State: Split post query fetching status from result mapping

[aduth]

Follow-up to #3487 (comment)

This pull request seeks to split the posts.queries state subtree, which currently tracks both fetching status and response results for a query, to separate subtrees (posts.queries and post.queryRequests). Benefits include:

• Fetching status should not be persisted, whereas query results should. Separating them makes this more feasible.
• Simplifies structure of state tree, removing need to check for whether query is "tracked" before return result from selector. Also leads to simpler-to-follow reducer logic and decreased nesting (fewer Object.assign).

Testing instructions:

Verify that there are no regressions, particularly around the <PostSelector /> component, and ensure that fetching status is properly tracked such to avoid unnecessary excessive requests.

Repeat testing instructions from #2350.

Ensure Mocha tests pass by running make test from client/state/posts.

Verify state persistence behaves as expected. See #3671 (comment) .

Follow-up tasks:

• Rename posts.query to posts.queryResults
• Rename posts.queriesLastPage to posts.queryLastPage
• Add tests to ensure that reducer keys are included on the default export (easy to miss)

/cc @gwwar

[aduth]

@gwwar : This has been rebased to account for the merging of #3487, and also includes a posts query schema in 70ffb2e (validating JSON strings with RegEx is... fun 😉 ).

[aduth]

Notably, now that a schema is included, one should also test that schema persistence behaves correctly for query results.

1. Start Node process with ENABLE_FEATURES=persist-redux make run
2. Navigate to <PostSelector /> app components demo
3. Enable persistence debugging by entering localStorage.debug = 'calypso:state' in your developer tools console
4. Refresh the page
5. Note that persisted state is restored, including posts.queries, without validation warnings

[gwwar]

Fun 😄 Since we don't parse this later I'm not sure if we need to be this strict.

[aduth]

Since we don't parse this later I'm not sure if we need to be this strict.

My main concern is that there's a real possibility that we change the syntax of the keys. I suppose I could be a bit more lax about it, e.g. \{[^\}]*\} instead of the more complete JSON validation I have here.

[gwwar]

👍 Changes look great. I like how the tree is being simplified. I verified that testing instructions worked, and also tested that the editor still loads properly when post/items data is thrown out. 🚢

[gwwar]

Also, persist-redux is now enabled on dev/horizon. So to test the alternative pathway, it would be:

DISABLE_FEATURES=persist-redux make run

[aduth]

@gwwar : Rebased a83c638 includes a slightly more relaxed property pattern. Also includes a test to ensure that invalid persisted state is discarded. Tested as well with disabled persistence. Will plan to merge shortly after tests pass.