Added the `DistanceUnit.NAUTICALMILES` enumeration

label with the corresponding *NM* and *nmi* unit
suffixes. Update the docs to match.

Closes #5085

docs/reference/api-conventions.asciidoc

@@ -171,7 +171,7 @@ Kilometer::     `km` or `kilometers`
 Meter::         `m` or `meters`
 Centimeter::    `cm` or `centimeters`
 Millimeter::    `mm` or `millimeters`
-
+Nautical mile:: `NM`, `nmi` or `nauticalmiles`
 
 [[fuzziness]]
 [float]

src/main/java/org/elasticsearch/common/unit/DistanceUnit.java

@@ -37,11 +37,14 @@ public enum DistanceUnit {
     INCH(0.0254, "in", "inch"),
     YARD(0.9144, "yd", "yards"),
     FEET(0.3048, "ft", "feet"),
-    MILES(1609.344, "mi", "miles"),
     KILOMETERS(1000.0, "km", "kilometers"),
+    NAUTICALMILES(1852.0, "NM", "nmi", "nauticalmiles"),
     MILLIMETERS(0.001, "mm", "millimeters"),
     CENTIMETERS(0.01, "cm", "centimeters"),
 
+    // 'm' is a suffix of 'nmi' so it must follow 'nmi'
+    MILES(1609.344, "mi", "miles"),
+
     // since 'm' is suffix of other unit
     // it must be the last entry of unit
     // names ending with 'm'. otherwise

src/test/java/org/elasticsearch/common/unit/DistanceUnitTests.java

@@ -35,6 +35,7 @@ public class DistanceUnitTests extends ElasticsearchTestCase {
         assertThat(DistanceUnit.KILOMETERS.convert(10, DistanceUnit.MILES), closeTo(16.09344, 0.001));
         assertThat(DistanceUnit.MILES.convert(10, DistanceUnit.MILES), closeTo(10, 0.001));
         assertThat(DistanceUnit.MILES.convert(10, DistanceUnit.KILOMETERS), closeTo(6.21371192, 0.001));
+        assertThat(DistanceUnit.NAUTICALMILES.convert(10, DistanceUnit.MILES), closeTo(8.689762, 0.001));
         assertThat(DistanceUnit.KILOMETERS.convert(10, DistanceUnit.KILOMETERS), closeTo(10, 0.001));
         assertThat(DistanceUnit.KILOMETERS.convert(10, DistanceUnit.METERS), closeTo(0.01, 0.00001));
         assertThat(DistanceUnit.KILOMETERS.convert(1000,DistanceUnit.METERS), closeTo(1, 0.001));
@@ -46,6 +47,8 @@ public class DistanceUnitTests extends ElasticsearchTestCase {
         assertThat(DistanceUnit.Distance.parseDistance("50km").unit, equalTo(DistanceUnit.KILOMETERS));
         assertThat(DistanceUnit.Distance.parseDistance("500m").unit, equalTo(DistanceUnit.METERS));
         assertThat(DistanceUnit.Distance.parseDistance("51mi").unit, equalTo(DistanceUnit.MILES));
+        assertThat(DistanceUnit.Distance.parseDistance("53nmi").unit, equalTo(DistanceUnit.NAUTICALMILES));
+        assertThat(DistanceUnit.Distance.parseDistance("53NM").unit, equalTo(DistanceUnit.NAUTICALMILES));
         assertThat(DistanceUnit.Distance.parseDistance("52yd").unit, equalTo(DistanceUnit.YARD));
         assertThat(DistanceUnit.Distance.parseDistance("12in").unit, equalTo(DistanceUnit.INCH));
         assertThat(DistanceUnit.Distance.parseDistance("23mm").unit, equalTo(DistanceUnit.MILLIMETERS));