README.md

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