3eaa785daa
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 entail `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 r? ```@compiler-errors``` |
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