[analyzer][NFC] Fix dangling StringRef in barely used code

[donat.nagy]

Summary

CheckerContext::getNoteTag has a shorthand version that takes a plain 'StringRef Note' instead of a lambda that calculates the note.

The old implementation of this method was incorrect because it created a lambda that captured the StringRef, which was dereferenced much later, when the NoteTags were visited.

In the current codebase this does not cause errors because this method is called only once, and there the Note argument is a string literal that remains valid. However, I tried to use this method in a checker that I was prototyping, and there it printed random memory junk (instead of the message that I composed in a local variable).

[balazske]

This is actually needed to get correct bug reports in D153612, otherwise I got garbage messages (probably a std::string stack variable was passed to the getNoteTag function). I would not say that this is NFC because it is a bugfix.

clang/include/clang/StaticAnalyzer/Core/PathSensitive/CheckerContext.h

public:
   /// A shorthand version of getNoteTag that accepts a plain note.
   ///
   /// @param Note The note.
   /// @param IsPrunable Whether the note is prunable. It allows BugReporter
   ///        to omit the note from the report if it would make the displayed
   ///        bug path significantly shorter.
   const NoteTag *getNoteTag(StringRef Note, bool IsPrunable = false) {
     return getNoteTag(
-        [Note](BugReporterContext &,
-               PathSensitiveBugReport &) { return std::string(Note); },
+        [Note = std::string(Note)](BugReporterContext &,
+               PathSensitiveBugReport &) { return Note; },
         IsPrunable);
   }
 
   /// A shorthand version of getNoteTag that accepts a lambda with stream for
   /// note.
   ///
   /// @param Cb Callback with 'BugReport &' and 'llvm::raw_ostream &'.
   /// @param IsPrunable Whether the note is prunable. It allows BugReporter