Create composer_prevent_upgrade_conflicts.rst

setup/composer_prevent_upgrade_conflicts.rst

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+
+.. index::
+ double: Composer; Conflicts
+
+How to prevent PHP conflicts during upgrades when using Composer
+================================================================
+
+Each Symfony release is guaranteed to work with a specific PHP version,
+so for example when you download and install Symfony 2.8 you are
+sure that it can work on PHP 5.4.16.
+
+When you upgrade Symfony (e.g. from 2.8.25 to 2.8.26) you must be sure that
+all the upgraded dependencies are still compatible with your own PHP version
+running in your production server (e.g. the old PHP 5.4.16).
+
+Achieving this is very simple: just remember to add such constraints in your
+``composer.json`` file located in your project root directory (my_project_name),
+so that when you will launch updates that would not be a pain. Just replace these lines::
+
+ // my_project_name/composer.json
+ "config": {
+ "bin-dir": "bin"
+ },
+
+with these::
+
+ // my_project_name/composer.json
+ "config": {
+ "bin-dir": "bin",
+ "platform": {
+ "php": "5.4.16"
+ }
+ },
+
+and enjoy your Symfony upgrades.