Struct WithSource 

pub struct WithSource<E>(pub E);

Wrapper that formats the full error chain for tool responses.

By default, tool errors only show the top-level message from [Display]. When using thiserror with #[source], nested error causes are attached but not displayed. This wrapper traverses the Error::source chain to produce a complete message like "google API error: HTTP request failed: connection refused".

This pattern follows the design from The elements of Rust error handling: keep Display impls minimal and let callers decide when to show the full chain.

When to Use

Use WithSource when your error type has nested causes that would help the LLM understand what went wrong. This is especially useful for errors from external services, I/O operations, or any chain where the root cause provides actionable information.

Example

use mercutio::WithSource;

async fn handle_tool(tool: MyTools) -> Result<String, WithSource<MyError>> {
    let data = fetch_api().map_err(WithSource)?;
    Ok(format!("Got: {data}"))
}

Without WithSource, an API failure might show: "API request failed"

With WithSource, it shows: "API request failed: HTTP error: 403 Forbidden"

Tuple Fields

0: E

Trait Implementations

impl<E: Debug> Debug for WithSource<E>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<E: Error> Display for WithSource<E>

fn fmt(&self, f: &mut Formatter<'_>) -> Result

Formats the value using the given formatter.

impl<E: Error> Error for WithSource<E>

fn source(&self) -> Option<&(dyn Error + 'static)>

Returns the lower-level source of this error, if any.

fn description(&self) -> &str

👎Deprecated since 1.42.0:

use the Display impl or to_string()

fn cause(&self) -> Option<&dyn Error>

👎Deprecated since 1.33.0:

replaced by Error::source, which can support downcasting

fn provide<'a>(&'a self, request: &mut Request<'a>)

🔬This is a nightly-only experimental API. (error_generic_member_access)

Provides type-based access to context intended for error reports.

impl<E: Error> From<E> for WithSource<E>

fn from(err: E) -> Self

Converts to this type from the input type.