[clangd] Add --query-driver flag to clangd-indexer

[tetsuo-cpp]

Summary

When using clangd for cross-compiled projects, it's necessary to use the --query-driver flag so that clangd can extract the compiler's built-in header paths. However, there's no such flag for clangd-indexer so we're unable to build a working static index for these projects.

This patch adds a --query-driver flag to clangd-indexer for this scenario.

I saw some tests under clang-tools-extra/clangd/test/ but I think the cross-compilation case is a bit more complex to test. Let me know if you'd like me to look into this further.

Resolves: https://github.com/clangd/clangd/issues/1717

[nridge]

Thanks for the patch!

My thoughts are:

• As mentioned in the issue, I think this fills a logical gap: clangd-indexer is an alternative way of generating a project index to clangd's background indexer, so if clangd has a configuration feature needed for some projects (such as --query-driver), clangd-indexer should have an equivalent ability. (Processing .clangd config files is another such gap that I think would make sense to fill in the future.)
• The implementation is straightforward. I don't think it's interesting enough to warrant spending time writing an automated test for this (especially given that our existing system-include-extractor.test is not particularly easy / pleasant to work with.)

I would suggest waiting a few days to see if Sam has any input, otherwise I think this should be good to merge. Let me know if you need me to commit it.

[tetsuo-cpp]

Thanks for the review @nridge! I'd really appreciate if you could help me with the commit (I don't have commit access).

[nridge]

Committed, thanks!

clang-tools-extra/clangd/indexer/IndexerMain.cpp

 static llvm::cl::opt<IndexFileFormat>
     Format("format", llvm::cl::desc("Format of the index to be written"),
            llvm::cl::values(clEnumValN(IndexFileFormat::YAML, "yaml",
                                        "human-readable YAML format"),
                             clEnumValN(IndexFileFormat::RIFF, "binary",
                                        "binary RIFF format")),
            llvm::cl::init(IndexFileFormat::RIFF));
 
+static llvm::cl::list<std::string> QueryDriverGlobs{
+    "query-driver",
+    llvm::cl::desc(
+        "Comma separated list of globs for white-listing gcc-compatible "
+        "drivers that are safe to execute. Drivers matching any of these globs "
+        "will be used to extract system includes. e.g. "
+        "/usr/bin/**/clang-*,/path/to/repo/**/g++-*"),
+    llvm::cl::CommaSeparated,
+};
+
 class IndexActionFactory : public tooling::FrontendActionFactory {
 public:
   IndexActionFactory(IndexFileIn &Result) : Result(Result) {}
 
   std::unique_ptr<FrontendAction> create() override {
     SymbolCollector::Options Opts;
     Opts.CountReferences = true;
     Opts.FileFilter = [&](const SourceManager &SM, FileID FID) {
int main(int argc, const char **argv) {
 
   if (!Executor) {
     llvm::errs() << llvm::toString(Executor.takeError()) << "\n";
     return 1;
   }
 
   // Collect symbols found in each translation unit, merging as we go.
   clang::clangd::IndexFileIn Data;
+  auto Mangler = std::make_shared<clang::clangd::CommandMangler>(
+      clang::clangd::CommandMangler::detect());
+  Mangler->SystemIncludeExtractor = clang::clangd::getSystemIncludeExtractor(
+      static_cast<llvm::ArrayRef<std::string>>(
+          clang::clangd::QueryDriverGlobs));
   auto Err = Executor->get()->execute(
       std::make_unique<clang::clangd::IndexActionFactory>(Data),
       clang::tooling::ArgumentsAdjuster(
-          [Mangler = std::make_shared<clang::clangd::CommandMangler>(
-               clang::clangd::CommandMangler::detect())](
-              const std::vector<std::string> &Args, llvm::StringRef File) {
+          [Mangler = std::move(Mangler)](const std::vector<std::string> &Args,
+                                         llvm::StringRef File) {
             clang::tooling::CompileCommand Cmd;
             Cmd.CommandLine = Args;
             Mangler->operator()(Cmd, File);
             return Cmd.CommandLine;
           }));
   if (Err) {
     clang::clangd::elog("{0}", std::move(Err));
   }
 
   // Emit collected data.
   clang::clangd::IndexFileOut Out(Data);
   Out.Format = clang::clangd::Format;
   llvm::outs() << Out;
   return 0;
 }