Use p2197 format for complex by default

Author: vitaut

include/fmt/std.h

@@ -595,8 +595,8 @@ struct formatter<std::complex<F>, Char> : nested_formatter<F, Char> {
 
     template <typename OutputIt>
     FMT_CONSTEXPR auto operator()(OutputIt out) -> OutputIt {
-      auto format =
-          detail::string_literal<Char, '(', '{', '}', ',', '{', '}', ')'>{};
+      auto format = detail::string_literal<Char, '(', '{', '}', '+', '{', '}',
+                                           'i', ')'>{};
       return fmt::format_to(out, basic_string_view<Char>(format),
                             f->nested(c.real()), f->nested(c.imag()));
     }

test/std-test.cc

@@ -66,9 +66,9 @@ TEST(std_test, thread_id) {
 }
 
 TEST(std_test, complex) {
-  EXPECT_EQ(fmt::format("{}", std::complex<double>(1, 2.2)), "(1,2.2)");
+  EXPECT_EQ(fmt::format("{}", std::complex<double>(1, 2.2)), "(1+2.2i)");
   EXPECT_EQ(fmt::format("{:>20.2f}", std::complex<double>(1, 2.2)),
-            "         (1.00,2.20)");
+            "        (1.00+2.20i)");
 }
 
 #ifdef __cpp_lib_source_location

test/xchar-test.cc

@@ -584,9 +584,9 @@ TEST(locale_test, sign) {
 
 TEST(std_test_xchar, complex) {
   auto s = fmt::format(L"{}", std::complex<double>(1, 2));
-  EXPECT_EQ(s, L"(1,2)");
-  EXPECT_EQ(fmt::format(L"{:.2f}", std::complex<double>(1, 2)), L"(1.00,2.00)");
-  EXPECT_EQ(fmt::format(L"{:8}", std::complex<double>(1, 2)), L"(1,2)   ");
+  EXPECT_EQ(s, L"(1+2i)");
+  EXPECT_EQ(fmt::format(L"{:.2f}", std::complex<double>(1, 2)), L"(1.00+2.00i)");
+  EXPECT_EQ(fmt::format(L"{:8}", std::complex<double>(1, 2)), L"(1+2i)  ");
 }
 
 TEST(std_test_xchar, optional) {