[clang] [Clang][P1061] Add stuctured binding packs (PR #121417)

[Younan Zhang via cfe-commits]

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@@ -15991,6 +15998,24 @@ TreeTransform<Derived>::TransformFunctionParmPackExpr(FunctionParmPackExpr *E) {
   return E;
 }
 
+template <typename Derived>
+ExprResult TreeTransform<Derived>::TransformResolvedUnexpandedPackExpr(
+    ResolvedUnexpandedPackExpr *E) {
+  bool ArgumentChanged = false;
+  SmallVector<Expr *, 12> NewExprs;
+  if (TransformExprs(E->getExprs().begin(), E->getNumExprs(),
+                     /*IsCall=*/false, NewExprs, &ArgumentChanged))
+    return ExprError();
+
+  if (!AlwaysRebuild() && !ArgumentChanged)
+    return E;
+
+  // NOTE: The type is just a superficial PackExpansionType
+  //       that needs no substitution.
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zyn0217 wrote:

Can we add a caveat to `ResolvedUnexpandedPackExpr` to highlight such a thing? People might be confused about an expanded ResolvedUnexpandedPackExpr still having an unexpanded PackExpansionType.

https://github.com/llvm/llvm-project/pull/121417