add: support for ruff as a Python linter and fixer (#4347)

this commit adds ruff as both a Python linter and fixer, together with
some tests and documentation.

ruff repo: https://github.com/charliermarsh/ruff

autoload/ale/fixers/ruff.vim

@@ -0,0 +1,54 @@
+" Author: Yining <zhang.yining@gmail.com>
+" Description: ruff as ALE fixer for python files
+
+function! ale#fixers#ruff#GetCwd(buffer) abort
+    if ale#Var(a:buffer, 'python_ruff_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 ''
+endfunction
+
+function! ale#fixers#ruff#GetExecutable(buffer) abort
+    if (ale#Var(a:buffer, 'python_auto_pipenv') || ale#Var(a:buffer, 'python_ruff_auto_pipenv'))
+    \ && ale#python#PipenvPresent(a:buffer)
+        return 'pipenv'
+    endif
+
+    if (ale#Var(a:buffer, 'python_auto_poetry') || ale#Var(a:buffer, 'python_ruff_auto_poetry'))
+    \ && ale#python#PoetryPresent(a:buffer)
+        return 'poetry'
+    endif
+
+    return ale#python#FindExecutable(a:buffer, 'python_ruff', ['ruff'])
+endfunction
+
+function! ale#fixers#ruff#GetCommand(buffer, version) abort
+    let l:executable = ale_linters#python#ruff#GetExecutable(a:buffer)
+    let l:exec_args = l:executable =~? 'pipenv\|poetry$'
+    \   ? ' run ruff'
+    \   : ''
+
+    " NOTE: ruff version `0.0.72` implement `--fix` with stdin
+    return ale#Escape(l:executable) . l:exec_args
+    \   . ale#Pad(ale#Var(a:buffer, 'python_ruff_options'))
+    \   . ' --fix'
+    \   .  (ale#semver#GTE(a:version, [0, 0, 72]) ? ' -' : ' %s')
+endfunction
+
+function! ale#fixers#ruff#Fix(buffer) abort
+    let l:fix_cmd = {buffer -> ale#semver#RunWithVersionCheck(
+    \     buffer,
+    \     ale#fixers#ruff#GetExecutable(buffer),
+    \     '%e --version',
+    \     function('ale#fixers#ruff#GetCommand'),
+    \ )}(a:buffer)
+
+    return {
+    \ 'cwd': ale#fixers#ruff#GetCwd(a:buffer),
+    \ 'command': l:fix_cmd,
+    \}
+endfunction