fix(gatsby-source-contentful): maintain back reference map between runs

[pieh]

Description

Some Contentful delta sync updates are currently stripping previously created back reference links when they shouldn't.

This happen because when we create a link map (which we call foreighReferenceMap in the plugin) we only used entries that were created or updated since last sync. If sync didn't update referencing entry, then updated entries would lose backreferences to referecing entry.

To fix the problem this PR maintains state of foreighReferenceMap between sourceNodes runs keeping it fully saturated at all times. Traversing everything in each sourceNodes runs would be expensive so foreignReferenceMap now also have sort of "delta updates":

• I introduced foreignReferenceMapState which is object with
  • backLinks (which is exact same structure as foreignReferenceMap, so can be used as-is in later stages of sourcing, without having to refactor bunch of code in the plugin)
  • links which is somewhat reverse mapping - keys are contentful's id and values is array of field names in backLinks - this is done to be able to do guided deletions without nested for loops if we would only have backLinks ( similar to what perf(gatsby): fix performance regression with query dependency cleaning #28032 did for increased perf to similar data structure problem)
• on update
  • I clear out references for any of created/updated OR deleted entries (new)
  • I traverse created/updated entries to regenerate links data for it

Related Issues

[ch-59240]

[axe312ger]

Can't see any logic issues, plus tests are green.

This should definitely improve the reliability of the plugin!

Thank you!

[axe312ger]

🥂

[pieh]

Published in:

• gatsby-source-contentful@7.23.1
• gatsby-source-contentful@8.4.1