[clangd] Don't crash on `#pragma clang __debug parser_crash`

[ArcsinX]

Summary

Currently, clangd crashes when opening a file with #pragma clang __debug parser_crash (e.g. clang/test/Modules/Inputs/crash.h).
This patch disables these crashes.

[kadircet]

thanks, lgtm!

clang-tools-extra/clangd/Compiler.cpp

buildCompilerInvocation(const ParseInputs &Inputs, clang::DiagnosticConsumer &D,
   // Disable any pch generation/usage operations. Since serialized preamble
   // format is unstable, using an incompatible one might result in unexpected
   // behaviours, including crashes.
   CI->getPreprocessorOpts().ImplicitPCHInclude.clear();
   CI->getPreprocessorOpts().PrecompiledPreambleBytes = {0, false};
   CI->getPreprocessorOpts().PCHThroughHeader.clear();
   CI->getPreprocessorOpts().PCHWithHdrStop = false;
   CI->getPreprocessorOpts().PCHWithHdrStopCreate = false;
+  // Don't crash on `#pragma clang __debug parser_crash`
+  CI->getPreprocessorOpts().DisablePragmaDebugCrash = true;
 
   // Recovery expression currently only works for C++.
   if (CI->getLangOpts()->CPlusPlus) {
     CI->getLangOpts()->RecoveryAST = Inputs.Opts.BuildRecoveryAST;
     CI->getLangOpts()->RecoveryASTType = Inputs.Opts.PreserveRecoveryASTType;
   }
   return CI;
 }

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

EXPECT_THAT(buildCompilerInvocation(TU.inputs(FS), Diags)
                   .ImplicitPCHInclude,
               IsEmpty());
   EXPECT_THAT(buildCompilerInvocation(TU.inputs(FS), Diags)
                   ->getPreprocessorOpts()
                   .PCHThroughHeader,
               IsEmpty());
 }
 
+TEST(BuildCompilerInvocation, PragmaDebugCrash) {
+  TestTU TU = TestTU::withCode("#pragma clang __debug parser_crash");
+  TU.build(); // no-crash
+}
+
 } // namespace
 } // namespace clangd
 } // namespace clang