Tested on x86_64-pc-linux-gnu, does this look OK for trunk/15?
-- >8 --
This std::expected friend operator== is prone to constraint recursion
after CWG 2369 for the same reason as basic_const_iterator's comparison
operators were before the r15-7757-g4342c50ca84ae5 workaround. This
patch works around the constraint recursion here in a similar manner,
by making the function parameter of type std::expected dependent in a
trivial way.
PR libstdc++/119714
PR libstdc++/112490
libstdc++-v3/ChangeLog:
* include/std/expected (expected::operator==): Replace
non-dependent std::expected function parameter with a dependent
one of type expected<_Vp, _Er> where _Vp matches _Tp.
* testsuite/20_util/expected/119714.cc: New test.
---
libstdc++-v3/include/std/expected | 4 ++--
libstdc++-v3/testsuite/20_util/expected/119714.cc | 9 +++++++++
2 files changed, 11 insertions(+), 2 deletions(-)
create mode 100644 libstdc++-v3/testsuite/20_util/expected/119714.cc
diff --git a/libstdc++-v3/include/std/expected
b/libstdc++-v3/include/std/expected
index 5dc1dfbe5b8a..60f1565f15b9 100644
--- a/libstdc++-v3/include/std/expected
+++ b/libstdc++-v3/include/std/expected
@@ -1169,13 +1169,13 @@ namespace __expected
return !__y.has_value() && bool(__x.error() == __y.error());
}
- template<typename _Up>
+ template<typename _Up, same_as<_Tp> _Vp>
requires (!__expected::__is_expected<_Up>)
&& requires (const _Tp& __t, const _Up& __u) {
{ __t == __u } -> convertible_to<bool>;
}
friend constexpr bool
- operator==(const expected& __x, const _Up& __v)
+ operator==(const expected<_Vp, _Er>& __x, const _Up& __v)
noexcept(noexcept(bool(*__x == __v)))
{ return __x.has_value() && bool(*__x == __v); }
diff --git a/libstdc++-v3/testsuite/20_util/expected/119714.cc
b/libstdc++-v3/testsuite/20_util/expected/119714.cc
new file mode 100644
index 000000000000..a8dc6e891e1d
--- /dev/null
+++ b/libstdc++-v3/testsuite/20_util/expected/119714.cc
@@ -0,0 +1,9 @@
+// { dg-do compile { target c++23 } }
+
+// PR libstdc++/119714 - constraint recursion with std::expected::operator==
+
+#include <expected>
+#include <vector>
+
+using I = std::vector<std::expected<int,int>>::iterator;
+static_assert(std::totally_ordered<I>);
--
2.49.0.503.g6c0bd1fc70
