Graphql-compiler

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- Fix overly strict type check on :code:`recurse` directives involving a
union type.
`131 <https://github.com/kensho-technologies/graphql-compiler/pull/131>`__

Thanks to :code:`cw6515` for the fix!

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- Fix a bug that arose when using certain type coercions that the
compiler optimizes away to a no-op.
`127 <https://github.com/kensho-technologies/graphql-compiler/pull/127>`__

Thanks to :code:`bojanserafimov` for the fix!

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- Allow :code:`optional` vertex fields nested inside other :code:`optional`
vertex fields.
`120 <https://github.com/kensho-technologies/graphql-compiler/pull/120>`__
- Fix a bug that accidentally disallowed having two :code:`recurse`
directives within the same vertex field.
`115 <https://github.com/kensho-technologies/graphql-compiler/pull/115>`__
- Enforce that all required directives are present in the schema.
`114 <https://github.com/kensho-technologies/graphql-compiler/pull/114>`__
- Under the hood, made fairly major changes to how query metadata is
tracked and processed.

Thanks to :code:`amartyashankha`, :code:`cw6515`, and :code:`yangsong97` for their
contributions!

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- Fix possible incorrect query execution due to dropped type coercions.
`110 <https://github.com/kensho-technologies/graphql-compiler/pull/110>`__
`113 <https://github.com/kensho-technologies/graphql-compiler/pull/113>`__

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- Add a new :code:`filter` operator: :code:`intersects`.
`100 <https://github.com/kensho-technologies/graphql-compiler/pull/100>`__
- Add an optimization that helps OrientDB choose a good starting point
for query evaluation.
`102 <https://github.com/kensho-technologies/graphql-compiler/pull/102>`__

The new optimization pass manages what type information is visible at
different points in the generated query. By exposing additional type
information, or hiding existing type information, the compiler maximizes
the likelihood that OrientDB will start evaluating the query at the
location of lowest cardinality. This produces a massive performance
benefit -- up to 1000x on some queries!

Thanks to :code:`yangsong97` for making his first contribution with the
:code:`intersects` operator!

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- Fix incorrect filtering in :code:`optional` locations.
`95 <https://github.com/kensho-technologies/graphql-compiler/pull/95>`__

Thanks to :code:`amartyashankha` for the fix!