make sure php version errors are less misleading

* determine conflicting version in problem using pool package
* hide version in rule to keep it generic rather than possibly misleading

fixes #4319

src/Composer/DependencyResolver/Problem.php

@@ -87,8 +87,12 @@ class Problem
             }
 
             if ($job && $job['cmd'] === 'install' && empty($packages)) {
+
                 // handle php/hhvm
                 if ($job['packageName'] === 'php' || $job['packageName'] === 'php-64bit' || $job['packageName'] === 'hhvm') {
+                    $available = $this->pool->whatProvides($job['packageName']);
+                    $version = count($available) ? $available[0]->getPrettyVersion() : phpversion();
+
                     $msg = "\n    - This package requires ".$job['packageName'].$this->constraintToText($job['constraint']).' but ';
 
                     if (defined('HHVM_VERSION')) {
@@ -97,7 +101,7 @@ class Problem
                         return $msg . 'you are running this with PHP and not HHVM.';
                     }
 
-                    return $msg . 'your PHP version ('.  phpversion().') does not satisfy that requirement.';
+                    return $msg . 'your PHP version ('. $version .') does not satisfy that requirement.';
                 }
 
                 // handle php extensions

src/Composer/DependencyResolver/Rule.php

@@ -199,16 +199,17 @@ class Rule
                 } else {
                     $targetName = $this->reasonData->getTarget();
 
-                    // handle php extensions
                     if ($targetName === 'php' || $targetName === 'php-64bit' || $targetName === 'hhvm') {
+                        // handle php/hhvm
                         if (defined('HHVM_VERSION')) {
                             $text .= ' -> your HHVM version does not satisfy that requirement.';
                         } elseif ($targetName === 'hhvm') {
                             $text .= ' -> you are running this with PHP and not HHVM.';
                         } else {
-                            $text .= ' -> your PHP version ('.  phpversion().') does not satisfy that requirement.';
+                            $text .= ' -> your PHP version does not satisfy that requirement.';
                         }
                     } elseif (0 === strpos($targetName, 'ext-')) {
+                        // handle php extensions
                         $ext = substr($targetName, 4);
                         $error = extension_loaded($ext) ? 'has the wrong version ('.(phpversion($ext) ?: '0').') installed' : 'is missing from your system';