https://gcc.gnu.org/g:94438ca82792063abf05823326695af25ab02d17
commit r15-9325-g94438ca82792063abf05823326695af25ab02d17
Author: Jason Merrill <ja...@redhat.com>
Date: Tue Apr 8 15:53:34 2025 -0400
c++: lambda in concept [PR118698]
When normalizing is_foo for <T>, we get to normalizing
callable<decltype(...),T> for <T,foo>, which means substituting <T,foo> into
<decltype(...),T>.
Since r14-9938, because in_template_context is false we return the lambda
unchanged, just with LAMBDA_EXPR_EXTRA_ARGS set, so the closure type still
refers to the is_specialization_of tparms in its CLASSTYPE_TEMPLATE_INFO.
So then in normalize_atom caching find_template_parameters walks over the
parameter mapping; any_template_parm_r walks into the TREE_TYPE of a
LAMBDA_EXPR without considering EXTRA_ARGS and finds a template parm from
the wrong parameter list.
But since r15-3530 we expect to set tf_partial when substituting with
dependent arguments, so we should set that when normalizing. And then
tf_partial causes TREE_STATIC to be set on the EXTRA_ARGS, meaning that
those args will replace all the template parms in the rest of the lambda, so
we can walk just the EXTRA_ARGS and ignore the rest.
PR c++/118698
gcc/cp/ChangeLog:
* constraint.cc (struct norm_info): Add tf_partial.
* pt.cc (any_template_parm_r): Handle LAMBDA_EXPR_EXTRA_ARGS.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-lambda22.C: New test.
Diff:
---
gcc/cp/constraint.cc | 2 +-
gcc/cp/pt.cc | 12 ++++++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-lambda22.C | 21 +++++++++++++++++++++
3 files changed, 34 insertions(+), 1 deletion(-)
diff --git a/gcc/cp/constraint.cc b/gcc/cp/constraint.cc
index a9caba8e2cc7..2f1678ce4ff9 100644
--- a/gcc/cp/constraint.cc
+++ b/gcc/cp/constraint.cc
@@ -354,7 +354,7 @@ struct norm_info : subst_info
/* Construct a top-level context for DECL. */
norm_info (tree in_decl, bool diag)
- : subst_info (tf_warning_or_error, in_decl),
+ : subst_info (tf_warning_or_error|tf_partial, in_decl),
generate_diagnostics (diag)
{
if (in_decl)
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 8f35fa702a21..0e120c4040ed 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -11117,6 +11117,18 @@ any_template_parm_r (tree t, void *data)
case LAMBDA_EXPR:
{
+ /* TREE_STATIC on LAMBDA_EXPR_EXTRA_ARGS means a full set of
+ arguments, so we can just look there; they will replace
+ any template parms in the rest of the LAMBDA_EXPR. */
+ if (tree args = LAMBDA_EXPR_EXTRA_ARGS (t))
+ {
+ WALK_SUBTREE (args);
+ /* Without TREE_STATIC the args are just outer levels, so we'd
+ still need to look through the lambda for just inner
+ parameters. Hopefully that's not necessary. */
+ gcc_checking_assert (TREE_STATIC (args));
+ return 0;
+ }
/* Look in the parms and body. */
tree fn = lambda_function (t);
WALK_SUBTREE (TREE_TYPE (fn));
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda22.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda22.C
new file mode 100644
index 000000000000..2437b7e06a94
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda22.C
@@ -0,0 +1,21 @@
+// PR c++/118698
+// { dg-do compile { target c++20 } }
+
+template <typename T> struct foo {};
+template <typename T> struct bar {};
+
+template <class T> T&& declval ();
+
+template <typename T, typename U>
+concept callable = requires { declval<T>()(declval<U>()); };
+
+template <typename T, template <typename...> typename U>
+concept is_specialization_of = callable<decltype([]<typename... Args>(
U<Args...> const& ) { }),T>;
+
+static_assert( is_specialization_of<foo<int>,foo> == true );
+static_assert( is_specialization_of<foo<int>,bar> == false );
+
+template <typename T> concept is_foo = is_specialization_of<T,foo>;
+
+static_assert( is_foo<foo<int>> );
+static_assert( is_foo<bar<int>> == false );
