[ObjcHeader] Fix objc header generation when pch is explicited passed

When swift-frontend is explicitly passed the pch file as bridging header
on command-line through `-import-objc-header`, it needs to print the
original source file name if needed to the generated objc header.

rdar://109411245

include/swift/ClangImporter/ClangImporter.h

@@ -403,6 +403,9 @@ public:
   /// if we need to persist a PCH for later reuse.
   bool canReadPCH(StringRef PCHFilename);
 
+  /// Reads the original source file name from PCH.
+  std::string getOriginalSourceFile(StringRef PCHFilename);
+
   /// Makes a temporary replica of the ClangImporter's CompilerInstance, reads a
   /// module map into the replica and emits a PCM file for one of the modules it
   /// declares. Delegates to clang for everything except construction of the

include/swift/Frontend/Frontend.h

@@ -667,6 +667,9 @@ public:
   /// file.
   SourceFile *getIDEInspectionFile() const;
 
+  /// Retrieve the printing path for bridging header.
+  std::string getBridgingHeaderPath() const;
+
 private:
   /// Set up the file system by loading and validating all VFS overlay YAML
   /// files. If the process of validating VFS files failed, or the overlay

lib/ClangImporter/ClangImporter.cpp

@@ -915,6 +915,12 @@ bool ClangImporter::canReadPCH(StringRef PCHFilename) {
   llvm_unreachable("unhandled result");
 }
 
+std::string ClangImporter::getOriginalSourceFile(StringRef PCHFilename) {
+  return clang::ASTReader::getOriginalSourceFile(
+      PCHFilename.str(), Impl.Instance->getFileManager(),
+      Impl.Instance->getPCHContainerReader(), Impl.Instance->getDiagnostics());
+}
+
 Optional<std::string>
 ClangImporter::getPCHFilename(const ClangImporterOptions &ImporterOptions,
                               StringRef SwiftPCHHash, bool &isExplicit) {

lib/Frontend/Frontend.cpp

@@ -818,6 +818,26 @@ SourceFile *CompilerInstance::getIDEInspectionFile() const {
   return evaluateOrDefault(eval, IDEInspectionFileRequest{mod}, nullptr);
 }
 
+static inline bool isPCHFilenameExtension(StringRef path) {
+  return llvm::sys::path::extension(path)
+    .endswith(file_types::getExtension(file_types::TY_PCH));
+}
+
+std::string CompilerInstance::getBridgingHeaderPath() const {
+  const FrontendOptions &opts = Invocation.getFrontendOptions();
+  if (!isPCHFilenameExtension(opts.ImplicitObjCHeaderPath))
+    return opts.ImplicitObjCHeaderPath;
+
+  auto clangImporter =
+      static_cast<ClangImporter *>(getASTContext().getClangModuleLoader());
+
+  // No clang importer created. Report error?
+  if (!clangImporter)
+    return std::string();
+
+  return clangImporter->getOriginalSourceFile(opts.ImplicitObjCHeaderPath);
+}
+
 bool CompilerInstance::setUpInputs() {
   // Adds to InputSourceCodeBufferIDs, so may need to happen before the
   // per-input setup.

lib/FrontendTool/FrontendTool.cpp

@@ -912,17 +912,14 @@ static bool emitAnyWholeModulePostTypeCheckSupplementaryOutputs(
 
   if ((!Context.hadError() || opts.AllowModuleWithCompilerErrors) &&
       opts.InputsAndOutputs.hasClangHeaderOutputPath()) {
-    std::string BridgingHeaderPathForPrint;
-    if (!opts.ImplicitObjCHeaderPath.empty()) {
+    std::string BridgingHeaderPathForPrint = Instance.getBridgingHeaderPath();
+    if (!BridgingHeaderPathForPrint.empty()) {
       if (opts.BridgingHeaderDirForPrint.has_value()) {
         // User specified preferred directory for including, use that dir.
         llvm::SmallString<32> Buffer(*opts.BridgingHeaderDirForPrint);
         llvm::sys::path::append(Buffer,
-          llvm::sys::path::filename(opts.ImplicitObjCHeaderPath));
+          llvm::sys::path::filename(BridgingHeaderPathForPrint));
         BridgingHeaderPathForPrint = (std::string)Buffer;
-      } else {
-        // By default, include the given bridging header path directly.
-        BridgingHeaderPathForPrint = opts.ImplicitObjCHeaderPath;
       }
     }
     hadAnyError |= printAsClangHeaderIfNeeded(

test/PrintAsObjC/Inputs/bridging_header-Bridging-Header.h

@@ -0,0 +1,5 @@
+@import Foundation;
+
+@protocol TestProto
+@property id strongProp;
+@end

test/PrintAsObjC/Inputs/custom-modules/bridging_header/bridging_header.h

@@ -0,0 +1,8 @@
+#import <Foundation.h>
+
+@interface ObjCClass : NSObject
+
+- (nullable id)swiftMethod;
+
+@end
+

test/PrintAsObjC/Inputs/custom-modules/module.map

@@ -63,3 +63,8 @@ module objc_implementation {
   header "objc_implementation/objc_implementation.h"
   export *
 }
+
+module bridging_header {
+  header "bridging_header/bridging_header.h"
+  export *
+}

test/PrintAsObjC/bridging_header.swift

@@ -0,0 +1,15 @@
+// REQUIRES: objc_interop
+
+// RUN: %empty-directory(%t)
+
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -emit-pch -o %t/bridging-header.pch %S/Inputs/bridging_header-Bridging-Header.h
+// RUN: %target-swift-frontend(mock-sdk: -sdk %S/../Inputs/clang-importer-sdk -I %t) -emit-module -I %S/Inputs/custom-modules -import-objc-header %t/bridging-header.pch -import-underlying-module -o %t %s -disable-objc-attr-requires-foundation-module -emit-objc-header-path %t/bridging_header-Swift.h
+
+// RUN: %FileCheck %s --input-file %t/bridging_header-Swift.h
+
+// CHECK: bridging_header-Bridging-Header.h
+// CHECK-NOT: bridging-header.pch
+
+@objc class Test : NSObject, TestProto {
+  var strongProp: Any?
+}