Add conditional requirement

[tdelmas]

Supersede #59 at the request of @PierrickP

This PR adds a first batch of conditional checks such as:

• Files required depending on the content of other files
• Fields required depending on the content of other files
• Value of fields depending on the content of other files (e.g. the validity of ids referring to an object in another file)

From @isabelle-dr #59 (comment) :

• default_pricing_plan_id in vehicle_types.json is checked (requirement and value)
• vehicle_types_available in station_status.json requirement is checked
• num_docks_available in station_status.json can't be automatically checked because it depends on something not defined in the files: REQUIRED except for stations that have unlimited docking capacity. It could be done in a separate PR as a checkbox option in the validator UI such as "[ ] All stations limited docking capacity".
• vehicle_docks_available in station_status.json can't be automatically checked because it depends on something not defined in the files: REQUIRED in feeds where [...] certain docks are only able to accept certain vehicle types. It could be done in a separate PR as a checkbox option in the validator UI such as "[ ] All stations accepts all vehicle types".
• system_id in free_bike_status.json is not touched by that PR.
• lat and lon in free_bike_status.json : As the conditional is between two fields of the same object, it has been fixed in the schemas: Improved schema gbfs-json-schema#66
• vehicle_type_id in free_bike_status.json is checked (requirement and value)
• current_range_meters in free_bike_status.json requirement is checked
• the file vehicle_types.json conditional requirement is checked

Also, this PR adds the following checks:

• The conditional requirement of system_pricing_plans.json
• The conditional requirement and value of default_pricing_plan_id in vehicle_types.json
• The conditional requirement of rental_apps in system_information.json
• The conditional requirement of rental_apps in system_information.json
• The conditional requirement of rental_apps.ios.store_uri and rental_apps.android.store_uri in system_information.json

Other changes on this PR:

• Update of https://github.com/MobilityData/gbfs-json-schema (it was required as tests were falling due to invalid json syntax)
• Adds an option to download the generated schema used for the validation
  

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[isabelle-dr]

Thank you for working on this! 🙏

[isabelle-dr]

Hello,

This contribution is amazing 🔥
I opened #64 to update the documentation so it reflects all this work. I know we require one review before merging - can you wait for a review by a MobilityData as well in the future?
🙏🙏🙏

[nbdh]

Hi @PierrickP,

thanks for your work!

I suspect that this change broke #41. For v2.2 feeds the vehicle_types.json is thought to be required again, even if the criteria stated in gbfs.md

REQUIRED of systems that include information about vehicle types in the free_bike_status file.

is not given.

Example feed: https://gbfs-validator.netlify.app/?url=https%3A%2F%2Fgbfs.nextbike.net%2Fmaps%2Fgbfs%2Fv2%2Fnextbike_le%2Fgbfs.json
which states

Missing file and required

for the vehicle_types.json.

Should I open a new issue?

Best regards