Is this issue a regression of the fix for T377389 ? (https://gerrit.wikimedia.org/r/c/mediawiki/extensions/MobileFrontend/+/1088287 )

Seems like the section has an ID -1 which breaks assumptions made in the PHP transforms cc @SToyofuku-WMF and @LMora-WMF as this might be relevant to patches you are currently working on?

Interesting - do we know whether the ID of -1 is coming from the template or from the make sections transform hitting an error?

The data-mw-section-id attribute will either be "0" or greater and correspond exactly to a PHP section ID (as used for action=edit for example), or will be "-1" (indicating an uneditable non-pseudo section) or "-2" (indicating a pseudo-section, which is also uneditable).

https://www.mediawiki.org/wiki/Specs/HTML/2.8.0#Headings_and_Sections

Gotcha, thank you! Since it's parsoid specific we should definitely prioritize getting this fixed, but I don't believe it's related to the work we're doing right now in T374883

@SToyofuku-WMF this looks like an issue in the parser, not MobileFrontend.
I've started a Slack thread with Content transform team.

We are wrapping "well formed" sections, which are those we can support section editing on. I suppose we could also wrap malformed sections as well, but we'd probably skip adding section edit links to those sections. That might cause other issues.

I think we can arrange to wrap data-mw-section-id=-1 sections. But how do you expect data-mw-section-id=-2 sections to work? (See https://www.mediawiki.org/wiki/Parsing/Notes/Section_Wrapping#Pseudo-sections ).

Not sure if T384490: Include directives on a line with headings prevent the legacy parser from generating section edit links is related.

T373400: Bug in HandleParsoidSectionLinks - seems to skip some headings? may also be related, in so far as that task removed some wrappers.

Change #1113542 had a related patch set uploaded (by C. Scott Ananian; author: C. Scott Ananian):

[mediawiki/core@master] WIP: HandleParsoidSectionLinks: add collapsible wrappers around uneditable sections

https://gerrit.wikimedia.org/r/1113542

Note, we do plan to work on the logic in T374883: Section collapsing should not apply to certain pages - if a section is wrapped in a DIV it shouldn't be collapsed. In this situation, I honestly wouldn't even create a section element to be consistent with how the legacy parser in MobileFrontend works.