[clang] Reapply "[Clang] Transform lambda's constraints when instantiating parameter mapping (PR #207966)

[Corentin Jabot via cfe-commits]

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@@ -16095,8 +16097,16 @@ TreeTransform<Derived>::TransformLambdaExpr(LambdaExpr *E) {
   assert(FPTL && "Not a FunctionProtoType?");
 
   AssociatedConstraint TRC = E->getCallOperator()->getTrailingRequiresClause();
-  // If the concept refers to any outer parameter packs, we track the SubstIndex
-  // for evaluation.
+  if (TRC) {
+    ExprResult E = getDerived().TransformLambdaConstraint(
+        const_cast<Expr *>(TRC.ConstraintExpr));
+    if (E.isInvalid())
+      return E;
+    TRC.ConstraintExpr = E.get();
+  }
+  // If the concept refers to any outer parameter packs, we track the
+  // SubstIndex for evaluation.
+  // FIXME: This seems unnecessary after transforming lambda constraints.
   if (TRC && TRC.ConstraintExpr->containsUnexpandedParameterPack() &&
       !TRC.ArgPackSubstIndex)
     TRC.ArgPackSubstIndex = SemaRef.ArgPackSubstIndex;
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cor3ntin wrote:

Did you try to remove that?

https://github.com/llvm/llvm-project/pull/207966