Infer input fields from setFieldsOnGraphQLNodeType

[Zalastax]

Makes fields added by setFieldsOnGraphQLNodeType filterable and sortable.
I didn't see any uses of setFieldsOnGraphQLNodeType in the tests so adding new tests felt like a non-starter.

Closes #1931

[KyleAMathews]

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[KyleAMathews]

Hey! From a quick read through everything looks very sensible & workable. Thanks!

Would love some tests for the new functionality. The reason there's not any existing tests is core to this point has had nothing to do with setFieldsOnGraphQLNodeType so if things failed, it was on the userland code to handle it. The GraphQL schema inference parts of the code are complex & core to Gatsby so we need to keep them very well tested.

[Zalastax]

Good, no problem. It would really help if you can show me how to add usage of setFieldsOnGraphQLNodeType to the tests, if you have the time.

[KyleAMathews]

@Zalastax awesome! Basically what you want to do is simulate creating various schemas with different GraphQL types usingsetFieldsOnGraphQLNodeType and assert that the correct connection input fields are being created.

Some of the tests in here should be a good guide: https://github.com/gatsbyjs/gatsby/tree/master/packages/gatsby/src/schema/__tests__

[KyleAMathews]

Happy to answer more questions about the process as you dive in!

[Zalastax]

How do I mock api-runner-node? If my test can provide the result of that call, then the rest is a piece of cake. I could of course change the code to instead provide the result of await apiRunner(`setFieldsOnGraphQLNodeType` to createType, but it seems nicer to create some fake plugins.

[KyleAMathews]

No need to mock it, that's overkill. Just manually add additional GraphQL fields that aren't in the node data.

[Zalastax]

But I need https://github.com/Zalastax/gatsby/blob/0f8bffaaac491cd0ed015f7764e8acd2289bade0/packages/gatsby/src/schema/build-node-types.js#L129-L133 to get a list of fields to add? Sorry if I'm missing something.

[KyleAMathews]

There's nothing special about that code. It just calls plugins and gets an array of graphql fields. You're testing the inference code not how gatsby gets fields from plugins.

[Zalastax]

Ah, you mean to just test https://github.com/Zalastax/gatsby/blob/0f8bffaaac491cd0ed015f7764e8acd2289bade0/packages/gatsby/src/schema/infer-graphql-input-fields-from-fields.js#L178, not the whole https://github.com/Zalastax/gatsby/blob/0f8bffaaac491cd0ed015f7764e8acd2289bade0/packages/gatsby/src/schema/build-node-types.js#L28. Sure thing!

[Zalastax]

@KyleAMathews I'm quite happy with this now 😃. Tell me if you need something more before merging.

[KyleAMathews]

Hey this looks really really good! Thanks for adding this! Some tricky code but definitely fills in a big missing piece to Gatsby's GraphQL story 🙏

[jlengstorf]

Hiya @Zalastax! 👋

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