Reject context-dependent enum discriminants - #3631
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Derives that validate enum tags copy explicit discriminants into a helper enum. Context-dependent expressions can evaluate differently in that helper, allowing the generated validator to accept an invalid original-enum tag. Restrict copied discriminants to a compiler-defined, repeatable grammar of integer and byte literals with primitive arithmetic and bitwise operations. Reject paths, macros, calls, casts, attributes, and other context-bearing forms before emitting any unsafe impl. Preserve the skip-on-error dependency chain for exhaustive enums, including fieldful variants whose zero tag cannot be identified syntactically, and add cross-toolchain regressions. Closes #3619 *Authored by an AI agent acting on Josh Liebow-Feeser's behalf.* gherrit-pr-id: Gifjr6pbpu4fh6t7qbzuuqczj3odny3ck
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| /// When this derive needs to reproduce an enum's explicit discriminants in |
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When users apply #[derive(FromZeros)] to a non-exhaustive enum such as one with A = 0, B = CONST, or #[derive(FromBytes)] to a fieldful exhaustive enum, those entry points call derive_try_from_bytes and now reject the constant-path discriminant. However, their own Analysis sections still present representation, zero-tag, and field bounds as the complete requirements, so users consulting derive.FromZeros or derive.FromBytes will not discover this new limitation. Add the conditional discriminant grammar, including the fieldless full-domain exception, to both composite-derive sections.
AGENTS.md reference: zerocopy/AGENTS.md:L37-L38
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Derives that validate enum tags copy explicit discriminants into a helper
enum. Context-dependent expressions can evaluate differently in that helper,
allowing the generated validator to accept an invalid original-enum tag.
Restrict copied discriminants to a compiler-defined, repeatable grammar of
integer and byte literals with primitive arithmetic and bitwise operations.
Reject paths, macros, calls, casts, attributes, and other context-bearing
forms before emitting any unsafe impl. Preserve the skip-on-error dependency
chain for exhaustive enums, including fieldful variants whose zero tag cannot
be identified syntactically, and add cross-toolchain regressions.
Closes #3619
Authored by an AI agent acting on Josh Liebow-Feeser's behalf.
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git fetch origin refs/heads/Gifjr6pbpu4fh6t7qbzuuqczj3odny3ck && git checkout -b pr-Gifjr6pbpu4fh6t7qbzuuqczj3odny3ck FETCH_HEADCheckout
git fetch origin refs/heads/Gifjr6pbpu4fh6t7qbzuuqczj3odny3ck && git checkout FETCH_HEADCherry Pick
git fetch origin refs/heads/Gifjr6pbpu4fh6t7qbzuuqczj3odny3ck && git cherry-pick FETCH_HEADPull
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