5 files changed, 19 insertions, 7 deletions

diff --git a/clang-tools-extra/clangd/Compiler.cpp b/clang-tools-extra/clangd/Compiler.cpp
index 795fd008259..eae753b5c9b 100644
--- a/clang-tools-extra/clangd/Compiler.cpp
+++ b/clang-tools-extra/clangd/Compiler.cpp
@@ -42,7 +42,8 @@ void IgnoreDiagnostics::HandleDiagnostic(DiagnosticsEngine::Level DiagLevel,
 
 std::unique_ptr<CompilerInvocation>
 buildCompilerInvocation(const ParseInputs &Inputs,
-                        clang::DiagnosticConsumer &D) {
+                        clang::DiagnosticConsumer &D,
+                        std::vector<std::string> *CC1Args) {
   std::vector<const char *> ArgStrs;
   for (const auto &S : Inputs.CompileCommand.CommandLine)
     ArgStrs.push_back(S.c_str());
@@ -57,7 +58,7 @@ buildCompilerInvocation(const ParseInputs &Inputs,
       CompilerInstance::createDiagnostics(new DiagnosticOptions, &D, false);
   std::unique_ptr<CompilerInvocation> CI = createInvocationFromCommandLine(
       ArgStrs, CommandLineDiagsEngine, Inputs.FS,
-      /*ShouldRecoverOnErrors=*/true);
+      /*ShouldRecoverOnErrors=*/true, CC1Args);
   if (!CI)
     return nullptr;
   // createInvocationFromCommandLine sets DisableFree.
diff --git a/clang-tools-extra/clangd/Compiler.h b/clang-tools-extra/clangd/Compiler.h
index 6ab1b0f075f..51414c37fc0 100644
--- a/clang-tools-extra/clangd/Compiler.h
+++ b/clang-tools-extra/clangd/Compiler.h
@@ -52,8 +52,8 @@ struct ParseInputs {
 
 /// Builds compiler invocation that could be used to build AST or preamble.
 std::unique_ptr<CompilerInvocation>
-buildCompilerInvocation(const ParseInputs &Inputs,
-                        clang::DiagnosticConsumer &D);
+buildCompilerInvocation(const ParseInputs &Inputs, clang::DiagnosticConsumer &D,
+                        std::vector<std::string> *CC1Args = nullptr);
 
 /// Creates a compiler instance, configured so that:
 ///   - Contents of the parsed file are remapped to \p MainFile.
diff --git a/clang-tools-extra/clangd/TUScheduler.cpp b/clang-tools-extra/clangd/TUScheduler.cpp
index d740c387369..b51221d7d90 100644
--- a/clang-tools-extra/clangd/TUScheduler.cpp
+++ b/clang-tools-extra/clangd/TUScheduler.cpp
@@ -407,8 +407,12 @@ void ASTWorker::update(ParseInputs Inputs, WantDiagnostics WantDiags) {
         llvm::join(Inputs.CompileCommand.CommandLine, " "));
     // Rebuild the preamble and the AST.
     StoreDiags CompilerInvocationDiagConsumer;
+    std::vector<std::string> CC1Args;
     std::unique_ptr<CompilerInvocation> Invocation =
         buildCompilerInvocation(Inputs, CompilerInvocationDiagConsumer);
+    // Log cc1 args even (especially!) if creating invocation failed.
+    if (!CC1Args.empty())
+      vlog("cc1 args: {0}", llvm::join(CC1Args, " "));
     std::vector<Diag> CompilerInvocationDiags =
         CompilerInvocationDiagConsumer.take();
     if (!Invocation) {
diff --git a/clang/include/clang/Frontend/Utils.h b/clang/include/clang/Frontend/Utils.h
index 0f9b17ee508..2b142122cb6 100644
--- a/clang/include/clang/Frontend/Utils.h
+++ b/clang/include/clang/Frontend/Utils.h
@@ -217,14 +217,18 @@ createChainedIncludesSource(CompilerInstance &CI,
 /// non-null (and possibly incorrect) CompilerInvocation if any errors were
 /// encountered. When this flag is false, always return null on errors.
 ///
-/// \return A CompilerInvocation, or 0 if none was built for the given
+/// \param CC1Args - if non-null, will be populated with the args to cc1
+/// expanded from \p Args. May be set even if nullptr is returned.
+///
+/// \return A CompilerInvocation, or nullptr if none was built for the given
 /// argument vector.
 std::unique_ptr<CompilerInvocation> createInvocationFromCommandLine(
     ArrayRef<const char *> Args,
     IntrusiveRefCntPtr<DiagnosticsEngine> Diags =
         IntrusiveRefCntPtr<DiagnosticsEngine>(),
     IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS = nullptr,
-    bool ShouldRecoverOnErrors = false);
+    bool ShouldRecoverOnErrors = false,
+    std::vector<std::string> *CC1Args = nullptr);
 
 /// Return the value of the last argument as an integer, or a default. If Diags
 /// is non-null, emits an error if the argument is given, but non-integral.
diff --git a/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp b/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp
index ab62b633cda..18c4814bbd5 100644
--- a/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp
+++ b/clang/lib/Frontend/CreateInvocationFromCommandLine.cpp
@@ -26,7 +26,8 @@ using namespace llvm::opt;
 
 std::unique_ptr<CompilerInvocation> clang::createInvocationFromCommandLine(
     ArrayRef<const char *> ArgList, IntrusiveRefCntPtr<DiagnosticsEngine> Diags,
-    IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS, bool ShouldRecoverOnErorrs) {
+    IntrusiveRefCntPtr<llvm::vfs::FileSystem> VFS, bool ShouldRecoverOnErorrs,
+    std::vector<std::string> *CC1Args) {
   if (!Diags.get()) {
     // No diagnostics engine was provided, so create our own diagnostics object
     // with the default options.
@@ -89,6 +90,8 @@ std::unique_ptr<CompilerInvocation> clang::createInvocationFromCommandLine(
   }
 
   const ArgStringList &CCArgs = Cmd.getArguments();
+  if (CC1Args)
+    *CC1Args = {CCArgs.begin(), CCArgs.end()};
   auto CI = std::make_unique<CompilerInvocation>();
   if (!CompilerInvocation::CreateFromArgs(*CI, CCArgs, *Diags) &&
       !ShouldRecoverOnErorrs)