Fallback to frontmatter excerpt if available

[chiedo]

Currently if there is no node.edge.excerpt, the frontmatter excerpt is still overwritten.

This fixes that.

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[KyleAMathews]

A little worried this is making the default setup too specific. If a user hasn't added excerpt to their frontmatter, then they'll get a cryptic GraphQL error (which we really need to improve).

Perhaps it'd be better if you just overrode the query/serializer for your site?

@nicholaswyoung thoughts?

[chiedo]

Good point @KyleAMathews

I don't see an obvious way to override the serializer. I may be missing something?

If not, I'll submit a PR.

[KyleAMathews]

Oh you're right, doesn't look there is a way yet.

[chiedo]

Want me to work on that and PR?

[KyleAMathews]

So it looks like you can pass custom serializers but it's not documented :-)

gatsby/packages/gatsby-plugin-feed/src/gatsby-node.js

Line 53 in 529acc4

f.serialize && typeof f.serialize === `function` ? f.serialize : serialize

A PR adding documentation would be most excellent!

[chiedo]

Will do! :)

[secretfader]

I'm just now seeing this. Having GitHub notifications pushed aside in the segmented Gmail inbox is still... interesting.

Yeah, I do a lot of work with custom serializers on my site, which is principally why I wrote #1548. I just saw #1681, so I assume this is fixed. :)