I (@Daimona) think that extensions should *not* have an explicit PHP version requirement, unless it's (meant to be) different from the one in core.

That's kinda the view I'd taken, at least when adding or suggesting others to add them. For example the WebAuthn, which needed PHP 7.2 due the the 3rd party libraries it used, but it was mostly developed when MW master still needed HHVM support and therefore it could've used HHVM

It's worth noting an extension can set it in extension.json too, which can have differing results. Which can potentially give some other clues... If the file has a requires MW >= some old version, the PHP version might make more sense. Especially as we're trying to be more rigorous about setting the requires MW in extension.json, so we don't necessarily have to enforce the "use the same branch of MW for the extension" -- if master says it should work... It should work (or else that's a separate bug)

I implemented the php requirements for extension.json, and @Legoktm and me thought it should be used the same way @Daimona proposes: A php requirement should only be specified, if an extension requires a php version higher than the minimum supported php version for the minimum supported MW core version. I think for composer.json, we should use the same approach.

In T235160#5564075, @MGChecker wrote:

I implemented the php requirements for extension.json, and @Legoktm and me thought it should be used the same way @Daimona proposes: A php requirement should only be specified, if an extension requires a php version higher than the minimum supported php version for the minimum supported MW core version. I think for composer.json, we should use the same approach.

Got the task/reference to hand? Always worth linking back where possible

T197535: extension.json should be able to express dependency on PHP version / PHP extension version and https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/458940/