[clang] [clang] Add -Wmissing-designated-field-initializers (PR #81364)

[Erich Keane via cfe-commits]

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@@ -2363,8 +2356,11 @@ void InitListChecker::CheckStructUnionTypes(
   }
 
   // Emit warnings for missing struct field initializers.
-  if (!VerifyOnly && InitializedSomething && CheckForMissingFields &&
-      !RD->isUnion()) {
+  // This check is disabled for designated initializers in C.
+  // This matches gcc behaviour.
+  if (!VerifyOnly && InitializedSomething && !RD->isUnion() &&
+      !IList->isIdiomaticZeroInitializer(SemaRef.getLangOpts()) &&
+      !(HasDesignatedInit && !SemaRef.getLangOpts().CPlusPlus)) {
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erichkeane wrote:

I'm not asking to add a level/'if'.  I'm asking for declaring a set of bools above this 'if' that better reflect what is being tested.  With HasDesignatedInit/CPlusPlus checks only being vaguely related, and the 'sort' of the checks not really being clear, I am asking for the list of '!'s to be shorter/grouped into a couple of 'bools' with descriptive names.

https://github.com/llvm/llvm-project/pull/81364