shepmaster
commented
2 years ago If I understand what you want, I'd probably end up with
#[derive(Debug, Snafu)]
pub enum Error {
#[snafu(display("Parse Error on {field}: {source}"))]
ParseError {
field: String,
source: InnerParseError,
},
}
#[derive(Debug, Snafu)]
pub enum InnerParseError {
#[snafu(display("YAMLError {source}"))]
YamlError { source: serde_yaml::Error },
#[snafu(display("JSONError {source}"))]
JsonError { source: serde_json::Error },
#[snafu(display("{message}"))]
MessageError { message: String },
}
fn main_wrapped() -> Result<String, Error> {
let r: i32 = rand::thread_rng().gen_range(0..3);
Ok(match r {
0 => {
let _ = serde_yaml::from_str("invalid yaml")
.context(YamlSnafu)
.context(ParseSnafu { field: "0" })?;
"0".to_string()
}
1 => {
let _ = serde_json::from_str("invalid json")
.context(JsonSnafu)
.context(ParseSnafu { field: "0" })?;
"1".to_string()
}
_ => {
return MessageSnafu { message: "blah" }
.fail()
.context(ParseSnafu { field: "2" })
}
})
}Thoughts I had while reading your code:
- Why use
source(false)? That seems to make your code harder to use and I'm not seeing the benefit. - Why use a string error? While SNAFU has stringly-typed errors like
Whatever, I don't like them and would encourage having explicitly listed errors. - The
fieldfield appears to be wrong in the1match arm. ensure(false, ...)always produces anErr, so I'd prefer to usefail.- It's debatable to include the
sourcein theDisplayimplementation message as the formatting tends to suck because everything is forced to be on one line. - I don't see anything wrong with repeating the field in each variant of
InnerParseErrorand flattening them out.
Another option, which avoids the repetition of the ParseSnafu, is to use an IIFE (or a try block in nightly Rust). I also switched field to be an i32:
fn main_wrapped() -> Result<String, Error> {
let field: i32 = rand::thread_rng().gen_range(0..3);
let tmp = (|| {
Ok(match field {
0 => {
let _ = serde_yaml::from_str("invalid yaml").context(YamlSnafu)?;
"0".to_string()
}
1 => {
let _ = serde_json::from_str("invalid json").context(JsonSnafu)?;
"1".to_string()
}
_ => return MessageSnafu { message: "blah" }.fail(),
})
})();
tmp.context(ParseSnafu { field })
}If you really don't have anything to add to the JSON / YAML errors and each can only occur exactly once, then you can remove all context from them:
#[derive(Debug, Snafu)]
pub enum InnerParseError {
#[snafu(context(false), display("{source}"))]
YamlError { source: serde_yaml::Error },
#[snafu(context(false), display("{source}"))]
JsonError { source: serde_json::Error },
#[snafu(display("{message}"))]
MessageError { message: String },
}
fn main_wrapped() -> Result<String, Error> {
let field: i32 = rand::thread_rng().gen_range(0..3);
let tmp = (|| {
Ok(match field {
0 => {
let _ = serde_yaml::from_str("invalid yaml")?;
"0".to_string()
}
1 => {
let _ = serde_json::from_str("invalid json")?;
"1".to_string()
}
_ => return MessageSnafu { message: "blah" }.fail(),
})
})();
tmp.context(ParseSnafu { field })
}
bryanlarsen
mplanchard
The documentation talks about splitting a source error into two separate errors. In my experience the converse also often happens, sometimes you want to combine several source errors into a single one. However as a newbie, I've been unable to make this happen. I've attached an MRE of one attempt, but I'm not necessarily asking for how to make my MRE compile -- something completely different that matches my use case would be awesome. For example, I use the InnerError pattern and source(false) but a less verbose solution that doesn't need one or both of those likely would be even better.