<format>: Alternate form general floating-point width handling (#5261)

Co-authored-by: alexprabhatbara <[email protected]>

Author: alexprabhat99

stl/inc/format

@@ -2145,6 +2145,8 @@ _NODISCARD _OutputIt _Fmt_write(
     case 'g':
         if (_Precision == -1) {
             _Precision = 6;
+        } else if (_Precision == 0) {
+            _Precision = 1;
         }
         _Format = chars_format::general;
         break;

tests/std/tests/P0645R10_text_formatting_formatting/test.cpp

@@ -835,6 +835,7 @@ void test_float_specs() {
     assert(format(STR("{:3}"), Float{0}) == STR("  0"));
     assert(format(STR("{:#9G}"), Float{12.2}) == STR("  12.2000"));
     assert(format(STR("{:#12g}"), Float{1'000'000}) == STR(" 1.00000e+06"));
+    assert(format(STR("[{:#6.0g}]"), 1.234e-37) == STR("[1.e-37]"));
 
     // Precision
     Float value = 1234.52734375;