add below content to ~/.vimrc, use :FormatXML to format xml
function! DoPrettyXML()
" save the filetype so we can restore it later
let l:origft = &ft
set ft=
" delete the xml header if it exists. This will
" permit us to surround the document with fake tags
" without creating invalid xml.
1s/<?xml .*?>//e
" insert fake tags around the entire document.
" This will permit us to pretty-format excerpts of
" XML that may contain multiple top-level elements.
0put ='<PrettyXML>'
$put ='</PrettyXML>'
silent %!xmllint --format -
" xmllint will insert an <?xml?> header. it's easy enough to delete
" if you don't want it.
" delete the fake tags
2d
$d
" restore the 'normal' indentation, which is one extra level
" too deep due to the extra tags we wrapped around the document.
silent %<
" back to home
1
" restore the filetype
exe "set ft=" . l:origft
endfunction
command! PrettyXML call DoPrettyXML()
" XML formatter
function! DoFormatXML() range
" Save the file type
let l:origft = &ft
" Clean the file type
set ft=
" Add fake initial tag (so we can process multiple top-level elements)
exe ":let l:beforeFirstLine=" . a:firstline . "-1"
if l:beforeFirstLine < 0
let l:beforeFirstLine=0
endif
exe a:lastline . "put ='</PrettyXML>'"
exe l:beforeFirstLine . "put ='<PrettyXML>'"
exe ":let l:newLastLine=" . a:lastline . "+2"
if l:newLastLine > line('$')
let l:newLastLine=line('$')
endif
" Remove XML header
exe ":" . a:firstline . "," . a:lastline . "s/<\?xml\\_.*\?>\\_s*//e"
" Recalculate last line of the edited code
let l:newLastLine=search('</PrettyXML>')
" Execute external formatter
exe ":silent " . a:firstline . "," . l:newLastLine . "!xmllint --noblanks --format --recover -"
" Recalculate first and last lines of the edited code
let l:newFirstLine=search('<PrettyXML>')
let l:newLastLine=search('</PrettyXML>')
" Get inner range
let l:innerFirstLine=l:newFirstLine+1
let l:innerLastLine=l:newLastLine-1
" Remove extra unnecessary indentation
exe ":silent " . l:innerFirstLine . "," . l:innerLastLine "s/^ //e"
" Remove fake tag
exe l:newLastLine . "d"
exe l:newFirstLine . "d"
" Put the cursor at the first line of the edited code
exe ":" . l:newFirstLine
" Restore the file type
exe "set ft=" . l:origft
endfunction
command! -range=% FormatXML <line1>,<line2>call DoFormatXML()
nmap <silent> <leader>x :%FormatXML<CR>
vmap <silent> <leader>x :FormatXML<CR>