ICU-12979 Fix \Q...\E in UnicodeRegex#transform (#23)

icu4j/main/classes/core/src/com/ibm/icu/impl/UnicodeRegex.java

@@ -116,7 +116,7 @@ public class UnicodeRegex implements Cloneable, Freezable<UnicodeRegex>, StringT
 
             case 1: // we are after a \
                 if (ch == 'Q') {
-                    state = 1;
+                    state = 2;
                 } else {
                     state = 0;
                 }
@@ -128,11 +128,12 @@ public class UnicodeRegex implements Cloneable, Freezable<UnicodeRegex>, StringT
                 }
                 break;
 
-            case 3: // we are in at \Q...\
+            case 3: // we are in a \Q...\
                 if (ch == 'E') {
                     state = 0;
+                } else if (ch != '\\') {
+                    state = 2;
                 }
-                state = 2;
                 break;
             }
             result.append(ch);

icu4j/main/tests/translit/src/com/ibm/icu/dev/test/translit/RegexUtilitiesTest.java

@@ -216,6 +216,29 @@ public class RegexUtilitiesTest extends TestFmwk {
         }
     }
 
+    /**
+     * Check {@code \Q} and {@code \E}.
+     */
+    @Test
+    public void TestTransformQuotation() {
+        String[][] tests = {
+                {"a\\Qb", "a\\Qb"},
+                {"a\\Eb", "a\\Eb"},
+                {"\\Q[ba]", "\\Q[ba]"},
+                {"\\\\Q[ba]", "\\\\Q[ab]"},
+                {"\\Q[ba]\\e[ba]", "\\Q[ba]\\e[ba]"},
+                {"\\Q[ba]\\E[ba]", "\\Q[ba]\\E[ab]"},
+                {"\\Q[ba]\\\\E[ba]", "\\Q[ba]\\\\E[ab]"},
+        };
+        UnicodeRegex regex = new UnicodeRegex();
+        for (int i = 0; i < tests.length; ++i) {
+            final String source = tests[i][0];
+            String expected = tests[i][1];
+            String actual = regex.transform(source);
+            assertEquals(source, expected, actual);
+        }
+    }
+
     /**
      * Utility for checking patterns
      */