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 that give helpful tips to newbies and catch oversights.
   5
   6 [Jump to usage instructions](#usage)
   7
   8 ##Lints
   9 There are 56 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_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
  25 [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)
  26 [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op)                             | warn    | using identity operations, e.g. `x + 0` or `y / 1`
  27 [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`
  28 [inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always)                         | warn    | `#[inline(always)]` is a bad idea in most cases
  29 [iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop)                       | warn    | for-looping over `_.next()` which is probably not intended
  30 [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()`
  31 [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
  32 [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 function
  33 [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
  34 [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
  35 [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
  36 [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
  37 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one)                               | warn    | taking a number modulo 1, which always returns 0
  38 [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)
  39 [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 }`
  40 [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
  41 [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
  42 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return)                     | warn    | using a return statement like `return expr;` where an expression would suffice
  43 [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
  44 [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()`
  45 [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
  46 [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
  47 [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
  48 [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`)
  49 [redundant_pattern](https://github.com/Manishearth/rust-clippy/wiki#redundant_pattern)                 | warn    | using `name @ _` in a pattern
  50 [result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used)               | allow   | using `Result.unwrap()`, which might be better handled
  51 [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`
  52 [shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same)                             | allow   | rebinding a name to itself, e.g. `let mut x = &mut x`
  53 [shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated)                   | allow   | The name is re-bound without even using the original value
  54 [should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait)       | warn    | defining a method that should be implementing a std trait
  55 [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
  56 [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()`
  57 [string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add)                               | allow   | using `x + ..` where x is a `String`; suggests using `push_str()` instead
  58 [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
  59 [string_to_string](https://github.com/Manishearth/rust-clippy/wiki#string_to_string)                   | warn    | calling `String.to_string()` which is a no-op
  60 [toplevel_ref_arg](https://github.com/Manishearth/rust-clippy/wiki#toplevel_ref_arg)                   | warn    | a function argument is declared `ref` (i.e. `fn foo(ref x: u8)`, but not `fn foo((ref x, ref y): (u8, u8))`)
  61 [type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity)                     | warn    | usage of very complex types; recommends factoring out parts into `type` definitions
  62 [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)
  63 [unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp)                                   | warn    | comparing unit values (which is always `true` or `false`, respectively)
  64 [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
  65 [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
  66 [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
  67 [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
  68 [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
  69
  70 More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
  71
  72 ##Usage
  73
  74 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.
  75
  76 Add in your `Cargo.toml`:
  77 ```toml
  78 [dependencies]
  79 clippy = "*"
  80 ```
  81
  82 You may also use [`cargo clippy`](https://github.com/arcnmx/cargo-clippy), a custom cargo subcommand that runs clippy on a given project.
  83
  84 Sample `main.rs`:
  85 ```rust
  86 #![feature(plugin)]
  87
  88 #![plugin(clippy)]
  89
  90
  91 fn main(){
  92     let x = Some(1u8);
  93     match x {
  94         Some(y) => println!("{:?}", y),
  95         _ => ()
  96     }
  97 }
  98 ```
  99
 100 Produces this warning:
 101 ```
 102 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
 103 src/main.rs:8     match x {
 104 src/main.rs:9         Some(y) => println!("{:?}", y),
 105 src/main.rs:10         _ => ()
 106 src/main.rs:11     }
 107 src/main.rs:8:5: 11:6 help: Try
 108 if let Some(y) = x { println!("{:?}", y) }
 109 ```
 110
 111 You can add options  to `allow`/`warn`/`deny`:
 112 - the whole set using the `clippy` lint group (`#![deny(clippy)]`, etc)
 113 - only some lints (`#![deny(single_match, box_vec)]`, etc)
 114 - `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
 115
 116 Note: `deny` produces errors instead of warnings
 117
 118 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
 119 in your code, you can use:
 120
 121 ```
 122 cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
 123 ```
 124
 125 Be sure that clippy was compiled with the same version of rustc that cargo invokes here!
 126
 127 ##License
 128 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.