Some company backends should be grouped

[ejez]

Associated PR: #4476

Some company backends can completely shadow other backends following them. For example, having company-backends as (company-dabbrev company-yasnippet company-ispell) will make company-yasnippet and company-ispell completely useless, because company-dabbrev will always answer: "Yes! I will try to find completion candidates" (even if later on it comes up with an empty list of candidates). This makes the backends following it unreachable.

To solve this issue, these backends should be grouped, which results in merging the completion results.

To identify the backends having this behavior, we can check their docs or by trying them.

company-yasnippet has this behavior:
https://github.com/company-mode/company-mode/blob/0edc87d423b83c707e6c708f421d96f4d198803d/company-yasnippet.el#L134
(it gives recommendations on grouping)

For more info about grouping backends, see:
https://github.com/company-mode/company-mode/blob/0edc87d423b83c707e6c708f421d96f4d198803d/company.el#L452

As an example, the current doom configuration results in the following for org-mode:
(company-capf company-dabbrev company-yasnippet company-ispell)

which results in company-yasnippet and company-ispell being meaningless and unreachable.

The associated PR solves the issue for text-mode and its derived org-mode. It results in having company-backends set to (company-capf (:separate company-dabbrev company-yasnippet company-ispell)) (doom sync might be needed for the changes to take effect)

(prog-mode and other lang modes might need also a review)

[miguelmartin75]

For prog-mode this is an issue as well w.r.t ordering of completions.

For example in C++ with current settings, typing inc mixes LSP completions and snippet completions:

If instead you (setq company-backends '((:separate company-yasnippet company-capf))), we get snippets as first priority and then capf (lsp) completions second. Having the ordering is essentially required if you have have company tng mode enabled.

[ejez]

I have the following for prog modes:

(set-company-backend! 'prog-mode
  '(:separate company-capf company-yasnippet company-dabbrev company-ispell))

However, I noticed that lsp-mode overrides my config and prepends company-capf to company-backends, which results in shadowing the other backends. To avoid this issue we can remove the lsp added entry using lsp-after-open-hook:

(when (and (featurep! :tools lsp) (not (featurep! :tools lsp +eglot)))
  (use-package! lsp-mode :defer t :config
    (add-hook! lsp-after-open
      (setq company-backends (remove 'company-capf company-backends)))))

[pawsen]

doom also change the backend for dap-ui-repl - by setting it to company-capf.

workflow for dap-debug for python file.

• set breakpoint (dap-breakpoint-add)
• run dap-debug
• run dap-ui-repl
• list company backend (company-diag)

company-backends: (company-capf)

Used backend: company-capf
Value of c-a-p-f: (comint-completion-at-point t)
Major mode: dap-ui-repl-mode
Prefix: nil
Completions: none

This breaks the completion in the dap-ui-repl.
dap-mode sets the backend to (setq-local company-backends '(dap-ui-repl-company)).
We need to keep this;
How do I prevent doom from overwriting company-backends for this repl?

I can set the backend manually by M-: (setq-local company-backends '(dap-ui-repl-company)) in the repl buffer.

Some additional info:
M-x debug-on-variable-change for company-backends and running dap-ui-repl result in the the following two backtraces:

1. https://pastebin.ubuntu.com/p/g87kqdTjr9/
2. https://pastebin.ubuntu.com/p/r4xGhf37ry/

Disable the debug with M-x cancel-debug-watch

debug--implement-debug-watch(company-backends (company-capf) set #<buffer *dap-ui-repl*>)
  set(company-backends (company-capf))
  (or (memq major-mode '(fundamental-mode special-mode)) buffer-read-only (doom-temp-buffer-p (or (buffer-base-buffer) (current-buffer))) (set (make-local-variable 'company-backends) (+company--backends)))
  +company-init-backends-h()

See lsp-mode gitter for initial help by @yyoncho.