[gatsby-source-contentful] Allow for cached content whenever possible

Hi, this is my first issue, I could not find duplicates but sorry in advance if it exists. Also, thank you for a great plugin.

Summary

Allow for something like GATSBY_CONTENTFUL_OFFLINE=prefer which always uses cached data (if exists) in development

Motivation

I’m working on a project with a pretty large amount of contentful data. Having contentful data completely synced all the time is not a priority for my use case, so I would like a way to (at least attempt to) manually opt out of contentful re-sync whenever I add a dependency, change a gatsby-*.js file, etc.

It will considerably speed development time for me. Hope this is possible.

Thanks.

[TylerBarnes]

Hey @doronnac , thanks for the feature request! This would actually be a Gatsby core feature, not specific to the contentful plugin, and this is not currently possible. Right now, the entire cache for all plugins is invalidated if gatsby-*.js files or dependencies are changed, regardless of wether it’s needed or not. Work is currently being done to selectively invalidate the cache of only the plugins that need it, see https://github.com/gatsbyjs/gatsby/pull/8379. Once that’s merged though, it wont solve your problem. IMO we need a gatsby-node API for plugins to run logic to decide if their cache (or parts of their cache) should be invalidated.

[muescha]

@doronnac maybe then should help an external cache/proxy/vcr for your test setup?

something like the “famous” VCR ruby gem i found (but not tested):

• node-vcr (based on flickr/yakbak & talkback)