[clang] [clang] Fix handling of explicit-`this` functions as template arguments (PR #133748)

[Eli Friedman via cfe-commits]

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@@ -7558,6 +7558,18 @@ ExprResult Sema::BuildExpressionFromDeclTemplateArgument(
   } else {
     assert(ParamType->isReferenceType() &&
            "unexpected type for decl template argument");
+
+    if (auto *Method = dyn_cast<CXXMethodDecl>(VD);
+        Method && Method->isExplicitObjectMemberFunction()) {
+      // If the argument is an explicit object member function,
+      // RefExpr is currently a prvalue. Make it an lvalue.
+      RefExpr = ImplicitCastExpr::Create(
+          Context, RefExpr.get()->getType(), CK_NoOp, RefExpr.get(),
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efriedma-quic wrote:

I don't think CK_NoOp is the right CastKind, even if it appears to work for simple cases.  Either we should just use UO_Deref, or we should create a new CastKind.

https://github.com/llvm/llvm-project/pull/133748