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 59 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 [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`)
  24 [explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop)         | warn    | for-looping with an explicit counter when `_.enumerate()` would do
  25 [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
  26 [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)
  27 [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op)                             | warn    | using identity operations, e.g. `x + 0` or `y / 1`
  28 [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`
  29 [inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always)                         | warn    | `#[inline(always)]` is a bad idea in most cases
  30 [iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop)                       | warn    | for-looping over `_.next()` which is probably not intended
  31 [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()`
  32 [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
  33 [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
  34 [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
  35 [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 RingBuf
  36 [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
  37 [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
  38 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one)                               | warn    | taking a number modulo 1, which always returns 0
  39 [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)
  40 [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 }`
  41 [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
  42 [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
  43 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return)                     | warn    | using a return statement like `return expr;` where an expression would suffice
  44 [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
  45 [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()`
  46 [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
  47 [ptr_arg](https://github.com/Manishearth/rust-clippy/wiki#ptr_arg)                                     | allow   | fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively
  48 [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
  49 [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`)
  50 [redundant_pattern](https://github.com/Manishearth/rust-clippy/wiki#redundant_pattern)                 | warn    | using `name @ _` in a pattern
  51 [result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used)               | allow   | using `Result.unwrap()`, which might be better handled
  52 [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`
  53 [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`
  54 [shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same)                             | allow   | rebinding a name to itself, e.g. `let mut x = &mut x`
  55 [shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated)                   | allow   | The name is re-bound without even using the original value
  56 [should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait)       | warn    | defining a method that should be implementing a std trait
  57 [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
  58 [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()`
  59 [string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add)                               | allow   | using `x + ..` where x is a `String`; suggests using `push_str()` instead
  60 [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
  61 [string_to_string](https://github.com/Manishearth/rust-clippy/wiki#string_to_string)                   | warn    | calling `String.to_string()` which is a no-op
  62 [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 `&`.
  63 [type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity)                     | warn    | usage of very complex types; recommends factoring out parts into `type` definitions
  64 [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)
  65 [unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp)                                   | warn    | comparing unit values (which is always `true` or `false`, respectively)
  66 [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
  67 [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
  68 [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
  69 [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
  70 [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
  71 [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
  72
  73 More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
  74
  75 ##Usage
  76
  77 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.
  78
  79 Add in your `Cargo.toml`:
  80 ```toml
  81 [dependencies]
  82 clippy = "*"
  83 ```
  84
  85 You may also use [`cargo clippy`](https://github.com/arcnmx/cargo-clippy), a custom cargo subcommand that runs clippy on a given project.
  86
  87 Sample `main.rs`:
  88 ```rust
  89 #![feature(plugin)]
  90
  91 #![plugin(clippy)]
  92
  93
  94 fn main(){
  95     let x = Some(1u8);
  96     match x {
  97         Some(y) => println!("{:?}", y),
  98         _ => ()
  99     }
 100 }
 101 ```
 102
 103 Produces this warning:
 104 ```
 105 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
 106 src/main.rs:8     match x {
 107 src/main.rs:9         Some(y) => println!("{:?}", y),
 108 src/main.rs:10         _ => ()
 109 src/main.rs:11     }
 110 src/main.rs:8:5: 11:6 help: Try
 111 if let Some(y) = x { println!("{:?}", y) }
 112 ```
 113
 114 You can add options  to `allow`/`warn`/`deny`:
 115 - the whole set using the `clippy` lint group (`#![deny(clippy)]`, etc)
 116 - only some lints (`#![deny(single_match, box_vec)]`, etc)
 117 - `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
 118
 119 Note: `deny` produces errors instead of warnings
 120
 121 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
 122 in your code, you can use:
 123
 124 ```
 125 cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
 126 ```
 127
 128 *[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!
 129
 130 ##License
 131 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.