libstdc++: Fix formatting of negative chrono::hh_mm_ss

When formatting with an empty chrono spec ("{}") two minus signs were
being added to hh_mm_ss values. This is because the __is_neg flag was
checked to add one explicitly, and then the ostream operator added
another one.

We should only check the __is_neg flag for durations, because those are
the only types which are modified to be non-negative before calling
_M_format. We don't change hh_mm_ss values to be negative, because that
would require performing arithmetic on the hh_mm_ss members to sum them,
and then again to construct a new hh_mm_ss object with the positive
value.  Instead, we can just be careful about using the __is_neg flag
correctly.

To fix the bug, _M_format_to_ostream no longer checks the __is_neg flag
for non-durations, and _M_format doesn't set it for hh_mm_ss until after
the call to _M_format_to_ostream. We can also avoid setting it for types
that it doesn't apply to, by making the __print_sign lambda only inspect
it for duration and hh_mm_ss types.

libstdc++-v3/ChangeLog:

	* include/bits/chrono_io.h (__formatter_chrono::_M_format):
	Do not set __is_neg for hh_mm_ss before calling
	_M_format_to_ostream. Change __print_sign lambda to only check
	__is_neg for durations and hh_mm_ss types.
	(__formatter_chrono::_M_format_to_ostream): Only check __is_neg
	for duration types.
	* testsuite/std/time/hh_mm_ss/io.cc: Check negative values.

diff --git a/libstdc++-v3/include/bits/chrono_io.h b/libstdc++-v3/include/bits/chrono_io.h
index 0c5f9f5058b47cec99e8bf89c6d88425c34405c4..c95301361d877f1d168b7fe7316222c271b4e8d7 100644 (file)
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -486,11 +486,6 @@ namespace __format
        _M_format(const _Tp& __t, _FormatContext& __fc,
                  bool __is_neg = false) const
        {
-         if constexpr (__is_specialization_of<_Tp, chrono::hh_mm_ss>)
-           __is_neg = __t.is_negative();
-         else if constexpr (!chrono::__is_duration_v<_Tp>)
-           __is_neg = false;
-
          auto __first = _M_spec._M_chrono_specs.begin();
          const auto __last = _M_spec._M_chrono_specs.end();
          if (__first == __last)
@@ -513,12 +508,19 @@ namespace __format
          else
            __out = __sink.out();
 
+         // formatter<duration> passes the correct value of __is_neg
+         // for durations but for hh_mm_ss we decide it here.
+         if constexpr (__is_specialization_of<_Tp, chrono::hh_mm_ss>)
+           __is_neg = __t.is_negative();
+
          auto __print_sign = [&__is_neg, &__out] {
-           if (__is_neg)
-             {
-               *__out++ = _S_plus_minus[1];
-               __is_neg = false;
-             }
+           if constexpr (chrono::__is_duration_v<_Tp>
+                           || __is_specialization_of<_Tp, chrono::hh_mm_ss>)
+             if (__is_neg)
+               {
+                 *__out++ = _S_plus_minus[1];
+                 __is_neg = false;
+               }
            return std::move(__out);
          };
 
@@ -708,8 +710,9 @@ namespace __format
                __os << __t._M_date << ' ' << __t._M_time;
              else
                {
-                 if (__is_neg) [[unlikely]]
-                   __os << _S_plus_minus[1];
+                 if constexpr (chrono::__is_duration_v<_Tp>)
+                   if (__is_neg) [[unlikely]]
+                     __os << _S_plus_minus[1];
                  __os << __t;
                }
 

diff --git a/libstdc++-v3/testsuite/std/time/hh_mm_ss/io.cc b/libstdc++-v3/testsuite/std/time/hh_mm_ss/io.cc
index 072234328c73b6fa6453a1102e6306c9779508aa..ddb1ad77d1ea159187ea2f52ea38b159d76a1c67 100644 (file)
--- a/libstdc++-v3/testsuite/std/time/hh_mm_ss/io.cc
+++ b/libstdc++-v3/testsuite/std/time/hh_mm_ss/io.cc
@@ -47,9 +47,13 @@ test_format()
 
   auto s = std::format("{}", hh_mm_ss{1h + 23min + 45s});
   VERIFY( s == "01:23:45" );
+  s = std::format("{}", hh_mm_ss{-42min});
+  VERIFY( s == "-00:42:00" );
 
   auto ws = std::format(L"{}", hh_mm_ss{1h + 23min + 45s});
   VERIFY( ws == L"01:23:45" );
+  ws = std::format(L"{}", hh_mm_ss{-42min});
+  VERIFY( ws == L"-00:42:00" );
 
   // Locale-specific formats:
   auto loc = std::locale::classic();