fix fragment definition directive variable handling

[jbellenger]

Hi there! I'm the maintainer of graphql-conformance, which verifies spec conformance across the graphql ecosystem.

I noticed that gqlgen had some test failures that appear to originate in gqlparser.

The issue is that gqlparser does not walk directives on fragment definitions. When those directives are the only use of a variable, then those variables will be marked as unused and will incorrectly produce a validation error.

For example, in this configuration:

# schema
directive @testDirective(x: Int) on FRAGMENT_DEFINITION
type Query { placeholder: Int! }

# query
query ($x:Int) { ... F }
fragment F on Query @testDirective(x:$x) { __typename }

gqlparser produces this error:

query:2:8: Variable "$x" is never used.

This PR fixes this by walking directives of fragment definitions.

Thank you for considering this PR! I'm not familiar with this code-base or its conventions, so please feel free to point out any issue no matter how small.

[coveralls]

coverage: 87.265% (+0.02%) from 87.245% — jbellenger:fix-fragment-definition-directive-vars into vektah:master

[StevenACoffman]

@jbellenger thanks for this! Tha validation rules in gqlparser are imported directly from the reference implementation test suite using this process: https://github.com/vektah/gqlparser/tree/master/validator/imported

I'm wondering if there's a similar way to collect and export from your repository.

[jbellenger]

Hi @StevenACoffman ! This is an interesting idea. The test corpus and the system that manages it is currently in flux and I don't think it's stable enough to build on (yet).

But this use-case has been in the back of my mind for a little while -- let me think about it for a bit and then follow-up with you.