Add support for xmllint as a fixer.

autoload/ale/fix/registry.vim

@@ -225,6 +225,11 @@ let s:default_registry = {
 \       'suggested_filetypes': ['dart'],
 \       'description': 'Fix Dart files with dartfmt.',
 \   },
+\   'xmllint': {
+\       'function': 'ale#fixers#xmllint#Fix',
+\       'suggested_filetypes': ['xml'],
+\       'description': 'Fix XML files with xmllint.',
+\   },
 \}
 
 " Reset the function registry to the default entries.

autoload/ale/fixers/xmllint.vim

@@ -0,0 +1,27 @@
+" Author: Cyril Roelandt <tipecaml@gmail.com>
+" Description: Integration of xmllint with ALE.
+
+call ale#Set('xml_xmllint_executable', 'xmllint')
+call ale#Set('xml_xmllint_options', '')
+call ale#Set('xml_xmllint_indentsize', 2)
+
+function! ale#fixers#xmllint#Fix(buffer) abort
+    let l:executable = ale#Escape(ale#Var(a:buffer, 'xml_xmllint_executable'))
+    let l:filename = ale#Escape(bufname(a:buffer))
+    let l:command = l:executable . ' --format ' . l:filename
+
+    let l:indent = ale#Var(a:buffer, 'xml_xmllint_indentsize')
+    if l:indent isnot# ''
+        let l:env = ale#Env('XMLLINT_INDENT', repeat(' ', l:indent))
+        let l:command = l:env . l:command
+    endif
+
+    let l:options = ale#Var(a:buffer, 'xml_xmllint_options')
+    if l:options isnot# ''
+        let l:command .= ' ' . l:options
+    endif
+
+    return {
+    \   'command': l:command
+    \}
+endfunction

doc/ale-xml.txt

@@ -21,6 +21,14 @@ g:ale_xml_xmllint_options                           *g:ale_xml_xmllint_options*
   This variable can be set to pass additional options to xmllint.
 
 
+g:ale_xml_xmllint_indentsize                     *g:ale_xml_xmllint_indentsize*
+                                                 *b:ale_xml_xmllint_indentsize*
+  Type: |Number|
+  Default: 2
+
+  This variable can be sent to specify the amount of spaces used for
+  indentation.
+
 ===============================================================================
   vim:tw=78:ts=2:sts=2:sw=2:ft=help:norl:
 

test/fixers/test_xmllint_fixer_callback.vader

@@ -0,0 +1,46 @@
+Before:
+  Save g:ale_xml_xmllint_executable
+  Save g:ale_xml_xmllint_indentsize
+  Save g:ale_xml_xmllint_options
+
+  let g:ale_xml_xmllint_executable = '/path/to/xmllint'
+  let g:ale_xml_xmllint_indentsize = ''
+  let g:ale_xml_xmllint_options = ''
+
+  call ale#test#SetDirectory('/testplugin/test/fixers')
+
+After:
+  Restore
+
+Execute(The xmllint callback should return the correct default command):
+  AssertEqual
+  \ {
+  \   'command': ale#Escape('/path/to/xmllint')
+  \     . ' --format '
+  \     . ale#Escape(bufname(bufnr('')))
+  \ },
+  \ ale#fixers#xmllint#Fix(bufnr(''))
+
+Execute(The xmllint callback should include the XMLLINT_INDENT variable):
+  let g:ale_xml_xmllint_indentsize = 2
+
+  AssertEqual
+  \ {
+  \   'command': ale#Env('XMLLINT_INDENT', '  ')
+  \     . ale#Escape('/path/to/xmllint')
+  \     . ' --format '
+  \     . ale#Escape(bufname(bufnr('')))
+  \ },
+  \ ale#fixers#xmllint#Fix(bufnr(''))
+
+Execute(The xmllint callback should include additional options):
+  let g:ale_xml_xmllint_options = '--nonet'
+
+  AssertEqual
+  \ {
+  \   'command': ale#Escape('/path/to/xmllint')
+  \     . ' --format '
+  \     . ale#Escape(bufname(bufnr('')))
+  \     . ' --nonet'
+  \ },
+  \ ale#fixers#xmllint#Fix(bufnr(''))