Adds fluent setters for PHP (#3130)

php/tests/generated_class_test.php

@@ -877,4 +877,17 @@ class GeneratedClassTest extends TestBase
         $m = new \Foo\PBEmpty();
         $m = new \PrefixEmpty();
     }
+
+    #########################################################
+    # Test fluent setters.
+    #########################################################
+
+    public function testFluentSetters()
+    {
+        $m = (new TestMessage())
+            ->setOptionalInt32(1)
+            ->setOptionalInt64(2);
+        $this->assertSame(1, $m->getOptionalInt32());
+        $this->assertSame(2, $m->getOptionalInt64());
+    }
 }

src/google/protobuf/compiler/php/php_generator.cc

@@ -530,6 +530,8 @@ void GenerateFieldAccessor(const FieldDescriptor* field, bool is_descriptor,
         "field_name", field->name());
   }
 
+  printer->Print("\nreturn $this;\n");
+
   Outdent(printer);
 
   printer->Print(