[PATCH] c++: implicit dummy object in requires clause [PR103198]

Patrick Palka ppalka@redhat.com
Fri Nov 12 01:25:29 GMT 2021


In the testcase below satisfaction misbehaves for f and g ultimately
because find_template_parameters fails to notice that the constraint
'val.x' depends on the template parameters of the class template.
In contrast, satisfaction works just fine for h.

The problem seems to come down to a difference in how any_template_parm_r
handles 'this' vs a dummy object: we walk TREE_TYPE of the former but
not the latter, and this causes us to miss the tparm dependencies in
f/g's constraints since in their case the implicit object parameter
through which we access 'val' is a dummy object.  (For h, since we know
it's a non-static member function when parsing its trailing constraints,
the implicit object parameter is 'this' instead of a dummy object.)

This patch fixes this inconsistency by making any_template_parm_r also
walk into the TREE_TYPE of a dummy object, as is already done for
'this'.

Bootstrapped and regtested on x86_64-pc-linux-gnu, also tested on
cmcstl2 and range-v3, does this look OK for trunk and 11?

	PR c++/103198

gcc/cp/ChangeLog:

	* pt.c (any_template_parm_r): Walk the TREE_TYPE of a dummy
	object.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-this1.C: New test.
---
 gcc/cp/pt.c                                 |  5 ++++
 gcc/testsuite/g++.dg/cpp2a/concepts-this1.C | 30 +++++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-this1.C

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 82bf7dc26f6..fa55857d783 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -10766,6 +10766,11 @@ any_template_parm_r (tree t, void *data)
 	WALK_SUBTREE (TREE_TYPE (t));
       break;
 
+    case CONVERT_EXPR:
+      if (is_dummy_object (t))
+	WALK_SUBTREE (TREE_TYPE (t));
+      break;
+
     default:
       break;
     }
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-this1.C b/gcc/testsuite/g++.dg/cpp2a/concepts-this1.C
new file mode 100644
index 00000000000..d717028201a
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-this1.C
@@ -0,0 +1,30 @@
+// PR c++/103198
+// { dg-do compile { target c++20 } }
+
+template<class T, class = void>
+struct A {
+  T val;
+
+  template<class U>
+    requires requires { val.x; }
+  void f(U);
+
+  static void g(int)
+    requires requires { val.x; };
+
+  void h(int)
+    requires requires { val.x; };
+};
+
+struct B { int x; };
+struct C { };
+
+int main() {
+  A<B>().f(0);
+  A<B>().g(0);
+  A<B>().h(0);
+
+  A<C>().f(0); // { dg-error "no match" }
+  A<C>().g(0); // { dg-error "no match" }
+  A<C>().h(0); // { dg-error "no match" }
+}
-- 
2.34.0.rc2.9.g4d53e91c6b



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