New comment by 0x5c on void-packages repository

https://github.com/void-linux/void-packages/issues/29207#issuecomment-1120329925

Comment:
I've hit this in https://github.com/void-linux/void-packages/pull/37013, and I know what might be happening in the case of all of those packages. Essentially cargo arbitrarily decides to drop a feature from a transient dependency (with no indication of why). You can see it when comparing the command cargo runs at build and at install for the deepest dependency that gets rebuilt (the command is shown when adding `-vv`).

In the case of #37013, the dependency that gets rebuilt is `syn` because cargo drops its `full` feature. There's no apparent reason for that drop, and it might even be a bug somewhere. The short-term fix was to explicitly add that feature for that dependency in the top crate's Cargo.toml.