README.md

   1 # rust-clippy
   2
   3 [![Build Status](https://travis-ci.org/rust-lang-nursery/rust-clippy.svg?branch=master)](https://travis-ci.org/rust-lang-nursery/rust-clippy)
   4 [![Windows build status](https://ci.appveyor.com/api/projects/status/github/rust-lang-nursery/rust-clippy?svg=true)](https://ci.appveyor.com/project/rust-lang-nursery/rust-clippy)
   5 [![Clippy Linting Result](http://clippy.bashy.io/github/rust-lang-nursery/rust-clippy/master/badge.svg)](http://clippy.bashy.io/github/rust-lang-nursery/rust-clippy/master/log)
   6 [![Current Version](http://meritbadge.herokuapp.com/clippy)](https://crates.io/crates/clippy)
   7 [![License: MPL-2.0](https://img.shields.io/crates/l/clippy.svg)](#License)
   8
   9 A collection of lints to catch common mistakes and improve your Rust code.
  10
  11 Table of contents:
  12
  13 *   [Lint list](#lints)
  14 *   [Usage instructions](#usage)
  15 *   [Configuration](#configuration)
  16 *   [License](#license)
  17
  18 ## Usage
  19
  20 Since this is a tool for helping the developer of a library or application
  21 write better code, it is recommended not to include clippy as a hard dependency.
  22 Options include using it as an optional dependency, as a cargo subcommand, or
  23 as an included feature during build. All of these options are detailed below.
  24
  25 As a general rule clippy will only work with the *latest* Rust nightly for now.
  26
  27 ### Optional dependency
  28
  29 If you want to make clippy an optional dependency, you can do the following:
  30
  31 In your `Cargo.toml`:
  32
  33 ```toml
  34 [dependencies]
  35 clippy = {version = "*", optional = true}
  36
  37 [features]
  38 default = []
  39 ```
  40
  41 And, in your `main.rs` or `lib.rs`:
  42
  43 ```rust
  44 #![cfg_attr(feature="clippy", feature(plugin))]
  45
  46 #![cfg_attr(feature="clippy", plugin(clippy))]
  47 ```
  48
  49 Then build by enabling the feature: `cargo build --features "clippy"`
  50
  51 Instead of adding the `cfg_attr` attributes you can also run clippy on demand:
  52 `cargo rustc --features clippy -- -Z no-trans -Z extra-plugins=clippy`
  53 (the `-Z no trans`, while not necessary, will stop the compilation process after
  54 typechecking (and lints) have completed, which can significantly reduce the runtime).
  55
  56 ### As a cargo subcommand (`cargo clippy`)
  57
  58 An alternate way to use clippy is by installing clippy through cargo as a cargo
  59 subcommand.
  60
  61 ```terminal
  62 cargo install clippy
  63 ```
  64
  65 Now you can run clippy by invoking `cargo clippy`, or
  66 `rustup run nightly cargo clippy` directly from a directory that is usually
  67 compiled with stable.
  68
  69 In case you are not using rustup, you need to set the environment flag
  70 `SYSROOT` during installation so clippy knows where to find `librustc` and
  71 similar crates.
  72
  73 ```terminal
  74 SYSROOT=/path/to/rustc/sysroot cargo install clippy
  75 ```
  76
  77 ### Running clippy from the command line without installing
  78
  79 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
  80 in your code, you can use:
  81
  82 ```terminal
  83 cargo rustc -- -L /path/to/clippy_so/dir/ -Z extra-plugins=clippy
  84 ```
  85
  86 *[Note](https://github.com/rust-lang-nursery/rust-clippy/wiki#a-word-of-warning):*
  87 Be sure that clippy was compiled with the same version of rustc that cargo invokes here!
  88
  89 ### As a Compiler Plugin
  90
  91 *Note:* This is not a recommended installation method.
  92
  93 Since stable Rust is backwards compatible, you should be able to
  94 compile your stable programs with nightly Rust with clippy plugged in to
  95 circumvent this.
  96
  97 Add in your `Cargo.toml`:
  98
  99 ```toml
 100 [dependencies]
 101 clippy = "*"
 102 ```
 103
 104 You then need to add `#![feature(plugin)]` and `#![plugin(clippy)]` to the top
 105 of your crate entry point (`main.rs` or `lib.rs`).
 106
 107 Sample `main.rs`:
 108
 109 ```rust
 110 #![feature(plugin)]
 111
 112 #![plugin(clippy)]
 113
 114
 115 fn main(){
 116     let x = Some(1u8);
 117     match x {
 118         Some(y) => println!("{:?}", y),
 119         _ => ()
 120     }
 121 }
 122 ```
 123
 124 Produces this warning:
 125
 126 ```terminal
 127 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
 128 src/main.rs:8     match x {
 129 src/main.rs:9         Some(y) => println!("{:?}", y),
 130 src/main.rs:10         _ => ()
 131 src/main.rs:11     }
 132 src/main.rs:8:5: 11:6 help: Try
 133 if let Some(y) = x { println!("{:?}", y) }
 134 ```
 135
 136 ## Configuration
 137
 138 Some lints can be configured in a `clippy.toml` file. It contains basic `variable = value` mapping eg.
 139
 140 ```toml
 141 blacklisted-names = ["toto", "tata", "titi"]
 142 cyclomatic-complexity-threshold = 30
 143 ```
 144
 145 See the wiki for more information about which lints can be configured and the
 146 meaning of the variables.
 147
 148 You can also specify the path to the configuration file with:
 149
 150 ```rust
 151 #![plugin(clippy(conf_file="path/to/clippy's/configuration"))]
 152 ```
 153
 154 To deactivate the “for further information visit *wiki-link*” message you can
 155 define the `CLIPPY_DISABLE_WIKI_LINKS` environment variable.
 156
 157 ### Allowing/denying lints
 158
 159 You can add options  to `allow`/`warn`/`deny`:
 160
 161 *   the whole set of `Warn` lints using the `clippy` lint group (`#![deny(clippy)]`)
 162
 163 *   all lints using both the `clippy` and `clippy_pedantic` lint groups (`#![deny(clippy)]`,
 164     `#![deny(clippy_pedantic)]`). Note that `clippy_pedantic` contains some very aggressive
 165     lints prone to false positives.
 166
 167 *   only some lints (`#![deny(single_match, box_vec)]`, etc)
 168
 169 *   `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
 170
 171 Note: `deny` produces errors instead of warnings.
 172
 173 For convenience, `cargo clippy` automatically defines a `cargo-clippy`
 174 features. This lets you set lints level and compile with or without clippy
 175 transparently:
 176
 177 ```rust
 178 #[cfg_attr(feature = "cargo-clippy", allow(needless_lifetimes))]
 179 ```
 180
 181 ## Lints
 182
 183 There are 205 lints included in this crate:
 184
 185 name                                                                                                                         | default | triggers on
 186 -----------------------------------------------------------------------------------------------------------------------------|---------|----------------------------------------------------------------------------------------------------------------------------------
 187 [absurd_extreme_comparisons](https://github.com/rust-lang-nursery/rust-clippy/wiki#absurd_extreme_comparisons)               | warn    | a comparison with a maximum or minimum value that is always true or false
 188 [almost_swapped](https://github.com/rust-lang-nursery/rust-clippy/wiki#almost_swapped)                                       | warn    | `foo = bar; bar = foo` sequence
 189 [approx_constant](https://github.com/rust-lang-nursery/rust-clippy/wiki#approx_constant)                                     | warn    | the approximate of a known float constant (in `std::fXX::consts`)
 190 [assign_op_pattern](https://github.com/rust-lang-nursery/rust-clippy/wiki#assign_op_pattern)                                 | warn    | assigning the result of an operation on a variable to that same variable
 191 [assign_ops](https://github.com/rust-lang-nursery/rust-clippy/wiki#assign_ops)                                               | allow   | any compound assignment operation
 192 [bad_bit_mask](https://github.com/rust-lang-nursery/rust-clippy/wiki#bad_bit_mask)                                           | warn    | expressions of the form `_ & mask == select` that will only ever return `true` or `false`
 193 [blacklisted_name](https://github.com/rust-lang-nursery/rust-clippy/wiki#blacklisted_name)                                   | warn    | usage of a blacklisted/placeholder name
 194 [block_in_if_condition_expr](https://github.com/rust-lang-nursery/rust-clippy/wiki#block_in_if_condition_expr)               | warn    | braces that can be eliminated in conditions, e.g. `if { true } ...`
 195 [block_in_if_condition_stmt](https://github.com/rust-lang-nursery/rust-clippy/wiki#block_in_if_condition_stmt)               | warn    | complex blocks in conditions, e.g. `if { let x = true; x } ...`
 196 [bool_comparison](https://github.com/rust-lang-nursery/rust-clippy/wiki#bool_comparison)                                     | warn    | comparing a variable to a boolean, e.g. `if x == true`
 197 [borrowed_box](https://github.com/rust-lang-nursery/rust-clippy/wiki#borrowed_box)                                           | warn    | a borrow of a boxed type
 198 [box_vec](https://github.com/rust-lang-nursery/rust-clippy/wiki#box_vec)                                                     | warn    | usage of `Box<Vec<T>>`, vector elements are already on the heap
 199 [boxed_local](https://github.com/rust-lang-nursery/rust-clippy/wiki#boxed_local)                                             | warn    | using `Box<T>` where unnecessary
 200 [builtin_type_shadow](https://github.com/rust-lang-nursery/rust-clippy/wiki#builtin_type_shadow)                             | warn    | shadowing a builtin type
 201 [cast_possible_truncation](https://github.com/rust-lang-nursery/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`
 202 [cast_possible_wrap](https://github.com/rust-lang-nursery/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`
 203 [cast_precision_loss](https://github.com/rust-lang-nursery/rust-clippy/wiki#cast_precision_loss)                             | allow   | casts that cause loss of precision, e.g. `x as f32` where `x: u64`
 204 [cast_sign_loss](https://github.com/rust-lang-nursery/rust-clippy/wiki#cast_sign_loss)                                       | allow   | casts from signed types to unsigned types, e.g. `x as u32` where `x: i32`
 205 [char_lit_as_u8](https://github.com/rust-lang-nursery/rust-clippy/wiki#char_lit_as_u8)                                       | warn    | casting a character literal to u8
 206 [chars_next_cmp](https://github.com/rust-lang-nursery/rust-clippy/wiki#chars_next_cmp)                                       | warn    | using `.chars().next()` to check if a string starts with a char
 207 [clone_double_ref](https://github.com/rust-lang-nursery/rust-clippy/wiki#clone_double_ref)                                   | warn    | using `clone` on `&&T`
 208 [clone_on_copy](https://github.com/rust-lang-nursery/rust-clippy/wiki#clone_on_copy)                                         | warn    | using `clone` on a `Copy` type
 209 [cmp_nan](https://github.com/rust-lang-nursery/rust-clippy/wiki#cmp_nan)                                                     | deny    | comparisons to NAN, which will always return false, probably not intended
 210 [cmp_null](https://github.com/rust-lang-nursery/rust-clippy/wiki#cmp_null)                                                   | warn    | comparing a pointer to a null pointer, suggesting to use `.is_null()` instead.
 211 [cmp_owned](https://github.com/rust-lang-nursery/rust-clippy/wiki#cmp_owned)                                                 | warn    | creating owned instances for comparing with others, e.g. `x == "foo".to_string()`
 212 [collapsible_if](https://github.com/rust-lang-nursery/rust-clippy/wiki#collapsible_if)                                       | warn    | `if`s that can be collapsed (e.g. `if x { if y { ... } }` and `else { if x { ... } }`)
 213 [crosspointer_transmute](https://github.com/rust-lang-nursery/rust-clippy/wiki#crosspointer_transmute)                       | warn    | transmutes that have to or from types that are a pointer to the other
 214 [cyclomatic_complexity](https://github.com/rust-lang-nursery/rust-clippy/wiki#cyclomatic_complexity)                         | warn    | functions that should be split up into multiple functions
 215 [deprecated_semver](https://github.com/rust-lang-nursery/rust-clippy/wiki#deprecated_semver)                                 | warn    | use of `#[deprecated(since = "x")]` where x is not semver
 216 [deref_addrof](https://github.com/rust-lang-nursery/rust-clippy/wiki#deref_addrof)                                           | warn    | use of `*&` or `*&mut` in an expression
 217 [derive_hash_xor_eq](https://github.com/rust-lang-nursery/rust-clippy/wiki#derive_hash_xor_eq)                               | warn    | deriving `Hash` but implementing `PartialEq` explicitly
 218 [diverging_sub_expression](https://github.com/rust-lang-nursery/rust-clippy/wiki#diverging_sub_expression)                   | warn    | whether an expression contains a diverging sub expression
 219 [doc_markdown](https://github.com/rust-lang-nursery/rust-clippy/wiki#doc_markdown)                                           | warn    | presence of `_`, `::` or camel-case outside backticks in documentation
 220 [double_neg](https://github.com/rust-lang-nursery/rust-clippy/wiki#double_neg)                                               | warn    | `--x`, which is a double negation of `x` and not a pre-decrement as in C/C++
 221 [double_parens](https://github.com/rust-lang-nursery/rust-clippy/wiki#double_parens)                                         | warn    | Warn on unnecessary double parentheses
 222 [drop_copy](https://github.com/rust-lang-nursery/rust-clippy/wiki#drop_copy)                                                 | warn    | calls to `std::mem::drop` with a value that implements Copy
 223 [drop_ref](https://github.com/rust-lang-nursery/rust-clippy/wiki#drop_ref)                                                   | warn    | calls to `std::mem::drop` with a reference instead of an owned value
 224 [duplicate_underscore_argument](https://github.com/rust-lang-nursery/rust-clippy/wiki#duplicate_underscore_argument)         | warn    | function arguments having names which only differ by an underscore
 225 [empty_enum](https://github.com/rust-lang-nursery/rust-clippy/wiki#empty_enum)                                               | allow   | enum with no variants
 226 [empty_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#empty_loop)                                               | warn    | empty `loop {}`, which should block or sleep
 227 [enum_clike_unportable_variant](https://github.com/rust-lang-nursery/rust-clippy/wiki#enum_clike_unportable_variant)         | warn    | C-like enums that are `repr(isize/usize)` and have values that don't fit into an `i32`
 228 [enum_glob_use](https://github.com/rust-lang-nursery/rust-clippy/wiki#enum_glob_use)                                         | allow   | use items that import all variants of an enum
 229 [enum_variant_names](https://github.com/rust-lang-nursery/rust-clippy/wiki#enum_variant_names)                               | warn    | enums where all variants share a prefix/postfix
 230 [eq_op](https://github.com/rust-lang-nursery/rust-clippy/wiki#eq_op)                                                         | warn    | equal operands on both sides of a comparison or bitwise combination (e.g. `x == x`)
 231 [eval_order_dependence](https://github.com/rust-lang-nursery/rust-clippy/wiki#eval_order_dependence)                         | warn    | whether a variable read occurs before a write depends on sub-expression evaluation order
 232 [expl_impl_clone_on_copy](https://github.com/rust-lang-nursery/rust-clippy/wiki#expl_impl_clone_on_copy)                     | warn    | implementing `Clone` explicitly on `Copy` types
 233 [explicit_counter_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#explicit_counter_loop)                         | warn    | for-looping with an explicit counter when `_.enumerate()` would do
 234 [explicit_into_iter_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#explicit_into_iter_loop)                     | warn    | for-looping over `_.into_iter()` when `_` would do
 235 [explicit_iter_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#explicit_iter_loop)                               | warn    | for-looping over `_.iter()` or `_.iter_mut()` when `&_` or `&mut _` would do
 236 [filter_map](https://github.com/rust-lang-nursery/rust-clippy/wiki#filter_map)                                               | allow   | using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call
 237 [filter_next](https://github.com/rust-lang-nursery/rust-clippy/wiki#filter_next)                                             | warn    | using `filter(p).next()`, which is more succinctly expressed as `.find(p)`
 238 [float_arithmetic](https://github.com/rust-lang-nursery/rust-clippy/wiki#float_arithmetic)                                   | allow   | any floating-point arithmetic statement
 239 [float_cmp](https://github.com/rust-lang-nursery/rust-clippy/wiki#float_cmp)                                                 | warn    | using `==` or `!=` on float values instead of comparing difference with an epsilon
 240 [for_kv_map](https://github.com/rust-lang-nursery/rust-clippy/wiki#for_kv_map)                                               | warn    | looping on a map using `iter` when `keys` or `values` would do
 241 [for_loop_over_option](https://github.com/rust-lang-nursery/rust-clippy/wiki#for_loop_over_option)                           | warn    | for-looping over an `Option`, which is more clearly expressed as an `if let`
 242 [for_loop_over_result](https://github.com/rust-lang-nursery/rust-clippy/wiki#for_loop_over_result)                           | warn    | for-looping over a `Result`, which is more clearly expressed as an `if let`
 243 [forget_copy](https://github.com/rust-lang-nursery/rust-clippy/wiki#forget_copy)                                             | warn    | calls to `std::mem::forget` with a value that implements Copy
 244 [forget_ref](https://github.com/rust-lang-nursery/rust-clippy/wiki#forget_ref)                                               | warn    | calls to `std::mem::forget` with a reference instead of an owned value
 245 [get_unwrap](https://github.com/rust-lang-nursery/rust-clippy/wiki#get_unwrap)                                               | warn    | using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead
 246 [identity_op](https://github.com/rust-lang-nursery/rust-clippy/wiki#identity_op)                                             | warn    | using identity operations, e.g. `x + 0` or `y / 1`
 247 [if_let_redundant_pattern_matching](https://github.com/rust-lang-nursery/rust-clippy/wiki#if_let_redundant_pattern_matching) | warn    | use the proper utility function avoiding an `if let`
 248 [if_let_some_result](https://github.com/rust-lang-nursery/rust-clippy/wiki#if_let_some_result)                               | warn    | usage of `ok()` in `if let Some(pat)` statements is unnecessary, match on `Ok(pat)` instead
 249 [if_not_else](https://github.com/rust-lang-nursery/rust-clippy/wiki#if_not_else)                                             | allow   | `if` branches that could be swapped so no negation operation is necessary on the condition
 250 [if_same_then_else](https://github.com/rust-lang-nursery/rust-clippy/wiki#if_same_then_else)                                 | warn    | if with the same *then* and *else* blocks
 251 [ifs_same_cond](https://github.com/rust-lang-nursery/rust-clippy/wiki#ifs_same_cond)                                         | warn    | consecutive `ifs` with the same condition
 252 [inconsistent_digit_grouping](https://github.com/rust-lang-nursery/rust-clippy/wiki#inconsistent_digit_grouping)             | warn    | integer literals with digits grouped inconsistently
 253 [indexing_slicing](https://github.com/rust-lang-nursery/rust-clippy/wiki#indexing_slicing)                                   | allow   | indexing/slicing usage
 254 [ineffective_bit_mask](https://github.com/rust-lang-nursery/rust-clippy/wiki#ineffective_bit_mask)                           | warn    | expressions where a bit mask will be rendered useless by a comparison, e.g. `(x | 1) > 2`
 255 [inline_always](https://github.com/rust-lang-nursery/rust-clippy/wiki#inline_always)                                         | warn    | use of `#[inline(always)]`
 256 [integer_arithmetic](https://github.com/rust-lang-nursery/rust-clippy/wiki#integer_arithmetic)                               | allow   | any integer arithmetic statement
 257 [invalid_regex](https://github.com/rust-lang-nursery/rust-clippy/wiki#invalid_regex)                                         | deny    | invalid regular expressions
 258 [invalid_upcast_comparisons](https://github.com/rust-lang-nursery/rust-clippy/wiki#invalid_upcast_comparisons)               | allow   | a comparison involving an upcast which is always true or false
 259 [items_after_statements](https://github.com/rust-lang-nursery/rust-clippy/wiki#items_after_statements)                       | allow   | blocks where an item comes after a statement
 260 [iter_cloned_collect](https://github.com/rust-lang-nursery/rust-clippy/wiki#iter_cloned_collect)                             | warn    | using `.cloned().collect()` on slice to create a `Vec`
 261 [iter_next_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#iter_next_loop)                                       | warn    | for-looping over `_.next()` which is probably not intended
 262 [iter_nth](https://github.com/rust-lang-nursery/rust-clippy/wiki#iter_nth)                                                   | warn    | using `.iter().nth()` on a standard library type with O(1) element access
 263 [iter_skip_next](https://github.com/rust-lang-nursery/rust-clippy/wiki#iter_skip_next)                                       | warn    | using `.skip(x).next()` on an iterator
 264 [iterator_step_by_zero](https://github.com/rust-lang-nursery/rust-clippy/wiki#iterator_step_by_zero)                         | warn    | using `Iterator::step_by(0)`, which produces an infinite iterator
 265 [large_digit_groups](https://github.com/rust-lang-nursery/rust-clippy/wiki#large_digit_groups)                               | warn    | grouping digits into groups that are too large
 266 [large_enum_variant](https://github.com/rust-lang-nursery/rust-clippy/wiki#large_enum_variant)                               | warn    | large size difference between variants on an enum
 267 [len_without_is_empty](https://github.com/rust-lang-nursery/rust-clippy/wiki#len_without_is_empty)                           | warn    | traits or impls with a public `len` method but no corresponding `is_empty` method
 268 [len_zero](https://github.com/rust-lang-nursery/rust-clippy/wiki#len_zero)                                                   | warn    | checking `.len() == 0` or `.len() > 0` (or similar) when `.is_empty()` could be used instead
 269 [let_and_return](https://github.com/rust-lang-nursery/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
 270 [let_unit_value](https://github.com/rust-lang-nursery/rust-clippy/wiki#let_unit_value)                                       | warn    | creating a let binding to a value of unit type, which usually can't be used afterwards
 271 [linkedlist](https://github.com/rust-lang-nursery/rust-clippy/wiki#linkedlist)                                               | warn    | usage of LinkedList, usually a vector is faster, or a more specialized data structure like a VecDeque
 272 [logic_bug](https://github.com/rust-lang-nursery/rust-clippy/wiki#logic_bug)                                                 | warn    | boolean expressions that contain terminals which can be eliminated
 273 [manual_swap](https://github.com/rust-lang-nursery/rust-clippy/wiki#manual_swap)                                             | warn    | manual swap of two variables
 274 [many_single_char_names](https://github.com/rust-lang-nursery/rust-clippy/wiki#many_single_char_names)                       | warn    | too many single character bindings
 275 [map_clone](https://github.com/rust-lang-nursery/rust-clippy/wiki#map_clone)                                                 | warn    | using `.map(|x| x.clone())` to clone an iterator or option's contents
 276 [map_entry](https://github.com/rust-lang-nursery/rust-clippy/wiki#map_entry)                                                 | warn    | use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`
 277 [match_bool](https://github.com/rust-lang-nursery/rust-clippy/wiki#match_bool)                                               | warn    | a match on a boolean expression instead of an `if..else` block
 278 [match_overlapping_arm](https://github.com/rust-lang-nursery/rust-clippy/wiki#match_overlapping_arm)                         | warn    | a match with overlapping arms
 279 [match_ref_pats](https://github.com/rust-lang-nursery/rust-clippy/wiki#match_ref_pats)                                       | warn    | a match or `if let` with all arms prefixed with `&` instead of deref-ing the match expression
 280 [match_same_arms](https://github.com/rust-lang-nursery/rust-clippy/wiki#match_same_arms)                                     | warn    | `match` with identical arm bodies
 281 [match_wild_err_arm](https://github.com/rust-lang-nursery/rust-clippy/wiki#match_wild_err_arm)                               | warn    | a match with `Err(_)` arm and take drastic actions
 282 [mem_forget](https://github.com/rust-lang-nursery/rust-clippy/wiki#mem_forget)                                               | allow   | `mem::forget` usage on `Drop` types, likely to cause memory leaks
 283 [min_max](https://github.com/rust-lang-nursery/rust-clippy/wiki#min_max)                                                     | warn    | `min(_, max(_, _))` (or vice versa) with bounds clamping the result to a constant
 284 [misrefactored_assign_op](https://github.com/rust-lang-nursery/rust-clippy/wiki#misrefactored_assign_op)                     | warn    | having a variable on both sides of an assign op
 285 [missing_docs_in_private_items](https://github.com/rust-lang-nursery/rust-clippy/wiki#missing_docs_in_private_items)         | allow   | detects missing documentation for public and private members
 286 [mixed_case_hex_literals](https://github.com/rust-lang-nursery/rust-clippy/wiki#mixed_case_hex_literals)                     | warn    | hex literals whose letter digits are not consistently upper- or lowercased
 287 [module_inception](https://github.com/rust-lang-nursery/rust-clippy/wiki#module_inception)                                   | warn    | modules that have the same name as their parent module
 288 [modulo_one](https://github.com/rust-lang-nursery/rust-clippy/wiki#modulo_one)                                               | warn    | taking a number modulo 1, which always returns 0
 289 [mut_from_ref](https://github.com/rust-lang-nursery/rust-clippy/wiki#mut_from_ref)                                           | warn    | fns that create mutable refs from immutable ref args
 290 [mut_mut](https://github.com/rust-lang-nursery/rust-clippy/wiki#mut_mut)                                                     | allow   | usage of double-mut refs, e.g. `&mut &mut ...`
 291 [mutex_atomic](https://github.com/rust-lang-nursery/rust-clippy/wiki#mutex_atomic)                                           | warn    | using a mutex where an atomic value could be used instead
 292 [mutex_integer](https://github.com/rust-lang-nursery/rust-clippy/wiki#mutex_integer)                                         | allow   | using a mutex for an integer type
 293 [needless_bool](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_bool)                                         | warn    | if-statements with plain booleans in the then- and else-clause, e.g. `if p { true } else { false }`
 294 [needless_borrow](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_borrow)                                     | warn    | taking a reference that is going to be automatically dereferenced
 295 [needless_borrowed_reference](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_borrowed_reference)             | warn    | taking a needless borrowed reference
 296 [needless_continue](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_continue)                                 | warn    | `continue` statements that can be replaced by a rearrangement of code
 297 [needless_lifetimes](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_lifetimes)                               | warn    | using explicit lifetimes for references in function arguments when elision rules would allow omitting them
 298 [needless_pass_by_value](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_pass_by_value)                       | warn    | functions taking arguments by value, but not consuming them in its body
 299 [needless_range_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_range_loop)                             | warn    | for-looping over a range of indices where an iterator over items would do
 300 [needless_return](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_return)                                     | warn    | using a return statement like `return expr;` where an expression would suffice
 301 [needless_update](https://github.com/rust-lang-nursery/rust-clippy/wiki#needless_update)                                     | warn    | using `Foo { ..base }` when there are no missing fields
 302 [neg_multiply](https://github.com/rust-lang-nursery/rust-clippy/wiki#neg_multiply)                                           | warn    | multiplying integers with -1
 303 [never_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#never_loop)                                               | warn    | any loop that will always `break` or `return`
 304 [new_ret_no_self](https://github.com/rust-lang-nursery/rust-clippy/wiki#new_ret_no_self)                                     | warn    | not returning `Self` in a `new` method
 305 [new_without_default](https://github.com/rust-lang-nursery/rust-clippy/wiki#new_without_default)                             | warn    | `fn new() -> Self` method without `Default` implementation
 306 [new_without_default_derive](https://github.com/rust-lang-nursery/rust-clippy/wiki#new_without_default_derive)               | warn    | `fn new() -> Self` without `#[derive]`able `Default` implementation
 307 [no_effect](https://github.com/rust-lang-nursery/rust-clippy/wiki#no_effect)                                                 | warn    | statements with no effect
 308 [non_ascii_literal](https://github.com/rust-lang-nursery/rust-clippy/wiki#non_ascii_literal)                                 | allow   | using any literal non-ASCII chars in a string literal instead of using the `\\u` escape
 309 [nonminimal_bool](https://github.com/rust-lang-nursery/rust-clippy/wiki#nonminimal_bool)                                     | allow   | boolean expressions that can be written more concisely
 310 [nonsensical_open_options](https://github.com/rust-lang-nursery/rust-clippy/wiki#nonsensical_open_options)                   | warn    | nonsensical combination of options for opening a file
 311 [not_unsafe_ptr_arg_deref](https://github.com/rust-lang-nursery/rust-clippy/wiki#not_unsafe_ptr_arg_deref)                   | warn    | public functions dereferencing raw pointer arguments but not marked `unsafe`
 312 [ok_expect](https://github.com/rust-lang-nursery/rust-clippy/wiki#ok_expect)                                                 | warn    | using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result
 313 [op_ref](https://github.com/rust-lang-nursery/rust-clippy/wiki#op_ref)                                                       | warn    | taking a reference to satisfy the type constraints on `==`
 314 [option_map_unwrap_or](https://github.com/rust-lang-nursery/rust-clippy/wiki#option_map_unwrap_or)                           | allow   | using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`
 315 [option_map_unwrap_or_else](https://github.com/rust-lang-nursery/rust-clippy/wiki#option_map_unwrap_or_else)                 | allow   | using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`
 316 [option_unwrap_used](https://github.com/rust-lang-nursery/rust-clippy/wiki#option_unwrap_used)                               | allow   | using `Option.unwrap()`, which should at least get a better message using `expect()`
 317 [or_fun_call](https://github.com/rust-lang-nursery/rust-clippy/wiki#or_fun_call)                                             | warn    | using any `*or` method with a function call, which suggests `*or_else`
 318 [out_of_bounds_indexing](https://github.com/rust-lang-nursery/rust-clippy/wiki#out_of_bounds_indexing)                       | deny    | out of bounds constant indexing
 319 [overflow_check_conditional](https://github.com/rust-lang-nursery/rust-clippy/wiki#overflow_check_conditional)               | warn    | overflow checks inspired by C which are likely to panic
 320 [panic_params](https://github.com/rust-lang-nursery/rust-clippy/wiki#panic_params)                                           | warn    | missing parameters in `panic!` calls
 321 [partialeq_ne_impl](https://github.com/rust-lang-nursery/rust-clippy/wiki#partialeq_ne_impl)                                 | warn    | re-implementing `PartialEq::ne`
 322 [possible_missing_comma](https://github.com/rust-lang-nursery/rust-clippy/wiki#possible_missing_comma)                       | warn    | possible missing comma in array
 323 [precedence](https://github.com/rust-lang-nursery/rust-clippy/wiki#precedence)                                               | warn    | operations where precedence may be unclear
 324 [print_stdout](https://github.com/rust-lang-nursery/rust-clippy/wiki#print_stdout)                                           | allow   | printing on stdout
 325 [print_with_newline](https://github.com/rust-lang-nursery/rust-clippy/wiki#print_with_newline)                               | warn    | using `print!()` with a format string that ends in a newline
 326 [ptr_arg](https://github.com/rust-lang-nursery/rust-clippy/wiki#ptr_arg)                                                     | warn    | fn arguments of the type `&Vec<...>` or `&String`, suggesting to use `&[...]` or `&str` instead, respectively
 327 [pub_enum_variant_names](https://github.com/rust-lang-nursery/rust-clippy/wiki#pub_enum_variant_names)                       | allow   | enums where all variants share a prefix/postfix
 328 [range_zip_with_len](https://github.com/rust-lang-nursery/rust-clippy/wiki#range_zip_with_len)                               | warn    | zipping iterator with a range when `enumerate()` would do
 329 [redundant_closure](https://github.com/rust-lang-nursery/rust-clippy/wiki#redundant_closure)                                 | warn    | redundant closures, i.e. `|a| foo(a)` (which can be written as just `foo`)
 330 [redundant_closure_call](https://github.com/rust-lang-nursery/rust-clippy/wiki#redundant_closure_call)                       | warn    | throwaway closures called in the expression they are defined
 331 [redundant_pattern](https://github.com/rust-lang-nursery/rust-clippy/wiki#redundant_pattern)                                 | warn    | using `name @ _` in a pattern
 332 [regex_macro](https://github.com/rust-lang-nursery/rust-clippy/wiki#regex_macro)                                             | warn    | use of `regex!(_)` instead of `Regex::new(_)`
 333 [result_unwrap_used](https://github.com/rust-lang-nursery/rust-clippy/wiki#result_unwrap_used)                               | allow   | using `Result.unwrap()`, which might be better handled
 334 [reverse_range_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#reverse_range_loop)                               | warn    | iteration over an empty range, such as `10..0` or `5..5`
 335 [search_is_some](https://github.com/rust-lang-nursery/rust-clippy/wiki#search_is_some)                                       | warn    | using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`
 336 [serde_api_misuse](https://github.com/rust-lang-nursery/rust-clippy/wiki#serde_api_misuse)                                   | warn    | various things that will negatively affect your serde experience
 337 [shadow_reuse](https://github.com/rust-lang-nursery/rust-clippy/wiki#shadow_reuse)                                           | allow   | rebinding a name to an expression that re-uses the original value, e.g. `let x = x + 1`
 338 [shadow_same](https://github.com/rust-lang-nursery/rust-clippy/wiki#shadow_same)                                             | allow   | rebinding a name to itself, e.g. `let mut x = &mut x`
 339 [shadow_unrelated](https://github.com/rust-lang-nursery/rust-clippy/wiki#shadow_unrelated)                                   | allow   | rebinding a name without even using the original value
 340 [short_circuit_statement](https://github.com/rust-lang-nursery/rust-clippy/wiki#short_circuit_statement)                     | warn    | using a short circuit boolean condition as a statement
 341 [should_assert_eq](https://github.com/rust-lang-nursery/rust-clippy/wiki#should_assert_eq)                                   | warn    | using `assert` macro for asserting equality
 342 [should_implement_trait](https://github.com/rust-lang-nursery/rust-clippy/wiki#should_implement_trait)                       | warn    | defining a method that should be implementing a std trait
 343 [similar_names](https://github.com/rust-lang-nursery/rust-clippy/wiki#similar_names)                                         | allow   | similarly named items and bindings
 344 [single_char_pattern](https://github.com/rust-lang-nursery/rust-clippy/wiki#single_char_pattern)                             | warn    | using a single-character str where a char could be used, e.g. `_.split("x")`
 345 [single_match](https://github.com/rust-lang-nursery/rust-clippy/wiki#single_match)                                           | warn    | a match statement with a single nontrivial arm (i.e. where the other arm is `_ => {}`) instead of `if let`
 346 [single_match_else](https://github.com/rust-lang-nursery/rust-clippy/wiki#single_match_else)                                 | allow   | a match statement with a two arms where the second arm's pattern is a wildcard instead of `if let`
 347 [string_add](https://github.com/rust-lang-nursery/rust-clippy/wiki#string_add)                                               | allow   | using `x + ..` where x is a `String` instead of `push_str()`
 348 [string_add_assign](https://github.com/rust-lang-nursery/rust-clippy/wiki#string_add_assign)                                 | allow   | using `x = x + ..` where x is a `String` instead of `push_str()`
 349 [string_extend_chars](https://github.com/rust-lang-nursery/rust-clippy/wiki#string_extend_chars)                             | warn    | using `x.extend(s.chars())` where s is a `&str` or `String`
 350 [string_lit_as_bytes](https://github.com/rust-lang-nursery/rust-clippy/wiki#string_lit_as_bytes)                             | warn    | calling `as_bytes` on a string literal instead of using a byte string literal
 351 [stutter](https://github.com/rust-lang-nursery/rust-clippy/wiki#stutter)                                                     | allow   | type names prefixed/postfixed with their containing module's name
 352 [suspicious_assignment_formatting](https://github.com/rust-lang-nursery/rust-clippy/wiki#suspicious_assignment_formatting)   | warn    | suspicious formatting of `*=`, `-=` or `!=`
 353 [suspicious_else_formatting](https://github.com/rust-lang-nursery/rust-clippy/wiki#suspicious_else_formatting)               | warn    | suspicious formatting of `else if`
 354 [temporary_assignment](https://github.com/rust-lang-nursery/rust-clippy/wiki#temporary_assignment)                           | warn    | assignments to temporaries
 355 [temporary_cstring_as_ptr](https://github.com/rust-lang-nursery/rust-clippy/wiki#temporary_cstring_as_ptr)                   | warn    | getting the inner pointer of a temporary `CString`
 356 [too_many_arguments](https://github.com/rust-lang-nursery/rust-clippy/wiki#too_many_arguments)                               | warn    | functions with too many arguments
 357 [toplevel_ref_arg](https://github.com/rust-lang-nursery/rust-clippy/wiki#toplevel_ref_arg)                                   | warn    | an entire binding declared as `ref`, in a function argument or a `let` statement
 358 [transmute_ptr_to_ref](https://github.com/rust-lang-nursery/rust-clippy/wiki#transmute_ptr_to_ref)                           | warn    | transmutes from a pointer to a reference type
 359 [trivial_regex](https://github.com/rust-lang-nursery/rust-clippy/wiki#trivial_regex)                                         | warn    | trivial regular expressions
 360 [type_complexity](https://github.com/rust-lang-nursery/rust-clippy/wiki#type_complexity)                                     | warn    | usage of very complex types that might be better factored into `type` definitions
 361 [unicode_not_nfc](https://github.com/rust-lang-nursery/rust-clippy/wiki#unicode_not_nfc)                                     | allow   | using a unicode literal not in NFC normal form (see [unicode tr15](http://www.unicode.org/reports/tr15/) for further information)
 362 [unit_cmp](https://github.com/rust-lang-nursery/rust-clippy/wiki#unit_cmp)                                                   | warn    | comparing unit values
 363 [unnecessary_cast](https://github.com/rust-lang-nursery/rust-clippy/wiki#unnecessary_cast)                                   | warn    | cast to the same type, e.g. `x as i32` where `x: i32`
 364 [unnecessary_mut_passed](https://github.com/rust-lang-nursery/rust-clippy/wiki#unnecessary_mut_passed)                       | warn    | an argument passed as a mutable reference although the callee only demands an immutable reference
 365 [unnecessary_operation](https://github.com/rust-lang-nursery/rust-clippy/wiki#unnecessary_operation)                         | warn    | outer expressions with no effect
 366 [unneeded_field_pattern](https://github.com/rust-lang-nursery/rust-clippy/wiki#unneeded_field_pattern)                       | warn    | struct fields bound to a wildcard instead of using `..`
 367 [unreadable_literal](https://github.com/rust-lang-nursery/rust-clippy/wiki#unreadable_literal)                               | warn    | long integer literal without underscores
 368 [unsafe_removed_from_name](https://github.com/rust-lang-nursery/rust-clippy/wiki#unsafe_removed_from_name)                   | warn    | `unsafe` removed from API names on import
 369 [unseparated_literal_suffix](https://github.com/rust-lang-nursery/rust-clippy/wiki#unseparated_literal_suffix)               | allow   | literals whose suffix is not separated by an underscore
 370 [unused_collect](https://github.com/rust-lang-nursery/rust-clippy/wiki#unused_collect)                                       | warn    | `collect()`ing an iterator without using the result; this is usually better written as a for loop
 371 [unused_io_amount](https://github.com/rust-lang-nursery/rust-clippy/wiki#unused_io_amount)                                   | deny    | unused written/read amount
 372 [unused_label](https://github.com/rust-lang-nursery/rust-clippy/wiki#unused_label)                                           | warn    | unused labels
 373 [unused_lifetimes](https://github.com/rust-lang-nursery/rust-clippy/wiki#unused_lifetimes)                                   | warn    | unused lifetimes in function definitions
 374 [use_debug](https://github.com/rust-lang-nursery/rust-clippy/wiki#use_debug)                                                 | allow   | use of `Debug`-based formatting
 375 [use_self](https://github.com/rust-lang-nursery/rust-clippy/wiki#use_self)                                                   | allow   | Unnecessary structure name repetition whereas `Self` is applicable
 376 [used_underscore_binding](https://github.com/rust-lang-nursery/rust-clippy/wiki#used_underscore_binding)                     | allow   | using a binding which is prefixed with an underscore
 377 [useless_attribute](https://github.com/rust-lang-nursery/rust-clippy/wiki#useless_attribute)                                 | warn    | use of lint attributes on `extern crate` items
 378 [useless_format](https://github.com/rust-lang-nursery/rust-clippy/wiki#useless_format)                                       | warn    | useless use of `format!`
 379 [useless_let_if_seq](https://github.com/rust-lang-nursery/rust-clippy/wiki#useless_let_if_seq)                               | warn    | unidiomatic `let mut` declaration followed by initialization in `if`
 380 [useless_transmute](https://github.com/rust-lang-nursery/rust-clippy/wiki#useless_transmute)                                 | warn    | transmutes that have the same to and from types or could be a cast/coercion
 381 [useless_vec](https://github.com/rust-lang-nursery/rust-clippy/wiki#useless_vec)                                             | warn    | useless `vec!`
 382 [verbose_bit_mask](https://github.com/rust-lang-nursery/rust-clippy/wiki#verbose_bit_mask)                                   | warn    | expressions where a bit mask is less readable than the corresponding method call
 383 [while_let_loop](https://github.com/rust-lang-nursery/rust-clippy/wiki#while_let_loop)                                       | warn    | `loop { if let { ... } else break }`, which can be written as a `while let` loop
 384 [while_let_on_iterator](https://github.com/rust-lang-nursery/rust-clippy/wiki#while_let_on_iterator)                         | warn    | using a while-let loop instead of a for loop on an iterator
 385 [wrong_pub_self_convention](https://github.com/rust-lang-nursery/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
 386 [wrong_self_convention](https://github.com/rust-lang-nursery/rust-clippy/wiki#wrong_self_convention)                         | warn    | defining a method named with an established prefix (like "into_") that takes `self` with the wrong convention
 387 [wrong_transmute](https://github.com/rust-lang-nursery/rust-clippy/wiki#wrong_transmute)                                     | warn    | transmutes that are confusing at best, undefined behaviour at worst and always useless
 388 [zero_divided_by_zero](https://github.com/rust-lang-nursery/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
 389 [zero_prefixed_literal](https://github.com/rust-lang-nursery/rust-clippy/wiki#zero_prefixed_literal)                         | warn    | integer literals starting with `0`
 390 [zero_ptr](https://github.com/rust-lang-nursery/rust-clippy/wiki#zero_ptr)                                                   | warn    | using 0 as *{const, mut} T
 391 [zero_width_space](https://github.com/rust-lang-nursery/rust-clippy/wiki#zero_width_space)                                   | deny    | using a zero-width space in a string literal, which is confusing
 392
 393 More to come, please [file an issue](https://github.com/rust-lang-nursery/rust-clippy/issues) if you have ideas!
 394
 395 ## License
 396
 397 Licensed under [MPL](https://www.mozilla.org/MPL/2.0/).
 398 If you're having issues with the license, let me know and I'll try to change it to something more permissive.