[Bridging PCH] Add ClangImporter::emitBridgingPCH.

Author: graydon

include/swift/ClangImporter/ClangImporter.h

@@ -218,6 +218,14 @@ class ClangImporter final : public ClangModuleLoader {
   std::string getBridgingHeaderContents(StringRef headerPath, off_t &fileSize,
                                         time_t &fileModTime);
 
+  /// Makes a temporary replica of the ClangImporter's CompilerInstance, reads
+  /// an Objective-C header file into the replica and emits a PCH file of its
+  /// content. Delegates to clang for everything except construction of the
+  /// replica.
+  ///
+  /// \sa clang::GeneratePCHAction
+  bool emitBridgingPCH(StringRef headerPath, StringRef outputPCHPath);
+
   const clang::Module *getClangOwningModule(ClangNode Node) const;
   bool hasTypedef(const clang::Decl *typeDecl) const;
 

lib/ClangImporter/ClangImporter.cpp

@@ -994,6 +994,41 @@ std::string ClangImporter::getBridgingHeaderContents(StringRef headerPath,
   return result;
 }
 
+bool
+ClangImporter::emitBridgingPCH(StringRef headerPath,
+                               StringRef outputPCHPath) {
+  llvm::IntrusiveRefCntPtr<clang::CompilerInvocation> invocation{
+    new clang::CompilerInvocation(*Impl.Invocation)
+  };
+  invocation->getFrontendOpts().DisableFree = false;
+  invocation->getFrontendOpts().Inputs.clear();
+  invocation->getFrontendOpts().Inputs.push_back(
+      clang::FrontendInputFile(headerPath, clang::IK_ObjC));
+  invocation->getFrontendOpts().OutputFile = outputPCHPath;
+  invocation->getPreprocessorOpts().resetNonModularOptions();
+
+  clang::CompilerInstance emitInstance(
+    Impl.Instance->getPCHContainerOperations());
+  emitInstance.setInvocation(&*invocation);
+  emitInstance.createDiagnostics(&Impl.Instance->getDiagnosticClient(),
+                                 false);
+
+  clang::FileManager &fileManager = Impl.Instance->getFileManager();
+  emitInstance.setFileManager(&fileManager);
+  emitInstance.createSourceManager(fileManager);
+  emitInstance.setTarget(&Impl.Instance->getTarget());
+
+  clang::GeneratePCHAction action;
+  emitInstance.ExecuteAction(action);
+  if (emitInstance.getDiagnostics().hasErrorOccurred()) {
+    Impl.SwiftContext.Diags.diagnose({},
+                                     diag::bridging_header_pch_error,
+                                     outputPCHPath, headerPath);
+    return true;
+  }
+  return false;
+}
+
 void ClangImporter::collectSubModuleNames(
     ArrayRef<std::pair<Identifier, SourceLoc>> path,
     std::vector<std::string> &names) {