Improved the error message for "-dev" versions

Author: javiereguiluz

src/Symfony/Installer/NewCommand.php

@@ -113,7 +113,7 @@ protected function checkSymfonyVersionIsInstallable()
 
         // validate semver syntax
         if (!preg_match('/^2\.\d(?:\.\d{1,2})?(-(dev|BETA)\d*)?$/', $this->version)) {
-            throw new \RuntimeException('The Symfony version should be 2.N or 2.N.M, where N = 0..9 and M = 0..99.');
+            throw new \RuntimeException('The Symfony version should be 2.N or 2.N.M, where N = 0..9 and M = 0..99. The special "-dev" or "-BETA" suffixes are also supported.');
         }
 
         if (preg_match('/^2\.\d$/', $this->version)) {
@@ -171,8 +171,20 @@ protected function checkSymfonyVersionIsInstallable()
             ));
         }
 
+        // "-dev" versions are not supported because Symfony doesn't provide packages for them
+        if (preg_match('/^.*\-dev$/', $this->version)) {
+            throw new \RuntimeException(sprintf(
+                "The selected version (%s) cannot be installed because it hasn't\n".
+                "been published as a package yet. Read the following article for\n".
+                "an alternative installation method:\n\n".
+                "> How to Install or Upgrade to the Latest, Unreleased Symfony Version\n".
+                "> http://symfony.com/doc/current/cookbook/install/unstable_versions.html",
+                $this->version
+            ));
+        }
+
         // warn the user when downloading an unstable version
-        if (preg_match('/^.*\-(dev|BETA)\d*$/', $this->version)) {
+        if (preg_match('/^.*\-BETA\d*$/', $this->version)) {
             $this->output->writeln("\n <bg=red> WARNING </> You are downloading an unstable Symfony version.");
         }