PR for llvm/llvm-project#79568

[zyn0217]

Backporting #79568 to clang 18.

[llvmbot]

@llvm/pr-subscribers-clang

Author: Younan Zhang (zyn0217)

Changes

Backporting #79568 to clang 18.

---

Full diff: https://github.com/llvm/llvm-project/pull/80120.diff

3 Files Affected:

• (modified) clang/docs/ReleaseNotes.rst (+4)
• (modified) clang/lib/Sema/SemaConcept.cpp (+6-2)
• (modified) clang/test/SemaTemplate/concepts-lambda.cpp (+18)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 060bc7669b72a..da52d5ac4d3c6 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 acfc00f412540..88fc846c89e42 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 7e431529427df..0b7580f91043c 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

[erichkeane]

Does this fix a regression against 17? I didn't think it did?

[zyn0217]

I think this is a regression from clang 16. https://cpp1.godbolt.org/z/1PnWbvY1r

[zyn0217]

@tstellar Would you mind merging this PR? Thank you in advance!