add: pycln as a python linter and fixer (#4415)

this commit adds pycln as a Python linter and fixer, together with some
tests and documentation. It addresses #4340

pycln repo: https://github.com/hadialqattan/pycln

autoload/ale/fix/registry.vim

@@ -585,6 +585,11 @@ let s:default_registry = {
 \       'function': 'ale#fixers#ruff#Fix',
 \       'suggested_filetypes': ['python'],
 \       'description': 'Fix python files with ruff.',
+\   },
+\   'pycln': {
+\       'function': 'ale#fixers#pycln#Fix',
+\       'suggested_filetypes': ['python'],
+\       'description': 'remove unused python import statements',
 \   }
 \}
 

autoload/ale/fixers/pycln.vim

@@ -0,0 +1,90 @@
+" Author: Yining <zhang.yining@gmail.com>
+" Description: pycln as ALE fixer for python files
+
+call ale#Set('python_pycln_executable', 'pycln')
+call ale#Set('python_pycln_options', '')
+call ale#Set('python_pycln_use_global', get(g:, 'ale_use_global_executables', 0))
+call ale#Set('python_pycln_change_directory', 1)
+call ale#Set('python_pycln_auto_pipenv', 0)
+call ale#Set('python_pycln_auto_poetry', 0)
+call ale#Set('python_pycln_config_file', '')
+
+function! ale#fixers#pycln#GetCwd(buffer) abort
+    if ale#Var(a:buffer, 'python_pycln_change_directory')
+        " Run from project root if found, else from buffer dir.
+        let l:project_root = ale#python#FindProjectRoot(a:buffer)
+
+        return !empty(l:project_root) ? l:project_root : '%s:h'
+    endif
+
+    return '%s:h'
+endfunction
+
+function! ale#fixers#pycln#GetExecutable(buffer) abort
+    if (ale#Var(a:buffer, 'python_auto_pipenv') || ale#Var(a:buffer, 'python_pycln_auto_pipenv'))
+    \ && ale#python#PipenvPresent(a:buffer)
+        return 'pipenv'
+    endif
+
+    if (ale#Var(a:buffer, 'python_auto_poetry') || ale#Var(a:buffer, 'python_pycln_auto_poetry'))
+    \ && ale#python#PoetryPresent(a:buffer)
+        return 'poetry'
+    endif
+
+    return ale#python#FindExecutable(a:buffer, 'python_pycln', ['pycln'])
+endfunction
+
+function! ale#fixers#pycln#GetCommand(buffer) abort
+    let l:executable = ale#fixers#pycln#GetExecutable(a:buffer)
+    let l:exec_args = l:executable =~? 'pipenv\|poetry$'
+    \   ? ' run pycln'
+    \   : ''
+
+    return ale#Escape(l:executable) . l:exec_args
+endfunction
+
+function! ale#fixers#pycln#FixForVersion(buffer, version) abort
+    let l:executable = ale#fixers#pycln#GetExecutable(a:buffer)
+    let l:cmd = [ale#Escape(l:executable)]
+
+    if l:executable =~? 'pipenv\|poetry$'
+        call extend(l:cmd, ['run', 'pycln'])
+    endif
+
+    let l:options = ale#Var(a:buffer, 'python_pycln_options')
+
+    if !empty(l:options)
+        call add(l:cmd, l:options)
+    endif
+
+    let l:config_file = ale#Var(a:buffer, 'python_pycln_config_file')
+    let l:config_file = l:options !~# '\v(^| )--config ' && !empty(l:config_file)
+    \   ? ale#Escape(ale#path#Simplify(l:config_file))
+    \   : ''
+
+    if !empty(l:config_file)
+        call add(l:cmd, '--config ' . l:config_file)
+    endif
+
+    call add(l:cmd, '--silence')
+
+    " NOTE: pycln version `1.3.0` support reading from stdin
+    call add(l:cmd, ale#semver#GTE(a:version, [1, 3, 0]) ? '-' : '%s')
+
+    return {
+    \   'cwd': ale#fixers#pycln#GetCwd(a:buffer),
+    \   'command': join(l:cmd, ' '),
+    \}
+endfunction
+
+function! ale#fixers#pycln#Fix(buffer) abort
+    let l:executable = ale#fixers#pycln#GetExecutable(a:buffer)
+    let l:command = ale#fixers#pycln#GetCommand(a:buffer) . ale#Pad('--version')
+
+    return ale#semver#RunWithVersionCheck(
+    \     a:buffer,
+    \     l:executable,
+    \     l:command,
+    \     function('ale#fixers#pycln#FixForVersion'),
+    \)
+endfunction