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

[via cfe-commits]

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@@ -6457,6 +6472,18 @@ void InitializationSequence::InitializeFrom(Sema &S,
     }
   }
 
+  if (!S.getLangOpts().CPlusPlus &&
+      Kind.getKind() == InitializationKind::IK_Default) {
+    RecordDecl *Rec = DestType->getAsRecordDecl();
+    if (Rec && Rec->hasUninitializedExplicitInitFields()) {
+      VarDecl *Var = dyn_cast_or_null<VarDecl>(Entity.getDecl());
+      if (Var && !Initializer) {
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higher-performance wrote:

> What is the `VarDecl` here? Again, we have access to the record-decl, so why can't we get the field name here?

The `VarDecl` isn't the field within the class. It's the default-initialized variable that's missing the field initialization. We don't know which field is missing (again, per above).

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