xref-find-definition for project dependencies

[wpcarro]

Loving lsp-haskell so far. Is it possible to have xref-find-definition for Base and a project's dependencies?

[wraithm]

Yes, I'm having issues with xref-find-definition in a multi-package project. It won't jump to a definition across package boundaries.

It would be great if xref-find-definition fell back to using tags if nothing is found in the current project.

[michaelpj]

For the LSP case, this is a haskell-language-server issue, which I think is already tracked (for example haskell/haskell-language-server#44).

Re: falling back to tags, I think we shouldn't do more here since we're really just a client for lsp-mode. But we also recommend that people enable haskell-mode, which might add jump handlers that user tags?

[michaelpj]

Re: using tags, it seems that it's not currently possible to augment the lsp-mode xref backend with another one (https://gitter.im/emacs-lsp/lsp-mode?at=5f6c9a025efe9467b1127f85). So this is probably not something we can fix easily, unfortunately.