Fix false positive date detection with trailing dot (#116953)

docs/changelog/116953.yaml

@@ -0,0 +1,6 @@
+pr: 116953
+summary: Fix false positive date detection with trailing dot
+area: Mapping
+type: bug
+issues:
+ - 116946

server/src/main/java/org/elasticsearch/common/time/EpochTime.java

@@ -246,7 +246,10 @@ public long getFrom(TemporalAccessor temporal) {
         .toFormatter(Locale.ROOT);
 
     // this supports milliseconds ending in dot
-    private static final DateTimeFormatter MILLISECONDS_FORMATTER2 = new DateTimeFormatterBuilder().append(MILLISECONDS_FORMATTER1)
+    private static final DateTimeFormatter MILLISECONDS_FORMATTER2 = new DateTimeFormatterBuilder().optionalStart()
+        .appendText(NEGATIVE_SIGN_FIELD, Map.of(-1L, "-")) // field is only created in the presence of a '-' char.
+        .optionalEnd()
+        .appendValue(UNSIGNED_MILLIS, 1, 19, SignStyle.NOT_NEGATIVE)
         .appendLiteral('.')
         .toFormatter(Locale.ROOT);
 

server/src/test/java/org/elasticsearch/common/time/DateFormattersTests.java

@@ -260,6 +260,17 @@ public void testEpochMillisParser() {
             assertThat(formatter.format(instant), is("-0.12345"));
             assertThat(Instant.from(formatter.parse(formatter.format(instant))), is(instant));
         }
+        {
+            Instant instant = Instant.from(formatter.parse("12345."));
+            assertThat(instant.getEpochSecond(), is(12L));
+            assertThat(instant.getNano(), is(345_000_000));
+            assertThat(formatter.format(instant), is("12345"));
+            assertThat(Instant.from(formatter.parse(formatter.format(instant))), is(instant));
+        }
+        {
+            IllegalArgumentException e = expectThrows(IllegalArgumentException.class, () -> formatter.parse("12345.0."));
+            assertThat(e.getMessage(), is("failed to parse date field [12345.0.] with format [epoch_millis]"));
+        }
     }
 
     /**

server/src/test/java/org/elasticsearch/index/mapper/DynamicMappingTests.java

@@ -597,6 +597,23 @@ private void doTestDefaultFloatingPointMappings(DocumentMapper mapper, XContentB
         assertThat(((FieldMapper) update.getRoot().getMapper("quux")).fieldType().typeName(), equalTo("float"));
     }
 
+    public void testDateDetectionEnabled() throws Exception {
+        MapperService mapperService = createMapperService(topMapping(b -> b.field("date_detection", true)));
+
+        ParsedDocument doc = mapperService.documentMapper().parse(source(b -> {
+            b.field("date", "2024-11-18");
+            b.field("no_date", "128.0.");
+        }));
+        assertNotNull(doc.dynamicMappingsUpdate());
+        merge(mapperService, dynamicMapping(doc.dynamicMappingsUpdate()));
+
+        Mapper mapper = mapperService.documentMapper().mappers().getMapper("date");
+        assertThat(mapper.typeName(), equalTo("date"));
+
+        mapper = mapperService.documentMapper().mappers().getMapper("no_date");
+        assertThat(mapper.typeName(), equalTo("text"));
+    }
+
     public void testNumericDetectionEnabled() throws Exception {
         MapperService mapperService = createMapperService(topMapping(b -> b.field("numeric_detection", true)));