[clang] Add support for passing FileSystem to buildASTFromCodeWithArgs() (#123042)

This would allow tools that don't use the real file system to use this
function.

Author: bricknerb

clang/include/clang/Tooling/Tooling.h

@@ -223,7 +223,11 @@ buildASTFromCode(StringRef Code, StringRef FileName = "input.cc",
 /// \param PCHContainerOps The PCHContainerOperations for loading and creating
 /// clang modules.
 ///
-/// \param Adjuster A function to filter the command line arguments as specified.
+/// \param Adjuster A function to filter the command line arguments as
+/// specified.
+///
+/// \param BaseFS FileSystem for managing and looking up files.
+/// VirtualMappedFiles takes precedence.
 ///
 /// \return The resulting AST or null if an error occurred.
 std::unique_ptr<ASTUnit> buildASTFromCodeWithArgs(
@@ -233,7 +237,9 @@ std::unique_ptr<ASTUnit> buildASTFromCodeWithArgs(
         std::make_shared<PCHContainerOperations>(),
     ArgumentsAdjuster Adjuster = getClangStripDependencyFileAdjuster(),
     const FileContentMappings &VirtualMappedFiles = FileContentMappings(),
-    DiagnosticConsumer *DiagConsumer = nullptr);
+    DiagnosticConsumer *DiagConsumer = nullptr,
+    IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS =
+        llvm::vfs::getRealFileSystem());
 
 /// Utility to run a FrontendAction in a single clang invocation.
 class ToolInvocation {

clang/lib/Tooling/Tooling.cpp

@@ -692,11 +692,12 @@ std::unique_ptr<ASTUnit> buildASTFromCodeWithArgs(
     StringRef Code, const std::vector<std::string> &Args, StringRef FileName,
     StringRef ToolName, std::shared_ptr<PCHContainerOperations> PCHContainerOps,
     ArgumentsAdjuster Adjuster, const FileContentMappings &VirtualMappedFiles,
-    DiagnosticConsumer *DiagConsumer) {
+    DiagnosticConsumer *DiagConsumer,
+    IntrusiveRefCntPtr<llvm::vfs::FileSystem> BaseFS) {
   std::vector<std::unique_ptr<ASTUnit>> ASTs;
   ASTBuilderAction Action(ASTs);
   llvm::IntrusiveRefCntPtr<llvm::vfs::OverlayFileSystem> OverlayFileSystem(
-      new llvm::vfs::OverlayFileSystem(llvm::vfs::getRealFileSystem()));
+      new llvm::vfs::OverlayFileSystem(std::move(BaseFS)));
   llvm::IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> InMemoryFileSystem(
       new llvm::vfs::InMemoryFileSystem);
   OverlayFileSystem->pushOverlay(InMemoryFileSystem);

clang/unittests/Tooling/ToolingTest.cpp

@@ -152,6 +152,20 @@ TEST(buildASTFromCode, ReportsErrors) {
   EXPECT_EQ(1u, Consumer.NumDiagnosticsSeen);
 }
 
+TEST(buildASTFromCode, FileSystem) {
+  llvm::IntrusiveRefCntPtr<llvm::vfs::InMemoryFileSystem> InMemoryFileSystem(
+      new llvm::vfs::InMemoryFileSystem);
+  InMemoryFileSystem->addFile("included_file.h", 0,
+                              llvm::MemoryBuffer::getMemBufferCopy("class X;"));
+  std::unique_ptr<ASTUnit> AST = buildASTFromCodeWithArgs(
+      R"(#include "included_file.h")", {}, "input.cc", "clang-tool",
+      std::make_shared<PCHContainerOperations>(),
+      getClangStripDependencyFileAdjuster(), FileContentMappings(), nullptr,
+      InMemoryFileSystem);
+  ASSERT_TRUE(AST.get());
+  EXPECT_TRUE(FindClassDeclX(AST.get()));
+}
+
 TEST(newFrontendActionFactory, CreatesFrontendActionFactoryFromType) {
   std::unique_ptr<FrontendActionFactory> Factory(
       newFrontendActionFactory<SyntaxOnlyAction>());