fix LOGBACK-971 CharSequenceToRegexMapper#findMinMaxLengthsInSymbols(…

…) always returns min=0

logback-core/src/main/java/ch/qos/logback/core/util/CharSequenceToRegexMapper.java

@@ -110,11 +110,14 @@ private String symbolArrayToRegex(String[] symbolArray) {
     return ".{" + minMax[0] + "," + minMax[1] + "}";
   }
 
-  private int[] findMinMaxLengthsInSymbols(String[] symbols) {
+  static int[] findMinMaxLengthsInSymbols(String[] symbols) {
     int min = Integer.MAX_VALUE;
     int max = 0;
     for (String symbol : symbols) {
       int len = symbol.length();
+      // some SENTINEL values can be empty strings, the month at index 12 or the weekday at index 0
+      if(len == 0)
+        continue;
       min = Math.min(min, len);
       max = Math.max(max, len);
     }

logback-core/src/test/java/ch/qos/logback/core/util/CharSequenceToRegexMapperTest.java

@@ -0,0 +1,72 @@
+package ch.qos.logback.core.util;
+
+import org.junit.After;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import java.text.DateFormatSymbols;
+import java.util.Locale;
+
+import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertEquals;
+
+
+public class CharSequenceToRegexMapperTest {
+  static Locale KO_LOCALE = new Locale("ko", "KR");
+  Locale oldLocale = Locale.getDefault();
+
+  @After
+  public void tearDown() {
+    Locale.setDefault(oldLocale);
+  }
+
+  @Test
+  public void findMinMaxLengthsInSymbolsWithTrivialInputs() {
+    String[] symbols = new String[]{"a", "bb"};
+    int[] results = CharSequenceToRegexMapper.findMinMaxLengthsInSymbols(symbols);
+    assertEquals(1, results[0]);
+    assertEquals(2, results[1]);
+  }
+
+  @Test
+  public void emptyStringValuesShouldBeIgnoredByFindMinMaxLengthsInSymbols() {
+    String[] symbols = new String[]{"aaa", ""};
+    int[] results = CharSequenceToRegexMapper.findMinMaxLengthsInSymbols(symbols);
+    assertEquals(3, results[0]);
+    assertEquals(3, results[1]);
+  }
+
+
+  @Test
+  @Ignore
+  public void noneOfTheSymbolsAreOfZeroLengthForKorean() {
+    Locale.setDefault(KO_LOCALE);
+    noneOfTheSymbolsAreOfZeroLength();
+  }
+
+  @Test
+  @Ignore
+  public void noneOfTheSymbolsAreOfZeroLengthForSwiss() {
+    Locale.setDefault(new Locale("fr", "CH"));
+    noneOfTheSymbolsAreOfZeroLength();
+  }
+
+  private void noneOfTheSymbolsAreOfZeroLength() {
+    DateFormatSymbols dateFormatSymbols = DateFormatSymbols.getInstance();
+    //checkEmptyString(dateFormatSymbols.getShortMonths(), "ShortMonths");
+    //checkEmptyString(dateFormatSymbols.getMonths(), "Months");
+    checkEmptyString(dateFormatSymbols.getShortWeekdays(), "ShortWeekdays");
+    checkEmptyString(dateFormatSymbols.getWeekdays(), "Weekdays");
+    checkEmptyString(dateFormatSymbols.getAmPmStrings(), "AmPmStrings");
+
+  }
+
+  private void checkEmptyString(String[] symbolArray, String category) {
+    for (String s : symbolArray) {
+      System.out.println(category + " [" + s + "]");
+      assertTrue(category + " contains empty strings", s.length() > 0);
+    }
+  }
+
+
+}

logback-core/src/test/java/ch/qos/logback/core/util/PackageTest.java

@@ -25,6 +25,7 @@
   OptionHelperTest.class,
   StatusPrinterTest.class,
   TimeUtilTest.class,
-  ContentTypeUtilTest.class})
+  ContentTypeUtilTest.class,
+  CharSequenceToRegexMapperTest.class})
 public class PackageTest {
 }