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