[cfe-dev] How to determine if a raw_id token is a macro name?

[Ben Boeckel via cfe-dev]

On Fri, Jan 07, 2022 at 07:45:23 -0500, David Rector via cfe-dev wrote:
> I believe the best you can do is to convert the string to an
> IdentifierInfo and access hadMacroDefinition:
> ```
> IdentifierInfo &FooII = Context.Idents.get("Foo");
> bool FooMaybeMacroName = FooII.hadMacroDefinition();
> ```
> This won’t be perfect — it won’t tell you whether Foo was defined at
> the particular SourceLocation you are interested in, only whether at
> some point in the TU a macro with that name was defined.
> 
> It would be nice to be able to test `FooII.hasMacroDefinition()`
> instead, but the problem mentioned in the other thread rears its head
> here too: the AST matching on which clang tidy depends is all done
> during HandleTranslationUnit, *after* all parsing has completed, so
> hasMacroDefinition() will only return true if a macro with that name
> was not #undef’d.  

Ignoring the state tracking problem, what happens with use of `foo`
after `#define foo foo`? More reaslistic usages in this SO thread:

    https://stackoverflow.com/questions/46797804/defining-something-to-itself-in-c-preprocessor

--Ben