Implement Rust object API defaults (#6444)

* Implment Rust object API defaults

* satisfy return analysis

* git clang format

Co-authored-by: Casper Neo <cneo@google.com>

tests/rust_usage_test/tests/integration_test.rs

@@ -115,6 +115,74 @@ fn macro_check_is_some() {
     assert!(check_is_some!(none).is_err());
 }
 
+#[test]
+fn object_api_defaults() {
+    use my_game::example::*;
+    assert_eq!(
+        Vec3T::default(), Vec3T {
+        x: 0.0,
+        y: 0.0,
+        z: 0.0,
+        test1: 0.0,
+        test2: Color::empty(),
+        test3: TestT {
+            a: 0,
+            b: 0
+        }
+    });
+    assert_eq!(
+        MonsterT::default(),
+        MonsterT {
+            pos: None,
+            hp: 100,
+            mana: 150,
+            name: String::new(),  // required string => default is empty string.
+            color: Color::Blue,
+            inventory: None,
+            testarrayoftables: None,
+            testarrayofstring: None,
+            testarrayofstring2: None,
+            testarrayofbools: None,
+            testarrayofsortedstruct: None,
+            enemy: None,
+            test: AnyT::NONE,
+            test4: None,
+            test5: None,
+            testnestedflatbuffer: None,
+            testempty: None,
+            testbool: false,
+            testhashs32_fnv1: 0,
+            testhashu32_fnv1: 0,
+            testhashs64_fnv1: 0,
+            testhashu64_fnv1: 0,
+            testhashs32_fnv1a: 0,
+            testhashu32_fnv1a: 0,
+            testhashs64_fnv1a: 0,
+            testhashu64_fnv1a: 0,
+            testf: 3.14159,
+            testf2: 3.0,
+            testf3: 0.0,
+            flex: None,
+            vector_of_longs: None,
+            vector_of_doubles: None,
+            parent_namespace_test: None,
+            vector_of_referrables: None,
+            single_weak_reference: 0,
+            vector_of_weak_references: None,
+            vector_of_strong_referrables: None,
+            co_owning_reference: 0,
+            vector_of_co_owning_references: None,
+            non_owning_reference: 0,
+            vector_of_non_owning_references: None,
+            any_unique: AnyUniqueAliasesT::NONE,
+            any_ambiguous: AnyAmbiguousAliasesT::NONE,
+            vector_of_enums: None,
+            signed_enum: Race::None,
+            testrequirednestedflatbuffer: None,  // despite the name, it is not required.
+            scalar_key_sorted_tables: None,
+        }
+    );
+}
 
 fn create_serialized_example_with_generated_code(builder: &mut flatbuffers::FlatBufferBuilder) {
     let mon = {

tests/rust_usage_test/tests/optional_scalars_test.rs

@@ -95,3 +95,55 @@ make_test!(
      OptionalByte::None,
      OptionalByte::One
 );
+
+#[test]
+fn object_api_defaults() {
+    assert_eq!(
+        ScalarStuffT::default(),
+        ScalarStuffT {
+            just_i8: 0,
+            maybe_i8: None,
+            default_i8: 42,
+            just_u8: 0,
+            maybe_u8: None,
+            default_u8: 42,
+
+            just_i16: 0,
+            maybe_i16: None,
+            default_i16: 42,
+            just_u16: 0,
+            maybe_u16: None,
+            default_u16: 42,
+
+            just_i32: 0,
+            maybe_i32: None,
+            default_i32: 42,
+            just_u32: 0,
+            maybe_u32: None,
+            default_u32: 42,
+
+            just_i64: 0,
+            maybe_i64: None,
+            default_i64: 42,
+            just_u64: 0,
+            maybe_u64: None,
+            default_u64: 42,
+
+            just_f32: 0.0,
+            maybe_f32: None,
+            default_f32: 42.0,
+            just_f64: 0.0,
+            maybe_f64: None,
+            default_f64: 42.0,
+
+            just_bool: false,
+            maybe_bool: None,
+            default_bool: true,
+
+            just_enum: OptionalByte::None,
+            maybe_enum: None,
+            default_enum: OptionalByte::One,
+
+        }
+    );
+}