Implement derive macro for ToVariant and FromVariant

The macro does the following mapping between Rust structures and Godot types:

- `Newtype(inner)` are mapped to `inner`
- `Tuple(a, b, c)` are mapped to `[a, b, c]`
- `Struct { a, b, c }` are mapped to `{ "a": a, "b": b, "c": c }`
- `Unit` are mapped to `{}`
- `Enum::Variant(a, b, c)` are mapped to `{ "Variant": [a, b, c] }`

Author: toasteater

gdnative-core/src/variant.rs

@@ -688,6 +688,25 @@ godot_test!(
         assert!(v_m1.try_to_f64().is_none());
         assert!(v_m1.try_to_array().is_none());
     }
+
+    test_variant_bool {
+        let v_true = Variant::from_bool(true);
+        assert_eq!(v_true.get_type(), VariantType::Bool);
+
+        assert!(!v_true.is_nil());
+        assert_eq!(v_true.try_to_bool(), Some(true));
+        assert!(v_true.try_to_f64().is_none());
+        assert!(v_true.try_to_array().is_none());
+
+        let v_false = Variant::from_bool(false);
+        assert_eq!(v_false.get_type(), VariantType::Bool);
+
+        assert!(!v_false.is_nil());
+        assert_eq!(v_false.try_to_bool(), Some(false));
+        assert!(v_false.try_to_f64().is_none());
+        assert!(v_false.try_to_array().is_none());
+
+    }
 );
 
 /// Types that can be converted to a `Variant`.

gdnative-derive/Cargo.toml

@@ -15,3 +15,4 @@ proc-macro = true
 [dependencies]
 syn = { version = "0.15.29", features = ["full", "extra-traits"] }
 quote = "0.6.11"
+proc-macro2 = "^0.4.4"