[clang] [Clang] enhance diagnostic by attaching source location to deduced type in trailing return without auto (PR #115786)

[Mariya Podchishchaeva via cfe-commits]

================
@@ -4887,9 +4887,18 @@ static TypeSourceInfo *GetFullTypeForDeclarator(TypeProcessingState &state,
                       cast<AutoType>(T)->getKeyword() !=
                           AutoTypeKeyword::Auto ||
                       cast<AutoType>(T)->isConstrained())) {
-            S.Diag(D.getDeclSpec().getTypeSpecTypeLoc(),
-                   diag::err_trailing_return_without_auto)
-                << T << D.getDeclSpec().getSourceRange();
+            SourceLocation Loc = D.getDeclSpec().getTypeSpecTypeLoc();
+            SourceRange SR = D.getDeclSpec().getSourceRange();
+            if (Loc.isInvalid()) {
----------------
Fznamznon wrote:

Could you please add a comment explaining what is being done here? It is clear from the context of the patch, but I don't think it is easy to understand when simply browsing through the code.

https://github.com/llvm/llvm-project/pull/115786