Handle optional fields correctly in Message_get method (#18982)

Refactor the Message_get method to accurately handle optional fields with presence checks by returning NULL if the field is not set. Also, add new unit tests in WellKnownTest.php to ensure correct behavior of reflection properties for optional fields with various data types.

should fix https://github.com/protocolbuffers/protobuf/issues/18966

Closes #18982

COPYBARA_INTEGRATE_REVIEW=https://github.com/protocolbuffers/protobuf/pull/18982 from s2x:fix-property-reflection-values 9d7030bfb5
PiperOrigin-RevId: 701986724

php/ext/google/protobuf/message.c

@@ -312,7 +312,13 @@ static zval* Message_read_property(zend_object* obj, zend_string* member,
   const upb_FieldDef* f = get_field(intern, member);
 
   if (!f) return &EG(uninitialized_zval);
-  Message_get(intern, f, rv);
+
+  if (upb_FieldDef_IsOptional(f) && upb_FieldDef_HasPresence(f) &&
+      Message_has_property(obj, member, 0, cache_slot) == false) {
+    ZVAL_NULL(rv);
+  } else {
+    Message_get(intern, f, rv);
+  }
   return rv;
 }
 

php/tests/WellKnownTest.php

@@ -416,4 +416,44 @@ class WellKnownTest extends TestBase {
             ['\Google\Protobuf\Syntax'],
         ];
     }
+
+    /**
+     * @dataProvider optionalFieldsDataProvider
+     */
+    public function testReflectionProperty($property, $default)
+    {
+        $testMessage = new TestMessage();
+
+        $functionName = implode('', array_map('ucwords', explode('_', $property)));
+
+        $reflectionProperty = new \ReflectionProperty($testMessage, $property);
+
+        self::assertFalse(call_user_func([$testMessage, 'has'.$functionName]));
+        self::assertEquals($default, call_user_func([$testMessage, 'get'.$functionName]));
+        self::assertNull($reflectionProperty->getValue($testMessage));
+    }
+
+    public function optionalFieldsDataProvider()
+    {
+        return [
+            ['true_optional_int32', 0],
+            ['true_optional_int64', 0],
+            ['true_optional_uint32', 0],
+            ['true_optional_uint64', 0],
+            ['true_optional_sint32', 0],
+            ['true_optional_sint64', 0],
+            ['true_optional_fixed32', 0],
+            ['true_optional_fixed64', 0],
+            ['true_optional_sfixed32', 0],
+            ['true_optional_sfixed64', 0],
+            ['true_optional_float', 0.0],
+            ['true_optional_double', 0.0],
+            ['true_optional_bool', false],
+            ['true_optional_string', ''],
+            ['true_optional_bytes', ''],
+            ['true_optional_enum', null],
+            ['true_optional_message', null],
+            ['true_optional_included_message', null],
+        ];
+    }
 }