crypto: mark errors as `non_exhaustive`

To improve crate version churn, mark the error types as `non_exhaustive`.
This removes the need to change the version number of the crate when adding a
new variant.

Note that these errors are never matched on, so no other code is changed in
dependent crates.

crates/radicle-crypto/src/lib.rs

@@ -28,6 +28,7 @@ pub type SharedSecret = [u8; 32];
 /// Error returned if signing fails, eg. due to an HSM or KMS.
 #[derive(Debug, Clone, Error)]
 #[error(transparent)]
+#[non_exhaustive]
 pub struct SignerError {
     #[from]
     source: Arc<dyn std::error::Error + Send + Sync>,
@@ -93,6 +94,7 @@ impl fmt::Debug for Signature {
 }
 
 #[derive(Error, Debug)]
+#[non_exhaustive]
 pub enum SignatureError {
     #[error("invalid multibase string: {0}")]
     Multibase(#[from] multibase::Error),
@@ -273,6 +275,7 @@ impl Deref for SecretKey {
 }
 
 #[derive(Error, Debug)]
+#[non_exhaustive]
 pub enum PublicKeyError {
     #[error("invalid length {0}")]
     InvalidLength(usize),

crates/radicle-crypto/src/ssh.rs

@@ -16,6 +16,7 @@ use crate::PublicKey;
 pub use keystore::{Keystore, Passphrase};
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum ExtendedSignatureError {
     #[error(transparent)]
     Ssh(#[from] ssh_key::Error),
@@ -128,6 +129,7 @@ pub mod fmt {
 }
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum SignatureError {
     #[error(transparent)]
     Invalid(#[from] crypto::Error),
@@ -164,6 +166,7 @@ impl Encodable for crypto::Signature {
 }
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum PublicKeyError {
     #[error(transparent)]
     Invalid(#[from] crypto::Error),
@@ -199,6 +202,7 @@ impl Encodable for PublicKey {
 }
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum SecretKeyError {
     #[error(transparent)]
     Encoding(#[from] encoding::Error),

crates/radicle-crypto/src/ssh/keystore.rs

@@ -15,6 +15,7 @@ use super::ExtendedSignature;
 pub type Passphrase = Zeroizing<String>;
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum Error {
     #[error(transparent)]
     Io(#[from] io::Error),
@@ -227,6 +228,7 @@ impl Keystore {
 }
 
 #[derive(Debug, Error)]
+#[non_exhaustive]
 pub enum MemorySignerError {
     #[error(transparent)]
     Keystore(#[from] Error),