runtime(astro): Add filetype, syntax and indent plugin

related: #14558
closes: #14561

ported from: https://github.com/wuelnerdotexe/vim-astro

Signed-off-by: Philip H <47042125+pheiduck@users.noreply.github.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>

runtime/indent/astro.vim

@@ -0,0 +1,88 @@
+" Vim indent file (experimental).
+" Language:    Astro
+" Author:      Wuelner Martínez <wuelner.martinez@outlook.com>
+" Maintainer:  Wuelner Martínez <wuelner.martinez@outlook.com>
+" URL:         https://github.com/wuelnerdotexe/vim-astro
+" Last Change: 2022 Aug 07
+" Based On:    Evan Lecklider's vim-svelte
+" Changes:     See https://github.com/evanleck/vim-svelte
+" Credits:     See vim-svelte on github
+
+" Only load this indent file when no other was loaded yet.
+if exists('b:did_indent')
+  finish
+endif
+
+let b:html_indent_script1 = 'inc'
+let b:html_indent_style1 = 'inc'
+
+" Embedded HTML indent.
+runtime! indent/html.vim
+let s:html_indent = &l:indentexpr
+unlet b:did_indent
+
+let b:did_indent = 1
+
+setlocal indentexpr=GetAstroIndent()
+setlocal indentkeys=<>>,/,0{,{,},0},0),0],0\,<<>,,!^F,*<Return>,o,O,e,;
+
+let b:undo_indent = 'setl inde< indk<'
+
+" Only define the function once.
+if exists('*GetAstroIndent')
+  finish
+endif
+
+let s:cpoptions_save = &cpoptions
+setlocal cpoptions&vim
+
+function! GetAstroIndent()
+  let l:current_line_number = v:lnum
+
+  if l:current_line_number == 0
+    return 0
+  endif
+
+  let l:current_line = getline(l:current_line_number)
+
+  if l:current_line =~ '^\s*</\?\(script\|style\)'
+    return 0
+  endif
+
+  let l:previous_line_number = prevnonblank(l:current_line_number - 1)
+  let l:previous_line = getline(l:previous_line_number)
+  let l:previous_line_indent = indent(l:previous_line_number)
+
+  if l:previous_line =~ '^\s*</\?\(script\|style\)'
+    return l:previous_line_indent + shiftwidth()
+  endif
+
+  execute 'let l:indent = ' . s:html_indent
+
+  if searchpair('<style>', '', '</style>', 'bW') &&
+        \ l:previous_line =~ ';$' && l:current_line !~ '}'
+    return l:previous_line_indent
+  endif
+
+  if synID(l:previous_line_number, match(
+        \   l:previous_line, '\S'
+        \ ) + 1, 0) == hlID('htmlTag') && synID(l:current_line_number, match(
+        \  l:current_line, '\S'
+        \ ) + 1, 0) != hlID('htmlEndTag')
+    let l:indents_match = l:indent == l:previous_line_indent
+    let l:previous_closes = l:previous_line =~ '/>$'
+
+    if l:indents_match &&
+          \ !l:previous_closes && l:previous_line =~ '<\(\u\|\l\+:\l\+\)'
+      return l:previous_line_indent + shiftwidth()
+    elseif !l:indents_match && l:previous_closes
+      return l:previous_line_indent
+    endif
+  endif
+
+  return l:indent
+endfunction
+
+let &cpoptions = s:cpoptions_save
+unlet s:cpoptions_save
+" vim: ts=8