Detect and warn JSON encoding failures, refs #3786

src/Composer/Json/JsonFile.php

@@ -184,6 +184,9 @@ class JsonFile
     {
         if (version_compare(PHP_VERSION, '5.4', '>=')) {
             $json = json_encode($data, $options);
+            if (false === $json) {
+                self::throwEncodeError(json_last_error());
+            }
 
             //  compact brackets to follow recent php versions
             if (PHP_VERSION_ID < 50428 || (PHP_VERSION_ID >= 50500 && PHP_VERSION_ID < 50512) || (defined('JSON_C_VERSION') && version_compare(phpversion('json'), '1.3.6', '<'))) {
@@ -195,6 +198,9 @@ class JsonFile
         }
 
         $json = json_encode($data);
+        if (false === $json) {
+            self::throwEncodeError(json_last_error());
+        }
 
         $prettyPrint = (bool) ($options & self::JSON_PRETTY_PRINT);
         $unescapeUnicode = (bool) ($options & self::JSON_UNESCAPED_UNICODE);
@@ -209,6 +215,28 @@ class JsonFile
         return $result;
     }
 
+    private static function throwEncodeError($code)
+    {
+        switch ($code) {
+            case JSON_ERROR_DEPTH:
+                $msg = 'Maximum stack depth exceeded';
+            break;
+            case JSON_ERROR_STATE_MISMATCH:
+                $msg = 'Underflow or the modes mismatch';
+            break;
+            case JSON_ERROR_CTRL_CHAR:
+                $msg = 'Unexpected control character found';
+            break;
+            case JSON_ERROR_UTF8:
+                $msg = 'Malformed UTF-8 characters, possibly incorrectly encoded';
+            break;
+            default:
+                $msg = 'Unknown error';
+        }
+
+        throw new \RuntimeException('JSON encoding failed: '.$msg);
+    }
+
     /**
      * Parses json string and returns hash.
      *