runtime(html): Optionally fold tags with the "expr" method
Tag folding poses a few difficulties. Many elements, e.g.
"blockquote", are always delimited by start and end tags;
end tags for some elements, e.g. "p", can be omitted in
certain contexts; void elements, e.g. "hr", have no end tag.
Although the rules for supporting omissible end tags are
ad-hoc and involved, they apply to elements in scope.
Assuming syntactical wellformedness, an end tag can be
associated with its nearest matching start tag discoverable
in scope and towards the beginning of a file, whereas all
unbalanced tags and inlined tags can be disregarded.
For example:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en"> <!-- >1 : 1 -->
<body> <!-- >2 : 2 -->
<p>Paragraph #1. <!-- = : 2 -->
<p> <!-- >3 : 3 -->
Paragraph #2. <!-- = : 3 -->
</p> <!-- <3 : 3 -->
<p>Paragraph #3.</p> <!-- = : 2 -->
</body> <!-- <2 : 2 -->
</html> <!-- <1 : 1 -->
------------------------------------------------------------
(HTML comments here, "<!-- ... -->", record two values for
each folded line that are separated by ":", a value obtained
from "&foldexpr" and a value obtained from "foldlevel()".)
Innermost foldedable tags will be flattened. For example:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en"> <!-- >1 : 1 -->
<body> <!-- >2 : 2 -->
<div class="block"> <!-- >3 : 3 -->
<pre><code> <!-- >4 : 4 -->
[CODE SNIPPET] <!-- = : 4 -->
</code></pre> <!-- <4 : 4 -->
</div> <!-- <3 : 3 -->
</body> <!-- <2 : 2 -->
</html> <!-- <1 : 1 -->
------------------------------------------------------------
No folding will be requested for the "<code>"-"</code>" tag
pair and reflected by "&foldexpr" because such a fold would
have claimed the same lines that the immediate fold of the
"<pre>"-"</pre>" tag already claims.
Run-on folded tags may confuse Vim. When a file such as:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en"> <!-- >1 : 1 -->
<body> <!-- >2 : 2 -->
<div class="block"> <!-- >3 : 3 -->
<pre> <!-- >4 : 4 -->
<code> <!-- >5 : 5 -->
[CODE SNIPPET #1] <!-- = : 5 -->
</code> <!-- <5 : 5 -->
</pre> <!-- <4 : 4 -->
</div> <!-- <3 : 3 -->
<!-- = : 3 -->
<div class="block"> <!-- >3 : 3 -->
<pre> <!-- >4 : 4 -->
<code> <!-- >5 : 5 -->
[CODE SNIPPET #2] <!-- = : 5 -->
</code> <!-- <5 : 5 -->
</pre> <!-- <4 : 4 -->
</div> <!-- <3 : 3 -->
</body> <!-- <2 : 2 -->
</html> <!-- <1 : 1 -->
------------------------------------------------------------
is reformatted as follows:
------------------------------------------------------------
<!DOCTYPE html>
<html lang="en"> <!-- >1 : 1 -->
<body> <!-- >2 : 2 -->
<div class="block"> <!-- >3 : 3 -->
<pre> <!-- >4 : 4 -->
<code> <!-- >5 : 5 -->
[CODE SNIPPET #1] <!-- = : 5 -->
</code> <!-- <5 : 5 -->
</pre> <!-- <4 : 4 -->
</div><div class="block"><pre><code> <!-- <3 : 3 -->
[CODE SNIPPET #2] <!-- = : 2 ? -->
</code> <!-- <5 : 2 ? -->
</pre> <!-- <4 : 2 ? -->
</div> <!-- <3 : 2 ? -->
</body> <!-- <2 : 2 -->
</html> <!-- <1 : 1 -->
------------------------------------------------------------
"&foldexpr" values will not be used as is for the lines
between (and including) "[CODE SNIPPET #2]" and "</div>".
(Cf. v9.1.0002.)
Having syntax highlighting in effect, tag folding using the
"fold-expr" method can be enabled with:
------------------------------------------------------------
let g:html_expr_folding = 1
------------------------------------------------------------
By default, tag folding will be redone from scratch after
each occurrence of a TextChanged or an InsertLeave event.
Such frequency may not be desired, especially for large
files, and this recomputation can be disabled with:
------------------------------------------------------------
let g:html_expr_folding_without_recomputation = 1
doautocmd FileType
------------------------------------------------------------
To force another recomputation, do:
------------------------------------------------------------
unlet! b:foldsmap
normal zx
------------------------------------------------------------
References:
https://web.archive.org/web/20250328105626/https://html.spec.whatwg.org/multipage/syntax.html#optional-tags
https://en.wikipedia.org/wiki/Dangling_else
closes: #17141
Signed-off-by: Aliaksei Budavei <0x000c70@gmail.com>
Signed-off-by: Christian Brabandt <cb@256bit.org>
diff --git a/runtime/ftplugin/html.vim b/runtime/ftplugin/html.vim
index 5495f85..7736b5b 100644
--- a/runtime/ftplugin/html.vim
+++ b/runtime/ftplugin/html.vim
@@ -3,7 +3,8 @@
" Maintainer: Doug Kearns <dougkearns@gmail.com>
" Previous Maintainer: Dan Sharp
" Last Change: 2024 Jan 14
-" 2024 May 24 by Riley Bruins <ribru17@gmail.com> ('commentstring')
+" 2024 May 24 update 'commentstring' option
+" 2025 May 10 add expression folding #17141
if exists("b:did_ftplugin")
finish
@@ -56,5 +57,52 @@
let b:undo_ftplugin ..= " | unlet! b:browsefilter b:html_set_browsefilter"
endif
+if has("folding") && get(g:, "html_expr_folding", 0)
+ function! HTMLTagFold() abort
+ if empty(get(b:, "foldsmap", {}))
+ if empty(get(b:, "current_syntax", ''))
+ return '0'
+ else
+ let b:foldsmap = htmlfold#MapBalancedTags()
+ endif
+ endif
+
+ return get(b:foldsmap, v:lnum, '=')
+ endfunction
+
+ setlocal foldexpr=HTMLTagFold()
+ setlocal foldmethod=expr
+ let b:undo_ftplugin ..= " | setlocal foldexpr< foldmethod<"
+
+ if !get(g:, "html_expr_folding_without_recomputation", 0)
+ augroup htmltagfold
+ autocmd! htmltagfold
+ autocmd TextChanged,InsertLeave <buffer> let b:foldsmap = {}
+ augroup END
+
+ " XXX: Keep ":autocmd" last in "b:undo_ftplugin" (see ":help :bar").
+ let b:undo_ftplugin ..= " | silent! autocmd! htmltagfold * <buffer>"
+ endif
+endif
+
let &cpo = s:save_cpo
unlet s:save_cpo
+
+" See ":help vim9-mix".
+if !has("vim9script")
+ finish
+endif
+
+if exists("*g:HTMLTagFold")
+ def! g:HTMLTagFold(): string
+ if empty(get(b:, "foldsmap", {}))
+ if empty(get(b:, "current_syntax", ''))
+ return '0'
+ else
+ b:foldsmap = g:htmlfold#MapBalancedTags()
+ endif
+ endif
+
+ return get(b:foldsmap, v:lnum, '=')
+ enddef
+endif