find_template_parameters needs to find the mention of T in the lambda.
Fixing that leaves this as a hard error, which may be surprising but is
consistent with lambdas in other SFINAE contexts like template argument
deduction.
Tested x86_64-pc-linux-gnu, applying to trunk.
gcc/cp/ChangeLog
2020-02-15 Jason Merrill <ja...@redhat.com>
PR c++/92556
* pt.c (any_template_parm_r): Look into lambda body.
---
gcc/cp/pt.c | 9 +++++++++
gcc/testsuite/g++.dg/cpp2a/concepts-lambda5.C | 10 ++++++++++
2 files changed, 19 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-lambda5.C
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index d19bde7bcbe..6c9abb8f3d3 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -10479,6 +10479,15 @@ any_template_parm_r (tree t, void *data)
}
break;
+ case LAMBDA_EXPR:
+ {
+ /* Look in the parms and body. */
+ tree fn = lambda_function (t);
+ WALK_SUBTREE (TREE_TYPE (fn));
+ WALK_SUBTREE (DECL_SAVED_TREE (fn));
+ }
+ break;
+
default:
break;
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-lambda5.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda5.C
new file mode 100644
index 00000000000..fe471899c14
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-lambda5.C
@@ -0,0 +1,10 @@
+// PR c++/92556
+// { dg-do compile { target c++2a } }
+
+// Having this as a hard error is consistent with template argument deduction;
+// it's an open core issue (jason 2020-02-14).
+template <class T> concept has_value
+ = requires { []{T::value;}; }; // { dg-error "" }
+template <has_value T> void f() { }
+template <class T> void f() { }
+void q() { f<int>(); }
base-commit: d71365427670a791c5b54bfec6e3d41210844a8a
--
2.18.1
