6dc75f0c5d
This patch adds tests for Rust 1.54.0, 1.55.0 and 1.56.0. To make the tests pass, we have to take care of some changes like more details elements and changed heading levels. To make it easier to generate the tests for new Rust versions, we also add two bash scripts that take care of that.
140 lines
5.2 KiB
Plaintext
140 lines
5.2 KiB
Plaintext
---
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source: tests/output.rs
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expression: "get_stdout(path, &[\"anyhow\"])"
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---
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anyhow Module anyhow rusty-man
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DESCRIPTION
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[[github]][1] [[crates-io]][2] [[docs-rs]][3]
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This library provides `anyhow::Error`, a trait object based error type for easy idiomatic
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error handling in Rust applications.
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# Details
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* Use `Result<T, anyhow::Error>`, or equivalently `anyhow::Result<T>`, as the return type of
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any fallible function.
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Within the function, use `?` to easily propagate any error that implements the
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`std::error::Error` trait.
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use anyhow::Result;
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fn get_cluster_info() -> Result<ClusterMap> {
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let config = std::fs::read_to_string("cluster.json")?;
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let map: ClusterMap = serde_json::from_str(&config)?;
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Ok(map)
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}
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* Attach context to help the person troubleshooting the error understand where things went
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wrong. A low-level error like “No such file or directory” can be annoying to debug without
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more context about what higher level step the application was in the middle of.
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use anyhow::{Context, Result};
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fn main() -> Result<()> {
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...
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it.detach().context("Failed to detach the important thing")?;
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let content = std::fs::read(path)
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.with_context(|| format!("Failed to read instrs from {}", path))?;
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...
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}
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`Error: Failed to read instrs from ./path/to/instrs.json
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Caused by:
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No such file or directory (os error 2)
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`
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* Downcasting is supported and can be by value, by shared reference, or by mutable reference
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as needed.
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// If the error was caused by redaction, then return a
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// tombstone instead of the content.
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match root_cause.downcast_ref::<DataStoreError>() {
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Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),
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None => Err(error),
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}
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* If using the nightly channel, a backtrace is captured and printed with the error if the
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underlying error type does not already provide its own. In order to see backtraces, they
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must be enabled through the environment variables described in [`std::backtrace`][1]:
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* If you want panics and errors to both have backtraces, set `RUST_BACKTRACE=1`;
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* If you want only errors to have backtraces, set `RUST_LIB_BACKTRACE=1`;
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* If you want only panics to have backtraces, set `RUST_BACKTRACE=1` and
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`RUST_LIB_BACKTRACE=0`.
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The tracking issue for this feature is [rust-lang/rust#53487][2].
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[1] https://doc.rust-lang.org/std/backtrace/index.html#environment-variables
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[2] https://github.com/rust-lang/rust/issues/53487
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* Anyhow works with any error type that has an impl of `std::error::Error`, including ones
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defined in your crate. We do not bundle a `derive(Error)` macro but you can write the impls
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yourself or use a standalone macro like [thiserror][1].
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use thiserror::Error;
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#[derive(Error, Debug)]
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pub enum FormatError {
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#[error("Invalid header (expected {expected:?}, got {found:?})")]
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InvalidHeader {
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expected: String,
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found: String,
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},
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#[error("Missing attribute: {0}")]
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MissingAttribute(String),
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}
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[1] https://github.com/dtolnay/thiserror
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* One-off error messages can be constructed using the `anyhow!` macro, which supports string
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interpolation and produces an `anyhow::Error`.
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return Err(anyhow!("Missing attribute: {}", missing));
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A `bail!` macro is provided as a shorthand for the same early return.
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bail!("Missing attribute: {}", missing);
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# No-std support
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In no_std mode, the same API is almost all available and works the same way. To depend on
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Anyhow in no_std mode, disable our default enabled “std” feature in Cargo.toml. A global
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allocator is required.
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`[dependencies]
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anyhow = { version = "1.0", default-features = false }
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`
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Since the `?`-based error conversions would normally rely on the `std::error::Error` trait
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which is only available through std, no_std mode will require an explicit
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`.map_err(Error::msg)` when working with a non-Anyhow error type inside a function that
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returns Anyhow’s error type.
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[1] https://github.com/dtolnay/anyhow
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[2] https://crates.io/crates/anyhow
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[3] https://docs.rs/anyhow
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MACROS
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anyhow
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Construct an ad-hoc error from a string or existing non-`anyhow` error value.
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bail
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Return early with an error.
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ensure
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Return early with an error if a condition is not satisfied.
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STRUCTS
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Chain
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Iterator of a chain of source errors.
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Error
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The `Error` type, a wrapper around a dynamic error type.
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TRAITS
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Context
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Provides the `context` method for `Result`.
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TYPEDEFS
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Result
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`Result<T, Error>`
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