Support cross-repository references

[felixfbecker]

Flow

• Extension makes go-to-definition request to find canonical source location. Remember definition URL
• Extension uses npm API to find all packages depending on the containing package (from closest package.json, discover this through the extension or raw API).
• For each dependent
  • Extension maps package name to repository clone URL and rev from repository and gitHead fields (gitHead requires an npm registry request to work around support gitHead property in package.json yarnpkg/yarn#2978)
  • Extension resolves clone URL + rev to Sourcegraph raw root URI (TODO: add API for this)
  • Extension authenticates root URI with access token
  • Extension creates language server connection for that root URI
  • Extension sends find-references request on the definition URL
    • Server recognizes definition URL is an out-of-workspace URL
    • Server uses raw API to find and get closest package.json to definition URL (walking parent directories of definition URL upwards)
    • Server parses out the package name
    • Server searches for **/node_modules/${packageName} in workspace
    • Server resolves package-root-relative URL for source file from package root (package.json location)
    • Server searches for **/*.d.ts.map declaration maps in package root in node_modules
    • Server finds the .d.ts.map that maps to the package-root-relative URL
    • Server reverse-maps the source definition position to the .d.ts position (line+character) using source-map library
    • Server rewrites the TextDocumentPositionParams of the find-references request with the file: URI of the .d.ts and the .d.ts position
    • Server forwards the request to the language server
• Extension concatenates results from all the dependents and returns them to Sourcegraph

Status

Implemented in branch. To test:

• TypeScript projects with single root package.json
• Multiple package.json in monorepo
• Typings in DefinitelyTyped (without declaration map)
• Single typings file (without declaration map) published in package

[slimsag]

TODO: how to map clone URL to Sourcegraph URL

There is a really nice recently-added API to do this, but it's not exposed via graphql or anything yet: https://sourcegraph.com/search?q=repo:%5Egithub%5C.com/sourcegraph/sourcegraph%24+reposource%5C.CloneURLToRepoName