rspec/rules/S7461/rust/rule.adoc

== Why is this an issue?

When a type implements `Borrow<T>`, it should provide consistent behavior between the borrowed and owned values, especially regarding `Eq`, `Ord`, and `Hash`. However, `str` and `[u8]` have different Hash implementations, leading to inconsistent hash values for the same underlying data when accessed through different Borrow implementations. This violates the principle that `hash(x) == hash((x as Borrow<[u8]>).borrow()) == hash((x as Borrow<str>).borrow())` must hold, and can cause issues with hash-based collections and comparisons.

=== Code examples

==== Noncompliant code example

[source,rust]
----
use std::borrow::Borrow;
use std::hash::{Hash, Hasher};

struct ExampleType {
    data: String,
}

impl Hash for ExampleType {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.data.hash(state); // Noncompliant: Inconsistent Hash
    }
}

impl Borrow<str> for ExampleType {
    fn borrow(&self) -> &str {
        &self.data
    }
}

impl Borrow<[u8]> for ExampleType {
    fn borrow(&self) -> &[u8] {
        self.data.as_bytes()
    }
}
----

== Resources
=== Documentation

* Clippy Lints - https://rust-lang.github.io/rust-clippy/master/index.html#impl_hash_borrow_with_str_and_bytes