company-mode is eating keystrokes when showing preview for a single candidate (using company-ghc)

[unthingable]

When typing moderately fast, around the time preview is shown, a character often doesn't make it.

Example: slowly typing readf triggers a preview ile. When typing fast enough, I usually end up with readfle.

Using company-ghc backend, if that makes any difference.

[dgutov]

What's your OS, Emacs and Company versions?

I've never seen the behavior you're describing. Can you reproduce it with, say, company-dabbrev (try a text-mode buffer)?

[unthingable]

OSX 10.9.5, Emacs 24.4 (9.0), company-20141107.552, company-ghc-20141030.704

In text-mode it seems fine, but in haskell-mode it's reproducible fairly reliably. Curiously, it's happening to a completion inside a function, but not outside:

readConfig prefix dir = do
  files <- getDirectoryContents dir
  readfle
  readile

readfile
readfile
readfile

I would guess there is extra work happening, trying to guess types and what not, and somehow it's affecting the echoing behavior.

UPD: this stops when company-ghc is not in the list of backends, so that guess is at least dubious.

[unthingable]

A trace, the "i" is being lost:

1 -> (company-ghc-candidates #("read" 0 4 (fontified t)))
1 <- company-ghc-candidates: (#("readable" 0 1 (:module "System.Directory")) #("readfile" 0 1 (:module #1="Data.ConfigFile")) #("readhandle" 0 1 (:module #1#)) #("readstring" 0 1 (:module #1#)))
======================================================================
1 -> (company-ghc-prefix)
1 <- company-ghc-prefix: #("readf" 0 5 (fontified nil))
======================================================================
1 -> (company-ghc-prefix)
1 <- company-ghc-prefix: #("readfl" 0 6 (fontified nil))
======================================================================
1 -> (company-ghc-prefix)
1 <- company-ghc-prefix: #("readfle" 0 7 (fontified t))
======================================================================
1 -> (company-ghc-candidates #("readfle" 0 7 (fontified t)))
1 <- company-ghc-candidates: nil

Same with trace enabled on company-ghc:

======================================================================
1 -> (company-ghc prefix)
| 2 -> (company-ghc-prefix)
| 2 <- company-ghc-prefix: #("re" 0 2 (fontified t))
1 <- company-ghc: #("re" 0 2 (fontified t))
======================================================================
1 -> (company-ghc prefix)
| 2 -> (company-ghc-prefix)
| 2 <- company-ghc-prefix: #("read" 0 4 (fontified t))
1 <- company-ghc: #("read" 0 4 (fontified t))
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc candidates #("read" 0 4 (fontified t)))
| 2 -> (company-ghc-candidates #("read" 0 4 (fontified t)))
| 2 <- company-ghc-candidates: (#("readable" 0 1 (:module "System.Directory")) #("readfile" 0 1 (:module #1="Data.ConfigFile")) #("readhandle" 0 1 (:module #1#)) #("readstring" 0 1 (:module #1#)))
1 <- company-ghc: (#("readable" 0 1 (:module "System.Directory")) #("readfile" 0 1 (:module #1="Data.ConfigFile")) #("readhandle" 0 1 (:module #1#)) #("readstring" 0 1 (:module #1#)))
======================================================================
1 -> (company-ghc sorted)
1 <- company-ghc: t
======================================================================
1 -> (company-ghc duplicates)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc annotation #("readable" 0 1 (:module "System.Directory")))
1 <- company-ghc: " System.Directory"
======================================================================
1 -> (company-ghc annotation #("readfile" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: " Data.ConfigFile"
======================================================================
1 -> (company-ghc annotation #("readhandle" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: " Data.ConfigFile"
======================================================================
1 -> (company-ghc annotation #("readstring" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: " Data.ConfigFile"
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc match #("readable" 0 1 (:module "System.Directory")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc match #("readfile" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc match #("readhandle" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc match #("readstring" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc meta #("readable" 0 1 (:module "System.Directory")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc no-cache #("read" 0 4 (fontified t)))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc prefix)
| 2 -> (company-ghc-prefix)
| 2 <- company-ghc-prefix: #("readf" 0 5 (fontified nil))
1 <- company-ghc: #("readf" 0 5 (fontified nil))
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc annotation #("readfile" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: " Data.ConfigFile"
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc match #("readfile" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc meta #("readfile" 0 1 (:module "Data.ConfigFile")))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc no-cache #("readf" 0 5 (fontified nil)))
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc prefix)
| 2 -> (company-ghc-prefix)
| 2 <- company-ghc-prefix: #("readfl" 0 6 (fontified nil))
1 <- company-ghc: #("readfl" 0 6 (fontified nil))
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc require-match)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc require-match)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc prefix)
| 2 -> (company-ghc-prefix)
| 2 <- company-ghc-prefix: #("readfle" 0 7 (fontified t))
1 <- company-ghc: #("readfle" 0 7 (fontified t))
======================================================================
1 -> (company-ghc ignore-case)
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc candidates #("readfle" 0 7 (fontified t)))
| 2 -> (company-ghc-candidates #("readfle" 0 7 (fontified t)))
| 2 <- company-ghc-candidates: nil
1 <- company-ghc: nil
======================================================================
1 -> (company-ghc sorted)
1 <- company-ghc: t
======================================================================
1 -> (company-ghc duplicates)
1 <- company-ghc: nil

[dgutov]

This "9.0" bit looks suspicious. Is it "Emacs for MacOS X", or some such?

I haven't tried company-ghc personally, and the closest bug to this description I've seen mentioned is this: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=18684

Can you reproduce this with a "bare" configuration, starting with emacs -Q and then maybe only adding company-ghc. Without the latter without be even better, of course.

Same with trace enabled on company-ghc:

The trace tells me that indeed it seems some keystrokes go missing, but not why, sorry.

[unthingable]

Ah, that's how OSX reported the version. Emacs itself says it's 24.4.1. Same behavior in 24.3.50.1.

Same behavior in "bare" configuration.

It seems to happen only with both haskell-mode is active and using company-ghc backend (that is, company-ghc backend works fine in text-mode).

[dgutov]

What about company-dabbrev in haskell-mode?

[unthingable]

company-dabbrev in haskell-mode: no problems.

[unthingable]

Also, scrolling through candidates with arrow keys, those seem to be getting dropped too.

[dgutov]

Well then, let's see what @iquiw says.

[unthingable]

OK, thanks for jumping on this so quickly.

I have found a fix of sorts, and perhaps narrowed it down: the problem seems to go away after removing company-echo-metadata-frontend from the list of frontends.

[dgutov]

Hmm, if so, you should be able to reproduce this with another backend that defines meta, such as company-clang or company-gtags.

And here a self-contained attempt to reproduce this without company-mode:

(defun cool-post-command ()
  (when (sit-for .01)
    (message "cool cool cool")))

(add-hook 'post-command-hook 'cool-post-command)

(Try it in a separate Emacs session).

[iquiw]

company-ghc's meta command communicates with external process ghc-modi, which can be slow.
I am not yet sure this is the cause of the problem though.
If so, I have a plan to avoid the communication with ghc-modi at meta command by iquiw/company-ghc#6

[dgutov]

@iquiw So, can you reproduce this?

I looked at the wrong function (company-ghc-complete-by-hoogle instead of company-ghc), so the situation is more complex than the example above, with the process communication and all, but it seems like a genuine Emacs bug anyway, which should be dissected and reported.

[iquiw]

I have not noticed the originally reported one.
But sometimes seen the scroll problem #226 (comment) (on Windows especially).

company-ghc's meta command calls ghc-sync-process through ghc-get-info.
https://github.com/kazu-yamamoto/ghc-mod/blob/master/elisp/ghc-process.el#L108-L123

[iquiw]

I found the cause is discard-input in ghc-sync-process.
https://github.com/kazu-yamamoto/ghc-mod/blob/master/elisp/ghc-process.el#L120

So it is neither company-mode's nor Emacs's issue.

@dgutov, I am not sure how it can be solved, so would very much appreciate it if you could give me any advice.
Anyway, I will open an issue in ghc-mod later.

[dgutov]

Obtaining process output synchronously is usually performed with accept-process-output, not sit-for. Here's an example: https://github.com/nonsequitur/inf-ruby/blob/master/inf-ruby.el#L500-L501

[iquiw]

I reported the issue in ghc-mod.

@dgutov @unthingable Thank you!

[unthingable]

@dgutov, sorry, I haven't had the time to try different backends as per your suggestion. If that's still needed, let me know.

[dgutov]

@unthingable Nope, thank you.

[dgutov]

This is more or less resolved.