[clang-tidy] Fix bugprone-bad-signal-to-kill-thread not working in clangd (#180711)

After preamble deserialization, `Token::getLiteralData()` returns
`nullptr` for macro tokens defined in headers. Fall back to
`SourceManager` to retrieve the token text from the source buffer.

Fixes https://github.com/clangd/clangd/issues/2473

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

@@ -38,9 +38,15 @@ void BadSignalToKillThreadCheck::check(const MatchFinder::MatchResult &Result) {
       return std::nullopt;
     const MacroInfo *MI = PP->getMacroInfo(It->first);
     const Token &T = MI->tokens().back();
-    if (!T.isLiteral() || !T.getLiteralData())
+
+    if (!T.isLiteral())
+      return std::nullopt;
+
+    SmallVector<char> Buffer;
+    bool Invalid = false;
+    const StringRef ValueStr = PP->getSpelling(T, Buffer, &Invalid);
+    if (Invalid)
       return std::nullopt;
-    const StringRef ValueStr = StringRef(T.getLiteralData(), T.getLength());
 
     llvm::APInt IntValue;
     constexpr unsigned AutoSenseRadix = 0;

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

@@ -823,6 +823,25 @@ TEST(DiagnosticTest, ClangTidyNoLiteralDataInMacroToken) {
   EXPECT_THAT(TU.build().getDiagnostics(), UnorderedElementsAre()); // no-crash
 }
 
+TEST(DiagnosticTest, BadSignalToKillThreadInPreamble) {
+  Annotations Main(R"cpp(
+    #include "signal.h"
+    using pthread_t = int;
+    int pthread_kill(pthread_t thread, int sig);
+    int func() {
+      pthread_t thread;
+      return pthread_kill(thread, 15);
+    }
+  )cpp");
+  TestTU TU = TestTU::withCode(Main.code());
+  TU.HeaderFilename = "signal.h";
+  TU.HeaderCode = "#define SIGTERM 15";
+  TU.ClangTidyProvider = addTidyChecks("bugprone-bad-signal-to-kill-thread");
+  EXPECT_THAT(TU.build().getDiagnostics(),
+              ifTidyChecks(UnorderedElementsAre(
+                  diagName("bugprone-bad-signal-to-kill-thread"))));
+}
+
 TEST(DiagnosticTest, ClangTidyMacroToEnumCheck) {
   Annotations Main(R"cpp(
     #if 1

clang-tools-extra/docs/ReleaseNotes.rst

@@ -144,6 +144,10 @@ Changes in existing checks
   <clang-tidy/checks/bugprone/argument-comment>` to also check for C++11
   inherited constructors.
 
+- Improved :doc:`bugprone-bad-signal-to-kill-thread
+  <clang-tidy/checks/bugprone/bad-signal-to-kill-thread>` check by fixing false
+  negatives when the ``SIGTERM`` macro is obtained from a precompiled header.
+
 - Improved :doc:`bugprone-exception-escape
   <clang-tidy/checks/bugprone/exception-escape>` check by adding
   `TreatFunctionsWithoutSpecificationAsThrowing` option to support reporting