Completer improvements: kernel type mapping and dynamic documentation

[krassowski]

References

• provides mechanism for mapping between some kernel types and LSP types for icons selection, fixes Provide mapping between some kernel types and LSP types? #333
  • motivated by IJulia returning very different types than LSP types and IPython returning <unknown> if it cannot match a type
• implements completionItem/resolve to allow for:
  • display of documentation panel with R language server which does not send documentation in the first request but requires completionItem/resolve
  • faster completion (Slow completion for large Python packages when using the default pyls #272) once pyls or jedi-language-server implement completionItem/resolve too
  • store original completionItem and resolve using exactly it?
  • add test with R language server
  • open issues on pyls and jedi proposing to implement completionItem/resolve; create a PR in the repo that will accept such a contribution (help welcome!)
• makes use of newly exposed Completer.IRenderer, for implementation of active item tracking and implements makrdown rendering of documentation in Completer.IRenderer
• add support for deprecation via CompletionItemTag.Deprecated
  • declare tag support
  • check if any supported server implements it and if yes, test it; checked that do not support: jedi, julia, pyls, R; maybe javascript/typescript server?

Related upstream PR:

• Allow to substitute the default completer renderer jupyterlab/jupyterlab#8930
• Allow for lazily retrieved documentation (with a getter) jupyterlab/jupyterlab#9643
• Move documentation panel rendering to renderer jupyterlab/jupyterlab#9663

Code changes

Added LazyCompletionItem class implementing CompletionHandler.ICompletionItem but also doing much more to workaround the limited flexibility of upstream (see the self-reference trick to workaround jupyterlab/jupyterlab#9643). The new object-oriented code reduced complexity of the completion handler making it considerable more pleasant and enabled implementation of completionItem/resolve.

User-facing changes

• Documentation panel renders markdown if server provided markdown
  • only for completionItem/resolve retrieved docs for now
  • for all servers once Move documentation panel rendering to renderer jupyterlab/jupyterlab#9663 gets merged and released
• Documentation panel works with R 🎉 (and other language servers that use completionItem/resolve, e.g. javascript/typescript)

Backwards-incompatible changes

Chores

• linted
• tested
• documented
• changelog entry

[krassowski]

The lint failure seems to be due to the changes in the new mypy release (0.800). changelog.

• Also, I can confirm that Windows failures reveled a further issue with completion for large namespaces. Yet to be investigated.