[gcc r14-10696] c++: CWG 2789 and usings [PR116492]

[Patrick Palka via Gcc-cvs]

https://gcc.gnu.org/g:659f32ea9de57661f8a37dcfb0b9a01bfe29acce

commit r14-10696-g659f32ea9de57661f8a37dcfb0b9a01bfe29acce
Author: Patrick Palka <ppa...@redhat.com>
Date:   Fri Sep 20 17:37:03 2024 -0400

    c++: CWG 2789 and usings [PR116492]
    
    For GCC 14, narrowly fix this PR by implementing the missing
    
      - 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.
    
    Reviewed-by: Jason Merrill <ja...@redhat.com>

Diff:
---
 gcc/cp/call.cc                                       |  8 ++++++++
 gcc/testsuite/g++.dg/cpp2a/concepts-inherit-ctor12.C | 16 ++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index 0f4eeeb53951..492d17b17446 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -12826,6 +12826,14 @@ 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))))
+    /* This should 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).  */
+    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 000000000000..3e5dbfc37ad0
--- /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.