TexLab Linter (maybe in general): Allow modifying `lsp_config`

[cpiber]

TexLab is configured solely by use of LSP configuration, set via lsp_config. ALE does not provide any way of setting that (and does not currently set it at all). Allowing to set that might also be useful for other linters.

[cpiber]

Since I now sunk a few hours into this, maybe this is of help to some...

Assuming a version of ALE that allows lsp_config (or initial_configuration) for texlab:

diff --git a/ale_linters/tex/texlab.vim b/ale_linters/tex/texlab.vim
index 0794bf5..cb660e1 100644
--- a/ale_linters/tex/texlab.vim
+++ b/ale_linters/tex/texlab.vim
@@ -4,6 +4,7 @@

 call ale#Set('tex_texlab_executable', 'texlab')
 call ale#Set('tex_texlab_options', '')
+call ale#Set('tex_texlab_config', {})

 function! ale_linters#tex#texlab#GetProjectRoot(buffer) abort
     let l:git_path = ale#path#FindNearestDirectory(a:buffer, '.git')
@@ -18,6 +19,7 @@ endfunction
 call ale#linter#Define('tex', {
 \   'name': 'texlab',
 \   'lsp': 'stdio',
+\   'lsp_config': {b -> ale#Var(b, 'tex_texlab_config')},
 \   'executable': {b -> ale#Var(b, 'tex_texlab_executable')},
 \   'command': function('ale_linters#tex#texlab#GetCommand'),
 \   'project_root': function('ale_linters#tex#texlab#GetProjectRoot'),

You can configure texlab like this:

let g:ale_tex_texlab_config = {"build":{"onSave":v:true}}

Note the explicit dictionary and no (!) texlab root.

I wouldn't recommend enabling forwardSearchAfter, it didn't work properly in my experience[^1]. An alternative command you can call whenever you want to open the pdf and jump to the current position:

fun! ForwardSearch()
    call ale#lsp_linter#SendRequest(bufnr('%'), 'texlab', [0, 'textDocument/forwardSearch', {'textDocument':{'uri':ale#path#ToURI(expand('#'.bufnr('%').':p'))},'position':{'line':line('.'),'character':col('.')}}])
endfun
command! -nargs=0 FwdSearch call ForwardSearch()

See the docs on how to configure the pdf viewer. I have not managed to make inverse search work.

[^1]: PDF viewer reloaded twice, and position was bogus; probably because full document is sent each time instead of just the diff. Also this takes focus from vim.

[hsanson]

@cpiber based on your work I implemented a PR #4027 that allows to configure texlab LSP settings. Appreciated if you can check the PR and let me know if it works for you.