4b3ece475d
Derive expansions for packed structs cause move errors because they prefer copying over borrowing since borrowing the fields of a packed struct can result in unaligned access and therefore undefined behaviour. This underlying cause of the errors, however, is not apparent to the user. We add a diagnostic note here to remedy that.
77 lines
3.7 KiB
Plaintext
77 lines
3.7 KiB
Plaintext
warning: byte slice in a packed struct that derives a built-in trait
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--> $DIR/deriving-with-repr-packed.rs:31:5
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LL | #[derive(Debug)]
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| ----- in this derive macro expansion
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...
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LL | data: [u8],
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| ^^^^^^^^^^
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= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
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= note: for more information, see issue #107457 <https://github.com/rust-lang/rust/issues/107457>
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= help: consider implementing the trait by hand, or remove the `packed` attribute
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= note: `#[warn(byte_slice_in_packed_struct_with_derive)]` on by default
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= note: this warning originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
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warning: string slice in a packed struct that derives a built-in trait
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--> $DIR/deriving-with-repr-packed.rs:41:5
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LL | #[derive(Debug)]
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| ----- in this derive macro expansion
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...
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LL | data: str,
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| ^^^^^^^^^
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= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
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= note: for more information, see issue #107457 <https://github.com/rust-lang/rust/issues/107457>
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= help: consider implementing the trait by hand, or remove the `packed` attribute
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= note: this warning originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
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error[E0507]: cannot move out of `self` which is behind a shared reference
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--> $DIR/deriving-with-repr-packed.rs:22:10
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LL | #[derive(Debug, Default)]
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| ----- in this derive macro expansion
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LL | #[repr(packed)]
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LL | struct X(Y);
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| ^ move occurs because `self.0` has type `Y`, which does not implement the `Copy` trait
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= note: `#[derive(Debug)]` triggers a move because taking references to the fields of a packed struct is undefined behaviour
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= note: this error originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
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error: aborting due to previous error; 2 warnings emitted
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For more information about this error, try `rustc --explain E0507`.
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Future incompatibility report: Future breakage diagnostic:
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warning: byte slice in a packed struct that derives a built-in trait
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--> $DIR/deriving-with-repr-packed.rs:31:5
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LL | #[derive(Debug)]
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| ----- in this derive macro expansion
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...
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LL | data: [u8],
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| ^^^^^^^^^^
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= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
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= note: for more information, see issue #107457 <https://github.com/rust-lang/rust/issues/107457>
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= help: consider implementing the trait by hand, or remove the `packed` attribute
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= note: `#[warn(byte_slice_in_packed_struct_with_derive)]` on by default
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= note: this warning originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
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Future breakage diagnostic:
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warning: string slice in a packed struct that derives a built-in trait
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--> $DIR/deriving-with-repr-packed.rs:41:5
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LL | #[derive(Debug)]
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| ----- in this derive macro expansion
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...
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LL | data: str,
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| ^^^^^^^^^
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= warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
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= note: for more information, see issue #107457 <https://github.com/rust-lang/rust/issues/107457>
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= help: consider implementing the trait by hand, or remove the `packed` attribute
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= note: `#[warn(byte_slice_in_packed_struct_with_derive)]` on by default
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= note: this warning originates in the derive macro `Debug` (in Nightly builds, run with -Z macro-backtrace for more info)
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