[Concepts] Traverse the instantiation chain for parameter injection i…

…nside a constraint scope (#79568)

We preserve the trailing requires-expression during the lambda
expression transformation. In order to get those referenced parameters
inside a requires-expression properly resolved to the instantiated
decls, we intended to inject these 'original' `ParmVarDecls` to the
current instantiaion scope, at `Sema::SetupConstraintScope`.

The previous approach seems to overlook nested instantiation chains,
leading to the crash within a nested lambda followed by a requires
clause.

This fixes #73418.

clang/docs/ReleaseNotes.rst

@@ -119,6 +119,9 @@ Bug Fixes to C++ Support
   parameter where we did an incorrect specialization of the initialization of
   the default parameter.
   Fixes (`#68490 <https://github.com/llvm/llvm-project/issues/68490>`_)
+- Fixed a bug where variables referenced by requires-clauses inside
+  nested generic lambdas were not properly injected into the constraint scope.
+  (`#73418 <https://github.com/llvm/llvm-project/issues/73418>`_)
 
 Bug Fixes to AST Handling
 ^^^^^^^^^^^^^^^^^^^^^^^^^

clang/lib/Sema/SemaConcept.cpp

@@ -612,8 +612,12 @@ bool Sema::SetupConstraintScope(
 
     // If this is a member function, make sure we get the parameters that
     // reference the original primary template.
-    if (const auto *FromMemTempl =
-            PrimaryTemplate->getInstantiatedFromMemberTemplate()) {
+    // We walk up the instantiated template chain so that nested lambdas get
+    // handled properly.
+    for (FunctionTemplateDecl *FromMemTempl =
+             PrimaryTemplate->getInstantiatedFromMemberTemplate();
+         FromMemTempl;
+         FromMemTempl = FromMemTempl->getInstantiatedFromMemberTemplate()) {
       if (addInstantiatedParametersToScope(FD, FromMemTempl->getTemplatedDecl(),
                                            Scope, MLTAL))
         return true;

clang/test/SemaTemplate/concepts-lambda.cpp

@@ -149,3 +149,21 @@ void foo() {
   auto caller = make_caller.operator()<&S1::f1>();
 }
 } // namespace ReturnTypeRequirementInLambda
+
+namespace GH73418 {
+void foo() {
+  int x;
+  [&x](auto) {
+    return [](auto y) {
+      return [](auto obj, auto... params)
+        requires requires {
+          sizeof...(params);
+          [](auto... pack) {
+            return sizeof...(pack);
+          }(params...);
+        }
+      { return false; }(y);
+    }(x);
+  }(x);
+}
+} // namespace GH73418