In the testcase below, we never substitute function-template arguments
into f15<int>'s placeholder-return-type constraint, which leads to us
incorrectly rejecting this instantiation in do_auto_deduction due to
satisfaction failure (of the constraint SameAs<int, decltype(x)>).
The fact that we incorrectly reject this testcase is masked by the
other instantiation f15<char>, which we correctly reject and diagnose
(by accident).
A good place to do this missing substitution seems to be during
TEMPLATE_TYPE_PARM level lowering. So this patch adds a call to
tsubst_constraint there, and also adds dg-bogus directives to this
testcase wherever we expect instantiation to succeed. (So without the
substitution fix, this last dg-bogus would FAIL).
Successfully tested on x86_64-pc-linux-gnu, and also on the cmcstl2 and
range-v3 projects. Does this look OK to commit?
gcc/cp/ChangeLog:
PR c++/96443
* pt.c (tsubst) <case TEMPLATE_TYPE_PARM>: Substitute into
the constraints on a placeholder type when its level.
gcc/testsuite/ChangeLog:
PR c++/96443
* g++.dg/cpp2a/concepts-ts1.C: Add dg-bogus wherever we expect
instantiation to succeed.
---
gcc/cp/pt.c | 7 ++++---
gcc/testsuite/g++.dg/cpp2a/concepts-ts1.C | 8 ++++----
2 files changed, 8 insertions(+), 7 deletions(-)
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index e7496002c1c..04bf6da0cdd 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -15524,10 +15524,11 @@ tsubst (tree t, tree args, tsubst_flags_t complain,
tree in_decl)
if (TREE_CODE (t) == TEMPLATE_TYPE_PARM)
{
- /* Propagate constraints on placeholders since they are
- only instantiated during satisfaction. */
+ /* Substitute constraints on placeholder when reducing
+ their level. */
if (tree constr = PLACEHOLDER_TYPE_CONSTRAINTS (t))
- PLACEHOLDER_TYPE_CONSTRAINTS (r) = constr;
+ PLACEHOLDER_TYPE_CONSTRAINTS (r)
+ = tsubst_constraint (constr, args, complain, in_decl);
else if (tree pl = CLASS_PLACEHOLDER_TEMPLATE (t))
{
pl = tsubst_copy (pl, args, complain, in_decl);
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-ts1.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-ts1.C
index 1cefe3b243f..1a9b71c2296 100644
--- a/gcc/testsuite/g++.dg/cpp2a/concepts-ts1.C
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-ts1.C
@@ -34,13 +34,13 @@ auto f15(auto x) -> SameAs<decltype(x)> { return 0; } // {
dg-error "deduced ret
void driver()
{
- f1(0);
+ f1(0); // { dg-bogus "" }
f2(0); // { dg-error "" }
- f3(0);
+ f3(0); // { dg-bogus "" }
f3('a'); // { dg-error "" }
- f4(0, 0);
+ f4(0, 0); // { dg-bogus "" }
f4(0, 'a'); // { dg-error "" }
- f15(0);
+ f15(0); // { dg-bogus "" }
f15('a'); // { dg-message "" }
}
--
2.28.0.89.g85b4e0a6dc
