[clang] [clang-tools-extra] [Clang] [Sema] Diagnose unknown std::initializer_list layout in SemaInit (PR #95580)

[via cfe-commits]

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@@ -9392,6 +9392,57 @@ ExprResult InitializationSequence::Perform(Sema &S,
       // Wrap it in a construction of a std::initializer_list<T>.
       CurInit = new (S.Context) CXXStdInitializerListExpr(Step->Type, MTE);
 
+      if (!Step->Type->isDependentType()) {
+        assert(S.isCompleteType(CurInit.get()->getExprLoc(), Step->Type,
+                                Sema::CompleteTypeKind::Normal) &&
+               "std::initializer_list<E> incomplete when used during "
+               "initialization");
+        QualType ElementType;
+        [[maybe_unused]] bool IsStdInitializerList =
+            S.isStdInitializerList(Step->Type, &ElementType);
+        assert(IsStdInitializerList &&
+               "StdInitializerList step to non-std::initializer_list");
+        RecordDecl *Record = Step->Type->castAs<RecordType>()->getDecl();
+
+        auto InvalidType = [&] {
+          S.Diag(Record->getLocation(),
+                 diag::err_std_initializer_list_malformed)
+              << Step->Type.getUnqualifiedType();
+          return ExprError();
+        };
+
+        // FIXME: What if the initializer_list type has base classes, etc?
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Sirraide wrote:

We should check for that here. I don’t think there is a point in allowing `std::initializer_list` have bases or be polymorphic.

https://github.com/llvm/llvm-project/pull/95580