Bug 1572030 - Reland Add support for experiments in modernConfig r=Standard8

This reverts commit 6e8f8684501061d1d759d1dab40b867e90f2b85d.

Differential Revision: https://phabricator.services.mozilla.com/D44376

--HG--
extra : moz-landing-system : lando

toolkit/components/search/SearchEngineSelector.jsm

@@ -14,6 +14,7 @@ XPCOMUtils.defineLazyGlobalGetters(this, ["fetch"]);
 
 XPCOMUtils.defineLazyModuleGetters(this, {
   SearchUtils: "resource://gre/modules/SearchUtils.jsm",
+  Services: "resource://gre/modules/Services.jsm",
 });
 
 const EXT_SEARCH_PREFIX = "resource://search-extensions/";
@@ -57,6 +58,7 @@ class SearchEngineSelector {
       throw new Error("region and locale parameters required");
     }
     log(`fetchEngineConfiguration ${region}:${locale}`);
+    let cohort = Services.prefs.getCharPref("browser.search.cohort", null);
     let engines = [];
     for (let config of this.configuration) {
       const appliesTo = config.appliesTo || [];
@@ -67,6 +69,9 @@ class SearchEngineSelector {
         let excluded =
           "excluded" in section &&
           this._isInSection(region, locale, section.excluded);
+        if ("cohort" in section && cohort != section.cohort) {
+          return false;
+        }
         return included && !excluded;
       });
 

toolkit/components/search/docs/SearchEngineConfiguration.rst

@@ -132,6 +132,36 @@ configuration object with the users locale. For example:
 Will report either ``us`` or ``gb`` as the ``webExtensionLocale``
 depending on the user.
 
+Experiments
+-----------
+
+We can run experiments by giving sections within ``appliesTo`` a
+``cohort`` value, the Search Service can then optionally pass in a
+matching ``cohort`` value to match those sections.
+
+Sections which have a ``cohort`` will not be used unless a matching
+``cohort`` has been passed in, for example:
+
+.. code-block:: js
+
+    "engine1": {
+      "webExtensionId": "webext",
+      "webExtensionVersion": "1.0",
+      "appliesTo": [{
+        "included": {
+          "everywhere": true
+        },
+        "cohort": "nov-16",
+        "webExtensionId": "webext-experimental",
+      }, {
+        "included": {
+          "everywhere": true
+        },
+        "webExtensionId": "webext-gb",
+        "webExtensionVersion": "1.2"
+      }]
+    }
+
 Engine Defaults
 ---------------
 

toolkit/components/search/tests/xpcshell/test_engine_selector.js

@@ -54,6 +54,10 @@ const CONFIG_URL =
             included: { everywhere: true },
             excluded: { regions: ["us"] },
           },
+          {
+            included: { everywhere: true },
+            cohort: "acohortid",
+          },
         ],
       },
       {
@@ -96,4 +100,15 @@ add_task(async function() {
     ["excite", "aol"],
     "The engines should be in the correct order"
   );
+
+  Services.prefs.setCharPref("browser.search.cohort", "acohortid");
+  ({ engines, privateDefault } = engineSelector.fetchEngineConfiguration(
+    "us",
+    "en-US"
+  ));
+  Assert.deepEqual(
+    engines.map(obj => obj.engineName),
+    ["lycos", "altavista", "aol", "excite"],
+    "Engines are in the correct order and include the cohort engine"
+  );
 });