[ScanDependency] Add -experimental-clang-importer-direct-cc1-scan

Add an experimental option to tell dependency scanner to report clang
cc1 args should be used to construct clang importer in all constructed
swift-frontend tasks.

include/swift/Basic/LangOptions.h

@@ -969,6 +969,10 @@ namespace swift {
     /// Using ClangIncludeTreeRoot for compilation.
     bool HasClangIncludeTreeRoot = false;
 
+    /// Whether the dependency scanner should construct all swift-frontend
+    /// invocations directly from clang cc1 args.
+    bool ClangImporterDirectCC1Scan = false;
+
     /// Return a hash code of any components from these options that should
     /// contribute to a Swift Bridging PCH hash.
     llvm::hash_code getPCHHashComponents() const {

include/swift/Option/Options.td

@@ -1894,6 +1894,11 @@ def gcc_toolchain: Separate<["-"], "gcc-toolchain">,
   MetaVarName<"<path>">,
   HelpText<"Specify a directory where the clang importer and clang linker can find headers and libraries">;
 
+def experimental_clang_importer_direct_cc1_scan:
+  Flag<["-"], "experimental-clang-importer-direct-cc1-scan">,
+  Flags<[FrontendOption, NewDriverOnlyOption, HelpHidden]>,
+  HelpText<"Enables swift driver to construct swift-frontend invocations using -direct-clang-cc1-module-build">;
+
 def cache_compile_job:  Flag<["-"], "cache-compile-job">,
   Flags<[FrontendOption, NewDriverOnlyOption]>,
   HelpText<"Enable compiler caching">;

lib/DependencyScan/ModuleDependencyScanner.cpp

@@ -347,6 +347,8 @@ ModuleDependencyScanner::getMainModuleDependencyInfo(
 
   std::string rootID;
   std::vector<std::string> buildArgs;
+  auto clangImporter =
+      static_cast<ClangImporter *>(ScanASTContext.getClangModuleLoader());
   if (tracker) {
     tracker->startTracking();
     for (auto fileUnit : mainModule->getFiles()) {
@@ -359,8 +361,6 @@ ModuleDependencyScanner::getMainModuleDependencyInfo(
         ScanCompilerInvocation.getSearchPathOptions());
     // Fetch some dependency files from clang importer.
     std::vector<std::string> clangDependencyFiles;
-    auto clangImporter =
-        static_cast<ClangImporter *>(ScanASTContext.getClangModuleLoader());
     clangImporter->addClangInvovcationDependencies(clangDependencyFiles);
     llvm::for_each(clangDependencyFiles,
                    [&](std::string &file) { tracker->trackFile(file); });
@@ -372,7 +372,9 @@ ModuleDependencyScanner::getMainModuleDependencyInfo(
       return std::make_error_code(std::errc::io_error);
     }
     rootID = root->getID().toString();
+  }
 
+  if (ScanASTContext.ClangImporterOpts.ClangImporterDirectCC1Scan) {
     buildArgs.push_back("-direct-clang-cc1-module-build");
     for (auto &arg : clangImporter->getSwiftExplicitModuleDirectCC1Args()) {
       buildArgs.push_back("-Xcc");

lib/Frontend/CompilerInvocation.cpp

@@ -1709,6 +1709,8 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts, ArgList &Args,
   Opts.DisableSourceImport |=
       Args.hasArg(OPT_disable_clangimporter_source_import);
 
+  Opts.ClangImporterDirectCC1Scan |=
+      Args.hasArg(OPT_experimental_clang_importer_direct_cc1_scan);
   // Forward the FrontendOptions to clang importer option so it can be
   // accessed when creating clang module compilation invocation.
   if (CASOpts.EnableCaching) {
@@ -1716,6 +1718,8 @@ static bool ParseClangImporterArgs(ClangImporterOptions &Opts, ArgList &Args,
     // useful in non-caching context.
     Opts.UseClangIncludeTree |= !Args.hasArg(OPT_no_clang_include_tree);
     Opts.HasClangIncludeTreeRoot |= Args.hasArg(OPT_clang_include_tree_root);
+    // Caching requires direct clang import cc1 scanning.
+    Opts.ClangImporterDirectCC1Scan = true;
   }
 
   // If in direct clang cc1 module build mode, return early.

lib/Frontend/ModuleInterfaceLoader.cpp

@@ -1677,6 +1677,8 @@ void InterfaceSubContextDelegateImpl::inheritOptionsForBuildingInterface(
 
   genericSubInvocation.getClangImporterOptions().DirectClangCC1ModuleBuild =
       clangImporterOpts.DirectClangCC1ModuleBuild;
+  genericSubInvocation.getClangImporterOptions().ClangImporterDirectCC1Scan =
+      clangImporterOpts.ClangImporterDirectCC1Scan;
 
   // Validate Clang modules once per-build session flags must be consistent
   // across all module sub-invocations

lib/Serialization/ScanningLoaders.cpp

@@ -160,7 +160,7 @@ SwiftModuleScanner::scanInterfaceFile(Twine moduleInterfacePath,
 
         // Handle clang arguments. For caching build, all arguments are passed
         // with `-direct-clang-cc1-module-build`.
-        if (Ctx.CASOpts.EnableCaching) {
+        if (Ctx.ClangImporterOpts.ClangImporterDirectCC1Scan) {
           Args.push_back("-direct-clang-cc1-module-build");
           auto *importer =
               static_cast<ClangImporter *>(Ctx.getClangModuleLoader());

test/ScanDependencies/direct_cc1_scan.swift

@@ -0,0 +1,30 @@
+// RUN: %empty-directory(%t)
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-module %t/A.swift -module-name A \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   -enable-library-evolution -swift-version 5 \
+// RUN:   -emit-module-interface-path %t/A.swiftinterface \
+// RUN:   -o %t/A.swiftmodule
+
+// RUN: %target-swift-frontend -scan-dependencies -o %t/deps.json -I %t \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   %t/test.swift -module-name Test -swift-version 5
+// RUN: %{python} %S/../CAS/Inputs/BuildCommandExtractor.py %t/deps.json A | %FileCheck %s --check-prefix CHECK-NO-DIRECT-CC1
+// RUN: %{python} %S/../CAS/Inputs/BuildCommandExtractor.py %t/deps.json Test | %FileCheck %s --allow-empty --check-prefix CHECK-NO-DIRECT-CC1
+
+// RUN: %target-swift-frontend -scan-dependencies -o %t/deps2.json -I %t \
+// RUN:   -disable-implicit-string-processing-module-import -disable-implicit-concurrency-module-import -parse-stdlib \
+// RUN:   %t/test.swift -module-name Test -swift-version 5 -experimental-clang-importer-direct-cc1-scan
+// RUN: %{python} %S/../CAS/Inputs/BuildCommandExtractor.py %t/deps2.json A | %FileCheck %s --check-prefix CHECK-DIRECT-CC1-SCAN
+// RUN: %{python} %S/../CAS/Inputs/BuildCommandExtractor.py %t/deps2.json Test | %FileCheck %s --check-prefix CHECK-DIRECT-CC1-SCAN
+
+// CHECK-NO-DIRECT-CC1-NOT: -direct-clang-cc1-module-build
+// CHECK-DIRECT-CC1-SCAN: -direct-clang-cc1-module-build
+
+//--- A.swift
+func a() {}
+
+//--- test.swift
+import A
+func test() {}