Attributes for Crate Authors

In some cases it is possible to extend Clippy coverage to 3rd party libraries. To do this, Clippy provides attributes that can be applied to items in the 3rd party crate.

#[clippy::format_args]

Available since Clippy v1.85

This attribute can be added to a macro that supports format!, println!, or similar syntax. It tells Clippy that the macro is a formatting macro, and that the arguments to the macro should be linted as if they were arguments to format!. Any lint that would apply to a format! call will also apply to the macro call. The macro may have additional arguments before the format string, and these will be ignored.

Example

/// A macro that prints a message if a condition is true.
#[macro_export]
#[clippy::format_args]
macro_rules! print_if {
    ($condition:expr, $($args:tt)+) => {{
        if $condition {
            println!($($args)+)
        }
    }};
}

#[clippy::has_significant_drop]

Available since Clippy v1.60

The clippy::has_significant_drop attribute can be added to types whose Drop impls have an important side effect, such as unlocking a mutex, making it important for users to be able to accurately understand their lifetimes. When a temporary is returned in a function call in a match scrutinee, its lifetime lasts until the end of the match block, which may be surprising.

Example

#[clippy::has_significant_drop]
struct CounterWrapper<'a> {
    counter: &'a Counter,
}

impl<'a> Drop for CounterWrapper<'a> {
    fn drop(&mut self) {
        self.counter.i.fetch_sub(1, Ordering::Relaxed);
    }
}