[clang] Add Clang attribute to ensure that fields are initialized explicitly (PR #102040)

[Ilya Biryukov via cfe-commits]

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@@ -743,6 +743,12 @@ void InitListChecker::FillInEmptyInitForField(unsigned Init, FieldDecl *Field,
         ILE->updateInit(SemaRef.Context, Init, Filler);
       return;
     }
+
+    if (Field->hasAttr<ExplicitInitAttr>()) {
+      SemaRef.Diag(ILE->getExprLoc(), diag::warn_field_requires_explicit_init)
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ilya-biryukov wrote:

Your other comment seems right.

`InitListChecker` should not produce any diagnostics when `VerifyOnly == true`, so we should only report the warning when the flag is false.

https://github.com/llvm/llvm-project/pull/102040