Optional Scalars support for Rust (#6034)

* First draft of rust optionals

* Code cleanup around ftBool and ftVectorOfBool

* Tests for Rust optional scalars

* test bools too

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

tests/rust_usage_test/Cargo.toml

@@ -1,7 +1,9 @@
 [package]
 name = "rust_usage_test"
 version = "0.1.0"
-authors = ["Robert Winslow <hello@rwinslow.com>", "FlatBuffers Maintainers"]
+authors = ["Robert Winslow <hello@rwinslow.com>",
+           "Casper Neo <cneo@google.com>",
+           "FlatBuffers Maintainers"]
 
 [dependencies]
 flatbuffers = { path = "../../rust/flatbuffers" }

tests/rust_usage_test/tests/integration_test.rs

@@ -27,6 +27,7 @@ extern crate serde_derive;
 extern crate quickcheck_derive;
 
 mod flexbuffers_tests;
+mod optional_scalars_test;
 
 #[allow(dead_code, unused_imports)]
 #[path = "../../include_test/include_test1_generated.rs"]
@@ -41,6 +42,10 @@ pub mod include_test2_generated;
 mod monster_test_generated;
 pub use monster_test_generated::my_game;
 
+#[allow(dead_code, unused_imports)]
+#[path = "../../optional_scalars_generated.rs"]
+mod optional_scalars_generated;
+
 #[rustfmt::skip] // TODO: Use standard rust formatting and remove dead code.
 #[allow(dead_code)]
 mod flatbuffers_tests {

tests/rust_usage_test/tests/optional_scalars_test.rs

@@ -0,0 +1,52 @@
+#[allow(dead_code, unused_imports)]
+#[path = "../../optional_scalars_generated.rs"]
+mod optional_scalars_generated;
+use crate::optional_scalars_generated::optional_scalars::*;
+
+// There are 3 variants of scalars in tables - those specified with default=42,
+// optional scalars, and those with nothing specified (implicitly default=0).
+// This tests that you can read what you write.
+macro_rules! make_test {
+    (
+        $test_name: ident,
+        $just: ident, $default: ident, $maybe: ident,
+        $five: expr, $zero: expr, $fortytwo: expr
+    ) => {
+        #[test]
+        fn $test_name() {
+            let mut builder = flatbuffers::FlatBufferBuilder::new();
+            // Test five makes sense when specified.
+            let ss = ScalarStuff::create(&mut builder, &ScalarStuffArgs {
+                $just: $five,
+                $default: $five,
+                $maybe: Some($five),
+                ..Default::default()
+            });
+            builder.finish(ss, None);
+
+            let s = flatbuffers::get_root::<ScalarStuff>(builder.finished_data());
+            assert_eq!(s.$just(), $five);
+            assert_eq!(s.$default(), $five);
+            assert_eq!(s.$maybe(), Some($five));
+
+            // Test defaults are used when not specified.
+            let s = flatbuffers::get_root::<ScalarStuff>(&[0; 8]);
+            assert_eq!(s.$just(), $zero);
+            assert_eq!(s.$default(), $fortytwo);
+            assert_eq!(s.$maybe(), None);
+        }
+
+    };
+}
+
+make_test!(optional_i8, just_i8, default_i8, maybe_i8, 5, 0, 42);
+make_test!(optional_u8, just_u8, default_u8, maybe_u8, 5, 0, 42);
+make_test!(optional_i16, just_i16, default_i16, maybe_i16, 5, 0, 42);
+make_test!(optional_u16, just_u16, default_u16, maybe_u16, 5, 0, 42);
+make_test!(optional_i32, just_i32, default_i32, maybe_i32, 5, 0, 42);
+make_test!(optional_u32, just_u32, default_u32, maybe_u32, 5, 0, 42);
+make_test!(optional_i64, just_i64, default_i64, maybe_i64, 5, 0, 42);
+make_test!(optional_u64, just_u64, default_u64, maybe_u64, 5, 0, 42);
+make_test!(optional_f32, just_f32, default_f32, maybe_f32, 5.0, 0.0, 42.0);
+make_test!(optional_f64, just_f64, default_f64, maybe_f64, 5.0, 0.0, 42.0);
+make_test!(optional_bool, just_bool, default_bool, maybe_bool, true, false, true);