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