Align @defer / @stream compiler assumptions to GraphQL spec

[tobias-tengler]

Changes

@stream

• Rename initial_count argument to initialCount
• Allow initial_count argument to be not defined, since the official directive definition specifies it as nullable and with a default value of 0
• Validate initialCount argument being a non-negative int, if it's defined
• Make if argument non-null

@defer

• Make if argument non-null

Open questions

• Should I also change the shape of @stream_connection? I haven't touched its signature yet, since it's not part of the GraphQL specification.
• Some of the changes in this PR are breaking changes. @stream / @defer are experimental features in OSS, so it shouldn't be a problem to just ship these changes. To my knowledge, Meta should be using these features in production though. Is this a blocker for these breaking changes?

Closes #4158

[alunyov]

Thanks for looking into this!

I think @rbalicki2 were also looking into this at some point (so maybe have more context).

Specifically for this PR - I don't think we will be able to land that internally. So we need to figure out the strategy on how to make this work.

Some high-level observations:

1. We need to be able to minimize the changes in this diff to reduce the risk of breaking things internally.

2. For the @defer/@stream we need to somehow express to the compiler what type of directive is expected. Maybe via config, I think we have schema_config section in the compiler config maybe put it there. We can add an explicit version - something like what type of arguments is expected, or even SDL for these directives, or maybe have something like enum DEFER_STREAM_MODE = CustomRelay | OSS

[tobias-tengler]

I also just watched the GraphQL spec meetings of December and there seems to be once more discussion around the shape of the response. In particular the necessity of the label on the directives is being put to question. It's also proposed to no longer include the path in each incremental patch. So I would anticipate that Relay might has to do some more changes to how @defer / @stream are handled in OSS. So having a config option might be the best thing to support Meta and OSS side-by-side.

[Tiedye]

Any updates?

[tobias-tengler]

I can have another go at this in the coming weeks. I'll try to add a config option and keep the default as the previous behavior so all the test changes and so on can be reverted again and we have a smaller diff to land

[tobias-tengler]

Closing this in favor of #4467