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Documents that `BikeshedIntrinsicFrom` models transmute-via-union, which is slightly more expressive than the transmute-via-cast implemented by `transmute_copy`. Additionally, we provide an implementation of transmute-via-union as a method on the `BikeshedIntrinsicFrom` trait with additional documentation on the boundary between trait invariants and caller obligations. Whether or not transmute-via-union is the right kind of transmute to model remains up for discussion [1]. Regardless, it seems wise to document the present behavior. [1] https://rust-lang.zulipchat.com/#narrow/stream/216762-project-safe-transmute/topic/What.20'kind'.20of.20transmute.20to.20model.3F/near/426331967
31 lines
1.5 KiB
Plaintext
31 lines
1.5 KiB
Plaintext
error[E0308]: cannot coerce intrinsics to function pointers
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--> $DIR/reify-intrinsic.rs:6:64
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LL | let _: unsafe extern "rust-intrinsic" fn(isize) -> usize = std::mem::transmute;
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| ------------------------------------------------- ^^^^^^^^^^^^^^^^^^^ cannot coerce intrinsics to function pointers
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| expected due to this
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= note: expected fn pointer `unsafe extern "rust-intrinsic" fn(isize) -> usize`
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found fn item `unsafe extern "rust-intrinsic" fn(_) -> _ {std::intrinsics::transmute::<_, _>}`
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error[E0606]: casting `unsafe extern "rust-intrinsic" fn(_) -> _ {std::intrinsics::transmute::<_, _>}` as `unsafe extern "rust-intrinsic" fn(isize) -> usize` is invalid
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--> $DIR/reify-intrinsic.rs:11:13
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LL | let _ = std::mem::transmute as unsafe extern "rust-intrinsic" fn(isize) -> usize;
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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error[E0308]: cannot coerce intrinsics to function pointers
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--> $DIR/reify-intrinsic.rs:17:9
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LL | std::intrinsics::likely,
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| ^^^^^^^^^^^^^^^^^^^^^^^ cannot coerce intrinsics to function pointers
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= note: expected fn pointer `unsafe extern "rust-intrinsic" fn(_) -> _`
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found fn item `fn(_) -> _ {likely}`
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error: aborting due to 3 previous errors
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Some errors have detailed explanations: E0308, E0606.
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For more information about an error, try `rustc --explain E0308`.
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