Slow completion for rust strings and comments

[TatriX]

When company runs completion either using company-idle-delay or manually in the comments or strings it will hang emacs for up to several seconds. It looks like it makes a very generic query to the lsp server for every character I type.

On emacs-26 it works even worse because it spents 50% of the time in lsp--read-json, but I managed to fix it by using emacs-devel and use-native-json param for lsp-rust client.

- timer-event-handler                                            1253  20%
 - apply                                                         1248  20%
  - company-idle-begin                                           1044  17%
   - company-auto-begin                                           976  16%
    - company--perform                                            976  16%
     - company--begin-new                                         976  16%
      - company-calculate-candidates                              976  16%
       - company--fetch-candidates                                976  16%
        - company-call-backend-raw                                973  16%
         - apply                                                  973  16%
          - company-capf                                          973  16%
           - completion-all-completions                           973  16%
            - completion--nth-completion                          973  16%
             - completion--some                                   973  16%
              - #<compiled 0x1bf2da1>                             973  16%
               - completion-basic-all-completions                 353   5%
                - completion-pcm--all-completions                 353   5%
                 - all-completions                                353   5%
                  - #<compiled 0x1bf2a61>                         353   5%
                   - #<compiled 0x17a4605>                        353   5%
                    + lsp--send-request                           346   5%
                    + seq-map                                       4   0%
                      file-truename                                 3   0%
               - completion-pcm-all-completions                   331   5%
                - completion-pcm--find-all-completions                331   5%
                 - completion-pcm--all-completions                331   5%
                  - all-completions                               331   5%
                   - #<compiled 0x1bd761d>                        331   5%
                    - #<compiled 0x17a4605>                       331   5%
                     + lsp--send-request                          325   5%
                     + seq-map                                      6   0%
               + completion-emacs22-all-completions                289   4%
        + sit-for                                                   3   0%
   + company-post-command                                          68   1%
  + sp-show--pair-function                                        148   2%
  + #<compiled 0x1d93bf5>                                          12   0%
  + #<compiled 0x202bad>                                           11   0%
  + show-paren-function                                            10   0%
  + savehist-autosave                                               4   0%
 + timer-activate-when-idle                                         3   0%

[tigersoldier]

#57 is adding native JSON support. I don't think there is much company-lsp can do if the bottle neck is JSON parsing. Is it possible to configure Rust language server to return fewer completion results?

[TatriX]

I think it would be nice to prevent completion in strings in comments, but I'm not sure if this is possible.

[tigersoldier]

I think company-lsp already does that. Is it not working?

[TatriX]

The profile I've showed in the first post is made by typing random letters in the top level comment. lsp/rust related config:

(use-package lsp-mode)

(use-package lsp-ui
  :config
  (setq lsp-ui-sideline-delay 0.5))

(use-package lsp-rust
  :config
  (require 'lsp-ui)
  (add-hook 'lsp-mode-hook 'lsp-ui-mode))

(use-package company-lsp
  :config
  (push 'company-lsp company-backends)
  (setq company-lsp-enable-snippet nil))

(use-package rust-mode
  :config
  (add-hook 'rust-mode-hook #'lsp-rust-enable))

(use-package flycheck-rust
  :config (add-hook 'flycheck-mode-hook #'flycheck-rust-setup))

(use-package company
  :config
  (setq company-tooltip-limit 10
	company-idle-delay 0.05
	company-minimum-prefix-length 2
	company-show-numbers t
	company-tooltip-align-annotations t))

[Wojtek242]

As @tigersoldier soldier said, it looks like company-lsp doesn't trigger in comments or strings. I had the same problem, however, and I narrowed it down to flyspell and company-capf. What I did was to remove company-capf from the company backends in rust-mode and it works now. This is the ilne I added:

(add-hook 'rust-mode-hook
          (lambda () (setq company-backends
                           (delete 'company-capf company-backends))))

[TatriX]

(add-hook 'rust-mode-hook
          (lambda () (setq company-backends
                           (delete 'company-capf company-backends))))

This helps, thanks!