Fix formatting of s pattern

The specialized `SecondPatternSequence` formatter is optimized to format the `ss.?S*` patterns, where seconds are padded. For the not padded (and uncommon) `s` pattern, we should use the usual `DynamicPatternSequence`.

Author: ppkarwasz

log4j-core-test/src/test/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternDynamicFormatterTest.java

@@ -100,6 +100,9 @@ static List<Arguments> sequencingTestCases() {
         testCases.add(Arguments.of(
                 "HH:mm:ss.SSSSSS", ChronoUnit.MINUTES, asList(pDyn("HH':'mm':'", ChronoUnit.MINUTES), pSec(".", 6))));
 
+        // Seconds without padding
+        testCases.add(Arguments.of("s.SSS", ChronoUnit.SECONDS, asList(pDyn("s'.'", ChronoUnit.SECONDS), pMilliSec())));
+
         return testCases;
     }
 
@@ -352,7 +355,9 @@ static Stream<Arguments> formatterInputs() {
                         "yyyy-MM-dd'T'HH:mm:ss.SSS",
                         "yyyy-MM-dd'T'HH:mm:ss.SSSSSS",
                         "dd/MM/yy HH:mm:ss.SSS",
-                        "dd/MM/yyyy HH:mm:ss.SSS")
+                        "dd/MM/yyyy HH:mm:ss.SSS",
+                        // seconds without padding
+                        "s.SSS")
                 .flatMap(InstantPatternDynamicFormatterTest::formatterInputs);
     }
 

log4j-core/src/main/java/org/apache/logging/log4j/core/util/internal/instant/InstantPatternDynamicFormatter.java

@@ -239,7 +239,11 @@ private static List<PatternSequence> sequencePattern(final String pattern) {
                 final PatternSequence sequence;
                 switch (c) {
                     case 's':
-                        sequence = new SecondPatternSequence(true, "", 0);
+                        if (sequenceContent.length() == 2) {
+                            sequence = new SecondPatternSequence(true, "", 0);
+                        } else {
+                            sequence = new DynamicPatternSequence(sequenceContent);
+                        }
                         break;
                     case 'S':
                         sequence = new SecondPatternSequence(false, "", sequenceContent.length());