`registerContributor` is not called when yaml file is opened at vscode start

In our vscode-quarkus, we use registerContributor to manage Quarkus application.yaml. It starts working well but I have a problem with this following usecase: when I start vscode and I open application.yaml there are no validation which is done.

Indeed in this usecase, my registerContributor is registered AFTER the application.yaml is opened and yaml language server execute diagnostics. If I type some character, diagnostics is working.

My understand is that we need to start vscode-yaml to get the registerContributor. If application.yaml is opened, the registerContributor is done after.

See my PR at https://github.com/redhat-developer/vscode-quarkus/pull/189

IMHO to fix this issue, I think vscode-yaml should loop for each extension which wants to register JSON Schema with registerContributor (like Eclipse Plugin extension could do it).

For instance, a vscode extension could delcare in their package.json that:

contributeToJSonSchema: true

and the vscode extension should return a list of YamlSchemaContributor :

declare type YamlSchemaContributor = (schema: string,
  requestSchema: (resource: string) => string | undefined,
  requestSchemaContent: (uri: string) => Promise<string>) => void;

@JPinkney @itowlson what do you think about this idea?

Read the linked PR 189 and trace the registerContributor startup path, especially when diagnostics run for application.yaml opened at VS Code launch. Define the extension contribution mechanism and confirm that registered contributors are available before initial diagnostics, with startup-open validation matching validation after editing.