Suggest use of map_err for if let return pattern

What it does

When using if let Err to handle errors for cases like returning errors from functions, suggest use of map_err.

Lint Name

prefer_map_err_over_if_let

Category

style

Advantage

• Prevents more redundancy in code.
• Simplifies common error handling behavior.
• More elegant solution.

Drawbacks

Only suggestible with simple logic and (probably) more preferable in repetitive usage.

Example

So instead of

if let Err(e) = something {
    return Err(SomeError::new(e));
}

Suggest use of

something.map_err(|e| SomeError::new(e))?;

I'm new to Rust, so I'm hoping this is along the idiomatic path. I had used the first pattern a lot before realizingmap_err could potentially be a more elegant (and idiomatic?) solution.

Start by locating the Rust Clippy lint implementation and tests for prefer_map_err_over_if_let, then compare the two error-handling patterns in the examples. Done means the lint suggests map_err for simple return-error cases while avoiding cases involving more complex logic, as noted in the issue.