Bug 1868676 - Part 1: Allow snapshots of multiple contexts. r=barret,omc-reviewers,aminomancer

`ASRouterTargeting` does _not_ include the experiment details that
supply `activeExperiments`, `activeRollouts`, etc.  Those are combined
from additional contexts.  This patch makes it easy to do that
combination.

N.b.: the use of `Proxy` instances makes iteration tricky, so we avoid
it entirely.

Differential Revision: https://phabricator.services.mozilla.com/D200124

Author: ncalexan

browser/components/asrouter/modules/ASRouterTargeting.sys.mjs

@@ -1061,11 +1061,17 @@ export const ASRouterTargeting = {
    * Asynchronous getters are handled.  Getters that throw or reject
    * are ignored.
    *
-   * @param {object} target - the environment to snapshot.
-   * @return {object} snapshot of target with `environment` object and `version`
-   * integer.
+   * Leftward (earlier) targets supercede rightward (later) targets, just like
+   * `TargetingContext.combineContexts`.
+   *
+   * @param {object} options - object containing:
+   * @param {Array<object>|null} options.targets -
+   *        targeting environments to snapshot; (default: `[ASRouterTargeting.Environment]`)
+   * @return {object} snapshot of target with `environment` object and `version` integer.
    */
-  async getEnvironmentSnapshot(target = ASRouterTargeting.Environment) {
+  async getEnvironmentSnapshot({
+    targets = [ASRouterTargeting.Environment],
+  } = {}) {
     async function resolve(object) {
       if (typeof object === "object" && object !== null) {
         if (Array.isArray(object)) {
@@ -1105,7 +1111,13 @@ export const ASRouterTargeting = {
       return object;
     }
 
-    const environment = await resolve(target);
+    // We would like to use `TargetingContext.combineContexts`, but `Proxy`
+    // instances complicate iterating with `Object.keys`.  Instead, merge by
+    // hand after resolving.
+    const environment = {};
+    for (let target of targets.toReversed()) {
+      Object.assign(environment, await resolve(target));
+    }
 
     // Should we need to migrate in the future.
     const snapshot = { environment, version: 1 };

browser/components/asrouter/tests/xpcshell/test_ASRouterTargeting_snapshot.js

@@ -19,7 +19,9 @@ add_task(async function should_ignore_rejections() {
     },
   };
 
-  let snapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  let snapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
   Assert.deepEqual(snapshot, { environment: { foo: 1 }, version: 1 });
 });
 
@@ -51,7 +53,9 @@ add_task(async function nested_objects() {
     },
   };
 
-  const snapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  const snapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
   Assert.deepEqual(
     snapshot,
     {
@@ -85,7 +89,9 @@ add_task(async function arrays() {
     }),
   };
 
-  const snapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  const snapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
   Assert.deepEqual(
     snapshot,
     {
@@ -102,6 +108,32 @@ add_task(async function arrays() {
   );
 });
 
+add_task(async function target_order() {
+  let target1 = {
+    foo: 1,
+    bar: 1,
+    baz: 1,
+  };
+
+  let target2 = {
+    foo: 2,
+    bar: 2,
+  };
+
+  let target3 = {
+    foo: 3,
+  };
+
+  // target3 supercedes target2; both supercede target1.
+  let snapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target3, target2, target1],
+  });
+  Assert.deepEqual(snapshot, {
+    environment: { foo: 3, bar: 2, baz: 1 },
+    version: 1,
+  });
+});
+
 /*
  * NB: This test is last because it manipulates shutdown phases.
  *
@@ -132,7 +164,9 @@ add_task(async function should_ignore_rejections() {
     },
   };
 
-  let snapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  let snapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
   // `baz` is dropped since we're shutting down by the time it's processed.
   Assert.deepEqual(snapshot, { environment: { foo: 1, bar: 2 }, version: 1 });
 });

toolkit/components/backgroundtasks/tests/xpcshell/test_backgroundtask_experiments.js

@@ -277,7 +277,9 @@ add_task(async function test_backgroundtask_Nimbus_targeting() {
     currentDate: ASRouterTargeting.Environment.currentDate,
     firefoxVersion: ASRouterTargeting.Environment.firefoxVersion,
   };
-  let targetSnapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  let targetSnapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
 
   for (let [targeting, expectedLength] of TARGETING_LIST) {
     // Start fresh each time.
@@ -331,7 +333,9 @@ add_task(async function test_backgroundtask_Messaging_targeting() {
     currentDate: ASRouterTargeting.Environment.currentDate,
     firefoxVersion: ASRouterTargeting.Environment.firefoxVersion,
   };
-  let targetSnapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  let targetSnapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
 
   for (let [targeting, expectedLength] of TARGETING_LIST) {
     // Start fresh each time.

toolkit/components/backgroundtasks/tests/xpcshell/test_backgroundtasksutils.js

@@ -178,7 +178,9 @@ add_task(
       ),
       firefoxVersion: lazy.ASRouterTargeting.Environment.firefoxVersion,
     };
-    let expected = await lazy.ASRouterTargeting.getEnvironmentSnapshot(target);
+    let expected = await lazy.ASRouterTargeting.getEnvironmentSnapshot({
+      targets: [target],
+    });
 
     let snapshotFile = profile.rootDir.clone();
     snapshotFile.append("targeting.snapshot.json");

toolkit/mozapps/update/tests/unit_background_update/test_backgroundupdate_glean.js

@@ -169,7 +169,9 @@ add_task(async function test_targeting_exists() {
     profileAgeCreated: ASRouterTargeting.Environment.profileAgeCreated,
     firefoxVersion: ASRouterTargeting.Environment.firefoxVersion,
   };
-  let targetSnapshot = await ASRouterTargeting.getEnvironmentSnapshot(target);
+  let targetSnapshot = await ASRouterTargeting.getEnvironmentSnapshot({
+    targets: [target],
+  });
 
   await do_readTargeting(JSON.stringify(targetSnapshot), reason => {
     Assert.equal(true, Glean.backgroundUpdate.targetingExists.testGetValue());