On 9/20/24 7:34 PM, Patrick Palka wrote:
On Fri, 20 Sep 2024, Jason Merrill wrote:
On 9/20/24 6:51 PM, Patrick Palka wrote:
On Fri, 20 Sep 2024, Jason Merrill wrote:
On 9/18/24 10:59 PM, Patrick Palka wrote:
Bootstrapped and regtested on x86_64-pc-linux-gnu, does this
look OK for trunk? I'm not sure this is worth backporting
without the previous CWG 2273 tweak since it'll mean inconsistent
behavior between implict vs explicit object members in GCC 14: the call
to S<>{}.f() in concepts-memfun4.C would now return 10 (due to the CWG
2273 tiebreaker incorrectly triggering), while the g() and h() calls
would be ambiguous (since that tiebreaker doesn't consider object
correspondence).
Agreed, I wouldn't backport.
What do you think about enforcing this part of CWG 2789 only for
constructors in GCC 14? That would sidestep the inconsistency that
arises if we don't also backport the CWG 2273, and still fix the
testcase in the PR.
Like so?
That seems reasonable with a comment.
Ack, does
/* This really really be checked for all member functions as per
CWG2789, but for GCC 14 we check this only for constructors since
without r15-3740 doing so would result in inconsistent handling
of object parameters (such as in concepts-memfun4.C). */
work?
With "really really" fixed, yes.
-- >8 --
Subject: [PATCH GCC 14] c++: CWG 2789 and usings [PR116492]
For GCC 14, narrowly fix this PR by enforcing the unimplemented
- if they are member functions, both are direct members of the same
class, and
part of CWG 2789 for constructors only.
PR c++/116492
DR 2789
gcc/cp/ChangeLog:
* call.cc (cand_parms_match): Return false for constructors that
come from different classes.
gcc/testsuite/ChangeLog:
* g++.dg/cpp2a/concepts-inherit-ctor12.C: New test.
---
gcc/cp/call.cc | 4 ++++
.../g++.dg/cpp2a/concepts-inherit-ctor12.C | 16 ++++++++++++++++
2 files changed, 20 insertions(+)
create mode 100644 gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 0f4eeeb5395..5c7aaa6dcf1 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -12826,6 +12826,10 @@ cand_parms_match (z_candidate *c1, z_candidate *c2,
pmatch match_kind)
&& DECL_FUNCTION_MEMBER_P (fn2)))
/* Early escape. */;
+ else if ((DECL_INHERITED_CTOR (fn1) || DECL_INHERITED_CTOR (fn2))
+ && (DECL_CONTEXT (strip_inheriting_ctors (fn1))
+ != DECL_CONTEXT (strip_inheriting_ctors (fn2))))
+ return false;
/* CWG2789 is not adequate, it should specify corresponding object
parameters, not same typed object parameters. */
else if (!object_parms_correspond (c1, fn1, c2, fn2))
diff --git a/gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
b/gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
new file mode 100644
index 00000000000..3e5dbfc37ad
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C
@@ -0,0 +1,16 @@
+// PR c++/116492
+// CWG 2789
+// { dg-do compile { target c++20 } }
+
+template<class T>
+struct A {
+ A() requires true = delete;
+};
+
+struct B : A<int> {
+ B();
+ using A<int>::A;
+};
+
+B b; // OK, selects the non-inherited constructor over the more constrained
+ // inherited constructor.
