Extend non-interactive completions for identifiers from TAGS

[geraldus]

• make hasktags to work in non-interactive mode too
• combine TAGS completions with haskell-completions in non-interactive mode
• bring some light about this in docs
• interactive mode should override completion functions hook (as it does now)

Look like we can improve static completions to provide identifier and module name completions too making use of tags.

I need some time to do a basic research on this topic.

Moved documentation notes to #702

[geraldus]

The best way I can think of is to steal this code from company mode
https://github.com/company-mode/company-mode/blob/250ca1c395c6f05b733abce69a2d928b6cd31618/company-etags.el#L62-L84

@gracjan what would you say?

[geraldus]

Ok, let's not complicate things! I have a better solution. Default value of completion-at-point-functions is (tags-completion-at-point-function), so let's

• in haskell-mode set completion-at-point-functions to

(haskell-completions-completion-at-point tags-completion-at-point-function)

• in haskell-interactive-mode set completion-at-point-functions to

(haskell-completions-sync-repl-completion-at-point)

This should give tags completions in static mode even without any completion backend. company-mode automatically re-uses completion-at-point-functions by default. For interactive completions with company I would mention making company-backends list buffer-local for haskell buffers and prepending it with following grouped backend:

(company-capf company-dabbrev-code)

This adds dabbrev completion candidates to REPL completions, which is quite handy.

[gracjan]

Good idea.

[geraldus]

Good idea.

Ahh… Tags are generated only when session is present, so basically this won't work well: user must manually generate tags manually and visit it. Some features of Haskell Mode require minimal project information (without REPL), and I often think about such functionality. I think we should discuss this.

[gracjan]

See #964.

[geraldus]

@gracjan aha. I though about some very simple .cabal file lookup in static mode (just for tags generation, enabled extensions and modules related to current file); though it looks very simple I guess the complexity is hidden underneath, for example cashing issues and etc.

[geraldus]

I'm closing this