[gcc r11-9390] c++: implicit dummy object in requires clause [PR103198]

[Patrick Palka]

https://gcc.gnu.org/g:648d5aa56abd2a0ab36403dd1e14dd225402301a

commit r11-9390-g648d5aa56abd2a0ab36403dd1e14dd225402301a
Author: Patrick Palka <ppalka@redhat.com>
Date:   Thu Nov 18 19:32:22 2021 -0500

    c++: implicit dummy object in requires clause [PR103198]
    
    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 parms 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: it walks the 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 parm 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 parm is 'this', not a dummy object.)
    
    This patch fixes this inconsistency by making any_template_parm_r walk
    into the TREE_TYPE of a dummy object, like it already does for 'this'.
    
            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.
    
    (cherry picked from commit 09c24fe42ff2cef3f3291f5a7540a5835c08430c)

Diff:
---
 gcc/cp/pt.c                                 |  5 +++++
 gcc/testsuite/g++.dg/cpp2a/concepts-this1.C | 30 +++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index c1a60cae697..27016f90ec6 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -10757,6 +10757,11 @@ 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" }
+}