PgSelect now yields an object, not an array

[benjie]

Description

hasMore used to be hacked onto the returned array which was always a disgusting hack but it worked and I couldn't justify spending the time to fix it. But it turns out we need more stuff like that now that we're eradicating eval, for example we need to know what the indicies are that were used to select the orderBy values so that we can populate the cursors with them. Since we're likely to need more stuff like this in future, I've changed PgSelect to return an object, where one of the entries in the object is items which is the previous array; then I've added PgSelectRowsStep and PgUnionAllRowsStep to extract these items whilst still honouring stream/defer.

I've also updated Grafast to have a new convention method, ExecutableStep::items(), which will be called when a step is to be used in a list position. This gives the step a chance to return an alternative step to yield the list itself, this enables the PgSelect to be used directly in list positions (without having to .items() yourself manually), and to feed it to things like listTransform (each/filter/groupBy/etc). This minimizes the amount of rewriting necessary.

I've also merged the stream() and execute() methods - these are no longer separate methods, in fact stream() is no longer supported. The return signature of execute() has changed to accomodate this, but no change is needed on existing step classes unless they implement a stream() method.

I've also rewritten how the @stream directive is interpreted and moved it entirely to runtime, including in the output generation.

All of this is breaking.

Performance impact

Work towards:

• Epic: removing $step.eval() #2060

MAJOR CHANGE: I've deleted the optimizations of PgSelectStep, so SQL inlining will no longer occur. We'll restore this in a (much) later PR, but for now we need to focus on solving the above issue.

Security impact

Working towards eradicating step eval, so positive.

Checklist

• My code matches the project's code style and yarn lint:fix passes.
• I've added tests for the new feature, and yarn test passes.
• I have detailed the new feature in the relevant documentation.
• I have added this feature to 'Pending' in the RELEASE_NOTES.md file (if one exists).
• If this is a breaking change I've explained why.

[changeset-bot]

🦋 Changeset detected

Latest commit: 13a1219

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 15 packages

Name	Type
postgraphile	Patch
@dataplan/pg	Patch
grafast	Patch
graphile-utils	Patch
pgl	Patch
graphile	Patch
graphile-build-pg	Patch
@localrepo/grafast-bench	Patch
@dataplan/json	Patch
@grafserv/persisted	Patch
grafserv	Patch
ruru-components	Patch
@localrepo/grafast-website	Patch
graphile-build	Patch
graphile-export	Patch

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