Fixes component-renderer to allow for use of client-only-paths

[scottyeck]

According to #1501, it looks like client-only-paths are broken in 1.0. (It actually looks like this has been broken since v1.0.0-beta.6.)

Looks like componentShouldUpdate assumes that, a route-change should only trigger a re-render if its accompanied by a corresponding change in the higher-level pageResources.component. In theory, this makes sense, though it's directly in conflict with the notion of client-only paths. My thought is that the re-render should be triggered if either the component changes OR the found page has a corresponding matchPath, (as demonstrated in the client-only-paths docs), in which case gatsby may not know whether or not a re-render is necessary and should optimistically trigger one.

If there's a better way to go about this, great. 😎

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[KyleAMathews]

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[KyleAMathews]

Nice! I liked how tightly scoped the fix is. Don't fix one thing and inadvertently break another (like I did for beta.6 ;-))

[aliaksejenka]

With a current (1.9.67) version of Gatsby I came upon non-working links to the client-only path in production build. I found this thread and discovered the following mismatch between the contents of this fix and the master, in the loader.js:

  ...
  const done = () => {
    if (component && json && (!page.layoutComponentChunkName || layout)) {
      pathScriptsCache[path] = { component, json, layout } <<< here missing the "page" member
      const pageResources = { component, json, layout } <<< and here too

After I added that "page" member, links began to work. Maybe at some point it was overwritten with a "layout" by mistake?

[KyleAMathews]

@skorowarkin someone else was mentioning that this was broken — could you submit a PR with the fix!?

[aliaksejenka]

@KyleAMathews done: #2506