# rust-clippy
[](https://travis-ci.org/Manishearth/rust-clippy)
[](http://clippy.bashy.io/github/Manishearth/rust-clippy/master/log)
[](https://crates.io/crates/clippy)
[](#License)
A collection of lints to catch common mistakes and improve your Rust code.
Table of contents:
* [Lint list](#lints)
* [Usage instructions](#usage)
* [Configuration](#configuration)
* [*clippy-service*](#link-with-clippy-service)
* [License](#license)
## Lints
There are 149 lints included in this crate:
[absurd_extreme_comparisons](https://github.com/Manishearth/rust-clippy/wiki#absurd_extreme_comparisons) | warn | a comparison involving a maximum or minimum value involves a case that is always true or always false
[almost_swapped](https://github.com/Manishearth/rust-clippy/wiki#almost_swapped) | warn | `foo = bar; bar = foo` sequence
[approx_constant](https://github.com/Manishearth/rust-clippy/wiki#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
[assign_op_pattern](https://github.com/Manishearth/rust-clippy/wiki#assign_op_pattern) | warn | assigning the result of an operation on a variable to that same variable
[assign_ops](https://github.com/Manishearth/rust-clippy/wiki#assign_ops) | allow | Any assignment operation
[bad_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask) | 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)
[blacklisted_name](https://github.com/Manishearth/rust-clippy/wiki#blacklisted_name) | warn | usage of a blacklisted/placeholder name
[block_in_if_condition_expr](https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_expr) | warn | braces can be eliminated in conditions that are expressions, e.g `if { true } ...`
[block_in_if_condition_stmt](https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_stmt) | warn | avoid complex blocks in conditions, instead move the block higher and bind it with 'let'; e.g: `if { let x = true; x } ...`
[bool_comparison](https://github.com/Manishearth/rust-clippy/wiki#bool_comparison) | warn | comparing a variable to a boolean, e.g. `if x == true`
[box_vec](https://github.com/Manishearth/rust-clippy/wiki#box_vec) | warn | usage of `Box<Vec<T>>`, vector elements are already on the heap
[boxed_local](https://github.com/Manishearth/rust-clippy/wiki#boxed_local) | warn | using `Box<T>` where unnecessary
[cast_possible_truncation](https://github.com/Manishearth/rust-clippy/wiki#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](https://github.com/Manishearth/rust-clippy/wiki#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](https://github.com/Manishearth/rust-clippy/wiki#cast_precision_loss) | allow | casts that cause loss of precision, e.g `x as f32` where `x: u64`
[cast_sign_loss](https://github.com/Manishearth/rust-clippy/wiki#cast_sign_loss) | allow | casts from signed types to unsigned types, e.g `x as u32` where `x: i32`
[char_lit_as_u8](https://github.com/Manishearth/rust-clippy/wiki#char_lit_as_u8) | warn | Casting a character literal to u8
[chars_next_cmp](https://github.com/Manishearth/rust-clippy/wiki#chars_next_cmp) | warn | using `.chars().next()` to check if a string starts with a char
[clone_double_ref](https://github.com/Manishearth/rust-clippy/wiki#clone_double_ref) | warn | using `clone` on `&&T`
[clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#clone_on_copy) | warn | using `clone` on a `Copy` type
[cmp_nan](https://github.com/Manishearth/rust-clippy/wiki#cmp_nan) | deny | comparisons to NAN (which will always return false, which is probably not intended)
[cmp_owned](https://github.com/Manishearth/rust-clippy/wiki#cmp_owned) | warn | creating owned instances for comparing with others, e.g. `x == "foo".to_string()`
[collapsible_if](https://github.com/Manishearth/rust-clippy/wiki#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() }` and an `else { if .. } expression can be collapsed to `else 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 | `Warn` on `#[deprecated(since = "x")]` where x is not semver
[derive_hash_xor_eq](https://github.com/Manishearth/rust-clippy/wiki#derive_hash_xor_eq) | warn | deriving `Hash` but implementing `PartialEq` explicitly
[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 to `std::mem::drop` with a reference instead of an owned value, which will not call the `Drop::drop` method 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 | empty `loop {}` detected
[enum_clike_unportable_variant](https://github.com/Manishearth/rust-clippy/wiki#enum_clike_unportable_variant) | warn | finds C-like enums that are `repr(isize/usize)` and have values that don't fit into an `i32`
[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 | implementing `Clone` explicitly on `Copy` types
[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 `_.iter_mut()` when `&_` or `&mut _` would do
[extend_from_slice](https://github.com/Manishearth/rust-clippy/wiki#extend_from_slice) | warn | `.extend_from_slice(_)` is a faster way to extend a Vec by a slice
[filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next) | warn | using `filter(p).next()`, which is more succinctly expressed as `.find(p)`
[float_arithmetic](https://github.com/Manishearth/rust-clippy/wiki#float_arithmetic) | allow | Any floating-point arithmetic statement
[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 using `iter` when `keys` or `values` would do
[for_loop_over_option](https://github.com/Manishearth/rust-clippy/wiki#for_loop_over_option) | warn | for-looping over an `Option`, which is more clearly expressed as an `if let`
[for_loop_over_result](https://github.com/Manishearth/rust-clippy/wiki#for_loop_over_result) | warn | for-looping over a `Result`, which is more clearly expressed as an `if let`
[identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op) | warn | using identity operations, e.g. `x + 0` or `y / 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 | consecutive `ifs` with 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
[integer_arithmetic](https://github.com/Manishearth/rust-clippy/wiki#integer_arithmetic) | allow | Any integer arithmetic statement
[invalid_regex](https://github.com/Manishearth/rust-clippy/wiki#invalid_regex) | deny | finds invalid regular expressions in `Regex::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 `.is_empty()`
[len_zero](https://github.com/Manishearth/rust-clippy/wiki#len_zero) | warn | checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` 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 like `let x = expr; x` at 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 of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`
[match_bool](https://github.com/Manishearth/rust-clippy/wiki#match_bool) | warn | a match on boolean expression; recommends `if..else` block 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 or `if let` has 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 | `match` with identical arm bodies
[mem_forget](https://github.com/Manishearth/rust-clippy/wiki#mem_forget) | allow | `mem::forget` usage on `Drop` types 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_borrow](https://github.com/Manishearth/rust-clippy/wiki#needless_borrow) | warn | taking a reference that is going to be automatically dereferenced
[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 like `return 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 returning `Self` in a `new` method
[new_without_default](https://github.com/Manishearth/rust-clippy/wiki#new_without_default) | warn | `fn new() -> Self` method without `Default` implementation
[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 | using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result
[option_map_unwrap_or](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or) | warn | using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`
[option_map_unwrap_or_else](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or_else) | warn | using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`
[option_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#option_unwrap_used) | allow | using `Option.unwrap()`, which should at least get a better message using `expect()`
[or_fun_call](https://github.com/Manishearth/rust-clippy/wiki#or_fun_call) | warn | using any `*or` method when the `*or_else` would 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 in `panic!`
[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 `&str` instead, 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 just `foo`)
[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 | using `name @ _` in a pattern
[regex_macro](https://github.com/Manishearth/rust-clippy/wiki#regex_macro) | warn | finds use of `regex!(_)`, suggests `Regex::new(_)` instead
[result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used) | allow | using `Result.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 as `10..0` or `5..5`
[search_is_some](https://github.com/Manishearth/rust-clippy/wiki#search_is_some) | warn | using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`
[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) | allow | 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; recommends `if let` instead
[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; recommends `if let` instead
[string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add) | allow | using `x + ..` where x is a `String`; suggests using `push_str()` instead
[string_add_assign](https://github.com/Manishearth/rust-clippy/wiki#string_add_assign) | allow | using `x = x + ..` where x is a `String`; suggests using `push_str()` instead
[string_lit_as_bytes](https://github.com/Manishearth/rust-clippy/wiki#string_lit_as_bytes) | warn | calling `as_bytes` on 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 of `else 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 temporary `CString`
[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 as `ref`, in a function argument (`fn foo(ref x: Bar)`), or a `let` statement (`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 in `Regex::new(_)` invocations
[type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity) | warn | usage of very complex types; recommends factoring out parts into `type` definitions
[unicode_not_nfc](https://github.com/Manishearth/rust-clippy/wiki#unicode_not_nfc) | allow | using a unicode literal not in NFC normal form (see [unicode tr15](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 always `true` or `false`, 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 | use `Debug`-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 of `format!`
[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 | useless `vec!`
[while_let_loop](https://github.com/Manishearth/rust-clippy/wiki#while_let_loop) | warn | `loop { if let { ... } else break }` can be written as a `while let` loop
[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 takes `self` with 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 takes `self` with the wrong convention
[zero_divided_by_zero](https://github.com/Manishearth/rust-clippy/wiki#zero_divided_by_zero) | warn | usage of `0.0 / 0.0` to obtain NaN instead of std::f32::NaN or std::f64::NaN
[zero_width_space](https://github.com/Manishearth/rust-clippy/wiki#zero_width_space) | deny | using a zero-width space in a string literal, which is confusing
More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
## Usage
### As a Compiler Plugin
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
#![feature(plugin)]
#![plugin(clippy)]
fn main(){
let x = Some(1u8);
match x {
Some(y) => println!("{:?}", y),
_ => ()
}
}
```
Produces this warning:
```terminal
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) }
```
### As a cargo subcommand (`cargo clippy`)
An alternate way to use clippy is by installing clippy through cargo as a cargo
subcommand.
```terminal
cargo install clippy
```
Now you can run clippy by invoking `cargo clippy`, or
`multirust run nightly cargo clippy` directly from a directory that is usually
compiled with stable.
In case you are not using multirust, you need to set the environment flag
`SYSROOT` during installation so clippy knows where to find `librustc` and
similar crates.
```terminal
SYSROOT=/path/to/rustc/sysroot cargo install clippy
```
### Configuring clippy
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
### Running clippy from the command line without installing
To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
in your code, you can use:
```terminal
cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
```
*[Note](https://github.com/Manishearth/rust-clippy/wiki#a-word-of-warning):*
Be sure that clippy was compiled with the same version of rustc that cargo invokes here!
### Optional dependency
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
#![cfg_attr(feature="clippy", feature(plugin))]
#![cfg_attr(feature="clippy", plugin(clippy))]
```
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).
## Configuration
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
#![plugin(clippy(conf_file="path/to/clippy's/configuration"))]
```
## Link with clippy service
`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](https://clippy.bashy.io/).
## License
Licensed under [MPL](https://www.mozilla.org/MPL/2.0/).
If you're having issues with the license, let me know and I'll try to change it to something more permissive.