rust-clippy/README.md

#rust-clippy

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

##Lints There are 52 lints included in this crate:

name	default	meaning
approx_constant	warn	the approximate of a known float constant (in std::f64::consts or std::f32::consts) is found; suggests to use the constant
bad_bit_mask	deny	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)
box_vec	warn	usage of Box<Vec<T>>, vector elements are already on the heap
cast_possible_truncation	allow	casts that may cause truncation of the value, e.g x as u8 where x: u32, or x as i32 where x: f32
cast_possible_wrap	allow	casts that may cause wrapping around the value, e.g x as i32 where x: u32 and x > i32::MAX
cast_precision_loss	allow	casts that cause loss of precision, e.g x as f32 where x: u64
cast_sign_loss	allow	casts from signed types to unsigned types, e.g x as u32 where x: i32
cmp_nan	deny	comparisons to NAN (which will always return false, which is probably not intended)
cmp_owned	warn	creating owned instances for comparing with others, e.g. x == "foo".to_string()
collapsible_if	warn	two nested if-expressions can be collapsed into one, e.g. if x { if y { foo() } } can be written as if x && y { foo() }
eq_op	warn	equal operands on both sides of a comparison or bitwise combination (e.g. x == x)
explicit_iter_loop	warn	for-looping over _.iter() or _.iter_mut() when &_ or &mut _ would do
float_cmp	warn	using == or != on float values (as floating-point operations usually involve rounding errors, it is always better to check for approximate equality within small bounds)
identity_op	warn	using identity operations, e.g. x + 0 or y / 1
ineffective_bit_mask	warn	expressions where a bit mask will be rendered useless by a comparison, e.g. `(x
inline_always	warn	#[inline(always)] is a bad idea in most cases
iter_next_loop	warn	for-looping over _.next() which is probably not intended
len_without_is_empty	warn	traits and impls that have .len() but not .is_empty()
len_zero	warn	checking .len() == 0 or .len() > 0 (or similar) when .is_empty() could be used instead
let_and_return	warn	creating a let-binding and then immediately returning it like let x = expr; x at the end of a function
let_unit_value	warn	creating a let binding to a value of unit type, which usually can't be used afterwards
linkedlist	warn	usage of LinkedList, usually a vector is faster, or a more specialized data structure like a RingBuf
match_ref_pats	warn	a match has all arms prefixed with &; the match expression can be dereferenced instead
modulo_one	warn	taking a number modulo 1, which always returns 0
mut_mut	warn	usage of double-mut refs, e.g. &mut &mut ... (either copy'n'paste error, or shows a fundamental misunderstanding of references)
needless_bool	warn	if-statements with plain booleans in the then- and else-clause, e.g. if p { true } else { false }
needless_lifetimes	warn	using explicit lifetimes for references in function arguments when elision rules would allow omitting them
needless_range_loop	warn	for-looping over a range of indices where an iterator over items would do
needless_return	warn	using a return statement like return expr; where an expression would suffice
non_ascii_literal	allow	using any literal non-ASCII chars in a string literal; suggests using the \u escape instead
option_unwrap_used	allow	using Option.unwrap(), which should at least get a better message using expect()
precedence	warn	expressions where precedence may trip up the unwary reader of the source; suggests adding parentheses, e.g. x << 2 + y will be parsed as x << (2 + y)
ptr_arg	allow	fn arguments of the type &Vec<...> or &String, suggesting to use &[...] or &str instead, respectively
range_step_by_zero	warn	using Range::step_by(0), which produces an infinite iterator
redundant_closure	warn	using redundant closures, i.e. `
redundant_pattern	warn	using name @ _ in a pattern
result_unwrap_used	allow	using Result.unwrap(), which might be better handled
shadow_reuse	allow	rebinding a name to an expression that re-uses the original value, e.g. let x = x + 1
shadow_same	allow	rebinding a name to itself, e.g. let mut x = &mut x
shadow_unrelated	warn	The name is re-bound without even using the original value
should_implement_trait	warn	defining a method that should be implementing a std trait
single_match	warn	a match statement with a single nontrivial arm (i.e, where the other arm is _ => {}) is used; recommends if let instead
str_to_string	warn	using to_string() on a str, which should be to_owned()
string_add	allow	using x + .. where x is a String; suggests using push_str() instead
string_add_assign	allow	using x = x + .. where x is a String; suggests using push_str() instead
string_to_string	warn	calling String.to_string() which is a no-op
toplevel_ref_arg	warn	a function argument is declared ref (i.e. fn foo(ref x: u8), but not fn foo((ref x, ref y): (u8, u8)))
type_complexity	warn	usage of very complex types; recommends factoring out parts into type definitions
unit_cmp	warn	comparing unit values (which is always true or false, respectively)
unused_collect	warn	collect()ing an iterator without using the result; this is usually better written as a for loop
while_let_loop	warn	loop { if let { ... } else break } can be written as a while let loop
zero_width_space	deny	using a zero-width space in a string literal, which is confusing

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

##Usage

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:

[dependencies]
clippy = "*"

Sample main.rs:

#![feature(plugin)]

#![plugin(clippy)]


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

Produce this warning:

src/main.rs:8:5: 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/main.rs:8     match x {
src/main.rs:9         Some(y) => println!("{:?}", y),
src/main.rs:10         _ => ()
src/main.rs:11     }
src/main.rs:8:5: 11:6 help: Try
if let Some(y) = x { println!("{:?}", y) }

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

Note: deny produces errors instead of warnings

To have cargo compile your crate with clippy without needing #![plugin(clippy)] in your code, you can use:

cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy

##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.