I dont think that XDEBUG is stopping you download this repository, that message is just a informational warning.
The real problem is with the repository you are trying to download.
However, if you want to disable XDEBUG when using the PHP CLI you can do this :-
Edit the php.ini file used by the PHP CLI which is located in `\wamp\bin\php\php\php.ini
Very near the bottom of that file you will find a line like this _version numbers may differ depending on which version of WAMPServer/PHP you are running.
[xdebug] zend_extension ="D:/wamp/bin/php/php5.4.45/zend_ext/php_xdebug-2.3.3-5.4-vc9.dll" All you need to do is add a comment character (;) to that line like this
[xdebug] ;zend_extension ="D:/wamp/bin/php/php5.4.45/zend_ext/php_xdebug-2.3.3-5.4-vc9.dll" Save the file and it will be picked up by the next execution of the composer.exe
ADDITIONAL INFO:
I just ran your example with XDEBUG configured using a WAMPServer install V3.0.0 which has PHP5.6.15 and I got this result, suggesting that your issue is not XDEBUG but something else in your PHP or `composer' configuration.
D:\php_source>composer global require "laravel/installer=~1.1" D:\php_source>echo off You are running composer with xdebug enabled. This has a major impact on runtime performance. See https://getcomposer.org/xdebug Changed current directory to D:\wamp\composer You are running composer with xdebug enabled. This has a major impact on runtime performance. See https://getcomposer.org/xdebug ./composer.json has been created Loading composer repositories with package information Updating dependencies (including require-dev) - Installing symfony/process (v2.8.0) Downloading: 100% - Installing symfony/polyfill-mbstring (v1.0.0) Downloading: 100% - Installing symfony/console (v2.8.0) Downloading: 100% - Installing guzzlehttp/promises (1.0.3) Downloading: 100% - Installing psr/http-message (1.0) Downloading: 100% - Installing guzzlehttp/psr7 (1.2.1) Downloading: 100% - Installing guzzlehttp/guzzle (6.1.1) Downloading: 100% - Installing laravel/installer (v1.2.2) Downloading: 100% symfony/console suggests installing symfony/event-dispatcher () symfony/console suggests installing psr/log (For using the console logger) Writing lock file Generating autoload files