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* [gcc r13-7470] c++: fix explicit/copy problem [PR109247]
@ 2023-06-23 16:43 Jason Merrill
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From: Jason Merrill @ 2023-06-23 16:43 UTC (permalink / raw)
To: gcc-cvs
https://gcc.gnu.org/g:dc7f1bfbe5999e4639cf3f3afe70043b49352fdf
commit r13-7470-gdc7f1bfbe5999e4639cf3f3afe70043b49352fdf
Author: Jason Merrill <jason@redhat.com>
Date: Fri May 26 12:28:15 2023 -0400
c++: fix explicit/copy problem [PR109247]
In the testcase, the user wants the assignment to use the operator= declared
in the class, but because [over.match.list] says that explicit constructors
are also considered for list-initialization, as affirmed in CWG1228, we end
up choosing the implicitly-declared copy assignment operator, using the
explicit constructor template for the argument, which is ill-formed. Other
implementations haven't implemented CWG1228, so we keep getting bug reports.
Discussion in CWG led to the idea for this targeted relaxation: if we use an
explicit constructor for the conversion to the argument of a copy or move
special member function, that makes the candidate worse than another.
DR 2735
PR c++/109247
gcc/cp/ChangeLog:
* call.cc (sfk_copy_or_move): New.
(joust): Add tiebreaker for explicit conv and copy ctor.
gcc/testsuite/ChangeLog:
* g++.dg/cpp0x/initlist-explicit3.C: New test.
Diff:
---
gcc/cp/call.cc | 31 +++++++++++++++++++++++++
gcc/testsuite/g++.dg/cpp0x/initlist-explicit3.C | 15 ++++++++++++
2 files changed, 46 insertions(+)
diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index ee290fc03c4..867d7a5bee6 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -12608,6 +12608,17 @@ cand_parms_match (z_candidate *c1, z_candidate *c2)
return compparms (parms1, parms2);
}
+/* True iff FN is a copy or move constructor or assignment operator. */
+
+static bool
+sfk_copy_or_move (tree fn)
+{
+ if (TREE_CODE (fn) != FUNCTION_DECL)
+ return false;
+ special_function_kind sfk = special_function_p (fn);
+ return sfk >= sfk_copy_constructor && sfk <= sfk_move_assignment;
+}
+
/* Compare two candidates for overloading as described in
[over.match.best]. Return values:
@@ -12907,6 +12918,26 @@ joust (struct z_candidate *cand1, struct z_candidate *cand2, bool warn,
return winner;
}
+ /* CWG2735 (PR109247): A copy/move ctor/op= for which its operand uses an
+ explicit conversion (due to list-initialization) is worse. */
+ {
+ z_candidate *sp = nullptr;
+ if (sfk_copy_or_move (cand1->fn))
+ sp = cand1;
+ if (sfk_copy_or_move (cand2->fn))
+ sp = sp ? nullptr : cand2;
+ if (sp)
+ {
+ conversion *conv = sp->convs[!DECL_CONSTRUCTOR_P (sp->fn)];
+ if (conv->user_conv_p)
+ for (; conv; conv = next_conversion (conv))
+ if (conv->kind == ck_user
+ && DECL_P (conv->cand->fn)
+ && DECL_NONCONVERTING_P (conv->cand->fn))
+ return (sp == cand1) ? -1 : 1;
+ }
+ }
+
/* or, if not that,
F1 is a non-template function and F2 is a template function
specialization. */
diff --git a/gcc/testsuite/g++.dg/cpp0x/initlist-explicit3.C b/gcc/testsuite/g++.dg/cpp0x/initlist-explicit3.C
new file mode 100644
index 00000000000..b0c92784566
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp0x/initlist-explicit3.C
@@ -0,0 +1,15 @@
+// PR c++/109247
+// { dg-do compile { target c++11 } }
+
+template <typename _Tp> struct optional {
+ template <typename _Up> explicit optional(_Up);
+ template <typename _Up = _Tp> void operator=(_Up);
+};
+int setPattern_pattern;
+struct SourceBrush {
+ struct Brush {
+ int brush;
+ };
+ void setPattern() { m_brush = {setPattern_pattern}; }
+ optional<Brush> m_brush;
+};
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