[clangd] Bail gracefully if given an assembly or IR source file

[nridge]

Summary

The previous behaviour is to try to parse such files, and in some
cases assert or hang in components that don't expect these forms of
input, like TokenBuffer.

Fixes https://github.com/llvm/llvm-project/issues/62090

[nridge]

clang-tools-extra/clangd/unittests/ParsedASTTests.cpp

859

(I could alternatively give TestTU::build() an option to expect failure to build an AST.)

[nridge]

Review ping

[nridge]

Adding Sam, since you're on a review roll ;)

[sammccall]

In D149236#4597600, @nridge wrote:

Adding Sam, since you're on a review roll ;)

back from vacation :-)

clang-tools-extra/clangd/unittests/ParsedASTTests.cpp

868

(the mangler isn't relevant here I think)

[nridge]

Address review comment

clang-tools-extra/clangd/ParsedAST.cpp

ParsedAST::build(llvm::StringRef Filename, const ParseInputs &Inputs,
   trace::Span Tracer("BuildAST");
   SPAN_ATTACH(Tracer, "File", Filename);
 
   auto VFS = Inputs.TFS->view(Inputs.CompileCommand.Directory);
   if (Preamble && Preamble->StatCache)
     VFS = Preamble->StatCache->getConsumingFS(std::move(VFS));
 
   assert(CI);
+
+  if (CI->getFrontendOpts().Inputs.size() > 0) {
+    auto Lang = CI->getFrontendOpts().Inputs[0].getKind().getLanguage();
+    if (Lang == Language::Asm || Lang == Language::LLVM_IR) {
+      elog("Clangd does not support assembly or IR source files");
+      return std::nullopt;
+    }
+  }
+
   // Command-line parsing sets DisableFree to true by default, but we don't want
   // to leak memory in clangd.
   CI->getFrontendOpts().DisableFree = false;
   const PrecompiledPreamble *PreamblePCH =
       Preamble ? &Preamble->Preamble : nullptr;
 
   // This is on-by-default in windows to allow parsing SDK headers, but it
   // breaks many features. Disable it for the main-file (not preamble).

clang-tools-extra/clangd/unittests/ParsedASTTests.cpp

 //
 //===----------------------------------------------------------------------===//
 
 #include "../../clang-tidy/ClangTidyCheck.h"
 #include "../../clang-tidy/ClangTidyModule.h"
 #include "../../clang-tidy/ClangTidyModuleRegistry.h"
 #include "AST.h"
 #include "Annotations.h"
+#include "CompileCommands.h"
 #include "Compiler.h"
 #include "Diagnostics.h"
 #include "Headers.h"
 #include "ParsedAST.h"
 #include "Preamble.h"
 #include "SourceCode.h"
 #include "TestFS.h"
 #include "TestTU.h"
TEST(ParsedASTTest, DiscoversPragmaMarks) {
   )cpp";
   auto AST = TU.build();
 
   EXPECT_THAT(AST.getMarks(), ElementsAre(pragmaTrivia(" In Preamble"),
                                           pragmaTrivia(" - Something Impl"),
                                           pragmaTrivia(" End")));
 }
 
+TEST(ParsedASTTest, GracefulFailureOnAssemblyFile) {
+  std::string Filename = "TestTU.S";
+  std::string Code = R"S(
+main:
+    # test comment
+    bx lr
+  )S";
+
+  // The rest is a simplified version of TestTU::build().
+  // Don't call TestTU::build() itself because it would assert on
+  // failure to build an AST.
+  MockFS FS;
+  std::string FullFilename = testPath(Filename);
+  FS.Files[FullFilename] = Code;
+  ParseInputs Inputs;
+  auto &Argv = Inputs.CompileCommand.CommandLine;
+  Argv = {"clang"};
+  Argv.push_back(FullFilename);
+  auto Mangler = CommandMangler::forTests();
+  Mangler(Inputs.CompileCommand, FullFilename);
+  Inputs.CompileCommand.Filename = FullFilename;
+  Inputs.CompileCommand.Directory = testRoot();
+  Inputs.Contents = Code;
+  Inputs.TFS = &FS;
+  StoreDiags Diags;
+  auto CI = buildCompilerInvocation(Inputs, Diags);
+  assert(CI && "Failed to build compilation invocation.");
+  auto AST = ParsedAST::build(FullFilename, Inputs, std::move(CI), {}, nullptr);
+
+  EXPECT_FALSE(AST.has_value())
+      << "Should not try to build AST for assembly source file";
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang