Debugging an ale_plugin?

[frioux]

I'm trying to use metals as an LSP for scala and ALE is never even trying to run it. Are there suggested steps to try figuring out why this might be?

[hsanson]

Check ALEInfo output to see if there are any errors reported. If you are using vim you can add this to your configuration:

call ch_logfile(expand('/tmp/chlogfile.log'), 'w')

Then tail the /tmp/chlogfile.log that will output all iteraction between vim and the LSP if any.

[frioux]

This is useful! At least in my situation I can see ALE working for gopls, but for metals I see this in the log:

==== start log session ====             
  0.088466 : Starting job: /bin/zsh  -c  'scalac' -Ystop-after:parser '/run/shm/vv41oNM/2/OneDayDataset.scala'
  0.088511 on 0: Created channel                                                                          
  0.089414 : closing                        
  0.091350 : SafeState: Start triggering
  0.103279 : looking for messages on channels
  0.103315 : SafeState: back to waiting, triggering SafeStateAgain
  1.482179 : SafeState: reset: ins_typebuf()
  1.482310 : SafeState: Start triggering
  1.482341 : looking for messages on channels
  1.482354 : SafeState: back to waiting, triggering SafeStateAgain
  1.832171 : SafeState: reset: key typed
  1.832225 : SafeState: Start triggering
  1.832313 : looking for messages on channels
  1.832331 : SafeState: back to waiting, triggering SafeStateAgain
  1.908093 on 0: channel_select_check(): Read EOF from ch_part[1], closing
  1.908131 on 0: channel_select_check(): Read EOF from ch_part[2], closing
  1.908144 : looking for messages on channels
  1.908151 on 0: Closing channel because all readable fds are closed
  1.908157 on 0: Closing channel
  1.908166 on 0: Invoking callbacks and flushing buffers before closing
  1.908172 on 0: Invoking close callback <SNR>67_VimCloseCallback
  1.908303 : SafeState: back to waiting, triggering SafeStateAgain
  1.918499 : looking for messages on channels
  1.918591 on 0: Job ended
  1.918612 on 0: Invoking exit callback <SNR>67_VimExitCallback
  1.928270 on 0: Freeing job
  1.938888 : looking for messages on channels
  1.938942 on 0: Closing channel
  1.938963 on 0: Clearing channel
  1.938980 on 0: Freeing channel
  1.938997 : SafeState: back to waiting, triggering SafeStateAgain
  1.986058 : SafeState: reset: key typed
  1.986151 : SafeState: Start triggering
  1.986212 : looking for messages on channels
  1.986238 : SafeState: back to waiting, triggering SafeStateAgain
  2.070553 : SafeState: reset: key typed
  2.070660 : SafeState: Start triggering
  2.070736 : looking for messages on channels
  2.070765 : SafeState: back to waiting, triggering SafeStateAgain
  2.283010 : SafeState: reset: key typed
  2.283062 : SafeState: Start triggering
  2.283085 : looking for messages on channels
  2.283095 : SafeState: back to waiting, triggering SafeStateAgain
  2.591686 : SafeState: reset: key typed
  2.592032 : looking for messages on channels
  3.061237 : SafeState: Start triggering
  3.061386 : looking for messages on channels
  3.061407 : SafeState: back to waiting, triggering SafeStateAgain
  3.174424 : SafeState: reset: key typed

When I run ALEInfo I see this, which seems right?

 Current Filetype: scala                                                                                                                                                                                             
Available Linters: ['cspell', 'fsc', 'metals', 'sbtserver', 'scalac', 'scalastyle']                                                                                                                                  
  Enabled Linters: ['cspell', 'fsc', 'metals', 'sbtserver', 'scalac', 'scalastyle']                                                                                                                                  
  Ignored Linters: []                                                                                                                                                                                                
 Suggested Fixers:                                                                                                                                                                                                   
  'remove_trailing_lines' - Remove all blank lines at the end of a file.                                                                                                                                             
  'scalafmt' - Fix Scala files using scalafmt                                                                                                                                                                        
  'trim_whitespace' - Remove all trailing whitespace characters at the end of every line.                                                                                                                            
 Linter Variables:                                                                                                                                                                                                   
let g:ale_scala_metals_executable = 'metals'                                                                                                                                                                         
let g:ale_scala_metals_project_root = ''                                                                                                                                                                             

Any suggestions of what I should try next?

[hsanson]

Not sure what you are trying to do but if what you want is to get metals working then I think ALE is not finding the metals executable. ALEInfo should tell you what liners were found and executed.

[frioux]

It looks to me like it didn't even try metals? This is from the bottom:

  Command History:                                                                                                                                                                                                   
(executable check - failure) cspell                                                                                                                                                                                  
(executable check - failure) fsc                                                                                                                                                                                     
(executable check - success) scalac                                                                                                                                                                                  
(finished - exit code 0) ['/bin/zsh', '-c', '''scalac'' -Ystop-after:parser ''/run/shm/vv41oNM/2/OneDayDataset.scala''']                                                                                             
<<<NO OUTPUT RETURNED>>>                                                                                                                                                                                             
(executable check - failure) scalastyle 

[hsanson]

Most probably ALE is not finding the project root (see #4155). Execute this and see if a project root is being found:

:echo ale_linters#scala#metals#GetProjectRoot('')

If this returns empty it means no root is being found and ALE is not starting the LSP. Read the documentation in :h ale-scala-metals to see how ALE looks for the root and how to force it if not found.

[frioux]

Alright this got me the rest of the way there! I think the metals project root detection is broken, but I can create a ticket for that and manually configure it in the meantime. Thanks!