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rhai/src/reify.rs

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Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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/// Runs `$code` if `$old` is of type `$t`.
Fix errors.
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///
/// This macro is primarily used for type casting between known types.
Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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#[macro_export]
macro_rules! reify {
($old:ident, |$new:ident : $t:ty| $code:expr, || $fallback:expr) => {{
#[allow(unused_imports)]
Fix errors.
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use std::any::Any;
Remove reify_dynamic.
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if std::any::TypeId::of::<$t>() == std::any::Any::type_id(&$old) {
Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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// SAFETY: This is safe because we check to make sure the two types are
// actually the same type.
Fix errors.
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let $new: $t = unsafe { std::mem::transmute_copy(&std::mem::ManuallyDrop::new($old)) };
Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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$code
} else {
$fallback
}
}};
($old:expr, |$new:ident : $t:ty| $code:expr, || $fallback:expr) => {{
let old = $old;
Fix errors.
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reify!(old, |$new: $t| $code, || $fallback)
Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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}};
($old:ident, |$new:ident : $t:ty| $code:expr) => {
Fix errors.
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reify!($old, |$new: $t| $code, || ())
Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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};
($old:expr, |$new:ident : $t:ty| $code:expr) => {
Fix errors.
2022-02-06 16:02:59 +01:00
reify!($old, |$new: $t| $code, || ())
Remove unsound casting functions The casting functions in `unsafe.rs` were unsound (i.e., they allowed safe code to cause undefined behavior). While they did appear to be used in a way that wouldn't cause UB the fact that there exists unsound functions is unsettling. This commit removes those functions and replaces it with a macro that performs the same reification - the difference is that the macro call will also include the checks which are required to prevent UB. A macro was chosen instead of a function for two reasons: 1. A macro can keep the same code generation whereas a function would require going through an `Option` which has negative impacts on code generation (niche values cause poor DCE). 2. There exist other `unsafe` code blocks in the crate and an attempt to make Rhai 100% safe is completely out-of-scope for this merge request, so we may as well use `unsafe` in the macro. Regarding (2) above, I may come back at a later date with a 100% safe `reify` function but only once the other `unsafe` blocks are removed. For posterity, said function would look something like: ```rust fn reify<A: Any, C>(value: A) -> Option<C> { let mut v = Some(value); let v: &mut dyn Any = &mut v; v.downcast_mut::<Option<C>>().map(Option::take) } ```
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};
}
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