Rust error E0541: #### Note: this error code is no longer emitted by the compiler

The compiler team's explanation

Note: this error code is no longer emitted by the compiler.

An unknown meta item was used.

Erroneous code example:

#[deprecated(
    since="1.0.0",
    // error: unknown meta item
    reason="Example invalid meta item. Should be 'note'")
]
fn deprecated_function() {}

Meta items are the key-value pairs inside of an attribute. The keys provided must be one of the valid keys for the specified attribute.

To fix the problem, either remove the unknown meta item, or rename it if you provided the wrong name.

In the erroneous code example above, the wrong name was provided, so changing to a correct one it will fix the error. Example:

#[deprecated(
    since="1.0.0",
    note="This is a valid meta item for the deprecated attribute."
)]
fn deprecated_function() {}

From rustc --explain E0541 (1.99.0), part of the Rust project, MIT or Apache-2.0. Official page.