change failure to thiserror

courses/rust/projects/project-2/Cargo.toml

@@ -7,7 +7,7 @@ edition = "2018"
 
 [dependencies]
 clap = "2.32.0"
-failure = "0.1.5"
+thiserror = "1.0"
 serde = { version = "1.0.89", features = ["derive"] }
 serde_json = "1.0.39"
 

courses/rust/projects/project-2/README.md

@@ -12,7 +12,7 @@ command line_.
 - Map in-memory key-indexes to on-disk values
 - Periodically compact the log to remove stale data
 
-**Topics**: log-structured file I/O, bitcask, the `failure` crate, `Read` /
+**Topics**: log-structured file I/O, bitcask, the `thiserror` crate, `Read` /
 `Write` traits, the `serde` crate.
 
 - [Introduction](#user-content-introduction)
@@ -187,18 +187,18 @@ is crucial to Rust projects: decide on an error handling strategy.
 <!-- TODO outline strategies? -->
 
 Rust's error handling is powerful, but involves a lot of boilerplate to use
-correctly. For this project the [`failure`] crate will provide the tools to
+correctly. For this project the [`thiserror`] crate will provide the tools to
 easily handle errors of all kinds.
 
-[`failure`]: https://docs.rs/failure/0.1.5/failure/
+[`thiserror`]: https://docs.rs/thiserror/1.0.18/thiserror/
 
 The [failure guide][fg] describes [several] error handling patterns.
 
 [fg]: https://boats.gitlab.io/failure/
 [several]: https://boats.gitlab.io/failure/guidance.html
 
 Pick one of those strategies and, in your library, either define your own error
-type or import `failure`s `Error`. This is the error type you will use in all of
+type or import `thiserror`s `Error`. This is the error type you will use in all of
 your `Result`s, converting error types from other crates to your own with the
 `?` operator.
 
@@ -227,10 +227,10 @@ suite to compile (`cargo test --no-run`).
 -->
 
 _Note: Error-handling practices in Rust are still evolving. This course
-currently uses the [`failure`] crate to make defining error types easier. While
-`failure` has a good design, its use is [arguably not a best practice][nbp]. It
+currently uses the [`thiserror`] crate to make defining error types easier. While
+`thiserror` has a good design, its use is [arguably not a best practice][nbp]. It
 may not continue to be viewed favorably by Rust experts. Future iterations
-of the course will likely not use `failure`. In the meantime, it is fine, and
+of the course will likely not use `thiserror`. In the meantime, it is fine, and
 presents an opportunity to learn more of the history and nuance of Rust error
 handling._
 
@@ -258,7 +258,7 @@ This is the basic behavior of `kvs` with a log:
 - "set"
   - The user invokes `kvs set mykey myvalue`
    - `kvs` creates a value representing the "set" command, containing its key and
-    value
+      value
   - It then serializes that command to a `String`
   - It then appends the serialized command to a file containing the log
   - If that succeeds, it exits silently with error code 0

courses/rust/projects/project-2/src/error.rs

@@ -1,35 +1,23 @@
-use failure::Fail;
 use std::io;
+use thiserror::Error;
 
 /// Error type for kvs.
-#[derive(Fail, Debug)]
+#[derive(Error, Debug)]
 pub enum KvsError {
     /// IO error.
-    #[fail(display = "{}", _0)]
-    Io(#[cause] io::Error),
+    #[error("`{0}`")]
+    Io(#[from] io::Error),
     /// Serialization or deserialization error.
-    #[fail(display = "{}", _0)]
-    Serde(#[cause] serde_json::Error),
+    #[error("`{0}`")]
+    Serde(#[from] serde_json::Error),
     /// Removing non-existent key error.
-    #[fail(display = "Key not found")]
+    #[error("Key not found")]
     KeyNotFound,
     /// Unexpected command type error.
     /// It indicated a corrupted log or a program bug.
-    #[fail(display = "Unexpected command type")]
+    #[error("Unexpected command type")]
     UnexpectedCommandType,
 }
 
-impl From<io::Error> for KvsError {
-    fn from(err: io::Error) -> KvsError {
-        KvsError::Io(err)
-    }
-}
-
-impl From<serde_json::Error> for KvsError {
-    fn from(err: serde_json::Error) -> KvsError {
-        KvsError::Serde(err)
-    }
-}
-
 /// Result type for kvs.
 pub type Result<T> = std::result::Result<T, KvsError>;