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

[via cfe-commits]

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@@ -4561,6 +4569,13 @@ static void TryConstructorInitialization(Sema &S,
 
   CXXConstructorDecl *CtorDecl = cast<CXXConstructorDecl>(Best->Function);
   if (Result != OR_Deleted) {
+    if (!IsListInit && Kind.getKind() == InitializationKind::IK_Default &&
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higher-performance wrote:

> Right, but that is a property of the declaration 'elsewhere', not the initialization of the type here.

It's default-initialization of a type that has mandatory fields -- that means at least one initializer is missing, right? Or perhaps I'm not understanding what you mean.

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