Fix a few chrono formatting corner cases (#1178)

include/fmt/chrono.h

@@ -419,13 +419,10 @@ inline std::chrono::duration<Rep, std::milli> get_milliseconds(
 }
 
 template <typename Rep, typename OutputIt>
-OutputIt static format_chrono_duration_value(OutputIt out, Rep val,
-                                             int precision) {
-  if (precision < 0) {
-    return format_to(out, std::is_floating_point<Rep>::value ? "{:g}" : "{}",
-                     val);
-  }
-  return format_to(out, "{:.{}f}", val, precision);
+OutputIt format_chrono_duration_value(OutputIt out, Rep val, int precision) {
+  if (precision >= 0) return format_to(out, "{:.{}f}", val, precision);
+  return format_to(out, std::is_floating_point<Rep>::value ? "{:g}" : "{}",
+                   val);
 }
 
 template <typename Period, typename OutputIt>
@@ -441,20 +438,20 @@ struct chrono_formatter {
   FormatContext& context;
   OutputIt out;
   int precision;
-  Rep val;
-  typedef std::chrono::duration<Rep> seconds;
+  typedef typename std::conditional<std::is_integral<Rep>::value &&
+                                        sizeof(Rep) < sizeof(int),
+                                    int, Rep>::type rep;
+  rep val;
+  typedef std::chrono::duration<rep> seconds;
   seconds s;
-  typedef std::chrono::duration<Rep, std::milli> milliseconds;
+  typedef std::chrono::duration<rep, std::milli> milliseconds;
 
   typedef typename FormatContext::char_type char_type;
 
   explicit chrono_formatter(FormatContext& ctx, OutputIt o,
                             std::chrono::duration<Rep, Period> d)
       : context(ctx), out(o), val(d.count()) {
-    if (d.count() < 0) {
-      d = -d;
-      *out++ = '-';
-    }
+    if (d.count() < 0) d = -d;
     s = std::chrono::duration_cast<seconds>(d);
   }
 
@@ -476,7 +473,15 @@ struct chrono_formatter {
     return time;
   }
 
+  void write_sign() {
+    if (val < 0) {
+      *out++ = '-';
+      val = -val;
+    }
+  }
+
   void write(Rep value, int width) {
+    write_sign();
     if (isnan(value)) return write_nan();
     typedef typename int_traits<int>::main_type main_type;
     main_type n = to_unsigned(to_int(value));
@@ -570,6 +575,7 @@ struct chrono_formatter {
   void on_am_pm() { format_localized(time(), "%p"); }
 
   void on_duration_value() {
+    write_sign();
     out = format_chrono_duration_value(out, val, precision);
   }
 

test/chrono-test.cc

@@ -306,12 +306,22 @@ TEST(ChronoTest, InvalidColons) {
                fmt::format_error);
 }
 
+TEST(ChronoTest, NegativeDuration) {
+  EXPECT_EQ("-12345", fmt::format("{:%Q}", std::chrono::seconds(-12345)));
+  EXPECT_EQ("-03:25:45",
+            fmt::format("{:%H:%M:%S}", std::chrono::seconds(-12345)));
+  EXPECT_EQ("-00:01",
+            fmt::format("{:%M:%S}", std::chrono::duration<double>(-1)));
+  EXPECT_EQ("s", fmt::format("{:%q}", std::chrono::seconds(-12345)));
+  EXPECT_EQ("-00.127",
+            fmt::format("{:%S}",
+                        std::chrono::duration<signed char, std::milli>{-127}));
+}
+
 TEST(ChronoTest, SpecialDurations) {
   EXPECT_EQ(
       "40.",
       fmt::format("{:%S}", std::chrono::duration<double>(1e20)).substr(0, 3));
-  EXPECT_EQ("-00:01",
-            fmt::format("{:%M:%S}", std::chrono::duration<double>(-1)));
   auto nan = std::numeric_limits<double>::quiet_NaN();
   EXPECT_EQ(
       "nan nan nan nan.nan nan:nan nan",
@@ -322,6 +332,10 @@ TEST(ChronoTest, SpecialDurations) {
             "1Es");
   EXPECT_EQ(fmt::format("{}", std::chrono::duration<float, std::atto>(1)),
             "1as");
+  EXPECT_EQ(fmt::format("{:%R}", std::chrono::duration<char, std::mega>{2}),
+            "03:33");
+  EXPECT_EQ(fmt::format("{:%T}", std::chrono::duration<char, std::mega>{2}),
+            "03:33:20");
 }
 
 #endif  // FMT_STATIC_THOUSANDS_SEPARATOR