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 171 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 [diverging_sub_expression](https://github.com/Manishearth/rust-clippy/wiki#diverging_sub_expression)                 | warn    | whether an expression contains a diverging sub expression
  54 [doc_markdown](https://github.com/Manishearth/rust-clippy/wiki#doc_markdown)                                         | warn    | presence of `_`, `::` or camel-case outside backticks in documentation
  55 [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++
  56 [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
  57 [duplicate_underscore_argument](https://github.com/Manishearth/rust-clippy/wiki#duplicate_underscore_argument)       | warn    | function arguments having names which only differ by an underscore
  58 [empty_loop](https://github.com/Manishearth/rust-clippy/wiki#empty_loop)                                             | warn    | empty `loop {}`, which should block or sleep
  59 [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`
  60 [enum_glob_use](https://github.com/Manishearth/rust-clippy/wiki#enum_glob_use)                                       | allow   | use items that import all variants of an enum
  61 [enum_variant_names](https://github.com/Manishearth/rust-clippy/wiki#enum_variant_names)                             | warn    | enums where all variants share a prefix/postfix
  62 [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`)
  63 [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
  64 [expl_impl_clone_on_copy](https://github.com/Manishearth/rust-clippy/wiki#expl_impl_clone_on_copy)                   | warn    | implementing `Clone` explicitly on `Copy` types
  65 [explicit_counter_loop](https://github.com/Manishearth/rust-clippy/wiki#explicit_counter_loop)                       | warn    | for-looping with an explicit counter when `_.enumerate()` would do
  66 [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
  67 [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
  68 [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
  69 [filter_next](https://github.com/Manishearth/rust-clippy/wiki#filter_next)                                           | warn    | using `filter(p).next()`, which is more succinctly expressed as `.find(p)`
  70 [float_arithmetic](https://github.com/Manishearth/rust-clippy/wiki#float_arithmetic)                                 | allow   | any floating-point arithmetic statement
  71 [float_cmp](https://github.com/Manishearth/rust-clippy/wiki#float_cmp)                                               | warn    | using `==` or `!=` on float values instead of comparing difference with an epsilon
  72 [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
  73 [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`
  74 [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`
  75 [identity_op](https://github.com/Manishearth/rust-clippy/wiki#identity_op)                                           | warn    | using identity operations, e.g. `x + 0` or `y / 1`
  76 [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
  77 [if_same_then_else](https://github.com/Manishearth/rust-clippy/wiki#if_same_then_else)                               | warn    | if with the same *then* and *else* blocks
  78 [ifs_same_cond](https://github.com/Manishearth/rust-clippy/wiki#ifs_same_cond)                                       | warn    | consecutive `ifs` with the same condition
  79 [indexing_slicing](https://github.com/Manishearth/rust-clippy/wiki#indexing_slicing)                                 | allow   | indexing/slicing usage
  80 [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`
  81 [inline_always](https://github.com/Manishearth/rust-clippy/wiki#inline_always)                                       | warn    | use of `#[inline(always)]`
  82 [integer_arithmetic](https://github.com/Manishearth/rust-clippy/wiki#integer_arithmetic)                             | allow   | any integer arithmetic statement
  83 [invalid_regex](https://github.com/Manishearth/rust-clippy/wiki#invalid_regex)                                       | deny    | invalid regular expressions
  84 [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
  85 [items_after_statements](https://github.com/Manishearth/rust-clippy/wiki#items_after_statements)                     | allow   | blocks where an item comes after a statement
  86 [iter_next_loop](https://github.com/Manishearth/rust-clippy/wiki#iter_next_loop)                                     | warn    | for-looping over `_.next()` which is probably not intended
  87 [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
  88 [len_without_is_empty](https://github.com/Manishearth/rust-clippy/wiki#len_without_is_empty)                         | warn    | traits or impls with a public `len` method but no corresponding `is_empty` method
  89 [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
  90 [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
  91 [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
  92 [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
  93 [logic_bug](https://github.com/Manishearth/rust-clippy/wiki#logic_bug)                                               | warn    | boolean expressions that contain terminals which can be eliminated
  94 [manual_swap](https://github.com/Manishearth/rust-clippy/wiki#manual_swap)                                           | warn    | manual swap of two variables
  95 [many_single_char_names](https://github.com/Manishearth/rust-clippy/wiki#many_single_char_names)                     | warn    | too many single character bindings
  96 [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
  97 [map_entry](https://github.com/Manishearth/rust-clippy/wiki#map_entry)                                               | warn    | use of `contains_key` followed by `insert` on a `HashMap` or `BTreeMap`
  98 [match_bool](https://github.com/Manishearth/rust-clippy/wiki#match_bool)                                             | warn    | a match on a boolean expression instead of an `if..else` block
  99 [match_overlapping_arm](https://github.com/Manishearth/rust-clippy/wiki#match_overlapping_arm)                       | warn    | a match with overlapping arms
 100 [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
 101 [match_same_arms](https://github.com/Manishearth/rust-clippy/wiki#match_same_arms)                                   | warn    | `match` with identical arm bodies
 102 [mem_forget](https://github.com/Manishearth/rust-clippy/wiki#mem_forget)                                             | allow   | `mem::forget` usage on `Drop` types, likely to cause memory leaks
 103 [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
 104 [misrefactored_assign_op](https://github.com/Manishearth/rust-clippy/wiki#misrefactored_assign_op)                   | warn    | having a variable on both sides of an assign op
 105 [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
 106 [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
 107 [module_inception](https://github.com/Manishearth/rust-clippy/wiki#module_inception)                                 | warn    | modules that have the same name as their parent module
 108 [modulo_one](https://github.com/Manishearth/rust-clippy/wiki#modulo_one)                                             | warn    | taking a number modulo 1, which always returns 0
 109 [mut_mut](https://github.com/Manishearth/rust-clippy/wiki#mut_mut)                                                   | allow   | usage of double-mut refs, e.g. `&mut &mut ...`
 110 [mutex_atomic](https://github.com/Manishearth/rust-clippy/wiki#mutex_atomic)                                         | warn    | using a mutex where an atomic value could be used instead
 111 [mutex_integer](https://github.com/Manishearth/rust-clippy/wiki#mutex_integer)                                       | allow   | using a mutex for an integer type
 112 [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 }`
 113 [needless_borrow](https://github.com/Manishearth/rust-clippy/wiki#needless_borrow)                                   | warn    | taking a reference that is going to be automatically dereferenced
 114 [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
 115 [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
 116 [needless_return](https://github.com/Manishearth/rust-clippy/wiki#needless_return)                                   | warn    | using a return statement like `return expr;` where an expression would suffice
 117 [needless_update](https://github.com/Manishearth/rust-clippy/wiki#needless_update)                                   | warn    | using `Foo { ..base }` when there are no missing fields
 118 [neg_multiply](https://github.com/Manishearth/rust-clippy/wiki#neg_multiply)                                         | warn    | multiplying integers with -1
 119 [new_ret_no_self](https://github.com/Manishearth/rust-clippy/wiki#new_ret_no_self)                                   | warn    | not returning `Self` in a `new` method
 120 [new_without_default](https://github.com/Manishearth/rust-clippy/wiki#new_without_default)                           | warn    | `fn new() -> Self` method without `Default` implementation
 121 [new_without_default_derive](https://github.com/Manishearth/rust-clippy/wiki#new_without_default_derive)             | warn    | `fn new() -> Self` without `#[derive]`able `Default` implementation
 122 [no_effect](https://github.com/Manishearth/rust-clippy/wiki#no_effect)                                               | warn    | statements with no effect
 123 [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
 124 [nonminimal_bool](https://github.com/Manishearth/rust-clippy/wiki#nonminimal_bool)                                   | allow   | boolean expressions that can be written more concisely
 125 [nonsensical_open_options](https://github.com/Manishearth/rust-clippy/wiki#nonsensical_open_options)                 | warn    | nonsensical combination of options for opening a file
 126 [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`
 127 [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
 128 [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)`
 129 [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)`
 130 [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()`
 131 [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`
 132 [out_of_bounds_indexing](https://github.com/Manishearth/rust-clippy/wiki#out_of_bounds_indexing)                     | deny    | out of bounds constant indexing
 133 [overflow_check_conditional](https://github.com/Manishearth/rust-clippy/wiki#overflow_check_conditional)             | warn    | overflow checks inspired by C which are likely to panic
 134 [panic_params](https://github.com/Manishearth/rust-clippy/wiki#panic_params)                                         | warn    | missing parameters in `panic!` calls
 135 [precedence](https://github.com/Manishearth/rust-clippy/wiki#precedence)                                             | warn    | operations where precedence may be unclear
 136 [print_stdout](https://github.com/Manishearth/rust-clippy/wiki#print_stdout)                                         | allow   | printing on stdout
 137 [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
 138 [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
 139 [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
 140 [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
 141 [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`)
 142 [redundant_closure_call](https://github.com/Manishearth/rust-clippy/wiki#redundant_closure_call)                     | warn    | throwaway closures called in the expression they are defined
 143 [redundant_pattern](https://github.com/Manishearth/rust-clippy/wiki#redundant_pattern)                               | warn    | using `name @ _` in a pattern
 144 [regex_macro](https://github.com/Manishearth/rust-clippy/wiki#regex_macro)                                           | warn    | use of `regex!(_)` instead of `Regex::new(_)`
 145 [result_unwrap_used](https://github.com/Manishearth/rust-clippy/wiki#result_unwrap_used)                             | allow   | using `Result.unwrap()`, which might be better handled
 146 [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`
 147 [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()`
 148 [serde_api_misuse](https://github.com/Manishearth/rust-clippy/wiki#serde_api_misuse)                                 | warn    | various things that will negatively affect your serde experience
 149 [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`
 150 [shadow_same](https://github.com/Manishearth/rust-clippy/wiki#shadow_same)                                           | allow   | rebinding a name to itself, e.g. `let mut x = &mut x`
 151 [shadow_unrelated](https://github.com/Manishearth/rust-clippy/wiki#shadow_unrelated)                                 | allow   | rebinding a name without even using the original value
 152 [should_implement_trait](https://github.com/Manishearth/rust-clippy/wiki#should_implement_trait)                     | warn    | defining a method that should be implementing a std trait
 153 [similar_names](https://github.com/Manishearth/rust-clippy/wiki#similar_names)                                       | allow   | similarly named items and bindings
 154 [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")`
 155 [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`
 156 [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`
 157 [string_add](https://github.com/Manishearth/rust-clippy/wiki#string_add)                                             | allow   | using `x + ..` where x is a `String` instead of `push_str()`
 158 [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()`
 159 [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
 160 [stutter](https://github.com/Manishearth/rust-clippy/wiki#stutter)                                                   | allow   | type names prefixed/postfixed with their containing module's name
 161 [suspicious_assignment_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_assignment_formatting) | warn    | suspicious formatting of `*=`, `-=` or `!=`
 162 [suspicious_else_formatting](https://github.com/Manishearth/rust-clippy/wiki#suspicious_else_formatting)             | warn    | suspicious formatting of `else if`
 163 [temporary_assignment](https://github.com/Manishearth/rust-clippy/wiki#temporary_assignment)                         | warn    | assignments to temporaries
 164 [temporary_cstring_as_ptr](https://github.com/Manishearth/rust-clippy/wiki#temporary_cstring_as_ptr)                 | warn    | getting the inner pointer of a temporary `CString`
 165 [too_many_arguments](https://github.com/Manishearth/rust-clippy/wiki#too_many_arguments)                             | warn    | functions with too many arguments
 166 [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
 167 [transmute_ptr_to_ref](https://github.com/Manishearth/rust-clippy/wiki#transmute_ptr_to_ref)                         | warn    | transmutes from a pointer to a reference type
 168 [trivial_regex](https://github.com/Manishearth/rust-clippy/wiki#trivial_regex)                                       | warn    | trivial regular expressions
 169 [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
 170 [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)
 171 [unit_cmp](https://github.com/Manishearth/rust-clippy/wiki#unit_cmp)                                                 | warn    | comparing unit values
 172 [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
 173 [unnecessary_operation](https://github.com/Manishearth/rust-clippy/wiki#unnecessary_operation)                       | warn    | outer expressions with no effect
 174 [unneeded_field_pattern](https://github.com/Manishearth/rust-clippy/wiki#unneeded_field_pattern)                     | warn    | struct fields bound to a wildcard instead of using `..`
 175 [unsafe_removed_from_name](https://github.com/Manishearth/rust-clippy/wiki#unsafe_removed_from_name)                 | warn    | `unsafe` removed from API names on import
 176 [unseparated_literal_suffix](https://github.com/Manishearth/rust-clippy/wiki#unseparated_literal_suffix)             | allow   | literals whose suffix is not separated by an underscore
 177 [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
 178 [unused_label](https://github.com/Manishearth/rust-clippy/wiki#unused_label)                                         | warn    | unused labels
 179 [unused_lifetimes](https://github.com/Manishearth/rust-clippy/wiki#unused_lifetimes)                                 | warn    | unused lifetimes in function definitions
 180 [use_debug](https://github.com/Manishearth/rust-clippy/wiki#use_debug)                                               | allow   | use of `Debug`-based formatting
 181 [used_underscore_binding](https://github.com/Manishearth/rust-clippy/wiki#used_underscore_binding)                   | allow   | using a binding which is prefixed with an underscore
 182 [useless_attribute](https://github.com/Manishearth/rust-clippy/wiki#useless_attribute)                               | warn    | use of lint attributes on `extern crate` items
 183 [useless_format](https://github.com/Manishearth/rust-clippy/wiki#useless_format)                                     | warn    | useless use of `format!`
 184 [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`
 185 [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
 186 [useless_vec](https://github.com/Manishearth/rust-clippy/wiki#useless_vec)                                           | warn    | useless `vec!`
 187 [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
 188 [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
 189 [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
 190 [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
 191 [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
 192 [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
 193 [zero_prefixed_literal](https://github.com/Manishearth/rust-clippy/wiki#zero_prefixed_literal)                       | warn    | integer literals starting with `0`
 194 [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
 195
 196 More to come, please [file an issue](https://github.com/Manishearth/rust-clippy/issues) if you have ideas!
 197
 198 ## Usage
 199
 200 As a general rule clippy will only work with the *latest* Rust nightly for now.
 201
 202 ### As a Compiler Plugin
 203
 204 Since stable Rust is backwards compatible, you should be able to
 205 compile your stable programs with nightly Rust with clippy plugged in to
 206 circumvent this.
 207
 208 Add in your `Cargo.toml`:
 209
 210 ```toml
 211 [dependencies]
 212 clippy = "*"
 213 ```
 214
 215 You then need to add `#![feature(plugin)]` and `#![plugin(clippy)]` to the top
 216 of your crate entry point (`main.rs` or `lib.rs`).
 217
 218 Sample `main.rs`:
 219
 220 ```rust
 221 #![feature(plugin)]
 222
 223 #![plugin(clippy)]
 224
 225
 226 fn main(){
 227     let x = Some(1u8);
 228     match x {
 229         Some(y) => println!("{:?}", y),
 230         _ => ()
 231     }
 232 }
 233 ```
 234
 235 Produces this warning:
 236
 237 ```terminal
 238 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
 239 src/main.rs:8     match x {
 240 src/main.rs:9         Some(y) => println!("{:?}", y),
 241 src/main.rs:10         _ => ()
 242 src/main.rs:11     }
 243 src/main.rs:8:5: 11:6 help: Try
 244 if let Some(y) = x { println!("{:?}", y) }
 245 ```
 246
 247 ### As a cargo subcommand (`cargo clippy`)
 248
 249 An alternate way to use clippy is by installing clippy through cargo as a cargo
 250 subcommand.
 251
 252 ```terminal
 253 cargo install clippy
 254 ```
 255
 256 Now you can run clippy by invoking `cargo clippy`, or
 257 `rustup run nightly cargo clippy` directly from a directory that is usually
 258 compiled with stable.
 259
 260 In case you are not using rustup, you need to set the environment flag
 261 `SYSROOT` during installation so clippy knows where to find `librustc` and
 262 similar crates.
 263
 264 ```terminal
 265 SYSROOT=/path/to/rustc/sysroot cargo install clippy
 266 ```
 267
 268 ### Running clippy from the command line without installing
 269
 270 To have cargo compile your crate with clippy without needing `#![plugin(clippy)]`
 271 in your code, you can use:
 272
 273 ```terminal
 274 cargo rustc -- -L /path/to/clippy_so -Z extra-plugins=clippy
 275 ```
 276
 277 *[Note](https://github.com/Manishearth/rust-clippy/wiki#a-word-of-warning):*
 278 Be sure that clippy was compiled with the same version of rustc that cargo invokes here!
 279
 280 ### Optional dependency
 281
 282 If you want to make clippy an optional dependency, you can do the following:
 283
 284 In your `Cargo.toml`:
 285
 286 ```toml
 287 [dependencies]
 288 clippy = {version = "*", optional = true}
 289
 290 [features]
 291 default = []
 292 ```
 293
 294 And, in your `main.rs` or `lib.rs`:
 295
 296 ```rust
 297 #![cfg_attr(feature="clippy", feature(plugin))]
 298
 299 #![cfg_attr(feature="clippy", plugin(clippy))]
 300 ```
 301
 302 Then build by enabling the feature: `cargo build --features "clippy"`
 303
 304 Instead of adding the `cfg_attr` attributes you can also run clippy on demand:
 305 `cargo rustc --features clippy -- -Z no-trans -Z extra-plugins=clippy`
 306 (the `-Z no trans`, while not neccessary, will stop the compilation process after
 307 typechecking (and lints) have completed, which can significantly reduce the runtime).
 308
 309 ## Configuration
 310
 311 Some lints can be configured in a `clippy.toml` file. It contains basic `variable = value` mapping eg.
 312
 313 ```toml
 314 blacklisted-names = ["toto", "tata", "titi"]
 315 cyclomatic-complexity-threshold = 30
 316 ```
 317
 318 See the wiki for more information about which lints can be configured and the
 319 meaning of the variables.
 320
 321 You can also specify the path to the configuration file with:
 322
 323 ```rust
 324 #![plugin(clippy(conf_file="path/to/clippy's/configuration"))]
 325 ```
 326
 327 To deactivate the “for further information visit *wiki-link*” message you can
 328 define the `CLIPPY_DISABLE_WIKI_LINKS` environment variable.
 329
 330 ### Allowing/denying lints
 331
 332 You can add options  to `allow`/`warn`/`deny`:
 333
 334 *   the whole set of `Warn` lints using the `clippy` lint group (`#![deny(clippy)]`)
 335
 336 *   all lints using both the `clippy` and `clippy_pedantic` lint groups (`#![deny(clippy)]`,
 337     `#![deny(clippy_pedantic)]`). Note that `clippy_pedantic` contains some very aggressive
 338     lints prone to false positives.
 339
 340 *   only some lints (`#![deny(single_match, box_vec)]`, etc)
 341
 342 *   `allow`/`warn`/`deny` can be limited to a single function or module using `#[allow(...)]`, etc
 343
 344 Note: `deny` produces errors instead of warnings.
 345
 346 ## Link with clippy service
 347
 348 `clippy-service` is a rust web initiative providing `rust-clippy` as a web service.
 349
 350 Both projects are independent and maintained by different people
 351 (even if some `clippy-service`'s contributions are authored by some `rust-clippy` members).
 352
 353 You can check out this great service at [clippy.bashy.io](https://clippy.bashy.io/).
 354
 355 ## License
 356
 357 Licensed under [MPL](https://www.mozilla.org/MPL/2.0/).
 358 If you're having issues with the license, let me know and I'll try to change it to something more permissive.