3 [![Build Status](https://travis-ci.org/Manishearth/rust-clippy.svg?branch=master)](https://travis-ci.org/Manishearth/rust-clippy)
4 [![Clippy Linting Result](http://clippy.bashy.io/github/Manishearth/rust-clippy/master/badge.svg)](http://clippy.bashy.io/github/Manishearth/rust-clippy/master/log)
5 [![Current Version](http://meritbadge.herokuapp.com/clippy)](https://crates.io/crates/clippy)
6 [![License: MPL-2.0](https://img.shields.io/crates/l/clippy.svg)](#License)
8 A collection of lints to catch common mistakes and improve your Rust code.
13 * [Usage instructions](#usage)
14 * [Configuration](#configuration)
15 * [*clippy-service*](#link-with-clippy-service)
20 As a general rule clippy will only work with the *latest* Rust nightly for now.
22 ### As a Compiler Plugin
24 Since stable Rust is backwards compatible, you should be able to
25 compile your stable programs with nightly Rust with clippy plugged in to
28 Add in your `Cargo.toml`:
35 You then need to add `#![feature(plugin)]` and `#![plugin(clippy)]` to the top
36 of your crate entry point (`main.rs` or `lib.rs`).
49 Some(y) => println!("{:?}", y),
55 Produces this warning:
58 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
59 src/main.rs:8 match x {
60 src/main.rs:9 Some(y) => println!("{:?}", y),
61 src/main.rs:10 _ => ()
63 src/main.rs:8:5: 11:6 help: Try
64 if let Some(y) = x { println!("{:?}", y) }
67 ### As a cargo subcommand (`cargo clippy`)
69 An alternate way to use clippy is by installing clippy through cargo as a cargo
76 Now you can run clippy by invoking `cargo clippy`, or
77 `rustup run nightly cargo clippy` directly from a directory that is usually
80 In case you are not using rustup, you need to set the environment flag
81 `SYSROOT` during installation so clippy knows where to find `librustc` and
85 SYSROOT=/path/to/rustc/sysroot cargo install clippy
88 ### Running clippy from the command line without installing
90 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
91 in your code, you can use:
94 cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
97 *[Note](https://github.com/Manishearth/rust-clippy/wiki#a-word-of-warning):*
98 Be sure that clippy was compiled with the same version of rustc that cargo invokes here!
100 ### Optional dependency
102 If you want to make clippy an optional dependency, you can do the following:
104 In your `Cargo.toml`:
108 clippy = {version = "*", optional = true}
114 And, in your `main.rs` or `lib.rs`:
117 #![cfg_attr(feature="clippy", feature(plugin))]
119 #![cfg_attr(feature="clippy", plugin(clippy))]
122 Then build by enabling the feature: `cargo build --features "clippy"`
124 Instead of adding the `cfg_attr` attributes you can also run clippy on demand:
125 `cargo rustc --features clippy -- -Z no-trans -Z extra-plugins=clippy`
126 (the `-Z no trans`, while not neccessary, will stop the compilation process after
127 typechecking (and lints) have completed, which can significantly reduce the runtime).
131 Some lints can be configured in a `clippy.toml` file. It contains basic `variable = value` mapping eg.
134 blacklisted-names = ["toto", "tata", "titi"]
135 cyclomatic-complexity-threshold = 30
138 See the wiki for more information about which lints can be configured and the
139 meaning of the variables.
141 You can also specify the path to the configuration file with:
144 #![plugin(clippy(conf_file="path/to/clippy's/configuration"))]
147 To deactivate the “for further information visit *wiki-link*” message you can
148 define the `CLIPPY_DISABLE_WIKI_LINKS` environment variable.
150 ### Allowing/denying lints
152 You can add options to `allow`/`warn`/`deny`:
154 * the whole set of `Warn` lints using the `clippy` lint group (`#![deny(clippy)]`)
156 * all lints using both the `clippy` and `clippy_pedantic` lint groups (`#![deny(clippy)]`,
157 `#![deny(clippy_pedantic)]`). Note that `clippy_pedantic` contains some very aggressive
158 lints prone to false positives.
160 * only some lints (`#![deny(single_match, box_vec)]`, etc)
162 * `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
164 Note: `deny` produces errors instead of warnings.
166 For convenience, `cargo clippy` automatically defines a `cargo-clippy`
167 features. This lets you set lints level and compile with or without clippy
171 #[cfg_attr(feature = "cargo-clippy", allow(needless_lifetimes))]
174 ## Link with clippy service
176 `clippy-service` is a rust web initiative providing `rust-clippy` as a web service.
178 Both projects are independent and maintained by different people
179 (even if some `clippy-service`'s contributions are authored by some `rust-clippy` members).
181 You can check out this great service at [clippy.bashy.io](https://clippy.bashy.io/).
185 There are 177 lints included in this crate:
187 name | default | triggers on
188 -----------------------------------------------------------------------------------------------------------------------|---------|----------------------------------------------------------------------------------------------------------------------------------
189 [absurd_extreme_comparisons](https://github.com/Manishearth/rust-clippy/wiki#absurd_extreme_comparisons) | warn | a comparison with a maximum or minimum value that is always true or false
190 [almost_swapped](https://github.com/Manishearth/rust-clippy/wiki#almost_swapped) | warn | `foo = bar; bar = foo` sequence
191 [approx_constant](https://github.com/Manishearth/rust-clippy/wiki#approx_constant) | warn | the approximate of a known float constant (in `std::fXX::consts`)
192 [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
193 [assign_ops](https://github.com/Manishearth/rust-clippy/wiki#assign_ops) | allow | any compound assignment operation
194 [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`
195 [blacklisted_name](https://github.com/Manishearth/rust-clippy/wiki#blacklisted_name) | warn | usage of a blacklisted/placeholder name
196 [block_in_if_condition_expr](https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_expr) | warn | braces that can be eliminated in conditions, e.g `if { true } ...`
197 [block_in_if_condition_stmt](https://github.com/Manishearth/rust-clippy/wiki#block_in_if_condition_stmt) | warn | complex blocks in conditions, e.g. `if { let x = true; x } ...`
198 [bool_comparison](https://github.com/Manishearth/rust-clippy/wiki#bool_comparison) | warn | comparing a variable to a boolean, e.g. `if x == true`
199 [box_vec](https://github.com/Manishearth/rust-clippy/wiki#box_vec) | warn | usage of `Box<Vec<T>>`, vector elements are already on the heap
200 [boxed_local](https://github.com/Manishearth/rust-clippy/wiki#boxed_local) | warn | using `Box<T>` where unnecessary
201 [builtin_type_shadow](https://github.com/Manishearth/rust-clippy/wiki#builtin_type_shadow) | warn | shadowing a builtin type
202 [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`
203 [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`
204 [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`
205 [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`
206 [char_lit_as_u8](https://github.com/Manishearth/rust-clippy/wiki#char_lit_as_u8) | warn | casting a character literal to u8
207 [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
208 [clone_double_ref](https://github.com/Manishearth/rust-clippy/wiki#clone_double_ref) | warn | using `clone` on `&&T`
209 [clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#clone_on_copy) | warn | using `clone` on a `Copy` type
210 [cmp_nan](https://github.com/Manishearth/rust-clippy/wiki#cmp_nan) | deny | comparisons to NAN, which will always return false, probably not intended
211 [cmp_null](https://github.com/Manishearth/rust-clippy/wiki#cmp_null) | warn | comparing a pointer to a null pointer, suggesting to use `.is_null()` instead.
212 [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()`
213 [collapsible_if](https://github.com/Manishearth/rust-clippy/wiki#collapsible_if) | warn | `if`s that can be collapsed (e.g. `if x { if y { ... } }` and `else { if x { ... } }`)
214 [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
215 [cyclomatic_complexity](https://github.com/Manishearth/rust-clippy/wiki#cyclomatic_complexity) | warn | functions that should be split up into multiple functions
216 [deprecated_semver](https://github.com/Manishearth/rust-clippy/wiki#deprecated_semver) | warn | use of `#[deprecated(since = "x")]` where x is not semver
217 [derive_hash_xor_eq](https://github.com/Manishearth/rust-clippy/wiki#derive_hash_xor_eq) | warn | deriving `Hash` but implementing `PartialEq` explicitly
218 [diverging_sub_expression](https://github.com/Manishearth/rust-clippy/wiki#diverging_sub_expression) | warn | whether an expression contains a diverging sub expression
219 [doc_markdown](https://github.com/Manishearth/rust-clippy/wiki#doc_markdown) | warn | presence of `_`, `::` or camel-case outside backticks in documentation
220 [double_neg](https://github.com/Manishearth/rust-clippy/wiki#double_neg) | warn | `--x`, which is a double negation of `x` and not a pre-decrement as in C/C++
221 [drop_ref](https://github.com/Manishearth/rust-clippy/wiki#drop_ref) | warn | calls to `std::mem::drop` with a reference instead of an owned value
222 [duplicate_underscore_argument](https://github.com/Manishearth/rust-clippy/wiki#duplicate_underscore_argument) | warn | function arguments having names which only differ by an underscore
223 [empty_loop](https://github.com/Manishearth/rust-clippy/wiki#empty_loop) | warn | empty `loop {}`, which should block or sleep
224 [enum_clike_unportable_variant](https://github.com/Manishearth/rust-clippy/wiki#enum_clike_unportable_variant) | warn | C-like enums that are `repr(isize/usize)` and have values that don't fit into an `i32`
225 [enum_glob_use](https://github.com/Manishearth/rust-clippy/wiki#enum_glob_use) | allow | use items that import all variants of an enum
226 [enum_variant_names](https://github.com/Manishearth/rust-clippy/wiki#enum_variant_names) | warn | enums where all variants share a prefix/postfix
227 [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`)
228 [eval_order_dependence](https://github.com/Manishearth/rust-clippy/wiki#eval_order_dependence) | warn | whether a variable read occurs before a write depends on sub-expression evaluation order
229 [expl_impl_clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#expl_impl_clone_on_copy) | warn | implementing `Clone` explicitly on `Copy` types
230 [explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop) | warn | for-looping with an explicit counter when `_.enumerate()` would do
231 [explicit_into_iter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_into_iter_loop) | warn | for-looping over `_.into_iter()` when `_` would do
232 [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
233 [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
234 [filter_map](https://github.com/Manishearth/rust-clippy/wiki#filter_map) | allow | using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call
235 [filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next) | warn | using `filter(p).next()`, which is more succinctly expressed as `.find(p)`
236 [float_arithmetic](https://github.com/Manishearth/rust-clippy/wiki#float_arithmetic) | allow | any floating-point arithmetic statement
237 [float_cmp](https://github.com/Manishearth/rust-clippy/wiki#float_cmp) | warn | using `==` or `!=` on float values instead of comparing difference with an epsilon
238 [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
239 [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`
240 [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`
241 [get_unwrap](https://github.com/Manishearth/rust-clippy/wiki#get_unwrap) | warn | using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead
242 [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op) | warn | using identity operations, e.g. `x + 0` or `y / 1`
243 [if_let_redundant_pattern_matching](https://github.com/Manishearth/rust-clippy/wiki#if_let_redundant_pattern_matching) | warn | use the proper utility function avoiding an `if let`
244 [if_let_some_result](https://github.com/Manishearth/rust-clippy/wiki#if_let_some_result) | warn | usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead
245 [if_not_else](https://github.com/Manishearth/rust-clippy/wiki#if_not_else) | allow | `if` branches that could be swapped so no negation operation is necessary on the condition
246 [if_same_then_else](https://github.com/Manishearth/rust-clippy/wiki#if_same_then_else) | warn | if with the same *then* and *else* blocks
247 [ifs_same_cond](https://github.com/Manishearth/rust-clippy/wiki#ifs_same_cond) | warn | consecutive `ifs` with the same condition
248 [indexing_slicing](https://github.com/Manishearth/rust-clippy/wiki#indexing_slicing) | allow | indexing/slicing usage
249 [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`
250 [inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always) | warn | use of `#[inline(always)]`
251 [integer_arithmetic](https://github.com/Manishearth/rust-clippy/wiki#integer_arithmetic) | allow | any integer arithmetic statement
252 [invalid_regex](https://github.com/Manishearth/rust-clippy/wiki#invalid_regex) | deny | invalid regular expressions
253 [invalid_upcast_comparisons](https://github.com/Manishearth/rust-clippy/wiki#invalid_upcast_comparisons) | allow | a comparison involving an upcast which is always true or false
254 [items_after_statements](https://github.com/Manishearth/rust-clippy/wiki#items_after_statements) | allow | blocks where an item comes after a statement
255 [iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop) | warn | for-looping over `_.next()` which is probably not intended
256 [iter_nth](https://github.com/Manishearth/rust-clippy/wiki#iter_nth) | warn | using `.iter().nth()` on a standard library type with O(1) element access
257 [iter_skip_next](https://github.com/Manishearth/rust-clippy/wiki#iter_skip_next) | warn | using `.skip(x).next()` on an iterator
258 [len_without_is_empty](https://github.com/Manishearth/rust-clippy/wiki#len_without_is_empty) | warn | traits or impls with a public `len` method but no corresponding `is_empty` method
259 [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
260 [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
261 [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
262 [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
263 [logic_bug](https://github.com/Manishearth/rust-clippy/wiki#logic_bug) | warn | boolean expressions that contain terminals which can be eliminated
264 [manual_swap](https://github.com/Manishearth/rust-clippy/wiki#manual_swap) | warn | manual swap of two variables
265 [many_single_char_names](https://github.com/Manishearth/rust-clippy/wiki#many_single_char_names) | warn | too many single character bindings
266 [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
267 [map_entry](https://github.com/Manishearth/rust-clippy/wiki#map_entry) | warn | use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`
268 [match_bool](https://github.com/Manishearth/rust-clippy/wiki#match_bool) | warn | a match on a boolean expression instead of an `if..else` block
269 [match_overlapping_arm](https://github.com/Manishearth/rust-clippy/wiki#match_overlapping_arm) | warn | a match with overlapping arms
270 [match_ref_pats](https://github.com/Manishearth/rust-clippy/wiki#match_ref_pats) | warn | a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression
271 [match_same_arms](https://github.com/Manishearth/rust-clippy/wiki#match_same_arms) | warn | `match` with identical arm bodies
272 [mem_forget](https://github.com/Manishearth/rust-clippy/wiki#mem_forget) | allow | `mem::forget` usage on `Drop` types, likely to cause memory leaks
273 [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
274 [misrefactored_assign_op](https://github.com/Manishearth/rust-clippy/wiki#misrefactored_assign_op) | warn | having a variable on both sides of an assign op
275 [missing_docs_in_private_items](https://github.com/Manishearth/rust-clippy/wiki#missing_docs_in_private_items) | allow | detects missing documentation for public and private members
276 [mixed_case_hex_literals](https://github.com/Manishearth/rust-clippy/wiki#mixed_case_hex_literals) | warn | hex literals whose letter digits are not consistently upper- or lowercased
277 [module_inception](https://github.com/Manishearth/rust-clippy/wiki#module_inception) | warn | modules that have the same name as their parent module
278 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one) | warn | taking a number modulo 1, which always returns 0
279 [mut_mut](https://github.com/Manishearth/rust-clippy/wiki#mut_mut) | allow | usage of double-mut refs, e.g. `&mut &mut ...`
280 [mutex_atomic](https://github.com/Manishearth/rust-clippy/wiki#mutex_atomic) | warn | using a mutex where an atomic value could be used instead
281 [mutex_integer](https://github.com/Manishearth/rust-clippy/wiki#mutex_integer) | allow | using a mutex for an integer type
282 [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 }`
283 [needless_borrow](https://github.com/Manishearth/rust-clippy/wiki#needless_borrow) | warn | taking a reference that is going to be automatically dereferenced
284 [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
285 [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
286 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return) | warn | using a return statement like `return expr;` where an expression would suffice
287 [needless_update](https://github.com/Manishearth/rust-clippy/wiki#needless_update) | warn | using `Foo { ..base }` when there are no missing fields
288 [neg_multiply](https://github.com/Manishearth/rust-clippy/wiki#neg_multiply) | warn | multiplying integers with -1
289 [new_ret_no_self](https://github.com/Manishearth/rust-clippy/wiki#new_ret_no_self) | warn | not returning `Self` in a `new` method
290 [new_without_default](https://github.com/Manishearth/rust-clippy/wiki#new_without_default) | warn | `fn new() -> Self` method without `Default` implementation
291 [new_without_default_derive](https://github.com/Manishearth/rust-clippy/wiki#new_without_default_derive) | warn | `fn new() -> Self` without `#[derive]`able `Default` implementation
292 [no_effect](https://github.com/Manishearth/rust-clippy/wiki#no_effect) | warn | statements with no effect
293 [non_ascii_literal](https://github.com/Manishearth/rust-clippy/wiki#non_ascii_literal) | allow | using any literal non-ASCII chars in a string literal instead of using the `\\u` escape
294 [nonminimal_bool](https://github.com/Manishearth/rust-clippy/wiki#nonminimal_bool) | allow | boolean expressions that can be written more concisely
295 [nonsensical_open_options](https://github.com/Manishearth/rust-clippy/wiki#nonsensical_open_options) | warn | nonsensical combination of options for opening a file
296 [not_unsafe_ptr_arg_deref](https://github.com/Manishearth/rust-clippy/wiki#not_unsafe_ptr_arg_deref) | warn | public functions dereferencing raw pointer arguments but not marked `unsafe`
297 [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
298 [option_map_unwrap_or](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or) | allow | using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`
299 [option_map_unwrap_or_else](https://github.com/Manishearth/rust-clippy/wiki#option_map_unwrap_or_else) | allow | using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`
300 [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()`
301 [or_fun_call](https://github.com/Manishearth/rust-clippy/wiki#or_fun_call) | warn | using any `*or` method with a function call, which suggests `*or_else`
302 [out_of_bounds_indexing](https://github.com/Manishearth/rust-clippy/wiki#out_of_bounds_indexing) | deny | out of bounds constant indexing
303 [overflow_check_conditional](https://github.com/Manishearth/rust-clippy/wiki#overflow_check_conditional) | warn | overflow checks inspired by C which are likely to panic
304 [panic_params](https://github.com/Manishearth/rust-clippy/wiki#panic_params) | warn | missing parameters in `panic!` calls
305 [partialeq_ne_impl](https://github.com/Manishearth/rust-clippy/wiki#partialeq_ne_impl) | warn | re-implementing `PartialEq::ne`
306 [precedence](https://github.com/Manishearth/rust-clippy/wiki#precedence) | warn | operations where precedence may be unclear
307 [print_stdout](https://github.com/Manishearth/rust-clippy/wiki#print_stdout) | allow | printing on stdout
308 [print_with_newline](https://github.com/Manishearth/rust-clippy/wiki#print_with_newline) | warn | using `print!()` with a format string that ends in a newline
309 [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
310 [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
311 [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
312 [redundant_closure](https://github.com/Manishearth/rust-clippy/wiki#redundant_closure) | warn | redundant closures, i.e. `|a| foo(a)` (which can be written as just `foo`)
313 [redundant_closure_call](https://github.com/Manishearth/rust-clippy/wiki#redundant_closure_call) | warn | throwaway closures called in the expression they are defined
314 [redundant_pattern](https://github.com/Manishearth/rust-clippy/wiki#redundant_pattern) | warn | using `name @ _` in a pattern
315 [regex_macro](https://github.com/Manishearth/rust-clippy/wiki#regex_macro) | warn | use of `regex!(_)` instead of `Regex::new(_)`
316 [result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used) | allow | using `Result.unwrap()`, which might be better handled
317 [reverse_range_loop](https://github.com/Manishearth/rust-clippy/wiki#reverse_range_loop) | warn | iteration over an empty range, such as `10..0` or `5..5`
318 [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()`
319 [serde_api_misuse](https://github.com/Manishearth/rust-clippy/wiki#serde_api_misuse) | warn | various things that will negatively affect your serde experience
320 [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`
321 [shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same) | allow | rebinding a name to itself, e.g. `let mut x = &mut x`
322 [shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated) | allow | rebinding a name without even using the original value
323 [should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait) | warn | defining a method that should be implementing a std trait
324 [similar_names](https://github.com/Manishearth/rust-clippy/wiki#similar_names) | allow | similarly named items and bindings
325 [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")`
326 [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 `_ => {}`) instead of `if let`
327 [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 instead of `if let`
328 [string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add) | allow | using `x + ..` where x is a `String` instead of `push_str()`
329 [string_add_assign](https://github.com/Manishearth/rust-clippy/wiki#string_add_assign) | allow | using `x = x + ..` where x is a `String` instead of `push_str()`
330 [string_lit_as_bytes](https://github.com/Manishearth/rust-clippy/wiki#string_lit_as_bytes) | warn | calling `as_bytes` on a string literal instead of using a byte string literal
331 [stutter](https://github.com/Manishearth/rust-clippy/wiki#stutter) | allow | type names prefixed/postfixed with their containing module's name
332 [suspicious_assignment_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_assignment_formatting) | warn | suspicious formatting of `*=`, `-=` or `!=`
333 [suspicious_else_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_else_formatting) | warn | suspicious formatting of `else if`
334 [temporary_assignment](https://github.com/Manishearth/rust-clippy/wiki#temporary_assignment) | warn | assignments to temporaries
335 [temporary_cstring_as_ptr](https://github.com/Manishearth/rust-clippy/wiki#temporary_cstring_as_ptr) | warn | getting the inner pointer of a temporary `CString`
336 [too_many_arguments](https://github.com/Manishearth/rust-clippy/wiki#too_many_arguments) | warn | functions with too many arguments
337 [toplevel_ref_arg](https://github.com/Manishearth/rust-clippy/wiki#toplevel_ref_arg) | warn | an entire binding declared as `ref`, in a function argument or a `let` statement
338 [transmute_ptr_to_ref](https://github.com/Manishearth/rust-clippy/wiki#transmute_ptr_to_ref) | warn | transmutes from a pointer to a reference type
339 [trivial_regex](https://github.com/Manishearth/rust-clippy/wiki#trivial_regex) | warn | trivial regular expressions
340 [type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity) | warn | usage of very complex types that might be better factored into `type` definitions
341 [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)
342 [unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp) | warn | comparing unit values
343 [unnecessary_mut_passed](https://github.com/Manishearth/rust-clippy/wiki#unnecessary_mut_passed) | warn | an argument passed as a mutable reference although the callee only demands an immutable reference
344 [unnecessary_operation](https://github.com/Manishearth/rust-clippy/wiki#unnecessary_operation) | warn | outer expressions with no effect
345 [unneeded_field_pattern](https://github.com/Manishearth/rust-clippy/wiki#unneeded_field_pattern) | warn | struct fields bound to a wildcard instead of using `..`
346 [unsafe_removed_from_name](https://github.com/Manishearth/rust-clippy/wiki#unsafe_removed_from_name) | warn | `unsafe` removed from API names on import
347 [unseparated_literal_suffix](https://github.com/Manishearth/rust-clippy/wiki#unseparated_literal_suffix) | allow | literals whose suffix is not separated by an underscore
348 [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
349 [unused_label](https://github.com/Manishearth/rust-clippy/wiki#unused_label) | warn | unused labels
350 [unused_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#unused_lifetimes) | warn | unused lifetimes in function definitions
351 [use_debug](https://github.com/Manishearth/rust-clippy/wiki#use_debug) | allow | use of `Debug`-based formatting
352 [used_underscore_binding](https://github.com/Manishearth/rust-clippy/wiki#used_underscore_binding) | allow | using a binding which is prefixed with an underscore
353 [useless_attribute](https://github.com/Manishearth/rust-clippy/wiki#useless_attribute) | warn | use of lint attributes on `extern crate` items
354 [useless_format](https://github.com/Manishearth/rust-clippy/wiki#useless_format) | warn | useless use of `format!`
355 [useless_let_if_seq](https://github.com/Manishearth/rust-clippy/wiki#useless_let_if_seq) | warn | unidiomatic `let mut` declaration followed by initialization in `if`
356 [useless_transmute](https://github.com/Manishearth/rust-clippy/wiki#useless_transmute) | warn | transmutes that have the same to and from types or could be a cast/coercion
357 [useless_vec](https://github.com/Manishearth/rust-clippy/wiki#useless_vec) | warn | useless `vec!`
358 [while_let_loop](https://github.com/Manishearth/rust-clippy/wiki#while_let_loop) | warn | `loop { if let { ... } else break }`, which can be written as a `while let` loop
359 [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
360 [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
361 [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
362 [wrong_transmute](https://github.com/Manishearth/rust-clippy/wiki#wrong_transmute) | warn | transmutes that are confusing at best, undefined behaviour at worst and always useless
363 [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
364 [zero_prefixed_literal](https://github.com/Manishearth/rust-clippy/wiki#zero_prefixed_literal) | warn | integer literals starting with `0`
365 [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
367 More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
371 Licensed under [MPL](https://www.mozilla.org/MPL/2.0/).
372 If you're having issues with the license, let me know and I'll try to change it to something more permissive.