Extensions - Setup <classloader> during installation

[totten]

Overview

Extensions may define <classloader> rules, such as:

  <classloader>
    <psr0 prefix="CRM_" path="" />
    <psr4 prefix="Civi\" path="Civi"/>
  </classloader>

Any classloaders should take effect promptly during installation, to allow code like this:

function whizbang_civicrm_install() {
  \Civi\Whizbang\Setup::doStuff();
  \CRM_Whizbang_Setup::doMoreStuff();
}

For a more complete example, see: https://gist.github.com/totten/02e6e15c8a50aaca929b2206f2492de4

This is an extract from #20090.

Before

Classloaders are not available during installation.

The example doesn't work -- because hook_civicrm_install fires before ./Civi has been added to the classloader.

[bknix-min:~/bknix/build/dmaster/web/sites/all/modules/civicrm] cv en whizbang
Enabling extension "whizbang"


  [Symfony\Component\Debug\Exception\FatalThrowableError]
  Class 'Civi\Whizbang\Setup' not found


ext:enable [-r|--refresh] [--ignore-missing] [--level LEVEL] [-t|--test] [-U|--user USER] [--] [<key-or-name>]...

After

The classloader is updated before running install logic.

The example works:

[bknix-min:~/bknix/build/dmaster/web/sites/all/modules/civicrm/ext/whizbang] cv en whizbang
Enabling extension "whizbang"
Hello from /Users/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/ext/whizbang/Civi/Whizbang/Setup.php@7 circa 2021-04-17 04:47:13
Hello from /Users/totten/bknix/build/dmaster/web/sites/all/modules/civicrm/ext/whizbang/CRM/Whizbang/Setup.php@6 circa 2021-04-17 04:47:13

Technical Details

In theory, CRM_Extension_ClassLoader has a property $this->loader which (purported to) track the real/live loader. We need access to $this->loader to register extra classloading rules. Alas,$this->loader was null. So the patch fixes that.

[civibot]

(Standard links)

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[eileenmcnaughton]

This was pretty easy to test with the information provided & agree it's helpful