Reduce required sym features - #144
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`DeriveInput` covers everything the macro needs (attrs, vis, ident and the variants), but unlike `ItemEnum` it doesn't require `syn`s full feature. Applying #[bitenum] to a struct or union now reports a dedicated error instead of syn's generic "expected `enum`", spanned at the struct/union keyword.
The elements are re-tokenized and fed back into parse_argument_tokens anyway, so all this needed was a split at the top-level commas. syn::ExprArray requires the "full" feature. A group with the wrong delimiter, e.g. #[bits((0..=1), rw)], now reports an error rather than panicking in the unwrap that used to be here.
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- Reject genuinely empty elements in bit-range arrays (e.g. [0..=1,, 4..=5] or [,0..=1]) with a dedicated error instead of silently ignoring them; a trailing comma remains allowed. - Give delimiter-specific error messages when bit-ranges are wrapped in the wrong delimiters (parentheses, braces) instead of a generic message.
Covers the error messages introduced when #[bitenum] started parsing its input as a DeriveInput and bit-range arrays stopped being parsed via ExprArray: - #[bitenum] on a struct or a union reports a dedicated 'can only be applied to an enum' error, and the original item is still emitted (both tests reference the item, so a regression that dropped it would add a missing-type error and fail the test). - Non-bracket delimiters (e.g. (0..=1)) or empty elements (e.g. [0..=1,, 4..=5]) in bit-range arrays are rejected with a clear message.
bitbybit now depends on syn 3, but the committed lockfile for the excluded-from-workspace qemu-tests crate still pinned syn 2.0.104, so the build-no-std CI job would silently rewrite the lockfile on every build. Regenerate it: bitbybit resolves to syn 3.0.4 while the remaining crates (defmt-macros, cortex-m-rt, ...) stay on syn 2.0.119 as a separate version.
Describe the user-visible changes of PR danlehmann#144: the syn 3 upgrade (with the dropped 'full' feature) which has no API impact, the dedicated #[bitenum] error for non-enums, and the clearer bit-range array errors that replace a proc-macro panic.
danlehmann
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Aug 27, 2026
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While checking if something needs to be changed for #143 I noticed that the big
fullfeature ofsymmostly isn't necessary.In a local test this reduced the compile time from ~2s to ~1.3s. Feel free to drop if the extra code is not worth it.