An error report handler for panics and the eyre crate for colorful, consistent, and well
formatted error reports for all kinds of errors.
color_eyre helps you build error reports that look like this:
Add the following to your toml file:
[dependencies]
color-eyre = "0.6"And install the panic and error report handlers:
use color_eyre::eyre::Result;
fn main() -> Result<()> {
color_eyre::install()?;
// ...
# Ok(())
}If you don't plan on using tracing_error and SpanTrace you can disable the
tracing integration to cut down on unused dependencies:
[dependencies]
color-eyre = { version = "0.6", default-features = false }color-eyre defaults to capturing span traces. This is because SpanTrace
capture is significantly cheaper than Backtrace capture. However, like
backtraces, span traces are most useful for debugging applications, and it's
not uncommon to want to disable span trace capture by default to keep noise out
developer.
To disable span trace capture you must explicitly set one of the env variables
that regulate SpanTrace capture to "0":
if std::env::var("RUST_SPANTRACE").is_err() {
std::env::set_var("RUST_SPANTRACE", "0");
}In debug mode color-eyre behaves noticably worse than eyre. This is caused
by the fact that eyre uses std::backtrace::Backtrace instead of
backtrace::Backtrace. The std version of backtrace is precompiled with
optimizations, this means that whether or not you're in debug mode doesn't
matter much for how expensive backtrace capture is, it will always be in the
10s of milliseconds to capture. A debug version of backtrace::Backtrace
however isn't so lucky, and can take an order of magnitude more time to capture
a backtrace compared to its std counterpart.
Cargo profile
overrides
can be used to mitigate this problem. By configuring your project to always
build backtrace with optimizations you should get the same performance from
color-eyre that you're used to with eyre. To do so add the following to
your Cargo.toml:
[profile.dev.package.backtrace]
opt-level = 3color-eyre provides 3 different report formats for how it formats the captured SpanTrace
and Backtrace, minimal, short, and full. Take the below snippets of the output produced by examples/usage.rs:
Running cargo run --example usage without RUST_LIB_BACKTRACE set will produce a minimal
report like this:
Running RUST_LIB_BACKTRACE=1 cargo run --example usage tells color-eyre to use the short
format, which additionally capture a backtrace::Backtrace:
Finally, running RUST_LIB_BACKTRACE=full cargo run --example usage tells color-eyre to use
the full format, which in addition to the above will attempt to include source lines where the
error originated from, assuming it can find them on the disk.
Custom Sections for error reports via Section trait
The section module provides helpers for adding extra sections to error
reports. Sections are disinct from error messages and are displayed
independently from the chain of errors. Take this example of adding sections
to contain stderr and stdout from a failed command, taken from
examples/custom_section.rs:
use color_eyre::{eyre::eyre, SectionExt, Section, eyre::Report};
use std::process::Command;
use tracing::instrument;
trait Output {
fn output2(&mut self) -> Result<String, Report>;
}
impl Output for Command {
#[instrument]
fn output2(&mut self) -> Result<String, Report> {
let output = self.output()?;
let stdout = String::from_utf8_lossy(&output.stdout);
if !output.status.success() {
let stderr = String::from_utf8_lossy(&output.stderr);
Err(eyre!("cmd exited with non-zero status code"))
.with_section(move || stdout.trim().to_string().header("Stdout:"))
.with_section(move || stderr.trim().to_string().header("Stderr:"))
} else {
Ok(stdout.into())
}
}
}Here we have an function that, if the command exits unsuccessfully, creates a
report indicating the failure and attaches two sections, one for stdout and
one for stderr.
Running cargo run --example custom_section shows us how these sections are
included in the output:
Only the Stderr: section actually gets included. The cat command fails,
so stdout ends up being empty and is skipped in the final report. This gives
us a short and concise error report indicating exactly what was attempted and
how it failed.
It's not uncommon for programs like batched task runners or parsers to want to return an error with multiple sources. The current version of the error trait does not support this use case very well, though there is work being done to improve this.
For now however one way to work around this is to compose errors outside the
error trait. color-eyre supports such composition in its error reports via
the Section trait.
For an example of how to aggregate errors check out examples/multiple_errors.rs.
The pretty printing for backtraces and span traces isn't actually provided by
color-eyre, but instead comes from its dependencies color-backtrace and
color-spantrace. color-backtrace in particular has many more features
than are exported by color-eyre, such as customized color schemes, panic
hooks, and custom frame filters. The custom frame filters are particularly
useful when combined with color-eyre, so to enable their usage we provide
the install fn for setting up a custom BacktracePrinter with custom
filters installed.
For an example of how to setup custom filters, check out examples/custom_filter.rs.
Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in this crate by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.