[Semediawiki-user] Can't install SMW on 1.29.1

[Dan S. <dan...@ic...>]

I'm trying to follow the instructions here to install SMW on MediaWiki 1.29.1:

https://www.semantic-mediawiki.org/wiki/Help:Installation/Using_Composer_with_MediaWiki_1.25%2B

Composer reports a dependency error. I tried to work around it by mucking around in the "vendor" subdirectory, but I don't really know what I'm doing, and wasn't successful.

Here's the transcript:

---
$ -> ls
composer.phar           mediawiki-1.29.1.tar.gz

$ -> tar -xzf mediawiki-1.29.1.tar.gz 

$ -> cd mediawiki-1.29.1

$ -> php ../composer.phar require mediawiki/semantic-media-wiki "~2.5" --update-no-dev
./composer.json has been updated
> ComposerHookHandler::onPreUpdate
Loading composer repositories with package information
Updating dependencies
Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - The requested package justinrainbow/json-schema (installed at 5.2.0, required as ~3.0) is satisfiable by justinrainbow/json-schema[5.2.0] but these conflict with your requirements or minimum-stability.

Running update with --no-dev does not mean require-dev is ignored, it just means the packages will not be installed. If dev requirements are blocking the update you have to resolve those problems.

Installation failed, reverting ./composer.json to its original content.
---

I don't get this error when installing on MediaWiki 1.28.2, but I'm getting set up on a system with PHP 7.1, and per COMPATIBILITY.md, "PHP 7.1+ requires at least MediaWiki 1.29".

—Dan