[PATCH] D119778: [clang] Add a note "deducing return type for 'foo'"

[Richard Smith - zygoloid via Phabricator via cfe-commits]

rsmith added inline comments.


================
Comment at: clang/lib/Sema/SemaStmt.cpp:3804-3809
+    if (DAR != DAR_Succeeded) {
+      if (OrigResultType.getBeginLoc().isValid())
+        Diag(OrigResultType.getBeginLoc(), diag::note_deducing_return_type_for)
+            << FD << OrigResultType.getSourceRange();
       return true;
+    }
----------------
The approach of tacking a note onto the end of someone else's diagnostic is an antipattern and should be avoided in new code. For example, if `DeduceAutoType` produces an error (which is shown) then a warning (which is hidden), the note will be attached to the warning, and will not appear.

The right thing to do is to create a new kind of `CodeSynthesisContext` for this case and push that. Then we'll use the same logic as in template instantiation backtraces, and the note will get properly attached to the first emitted diagnostic within the context. This will also remove the need to track down all the different places that emit diagnostics (like we see below): you just push the context when you start doing the action you want to attach the note to and pop it when you're done. It'll also properly order the note with respect to other context notes.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D119778/new/

https://reviews.llvm.org/D119778