c++: Fix lambda in atomic constraint.

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.

gcc/cp/ChangeLog
2020-02-15  Jason Merrill  <jason@redhat.com>

	PR c++/92556
	* pt.c (any_template_parm_r): Look into lambda body.

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index ed6b0d0..6ac938b 100644 (file)
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,8 @@
 2020-02-15  Jason Merrill  <jason@redhat.com>
 
+       PR c++/92556
+       * pt.c (any_template_parm_r): Look into lambda body.
+
        PR c++/92583
        * pt.c (any_template_parm_r): Remove CONSTRUCTOR handling.
 

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index d19bde7..6c9abb8 100644 (file)
--- 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 (file)
index 0000000..fe47189
--- /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>(); }