#![warn(clippy::transmute_ptr_to_ptr)] #![allow(clippy::borrow_as_ptr)] // Make sure we can modify lifetimes, which is one of the recommended uses // of transmute // Make sure we can do static lifetime transmutes unsafe fn transmute_lifetime_to_static<'a, T>(t: &'a T) -> &'static T { std::mem::transmute::<&'a T, &'static T>(t) } // Make sure we can do non-static lifetime transmutes unsafe fn transmute_lifetime<'a, 'b, T>(t: &'a T, u: &'b T) -> &'b T { std::mem::transmute::<&'a T, &'b T>(t) } struct LifetimeParam<'a> { s: &'a str, } struct GenericParam<T> { t: T, } fn transmute_ptr_to_ptr() { let ptr = &1u32 as *const u32; let mut_ptr = &mut 1u32 as *mut u32; unsafe { // pointer-to-pointer transmutes; bad let _: *const f32 = std::mem::transmute(ptr); let _: *mut f32 = std::mem::transmute(mut_ptr); // ref-ref transmutes; bad let _: &f32 = std::mem::transmute(&1u32); let _: &f64 = std::mem::transmute(&1f32); // ^ this test is here because both f32 and f64 are the same TypeVariant, but they are not // the same type let _: &mut f32 = std::mem::transmute(&mut 1u32); let _: &GenericParam<f32> = std::mem::transmute(&GenericParam { t: 1u32 }); } // these are recommendations for solving the above; if these lint we need to update // those suggestions let _ = ptr as *const f32; let _ = mut_ptr as *mut f32; let _ = unsafe { &*(&1u32 as *const u32 as *const f32) }; let _ = unsafe { &mut *(&mut 1u32 as *mut u32 as *mut f32) }; // transmute internal lifetimes, should not lint let s = "hello world".to_owned(); let lp = LifetimeParam { s: &s }; let _: &LifetimeParam<'static> = unsafe { std::mem::transmute(&lp) }; let _: &GenericParam<&LifetimeParam<'static>> = unsafe { std::mem::transmute(&GenericParam { t: &lp }) }; } // dereferencing raw pointers in const contexts, should not lint as it's unstable (issue 5959) const _: &() = { struct Zst; let zst = &Zst; unsafe { std::mem::transmute::<&'static Zst, &'static ()>(zst) } }; fn main() {}