The template defaults to using extjsonuploader data. That works well in most cases, but not for supported MediaWiki version, where the value in extension.json means the MediaWiki version required for the current (master) version of the extension, while the template field is supposed to mean the oldest supported MediaWiki version (for extensions using the release branch compatibility policy, at least). I wonder if leaving the field empty would be a better default.
Topic on Template talk:Extension
I think it would make sense to use the version information from extjsonuploader data only when the compatibility policy is set to master. Otherwise, the value should be specified manually.
The field is almost always meaningless; yes, there's a 10-year-old version of the extension that used to work with MediaWiki 1.12 but no-one is testing it and certainly no-one is supporting it. Maybe we should label the field "minimum MW required by development branch" and have a second field for "oldest currently supported branch" which can be set manually (but only to a non-obsolete version, i.e. minimum 1.35 right now)?
Presumably it was tested 10 years ago when it was used with 1.12; shouldn't that be enough? For extensions following the release branch model, which get snapshotted biannually together with MediaWiki, being able to see how far those snapshots go back is a nice convenience. Someone using an old MediaWiki version presumably doesn't care about support, or doesn't have a choice.
(I can see how the "supported MediaWiki version" terminology could be misleading for something very old that the maintainer, if there's still one, won't entertain fixes for, but that's my mistake, the infobox doesn't use that wording.)
And I don't think using the field for "oldest MediaWiki version for which there is a compatible extension version" would crowd out more useful information - you are supposed to install the extension from the release branch matching your core version, so knowing what older core versions the extension's development branch or latest stable is compatible with seems quite useless.
For extensions using the master compatibility policy, I agree leaving the current behavior (using the extension.json field) makes more sense.
If the field is entered manually, it's often used to say what's the latest MediaWiki version where it has been tested. For example, unmaintained extensions may have an old value there and not work with the latest MediaWiki versions, or only support LTS versions.
"Latest MediaWiki version the extension is known to work with" is certainly more useful information than any of the alternatives mentioned above. The value pulled from extension.json isn't really useful for that purpose, though.
"Latest MediaWiki version the extension is known to work with" is certainly more useful information than any of the alternatives mentioned above.
If "known" we mean "tests pass", then for 99%+ of extensions that's just master.
"Known" would mean "someone tested the extension with this relase". The use case here is that someone adds (via extension.json or directly) something like "<= 1.35.0" (which at the time actually means 1.35-138), then 1.39 is released, drops deprecated features, which breaks the extension – knowing that the extension doesn't work with the latest MediaWiki release would be useful for more users than whether it can be made to work with 1.27 (or at least I'd hope so).
Then call it "last manually tested with"?
Continuing this conversation with a new title.