fortls with yegappan/lsp in standard vim - possible race condition

[TomMelt]

Describe the bug
When I open a fortran file, the fortls server doesn't always initialize.

To Reproduce
I am using vim with the following config:

$ vim --version                                                                                                                                                                                               
VIM - Vi IMproved 9.0 (2022 Jun 28, compiled Feb  2 2025 16:33:18)                                                                                                                                                                                            
Included patches: 1-45                                                                                                                                                                                                                                        
Compiled by melt@lenny                                                                                                                                                                                                                                        
Huge version with GTK3 GUI.  Features included (+) or not (-):                                                                                                                                                                                                
+acl               +file_in_path      +mouse_urxvt       -tag_any_white                                                                                                                                                                                       
+arabic            +find_in_path      +mouse_xterm       -tcl                                                                                                                                                                                                 
+autocmd           +float             +multi_byte        +termguicolors                                                                                                                                                                                       
+autochdir         +folding           +multi_lang        +terminal                                                                                                                                                                                            
-autoservername    -footer            -mzscheme          +terminfo                                                                                                                                                                                            
+balloon_eval      +fork()            +netbeans_intg     +termresponse                                                                                                                                                                                        
+balloon_eval_term -gettext           +num64             +textobjects                                                                                                                                                                                         
+browse            -hangul_input      +packages          +textprop                                                                                                                                                                                            
++builtin_terms    +iconv             +path_extra        +timers                                                                                                                                                                                              
+byte_offset       +insert_expand     -perl              +title                                                                                                                                                                                               
+channel           +ipv6              +persistent_undo   +toolbar                                                                                                                                                                                             
+cindent           +job               +popupwin          +user_commands                                                                                                                                                                                       
+clientserver      +jumplist          +postscript        +vartabs                                                                                                                                                                                             
+clipboard         +keymap            +printer           +vertsplit                                                                                                                                                                                           
+cmdline_compl     +lambda            +profile           +vim9script                                                                                                                                                                                          
+cmdline_hist      +langmap           -python            +viminfo                                                                                                                                                                                             
+cmdline_info      +libcall           +python3/dyn       +virtualedit                                                                                                                                                                                         
+comments          +linebreak         +quickfix          +visual                                                                                                                                                                                              
+conceal           +lispindent        +reltime           +visualextra                                                                                                                                                                                         
+cryptv            +listcmds          +rightleft         +vreplace                                                                                                                                                                                            
+cscope            +localmap          -ruby              +wildignore                                                                                                                                                                                          
+cursorbind        -lua               +scrollbind        +wildmenu                                                                                                                                                                                            
+cursorshape       +menu              +signs             +windows                                                                                                                                                                                             
+dialog_con_gui    +mksession         +smartindent       +writebackup
+diff              +modify_fname      -sodium            +X11
+digraphs          +mouse             -sound             -xfontset
+dnd               +mouseshape        +spell             +xim
-ebcdic            +mouse_dec         +startuptime       +xpm
+emacs_tags        -mouse_gpm         +statusline        +xsmp_interact
+eval              -mouse_jsbterm     -sun_workshop      +xterm_clipboard
+ex_extra          +mouse_netterm     +syntax            -xterm_save
+extra_search      +mouse_sgr         +tag_binary        
-farsi             -mouse_sysmouse    -tag_old_static

I am really struggling to identify where the issue comes from:

• yeggapan lsp
• vim
• or fortls

The reason I think it is fortls is because my other lsp's work fine and I have not had issues. I haven't changed my vim configuration for a while and it used to work just fine. That being said, the issue may not be fortls, but I don't know where to start debugging. I tried using yeggapan's lsp debug (:LspServer debug errors) but there's no error messages.

If someone could point me in the right direction to debug this, I would be grateful. When I test the LSP on CLI it seems to work e.g., I can run fortls --debug_filepath simple-mpi.f90 --debug_parser and it generates output as expected. So it's somewhere in the interface between the lsp client and vim and fortls. When I swap out fortls for fortran-language-server (and change the options) it works fine.

My config in vim for fortls is:

\ name: 'fortls',
\ filetype: 'fortran',
\ path: '/home/melt/.dotfiles/.vim/fortls/bin/fortls',
\ args: ['--hover_language', 'fortran', '--lowercase_intrinsics', '--notify_init', '--hover_signature', '--use_signature_help'],

Start with posting:
I think there may be a race condition or something... because sometimes the lsp initializes but 99% of the time it does not.

Here is the output from the fortls_debug.log:

$ cat fortls_debug.log 
DEBUG:fortls.constants:REQUEST 1 initialize

Expected behavior
I should be able to initialize the lsp and see its capabilities:

e.g., :LspServer show capabilities should show the capabilities instead of an empty list

Setup information (please complete the following information):

• OS: Ubuntu 24.04.2 LTS (Noble Numbat)
• Python Version: Python 3.12.3
• fortls Version I tried fortls-3.1.2 and fortls-3.0.0 - Code editor used Vim
• the Fortran extension for the code editor and its version [e.g. Modern Fortran v3.0.0] (if applicable)

Configuration information (please complete the following information):

• Your .fortlsrc or .fortls.json or .fortls configuration file OR any other JSON config being used (if any)
• Any settings specified through your extension [e.g. for VS Code settings from settings.json]

Additional context
Add any other context about the problem here.

[TomMelt]

Here is a screen cast showing that it eventually loads around the 20 s mark and then goes back to not initializing correctly.

Screencast.from.2025-03-04.12-22-43.webm

[gnikit]

Hm I'm not sure what to make out of this. I'm not familiar with yeggapan lsp in particular so I can't really advise you for the configuration. There are some lsp configuration on the fortls docs that I tried/used to use, but yeggapan is not one of them I believe.

It's definitely not an expected behaviour, fortls is able to initialise 1M lines of code on 4 cores in just a few seconds, so this is weird.

I'll try and look into this but my time for support tickets is rather limited these days.

The only thing that I can think of, without testing, is that maybe it's trying to index a massive workspace (i.e. directory) and recursing through all the subdirs is causing it to hang.

[TomMelt]

I was also worried it might be trying to go through large directory, so for the gif I moved the test program into its own (otherwise empty) folder, just under my home dir called ~/test, and it still does the same thing. None of my codes are "that" large so I was surprised. I should mention, before upgrading to Ubuntu 24 I had used fortls just fine for about a year with the existing setup. I only noticed it's broken after I switched to Ubuntu 24. I did a clean install tho, not a dist upgrade. But again, I didn't think that should affect it

[TomMelt]

Also thanks for getting back to me. I understand it's tricky to debug and even harder to find time. Thought I would raise it in case anyone else has the same issue.

[TomMelt]

interestingly, I tried on another machine and eventually the LSP loads but it takes on avg. 1 minute. I am going to try switching to coc and see if anything changes

[gnikit]

I suspect that there might be some conflict with your LSP setup in vim. Maybe try uninstalling and installing first and then forming a minimal vim environment just with the LSP and then slowly enabling a single plugin at a time.

[TomMelt]

good point. For now I just switched to coc and it seems to be better. But that's the lazy solution. I will go back when I get some time and try minimal environment. Thanks again for your help/suggestions