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 --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>;
--
2.40.0
