ -0,0 +1,5 @@
+// This file serves as a sanity check to ensure that the header is parseable
+// from C and that no C++ code has sneaked in.
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+typedef swiftscan_module_details_t _check_module_details_exists;
--- a/tools/libSwiftScan/libSwiftScan.cpp
+++ b/tools/libSwiftScan/libSwiftScan.cpp
@@ -0,0 +1,463 @@
+//===------------ DependencyScanImpl.cpp - Swift Compiler -----------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+//
+// Implementation of the dependency scanning C API
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift/Basic/LLVMInitialize.h"
+#include "swift/DependencyScan/DependencyScanImpl.h"
+#include "swift/DependencyScan/DependencyScanningTool.h"
+#include "swift/DependencyScan/StringUtils.h"
+
+using namespace swift::dependencies;
+
+DEFINE_SIMPLE_CONVERSION_FUNCTIONS(DependencyScanningTool, swiftscan_scanner_t);
+
+//=== Private Cleanup Functions -------------------------------------------===//
+
+/// Free the given string.
+void swiftscan_string_dispose(swiftscan_string_ref_t string) {
+  if (string.data)
+    free(const_cast<void *>(string.data));
+}
+
+/// Free the given string set.
+void swiftscan_string_set_dispose(swiftscan_string_set_t *set) {
+  for (unsigned SI = 0, SE = set->count; SI < SE; ++SI)
+    swiftscan_string_dispose(set->strings[SI]);
+  delete[] set->strings;
+  delete set;
+}
+
+void swiftscan_dependency_info_details_dispose(
+    swiftscan_module_details_t details) {
+  swiftscan_module_details_s *details_impl = details;
+  switch (details_impl->kind) {
+  case SWIFTSCAN_DEPENDENCY_INFO_SWIFT_TEXTUAL:
+    swiftscan_string_dispose(
+        details_impl->swift_textual_details.module_interface_path);
+    swiftscan_string_set_dispose(
+        details_impl->swift_textual_details.compiled_module_candidates);
+    swiftscan_string_dispose(
+        details_impl->swift_textual_details.bridging_header_path);
+    swiftscan_string_set_dispose(
+        details_impl->swift_textual_details.bridging_source_files);
+    swiftscan_string_set_dispose(
+        details_impl->swift_textual_details.bridging_module_dependencies);
+    swiftscan_string_set_dispose(
+        details_impl->swift_textual_details.command_line);
+    swiftscan_string_set_dispose(
+        details_impl->swift_textual_details.extra_pcm_args);
+    swiftscan_string_dispose(details_impl->swift_textual_details.context_hash);
+    break;
+  case SWIFTSCAN_DEPENDENCY_INFO_SWIFT_BINARY:
+    swiftscan_string_dispose(
+        details_impl->swift_binary_details.compiled_module_path);
+    swiftscan_string_dispose(
+        details_impl->swift_binary_details.module_doc_path);
+    swiftscan_string_dispose(
+        details_impl->swift_binary_details.module_source_info_path);
+    break;
+  case SWIFTSCAN_DEPENDENCY_INFO_SWIFT_PLACEHOLDER:
+    swiftscan_string_dispose(
+        details_impl->swift_placeholder_details.compiled_module_path);
+    swiftscan_string_dispose(
+        details_impl->swift_placeholder_details.module_doc_path);
+    swiftscan_string_dispose(
+        details_impl->swift_placeholder_details.module_source_info_path);
+    break;
+  case SWIFTSCAN_DEPENDENCY_INFO_CLANG:
+    swiftscan_string_dispose(details_impl->clang_details.module_map_path);
+    swiftscan_string_dispose(details_impl->clang_details.context_hash);
+    swiftscan_string_set_dispose(details_impl->clang_details.command_line);
+    break;
+  }
+  delete details_impl;
+}
+
+void swiftscan_dependency_info_dispose(swiftscan_dependency_info_t info) {
+  swiftscan_string_dispose(info->module_name);
+  swiftscan_string_dispose(info->module_path);
+  swiftscan_string_set_dispose(info->source_files);
+  swiftscan_string_set_dispose(info->direct_dependencies);
+  swiftscan_dependency_info_details_dispose(info->details);
+  delete info;
+}
+
+void swiftscan_dependency_set_dispose(swiftscan_dependency_set_t *set) {
+  for (size_t i = 0; i < set->count; ++i) {
+    swiftscan_dependency_info_dispose(set->modules[i]);
+  }
+  delete[] set->modules;
+  delete set;
+}
+
+//=== Scanner Functions ---------------------------------------------------===//
+
+swiftscan_scanner_t swiftscan_scanner_create(void) {
+  INITIALIZE_LLVM();
+  return wrap(new DependencyScanningTool());
+}
+
+void swiftscan_scanner_dispose(swiftscan_scanner_t c_scanner) {
+  delete unwrap(c_scanner);
+}
+
+swiftscan_dependency_graph_t
+swiftscan_dependency_graph_create(swiftscan_scanner_t scanner,
+                                  swiftscan_scan_invocation_t invocation) {
+  DependencyScanningTool *ScanningTool = unwrap(scanner);
+  int argc = invocation->argv->count;
+  std::vector<const char *> Compilation;
+  for (int i = 0; i < argc; ++i)
+    Compilation.push_back(get_C_string(invocation->argv->strings[i]));
+
+  // Execute the scan and bridge the result
+  auto ScanResult = ScanningTool->getDependencies(Compilation, {});
+  if (ScanResult.getError())
+    return nullptr;
+  auto DependencyGraph = std::move(*ScanResult);
+  return DependencyGraph;
+}
+
+swiftscan_batch_scan_result_t *
+swiftscan_batch_scan_result_create(swiftscan_scanner_t scanner,
+                                   swiftscan_batch_scan_input_t *batch_input,
+                                   swiftscan_scan_invocation_t invocation) {
+  DependencyScanningTool *ScanningTool = unwrap(scanner);
+  int argc = invocation->argv->count;
+  std::vector<const char *> Compilation;
+  for (int i = 0; i < argc; ++i)
+    Compilation.push_back(get_C_string(invocation->argv->strings[i]));
+
+  std::vector<BatchScanInput> BatchInput;
+  for (size_t i = 0; i < batch_input->count; ++i) {
+    swiftscan_batch_scan_entry_s *Entry = batch_input->modules[i];
+    BatchInput.push_back({get_C_string(Entry->module_name),
+                          get_C_string(Entry->arguments),
+                          /*outputPath*/ "", Entry->is_swift});
+  }
+
+  // Execute the scan and bridge the result
+  auto BatchScanResult =
+      ScanningTool->getDependencies(Compilation, BatchInput, {});
+  swiftscan_batch_scan_result_t *Result = new swiftscan_batch_scan_result_t;
+  auto ResultGraphs = new swiftscan_dependency_graph_t[BatchScanResult.size()];
+  for (size_t i = 0; i < BatchScanResult.size(); ++i) {
+    auto &ResultOrErr = BatchScanResult[i];
+    if (ResultOrErr.getError()) {
+      ResultGraphs[i] = nullptr;
+      continue;
+    }
+
+    ResultGraphs[i] = ResultOrErr.get();
+  }
+
+  Result->results = ResultGraphs;
+  Result->count = BatchScanResult.size();
+  return Result;
+}
+
+swiftscan_import_set_t
+swiftscan_import_set_create(swiftscan_scanner_t scanner,
+                            swiftscan_scan_invocation_t invocation) {
+  DependencyScanningTool *ScanningTool = unwrap(scanner);
+  int argc = invocation->argv->count;
+  std::vector<const char *> Compilation;
+  for (int i = 0; i < argc; ++i)
+    Compilation.push_back(get_C_string(invocation->argv->strings[i]));
+
+  // Execute the scan and bridge the result
+  auto PreScanResult = ScanningTool->getImports(Compilation);
+  if (PreScanResult.getError())
+    return nullptr;
+  auto ImportSet = std::move(*PreScanResult);
+  return ImportSet;
+}
+
+//=== Dependency Result Functions -----------------------------------------===//
+
+swiftscan_string_ref_t swiftscan_dependency_graph_get_main_module_name(
+    swiftscan_dependency_graph_t result) {
+  return result->main_module_name;
+}
+
+swiftscan_dependency_set_t *swiftscan_dependency_graph_get_dependencies(
+    swiftscan_dependency_graph_t result) {
+  return result->dependencies;
+}
+
+//=== Module Dependency Info query APIs -----------------------------------===//
+
+swiftscan_string_ref_t
+swiftscan_module_info_get_module_name(swiftscan_dependency_info_t info) {
+  return info->module_name;
+}
+
+swiftscan_string_ref_t
+swiftscan_module_info_get_module_path(swiftscan_dependency_info_t info) {
+  return info->module_path;
+}
+
+swiftscan_string_set_t *
+swiftscan_module_info_get_source_files(swiftscan_dependency_info_t info) {
+  return info->source_files;
+}
+
+swiftscan_string_set_t *swiftscan_module_info_get_direct_dependencies(
+    swiftscan_dependency_info_t info) {
+  return info->direct_dependencies;
+}
+
+swiftscan_module_details_t
+swiftscan_module_info_get_details(swiftscan_dependency_info_t info) {
+  return info->details;
+}
+
+//=== Swift Textual Module Details query APIs -----------------------------===//
+
+swiftscan_dependency_info_kind_t
+swiftscan_module_detail_get_kind(swiftscan_module_details_t details) {
+  return details->kind;
+}
+
+swiftscan_string_ref_t swiftscan_swift_textual_detail_get_module_interface_path(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.module_interface_path;
+}
+
+swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_compiled_module_candidates(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.compiled_module_candidates;
+}
+
+swiftscan_string_ref_t swiftscan_swift_textual_detail_get_bridging_header_path(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.bridging_header_path;
+}
+
+swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_bridging_source_files(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.bridging_source_files;
+}
+
+swiftscan_string_set_t *
+swiftscan_swift_textual_detail_get_bridging_module_dependencies(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.bridging_module_dependencies;
+}
+
+swiftscan_string_set_t *swiftscan_swift_textual_detail_get_command_line(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.command_line;
+}
+
+swiftscan_string_set_t *swiftscan_swift_textual_detail_get_extra_pcm_args(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.extra_pcm_args;
+}
+
+swiftscan_string_ref_t swiftscan_swift_textual_detail_get_context_hash(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.context_hash;
+}
+
+bool swiftscan_swift_textual_detail_get_is_framework(
+    swiftscan_module_details_t details) {
+  return details->swift_textual_details.is_framework;
+}
+
+//=== Swift Binary Module Details query APIs ------------------------------===//
+
+swiftscan_string_ref_t swiftscan_swift_binary_detail_get_compiled_module_path(
+    swiftscan_module_details_t details) {
+  return details->swift_binary_details.compiled_module_path;
+}
+
+swiftscan_string_ref_t swiftscan_swift_binary_detail_get_module_doc_path(
+    swiftscan_module_details_t details) {
+  return details->swift_binary_details.module_doc_path;
+}
+
+swiftscan_string_ref_t
+swiftscan_swift_binary_detail_get_module_source_info_path(
+    swiftscan_module_details_t details) {
+  return details->swift_binary_details.module_source_info_path;
+}
+
+//=== Swift Placeholder Module Details query APIs -------------------------===//
+
+swiftscan_string_ref_t
+swiftscan_swift_placeholder_detail_get_compiled_module_path(
+    swiftscan_module_details_t details) {
+  return details->swift_placeholder_details.module_source_info_path;
+}
+
+swiftscan_string_ref_t swiftscan_swift_placeholder_detail_get_module_doc_path(
+    swiftscan_module_details_t details) {
+  return details->swift_placeholder_details.module_source_info_path;
+}
+
+swiftscan_string_ref_t
+swiftscan_swift_placeholder_detail_get_module_source_info_path(
+    swiftscan_module_details_t details) {
+  return details->swift_placeholder_details.module_source_info_path;
+}
+
+//=== Clang Module Details query APIs -------------------------------------===//
+
+swiftscan_string_ref_t
+swiftscan_clang_detail_get_module_map_path(swiftscan_module_details_t details) {
+  return details->clang_details.module_map_path;
+}
+
+swiftscan_string_ref_t
+swiftscan_clang_detail_get_context_hash(swiftscan_module_details_t details) {
+  return details->clang_details.context_hash;
+}
+
+swiftscan_string_set_t *
+swiftscan_clang_detail_get_command_line(swiftscan_module_details_t details) {
+  return details->clang_details.command_line;
+}
+
+//=== Batch Scan Input Functions ------------------------------------------===//
+
+swiftscan_batch_scan_input_t *swiftscan_batch_scan_input_create() {
+  return new swiftscan_batch_scan_input_t;
+}
+
+void swiftscan_batch_scan_input_set_modules(
+    swiftscan_batch_scan_input_t *input, int count,
+    swiftscan_batch_scan_entry_t *modules) {
+  input->count = count;
+  input->modules = modules;
+}
+
+//=== Batch Scan Entry Functions ------------------------------------------===//
+
+swiftscan_batch_scan_entry_t swiftscan_batch_scan_entry_create() {
+  return new swiftscan_batch_scan_entry_s;
+}
+
+void swiftscan_batch_scan_entry_set_module_name(
+    swiftscan_batch_scan_entry_t entry, const char *name) {
+  entry->module_name = create_clone(name);
+}
+
+void swiftscan_batch_scan_entry_set_arguments(
+    swiftscan_batch_scan_entry_t entry, const char *arguments) {
+  entry->arguments = create_clone(arguments);
+}
+
+void swiftscan_batch_scan_entry_set_is_swift(swiftscan_batch_scan_entry_t entry,
+                                             bool is_swift) {
+  entry->is_swift = is_swift;
+}
+
+swiftscan_string_ref_t
+swiftscan_batch_scan_entry_get_module_name(swiftscan_batch_scan_entry_t entry) {
+  return entry->module_name;
+}
+
+swiftscan_string_ref_t
+swiftscan_batch_scan_entry_get_arguments(swiftscan_batch_scan_entry_t entry) {
+  return entry->arguments;
+}
+
+bool swiftscan_batch_scan_entry_get_is_swift(
+    swiftscan_batch_scan_entry_t entry) {
+  return entry->is_swift;
+}
+
+//=== Prescan Result Functions --------------------------------------------===//
+
+swiftscan_string_set_t *
+swiftscan_import_set_get_imports(swiftscan_import_set_t result) {
+  return result->imports;
+}
+
+//=== Scanner Invocation Functions ----------------------------------------===//
+
+swiftscan_scan_invocation_t swiftscan_scan_invocation_create() {
+  return new swiftscan_scan_invocation_s;
+}
+
+void swiftscan_scan_invocation_set_working_directory(
+    swiftscan_scan_invocation_t invocation, const char *working_directory) {
+  invocation->working_directory = create_clone(working_directory);
+}
+
+SWIFTSCAN_PUBLIC void
+swiftscan_scan_invocation_set_argv(swiftscan_scan_invocation_t invocation,
+                                   int argc, const char **argv) {
+  invocation->argv = create_set(argc, argv);
+}
+
+swiftscan_string_ref_t swiftscan_scan_invocation_get_working_directory(
+    swiftscan_scan_invocation_t invocation) {
+  return invocation->working_directory;
+}
+
+int swiftscan_scan_invocation_get_argc(swiftscan_scan_invocation_t invocation) {
+  return invocation->argv->count;
+}
+
+swiftscan_string_set_t *
+swiftscan_scan_invocation_get_argv(swiftscan_scan_invocation_t invocation) {
+  return invocation->argv;
+}
+
+//=== Public Cleanup Functions --------------------------------------------===//
+
+void swiftscan_dependency_graph_dispose(swiftscan_dependency_graph_t result) {
+  swiftscan_string_dispose(result->main_module_name);
+  swiftscan_dependency_set_dispose(result->dependencies);
+  delete result;
+}
+
+void swiftscan_import_set_dispose(swiftscan_import_set_t result) {
+  swiftscan_string_set_dispose(result->imports);
+  delete result;
+}
+
+void swiftscan_batch_scan_entry_dispose(swiftscan_batch_scan_entry_t entry) {
+  swiftscan_string_dispose(entry->module_name);
+  swiftscan_string_dispose(entry->arguments);
+  delete entry;
+}
+
+void swiftscan_batch_scan_input_dispose(swiftscan_batch_scan_input_t *input) {
+  for (size_t i = 0; i < input->count; ++i) {
+    swiftscan_batch_scan_entry_dispose(input->modules[i]);
+  }
+  delete[] input->modules;
+  delete input;
+}
+
+void swiftscan_batch_scan_result_dispose(
+    swiftscan_batch_scan_result_t *result) {
+  for (size_t i = 0; i < result->count; ++i) {
+    swiftscan_dependency_graph_dispose(result->results[i]);
+  }
+  delete[] result->results;
+  delete result;
+}
+
+void swiftscan_scan_invocation_dispose(swiftscan_scan_invocation_t invocation) {
+  swiftscan_string_dispose(invocation->working_directory);
+  swiftscan_string_set_dispose(invocation->argv);
+  delete invocation;
+}
--- a/tools/libSwiftScan/libSwiftScan.exports
+++ b/tools/libSwiftScan/libSwiftScan.exports
@@ -0,0 +1,53 @@
+swiftscan_dependency_graph_get_main_module_name
+swiftscan_dependency_graph_get_dependencies
+swiftscan_module_info_get_module_name
+swiftscan_module_info_get_module_path
+swiftscan_module_info_get_source_files
+swiftscan_module_info_get_direct_dependencies
+swiftscan_module_info_get_details
+swiftscan_module_detail_get_kind
+swiftscan_swift_textual_detail_get_module_interface_path
+swiftscan_swift_textual_detail_get_compiled_module_candidates
+swiftscan_swift_textual_detail_get_bridging_header_path
+swiftscan_swift_textual_detail_get_bridging_source_files
+swiftscan_swift_textual_detail_get_bridging_module_dependencies
+swiftscan_swift_textual_detail_get_command_line
+swiftscan_swift_textual_detail_get_extra_pcm_args
+swiftscan_swift_textual_detail_get_context_hash
+swiftscan_swift_textual_detail_get_is_framework
+swiftscan_swift_binary_detail_get_compiled_module_path
+swiftscan_swift_binary_detail_get_module_doc_path
+swiftscan_swift_binary_detail_get_module_source_info_path
+swiftscan_swift_placeholder_detail_get_compiled_module_path
+swiftscan_swift_placeholder_detail_get_module_doc_path
+swiftscan_swift_placeholder_detail_get_module_source_info_path
+swiftscan_clang_detail_get_module_map_path
+swiftscan_clang_detail_get_context_hash
+swiftscan_clang_detail_get_command_line
+swiftscan_batch_scan_input_set_modules
+swiftscan_batch_scan_entry_set_module_name
+swiftscan_batch_scan_entry_set_arguments
+swiftscan_batch_scan_entry_set_is_swift
+swiftscan_batch_scan_entry_get_module_name
+swiftscan_batch_scan_entry_get_arguments
+swiftscan_batch_scan_entry_get_is_swift
+swiftscan_import_set_get_imports
+swiftscan_scan_invocation_set_working_directory
+swiftscan_scan_invocation_set_argv
+swiftscan_scan_invocation_get_working_directory
+swiftscan_scan_invocation_get_argc
+swiftscan_scan_invocation_get_argv
+swiftscan_scan_invocation_create
+swiftscan_batch_scan_input_create
+swiftscan_batch_scan_entry_create
+swiftscan_dependency_graph_create
+swiftscan_batch_scan_result_create
+swiftscan_import_set_create
+swiftscan_scanner_create
+swiftscan_scan_invocation_dispose
+swiftscan_batch_scan_input_dispose
+swiftscan_batch_scan_entry_dispose
+swiftscan_dependency_graph_dispose
+swiftscan_batch_scan_result_dispose
+swiftscan_import_set_dispose
+swiftscan_scanner_dispose
--- a/unittests/CMakeLists.txt
+++ b/unittests/CMakeLists.txt
@@ -7,6 +7,7 @@ if(SWIFT_INCLUDE_TOOLS)
  add_subdirectory(AST)
  add_subdirectory(Basic)
  add_subdirectory(ClangImporter)
+  add_subdirectory(DependencyScan)
  add_subdirectory(Driver)
  add_subdirectory(FrontendTool)
  add_subdirectory(Localization)
--- a/unittests/DependencyScan/CMakeLists.txt
+++ b/unittests/DependencyScan/CMakeLists.txt
@@ -0,0 +1,11 @@
+add_swift_unittest(swiftScanTests
+  ScanFixture.cpp
+  ModuleDeps.cpp)
+
+target_link_libraries(swiftScanTests
+  PRIVATE
+    swiftDependencyScan
+    libSwiftScan)
+
+target_compile_definitions(swiftScanTests PRIVATE
+  SWIFTLIB_DIR=\"${SWIFTLIB_DIR}\")
--- a/unittests/DependencyScan/ModuleDeps.cpp
+++ b/unittests/DependencyScan/ModuleDeps.cpp
@@ -0,0 +1,187 @@
+//===---------------------- ModuleDeps.cpp --------------------------------===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "ScanFixture.h"
+#include "swift/Basic/Platform.h"
+#include "swift/Basic/Defer.h"
+#include "llvm/ADT/Triple.h"
+#include "llvm/Support/Host.h"
+#include "llvm/Support/Path.h"
+#include "llvm/Support/raw_ostream.h"
+#include "gtest/gtest.h"
+#include <string>
+
+using namespace swift;
+using namespace swift::unittest;
+using namespace swift::dependencies;
+
+static std::string createFilename(StringRef base, StringRef name) {
+  SmallString<256> path = base;
+  llvm::sys::path::append(path, name);
+  return llvm::Twine(path).str();
+}
+
+static bool emitFileWithContents(StringRef path, StringRef contents,
+                                 std::string *pathOut = nullptr) {
+  int FD;
+  if (llvm::sys::fs::openFileForWrite(path, FD))
+    return true;
+  if (pathOut)
+    *pathOut = path.str();
+  llvm::raw_fd_ostream file(FD, /*shouldClose=*/true);
+  file << contents;
+  return false;
+}
+
+static bool emitFileWithContents(StringRef base, StringRef name,
+                                 StringRef contents,
+                                 std::string *pathOut = nullptr) {
+  return emitFileWithContents(createFilename(base, name), contents, pathOut);
+}
+
+TEST_F(ScanTest, TestModuleDeps) {
+  SmallString<256> tempDir;
+  ASSERT_FALSE(llvm::sys::fs::createUniqueDirectory("ScanTest.TestModuleDeps", tempDir));
+  SWIFT_DEFER { llvm::sys::fs::remove_directories(tempDir); };
+
+  // Create test input file
+  std::string TestPathStr = createFilename(tempDir, "foo.swift");
+  ASSERT_FALSE(emitFileWithContents(tempDir, "foo.swift", "import A\n"));
+  llvm::dbgs() << "Input File: " << TestPathStr << "\n";
+
+  // Create includes
+  std::string IncludeDirPath = createFilename(tempDir, "include");
+  ASSERT_FALSE(llvm::sys::fs::create_directory(IncludeDirPath));
+  std::string CHeadersDirPath = createFilename(IncludeDirPath, "CHeaders");
+  ASSERT_FALSE(llvm::sys::fs::create_directory(CHeadersDirPath));
+  std::string SwiftDirPath = createFilename(IncludeDirPath, "Swift");
+  ASSERT_FALSE(llvm::sys::fs::create_directory(SwiftDirPath));
+
+  // Create imported module Swift interface files
+  ASSERT_FALSE(emitFileWithContents(SwiftDirPath, "A.swiftinterface",
+                                    "// swift-interface-format-version: 1.0\n\
+// swift-module-flags: -module-name A\n\
+import Swift\n\
+@_exported import A\n\
+public func overlayFuncA() { }\n"));
+  ASSERT_FALSE(emitFileWithContents(SwiftDirPath, "E.swiftinterface",
+                                    "// swift-interface-format-version: 1.0\n\
+// swift-module-flags: -module-name E\n\
+import Swift\n\
+public func funcE()\n"));
+  ASSERT_FALSE(emitFileWithContents(SwiftDirPath, "F.swiftinterface",
+                                    "// swift-interface-format-version: 1.0\n\
+// swift-module-flags: -module-name\n\
+import Swift\n\
+@_exported import F\n\
+public func funcF() { }"));
+  ASSERT_FALSE(emitFileWithContents(SwiftDirPath, "G.swiftinterface",
+                                    "// swift-interface-format-version: 1.0\n\
+// swift-module-flags: -module-name G -swift-version 5 -target x86_64-apple-macosx10.9\n\
+#if swift(>=5.0)\n\
+@_exported import G\n\
+import Swift\n\
+public func overlayFuncG() { }\n\
+let stringG : String = \"Build\"\n\
+#endif"));
+
+  // Create imported module C modulemap/headers
+  ASSERT_FALSE(
+      emitFileWithContents(CHeadersDirPath, "A.h", "void funcA(void);"));
+  ASSERT_FALSE(emitFileWithContents(CHeadersDirPath, "B.h", "#include \"A.h\"\
+void funcB(void);"));
+  ASSERT_FALSE(emitFileWithContents(CHeadersDirPath, "C.h", "#include \"B.h\"\n\
+void funcC(void);\
+const char* stringC() { return \"Module\"; }"));
+  ASSERT_FALSE(
+      emitFileWithContents(CHeadersDirPath, "D.h", "void funcD(void);"));
+  ASSERT_FALSE(
+      emitFileWithContents(CHeadersDirPath, "F.h", "void funcF(void);"));
+  ASSERT_FALSE(emitFileWithContents(
+      CHeadersDirPath, "G.h",
+      "#if __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 110000\n\
+#include \"X.h\"\n\
+#endif\n\
+void funcG(void);"));
+  ASSERT_FALSE(
+      emitFileWithContents(CHeadersDirPath, "X.h", "void funcX(void);"));
+  ASSERT_FALSE(emitFileWithContents(CHeadersDirPath, "Bridging.h",
+                                    "#include \"BridgingOther.h\"\n\
+int bridging_other(void);"));
+  ASSERT_FALSE(emitFileWithContents(CHeadersDirPath, "BridgingOther.h",
+                                    "#include \"F.h\"\n\
+int bridging_other(void);"));
+
+  ASSERT_FALSE(
+      emitFileWithContents(CHeadersDirPath, "module.modulemap", "module A {\n\
+header \"A.h\"\n\
+export *\n\
+}\n\
+module B {\n\
+header \"B.h\"\n\
+export *\n\
+}\n\
+module C {\n\
+header \"C.h\"\n\
+export *\n\
+}\n\
+module D {\n\
+header \"D.h\"\n\
+export *\n\
+}\n\
+module F {\n\
+header \"F.h\"\n\
+export *\n\
+}\n\
+module G {\n\
+header \"G.h\"\n\
+export *\n\
+}\n\
+module X {\n\
+header \"X.h\"\n\
+export *\n\
+}"));
+
+  // Paths to shims and stdlib
+  llvm::SmallString<128> ShimsLibDir = StdLibDir;
+  llvm::sys::path::append(ShimsLibDir, "shims");
+  auto Target = llvm::Triple(llvm::sys::getDefaultTargetTriple());
+  llvm::sys::path::append(StdLibDir, getPlatformNameForTriple(Target));
+
+  std::vector<std::string> CommandStrArr = {
+    std::string("'") + TestPathStr + std::string("'"),
+    std::string("-I ") + std::string("'") + SwiftDirPath + std::string("'"),
+    std::string("-I ") + std::string("'") + CHeadersDirPath + std::string("'"),
+    std::string("-I ") + std::string("'") + StdLibDir.str().str() + std::string("'"),
+    std::string("-I ") + std::string("'") + ShimsLibDir.str().str() + std::string("'")
+  };
+
+  // On Windows we need to add an extra escape for path separator characters because otherwise
+  // the command line tokenizer will treat them as escape characters.
+  for (size_t i = 0; i < CommandStrArr.size(); ++i) {
+    std::replace(CommandStrArr[i].begin(), CommandStrArr[i].end(), '\\', '/');
+  }
+
+  std::vector<const char*> Command;
+  llvm::dbgs() << "Compiler Command: \n";
+  for (auto &command : CommandStrArr) {
+    Command.push_back(command.c_str());
+    llvm::dbgs() << command.c_str() << "\n";
+  }
+  auto DependenciesOrErr = ScannerTool.getDependencies(Command, {});
+  ASSERT_FALSE(DependenciesOrErr.getError());
+  auto Dependencies = DependenciesOrErr.get();
+  // TODO: Output/verify dependency graph correctness
+  // llvm::dbgs() << "Deps: " << Dependencies << "\n";
+
+  swiftscan_dependency_graph_dispose(Dependencies);
+}
--- a/unittests/DependencyScan/ScanFixture.cpp
+++ b/unittests/DependencyScan/ScanFixture.cpp
@@ -0,0 +1,31 @@
+//===-------- ScanFixture.cpp - Dependency scanning tests -*- C++ -------*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "ScanFixture.h"
+#include "swift/Basic/LLVMInitialize.h"
+#include "llvm/Support/FileSystem.h"
+#include "gtest/gtest.h"
+
+using namespace swift;
+using namespace swift::unittest;
+using namespace swift::dependencies;
+
+ScanTest::ScanTest() : ScannerTool(), StdLibDir(SWIFTLIB_DIR) {
+  INITIALIZE_LLVM();
+  // Create a temporary filesystem workspace for this test.
+  llvm::sys::fs::createUniqueDirectory("ScanTest.Workspace",
+                                       TemporaryTestWorkspace);
+}
+
+ScanTest::~ScanTest() {
+  llvm::sys::fs::remove_directories(TemporaryTestWorkspace);
+}
--- a/unittests/DependencyScan/ScanFixture.h
+++ b/unittests/DependencyScan/ScanFixture.h
@@ -0,0 +1,40 @@
+//===-------- ScanFixture.h - Dependency scanning tests -*- C++ ---------*-===//
+//
+// This source file is part of the Swift.org open source project
+//
+// Copyright (c) 2014 - 2020 Apple Inc. and the Swift project authors
+// Licensed under Apache License v2.0 with Runtime Library Exception
+//
+// See https://swift.org/LICENSE.txt for license information
+// See https://swift.org/CONTRIBUTORS.txt for the list of Swift project authors
+//
+//===----------------------------------------------------------------------===//
+
+#include "swift-c/DependencyScan/DependencyScan.h"
+#include "swift/DependencyScan/DependencyScanningTool.h"
+#include "gtest/gtest.h"
+#include <string>
+
+using namespace swift::dependencies;
+
+namespace swift {
+namespace unittest {
+
+class ScanTest : public ::testing::Test {
+public:
+  ScanTest();
+  ~ScanTest();
+
+protected:
+  // The tool used to execute tests' scanning queries
+  DependencyScanningTool ScannerTool;
+
+  // Test workspace directory
+  llvm::SmallString<256> TemporaryTestWorkspace;
+
+  // Path to where the Swift standard library can be found
+  llvm::SmallString<128> StdLibDir;
+};
+
+} // end namespace unittest
+} // end namespace swift