#292062 follow-up

This follows-up on this master:broken issue: #292062 (closed)

What happened

Two MRs got merged consecutively:

• !48705 (merged) introduced a @connection directive in a GraphQL query because some paginated data had to be optimistically updated. The directive allowed the data to be stored in Apollo's cache with a static key, making it easier to read/write the cached query. More on this here: https://www.apollographql.com/docs/react/v2/caching/cache-interaction/#the-connection-directive
• !48940 (merged) introduced a test where the above query was being mocked via mock-apollo-client, which is what actually broke master.

Why?

What exactly happened is similar to what's described in this apollo-client issue: https://github.com/apollographql/apollo-client/issues/2518

When it encounters a @connection directive, apollo-client strips it out of the cache key when caching the data.

The thing is that mock-apollo-client uses apollo-client's actual cache layer, but it provides its own mocked link, with its own way of building cache keys that does not strip the @connection directive.

This results in a discrepancy between mocked request handlers and what's actually in the cache, as any query containing a @connection query can not be traced back to the cache.

So, when mocking apollo-client in tests, queries containing a @connection directive would always be considered not mocked and would never resolve properly.

How do we fix this?

• Revert the changes that caused the failure.
  • The failure was initially reported in #292062 (closed).
  • !48940 (merged) was identified as the culprit and got reverted in !49401 (merged)
• Contribute a fix to the upstream project.
  • A fix has been submitted to the upstream project: https://github.com/Mike-Gibson/mock-apollo-client/pull/20
  • It got merged and released in mock-apollo-client@0.5.0: https://github.com/Mike-Gibson/mock-apollo-client/releases/tag/v0.5.0
• Once the fix is merged and released, upgrade the package in GitLab.
  • Upgrade MR: !49467 (merged)
• Reintroduce the changes that caused the failures.
  • MR: !49435 (merged)
• Document the @connection key in GitLab's development docs.
  • Documentation MR: !49471 (merged)