A collection of lints to catch common mistakes and improve your Rust code.
Table of contents: * Lint list * Usage instructions * Configuration * clippy-service * License
There are 144 lints included in this crate:
name | default | meaning
---------------------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
absurdextremecomparisons | warn | a comparison involving a maximum or minimum value involves a case that is always true or always false
almostswapped | warn | foo = bar; bar = foo sequence
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)
blacklistedname | warn | usage of a blacklisted/placeholder name
blockinifconditionexpr | warn | braces can be eliminated in conditions that are expressions, e.g if { true } ...
blockinifconditionstmt | warn | avoid complex blocks in conditions, instead move the block higher and bind it with 'let'; e.g: if { let x = true; x } ...
boolcomparison | warn | comparing a variable to a boolean, e.g. if x == true
boxvec | warn | usage of Box<Vec<T>>, vector elements are already on the heap
boxedlocal | warn | using Boxx 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
charlitasu8 | warn | Casting a character literal to u8
charsnextcmp | warn | using .chars().next() to check if a string starts with a char
clonedoubleref | warn | using clone on &&T
cloneoncopy | warn | using clone on a Copy type
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() } and an else { if .. } expression can be collapsed toelse if
[crosspointer_transmute](https://github.com/Manishearth/rust-clippy/wiki#crosspointer_transmute) | warn | transmutes that have to or from types that are a pointer to the other
[cyclomatic_complexity](https://github.com/Manishearth/rust-clippy/wiki#cyclomatic_complexity) | warn | finds functions that should be split up into multiple functions
[deprecated_semver](https://github.com/Manishearth/rust-clippy/wiki#deprecated_semver) | warn |Warnon#[deprecated(since = "x")]where x is not semver
[derive_hash_xor_eq](https://github.com/Manishearth/rust-clippy/wiki#derive_hash_xor_eq) | warn | derivingHashbut implementingPartialEqexplicitly
[doc_markdown](https://github.com/Manishearth/rust-clippy/wiki#doc_markdown) | warn | checks for the presence of,::or camel-case outside ticks in documentation
[drop_ref](https://github.com/Manishearth/rust-clippy/wiki#drop_ref) | warn | call tostd::mem::dropwith a reference instead of an owned value, which will not call theDrop::dropmethod on the underlying value
[duplicate_underscore_argument](https://github.com/Manishearth/rust-clippy/wiki#duplicate_underscore_argument) | warn | Function arguments having names which only differ by an underscore
[empty_loop](https://github.com/Manishearth/rust-clippy/wiki#empty_loop) | warn | emptyloop {}detected
[enum_clike_unportable_variant](https://github.com/Manishearth/rust-clippy/wiki#enum_clike_unportable_variant) | warn | finds C-like enums that arerepr(isize/usize)and have values that don't fit into ani32
[enum_glob_use](https://github.com/Manishearth/rust-clippy/wiki#enum_glob_use) | allow | finds use items that import all variants of an enum
[enum_variant_names](https://github.com/Manishearth/rust-clippy/wiki#enum_variant_names) | warn | finds enums where all variants share a prefix/postfix
[eq_op](https://github.com/Manishearth/rust-clippy/wiki#eq_op) | warn | equal operands on both sides of a comparison or bitwise combination (e.g.x == x)
[expl_impl_clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#expl_impl_clone_on_copy) | warn | implementingCloneexplicitly onCopytypes
[explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop) | warn | for-looping with an explicit counter when.enumerate()would do
[explicit_iter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_iter_loop) | warn | for-looping over.iter()or.itermut()when&or&mut would do
[extend_from_slice](https://github.com/Manishearth/rust-clippy/wiki#extend_from_slice) | warn |.extendfromslice()is a faster way to extend a Vec by a slice
[filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next) | warn | usingfilter(p).next(), which is more succinctly expressed as.find(p)
[float_cmp](https://github.com/Manishearth/rust-clippy/wiki#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)
[for_kv_map](https://github.com/Manishearth/rust-clippy/wiki#for_kv_map) | warn | looping on a map usingiterwhenkeysorvalueswould do
[for_loop_over_option](https://github.com/Manishearth/rust-clippy/wiki#for_loop_over_option) | warn | for-looping over anOption, which is more clearly expressed as anif let
[for_loop_over_result](https://github.com/Manishearth/rust-clippy/wiki#for_loop_over_result) | warn | for-looping over aResult, which is more clearly expressed as anif let
[identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op) | warn | using identity operations, e.g.x + 0ory / 1
[if_not_else](https://github.com/Manishearth/rust-clippy/wiki#if_not_else) | allow | finds if branches that could be swapped so no negation operation is necessary on the condition
[if_same_then_else](https://github.com/Manishearth/rust-clippy/wiki#if_same_then_else) | warn | if with the same *then* and *else* blocks
[ifs_same_cond](https://github.com/Manishearth/rust-clippy/wiki#ifs_same_cond) | warn | consecutiveifswith the same condition
[indexing_slicing](https://github.com/Manishearth/rust-clippy/wiki#indexing_slicing) | allow | indexing/slicing usage
[ineffective_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#ineffective_bit_mask) | warn | expressions where a bit mask will be rendered useless by a comparison, e.g.(x | 1) > 2
[inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always) | warn |#[inline(always)]is a bad idea in most cases
[invalid_regex](https://github.com/Manishearth/rust-clippy/wiki#invalid_regex) | deny | finds invalid regular expressions inRegex::new()invocations
[invalid_upcast_comparisons](https://github.com/Manishearth/rust-clippy/wiki#invalid_upcast_comparisons) | warn | a comparison involving an upcast which is always true or false
[items_after_statements](https://github.com/Manishearth/rust-clippy/wiki#items_after_statements) | allow | finds blocks where an item comes after a statement
[iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop) | warn | for-looping over.next()which is probably not intended
[len_without_is_empty](https://github.com/Manishearth/rust-clippy/wiki#len_without_is_empty) | warn | traits and impls that have.len()but not.isempty()
[len_zero](https://github.com/Manishearth/rust-clippy/wiki#len_zero) | warn | checking.len() == 0or.len() > 0(or similar) when.isempty()could be used instead
[let_and_return](https://github.com/Manishearth/rust-clippy/wiki#let_and_return) | warn | creating a let-binding and then immediately returning it likelet x = expr; xat the end of a block
[let_unit_value](https://github.com/Manishearth/rust-clippy/wiki#let_unit_value) | warn | creating a let binding to a value of unit type, which usually can't be used afterwards
[linkedlist](https://github.com/Manishearth/rust-clippy/wiki#linkedlist) | warn | usage of LinkedList, usually a vector is faster, or a more specialized data structure like a VecDeque
[logic_bug](https://github.com/Manishearth/rust-clippy/wiki#logic_bug) | warn | checks for boolean expressions that contain terminals which can be eliminated
[manual_swap](https://github.com/Manishearth/rust-clippy/wiki#manual_swap) | warn | manual swap
[many_single_char_names](https://github.com/Manishearth/rust-clippy/wiki#many_single_char_names) | warn | too many single character bindings
[map_clone](https://github.com/Manishearth/rust-clippy/wiki#map_clone) | warn | using.map(|x| x.clone())to clone an iterator or option's contents (recommends.cloned()instead)
[map_entry](https://github.com/Manishearth/rust-clippy/wiki#map_entry) | warn | use ofcontainskeyfollowed byinserton aHashMaporBTreeMap
[match_bool](https://github.com/Manishearth/rust-clippy/wiki#match_bool) | warn | a match on boolean expression; recommendsif..elseblock instead
[match_overlapping_arm](https://github.com/Manishearth/rust-clippy/wiki#match_overlapping_arm) | warn | a match has overlapping arms
[match_ref_pats](https://github.com/Manishearth/rust-clippy/wiki#match_ref_pats) | warn | a match orif lethas all arms prefixed with&; the match expression can be dereferenced instead
[match_same_arms](https://github.com/Manishearth/rust-clippy/wiki#match_same_arms) | warn |matchwith identical arm bodies
[mem_forget](https://github.com/Manishearth/rust-clippy/wiki#mem_forget) | allow |mem::forgetusage onDroptypes is likely to cause memory leaks
[min_max](https://github.com/Manishearth/rust-clippy/wiki#min_max) | warn |min(, max(, _))(or vice versa) with bounds clamping the result to a constant
[modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one) | warn | taking a number modulo 1, which always returns 0
[mut_mut](https://github.com/Manishearth/rust-clippy/wiki#mut_mut) | allow | usage of double-mut refs, e.g.&mut &mut ...(either copy'n'paste error, or shows a fundamental misunderstanding of references)
[mutex_atomic](https://github.com/Manishearth/rust-clippy/wiki#mutex_atomic) | warn | using a Mutex where an atomic value could be used instead
[mutex_integer](https://github.com/Manishearth/rust-clippy/wiki#mutex_integer) | allow | using a Mutex for an integer type
[needless_bool](https://github.com/Manishearth/rust-clippy/wiki#needless_bool) | warn | if-statements with plain booleans in the then- and else-clause, e.g.if p { true } else { false }
[needless_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#needless_lifetimes) | warn | using explicit lifetimes for references in function arguments when elision rules would allow omitting them
[needless_range_loop](https://github.com/Manishearth/rust-clippy/wiki#needless_range_loop) | warn | for-looping over a range of indices where an iterator over items would do
[needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return) | warn | using a return statement likereturn expr;where an expression would suffice
[needless_update](https://github.com/Manishearth/rust-clippy/wiki#needless_update) | warn | using{ ..base }when there are no missing fields
[neg_multiply](https://github.com/Manishearth/rust-clippy/wiki#neg_multiply) | warn | Warns on multiplying integers with -1
[new_ret_no_self](https://github.com/Manishearth/rust-clippy/wiki#new_ret_no_self) | warn | not returningSelfin anewmethod
[new_without_default](https://github.com/Manishearth/rust-clippy/wiki#new_without_default) | warn |fn new() -> Selfmethod withoutDefaultimplementation
[no_effect](https://github.com/Manishearth/rust-clippy/wiki#no_effect) | warn | statements with no effect
[non_ascii_literal](https://github.com/Manishearth/rust-clippy/wiki#non_ascii_literal) | allow | using any literal non-ASCII chars in a string literal; suggests using the \\u escape instead
[nonminimal_bool](https://github.com/Manishearth/rust-clippy/wiki#nonminimal_bool) | allow | checks for boolean expressions that can be written more concisely
[nonsensical_open_options](https://github.com/Manishearth/rust-clippy/wiki#nonsensical_open_options) | warn | nonsensical combination of options for opening a file
[ok_expect](https://github.com/Manishearth/rust-clippy/wiki#ok_expect) | warn | usingok().expect(), which gives worse error messages than callingexpectdirectly on the Result
[option_map_unwrap_or](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or) | warn | usingOption.map(f).unwrapor(a), which is more succinctly expressed asmapor(a, f)
[option_map_unwrap_or_else](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or_else) | warn | usingOption.map(f).unwraporelse(g), which is more succinctly expressed asmaporelse(g, f)
[option_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#option_unwrap_used) | allow | usingOption.unwrap(), which should at least get a better message usingexpect()
[or_fun_call](https://github.com/Manishearth/rust-clippy/wiki#or_fun_call) | warn | using any*ormethod when the*orelsewould do
[out_of_bounds_indexing](https://github.com/Manishearth/rust-clippy/wiki#out_of_bounds_indexing) | deny | out of bound constant indexing
[overflow_check_conditional](https://github.com/Manishearth/rust-clippy/wiki#overflow_check_conditional) | warn | Using overflow checks which are likely to panic
[panic_params](https://github.com/Manishearth/rust-clippy/wiki#panic_params) | warn | missing parameters inpanic!
[precedence](https://github.com/Manishearth/rust-clippy/wiki#precedence) | warn | catches operations where precedence may be unclear. See the wiki for a list of cases caught
[print_stdout](https://github.com/Manishearth/rust-clippy/wiki#print_stdout) | allow | printing on stdout
[ptr_arg](https://github.com/Manishearth/rust-clippy/wiki#ptr_arg) | warn | fn arguments of the type&Vec<...>or&String, suggesting to use&[...]or&strinstead, respectively
[range_step_by_zero](https://github.com/Manishearth/rust-clippy/wiki#range_step_by_zero) | warn | using Range::step_by(0), which produces an infinite iterator
[range_zip_with_len](https://github.com/Manishearth/rust-clippy/wiki#range_zip_with_len) | warn | zipping iterator with a range when enumerate() would do
[redundant_closure](https://github.com/Manishearth/rust-clippy/wiki#redundant_closure) | warn | using redundant closures, i.e.|a| foo(a)(which can be written as justfoo)
[redundant_closure_call](https://github.com/Manishearth/rust-clippy/wiki#redundant_closure_call) | warn | Closures should not be called in the expression they are defined
[redundant_pattern](https://github.com/Manishearth/rust-clippy/wiki#redundant_pattern) | warn | usingname @ in a pattern
[regex_macro](https://github.com/Manishearth/rust-clippy/wiki#regex_macro) | warn | finds use ofregex!(), suggestsRegex::new()instead
[result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used) | allow | usingResult.unwrap(), which might be better handled
[reverse_range_loop](https://github.com/Manishearth/rust-clippy/wiki#reverse_range_loop) | warn | Iterating over an empty range, such as10..0or5..5
[search_is_some](https://github.com/Manishearth/rust-clippy/wiki#search_is_some) | warn | using an iterator search followed byissome(), which is more succinctly expressed as a call toany()
[shadow_reuse](https://github.com/Manishearth/rust-clippy/wiki#shadow_reuse) | allow | rebinding a name to an expression that re-uses the original value, e.g.let x = x + 1
[shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same) | allow | rebinding a name to itself, e.g.let mut x = &mut x
[shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated) | allow | The name is re-bound without even using the original value
[should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait) | warn | defining a method that should be implementing a std trait
[similar_names](https://github.com/Manishearth/rust-clippy/wiki#similar_names) | warn | similarly named items and bindings
[single_char_pattern](https://github.com/Manishearth/rust-clippy/wiki#single_char_pattern) | warn | using a single-character str where a char could be used, e.g..split("x")
[single_match](https://github.com/Manishearth/rust-clippy/wiki#single_match) | warn | a match statement with a single nontrivial arm (i.e, where the other arm is => {}) is used; recommendsif letinstead
[single_match_else](https://github.com/Manishearth/rust-clippy/wiki#single_match_else) | allow | a match statement with a two arms where the second arm's pattern is a wildcard; recommendsif letinstead
[string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add) | allow | usingx + ..where x is aString; suggests usingpushstr()instead
[string_add_assign](https://github.com/Manishearth/rust-clippy/wiki#string_add_assign) | allow | usingx = x + ..where x is aString; suggests usingpushstr()instead
[string_lit_as_bytes](https://github.com/Manishearth/rust-clippy/wiki#string_lit_as_bytes) | warn | callingasbyteson a string literal; suggests using a byte string literal instead
[suspicious_assignment_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_assignment_formatting) | warn | suspicious formatting of*=,-=or!=
[suspicious_else_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_else_formatting) | warn | suspicious formatting ofelse if
[temporary_assignment](https://github.com/Manishearth/rust-clippy/wiki#temporary_assignment) | warn | assignments to temporaries
[temporary_cstring_as_ptr](https://github.com/Manishearth/rust-clippy/wiki#temporary_cstring_as_ptr) | warn | getting the inner pointer of a temporaryCString
[too_many_arguments](https://github.com/Manishearth/rust-clippy/wiki#too_many_arguments) | warn | functions with too many arguments
[toplevel_ref_arg](https://github.com/Manishearth/rust-clippy/wiki#toplevel_ref_arg) | warn | An entire binding was declared asref, in a function argument (fn foo(ref x: Bar)), or aletstatement (let ref x = foo()). In such cases, it is preferred to take references with&.
[transmute_ptr_to_ref](https://github.com/Manishearth/rust-clippy/wiki#transmute_ptr_to_ref) | warn | transmutes from a pointer to a reference type
[trivial_regex](https://github.com/Manishearth/rust-clippy/wiki#trivial_regex) | warn | finds trivial regular expressions inRegex::new()invocations
[type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity) | warn | usage of very complex types; recommends factoring out parts intotypedefinitions
[unicode_not_nfc](https://github.com/Manishearth/rust-clippy/wiki#unicode_not_nfc) | allow | using a unicode literal not in NFC normal form (see http://www.unicode.org/reports/tr15/ for further information)
[unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp) | warn | comparing unit values (which is alwaystrueorfalse, respectively)
[unnecessary_mut_passed](https://github.com/Manishearth/rust-clippy/wiki#unnecessary_mut_passed) | warn | an argument is passed as a mutable reference although the function/method only demands an immutable reference
[unneeded_field_pattern](https://github.com/Manishearth/rust-clippy/wiki#unneeded_field_pattern) | warn | Struct fields are bound to a wildcard instead of using..
[unsafe_removed_from_name](https://github.com/Manishearth/rust-clippy/wiki#unsafe_removed_from_name) | warn | unsafe removed from name
[unused_collect](https://github.com/Manishearth/rust-clippy/wiki#unused_collect) | warn |collect()ing an iterator without using the result; this is usually better written as a for loop
[unused_label](https://github.com/Manishearth/rust-clippy/wiki#unused_label) | warn | unused label
[unused_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#unused_lifetimes) | warn | unused lifetimes in function definitions
[use_debug](https://github.com/Manishearth/rust-clippy/wiki#use_debug) | allow | useDebug-based formatting
[used_underscore_binding](https://github.com/Manishearth/rust-clippy/wiki#used_underscore_binding) | warn | using a binding which is prefixed with an underscore
[useless_format](https://github.com/Manishearth/rust-clippy/wiki#useless_format) | warn | useless use offormat!
[useless_transmute](https://github.com/Manishearth/rust-clippy/wiki#useless_transmute) | warn | transmutes that have the same to and from types
[useless_vec](https://github.com/Manishearth/rust-clippy/wiki#useless_vec) | warn | uselessvec!
[while_let_loop](https://github.com/Manishearth/rust-clippy/wiki#while_let_loop) | warn |loop { if let { ... } else break }can be written as awhile letloop
[while_let_on_iterator](https://github.com/Manishearth/rust-clippy/wiki#while_let_on_iterator) | warn | using a while-let loop instead of a for loop on an iterator
[wrong_pub_self_convention](https://github.com/Manishearth/rust-clippy/wiki#wrong_pub_self_convention) | allow | defining a public method named with an established prefix (like "into_") that takesselfwith the wrong convention
[wrong_self_convention](https://github.com/Manishearth/rust-clippy/wiki#wrong_self_convention) | warn | defining a method named with an established prefix (like "into_") that takesselfwith the wrong convention
[zero_divided_by_zero](https://github.com/Manishearth/rust-clippy/wiki#zero_divided_by_zero) | warn | usage of0.0 / 0.0` to obtain NaN instead of std::f32::NaN or std::f64::NaN
zerowidthspace | 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 then need to add #![feature(plugin)] and #![plugin(clippy)] to the top of your crate entry point (main.rs or lib.rs).
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) }
An alternate way to use clippy is by compiling and using cargo clippy, a custom cargo subcommand that runs clippy on a given project.
You can add options to allow/warn/deny:
- the whole set of Warn lints using the clippy lint group (#![deny(clippy)])
- all lints using both the clippy and clippy_pedantic lint groups (#![deny(clippy)], #![deny(clippy_pedantic)]). Note that clippy_pedantic contains some very aggressive lints prone to false positives.
- 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!
If you want to make clippy an optional dependency, you can do the following:
In your Cargo.toml:
```toml
[dependencies]
clippy = {version = "*", optional = true}
[features] default=[] ```
And, in your main.rs or lib.rs:
```rust
```
Instead of adding the cfg_attr attributes you can also run clippy on demand: cargo rustc --features clippy -- -Z no-trans -Z extra-plugins=clippy (the -Z no trans, while not neccessary, will stop the compilation process after typechecking (and lints) have completed, which can significantly reduce the runtime).
Some lints can be configured in a clippy.toml file. It contains basic variable = value mapping eg.
toml
blacklisted-names = ["toto", "tata", "titi"]
cyclomatic-complexity-threshold = 30
See the wiki for more information about which lints can be configured and the meaning of the variables.
You can also specify the path to the configuration file with: ```rust
```
clippy-service is a rust web initiative providing rust-clippy as a web service.
Both projects are independent and maintained by different people (even if some clippy-service's contributions are authored by some rust-clippy members).
You can check out this great service at clippy.bashy.io.
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.