From 221acd67ca50f8f069037e034a3250f13d75a9f5 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Thu, 26 May 2022 22:43:05 -0400
Subject: [PATCH] c++: lambda in concept [PR105652]

We currently check satisfaction in the context of the constrained
declaration (which may be wrong, see PR104111).  When checking C<int>
for S<int>, we currently substitute into the lambda in the context of
S<T> (rather than S<int>, which seems wrong if the above isn't wrong), so
the new closure type thinks its context is S<T>, which confuses debug
output.  For the moment, let's work around all of this by overriding the
context of the closure.

	PR c++/105652

gcc/cp/ChangeLog:

	* pt.cc (tsubst_lambda_expr): Don't let a namespace-scope lambda
	instantiate into a class-scope lambda.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-lambda20.C: New test.
---
 gcc/cp/pt.cc                                   | 17 ++++++++++++-----
 gcc/testsuite/g++.dg/cpp2a/concepts-lambda20.C | 17 +++++++++++++++++
 2 files changed, 29 insertions(+), 5 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda20.C

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 24bbe2f40608..f1f080531a67 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -19740,11 +19740,18 @@ tsubst_lambda_expr (tree t, tree args, tsubst_flags_t complain, tree in_decl)
     return error_mark_node;
 
   if (LAMBDA_EXPR_EXTRA_SCOPE (t) == NULL_TREE)
-    /* A lambda in a default argument outside a class gets no
-       LAMBDA_EXPR_EXTRA_SCOPE, as specified by the ABI.  But
-       tsubst_default_argument calls start_lambda_scope, so we need to
-       specifically ignore it here, and use the global scope.  */
-    record_null_lambda_scope (r);
+    {
+      /* A lambda in a default argument outside a class gets no
+	 LAMBDA_EXPR_EXTRA_SCOPE, as specified by the ABI.  But
+	 tsubst_default_argument calls start_lambda_scope, so we need to
+	 specifically ignore it here, and use the global scope.  */
+      record_null_lambda_scope (r);
+
+      /* If we're pushed into another scope (PR105652), fix it.  */
+      if (TYPE_NAMESPACE_SCOPE_P (TREE_TYPE (t)))
+	TYPE_CONTEXT (type) = DECL_CONTEXT (TYPE_NAME (type))
+	  = TYPE_CONTEXT (TREE_TYPE (t));
+    }
   else
     record_lambda_scope (r);
 
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda20.C b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda20.C
new file mode 100644
index 000000000000..40e5973176ea
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda20.C
@@ -0,0 +1,17 @@
+// PR c++/105652
+// { dg-do compile { target c++20 } }
+// { dg-additional-options -g }
+
+template<int>
+struct I {};
+
+template<class T>
+concept C = []<int N>(I<N>) { return true; } (I<0>{});
+
+template<class T>
+struct S { };
+
+template<C T>
+struct S<T> { constexpr static bool value = true; };
+
+static_assert(S<int>::value);
-- 
2.47.2