Convert integer to string if field is string field in json

json_decode automatically convert numeric string to integer, so that
we need to convert it back. However, this will suceed to parse invalid
json data with string field set as integer even though it should have failed.
Because, the failure case is less often than the succeeding case, we decided
to make this change. Users should make sure their data don't use integer for
string fields by themselves.

conformance/failure_list_php.txt

@@ -13,6 +13,8 @@ Required.Proto3.JsonInput.FloatFieldTooSmall
 Required.Proto3.JsonInput.DoubleFieldTooSmall
 Required.Proto3.JsonInput.Int32FieldNotInteger
 Required.Proto3.JsonInput.Int64FieldNotInteger
+Required.Proto3.JsonInput.RepeatedFieldWrongElementTypeExpectingStringsGotInt
+Required.Proto3.JsonInput.StringFieldNotAString
 Required.Proto3.JsonInput.Uint32FieldNotInteger
 Required.Proto3.JsonInput.Uint64FieldNotInteger
 Required.Proto3.JsonInput.Int32FieldLeadingSpace

php/src/Google/Protobuf/Internal/Message.php

@@ -832,6 +832,9 @@ class Message
                 if (is_null($value)) {
                     return $this->defaultValue($field);
                 }
+                if (is_numeric($value)) {
+                    return strval($value);
+                }
                 if (!is_string($value)) {
                     throw new GPBDecodeException(
                         "String field only accepts string value");

php/tests/encode_decode_test.php

@@ -1148,4 +1148,14 @@ class EncodeDecodeTest extends TestBase
                           $m->serializeToJsonString());
     }
 
+    public function testJsonDecodeNumericStringMapKey()
+    {
+        $m = new TestMessage();
+        $m->getMapStringString()["1"] = "1";
+        $data = $m->serializeToJsonString();
+        $this->assertSame("{\"mapStringString\":{\"1\":\"1\"}}", $data);
+        $n = new TestMessage();
+        $n->mergeFromJsonString($data);
+    }
+
 }