diff --git a/library/kani_macros/src/lib.rs b/library/kani_macros/src/lib.rs index 4e3a8d6f9f5b..6fe0979f08bc 100644 --- a/library/kani_macros/src/lib.rs +++ b/library/kani_macros/src/lib.rs @@ -103,16 +103,19 @@ pub fn unstable_feature(attr: TokenStream, item: TokenStream) -> TokenStream { /// Allow users to auto generate `Arbitrary` implementations by using /// `#[derive(Arbitrary)]` macro. /// -/// When using `#[derive(Arbitrary)]` on a struct, the `#[safety_constraint()]` -/// attribute can be added to its fields to indicate a type safety invariant -/// condition ``. Since `kani::any()` is always expected to produce -/// type-safe values, **adding `#[safety_constraint(...)]` to any fields will further -/// constrain the objects generated with `kani::any()`**. +/// ## Type safety specification with the `#[safety_constraint(...)]` attribute +/// +/// When using `#[derive(Arbitrary)]` on a struct, the +/// `#[safety_constraint()]` attribute can be added to either the struct +/// or its fields (but not both) to indicate a type safety invariant condition +/// ``. Since `kani::any()` is always expected to produce type-safe +/// values, **adding `#[safety_constraint(...)]` to the struct or any of its +/// fields will further constrain the objects generated with `kani::any()`**. /// /// For example, the `check_positive` harness in this code is expected to /// pass: /// -/// ```rs +/// ```rust /// #[derive(kani::Arbitrary)] /// struct AlwaysPositive { /// #[safety_constraint(*inner >= 0)] @@ -126,11 +129,11 @@ pub fn unstable_feature(attr: TokenStream, item: TokenStream) -> TokenStream { /// } /// ``` /// -/// Therefore, using the `#[safety_constraint(...)]` attribute can lead to vacuous +/// But using the `#[safety_constraint(...)]` attribute can lead to vacuous /// results when the values are over-constrained. For example, in this code /// the `check_positive` harness will pass too: /// -/// ```rs +/// ```rust /// #[derive(kani::Arbitrary)] /// struct AlwaysPositive { /// #[safety_constraint(*inner >= 0 && *inner < i32::MIN)] @@ -158,6 +161,45 @@ pub fn unstable_feature(attr: TokenStream, item: TokenStream) -> TokenStream { /// As usual, we recommend users to defend against these behaviors by using /// `kani::cover!(...)` checks and watching out for unreachable assertions in /// their project's code. +/// +/// ### Adding `#[safety_constraint(...)]` to the struct as opposed to its fields +/// +/// As mentioned earlier, the `#[safety_constraint(...)]` attribute can be added +/// to either the struct or its fields, but not to both. Adding the +/// `#[safety_constraint(...)]` attribute to both the struct and its fields will +/// result in an error. +/// +/// In practice, only one type of specification is need. If the condition for +/// the type safety invariant involves a relation between two or more struct +/// fields, the struct-level attribute should be used. Otherwise, using the +/// `#[safety_constraint(...)]` on field(s) is recommended since it helps with readability. +/// +/// For example, if we were defining a custom vector `MyVector` and wanted to +/// specify that the inner vector's length is always less than or equal to its +/// capacity, we should do it as follows: +/// +/// ```rust +/// #[derive(Arbitrary)] +/// #[safety_constraint(vector.len() <= *capacity)] +/// struct MyVector { +/// vector: Vec, +/// capacity: usize, +/// } +/// ``` +/// +/// However, if we were defining a struct whose fields are not related in any +/// way, we would prefer using the `#[safety_constraint(...)]` attribute on its +/// fields: +/// +/// ```rust +/// #[derive(Arbitrary)] +/// struct PositivePoint { +/// #[safety_constraint(*x >= 0)] +/// x: i32, +/// #[safety_constraint(*y >= 0)] +/// y: i32, +/// } +/// ``` #[proc_macro_error] #[proc_macro_derive(Arbitrary, attributes(safety_constraint))] pub fn derive_arbitrary(item: TokenStream) -> TokenStream { @@ -167,15 +209,19 @@ pub fn derive_arbitrary(item: TokenStream) -> TokenStream { /// Allow users to auto generate `Invariant` implementations by using /// `#[derive(Invariant)]` macro. /// -/// When using `#[derive(Invariant)]` on a struct, the `#[safety_constraint()]` -/// attribute can be added to its fields to indicate a type safety invariant -/// condition ``. This will ensure that the gets additionally checked when -/// using the `is_safe()` method generated by the `#[derive(Invariant)]` macro. +/// ## Type safety specification with the `#[safety_constraint(...)]` attribute +/// +/// When using `#[derive(Invariant)]` on a struct, the +/// `#[safety_constraint()]` attribute can be added to either the struct +/// or its fields (but not both) to indicate a type safety invariant condition +/// ``. This will ensure that the type-safety condition gets additionally +/// checked when using the `is_safe()` method automatically generated by the +/// `#[derive(Invariant)]` macro. /// /// For example, the `check_positive` harness in this code is expected to /// fail: /// -/// ```rs +/// ```rust /// #[derive(kani::Invariant)] /// struct AlwaysPositive { /// #[safety_constraint(*inner >= 0)] @@ -200,7 +246,7 @@ pub fn derive_arbitrary(item: TokenStream) -> TokenStream { /// For example, for the `AlwaysPositive` struct from above, we will generate /// the following implementation: /// -/// ```rs +/// ```rust /// impl kani::Invariant for AlwaysPositive { /// fn is_safe(&self) -> bool { /// let obj = self; @@ -212,6 +258,45 @@ pub fn derive_arbitrary(item: TokenStream) -> TokenStream { /// /// Note: the assignments to `obj` and `inner` are made so that we can treat the /// fields as if they were references. +/// +/// ### Adding `#[safety_constraint(...)]` to the struct as opposed to its fields +/// +/// As mentioned earlier, the `#[safety_constraint(...)]` attribute can be added +/// to either the struct or its fields, but not to both. Adding the +/// `#[safety_constraint(...)]` attribute to both the struct and its fields will +/// result in an error. +/// +/// In practice, only one type of specification is need. If the condition for +/// the type safety invariant involves a relation between two or more struct +/// fields, the struct-level attribute should be used. Otherwise, using the +/// `#[safety_constraint(...)]` is recommended since it helps with readability. +/// +/// For example, if we were defining a custom vector `MyVector` and wanted to +/// specify that the inner vector's length is always less than or equal to its +/// capacity, we should do it as follows: +/// +/// ```rust +/// #[derive(Invariant)] +/// #[safety_constraint(vector.len() <= *capacity)] +/// struct MyVector { +/// vector: Vec, +/// capacity: usize, +/// } +/// ``` +/// +/// However, if we were defining a struct whose fields are not related in any +/// way, we would prefer using the `#[safety_constraint(...)]` attribute on its +/// fields: +/// +/// ```rust +/// #[derive(Invariant)] +/// struct PositivePoint { +/// #[safety_constraint(*x >= 0)] +/// x: i32, +/// #[safety_constraint(*y >= 0)] +/// y: i32, +/// } +/// ``` #[proc_macro_error] #[proc_macro_derive(Invariant, attributes(safety_constraint))] pub fn derive_invariant(item: TokenStream) -> TokenStream {