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

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 #62090

Differential Revision: https://reviews.llvm.org/D149236

clang-tools-extra/clangd/ParsedAST.cpp

@@ -396,6 +396,15 @@ ParsedAST::build(llvm::StringRef Filename, const ParseInputs &Inputs,
     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;

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

@@ -13,6 +13,7 @@
 
 #include "../../clang-tidy/ClangTidyCheck.h"
 #include "AST.h"
+#include "CompileCommands.h"
 #include "Compiler.h"
 #include "Config.h"
 #include "Diagnostics.h"
@@ -731,6 +732,37 @@ TEST(ParsedASTTest, DiscoversPragmaMarks) {
                                           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);
+  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