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Make
Copy
unsafe to implement for ADTs with unsafe
fields
As a rule, the application of `unsafe` to a declaration requires that use-sites of that declaration also require `unsafe`. For example, a field declared `unsafe` may only be read in the lexical context of an `unsafe` block. For nearly all safe traits, the safety obligations of fields are explicitly discharged when they are mentioned in method definitions. For example, idiomatically implementing `Clone` (a safe trait) for a type with unsafe fields will require `unsafe` to clone those fields. Prior to this commit, `Copy` violated this rule. The trait is marked safe, and although it has no explicit methods, its implementation permits reads of `Self`. This commit resolves this by making `Copy` conditionally safe to implement. It remains safe to implement for ADTs without unsafe fields, but unsafe to implement for ADTs with unsafe fields. Tracking: rust-lang#132922
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,41 @@ | ||
//@ compile-flags: --crate-type=lib | ||
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#![feature(unsafe_fields)] | ||
#![allow(incomplete_features)] | ||
#![deny(missing_copy_implementations)] | ||
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mod good_safe_impl { | ||
enum SafeEnum { | ||
Safe(u8), | ||
} | ||
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impl Copy for SafeEnum {} | ||
} | ||
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mod bad_safe_impl { | ||
enum UnsafeEnum { | ||
Safe(u8), | ||
Unsafe { unsafe field: u8 }, | ||
} | ||
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impl Copy for UnsafeEnum {} | ||
//~^ ERROR the trait `Copy` requires an `unsafe impl` declaration | ||
} | ||
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mod good_unsafe_impl { | ||
enum UnsafeEnum { | ||
Safe(u8), | ||
Unsafe { unsafe field: u8 }, | ||
} | ||
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unsafe impl Copy for UnsafeEnum {} | ||
} | ||
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mod bad_unsafe_impl { | ||
enum SafeEnum { | ||
Safe(u8), | ||
} | ||
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unsafe impl Copy for SafeEnum {} | ||
//~^ ERROR implementing the trait `Copy` is not unsafe | ||
} |
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Original file line number | Diff line number | Diff line change |
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@@ -0,0 +1,28 @@ | ||
error[E0200]: the trait `Copy` requires an `unsafe impl` declaration | ||
--> $DIR/copy-trait.rs:21:5 | ||
| | ||
LL | impl Copy for UnsafeEnum {} | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | ||
= note: the trait `Copy` cannot be safely implemented for `bad_safe_impl::UnsafeEnum` because it has unsafe fields. Review the invariants of those fields before adding an `unsafe impl` | ||
help: add `unsafe` to this trait implementation | ||
| | ||
LL | unsafe impl Copy for UnsafeEnum {} | ||
| ++++++ | ||
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error[E0199]: implementing the trait `Copy` is not unsafe | ||
--> $DIR/copy-trait.rs:39:5 | ||
| | ||
LL | unsafe impl Copy for SafeEnum {} | ||
| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ | ||
| | ||
help: remove `unsafe` from this trait implementation | ||
| | ||
LL - unsafe impl Copy for SafeEnum {} | ||
LL + impl Copy for SafeEnum {} | ||
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error: aborting due to 2 previous errors | ||
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Some errors have detailed explanations: E0199, E0200. | ||
For more information about an error, try `rustc --explain E0199`. |