Add extensions property to GraphQLError.

[jckw]

Allows an extensions property to be passed when creating a GraphQLError as described in graphql-python/graphql-core#203.

This property is included in graphql-js, which makes graphql-python more accurately reflect it.

[jckw]

No idea why some tests are failing. Any help?

[nikordaris]

Run tox locally and commit what it fixes. it will fix the formatting errors for you in the future if you install the pre-commit hook

[nikordaris]

Also, you should probably add extensions to the slots list.

[nikordaris]

Another problem with this is the format_error doesn't merge extensions from original_error. This is a common issue in my opinion with graphql-core. The executor wraps all raised errors in a GraphQLLocatedError which masks the original error in error reporting.

[dcosson]

@jckw @nikordaris any chance of getting this merged to keep this library up to date with the graphql protocol?

[dan98765]

I've had to add 'extensions' as an override in our codebase since it's not in graphql-core yet.. so I'm also keen to see this feature merged. I do not see any tests added or updated so far.
@jckw - could you please add/update test(s) that exercise the new code?

[nikordaris]

I think we should close this PR in favor of graphql-python/graphql-core#214 since it is passing the build and addresses the issues brought up in this PR

[jckw]

Closed in favour of #214