Ergonomic trait-object error type for idiomatic application error handling; attach contextual messages, downcast to concrete error types, capture backtraces, and create errors with concise macros.
This is a Kotlin Multiplatform line-by-line transliteration port of dtolnay/anyhow.
Original Project: This port is based on dtolnay/anyhow. All design credit and project intent belong to the upstream authors; this repository is a faithful port to Kotlin Multiplatform with no behavioural changes intended.
This is an in-progress port. The goal is feature parity with the upstream Rust crate while providing a native Kotlin Multiplatform API. Every Kotlin file carries a // port-lint: source <path> header naming its upstream Rust counterpart so the AST-distance tool can track provenance.
dtolnay/anyhowThe text below is reproduced and lightly edited from
https://github.com/dtolnay/anyhow. It is the upstream project's own description and remains under the upstream authors' authorship; links have been rewritten to absolute upstream URLs so they continue to resolve from this repository.
This library provides anyhow::Error, a trait object based error type
for easy idiomatic error handling in Rust applications.
[dependencies]
anyhow = "1.0"
In no_std mode, almost all of the same API is available and works the same way. To depend on Anyhow in no_std mode, disable our default enabled "std" feature in Cargo.toml. A global allocator is required.
[dependencies]
anyhow = { version = "1.0", default-features = false }
With versions of Rust older than 1.81, no_std mode may require an additional
.map_err(Error::msg) when working with a non-Anyhow error type inside a
function that returns Anyhow's error type, as the trait that ?-based error
conversions are defined by is only available in std in those old versions.
The anyhow::Error type works something like failure::Error, but unlike
failure ours is built around the standard library's std::error::Error trait
rather than a separate trait failure::Fail. The standard library has adopted
the necessary improvements for this to be possible as part of RFC 2504.
Use Anyhow if you don't care what error type your functions return, you just want it to be easy. This is common in application code. Use thiserror if you are a library that wants to design your own dedicated error type(s) so that on failures the caller gets exactly the information that you choose.
dependencies {
implementation("io.github.kotlinmania:anyhow-kotlin:0.1.1")
}
./gradlew build
./gradlew test
See AGENTS.md and CLAUDE.md for translator discipline, port-lint header convention, and Rust → Kotlin idiom mapping.
This Kotlin port is distributed under the same MIT license as the upstream dtolnay/anyhow. See LICENSE (and any sibling LICENSE-* / NOTICE files mirrored from upstream) for the full text.
Original work copyrighted by the anyhow authors.
Kotlin port: Copyright (c) 2026 Sydney Renee and The Solace Project.
Thanks to the dtolnay/anyhow maintainers and contributors for the original Rust implementation. This port reproduces their work in Kotlin Multiplatform; bug reports about upstream design or behavior should go to the upstream repository.
Use Result<T, anyhow::Error>, or equivalently anyhow::Result<T>, as the
return type of any fallible function.
Within the function, use ? to easily propagate any error that implements the
std::error::Error trait.
use anyhow::Result;
fn get_cluster_info() -> Result<ClusterMap> {
let config = std::fs::read_to_string("cluster.json")?;
let map: ClusterMap = serde_json::from_str(&config)?;
Ok(map)
}
Attach context to help the person troubleshooting the error understand where things went wrong. A low-level error like "No such file or directory" can be annoying to debug without more context about what higher level step the application was in the middle of.
use anyhow::{Context, Result};
fn main() -> Result<()> {
...
it.detach().context("Failed to detach the important thing")?;
let content = std::fs::read(path)
.with_context(|| format!("Failed to read instrs from {}", path))?;
...
}
Error: Failed to read instrs from ./path/to/instrs.json
Caused by:
No such file or directory (os error 2)
Downcasting is supported and can be by value, by shared reference, or by mutable reference as needed.
// If the error was caused by redaction, then return a
// tombstone instead of the content.
match root_cause.downcast_ref::<DataStoreError>() {
Some(DataStoreError::Censored(_)) => Ok(Poll::Ready(REDACTED_CONTENT)),
None => Err(error),
}
If using Rust ≥ 1.65, a backtrace is captured and printed with the error if
the underlying error type does not already provide its own. In order to see
backtraces, they must be enabled through the environment variables described
in std::backtrace:
RUST_BACKTRACE=1;RUST_LIB_BACKTRACE=1;RUST_BACKTRACE=1 and
RUST_LIB_BACKTRACE=0.Anyhow works with any error type that has an impl of std::error::Error,
including ones defined in your crate. We do not bundle a derive(Error) macro
but you can write the impls yourself or use a standalone macro like
thiserror.
use thiserror::Error;
#[derive(Error, Debug)]
pub enum FormatError {
#[error("Invalid header (expected {expected:?}, got {found:?})")]
InvalidHeader {
expected: String,
found: String,
},
#[error("Missing attribute: {0}")]
MissingAttribute(String),
}
One-off error messages can be constructed using the anyhow! macro, which
supports string interpolation and produces an anyhow::Error.
return Err(anyhow!("Missing attribute: {}", missing));
A bail! macro is provided as a shorthand for the same early return.
bail!("Missing attribute: {}", missing);
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