Fix fatal error when Composer EventDispatcher called programmatically

This now reverts the second code modernization from 234 as well. Annoying, but so be it.

I've also now added warnings in both places which were modernized and for which the modernizations had to be reverted to hopefully prevent this happening again.

Fixes 247

Author: jrfnl

src/Plugin.php

@@ -12,7 +12,6 @@
 
 use Composer\Composer;
 use Composer\EventDispatcher\EventSubscriberInterface;
-use Composer\InstalledVersions;
 use Composer\IO\IOInterface;
 use Composer\Package\AliasPackage;
 use Composer\Package\PackageInterface;
@@ -551,6 +550,10 @@ private function getPHPCodeSnifferPackage($versionConstraint = null)
     /**
      * Returns the path to the PHP_CodeSniffer package installation location
      *
+     * {@internal Do NOT try to modernize via the Composer 2.2 API (`InstalledVersions::getInstallPath()`).
+     * Doing so doesn't play nice with other plugins.
+     * {@link https://github.com/PHPCSStandards/composer-installer/issues/239}}
+     *
      * @return string
      */
     private function getPHPCodeSnifferInstallPath()
@@ -561,16 +564,16 @@ private function getPHPCodeSnifferInstallPath()
     /**
      * Simple check if PHP_CodeSniffer is installed.
      *
+     * {@internal Do NOT try to modernize via the Composer 2.2 API (`InstalledVersions::isInstalled()`).
+     * Doing so doesn't play nice with integrations calling the Composer EventDispatcher programmatically.
+     * {@link https://github.com/PHPCSStandards/composer-installer/issues/247}}
+     *
      * @param null|string|\Composer\Semver\Constraint\ConstraintInterface $versionConstraint to match against
      *
      * @return bool Whether PHP_CodeSniffer is installed
      */
     private function isPHPCodeSnifferInstalled($versionConstraint = null)
     {
-        if ($versionConstraint === null) {
-            return InstalledVersions::isInstalled(self::PACKAGE_NAME);
-        }
-
         return ($this->getPHPCodeSnifferPackage($versionConstraint) !== null);
     }