[PATCH] D122983: [C11/C2x] Change the behavior of the implicit function declaration warning

Erich Keane via Phabricator via cfe-commits cfe-commits at lists.llvm.org
Mon Apr 4 07:19:19 PDT 2022

erichkeane added subscribers: MattDevereau, david-arm, paulwalker-arm, sdesmalen.
erichkeane added a comment.

I don't have any real comments (the changes are quite trivial), and I really like the approach here, I think it is more than generous.  I see the transition of 
C89/C99: Warn
C11/C17: Warn-as-default-error
C2x: Hard error

as a really gentle and explainable behavior, its just a shame it took us this long to do so.

I DO see that there are a ton of AArch64 Intrin tests that seem to have the same problems here (in Pre-commit-CI), that will need this change too, though they are questionably written.  I might suggest just adding the -std=c99 flag to all of those.  Attn: @paulwalker-arm @MattDevereau @david-arm @sdesmalen

Comment at: clang/docs/ReleaseNotes.rst:114
+- The ``-Wimplicit-function-declaration`` warning diagnostic now defaults to
+  emitting an error (which can be downgraded with ``-Wno-error``) in C11 and
+  C17 mode. This is because the feature was removed in C99 and cannot be
xbolva00 wrote:
> I would mention explicitly  -Wno-error= implicit-function-declaration as -Wno-error is a big hammer.
I think this is a valuable change, as suggested by @xbolva00 



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