Initialize well known type values (#6713)

* Initialize well known type values

Also fixes #6667

* Revert unwanted change

php/tests/encode_decode_test.php

@@ -5,6 +5,7 @@ require_once('test_util.php');
 
 use Google\Protobuf\RepeatedField;
 use Google\Protobuf\GPBType;
+use Foo\TestStringValue;
 use Foo\TestAny;
 use Foo\TestEnum;
 use Foo\TestMessage;
@@ -167,6 +168,14 @@ class EncodeDecodeTest extends TestBase
         $this->assertSame("\"a\"", $m->serializeToJsonString());
     }
 
+    public function testEncodeStringValue()
+    {
+        $m = new TestStringValue(['field' => new StringValue(['value' => ''])]);
+        var_dump($m->getField());
+        var_dump($m->serializeToJsonString());
+        $this->assertSame("{\"field\":\"\"}", $m->serializeToJsonString());
+    }
+
     public function testDecodeTopLevelBytesValue()
     {
         $m = new BytesValue();

php/tests/memory_leak_test.php

@@ -31,6 +31,7 @@ require_once('generated/Foo/TestPackedMessage.php');
 require_once('generated/Foo/TestPhpDoc.php');
 require_once('generated/Foo/TestRandomFieldOrder.php');
 require_once('generated/Foo/TestReverseFieldOrder.php');
+require_once('generated/Foo/TestStringValue.php');
 require_once('generated/Foo/TestUnpackedMessage.php');
 require_once('generated/Foo/testLowerCaseMessage.php');
 require_once('generated/Foo/testLowerCaseEnum.php');

php/tests/proto/test.proto

 syntax = "proto3";
 
 import 'google/protobuf/any.proto';
+import 'google/protobuf/wrappers.proto';
 import 'google/protobuf/struct.proto';
 import 'proto/test_include.proto';
 import 'proto/test_no_namespace.proto';
@@ -207,3 +208,7 @@ enum testLowerCaseEnum {
 message TestAny {
   google.protobuf.Any any = 1;
 }
+
+message TestStringValue {
+  google.protobuf.StringValue field = 1;
+}