diff mbox series

[1/2] c++: constrained template friend class matching [PR96830]

Message ID 20230314164146.1470993-1-ppalka@redhat.com
State Committed
Commit ec62dc95c4f8776c9f4eff2a9a06f9aef6a2d98a
Headers
Series [1/2] c++: constrained template friend class matching [PR96830] |

Commit Message

Patrick Palka March 14, 2023, 4:41 p.m. UTC 
  Here when instantiating a constrained template friend naming an already
declared class template, we erroneously pass the existing template's
constraints instead of the friend declaration's constraints to
redeclare_class_template, which causes the constraint comparison check
therein to always be vacuously true, and we fail to diagnose legitimate
constraint mismatches.

Bootstrapped and regtested on x86_64-pc-linxu-gnu, does this look OK for
trunk/12?

	PR c++/96830

gcc/cp/ChangeLog:

	* pt.cc (redeclare_class_template): Add missing "of" in
	constraint mismatch diagnostic.
	(tsubst_friend_class): For an already declared class template,
	substitute and pass the friend declaration's constraints to
	redeclare_class_template instead of passing the existing
	template's constraints.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/concepts-friend14.C: New test.
---
 gcc/cp/pt.cc                                  |  8 ++++--
 .../g++.dg/cpp2a/concepts-friend14.C          | 26 +++++++++++++++++++
 2 files changed, 32 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-friend14.C
diff mbox series

Patch

diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 85136df1730..053cc52b285 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -6377,7 +6377,7 @@  redeclare_class_template (tree type, tree parms, tree cons)
   if (!cp_tree_equal (req1, req2))
     {
       auto_diagnostic_group d;
-      error_at (input_location, "redeclaration %q#D with different "
+      error_at (input_location, "redeclaration of %q#D with different "
                                 "constraints", tmpl);
       inform (DECL_SOURCE_LOCATION (tmpl),
               "original declaration appeared here");
@@ -11503,7 +11503,11 @@  tsubst_friend_class (tree friend_tmpl, tree args)
 						 tf_warning_or_error);
           location_t saved_input_location = input_location;
           input_location = DECL_SOURCE_LOCATION (friend_tmpl);
-          tree cons = get_constraints (tmpl);
+	  tree cons = get_constraints (friend_tmpl);
+	  ++processing_template_decl;
+	  cons = tsubst_constraint_info (cons, args, tf_warning_or_error,
+					 DECL_FRIEND_CONTEXT (friend_tmpl));
+	  --processing_template_decl;
           redeclare_class_template (TREE_TYPE (tmpl), parms, cons);
           input_location = saved_input_location;
 	}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-friend14.C b/gcc/testsuite/g++.dg/cpp2a/concepts-friend14.C
new file mode 100644
index 00000000000..f46c7e4bdfb
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-friend14.C
@@ -0,0 +1,26 @@ 
+// PR c++/96830
+// { dg-do compile { target c++20 } }
+
+template<class T> requires true
+struct A {
+  template<class U> friend struct A;                   // { dg-error "different constraints" }
+  template<class U> requires (!!true) friend struct A; // { dg-error "different constraints" }
+};
+
+template<class T>
+struct B {
+  template<class U> requires true friend struct A;
+  template<class U> requires true friend struct B; // { dg-error "different constraints" }
+};
+
+template<class T> concept C = true;
+
+template<C T>
+struct D {
+  template<class U> friend struct D; // { dg-error "different constraints" }
+  template<C U> friend struct D;
+};
+
+template struct A<int>;
+template struct B<int>;
+template struct D<int>;