When modifying a protocol's struct that is used in plugins (such as Signature), you need to update the capnproto schema file and recompile it into the Rust source code.
The steps are as follows:
1. Change src/serializers/capnp/schema/plugin.capnp as necessary
2. Install capnp tool (it's a C++ binary, commonly available in package managers)
3. Install Rust support for capnp called capnpc-rust:
1. git clone https://github.com/capnproto/capnproto-rust somewhere
2. cd capnproto-rust/capnpc
3. cargo install --path=.
4. Then, call capnp compile -orust plugin.capnp (change path as necessary)
5. The result should be plugin_capnp.rs file: Use it to replace the old src/plugin_capnp.rs.
6. It needs to be autoformatted (cargo fmt --all)
7. Modify the serialize/deserialize functions. Check the following PRs for details:
* https://github.com/nushell/nushell/pull/4980
* https://github.com/nushell/nushell/pull/4920