test it

protokt-codegen/src/main/kotlin/protokt/v1/codegen/generate/Implements.kt

@@ -63,7 +63,8 @@ internal object Implements {
 
                     interfaceFields.values.forEach {
                         require(it.returnType.isMarkedNullable) {
-                            "Delegated properties must be nullable because message types are nullable"
+                            "Delegated properties must be nullable because message types are nullable; " +
+                                "property ${it.name} is non-nullable"
                         }
                     }
                     val delegatedFields = interfaceFields.values.filter { it.name !in fieldsByName.keys }

protokt-codegen/src/test/kotlin/protokt/v1/codegen/ImplementDelegationTest.kt

@@ -0,0 +1,34 @@
+/*
+ * Copyright (c) 2023 Toast, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package protokt.v1.codegen
+
+import com.google.common.truth.Truth.assertThat
+import org.junit.jupiter.api.Test
+
+class ImplementDelegationTest : AbstractProtoktCodegenTest() {
+    @Test
+    fun `delegate to interface with non-null property`() {
+        val result = runPlugin("implement_by_delegate_with_non_null_property.proto") as Failure
+
+        assertThat(result.err)
+            .contains("Delegated properties must be nullable because message types are nullable; property id is non-nullable")
+    }
+}
+
+@Suppress("UNUSED")
+interface Model {
+    val id: String
+}

protokt-codegen/src/test/resources/implement_by_delegate_with_non_null_property.proto

@@ -0,0 +1,32 @@
+/*
+ * Copyright (c) 2023 Toast, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+syntax = "proto3";
+
+package toasttab.protokt.v1.codegen.testing;
+
+import "protokt/v1/protokt.proto";
+
+message ImplementsModel {
+  option (.protokt.v1.class).implements = "protokt.v1.codegen.Model";
+
+  string id = 1;
+}
+
+message ImplementsWithDelegate {
+  option (.protokt.v1.class).implements = "protokt.v1.codegen.Model by model";
+
+  ImplementsModel model = 1;
+}