On 7/5/24 12:18 PM, Patrick Palka wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this look OK
for trunk/14 and perhaps 13?
Alternatively we can set current_template_parms from weakly_subsumes
instead, who has only one caller anyway.
Would it also work to pass tmpl instead of NULL_TREE to
get_normalized_constraints_from_info in weakly_subsumes?
-- >8 --
Here we normalize the constraint same_as<auto, bool> for the first
time during constraint subsumption checking of B / TT as part of ttp
coercion. During this normalization the set of in-scope template
parameters i.e. current_template_parms is empty, which tricks the
satisfaction cache into thinking that the satisfaction value of the
constraint is independent of its template parameters, and we incorrectly
conflate the satisfaction value with auto = bool vs auto = long and
accept the specialization A<long, B>.
This patch fixes this by setting current_template_parms appropirately
during subsumption checking.
PR c++/115656
gcc/cp/ChangeLog:
* pt.cc (is_compatible_template_arg): Set current_template_parms
around the call to weakly_subsumes.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-ttp7.C: New test.
---
gcc/cp/pt.cc | 4 ++++
gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C | 12 ++++++++++++
2 files changed, 16 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
diff --git a/gcc/cp/pt.cc b/gcc/cp/pt.cc
index 017cc7fd0ab..1f6553790a5 100644
--- a/gcc/cp/pt.cc
+++ b/gcc/cp/pt.cc
@@ -8493,6 +8493,10 @@ is_compatible_template_arg (tree parm, tree arg, tree
args)
return false;
}
+ /* Normalization needs to know the effective set of in-scope
+ template parameters. */
+ auto ctp = make_temp_override (current_template_parms,
+ DECL_TEMPLATE_PARMS (arg));
return weakly_subsumes (parm_cons, arg);
}
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
new file mode 100644
index 00000000000..bc123ecf75e
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ttp7.C
@@ -0,0 +1,12 @@
+// PR c++/115656
+// { dg-do compile { target c++20 } }
+
+template<class T, class U> concept same_as = __is_same(T, U);
+
+template<same_as<bool> U, template<same_as<bool>> class TT>
+struct A { };
+
+template<same_as<bool>> class B;
+
+A<bool, B> a1;
+A<long, B> a2; // { dg-error "constraint failure" }
