Fix Fuzziness#asDistance(String) (#39643)

Currently Fuzziness#asDistance(String) doesn't work for custom AUTO values. If
the fuzziness is AUTO, the method returns the correct edit distance to use,
depending on the input string, but for custom AUTO values it currently always
returns an edit distance of 1. Correcting this and adding unit and integration
tests to catch these cases.

Closes #39614

server/src/main/java/org/elasticsearch/common/unit/Fuzziness.java

@@ -186,7 +186,7 @@ public int asDistance() {
     }
 
     public int asDistance(String text) {
-        if (this.equals(AUTO)) { //AUTO
+        if (this.equals(AUTO) || isAutoWithCustomValues()) { //AUTO
             final int len = termLen(text);
             if (len < lowDistance) {
                 return 0;

server/src/test/java/org/elasticsearch/common/unit/FuzzinessTests.java

@@ -167,4 +167,28 @@ private static Fuzziness doSerializeRoundtrip(Fuzziness in) throws IOException {
         StreamInput streamInput = output.bytes().streamInput();
         return new Fuzziness(streamInput);
     }
+
+    public void testAsDistanceString() {
+        Fuzziness fuzziness = Fuzziness.build("0");
+        assertEquals(0, fuzziness.asDistance(randomAlphaOfLengthBetween(0, 10)));
+        fuzziness = Fuzziness.build("1");
+        assertEquals(1, fuzziness.asDistance(randomAlphaOfLengthBetween(0, 10)));
+        fuzziness = Fuzziness.build("2");
+        assertEquals(2, fuzziness.asDistance(randomAlphaOfLengthBetween(0, 10)));
+
+        fuzziness = Fuzziness.build("AUTO");
+        assertEquals(0, fuzziness.asDistance(""));
+        assertEquals(0, fuzziness.asDistance("ab"));
+        assertEquals(1, fuzziness.asDistance("abc"));
+        assertEquals(1, fuzziness.asDistance("abcde"));
+        assertEquals(2, fuzziness.asDistance("abcdef"));
+
+        fuzziness = Fuzziness.build("AUTO:5,7");
+        assertEquals(0, fuzziness.asDistance(""));
+        assertEquals(0, fuzziness.asDistance("abcd"));
+        assertEquals(1, fuzziness.asDistance("abcde"));
+        assertEquals(1, fuzziness.asDistance("abcdef"));
+        assertEquals(2, fuzziness.asDistance("abcdefg"));
+
+    }
 }

server/src/test/java/org/elasticsearch/search/query/SearchQueryIT.java

@@ -722,6 +722,32 @@ public void testMatchQueryNumeric() throws Exception {
         expectThrows(SearchPhaseExecutionException.class, () -> client().prepareSearch().setQuery(matchQuery("double", "2 3 4")).get());
     }
 
+    public void testMatchQueryFuzzy() throws Exception {
+        assertAcked(prepareCreate("test").addMapping("_doc", "text", "type=text"));
+
+        indexRandom(true, client().prepareIndex("test", "_doc", "1").setSource("text", "Unit"),
+                client().prepareIndex("test", "_doc", "2").setSource("text", "Unity"));
+
+        SearchResponse searchResponse = client().prepareSearch().setQuery(matchQuery("text", "uniy").fuzziness("0")).get();
+        assertHitCount(searchResponse, 0L);
+
+        searchResponse = client().prepareSearch().setQuery(matchQuery("text", "uniy").fuzziness("1")).get();
+        assertHitCount(searchResponse, 2L);
+        assertSearchHits(searchResponse, "1", "2");
+
+        searchResponse = client().prepareSearch().setQuery(matchQuery("text", "uniy").fuzziness("AUTO")).get();
+        assertHitCount(searchResponse, 2L);
+        assertSearchHits(searchResponse, "1", "2");
+
+        searchResponse = client().prepareSearch().setQuery(matchQuery("text", "uniy").fuzziness("AUTO:5,7")).get();
+        assertHitCount(searchResponse, 0L);
+
+        searchResponse = client().prepareSearch().setQuery(matchQuery("text", "unify").fuzziness("AUTO:5,7")).get();
+        assertHitCount(searchResponse, 1L);
+        assertSearchHits(searchResponse, "2");
+    }
+
+
     public void testMultiMatchQuery() throws Exception {
         createIndex("test");