New: Use typePolicies and makeVar to store client-side state

New Pattern Proposal: "Use typePolicies and makeVar to store client-side state"

Apollo Client 3 allows us to manage application state with type policies with reactive variables, this pattern may replace client-side resolvers (in some cases?).

Advantages of new pattern

1. Reactive variables (makeVar) manage updates in components automatically.
2. Current local resolvers are deprecated by Apollo Client: https://www.apollographql.com/docs/react/local-state/local-resolvers/, and will have to be reimplemented as part of the link chain.

Disadvantages of new pattern

1. We don't use mutations as with backend changes, and require one more inject to modify state.
2. We have yet one more way to state state on the client.
3. We don't have a good way to track local state of the reactive variable using Apollo devtools.
   • See related: https://github.com/apollographql/apollo-client-devtools/discussions/391

What is the impact on our existing codebase?

I expect that we will use the best tool on a case-by-case basis, and each product area will choose an approach that suits them, no sweeping changes.

Reference implementation

Introduce admin_runners_bulk_delete feature flag (gitlab-org/gitlab!81894 - merged)

New