create links for values of format: uri-reference

[twelvelabs]

This PR adds logic to findLinks to create links for relative path names when the associated JSON schema is configured with format: uri-reference.

Fixes: microsoft/vscode#128971
Unblocks: redhat-developer/vscode-yaml#559

A few notes:

• I tried to make the change as backwards compatible as possible by adding a new, optional schemaService param to findLinks.

• This was important because the YAML language server delegates to findLinks, and I'm primarily interested in getting this functionality working over there.

• I assumed that the fileExists check would be a requirement (i.e. links for non existent files would be a poor UX). It's only being ran for properties w/ format: uri-reference, so it shouldn't be much overhead, but I'm happy to remove if you disagree.

[twelvelabs]

@microsoft-github-policy-service agree

[twelvelabs]

ping @aeschli

[aeschli]

We want to run that code also in the browser, so we can not use NodeJS-API like fs.
Instead we need to provide file system access through an abstraction.
We already have that in the css-languageservice: https://github.com/microsoft/vscode-css-languageservice/blob/3e2d7992179c81dc327c5e1ec8b2ec59cb2220f1/src/cssLanguageTypes.ts#L285
Can you follow that example?

[twelvelabs]

Sure! If I'm understanding things correctly, it looks like I'll need to use stat (I didn't see an exists function in the fs provider docs) and handle the promise it returns.

Then when I eventually want to use this in the yaml language server, I'm assuming I'll need to do something similar to what you did here.

Please let me know if I'm not on right path.

[aeschli]

Looks like my link was corrupted, I updated it.

What's to do:

• add new type to jsonLanguageTypes.ts:

export interface FileSystemProvider {
	stat(uri: DocumentUri): Promise<FileStat>;
}

plus FileStat and FileType (copy these from the cssLanguageTypes)

• add a new property

	/**
	 * Abstract file system access away from the service.
	 * Used for dynamic link resolving, etc.
	 */
	fileSystemProvider?: FileSystemProvider;

to LanguageServiceParams

• pass that to your code and use it, if available (all is optional, we don't want to break existing clients)
• document these types in the CHANGELOG.md
• in followup PRs we have to update the consumers of the vscode-json-languageservice (yaml-extension and json-language-feature) to provide a FileSystemProvider implementation. I can do that for vscode-json-languageservice

[twelvelabs]

@aeschli Thanks for the detailed breakdown - made things much easier! I rebased against main and made the suggested changes.

I don't do much JavaScript development, and I'm not 100% happy w/ how complicated all the promise logic ended up where I'm checking if the file exists. If you have any suggestions for simplifying things, I'm all ears 😄.

[aeschli]

Please add specs here too, in particular what happens when the file does not exist.