[PATCH] libstdc++: Fix chrono::parse to read from wide strings [PR123147]

[Jonathan Wakely]

When we extract wide characters and insert them into a stringstream to
be parsed as a floating-point value, we should use a stringstream of
char, not wchar_t.

libstdc++-v3/ChangeLog:

        PR libstdc++/123147
        * include/bits/chrono_io.h (_Parser::operator()) <%S>: Use a
        buffer of narrow characters to be parsed by std::from_chars.
        * testsuite/std/time/parse/parse.cc: Check wchar_t parsing.
---

Tested x86_64-linux.

I think there are other problems in chrono::parse which also affect
narrow characters (e.g. we don't use the precision for %NS and I think
we use the precision wrong in general). But those are distinct from this
fix, which just makes sure that parsing wide strings isn't ill-formed.

 libstdc++-v3/include/bits/chrono_io.h          |  8 ++++----
 libstdc++-v3/testsuite/std/time/parse/parse.cc | 14 ++++++++++++++
 2 files changed, 18 insertions(+), 4 deletions(-)

diff --git a/libstdc++-v3/include/bits/chrono_io.h 
b/libstdc++-v3/include/bits/chrono_io.h
index 75dd532a8cb3..37a296fed7ec 100644
--- a/libstdc++-v3/include/bits/chrono_io.h
+++ b/libstdc++-v3/include/bits/chrono_io.h
@@ -4977,14 +4977,14 @@ namespace __detail
                    }
                  else // Read fractional seconds
                    {
-                     basic_stringstream<_CharT> __buf;
+                     stringstream __buf;
                      auto __digit = _S_try_read_digit(__is, __err);
                      if (__digit != -1)
                        {
-                         __buf.put(_CharT('0') + __digit);
+                         __buf.put('0' + __digit);
                          __digit = _S_try_read_digit(__is, __err);
                          if (__digit != -1)
-                           __buf.put(_CharT('0') + __digit);
+                           __buf.put('0' + __digit);
                        }
 
                      auto __i = __is.peek();
@@ -5009,7 +5009,7 @@ namespace __detail
                                {
                                  __digit = _S_try_read_digit(__is, __err);
                                  if (__digit != -1)
-                                   __buf.put(_CharT('0') + __digit);
+                                   __buf.put('0' + __digit);
                                  else
                                    break;
                                }
diff --git a/libstdc++-v3/testsuite/std/time/parse/parse.cc 
b/libstdc++-v3/testsuite/std/time/parse/parse.cc
index 78c761c115f6..d7c73a1150fc 100644
--- a/libstdc++-v3/testsuite/std/time/parse/parse.cc
+++ b/libstdc++-v3/testsuite/std/time/parse/parse.cc
@@ -317,6 +317,19 @@ test_modifiers()
   VERIFY( s == 12s );
 }
 
+void
+test_wchar()
+{
+  std::wistringstream is;
+  std::chrono::duration<double, std::milli> ms;
+
+  is.clear();
+  is.str(L"0.125");
+  is >> parse(L"%S", ms);
+  VERIFY( is.good() );
+  VERIFY( ms.count() == 125 );
+}
+
 int main()
 {
   test_recommended_practice();
@@ -324,4 +337,5 @@ int main()
   test_whitespace();
   test_errors();
   test_modifiers();
+  test_wchar();
 }
-- 
2.52.0