Added support for expanding response files in clang_Driver_getExternalActionsForCommand_v0.

This is necessary because build systems like SwiftBuild may pass arguments to the Clang driver via response files.
Without this, the response files are treated as inputs and passed along to the external actions themselves, which is incorrect.

This resolves swiftlang#10441.

Author: cwakamo

clang/tools/libclang/Driver.cpp

@@ -40,15 +40,29 @@ clang_Driver_getExternalActionsForCommand_v0(int ArgC, const char **ArgV,
   if (ArgC < 1)
     return nullptr;
 
-  CXDiagnosticSetDiagnosticConsumer DiagConsumer;
-  auto DiagOpts = CreateAndPopulateDiagOpts(ArrayRef(ArgV, ArgC));
-
   // Use createPhysicalFileSystem instead of getRealFileSystem so that
   // setCurrentWorkingDirectory doesn't change the working directory of the
   // process.
   std::unique_ptr<llvm::vfs::FileSystem> VFS =
       llvm::vfs::createPhysicalFileSystem();
 
+  CXDiagnosticSetDiagnosticConsumer DiagConsumer;
+
+  SmallVector<const char *, 256> Args(ArgV, ArgV + ArgC);
+  llvm::BumpPtrAllocator Alloc;
+  if (llvm::Error E =
+      driver::expandResponseFiles(Args, /*CLMode=*/false, Alloc)) {
+    // Construct a default DiagnosticOptions to use to emit the failure.
+    DiagnosticOptions DiagOpts;
+    auto Diags = CompilerInstance::createDiagnostics(*VFS, &DiagOpts,
+                                                     &DiagConsumer, false);
+
+    Diags->Report(diag::err_drv_expand_response_file)
+        << llvm::toString(std::move(E));
+    return nullptr;
+  }
+
+  auto DiagOpts = CreateAndPopulateDiagOpts(Args);
   auto Diags = CompilerInstance::createDiagnostics(*VFS, DiagOpts.release(),
                                                    &DiagConsumer, false);
   if (WorkingDirectory)
@@ -65,7 +79,7 @@ clang_Driver_getExternalActionsForCommand_v0(int ArgC, const char **ArgV,
                            VFS.release());
   TheDriver.setCheckInputsExist(false);
   std::unique_ptr<driver::Compilation> C(
-      TheDriver.BuildCompilation(ArrayRef(ArgV, ArgC)));
+      TheDriver.BuildCompilation(Args));
   if (!C || Diags->hasErrorOccurred()) {
     if (OutDiags)
       *OutDiags = DiagConsumer.getDiagnosticSet();

clang/unittests/libclang/DriverTest.cpp

@@ -11,6 +11,8 @@
 #include "llvm/Support/Debug.h"
 #include "gtest/gtest.h"
 
+#include "TestUtils.h"
+
 #define DEBUG_TYPE "driver-test"
 
 TEST(DriverTests, Basic) {
@@ -129,3 +131,44 @@ TEST(DriverTests, DriverParsesDiagnosticsOptions) {
   clang_disposeDiagnosticSet(Diags);
   clang_Driver_ExternalActionList_dispose(EAL);
 }
+
+class LibclangDriverResponseFileTest : public LibclangParseTest {};
+
+TEST_F(LibclangDriverResponseFileTest, DriverResponseFile) {
+  // Enable -Weverything (a flag not set by default) via a response file.
+  std::string ResponseFilename = "AdditionalOptions.resp";
+  WriteFile(ResponseFilename, "-Weverything\n");
+    
+  llvm::SmallString<256> ResponseArg("@");
+  ResponseArg.append(ResponseFilename);
+  
+  const char *ArgV[] = {"clang",
+                        ResponseArg.c_str(),
+                        "-c",
+                        "t.cpp",
+                        "-o",
+                        "t.o"};
+
+  CXDiagnosticSet Diags;
+  CXExternalActionList *EAL = clang_Driver_getExternalActionsForCommand_v0(
+      std::extent_v<decltype(ArgV)>, ArgV, nullptr, "/", &Diags);
+
+  ASSERT_NE(EAL, nullptr);
+  ASSERT_EQ(EAL->Count, 1);
+  ASSERT_EQ(nullptr, Diags);
+
+  auto *CompileAction = EAL->Actions[0];
+  ASSERT_GE(CompileAction->ArgC, 2);
+  EXPECT_STREQ(CompileAction->ArgV[0], "clang");
+  EXPECT_STREQ(CompileAction->ArgV[1], "-cc1");
+
+  const char **WFlag = std::find(CompileAction->ArgV,
+      CompileAction->ArgV + CompileAction->ArgC,
+       llvm::StringRef("-Weverything"));
+
+  ASSERT_NE(WFlag, CompileAction->ArgV + CompileAction->ArgC);
+  EXPECT_STREQ(*WFlag, "-Weverything");
+
+  clang_disposeDiagnosticSet(Diags);
+  clang_Driver_ExternalActionList_dispose(EAL);
+}