Maniphest T419726

Parsoid fails to expand transclusion generated by a Lua module on mnwiki
Closed, ResolvedPublic
Actions

Assigned To

Authored By

	ssastry
	Mar 11 2026, 3:55 PM

Description

See transcript below for a mnwiki wikitext snippet:

$ echo "{{Ангилал он}}" | php bin/parse.php --domain mn.wikipedia.org --dump tplsrc --pageName "Ангилал:1990 он"
[dump] ============================ template source ============================
TEMPLATE:Загвар:Ангилал_онTRANSCLUSION:"{{Ангилал он}}"
--------------------------------------------------------------------------------
<div {{Цагалбарын хэв}}>
...
</div>

The template generating the div's style attributes isn't expanded. It comes from these lines in this module.

This phab task is the only blocker for mnwiki. It affects likely *all* Category pages on this wiki.

Details

Related Changes in Gerrit:

	Subject	Repo	Branch	Lines +/-
	Remove double template expansion in html attributes	mediawiki/core	master	+22 -2

Customize query in gerrit

Related Objects

Mentioned In: T423188: Parsoid Read Views to deploy ~2026-04-16
T419482: Missing heading styles on a fiwiki infobox in Parsoid's rendering
Mentioned Here: T385806: Replace `{{#parsoid-fragment}}` with dedicated token

Event Timeline

ssastry created this task.Mar 11 2026, 3:55 PM

Restricted Application added a subscriber: Aklapper. · View Herald TranscriptMar 11 2026, 3:55 PM

ssastry renamed this task from Parsoid fails to expand template generated by a Lua module on mnwiki to Parsoid fails to expand transclusion generated by a Lua module on mnwiki.Mar 11 2026, 3:55 PM

ssastry updated the task description. (Show Details)

ABreault-WMF moved this task from Backlog to Work In Progress on the Content-Transform-Team board.Mar 12 2026, 2:09 PM

ABreault-WMF edited projects, added Content-Transform-Team (Work In Progress); removed Content-Transform-Team.

ABreault-WMF moved this task from Needs Triage to Bugs & Crashers on the Parsoid board.Mar 12 2026, 2:13 PM

ABreault-WMF moved this task from Uncategorized to Large Wikipedias on the Parsoid-Read-Views board.Mar 12 2026, 2:23 PM

ABreault-WMF edited projects, added Parsoid-Read-Views (Large Wikipedias); removed Parsoid-Read-Views.

cscott assigned this task to Jgiannelos.Mar 23 2026, 3:17 PM

cscott moved this task from Backlog to Q4 FY25-26 on the Content-Transform-Team (Work In Progress) board.

Jgiannelos moved this task from Q4 FY25-26 to In Progress on the Content-Transform-Team (Work In Progress) board.Mar 30 2026, 3:06 PM

I did some more debugging here. The reproduction steps for a simpler example is the following:

Create a template with some inline CSS styling: https://test.wikipedia.org/wiki/Template:NestedTemplateT419726
Create a lua module that returns an element with the template above as attribute: https://test.wikipedia.org/wiki/Module:T419726
Create a template that invokes the lua module: https://test.wikipedia.org/wiki/Template:T419726
Create a test page that transcludes the template: https://test.wikipedia.org/wiki/T419726

With parsoid as renderer the inline styling is not rendered but legacy renders it.

More specifically parsoid:

<div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr" data-mw-parsoid-version="0.23.0.0-alpha23" data-mw-html-version="2.8.0">
   <section data-mw-section-id="0" id="mwAQ">
      <div about="#mwt1" typeof="mw:Transclusion" data-mw='{"parts":[{"template":{"target":{"wt":"T419726","href":"./Template:T419726"},"params":{},"i":0}}]}' id="mwAg">


         <p>hello</p>


      </div>
   </section>
</div>

legacy:

<div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr">
   <div style="text-align:center; border:1px solid #ccc; background-color:pink">
     <p>hello</p>
</div>

The error is reproducible even with a simpler setup:

Template <- Lua <- Test Page

https://test.wikipedia.org/wiki/T419726-no-nesting?useparsoid=1
https://test.wikipedia.org/wiki/T419726-no-nesting?useparsoid=0

ABreault-WMF mentioned this in T419482: Missing heading styles on a fiwiki infobox in Parsoid's rendering.Mar 30 2026, 7:46 PM

For debugging purposes I tried this patch and it renders the output like legacy, because it allows expanding the templates from invoke:

diff --git a/src/Wt2Html/TT/TemplateHandler.php b/src/Wt2Html/TT/TemplateHandler.php
index 531a6d4ae..16fbfca2c 100644
--- a/src/Wt2Html/TT/TemplateHandler.php
+++ b/src/Wt2Html/TT/TemplateHandler.php
@@ -1058,7 +1058,7 @@ class TemplateHandler extends XMLTagBasedHandler {
                                        [
                                                // Template like content returned from the
                                                // preprocessor should not be further expanded
-                                               'expandTemplates' => false,
+                                               'expandTemplates' => true,
                                                'srcOffsets' => $srcOffsets,
                                        ] + $this->options

The issue here is that this is a decision made for reasons discussed here: https://phabricator.wikimedia.org/T385806 so I am not sure if this something we want to fix in parsoid.

Here's another interesting test case:

https://en.wikipedia.org/w/index.php?title=User:Cscott/T419726&useparsoid=1
vs
https://en.wikipedia.org/w/index.php?title=User:Cscott/T419726&useparsoid=0

Using this simple lua module: https://en.wikipedia.org/wiki/Module:User:Cscott/T419726

This is somewhat surprising: the "double expansion" of arguments seems limited to html tags, /not/ extension tags. (I had thought that the double expansion was happening when extension tag arguments were parsed.)

Change #1266328 had a related patch set uploaded (by Arlolra; author: Arlolra):

[mediawiki/core@master] Remove double template expansion in html attributes

https://gerrit.wikimedia.org/r/1266328

gerritbot added a project: Patch-For-Review.Apr 1 2026, 5:36 PM

Change #1266328 merged by jenkins-bot:

[mediawiki/core@master] Remove double template expansion in html attributes

https://gerrit.wikimedia.org/r/1266328

Maintenance_bot removed a project: Patch-For-Review.Apr 3 2026, 3:30 AM

ReleaseTaggerBot added a project: MW-1.46-notes (1.46.0-wmf.23; 2026-04-07).Apr 3 2026, 4:00 AM

Arlolra moved this task from In Progress to To Deploy on the Content-Transform-Team (Work In Progress) board.Apr 6 2026, 3:37 PM

ABreault-WMF moved this task from To Deploy to To Verify on the Content-Transform-Team (Work In Progress) board.Apr 9 2026, 6:22 PM