KOL-5 | feat: Enhance error handling with detailed KolmeError variants

[anakinzhed]

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[snoyberg]

Left some comments for a change in general direction. When this is ready for another review, let's get @MichaelNelo on this too so I'm not a bottleneck.

[anakinzhed]

@borsboom, Michael asked me to work with you in this PR.

[borsboom]

@anakinzhed I'm still familiarizing myself with the Kolme codebase, and this is a big PR. I'm working to understand the changes and figure out if there's a way we can avoid the stringy errors that are hard to avoid because of the traits that KolmeError derives. It might take me a little while to respond further, but I am working on it.

[borsboom]

Not easy to retrofit proper errors into a codebase like this, especially given the need for some errors to be serializable.

Aside from the comments I added to specific changes, I noticed there are still many uses of anyhow::Result which end up being "hidden" by error types implementing From<anyhow::Error> and stringifying them. Removing those, and any imports of anyhow::Result should help find them (as well as just searching the codebase anyhow).

[anakinzhed]

@borsboom Sorry for the delay. I believe I’ve addressed all of your comments. Please take a look.

[borsboom]

Great progress!

I notice there are still some places that are returning anyhow::Result (e.g. in packages/kolme/src/core/execute.rs). Where concrete error types are returned, they are being converted to anyhow::Error (e.g. return Err(KolmeExecuteError::…).into();).

Better would be for the functions to return a concrete error (e.g. fn …(…) -> Result<(), KolmeExecuteError>). Any upstream errors should be embedded in KolmeExecuteError, which is made easier using thiserror's #[from] annotation so that the ? operator still works. E.g.

pub enum KolmeExecuteError {
    …

    #[error("Public key error: {0}")]
    PublicKeyError(#[from] shared::cryptography::PublicKeyError),
}

If at all possible, anyhow should be removed from the dependencies entirely.