Eliminate safety issue in Resource::downcast*

- The previous implementation uses `mopa`, which has a known safety issue: chris-morgan/mopa#13 - This commit essentially inlines the code generated by the `mopafy!` macro provided by `mopa`, thus removing the dependency - Since `mopa::Any` was part of the public interface of the `Resource` trait, this is technically a breaking change Fixes #217
amethyst · Jul 10, 2022 · 2984837 · 2984837
1 parent 46314c2
commit 2984837
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diff --git a/Cargo.toml b/Cargo.toml
@@ -22,7 +22,6 @@ travis-ci = { repository = "amethyst/shred" }
 [dependencies]
 arrayvec = "0.7.2"
 hashbrown = "0.12"
-mopa = "0.2.2"
 rayon = { version = "1.5.0", optional = true }
 shred-derive = { path = "shred-derive", version = "0.6.3", optional = true }
 smallvec = "1.6.1"

diff --git a/src/meta.rs b/src/meta.rs
@@ -1,7 +1,6 @@
 use std::{any::TypeId, marker::PhantomData};
 
 use hashbrown::HashMap;
-use mopa::Any;
 
 use crate::{Resource, ResourceId, World};
 
@@ -291,7 +290,7 @@ impl<T: ?Sized> MetaTable<T> {
     pub fn get<'a>(&self, res: &'a dyn Resource) -> Option<&'a T> {
         unsafe {
             self.indices
-                .get(&Any::get_type_id(res))
+                .get(&res.type_id())
                 .map(move |&ind| &*self.fat[ind].create_ptr(res as *const _ as *const ()))
         }
     }
@@ -301,7 +300,7 @@ impl<T: ?Sized> MetaTable<T> {
     /// registered), this will return `None`.
     pub fn get_mut<'a>(&self, res: &'a dyn Resource) -> Option<&'a mut T> {
         unsafe {
-            self.indices.get(&Any::get_type_id(res)).map(move |&ind| {
+            self.indices.get(&res.type_id()).map(move |&ind| {
                 &mut *(self.fat[ind].create_ptr::<T>(res as *const _ as *const ()) as *mut T)
             })
         }

diff --git a/src/world/mod.rs b/src/world/mod.rs
@@ -7,13 +7,12 @@ pub use self::{
 };
 
 use std::{
-    any::TypeId,
+    any::{Any, TypeId},
     marker::PhantomData,
     ops::{Deref, DerefMut},
 };
 
 use hashbrown::HashMap;
-use mopa::Any;
 
 use crate::{
     cell::{Ref, RefMut, TrustCell},
@@ -24,6 +23,7 @@ use self::entry::create_entry;
 
 mod data;
 mod entry;
+mod res_downcast;
 #[macro_use]
 mod setup;
 
@@ -104,16 +104,6 @@ pub trait Resource: Any + Send + Sync + 'static {}
 #[cfg(not(feature = "parallel"))]
 pub trait Resource: Any + 'static {}
 
-mod __resource_mopafy_scope {
-    #![allow(clippy::all)]
-
-    use mopa::mopafy;
-
-    use super::Resource;
-
-    mopafy!(Resource);
-}
-
 #[cfg(feature = "parallel")]
 impl<T> Resource for T where T: Any + Send + Sync {}
 #[cfg(not(feature = "parallel"))]

diff --git a/src/world/res_downcast/COPYRIGHT b/src/world/res_downcast/COPYRIGHT
@@ -0,0 +1,4 @@
+
+This project is dual-licensed under the terms of the MIT and Apache (version 2.0) licenses.
+
+Copyright (c) 2014 Chris Morgan and The Rust Project Developers
diff --git a/src/world/res_downcast/LICENSE-APACHE b/src/world/res_downcast/LICENSE-APACHE
@@ -0,0 +1,201 @@
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diff --git a/src/world/res_downcast/LICENSE-MIT b/src/world/res_downcast/LICENSE-MIT
@@ -0,0 +1,25 @@
+Copyright (c) 2014 Chris Morgan and The Rust Project Developers
+
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
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diff --git a/src/world/res_downcast/mod.rs b/src/world/res_downcast/mod.rs
@@ -0,0 +1,75 @@
+//! Code is based on https://github.com/chris-morgan/mopa
+//! with the macro inlined for `Resource`. License files can be found in the
+//! directory of this source file, see COPYRIGHT, LICENSE-APACHE and
+//! LICENSE-MIT.
+
+#[cfg(test)]
+mod tests;
+
+use std::any::TypeId;
+
+use crate::Resource;
+
+impl dyn Resource {
+    /// Returns the boxed value if it is of type `T`, or `Err(Self)` if it
+    /// isn't.
+    #[inline]
+    pub fn downcast<T: Resource>(self: Box<Self>) -> Result<Box<T>, Box<Self>> {
+        if self.is::<T>() {
+            unsafe { Ok(self.downcast_unchecked()) }
+        } else {
+            Err(self)
+        }
+    }
+
+    /// Returns the boxed value, blindly assuming it to be of type `T`.
+    /// If you are not *absolutely certain* of `T`, you *must not* call this.
+    #[inline]
+    pub unsafe fn downcast_unchecked<T: Resource>(self: Box<Self>) -> Box<T> {
+        Box::from_raw(Box::into_raw(self) as *mut T)
+    }
+
+    /// Returns true if the boxed type is the same as `T`
+    #[inline]
+    pub fn is<T: Resource>(&self) -> bool {
+        TypeId::of::<T>() == self.type_id()
+    }
+
+    /// Returns some reference to the boxed value if it is of type `T`, or
+    /// `None` if it isn't.
+    #[inline]
+    pub fn downcast_ref<T: Resource>(&self) -> Option<&T> {
+        if self.is::<T>() {
+            unsafe { Some(self.downcast_ref_unchecked()) }
+        } else {
+            Option::None
+        }
+    }
+
+    /// Returns a reference to the boxed value, blindly assuming it to be of
+    /// type `T`. If you are not *absolutely certain* of `T`, you *must not*
+    /// call this.
+    #[inline]
+    pub unsafe fn downcast_ref_unchecked<T: Resource>(&self) -> &T {
+        &*(self as *const Self as *const T)
+    }
+
+    /// Returns some mutable reference to the boxed value if it is of type `T`,
+    /// or `None` if it isn't.
+    #[inline]
+    pub fn downcast_mut<T: Resource>(&mut self) -> Option<&mut T> {
+        if self.is::<T>() {
+            unsafe { Some(self.downcast_mut_unchecked()) }
+        } else {
+            Option::None
+        }
+    }
+
+    /// Returns a mutable reference to the boxed value, blindly assuming it to
+    /// be of type `T`. If you are not *absolutely certain* of `T`, you
+    /// *must not* call this.
+    #[inline]
+    pub unsafe fn downcast_mut_unchecked<T: Resource>(&mut self) -> &mut T {
+        &mut *(self as *mut Self as *mut T)
+    }
+}