README.md

   1 #rust-clippy
   2 [![Build Status](https://travis-ci.org/Manishearth/rust-clippy.svg?branch=master)](https://travis-ci.org/Manishearth/rust-clippy)
   3
   4 A collection of lints to catch common mistakes and improve your Rust code.
   5
   6 [Jump to usage instructions](#usage)
   7
   8 ##Lints
   9 There are 88 lints included in this crate:
  10
  11 name                                                                                                     | default | meaning
  12 ---------------------------------------------------------------------------------------------------------|---------|------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  13 [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
  14 [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)
  15 [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 } ...`
  16 [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 } ...`
  17 [box_vec](https://github.com/Manishearth/rust-clippy/wiki#box_vec)                                       | warn    | usage of `Box<Vec<T>>`, vector elements are already on the heap
  18 [boxed_local](https://github.com/Manishearth/rust-clippy/wiki#boxed_local)                               | warn    | using Box<T> where unnecessary
  19 [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`
  20 [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`
  21 [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`
  22 [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`
  23 [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)
  24 [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()`
  25 [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() }`
  26 [cyclomatic_complexity](https://github.com/Manishearth/rust-clippy/wiki#cyclomatic_complexity)           | warn    | finds functions that should be split up into multiple functions
  27 [empty_loop](https://github.com/Manishearth/rust-clippy/wiki#empty_loop)                                 | warn    | empty `loop {}` detected
  28 [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`)
  29 [explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop)           | warn    | for-looping with an explicit counter when `_.enumerate()` would do
  30 [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
  31 [filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next)                               | warn    | using `filter(p).next()`, which is more succinctly expressed as `.find(p)`
  32 [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)
  33 [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op)                               | warn    | using identity operations, e.g. `x + 0` or `y / 1`
  34 [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`
  35 [inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always)                           | warn    | `#[inline(always)]` is a bad idea in most cases
  36 [iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop)                         | warn    | for-looping over `_.next()` which is probably not intended
  37 [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()`
  38 [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
  39 [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
  40 [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
  41 [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
  42 [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)
  43 [match_bool](https://github.com/Manishearth/rust-clippy/wiki#match_bool)                                 | warn    | a match on boolean expression; recommends `if..else` block instead
  44 [match_ref_pats](https://github.com/Manishearth/rust-clippy/wiki#match_ref_pats)                         | warn    | a match has all arms prefixed with `&`; the match expression can be dereferenced instead
  45 [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
  46 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one)                                 | warn    | taking a number modulo 1, which always returns 0
  47 [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)
  48 [mutex_atomic](https://github.com/Manishearth/rust-clippy/wiki#mutex_atomic)                             | warn    | using a Mutex where an atomic value could be used instead
  49 [mutex_integer](https://github.com/Manishearth/rust-clippy/wiki#mutex_integer)                           | allow   | using a Mutex for an integer type
  50 [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 }`
  51 [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
  52 [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
  53 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return)                       | warn    | using a return statement like `return expr;` where an expression would suffice
  54 [needless_update](https://github.com/Manishearth/rust-clippy/wiki#needless_update)                       | warn    | using `{ ..base }` when there are no missing fields
  55 [no_effect](https://github.com/Manishearth/rust-clippy/wiki#no_effect)                                   | warn    | statements with no effect
  56 [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
  57 [nonsensical_open_options](https://github.com/Manishearth/rust-clippy/wiki#nonsensical_open_options)     | warn    | nonsensical combination of options for opening a file
  58 [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
  59 [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)`
  60 [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)`
  61 [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()`
  62 [out_of_bounds_indexing](https://github.com/Manishearth/rust-clippy/wiki#out_of_bounds_indexing)         | deny    | out of bound constant indexing
  63 [panic_params](https://github.com/Manishearth/rust-clippy/wiki#panic_params)                             | warn    | missing parameters in `panic!`
  64 [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
  65 [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
  66 [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
  67 [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
  68 [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`)
  69 [redundant_pattern](https://github.com/Manishearth/rust-clippy/wiki#redundant_pattern)                   | warn    | using `name @ _` in a pattern
  70 [result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used)                 | allow   | using `Result.unwrap()`, which might be better handled
  71 [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`
  72 [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()`
  73 [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`
  74 [shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same)                               | allow   | rebinding a name to itself, e.g. `let mut x = &mut x`
  75 [shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated)                     | allow   | The name is re-bound without even using the original value
  76 [should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait)         | warn    | defining a method that should be implementing a std trait
  77 [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
  78 [str_to_string](https://github.com/Manishearth/rust-clippy/wiki#str_to_string)                           | warn    | using `to_string()` on a str, which should be `to_owned()`
  79 [string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add)                                 | allow   | using `x + ..` where x is a `String`; suggests using `push_str()` instead
  80 [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
  81 [string_to_string](https://github.com/Manishearth/rust-clippy/wiki#string_to_string)                     | warn    | calling `String.to_string()` which is a no-op
  82 [temporary_assignment](https://github.com/Manishearth/rust-clippy/wiki#temporary_assignment)             | warn    | assignments to temporaries
  83 [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 `&`.
  84 [type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity)                       | warn    | usage of very complex types; recommends factoring out parts into `type` definitions
  85 [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)
  86 [unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp)                                     | warn    | comparing unit values (which is always `true` or `false`, respectively)
  87 [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
  88 [unneeded_field_pattern](https://github.com/Manishearth/rust-clippy/wiki#unneeded_field_pattern)         | warn    | Struct fields are bound to a wildcard instead of using `..`
  89 [unstable_as_mut_slice](https://github.com/Manishearth/rust-clippy/wiki#unstable_as_mut_slice)           | warn    | as_mut_slice is not stable and can be replaced by &mut v[..]see https://github.com/rust-lang/rust/issues/27729
  90 [unstable_as_slice](https://github.com/Manishearth/rust-clippy/wiki#unstable_as_slice)                   | warn    | as_slice is not stable and can be replaced by & v[..]see https://github.com/rust-lang/rust/issues/27729
  91 [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
  92 [unused_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#unused_lifetimes)                     | warn    | unused lifetimes in function definitions
  93 [used_underscore_binding](https://github.com/Manishearth/rust-clippy/wiki#used_underscore_binding)       | warn    | using a binding which is prefixed with an underscore
  94 [useless_transmute](https://github.com/Manishearth/rust-clippy/wiki#useless_transmute)                   | warn    | transmutes that have the same to and from types
  95 [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
  96 [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
  97 [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
  98 [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
  99 [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
 100 [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
 101
 102 More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
 103
 104 ##Usage
 105
 106 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.
 107
 108 Add in your `Cargo.toml`:
 109 ```toml
 110 [dependencies]
 111 clippy = "*"
 112 ```
 113
 114 You may also use [`cargo clippy`](https://github.com/arcnmx/cargo-clippy), a custom cargo subcommand that runs clippy on a given project.
 115
 116 Sample `main.rs`:
 117 ```rust
 118 #![feature(plugin)]
 119
 120 #![plugin(clippy)]
 121
 122
 123 fn main(){
 124     let x = Some(1u8);
 125     match x {
 126         Some(y) => println!("{:?}", y),
 127         _ => ()
 128     }
 129 }
 130 ```
 131
 132 Produces this warning:
 133 ```
 134 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
 135 src/main.rs:8     match x {
 136 src/main.rs:9         Some(y) => println!("{:?}", y),
 137 src/main.rs:10         _ => ()
 138 src/main.rs:11     }
 139 src/main.rs:8:5: 11:6 help: Try
 140 if let Some(y) = x { println!("{:?}", y) }
 141 ```
 142
 143 You can add options  to `allow`/`warn`/`deny`:
 144 - the whole set of `Warn` lints using the `clippy` lint group (`#![deny(clippy)]`)
 145 - 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.
 146 - only some lints (`#![deny(single_match, box_vec)]`, etc)
 147 - `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
 148
 149 Note: `deny` produces errors instead of warnings
 150
 151 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
 152 in your code, you can use:
 153
 154 ```
 155 cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
 156 ```
 157
 158 *[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!
 159
 160 If you want to make clippy an optional dependency, you can do the following:
 161
 162 In your `Cargo.toml`:
 163 ```toml
 164 [dependencies]
 165 clippy = {version = "*", optional = true}
 166
 167 [features]
 168 default=[]
 169 ```
 170
 171 And, in your `main.rs` or `lib.rs`:
 172
 173 ```rust
 174 #![cfg_attr(feature="clippy", feature(plugin))]
 175
 176 #![cfg_attr(feature="clippy", plugin(clippy))]
 177 ```
 178
 179 ##License
 180 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.