Is this a dupe of https://bugzilla.wikimedia.org/show_bug.cgi?id=50512#c0 ?

I talked about that briefly on IRC, we decided that since this is specifically about the namespace proposal, until we decided what to do about it, we'd leave both open. And closing that bug may not necessarily close this bug.

See also:
https://www.mediawiki.org/wiki/Requests_for_comment/Associated_namespaces#Use_case_2b:_Structured_template_documentation

Re-wording; this is blocked by https://www.mediawiki.org/wiki/Requests_for_comment/Associated_namespaces being implemented.

I've fiddled with this because either T487: RfC: Associated namespaces or T107595: [RFC] Multi-Content Revisions would both meet this need. I think the latter is both more likely to occur and a better outcome, but…

I do raise two issues against the proposal, at least for mandatory evaluation of JSON pages only.

• Pro #2 reads as: “Document templates without needing to make edits to templates that are potentially transcluded across large swaths of pages”
  • This goes for any kind of lengthy documentation, and is usually solved by transclusion of a separated /doc into main template page.
  • German Wikipedia is using that technique for any longer template documentation since 2008, and enforces TemplateData on separated docpage for all productive templates.
• There are JSON objects built by template-like transclusion via {{#tag:}} syntax.
  • See Kategorie:Vorlage:Metadokumentation on German Wikipedia – a dozen of so-called “meta documentation” pattern pages is generating nearly thousand TemplateData objects on particular template pages, controlled by template name and sometimes parameters.

Optional separated .json subpages may be introduced, but classic <templatedata> approach needs to be supported, too.

This could be held like doc subpages or currently deployed css subpages instead

In T56140#3143510, @PerfektesChaos wrote:

• There are JSON objects built by template-like transclusion via {{#tag:}} syntax.
  • See Kategorie:Vorlage:Metadokumentation on German Wikipedia – a dozen of so-called “meta documentation” pattern pages is generating nearly thousand TemplateData objects on particular template pages, controlled by template name and sometimes parameters.

Interesting. json-schema allows referencing/embedding other schemas by using a special "$ref": "[URI to another schema]" key. Maybe something like that could be implemented in TemplateData instead of requiring the use of parser functions.

Please note that these are not static pages.

• The URI comment looks like assigning a static page which is simply transcluded.
• Entire JSON TemplateData descriptions are generated individually by template or Lua programming; depending on parameters and existence of other pages.
• You may have a look e.g. at use of lang/Latn/Doku and the derived page.

See related approach by Module:TNT -- it stores templatedata as a table (example). In this case <templatedata> will be dynamically generated during the parse time, and is available to every language/every wiki.