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chore: add underlying error to lockfile error messages #4800

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May 4, 2023
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chore: add underlying error to lockfile error messages #4800

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2 changes: 1 addition & 1 deletion crates/turborepo-ffi/src/lockfile.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -23,7 +23,7 @@ impl From<Package> for proto::LockfilePackage {
enum Error {
#[error("error performing lockfile operation: {0}")]
Lockfile(#[from] turborepo_lockfiles::Error),
#[error("error decoding protobuf")]
#[error("error decoding protobuf: {0}")]
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Where would I begin to look up how this is working? I'd expect this diff to contain the actual value in addition to (what I assume is) the placeholder {0}. I'm guessing that means [error(...)] (macro??) is doing something fancy under the hood. But I don't know how to search for error 🤣

(Trying to learn Rust passively alongside reading the book)

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So it already included the value! The Error enum can be viewed as just:

enum Error {
    Lockfile(turborepo_lockfiles::Error),
    Protobuf(prost::DecodeError),
    BerryParse(turborepo_lockfiles::BerryError),
    UnsupportedPackageManager(proto::PackageManager),
}

All of the #[error(...)] and #[from] macros generate some code for us that makes this enum more ergonomic.

  • The #[error("error decoding protobuf: {0}")] line is used as a formatting string when deriving a Display implementation for the enum. To be exact it generates:
    write!( __formatter, "error decoding protobuf: {field__0}", field__0 = 0.as_display())
  • The #[from] macro generates a From implementation for us that converts the protobuf error into our enum. This is especially useful when combined with the ? syntax as it automatically attempts to convert to the correct error type.
impl std::convert::From<prost::DecodeError> for Error {
    #[allow(deprecated)]
    fn from(source: prost::DecodeError) -> Self {
        Error::Protobuf { 0: source }
    }
}

The easiest way to actually understand what a macro does is to open some code up that uses it and then use rust-analyzer's expand-macro-recursively command to see exactly what it's doing. (You can also try reading the macro source, but this takes way more time IMO)

Protobuf(#[from] prost::DecodeError),
#[error(transparent)]
BerryParse(#[from] turborepo_lockfiles::BerryError),
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6 changes: 3 additions & 3 deletions crates/turborepo-lockfiles/src/berry/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -21,13 +21,13 @@ use super::Lockfile;

#[derive(Debug, Error)]
pub enum Error {
#[error("unable to parse")]
#[error("unable to parse yaml: {0}")]
Parse(#[from] serde_yaml::Error),
#[error("unable to parse")]
#[error("unable to parse identifier: {0}")]
Identifiers(#[from] identifiers::Error),
#[error("unable to find original package in patch locator {0}")]
PatchMissingOriginalLocator(Locator<'static>),
#[error("unable to parse resolutions field")]
#[error("unable to parse resolutions field: {0}")]
Resolutions(#[from] resolution::Error),
#[error("unable to find entry for {0}")]
MissingPackageForLocator(Locator<'static>),
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2 changes: 1 addition & 1 deletion crates/turborepo-lockfiles/src/berry/resolution.rs
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Expand Up @@ -15,7 +15,7 @@ fn tag_regex() -> &'static Regex {

#[derive(Debug, Error)]
pub enum Error {
#[error("unable to parse")]
#[error("unable to parse: {0}")]
// Boxed due to this enum variant being much larger than the others
Pest(#[from] Box<pest::error::Error<Rule>>),
#[error("unexpected end of input")]
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2 changes: 1 addition & 1 deletion crates/turborepo-lockfiles/src/error.rs
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Expand Up @@ -8,7 +8,7 @@ pub enum Error {
MissingPackage(String),
#[error("Missing version from non-workspace package: '{0}'")]
MissingVersion(String),
#[error("Unable to convert from json")]
#[error("Unable to convert from json: {0}")]
JsonError(#[from] serde_json::Error),
#[error("Turbo doesn't support npm lockfiles without a 'packages' field")]
UnsupportedNpmVersion,
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