Fix watchFragment reports complete=false when from object is not identifiable

[ryo-manba]

Closes #12003

Fixes an issue where watchFragment incorrectly reported complete: true when the from object was not identifiable (cache.identify returned undefined).

This was created from the branch adds the failing test.
It might be better to merge that one first.

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Errors

react/api/react/components

• Cannot find module '@microsoft/tsdoc/schemas/tsdoc.schema.json' from '/var/task/node_modules/.pnpm/@microsoft[email protected]/node_modules/@microsoft/tsdoc-config/lib'
  react/api/react/hooks

• Cannot find module '@microsoft/tsdoc/schemas/tsdoc.schema.json' from '/var/task/node_modules/.pnpm/@microsoft[email protected]/node_modules/@microsoft/tsdoc-config/lib'
  react/data/queries

• Cannot find module '@microsoft/tsdoc/schemas/tsdoc.schema.json' from '/var/task/node_modules/.pnpm/@microsoft[email protected]/node_modules/@microsoft/tsdoc-config/lib'
  react/errors

• Transformer not found for component "DisplayClientError"
  react/local-state/managing-state-with-field-policies

• Could not parse expression with acorn

[jerelmiller]

Hey @ryo-manba 👋

Thanks for your patience!

I'd actually like to dig a layer deeper and see if we can fix the issue at the root. It looks like anything having to do with a Cache.DiffResult is affected by this issue. Since watchFragment calls cache.watch() under the hood, the issue is somewhere inside the result returned from that.

I can also reproduce the incorrect result using cache.diff with the following test:

test.only("reports diffs incorrectly", async () => {
  const cache = new InMemoryCache();

  console.log(
    cache.diff({
      query: cache["getFragmentDoc"](gql`
        fragment FooFragment on Foo {
          foo
        }
      `),
      id: cache.identify({}),
      returnPartialData: true,
      optimistic: true,
    })
  );

  await new Promise((res) => {
    const w = cache.watch({
      query: cache["getFragmentDoc"](gql`
        fragment FooFragment on Foo {
          foo
        }
      `),
      id: cache.identify({}),
      returnPartialData: true,
      immediate: true,
      optimistic: true,
      callback: (diff) => {
        console.log("callback", diff);

        res(void 0);
      },
    });
  });
});

If you paste and run this, you'll notice that cache.diff also returns a complete: true, even though it has no data.

From what I can tell, that getFragmentDoc thing is what triggers the issue. If I replace the document with a plain query, the data is properly reported as complete: false.

Let's see if we can fix it in the cache itself. Is this something you'd like to look into further?

[ryo-manba]

Thank you for the information!
I'll dig into it a bit more.

[ryo-manba]

Hi @jerelmiller,
I’ve made a change to check if a field exists when handling FRAGMENT_SPREAD.
The current implementation relies on complete: !missing to determine if the result is complete:

https://github.com/apollographql/apollo-client/blob/v3.13.0-rc.0/src/cache/inmemory/readFromStore.ts#L296

However, some tests are failing due to this change.
Is there any issue with this approach? If you have any feedback, please let me know!