diff --git a/compiler/rustc_data_structures/src/stable_hasher/tests.rs b/compiler/rustc_data_structures/src/stable_hasher/tests.rs index 391db67d29d..31190363eb6 100644 --- a/compiler/rustc_data_structures/src/stable_hasher/tests.rs +++ b/compiler/rustc_data_structures/src/stable_hasher/tests.rs @@ -98,3 +98,45 @@ fn test_hash_bit_matrix() { assert_ne!(a, b); assert_ne!(hash(&a), hash(&b)); } + +// Check that exchanging the value of two adjacent fields changes the hash. +#[test] +fn test_attribute_permutation() { + macro_rules! test_type { + ($ty: ty) => {{ + struct Foo { + a: $ty, + b: $ty, + } + + impl HashStable for Foo { + fn hash_stable(&self, hcx: &mut CTX, hasher: &mut StableHasher) { + self.a.hash_stable(hcx, hasher); + self.b.hash_stable(hcx, hasher); + } + } + + #[allow(overflowing_literals)] + let mut item = Foo { a: 0xFF, b: 0xFF_FF }; + let hash_a = hash(&item); + std::mem::swap(&mut item.a, &mut item.b); + let hash_b = hash(&item); + assert_ne!( + hash_a, + hash_b, + "The hash stayed the same after values were swapped for type `{}`!", + stringify!($ty) + ); + }}; + } + + test_type!(u16); + test_type!(u32); + test_type!(u64); + test_type!(u128); + + test_type!(i16); + test_type!(i32); + test_type!(i64); + test_type!(i128); +}