Revert "Check structural equality in QueryInfo#setDiff. (#6891)"

This reverts commit 24a4396, which
prevented some legitimate updates in https://studio.apollographql.com.
We will have to keep investigating #6888 to find a better solution.

CHANGELOG.md

@@ -2,9 +2,6 @@
 
 ## Bug Fixes
 
-- Check structural equality of diff results in `QueryInfo#setDiff` instead of reference equality. <br/>
-  [@benjamn](https://github.com/benjamn) in [#6891](https://github.com/apollographql/apollo-client/pull/6891)
-
 - Use `options.nextFetchPolicy` internally to restore original `FetchPolicy` after polling with `fetchPolicy: "network-only"`, so that polling does not interfere with normal query watching. <br/>
   [@benjamn](https://github.com/benjamn) in [#6893](https://github.com/apollographql/apollo-client/pull/6893)
 

src/__tests__/client.ts

@@ -3028,9 +3028,11 @@ describe('@connection', () => {
     client.cache.evict({ fieldName: "a" });
     await wait();
 
-    expect(checkLastResult(aResults, a456)).toBe(a456);
+    // The results are structurally the same, but the result objects have
+    // been recomputed for queries that involved the ROOT_QUERY.a field.
+    expect(checkLastResult(aResults, a456)).not.toBe(a456);
     expect(checkLastResult(bResults, bOyez)).toBe(bOyez);
-    expect(checkLastResult(abResults, a456bOyez)).toBe(a456bOyez);
+    expect(checkLastResult(abResults, a456bOyez)).not.toBe(a456bOyez);
 
     const cQuery = gql`{ c }`;
     // Passing cache-only as the fetchPolicy allows the { c: "see" }
@@ -3079,19 +3081,25 @@ describe('@connection', () => {
       { a: 123 },
       { a: 234 },
       { a: 456 },
+      // Delivered again because we explicitly called resetLastResults.
+      { a: 456 },
     ]);
 
     expect(bResults).toEqual([
       { b: "asdf" },
       { b: "ASDF" },
       { b: "oyez" },
+      // Delivered again because we explicitly called resetLastResults.
+      { b: "oyez" },
     ]);
 
     expect(abResults).toEqual([
       { a: 123, b: "asdf" },
       { a: 234, b: "asdf" },
       { a: 234, b: "ASDF" },
       { a: 456, b: "oyez" },
+      // Delivered again because we explicitly called resetLastResults.
+      { a: 456, b: "oyez" },
     ]);
 
     expect(cResults).toEqual([

src/core/QueryInfo.ts

@@ -149,8 +149,7 @@ export class QueryInfo {
     const oldDiff = this.diff;
     this.diff = diff;
     if (!this.dirty &&
-        !equal(oldDiff && oldDiff.result,
-               diff && diff.result)) {
+        (diff && diff.result) !== (oldDiff && oldDiff.result)) {
       this.dirty = true;
       if (!this.notifyTimeout) {
         this.notifyTimeout = setTimeout(() => this.notify(), 0);