[clangd] Fix crash in bugprone-bad-signal-to-kill-thread clang-tidy check.

Inside clangd, clang-tidy checks don't see preprocessor events in the preamble.
This leads to `Token::PtrData == nullptr` for tokens that the macro is defined to.
E.g. `#define SIGTERM 15`:
- Token::Kind == tok::numeric_constant (Token::isLiteral() == true)
- Token::UintData == 2
- Token::PtrData == nullptr

As the result of this, bugprone-bad-signal-to-kill-thread check crashes at null-dereference inside clangd.

Reviewed By: hokein

Differential Revision: https://reviews.llvm.org/D85417

Author: ArcsinX

clang-tools-extra/clang-tidy/bugprone/BadSignalToKillThreadCheck.cpp

@@ -39,7 +39,7 @@ void BadSignalToKillThreadCheck::check(const MatchFinder::MatchResult &Result) {
       return llvm::None;
     const MacroInfo *MI = PP->getMacroInfo(It->first);
     const Token &T = MI->tokens().back();
-    if (!T.isLiteral())
+    if (!T.isLiteral() || !T.getLiteralData())
       return llvm::None;
     StringRef ValueStr = StringRef(T.getLiteralData(), T.getLength());
 

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

@@ -438,6 +438,21 @@ TEST(DiagnosticTest, ClangTidySuppressionCommentTrumpsWarningAsError) {
   EXPECT_THAT(TU.build().getDiagnostics(), UnorderedElementsAre());
 }
 
+TEST(DiagnosticTest, ClangTidyNoLiteralDataInMacroToken) {
+  Annotations Main(R"cpp(
+    #define SIGTERM 15
+    using pthread_t = int;
+    int pthread_kill(pthread_t thread, int sig);
+    int func() {
+      pthread_t thread;
+      return pthread_kill(thread, 0);
+    }
+  )cpp");
+  TestTU TU = TestTU::withCode(Main.code());
+  TU.ClangTidyChecks = "-*,bugprone-bad-signal-to-kill-thread";
+  EXPECT_THAT(TU.build().getDiagnostics(), UnorderedElementsAre()); // no-crash
+}
+
 TEST(DiagnosticsTest, Preprocessor) {
   // This looks like a preamble, but there's an #else in the middle!
   // Check that: