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 ##Lints
   7 There are 51 lints included in this crate:
   8
   9 name                                                                                                 | default | meaning
  10 -----------------------------------------------------------------------------------------------------|---------|-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------
  11 [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
  12 [bad_bit_mask](https://github.com/Manishearth/rust-clippy/wiki#bad_bit_mask)                         | deny    | 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)
  13 [box_vec](https://github.com/Manishearth/rust-clippy/wiki#box_vec)                                   | warn    | usage of `Box<Vec<T>>`, vector elements are already on the heap
  14 [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`
  15 [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`
  16 [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`
  17 [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`
  18 [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)
  19 [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()`
  20 [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() }`
  21 [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`)
  22 [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
  23 [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)
  24 [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op)                           | warn    | using identity operations, e.g. `x + 0` or `y / 1`
  25 [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`
  26 [inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always)                       | warn    | `#[inline(always)]` is a bad idea in most cases
  27 [iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop)                     | warn    | for-looping over `_.next()` which is probably not intended
  28 [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()`
  29 [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
  30 [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
  31 [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
  32 [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
  33 [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
  34 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one)                             | warn    | taking a number modulo 1, which always returns 0
  35 [mut_mut](https://github.com/Manishearth/rust-clippy/wiki#mut_mut)                                   | warn    | usage of double-mut refs, e.g. `&mut &mut ...` (either copy'n'paste error, or shows a fundamental misunderstanding of references)
  36 [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 }`
  37 [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
  38 [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
  39 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return)                   | warn    | using a return statement like `return expr;` where an expression would suffice
  40 [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
  41 [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()`
  42 [precedence](https://github.com/Manishearth/rust-clippy/wiki#precedence)                             | warn    | expressions where precedence may trip up the unwary reader of the source; suggests adding parentheses, e.g. `x << 2 + y` will be parsed as `x << (2 + y)`
  43 [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
  44 [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
  45 [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`)
  46 [result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used)             | allow   | using `Result.unwrap()`, which might be better handled
  47 [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`
  48 [shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same)                           | allow   | rebinding a name to itself, e.g. `let mut x = &mut x`
  49 [shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated)                 | warn    | The name is re-bound without even using the original value
  50 [should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait)     | warn    | defining a method that should be implementing a std trait
  51 [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
  52 [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()`
  53 [string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add)                             | allow   | using `x + ..` where x is a `String`; suggests using `push_str()` instead
  54 [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
  55 [string_to_string](https://github.com/Manishearth/rust-clippy/wiki#string_to_string)                 | warn    | calling `String.to_string()` which is a no-op
  56 [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))`)
  57 [type_complexity](https://github.com/Manishearth/rust-clippy/wiki#type_complexity)                   | warn    | usage of very complex types; recommends factoring out parts into `type` definitions
  58 [unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp)                                 | warn    | comparing unit values (which is always `true` or `false`, respectively)
  59 [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
  60 [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
  61 [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
  62
  63 More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
  64
  65 ##Usage
  66
  67 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.
  68
  69 Add in your `Cargo.toml`:
  70 ```toml
  71 [dependencies]
  72 clippy = "*"
  73 ```
  74
  75 Sample `main.rs`:
  76 ```rust
  77 #![feature(plugin)]
  78
  79 #![plugin(clippy)]
  80
  81
  82 fn main(){
  83     let x = Some(1u8);
  84     match x {
  85         Some(y) => println!("{:?}", y),
  86         _ => ()
  87     }
  88 }
  89 ```
  90
  91 Produce this warning:
  92 ```
  93 src/main.rs:8:5: 11:6 warning: You seem to be trying to use match for destructuring a single type. Did you mean to use `if let`?, #[warn(single_match)] on by default
  94 src/main.rs:8     match x {
  95 src/main.rs:9         Some(y) => println!("{:?}", y),
  96 src/main.rs:10         _ => ()
  97 src/main.rs:11     }
  98 src/main.rs:8:5: 11:6 help: Try
  99 if let Some(y) = x { println!("{:?}", y) }
 100 ```
 101
 102 You can add options  to `allow`/`warn`/`deny`:
 103 - the whole set using the `clippy` lint group (`#![deny(clippy)]`, etc)
 104 - only some lints (`#![deny(single_match, box_vec)]`, etc)
 105 - `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
 106
 107 Note: `deny` produces errors instead of warnings
 108
 109 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
 110 in your code, you can use:
 111
 112 ```
 113 cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
 114 ```
 115
 116 ##License
 117 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.