TINKERPOP-3095: Provide a path for selecting script engine for traversals in TP4

CHANGELOG.asciidoc

@@ -27,6 +27,7 @@ image::https://raw.githubusercontent.com/apache/tinkerpop/master/docs/static/ima
 
 * Added a `Char` type to `gremlin-go` to represent the Gremlin `Character` type in `GremlinLang`.
 * Restricted GraphSON and Gryo `Class` deserialization to classes registered with `ClassRegistry.register()`, `registerStrategy()` or `registerStrategies()`.
+* Fixed `gremlin-javascript` to send the `language` set with `with_("language", ...)` on remote traversals instead of dropping it.
 * Fixed `gremlin-go` to report a malformed or truncated GraphBinary response as a deserialization error rather than a bare decoder message.
 * Added a per-request `language` option to the `gremlin-go` `RequestOptionsBuilder`, and honored `With("language", ...)` on traversals.
 * Changed `gremlin-go` per-request options set via `with()` to accept any numeric type holding an integer value an `int` can hold and to ignore other values rather than panicking.

docs/src/reference/gremlin-variants.asciidoc

@@ -2012,7 +2012,7 @@ Some connection options can also be set on individual requests made through the
 const vertices = await g.with_('timeoutMillis', 500).V().out('knows').toList()
 ----
 
-The following options are allowed on a per-request basis in this fashion: `batchSize`, `bulkResults`,
+The following options are allowed on a per-request basis in this fashion: `batchSize`, `bulkResults`, `language`,
 `materializeProperties` and `timeoutMillis`.
 
 NOTE: When submitting traversals through `DriverRemoteConnection`, `bulkResults` defaults to `true` per-request

gremlin-js/gremlin-javascript/lib/driver/driver-remote-connection.ts

@@ -85,6 +85,7 @@ export default class DriverRemoteConnection extends RemoteConnection {
         'batchSize',
         'materializeProperties',
         'bulkResults',
+        'language',
       ];
       for (const strategy of strategies) {
         for (const key in strategy.configuration) {

gremlin-js/gremlin-javascript/test/integration/remote-connection-tests.js

@@ -62,6 +62,20 @@ describe('DriverRemoteConnection', function () {
           assert.ok(err.statusException);
         });
     });
+    it('should send the with_() language to the server', async function () {
+      const g = anon.traversal().with_(connection);
+      await assert.rejects(g.with_('language', 'no-such-engine').inject(1).toList(), err => {
+        assert.strictEqual(err.statusCode, 400);
+        assert.strictEqual(err.statusException, 'InvalidRequestException');
+        assert.match(err.statusMessage, /Script engine \[no-such-engine\] is not available/);
+        return true;
+      });
+    });
+    it('should use the with_() language when it is available', async function () {
+      const g = anon.traversal().with_(connection);
+      const list = await g.with_('language', 'gremlin-lang').inject(1).toList();
+      assert.deepStrictEqual(list, [1]);
+    });
     it('should iterate ordered results', async function () {
       const g = anon.traversal().with_(connection);
       const traversal = g.V().has('name', P.within('marko', 'peter')).values('name').order();

gremlin-js/gremlin-javascript/test/unit/driver-remote-connection-test.js

@@ -20,6 +20,7 @@
 import assert from 'assert';
 import DriverRemoteConnection from '../../lib/driver/driver-remote-connection.js';
 import GremlinLang from '../../lib/process/gremlin-lang.js';
+import { OptionsStrategy } from '../../lib/process/traversal-strategy.js';
 
 describe('DriverRemoteConnection', function () {
   function createConnection(capture) {
@@ -54,4 +55,39 @@ describe('DriverRemoteConnection', function () {
 
     assert.strictEqual(captured.requestOptions.parameters, "['x':42]");
   });
+
+  describe('language', function () {
+    it('does not set a language when none is configured', async function () {
+      let captured;
+      const connection = createConnection(args => captured = args);
+
+      await connection.submit(new GremlinLang().addStep('V'));
+
+      assert.strictEqual(captured.requestOptions.language, undefined);
+    });
+
+    it('sends the language set with with_()', async function () {
+      let captured;
+      const connection = createConnection(args => captured = args);
+      const gremlinLang = new GremlinLang()
+        .addStep('V')
+        .addSource('withStrategies', [new OptionsStrategy({ language: 'my-engine' })]);
+
+      await connection.submit(gremlinLang);
+
+      assert.strictEqual(captured.requestOptions.language, 'my-engine');
+    });
+
+    it('does not render the language into the gremlin text', async function () {
+      let captured;
+      const connection = createConnection(args => captured = args);
+      const gremlinLang = new GremlinLang()
+        .addStep('V')
+        .addSource('withStrategies', [new OptionsStrategy({ language: 'my-engine' })]);
+
+      await connection.submit(gremlinLang);
+
+      assert.ok(!captured.gremlin.includes('language'));
+    });
+  });
 });