[clang] [clang][Sema] Fix initialization of `NonTypeTemplateParmDecl`... (PR #121768)

[Younan Zhang via cfe-commits]

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@@ -1235,15 +1235,24 @@ bool Sema::AttachTypeConstraint(AutoTypeLoc TL,
         << NewConstrainedParm->getTypeSourceInfo()
                ->getTypeLoc()
                .getSourceRange();
+    NewConstrainedParm->setPlaceholderTypeConstraint(
+        RecoveryExpr::Create(Context, OrigConstrainedParm->getType(),
+                             OrigConstrainedParm->getBeginLoc(),
+                             OrigConstrainedParm->getEndLoc(), {}));
     return true;
   }
   // FIXME: Concepts: This should be the type of the placeholder, but this is
   // unclear in the wording right now.
   DeclRefExpr *Ref =
       BuildDeclRefExpr(OrigConstrainedParm, OrigConstrainedParm->getType(),
                        VK_PRValue, OrigConstrainedParm->getLocation());
-  if (!Ref)
+  if (!Ref) {
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zyn0217 wrote:

+1, `BuildDeclRefExpr` wouldn't fail with a nullptr

https://github.com/llvm/llvm-project/pull/121768