Understanding Rust Error E0453

Introduction

Rust Error E0453 occurs when a 'lint check attribute' is overruled by a 'forbid directive' set as an attribute on an enclosing scope, or on the command line with the -F option. In this article, we'll discuss the error in detail, look at an erroneous code example, and learn how to fix it.

Error E0453 Explained

In Rust, lint checks help maintain code quality by ensuring specific code patterns are followed. Lint checks can be categorized into several levels: allow, warn, deny, and forbid. The first three levels can be overridden by inner lint check attributes. However, the 'forbid' level cannot be overridden, which can cause Error E0453. Let's examine an erroneous code example illustrating this error:

#![forbid(non_snake_case)]

#[allow(non_snake_case)]
fn main() {
    let MyNumber = 2; // error: allow(non_snake_case) overruled by outer
                      //        forbid(non_snake_case)
}

In this example, the 'forbid' lint setting for 'non_snake_case' is applied at the crate level. Inside the 'main' function, the inner 'allow' attribute tries to override the outer 'forbid' attribute, causing Error E0453.

Fixing Error E0453

To fix Error E0453, we can either change the lint level from 'forbid' to 'deny' to allow inner lint attributes, or we can modify the code to adhere to the lint check and remove the overruled attribute. Let's look at both solutions:

Solution 1: Change 'forbid' to 'deny'

In this solution, we change the outer lint check from 'forbid' to 'deny':

#![deny(non_snake_case)]

#[allow(non_snake_case)]
fn main() {
    let MyNumber = 2; // ok!
}

Now, the 'allow' attribute successfully overrides the 'deny' attribute, and the code compiles and runs without error.

Solution 2: Edit code to pass the lint check

Alternatively, we can edit the code to pass the lint check and eliminate the need for the inner attribute:

#![forbid(non_snake_case)]

fn main() {
    let my_number = 2;
}

In this version of the code, we changed the name of 'MyNumber' to 'my_number' to satisfy the 'non_snake_case' lint check, and we removed the inner 'allow' attribute. The code now compiles and runs without error.