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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: #132922
29 lines
964 B
Plaintext
29 lines
964 B
Plaintext
error[E0200]: the trait `Copy` requires an `unsafe impl` declaration
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--> $DIR/copy-trait.rs:21:5
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LL | impl Copy for UnsafeEnum {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^
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= 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`
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help: add `unsafe` to this trait implementation
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LL | unsafe impl Copy for UnsafeEnum {}
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| ++++++
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error[E0199]: implementing the trait `Copy` is not unsafe
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--> $DIR/copy-trait.rs:39:5
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LL | unsafe impl Copy for SafeEnum {}
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| ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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help: remove `unsafe` from this trait implementation
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LL - unsafe impl Copy for SafeEnum {}
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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.
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For more information about an error, try `rustc --explain E0199`.
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