Issue #22090: Fix '%' formatting for infinities and NaNs.

Lib/decimal.py

@@ -3769,6 +3769,8 @@ class Decimal(object):
         if self._is_special:
             sign = _format_sign(self._sign, spec)
             body = str(self.copy_abs())
+            if spec['type'] == '%':
+                body += '%'
             return _format_align(sign, body, spec)
 
         # a type of None defaults to 'g' or 'G', depending on context

Lib/test/test_decimal.py

@@ -1057,6 +1057,11 @@ class FormatTest(unittest.TestCase):
 
             # issue 6850
             ('a=-7.0', '0.12345', 'aaaa0.1'),
+
+            # issue 22090
+            ('<^+15.20%', 'inf', '<<+Infinity%<<<'),
+            ('\x07>,%', 'sNaN1234567', 'sNaN1234567%'),
+            ('=10.10%', 'NaN123', '   NaN123%'),
             ]
         for fmt, d, result in test_values:
             self.assertEqual(format(Decimal(d), fmt), result)

Modules/_decimal/libmpdec/io.c

@@ -446,7 +446,7 @@ _mpd_to_string(char **result, const mpd_t *dec, int flags, mpd_ssize_t dplace)
 
     if (mpd_isspecial(dec)) {
 
-        mem = sizeof "-Infinity";
+        mem = sizeof "-Infinity%";
         if (mpd_isnan(dec) && dec->len > 0) {
             /* diagnostic code */
             mem += dec->digits;
@@ -609,10 +609,10 @@ _mpd_to_string(char **result, const mpd_t *dec, int flags, mpd_ssize_t dplace)
             *cp++ = (flags&MPD_FMT_UPPER) ? 'E' : 'e';
             cp = exp_to_string(cp, ldigits-dplace);
         }
+    }
 
-        if (flags&MPD_FMT_PERCENT) {
-            *cp++ = '%';
-        }
+    if (flags&MPD_FMT_PERCENT) {
+        *cp++ = '%';
     }
 
     assert(cp < decstring+mem);
@@ -1260,6 +1260,9 @@ mpd_qformat_spec(const mpd_t *dec, const mpd_spec_t *spec,
             stackspec.align = '>';
             spec = &stackspec;
         }
+        if (type == '%') {
+            flags |= MPD_FMT_PERCENT;
+        }
     }
     else {
         uint32_t workstatus = 0;