Check $schema key inside the document to know what schema to validate against

[Zegnat]

Sometimes there are files where multiple schemas from the catalogue might match, e.g. a manifest.json file:

ℹ Processing ./src/manifest.json
ℹ Cache hit: using cached response from https://www.schemastore.org/api/json/catalog.json
ℹ Cache hit: using cached response from https://json.schemastore.org/schema-catalog.json
ℹ Searching for schema in https://www.schemastore.org/api/json/catalog.json ...
ℹ Found multiple possible matches for ./src/manifest.json. Possible matches:

  Foxx Manifest
  ArangoDB Foxx service manifest file
  https://json.schemastore.org/foxx-manifest.json

  UI5 Manifest
  UI5 Manifest (manifest.json)
  https://raw.githubusercontent.com/SAP/ui5-manifest/master/schema.json

  WebExtensions
  WebExtension manifest files
  https://json.schemastore.org/webextension.json

  Web App Manifest
  Web Application manifest file
  https://json.schemastore.org/web-manifest-combined.json

✖ Found multiple possible schemas to validate ./src/manifest.json

As I also depend on JSON schemas when editing these type of files, I often supply a specific $schema within the file so VSCode can manage. See the following screenshots showing how VSCode is warning me about all the keys before I add $schema:

1. Can v8r break ties based on the $schema member?
2. Should v8r go as far as to prefer the explicit $schema member over the catalogue?

In case of 2, it could save the entire round trip to schemastore.org. If all files in a repository include $schema it will not need to check a catalogue at all.

[Zegnat]

As an aside to this, it would be really nice if $schema was allowed by the v8r config schema. This would then allow the schema to be used by the code editor by doing something like the following:

{
    "$schema": "./node_modules/v8r/config-schema.json",
    "customCatalog": {
        "schemas": [
            {
                "name": "JSON schema for WebExtensions manifest files",
                "fileMatch": [
                    "manifest.json"
                ],
                "location": "https://json.schemastore.org/webextension.json"
            }
        ]
    }
}

Currently this cannot be done as v8r (correctly) validates its config file before using it, leading to an additional properties error because of $schema:

/Users/Zegnat/path/.v8rrc.json# must NOT have additional properties

[chris48s]

If you've got files where SchemaStore doesn't know how to validate them, you can use a custom catalog to tell v8r which schemas to use for which files.
This can either be a standalone catalog
https://chris48s.github.io/v8r/usage-examples/#using-a-custom-catlog
or you can do it in the config file
https://chris48s.github.io/v8r/configuration/
So there is a way to solve the case where there are multiple possible matches in schemastore.

This idea of files that contain a $schema key has come up once before a few years ago in #129
I asked some follow up questions but the original poster never responded so it never went anywhere. Maybe you have some info on how widespread this is or resources I could look at.

[Zegnat]

Thanks for linking the closed PR. I had looked through the repo before, but clearly still managed to somehow miss that one.

I am not sure how wide-spread the usage is. Like I described above, I mostly do it because it makes VSCode’s linting work and delivers auto-complete. It would not surprise me if this is how most people use it, which might be hard to track.

I will do some discovery work this weekend and see if I can find any projects that explicitly use or call out the use of $schema and then report back. Probably better to have this as an issue for discussing than immediately jump to a PR.