[clang] [Clang] Treat default template argument as constant expressions (PR #107073)

[Younan Zhang via cfe-commits]

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@@ -960,6 +960,8 @@ Parser::ParseNonTypeTemplateParameter(unsigned Depth, unsigned Position) {
       EnterExpressionEvaluationContext ConstantEvaluated(
           Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated);
       DefaultArg = Actions.CorrectDelayedTyposInExpr(ParseInitializer());
+      if (DefaultArg.isUsable())
+        DefaultArg = Actions.ActOnConstantExpression(DefaultArg);
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zyn0217 wrote:

(I noticed that provision from the comment in that function, but I still want to confirm what the intention is here)
So... this is invalid? This discrepancy could be rather confusing from what i see :(

https://github.com/llvm/llvm-project/pull/107073