Programmatically associate YAML files with schemas by other extensions

[akaroml]

Here to request a way of specifying a schema for a YAML file programmatically by other extensions.

Scenario

When a user modifies the content of a YAML, a third party can recognize the features of the new content and tell the YAML extension what schema to use for the document.
In this way, the YAML extension can focus on generic language features but let other extensions contribute the schema knowledge.
As user types, other extensions start to recognize the contents and specifies a schema on the fly. This is super useful when a user tries to write the YAML from scratch.

Current Implementation

Currently, a user needs to specify a schema for a YAML file inside the settings.json. The users have to fill the URL of the schema and persist that association inside settings.json. When there are multiple YAML files with different schemas, this work could be time consuming and error-prone.

Proposed Implementation

Besides hard-coding the schema association, we can let other extensions contribute the logic of associating schemas with YAML files. For example, the Kubernetes extension has the manifest file schema and can tell whether a YAML file conforms to the schema. So whenever the Kubernetes extension recognizes a YAML file, it tells the YAML extension to process that YAML file with the Kubernetes schema at runtime.

[JPinkney]

You can use the "json/schemaAssociations" notification in the language server to inject the schemas https://github.com/redhat-developer/yaml-language-server/blob/master/src/server.ts#L34-L36

[andxu]

see PR for integrating custom schema providers

[andxu]

The PR is merged.

[Nusserdt]

Can you provide an example how it works?

[Nusserdt]

I try something like:

const extension: vscode.Extension<any> = vscode.extensions.getExtension("redhat.vscode-yaml");
const client: any = await extension.activate();
client.registerContributor(SCHEMA, onRequestSchema, onRequestSchemaContent, "test: test");

But I don't get it to work. I think the problem here is that the functions onRequestSchema and onRequestSchemaContent never get called from the YAML extension api.

[Nusserdt]

I found a working minimal example here:
#216 (comment)

But I was not able to apply that on custom file types/languages (only directly on *.yaml)