Emacs ghc-mod hlint checking highlights at wrong position

[veniversum]

When checking with hlint in emacs, the first line of the file is highlighted/underlined as a warning or error instead of the actual place for the suggestion.

Running ghc-mod lint filename.hs in console correctly generates list of suggestions with line numbers and positions, e.g.

filename.hs:31:16: Warning: xx Found: xx Why not: xx

but only the first line of the file is underlined in emacs and the warning shown while hovered over.

emacs version: 25.0.50.1 ghc-mod version: 5.4.0.0 hlint version: 1.9.21

[jdreaver]

I'm experiencing the same thing. Did you ever find a fix?

[DanielG]

Usually this happens when the filenames don't match IIRC. Might that be the case?

[jdreaver]

When you say filenames don't match, do you mean file name and module name?

I tried ghc-mod in a file called Temp.hs, but I started the file with module Main where because it is meant to be an executable.

Here is what I put in /tmp/Test.hs:

module Main where

import Data.Ma -- Error here

main :: IO ()
main = putStrLn "hello"

Here is what ghc-mod check reports on the command line:

 tmp $ ghc-mod check Test.hs
Test.hs:3:8:Could not find module ‘Data.Ma’Perhaps you meant  Data.Map (from containers-0.5.6.2
@conta_LKCPrTJwOTOLk4OU37YmeN)  Data.Eq (from base-4.8.1.0)  Data.Ix (from base-4.8.1.0)Use -v 
to see a list of the files searched for.  

However, the red squiggly line is in the top left.

[DanielG]

You'll want to start looking somewhere around here: https://github.com/kazu-yamamoto/ghc-mod/blob/master/elisp/ghc-check.el#L156

That's where the overlays are constructed. If you trace through that you should be able to figure out why (file-equal-p ofile file) doesn't hold, which is what I meant by "file names don't match". IIRC that's the bit that decides whether the info is for the current buffer's file or another one, in which case we highlight the first line in the buffer instead.

You can use C-h C-f to jump to the definition of ghc-check-highlight-original-buffer inside Emacs. Using C-u C-M-x while point is in that source file will instrument the function using EDebug which will then break on the next entry and allow you to step through the evaluation with SPC (while displaying the current value in the minibuffer). You can use q to exit EDebug and just C-M-x to re-evaluate the function without instrumentation, also while point is in the function's body.

[veniversum]

When debugging in EDebug, it steps directly from Line 157 to the end of Line 201. Is that expected behavior?

[DanielG]

Yup: if (buffer-live-p buf) is nil.

(defmacro ghc-with-current-buffer (buf &rest body)
  ;; (declare (indent 1))
  `(if (buffer-live-p ,buf)
       (with-current-buffer ,buf
     ,@body)))

[veniversum]

This issue seems to have been fixed.