Commit: runtime(html): guard against an existing b:undo_ftplugin var

[Christian Brabandt]

runtime(html): guard against an existing b:undo_ftplugin var

Commit: https://github.com/vim/vim/commit/81ca9916d2fb2675a1a6da22fd68d26fb0ee8b8e
Author: D. Ben Knoble <ben.knob...@gmail.com>
Date: Sun Sep 14 04:42:25 2025 -0400

runtime(html): guard against an existing b:undo_ftplugin var

Filetype plugins should not assume they are the only file to execute on
behalf of a buffer's filetype: other filetypes may use them, and
dotted filetypes may cause multiple to run. When this occurs, they
should _build_ on their respective b:undo_ftplugin settings, not
overwrite each other.

For example, when using a dotted filetype wiki.markdown, the wiki
filetype plugins go first. Then, during the markdown filetype plugins,
the HTML plugin's unconditional assignment to b:undo_ftplugin trashes
any data previously stored there by the wiki filetype.

Follow the pattern elsewhere of assigning or appending conditionally.

closes: #18267

Signed-off-by: D. Ben Knoble <ben.knob...@gmail.com>
Signed-off-by: Doug Kearns <dougk...@gmail.com>
Signed-off-by: Christian Brabandt <c...@256bit.org>

diff --git a/runtime/ftplugin/html.vim b/runtime/ftplugin/html.vim
index 7736b5b05..26b99d2bc 100644
--- a/runtime/ftplugin/html.vim
+++ b/runtime/ftplugin/html.vim
@@ -2,9 +2,7 @@
" Language: HTML
" Maintainer: Doug Kearns <dougk...@gmail.com>
" Previous Maintainer: Dan Sharp
-" Last Change: 2024 Jan 14
-" 2024 May 24 update 'commentstring' option
-" 2025 May 10 add expression folding #17141
+" Last Change: 2025 Sep 12

if exists("b:did_ftplugin")
finish
@@ -18,7 +16,12 @@ setlocal matchpairs+=<:>
setlocal commentstring=<!--\ %s\ -->
setlocal comments=s:<!--,m:\ \ \ \ ,e:-->

-let b:undo_ftplugin = "setlocal comments< commentstring< matchpairs<"
+if exists('b:undo_ftplugin')
+ " no whitespace before |, handle possible :unmap at end of current value
+ let b:undo_ftplugin ..= "| setlocal comments< commentstring< matchpairs<"
+else
+ let b:undo_ftplugin = "setlocal comments< commentstring< matchpairs<"
+endif

if get(g:, "ft_html_autocomment", 0)
setlocal formatoptions-=t formatoptions+=croql