Generalize `AnyError`

[schreter]

Currently, openraft uses anyerror crate, which allows passing "any" errors.

However, AnyError is understandably somewhat limited, since it was written for general public. In our project, we use a different version of AnyError which allows better diagnostics and also stores some errors in-place. Plus, it won't panic on OOM.

Therefore, it would be helpful to generalize AnyError via the configuration to be able to use a different implementation. Since the API is quite small, it should be fairly trivial.

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[drmingdrmer]

Implemented in PR #1614.

Summary

Added a configurable ErrorSource type to RaftTypeConfig that allows users to provide custom error wrapper implementations with enhanced diagnostics, in-place storage, or OOM robustness.

Changes

New ErrorSource Trait

pub trait ErrorSource: OptionalFeatures + Error + Clone + 'static {
    /// Create an error from any error type.
    fn from_error<E: Error + 'static>(error: &E) -> Self;

    /// Create an error from a string message.
    fn from_string(msg: impl ToString) -> Self;

    /// Get the backtrace if captured. Default: None.
    fn backtrace_str(&self) -> Option<String> { None }
}

Added to RaftTypeConfig

pub trait RaftTypeConfig {
    // ... existing types ...
    type ErrorSource: ErrorSource;
}

Default value in declare_raft_types! macro: anyerror::AnyError

Generic Error Types

• NetworkError → NetworkError<C> (now generic over RaftTypeConfig)
• Unreachable → Unreachable<C> (now generic over RaftTypeConfig)
• StorageError updated to use C::ErrorSource

Convenience Methods

Added to TypeConfigExt:

• err_from_error<E>(error: &E) -> ErrorSourceOf<Self>
• err_from_string(msg: impl ToString) -> ErrorSourceOf<Self>

Migration

Default users (using declare_raft_types!): No changes needed.

Custom RaftTypeConfig users: Add type ErrorSource = anyerror::AnyError; to maintain existing behavior.

Custom error type users: Implement the ErrorSource trait for your type and set it in your config.