src/Composer/Downloader/DownloadManager.php
protected function resolvePackageInstallPreference(PackageInterface $package)
    {
        foreach ($this->packagePreferences as $pattern => $preference) {
            $pattern = '{^'.str_replace('\\*', '.*', preg_quote($pattern)).'$}i';
            if (preg_match($pattern, $package->getName())) {
                if ('dist' === $preference || (!$package->isDev() && 'auto' === $preference)) {
                    return 'dist';
                }

                return 'source';
            }
        }

        return $package->isDev() ? 'source' : 'dist';
    }
protected function resolvePackageInstallPreference(PackageInterface $package)
    {
        foreach ($this->packagePreferences as $pattern => $preference) {
            $pattern = '{^'.str_replace('\\*', '.*', preg_quote($pattern)).'$}i';
            if (preg_match($pattern, $package->getName())) {
                if ('dist' === $preference || (!$package->isDev() && 'auto' === $preference)) {
                    return 'dist';
                }

                return 'source';
            }
        }

        return $package->isDev() ? 'source' : 'dist';
    }
Determines the install preference of a package

@param PackageInterface $package package instance

@return string