From 16a8c31d342abed9c02493445c14c1bc7fd1519e Mon Sep 17 00:00:00 2001
From: Younan Zhang <zyn7109@gmail.com>
Date: Sat, 27 Jan 2024 15:42:52 +0800
Subject: [PATCH] [Concepts] Traverse the instantiation chain for parameter
 injection inside 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 https://github.com/llvm/llvm-project/issues/73418.
---
 clang/docs/ReleaseNotes.rst                 |  4 ++++
 clang/lib/Sema/SemaConcept.cpp              |  8 ++++++--
 clang/test/SemaTemplate/concepts-lambda.cpp | 18 ++++++++++++++++++
 3 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 060bc7669b72a5..da52d5ac4d3c6a 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -1054,6 +1054,10 @@ Bug Fixes to C++ Support
   Fixes (`#78830 <https://github.com/llvm/llvm-project/issues/78830>`_)
   Fixes (`#60085 <https://github.com/llvm/llvm-project/issues/60085>`_)
 
+- 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
 ^^^^^^^^^^^^^^^^^^^^^^^^^
 - Fixed an import failure of recursive friend class template.
diff --git a/clang/lib/Sema/SemaConcept.cpp b/clang/lib/Sema/SemaConcept.cpp
index acfc00f4125407..88fc846c89e42c 100644
--- a/clang/lib/Sema/SemaConcept.cpp
+++ b/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;
diff --git a/clang/test/SemaTemplate/concepts-lambda.cpp b/clang/test/SemaTemplate/concepts-lambda.cpp
index 7e431529427dff..0b7580f91043c7 100644
--- a/clang/test/SemaTemplate/concepts-lambda.cpp
+++ b/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