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

[Vadim D. 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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vvd170501 wrote:

@erichkeane, I did something like this before 83864610d6b6470a0f229c516821d8344d994562, but this adds another indentation level.

It's possible to calculate `DisableCheck` before the `if` statement, but it'll probably be less optimal than the current solution - if `VerifyOnly` is true, `DisableCheck` is not needed.

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