Revert #7276, but test garbage collection of ObservableQuery (#7695)

CHANGELOG.md

@@ -1,5 +1,10 @@
 ## Apollo Client 3.3.10 (not yet released)
 
+### Bug fixes
+
+- Revert PR [#7276](https://github.com/apollographql/apollo-client/pull/7276), but test that garbage collection reclaims torn-down `ObservableQuery` objects. <br/>
+  [@benjamn](https://github.com/benjamn) in [#7695](https://github.com/apollographql/apollo-client/pull/7695)
+
 ### Improvements
 
 - Avoid calling `forceUpdate` when component is unmounted. <br/>

scripts/memory/tests.js

@@ -48,19 +48,29 @@ function makeRegistry(callback, reject) {
 
 describe("garbage collection", () => {
   itAsync("should collect client.cache after client.stop()", (resolve, reject) => {
+    const expectedKeys = new Set([
+      "client.cache",
+      "ObservableQuery",
+    ]);
+
     const registry = makeRegistry(key => {
-      assert.strictEqual(key, "client.cache");
-      resolve();
+      if (expectedKeys.delete(key) && !expectedKeys.size) {
+        resolve();
+      }
     }, reject);
 
     const localVar = makeVar(123);
 
     (function (client) {
       registry.register(client.cache, "client.cache");
 
-      client.watchQuery({
+      const obsQuery = client.watchQuery({
         query: gql`query { local }`,
-      }).subscribe({
+      });
+
+      registry.register(obsQuery, "ObservableQuery");
+
+      obsQuery.subscribe({
         next(result) {
           assert.deepStrictEqual(result.data, {
             local: 123,
@@ -84,4 +94,55 @@ describe("garbage collection", () => {
       }),
     }));
   });
+
+  itAsync("should collect ObservableQuery after tear-down", (resolve, reject) => {
+    const expectedKeys = new Set([
+      "ObservableQuery",
+    ]);
+
+    const registry = makeRegistry(key => {
+      // Referring to client here should keep the client itself alive
+      // until after the ObservableQuery is (or should have been)
+      // collected. Collecting the ObservableQuery just because the whole
+      // client instance was collected is not interesting.
+      assert.strictEqual(client instanceof ApolloClient, true);
+
+      if (expectedKeys.delete(key) && !expectedKeys.size) {
+        resolve();
+      }
+    }, reject);
+
+    const localVar = makeVar(123);
+
+    const client = new ApolloClient({
+      cache: new InMemoryCache({
+        typePolicies: {
+          Query: {
+            fields: {
+              local() {
+                return localVar();
+              },
+            },
+          },
+        },
+      }),
+    });
+
+    (function () {
+      const obsQuery = client.watchQuery({
+        query: gql`query { local }`,
+      });
+
+      registry.register(obsQuery, "ObservableQuery");
+
+      const sub = obsQuery.subscribe({
+        next(result) {
+          assert.deepStrictEqual(result.data, {
+            local: 123,
+          });
+          sub.unsubscribe();
+        },
+      });
+    })();
+  });
 });

src/core/ObservableQuery.ts

@@ -633,11 +633,6 @@ once, rather than every time you call fetchMore.`);
       delete this.reobserver;
     }
 
-    // Since the user-provided context object can retain arbitrarily large
-    // amounts of memory, we delete it when the ObservableQuery is torn
-    // down, to avoid the possibility of memory leaks.
-    delete this.options.context;
-
     // stop all active GraphQL subscriptions
     this.subscriptions.forEach(sub => sub.unsubscribe());
     this.subscriptions.clear();