Allow setting default transport strategy for path repositories

This change allows setting COMPOSER_MIRROR_PATH_REPOS to 1
in the environment to set the default strategy to 'mirror'.

This allows using 'mirror' during deployments while still symlinking
on a development machine. The default is still overwritten by the
options on the repository configuration.

doc/03-cli.md

@@ -868,4 +868,10 @@ If set to 1, this env disables the warning about running commands as root/super
 It also disables automatic clearing of sudo sessions, so you should really only set this
 if you use Composer as super user at all times like in docker containers.
 
+### COMPOSER_MIRROR_PATH_REPOS
+
+If set to 1, this env changes the default path repository strategy to `mirror` instead
+of `symlink`. As it is the default strategy being set it can still be overwritten by
+repository options.
+
 ← [Libraries](02-libraries.md)  |  [Schema](04-schema.md) →

src/Composer/Downloader/PathDownloader.php

@@ -59,6 +59,11 @@ class PathDownloader extends FileDownloader implements VcsCapableDownloaderInter
         $currentStrategy = self::STRATEGY_SYMLINK;
         $allowedStrategies = array(self::STRATEGY_SYMLINK, self::STRATEGY_MIRROR);
 
+        $mirrorPathRepos = getenv('COMPOSER_MIRROR_PATH_REPOS');
+        if (true === (bool)$mirrorPathRepos) {
+            $currentStrategy = self::STRATEGY_MIRROR;
+        }
+
         if (true === $transportOptions['symlink']) {
             $currentStrategy = self::STRATEGY_SYMLINK;
             $allowedStrategies = array(self::STRATEGY_SYMLINK);