A collection of lints that give helpful tips to newbies and catch oversights.
There are 58 lints included in this crate:
name | default | meaning
-------------------------------------------------------------------------------------------------------|---------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
approxconstant | warn | the approximate of a known float constant (in std::f64::consts or std::f32::consts) is found; suggests to use the constant
badbitmask | warn | 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)
boxvec | warn | usage of Box<Vec<T>>, vector elements are already on the heap
castpossibletruncation | allow | casts that may cause truncation of the value, e.g x as u8 where x: u32, or x as i32 where x: f32
castpossiblewrap | allow | casts that may cause wrapping around the value, e.g x as i32 where x: u32 and x > i32::MAX
castprecisionloss | allow | casts that cause loss of precision, e.g x as f32 where x: u64
castsignloss | allow | casts from signed types to unsigned types, e.g x as u32 where x: i32
cmpnan | deny | comparisons to NAN (which will always return false, which is probably not intended)
cmpowned | warn | creating owned instances for comparing with others, e.g. x == "foo".to_string()
collapsibleif | 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() }
eqop | warn | equal operands on both sides of a comparison or bitwise combination (e.g. x == x)
explicitcounterloop | warn | for-looping with an explicit counter when _.enumerate() would do
explicititerloop | warn | for-looping over _.iter() or _.iter_mut() when &_ or &mut _ would do
floatcmp | 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)
identityop | warn | using identity operations, e.g. x + 0 or y / 1
ineffectivebitmask | warn | expressions where a bit mask will be rendered useless by a comparison, e.g. (x | 1) > 2
inlinealways | warn | #[inline(always)] is a bad idea in most cases
iternextloop | warn | for-looping over _.next() which is probably not intended
lenwithoutisempty | warn | traits and impls that have .len() but not .is_empty()
lenzero | warn | checking .len() == 0 or .len() > 0 (or similar) when .is_empty() could be used instead
letandreturn | warn | creating a let-binding and then immediately returning it like let x = expr; x at the end of a function
letunitvalue | 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
matchrefpats | warn | a match has all arms prefixed with &; the match expression can be dereferenced instead
minmax | warn | min(_, max(_, _)) (or vice versa) with bounds clamping the result to a constant
moduloone | warn | taking a number modulo 1, which always returns 0
mutmut | allow | usage of double-mut refs, e.g. &mut &mut ... (either copy'n'paste error, or shows a fundamental misunderstanding of references)
needlessbool | warn | if-statements with plain booleans in the then- and else-clause, e.g. if p { true } else { false }
needlesslifetimes | warn | using explicit lifetimes for references in function arguments when elision rules would allow omitting them
needlessrangeloop | warn | for-looping over a range of indices where an iterator over items would do
needlessreturn | warn | using a return statement like return expr; where an expression would suffice
nonasciiliteral | allow | using any literal non-ASCII chars in a string literal; suggests using the \u escape instead
optionunwrapused | allow | using Option.unwrap(), which should at least get a better message using expect()
precedence | warn | catches operations where precedence may be unclear. See the wiki for a list of cases caught
ptrarg | allow | fn arguments of the type &Vec<...> or &String, suggesting to use &[...] or &str instead, respectively
rangestepbyzero | warn | using Range::stepby(0), which produces an infinite iterator
redundantclosure | warn | using redundant closures, i.e. |a| foo(a) (which can be written as just foo)
redundantpattern | warn | using name @ _ in a pattern
resultunwrapused | allow | using Result.unwrap(), which might be better handled
reverserangeloop | warn | Iterating over an empty range, such as 10..0 or 5..5
shadowreuse | allow | rebinding a name to an expression that re-uses the original value, e.g. let x = x + 1
shadowsame | allow | rebinding a name to itself, e.g. let mut x = &mut x
shadowunrelated | allow | The name is re-bound without even using the original value
shouldimplementtrait | warn | defining a method that should be implementing a std trait
singlematch | warn | a match statement with a single nontrivial arm (i.e, where the other arm is _ => {}) is used; recommends if let instead
strtostring | warn | using to_string() on a str, which should be to_owned()
stringadd | allow | using x + .. where x is a String; suggests using push_str() instead
stringaddassign | allow | using x = x + .. where x is a String; suggests using push_str() instead
stringtostring | warn | calling String.to_string() which is a no-op
toplevelrefarg | warn | a function argument is declared ref (i.e. fn foo(ref x: u8), but not fn foo((ref x, ref y): (u8, u8)))
typecomplexity | warn | usage of very complex types; recommends factoring out parts into type definitions
unicodenotnfc | allow | using a unicode literal not in NFC normal form (see http://www.unicode.org/reports/tr15/ for further information)
unitcmp | warn | comparing unit values (which is always true or false, respectively)
unusedcollect | warn | collect()ing an iterator without using the result; this is usually better written as a for loop
whileletloop | warn | loop { if let { ... } else break } can be written as a while let loop
wrongpubselfconvention | allow | defining a public method named with an established prefix (like "into") that takes self with the wrong convention
wrongselfconvention | warn | defining a method named with an established prefix (like "into") that takes self with the wrong convention
zerowidth_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!
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:
toml
[dependencies]
clippy = "*"
You may also use cargo clippy, a custom cargo subcommand that runs clippy on a given project.
Sample main.rs:
```rust
fn main(){ let x = Some(1u8); match x { Some(y) => println!("{:?}", y), _ => () } } ```
Produces this warning:
src/main.rs:8:5: 11:6 warning: you seem to be trying to use match for destructuring a single type. Consider using `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
Note: Be sure that clippy was compiled with the same version of rustc that cargo invokes here!
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.