[clang] [Clang] add fix-it hints for unknown attributes (PR #141305)

[Erich Keane via cfe-commits]

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@@ -7867,15 +7865,16 @@ void Sema::checkUnusedDeclAttributes(Declarator &D) {
 
 void Sema::DiagnoseUnknownAttribute(const ParsedAttr &AL) {
   std::string NormalizedFullName = '\'' + AL.getNormalizedFullName() + '\'';
+  SourceRange NR = AL.getNormalizedRange();
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erichkeane wrote:

> What I was thinking is that if we have information about the `attribute-using prefix`, we could avoid normalization when suggesting a typo correction (while still using the scope::attr format in the diagnostic message). Instead, we could provide two separate fix-its: one for the scope and one for the attribute name. Not sure if that approach makes sense.

It DOES make sense.  I was sorta hoping we could come up with a method to do the two separate on an individual identifier basis (so doing 1 level of correction at a scope, then a separate on on the attribute itself).

BUT this requires us to act separately on the scope so we cna do some sort of validation/fixit.

https://github.com/llvm/llvm-project/pull/141305