refactor: add back Intertrait tests & Rc support

1 files changed, 224 insertions, 23 deletions

diff --git a/src/libs/intertrait/mod.rs b/src/libs/intertrait/mod.rs
index 2cdc67d..a8d912b 100644
--- a/src/libs/intertrait/mod.rs
+++ b/src/libs/intertrait/mod.rs
@@ -1,33 +1,52 @@
-/**
- * Originally from Intertrait by CodeChain
- *
- * <https://github.com/CodeChain-io/intertrait>
- * <https://crates.io/crates/intertrait/0.2.2>
- *
- * Licensed under either of
- *
- * Apache License, Version 2.0 (LICENSE-APACHE or <http://www.apache.org/licenses/LICENSE-2.0>)
- * MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
-
- * at your option.
-*/
+#![allow(clippy::module_name_repetitions)]
+
+//! A library providing direct casting among trait objects implemented by a type.
+//!
+//! In Rust, an object of a sub-trait of [`Any`] can be downcast to a concrete type
+//! at runtime if the type is known. But no direct casting between two trait objects
+//! (i.e. without involving the concrete type of the backing value) is possible
+//! (even no coercion from a trait object to that of its super-trait yet).
+//!
+//! With this crate, any trait object with [`CastFrom`] as its super-trait can be cast directly
+//! to another trait object implemented by the underlying type if the target traits are
+//! registered beforehand with the macros provided by this crate.
+//!
+//!
+//! Originally from Intertrait by CodeChain
+//!
+//! <https://github.com/CodeChain-io/intertrait>
+//! <https://crates.io/crates/intertrait/0.2.2>
+//!
+//! Licensed under either of
+//!
+//! Apache License, Version 2.0 (LICENSE-APACHE or <http://www.apache.org/licenses/LICENSE-2.0>)
+//! MIT license (LICENSE-MIT or <http://opensource.org/licenses/MIT>)
+//!
+//! at your option.
 use std::any::{Any, TypeId};
 use std::rc::Rc;
+use std::sync::Arc;
 
 use ahash::AHashMap;
 use linkme::distributed_slice;
 use once_cell::sync::Lazy;
 
-pub mod cast_box;
-pub mod cast_rc;
+pub mod cast;
 
 pub type BoxedCaster = Box<dyn Any + Send + Sync>;
 
-type CasterFn = fn() -> (TypeId, BoxedCaster);
-
+/// A distributed slice gathering constructor functions for [`Caster<T>`]s.
+///
+/// A constructor function returns `TypeId` of a concrete type involved in the casting
+/// and a `Box` of a trait object backed by a [`Caster<T>`].
+///
+/// [`Caster<T>`]: ./struct.Caster.html
 #[distributed_slice]
-pub static CASTERS: [CasterFn] = [..];
+pub static CASTERS: [fn() -> (TypeId, BoxedCaster)] = [..];
 
+/// A `HashMap` mapping `TypeId` of a [`Caster<T>`] to an instance of it.
+///
+/// [`Caster<T>`]: ./struct.Caster.html
 static CASTER_MAP: Lazy<AHashMap<(TypeId, TypeId), BoxedCaster>> = Lazy::new(|| {
     CASTERS
         .iter()
@@ -39,15 +58,31 @@ static CASTER_MAP: Lazy<AHashMap<(TypeId, TypeId), BoxedCaster>> = Lazy::new(||
         .collect()
 });
 
+fn cast_arc_panic<Trait: ?Sized + 'static>(_: Arc<dyn Any + Sync + Send>) -> Arc<Trait>
+{
+    panic!("Prepend [sync] to the list of target traits for Sync + Send types")
+}
+
+/// A `Caster` knows how to cast a reference to or `Box` of a trait object for `Any`
+/// to a trait object of trait `Trait`. Each `Caster` instance is specific to a concrete type.
+/// That is, it knows how to cast to single specific trait implemented by single specific type.
+///
+/// An implementation of a trait for a concrete type doesn't need to manually provide
+/// a `Caster`. Instead attach `#[cast_to]` to the `impl` block.
+#[doc(hidden)]
 pub struct Caster<Trait: ?Sized + 'static>
 {
     /// Casts a `Box` holding a trait object for `Any` to another `Box` holding a trait object
-    /// for `Trait`.
+    /// for trait `Trait`.
     pub cast_box: fn(from: Box<dyn Any>) -> Box<Trait>,
 
     /// Casts an `Rc` holding a trait object for `Any` to another `Rc` holding a trait object
-    /// for `Trait`.
+    /// for trait `Trait`.
     pub cast_rc: fn(from: Rc<dyn Any>) -> Rc<Trait>,
+
+    /// Casts an `Arc` holding a trait object for `Any + Sync + Send + 'static`
+    /// to another `Arc` holding a trait object for trait `Trait`.
+    pub cast_arc: fn(from: Arc<dyn Any + Sync + Send + 'static>) -> Arc<Trait>,
 }
 
 impl<Trait: ?Sized + 'static> Caster<Trait>
@@ -57,12 +92,29 @@ impl<Trait: ?Sized + 'static> Caster<Trait>
         cast_rc: fn(from: Rc<dyn Any>) -> Rc<Trait>,
     ) -> Caster<Trait>
     {
-        Caster::<Trait> { cast_box, cast_rc }
+        Caster::<Trait> {
+            cast_box,
+            cast_rc,
+            cast_arc: cast_arc_panic,
+        }
+    }
+
+    #[allow(clippy::similar_names)]
+    pub fn new_sync(
+        cast_box: fn(from: Box<dyn Any>) -> Box<Trait>,
+        cast_rc: fn(from: Rc<dyn Any>) -> Rc<Trait>,
+        cast_arc: fn(from: Arc<dyn Any + Sync + Send>) -> Arc<Trait>,
+    ) -> Caster<Trait>
+    {
+        Caster::<Trait> {
+            cast_box,
+            cast_rc,
+            cast_arc,
+        }
     }
 }
 
-/// Returns a `Caster<Implementation, Trait>` from a concrete type `Implementation`
-/// from inside `CASTER_MAP` to a `Trait` implemented by it.
+/// Returns a `Caster<S, Trait>` from a concrete type `S` to a trait `Trait` implemented by it.
 fn caster<Trait: ?Sized + 'static>(type_id: TypeId) -> Option<&'static Caster<Trait>>
 {
     CASTER_MAP
@@ -90,6 +142,24 @@ pub trait CastFrom: Any + 'static
     fn rc_any(self: Rc<Self>) -> Rc<dyn Any>;
 }
 
+/// `CastFromSync` must be extended by a trait that is `Any + Sync + Send + 'static`
+/// and wants to allow for casting into another trait behind references and smart pointers
+/// especially including `Arc`.
+///
+/// It is used for obtaining a trait object for [`Any + Sync + Send + 'static`] from an object
+/// for its sub-trait, and blanket implemented for all `Sized + Sync + Send + 'static` types.
+///
+/// # Examples
+/// ```ignore
+/// trait Source: CastFromSync {
+///     ...
+/// }
+/// ```
+pub trait CastFromSync: CastFrom + Sync + Send + 'static
+{
+    fn arc_any(self: Arc<Self>) -> Arc<dyn Any + Sync + Send + 'static>;
+}
+
 impl<Trait: Sized + Any + 'static> CastFrom for Trait
 {
     fn box_any(self: Box<Self>) -> Box<dyn Any>
@@ -116,6 +186,14 @@ impl CastFrom for dyn Any + 'static
     }
 }
 
+impl<Trait: Sized + Sync + Send + 'static> CastFromSync for Trait
+{
+    fn arc_any(self: Arc<Self>) -> Arc<dyn Any + Sync + Send + 'static>
+    {
+        self
+    }
+}
+
 impl CastFrom for dyn Any + Sync + Send + 'static
 {
     fn box_any(self: Box<Self>) -> Box<dyn Any>
@@ -128,3 +206,126 @@ impl CastFrom for dyn Any + Sync + Send + 'static
         self
     }
 }
+
+impl CastFromSync for dyn Any + Sync + Send + 'static
+{
+    fn arc_any(self: Arc<Self>) -> Arc<dyn Any + Sync + Send + 'static>
+    {
+        self
+    }
+}
+
+#[cfg(test)]
+mod tests
+{
+    use std::any::{Any, TypeId};
+    use std::fmt::{Debug, Display};
+
+    use linkme::distributed_slice;
+
+    #[allow(clippy::wildcard_imports)]
+    use super::cast::*;
+    use super::*;
+
+    #[distributed_slice(super::CASTERS)]
+    static TEST_CASTER: fn() -> (TypeId, BoxedCaster) = create_test_caster;
+
+    #[derive(Debug)]
+    struct TestStruct;
+
+    trait SourceTrait: CastFromSync {}
+
+    impl SourceTrait for TestStruct {}
+
+    fn create_test_caster() -> (TypeId, BoxedCaster)
+    {
+        let type_id = TypeId::of::<TestStruct>();
+        let caster = Box::new(Caster::<dyn Debug> {
+            cast_box: |from| from.downcast::<TestStruct>().unwrap(),
+            cast_rc: |from| from.downcast::<TestStruct>().unwrap(),
+            cast_arc: |from| from.downcast::<TestStruct>().unwrap(),
+        });
+        (type_id, caster)
+    }
+
+    #[test]
+    fn cast_box()
+    {
+        let ts = Box::new(TestStruct);
+        let st: Box<dyn SourceTrait> = ts;
+        let debug = st.cast::<dyn Debug>();
+        assert!(debug.is_ok());
+    }
+
+    #[test]
+    fn cast_rc()
+    {
+        let ts = Rc::new(TestStruct);
+        let st: Rc<dyn SourceTrait> = ts;
+        let debug = st.cast::<dyn Debug>();
+        assert!(debug.is_ok());
+    }
+
+    #[test]
+    fn cast_arc()
+    {
+        let ts = Arc::new(TestStruct);
+        let st: Arc<dyn SourceTrait> = ts;
+        let debug = st.cast::<dyn Debug>();
+        assert!(debug.is_ok());
+    }
+
+    #[test]
+    fn cast_box_wrong()
+    {
+        let ts = Box::new(TestStruct);
+        let st: Box<dyn SourceTrait> = ts;
+        let display = st.cast::<dyn Display>();
+        assert!(display.is_err());
+    }
+
+    #[test]
+    fn cast_rc_wrong()
+    {
+        let ts = Rc::new(TestStruct);
+        let st: Rc<dyn SourceTrait> = ts;
+        let display = st.cast::<dyn Display>();
+        assert!(display.is_err());
+    }
+
+    #[test]
+    fn cast_arc_wrong()
+    {
+        let ts = Arc::new(TestStruct);
+        let st: Arc<dyn SourceTrait> = ts;
+        let display = st.cast::<dyn Display>();
+        assert!(display.is_err());
+    }
+
+    #[test]
+    fn cast_box_from_any()
+    {
+        let ts = Box::new(TestStruct);
+        let st: Box<dyn Any> = ts;
+        let debug = st.cast::<dyn Debug>();
+        assert!(debug.is_ok());
+    }
+
+    #[test]
+    fn cast_rc_from_any()
+    {
+        let ts = Rc::new(TestStruct);
+        let st: Rc<dyn Any> = ts;
+        let debug = st.cast::<dyn Debug>();
+        assert!(debug.is_ok());
+    }
+
+    #[test]
+    fn cast_arc_from_any()
+    {
+        let ts = Arc::new(TestStruct);
+        let st: Arc<dyn Any + Send + Sync> = ts;
+        let debug = st.cast::<dyn Debug>();
+        assert!(debug.is_ok());
+    }
+}