issue 3033 (#3620)

* Add ale_python_pyls_options

* Add extra explanatory detail

* Fix alignment

* Fix test

ale_linters/python/pyls.vim

@@ -2,6 +2,7 @@
 " Description: A language server for Python
 
 call ale#Set('python_pyls_executable', 'pyls')
+call ale#Set('python_pyls_options', '')
 call ale#Set('python_pyls_use_global', get(g:, 'ale_use_global_executables', 0))
 call ale#Set('python_pyls_auto_pipenv', 0)
 call ale#Set('python_pyls_config', {})
@@ -22,7 +23,7 @@ function! ale_linters#python#pyls#GetCommand(buffer) abort
     \   ? ' run pyls'
     \   : ''
 
-    return ale#Escape(l:executable) . l:exec_args
+    return ale#Escape(l:executable) . l:exec_args . ale#Pad(ale#Var(a:buffer, 'python_pyls_options'))
 endfunction
 
 call ale#linter#Define('python', {

doc/ale-python.txt

@@ -688,6 +688,25 @@ g:ale_python_pyls_config                             *g:ale_python_pyls_config*
       \ }
 <
 
+g:ale_python_pyls_options                           *g:ale_python_pyls_options*
+                                                    *b:ale_python_pyls_options*
+  Type: |String|
+  Default: `''`
+
+  This variable can be changed to add command-line arguments to the pyls
+  invocation. Note that this is not the same thing as ale_python_pyls_config,
+  which allows configuration of how pyls functions; this is intended to
+  provide flexibility in how the pyls command is invoked.
+
+  For example, if you had installed `pyls` but your `pyls` executable was not
+  on your `PATH` for some reason, an alternative way to run the pyls server
+  would be:
+  let g:ale_python_pyls_executable = 'python3'
+  let g:ale_python_pyls_options = '-m pyls'
+
+  An example stragety for installing `pyls`:
+    `python3 -m pip install --user pyls`
+
 ===============================================================================
 pyre                                                          *ale-python-pyre*
 

test/command_callback/test_pyls_command_callback.vader

@@ -17,6 +17,11 @@ Execute(The pyls executable should be configurable):
 
   AssertLinter '~/.local/bin/pyls' , ale#Escape('~/.local/bin/pyls')
 
+Execute(The pyls command callback should let you set options):
+  let g:ale_python_pyls_options = '--some-option'
+
+  AssertLinter 'pyls', ale#Escape('pyls') . ' --some-option'
+
 Execute(The pyls executable should be run from the virtualenv path):
   call ale#test#SetFilename('python_paths/with_virtualenv/subdir/foo/bar.py')