clippy 0.0.6

A bunch of helpful lints to avoid common pitfalls in Rust failed to build clippy-0.0.6
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#rust-clippy Build Status

A collection of lints that give helpful tips to newbies and catch oversights.

##Lints Lints included in this crate:

  • single_match: Warns when a match statement with a single nontrivial arm (i.e, where the other arm is _ => {}) is used, and recommends if let instead.
  • box_vec: Warns on usage of Box<Vec<T>>
  • linkedlist: Warns on usage of LinkedList
  • str_to_string: Warns on usage of str::to_string()
  • toplevel_ref_arg: Warns when a function argument is declared ref (i.e. fn foo(ref x: u8), but not fn foo((ref x, ref y): (u8, u8)))
  • eq_op: Warns on equal operands on both sides of a comparison or bitwise combination
  • bad_bit_mask: Denies expressions of the form _ & mask == select that will only ever return true or false (because in the example select containing bits that mask doesn't have)
  • ineffective_bit_mask: Warns on expressions where a bit mask will be rendered useless by a comparison, e.g. (x | 1) > 2
  • needless_bool : Warns on if-statements with plain booleans in the then- and else-clause, e.g. if p { true } else { false }
  • ptr_arg: Warns on fn arguments of the type &Vec<...> or &String, suggesting to use &[...] or &str instead, respectively
  • approx_constant: Warns if the approximate of a known float constant (in std::f64::consts or std::f32::consts) is found and suggests to use the constant
  • cmp_nan: Denies comparisons to NAN (which will always return false, which is probably not intended)
  • float_cmp: Warns on == or != comparisons of floaty typed values. As floating-point operations usually involve rounding errors, it is always better to check for approximate equality within some small bounds
  • precedence: Warns on expressions where precedence may trip up the unwary reader of the source and suggests adding parenthesis, e.g. x << 2 + y will be parsed as x << (2 + y)
  • redundant_closure: Warns on usage of eta-reducible closures like |a| foo(a) (which can be written as just foo)
  • identity_op: Warns on identity operations like x + 0 or y / 1 (which can be reduced to x and y, respectively)
  • mut_mut: Warns on &mut &mut which is either a copy'n'paste error, or shows a fundamental misunderstanding of references
  • len_zero: Warns on _.len() == 0 and suggests using _.is_empty() (or similar comparisons with > or !=)
  • len_without_is_empty: Warns on traits or impls that have a .len() but no .is_empty() method
  • cmp_owned: Warns on creating owned instances for comparing with others, e.g. x == "foo".to_string()
  • inline_always: Warns on #[inline(always)], because in most cases it is a bad idea
  • collapsible_if: Warns on cases where two nested if-expressions can be collapsed into one, e.g. if x { if y { foo() } } can be written as if x && y { foo() }
  • zero_width_space: Warns on encountering a unicode zero-width space

To use, add the following lines to your Cargo.toml:

clippy = "*"

More to come, please file an issue if you have ideas!


Compiler plugins are highly unstable and will only work with a nightly Rust for now. Since stable Rust is backwards compatible, you should be able to compile your stable programs with nightly Rust with clippy plugged in to circumvent this.

Add in your Cargo.toml:

git = ""




fn main(){
    let x = Some(1u8);
    match x {
        Some(y) => println!("{:?}", y),
        _ => ()

Produce this warning:

src/ 11:6 warning: You seem to be trying to use match for destructuring a single type. Did you mean to use `if let`?, #[warn(single_match)] on by default
src/     match x {
src/         Some(y) => println!("{:?}", y),
src/         _ => ()
src/     }
src/ 11:6 note: Try if let Some(y) = x { ... }
src/     match x {
src/         Some(y) => println!("{:?}", y),
src/         _ => ()
src/     }

You can add options to allow/warn/deny:

  • the whole set using the clippy lint group (#![deny(clippy)], etc)
  • only some lints (#![deny(single_match, box_vec)], etc)
  • allow/warn/deny can be limited to a single function or module using #[allow(...)], etc

deny produces error instead of warnings

##License Licensed under MPL. If you're having issues with the license, let me know and I'll try to change it to something more permissive.