1 mod bind_instead_of_map;
4 mod chars_cmp_with_unwrap;
6 mod chars_last_cmp_with_unwrap;
8 mod chars_next_cmp_with_unwrap;
11 mod cloned_instead_of_copied;
15 mod extend_with_drain;
18 mod filter_map_identity;
21 mod flat_map_identity;
23 mod from_iter_instead_of_collect;
24 mod get_last_with_len;
27 mod inefficient_to_string;
30 mod is_digit_ascii_radix;
31 mod iter_cloned_collect;
36 mod iter_overeager_cloned;
39 mod iterator_step_by_zero;
40 mod manual_saturating_arithmetic;
41 mod manual_str_repeat;
42 mod map_collect_result_unit;
46 mod needless_option_as_deref;
47 mod needless_option_take;
48 mod no_effect_replace;
49 mod obfuscated_if_else;
51 mod option_as_ref_deref;
52 mod option_map_or_none;
53 mod option_map_unwrap_or;
57 mod single_char_add_str;
58 mod single_char_insert_string;
59 mod single_char_pattern;
60 mod single_char_push_string;
63 mod string_extend_chars;
65 mod suspicious_splitn;
66 mod uninit_assumed_init;
67 mod unnecessary_filter_map;
69 mod unnecessary_iter_cloned;
71 mod unnecessary_lazy_eval;
72 mod unnecessary_to_owned;
73 mod unwrap_or_else_default;
77 mod wrong_self_convention;
80 use bind_instead_of_map::BindInsteadOfMap;
81 use clippy_utils::consts::{constant, Constant};
82 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
83 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
84 use clippy_utils::{contains_return, get_trait_def_id, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
85 use if_chain::if_chain;
87 use rustc_hir::def::Res;
88 use rustc_hir::{Expr, ExprKind, PrimTy, QPath, TraitItem, TraitItemKind};
89 use rustc_lint::{LateContext, LateLintPass, LintContext};
90 use rustc_middle::lint::in_external_macro;
91 use rustc_middle::ty::{self, TraitRef, Ty};
92 use rustc_semver::RustcVersion;
93 use rustc_session::{declare_tool_lint, impl_lint_pass};
94 use rustc_span::{sym, Span};
95 use rustc_typeck::hir_ty_to_ty;
97 declare_clippy_lint! {
99 /// Checks for usages of `cloned()` on an `Iterator` or `Option` where
100 /// `copied()` could be used instead.
102 /// ### Why is this bad?
103 /// `copied()` is better because it guarantees that the type being cloned
104 /// implements `Copy`.
108 /// [1, 2, 3].iter().cloned();
112 /// [1, 2, 3].iter().copied();
114 #[clippy::version = "1.53.0"]
115 pub CLONED_INSTEAD_OF_COPIED,
117 "used `cloned` where `copied` could be used instead"
120 declare_clippy_lint! {
122 /// Checks for usage of `_.cloned().<func>()` where call to `.cloned()` can be postponed.
124 /// ### Why is this bad?
125 /// It's often inefficient to clone all elements of an iterator, when eventually, only some
126 /// of them will be consumed.
128 /// ### Known Problems
129 /// This `lint` removes the side of effect of cloning items in the iterator.
130 /// A code that relies on that side-effect could fail.
134 /// # let vec = vec!["string".to_string()];
135 /// vec.iter().cloned().take(10);
136 /// vec.iter().cloned().last();
141 /// # let vec = vec!["string".to_string()];
142 /// vec.iter().take(10).cloned();
143 /// vec.iter().last().cloned();
145 #[clippy::version = "1.60.0"]
146 pub ITER_OVEREAGER_CLONED,
148 "using `cloned()` early with `Iterator::iter()` can lead to some performance inefficiencies"
151 declare_clippy_lint! {
153 /// Checks for usages of `Iterator::flat_map()` where `filter_map()` could be
156 /// ### Why is this bad?
157 /// When applicable, `filter_map()` is more clear since it shows that
158 /// `Option` is used to produce 0 or 1 items.
162 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().flat_map(|x| x.parse().ok()).collect();
166 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().filter_map(|x| x.parse().ok()).collect();
168 #[clippy::version = "1.53.0"]
171 "used `flat_map` where `filter_map` could be used instead"
174 declare_clippy_lint! {
176 /// Checks for `.unwrap()` calls on `Option`s and on `Result`s.
178 /// ### Why is this bad?
179 /// It is better to handle the `None` or `Err` case,
180 /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
181 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
182 /// `Allow` by default.
184 /// `result.unwrap()` will let the thread panic on `Err` values.
185 /// Normally, you want to implement more sophisticated error handling,
186 /// and propagate errors upwards with `?` operator.
188 /// Even if you want to panic on errors, not all `Error`s implement good
189 /// messages on display. Therefore, it may be beneficial to look at the places
190 /// where they may get displayed. Activate this lint to do just that.
194 /// # let option = Some(1);
195 /// # let result: Result<usize, ()> = Ok(1);
202 /// # let option = Some(1);
203 /// # let result: Result<usize, ()> = Ok(1);
204 /// option.expect("more helpful message");
205 /// result.expect("more helpful message");
207 #[clippy::version = "1.45.0"]
210 "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
213 declare_clippy_lint! {
215 /// Checks for `.expect()` calls on `Option`s and `Result`s.
217 /// ### Why is this bad?
218 /// Usually it is better to handle the `None` or `Err` case.
219 /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
220 /// this lint is `Allow` by default.
222 /// `result.expect()` will let the thread panic on `Err`
223 /// values. Normally, you want to implement more sophisticated error handling,
224 /// and propagate errors upwards with `?` operator.
228 /// # let option = Some(1);
229 /// # let result: Result<usize, ()> = Ok(1);
230 /// option.expect("one");
231 /// result.expect("one");
236 /// # let option = Some(1);
237 /// # let result: Result<usize, ()> = Ok(1);
244 #[clippy::version = "1.45.0"]
247 "using `.expect()` on `Result` or `Option`, which might be better handled"
250 declare_clippy_lint! {
252 /// Checks for methods that should live in a trait
253 /// implementation of a `std` trait (see [llogiq's blog
254 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
255 /// information) instead of an inherent implementation.
257 /// ### Why is this bad?
258 /// Implementing the traits improve ergonomics for users of
259 /// the code, often with very little cost. Also people seeing a `mul(...)`
261 /// may expect `*` to work equally, so you should have good reason to disappoint
268 /// fn add(&self, other: &X) -> X {
274 #[clippy::version = "pre 1.29.0"]
275 pub SHOULD_IMPLEMENT_TRAIT,
277 "defining a method that should be implementing a std trait"
280 declare_clippy_lint! {
282 /// Checks for methods with certain name prefixes and which
283 /// doesn't match how self is taken. The actual rules are:
285 /// |Prefix |Postfix |`self` taken | `self` type |
286 /// |-------|------------|-------------------------------|--------------|
287 /// |`as_` | none |`&self` or `&mut self` | any |
288 /// |`from_`| none | none | any |
289 /// |`into_`| none |`self` | any |
290 /// |`is_` | none |`&mut self` or `&self` or none | any |
291 /// |`to_` | `_mut` |`&mut self` | any |
292 /// |`to_` | not `_mut` |`self` | `Copy` |
293 /// |`to_` | not `_mut` |`&self` | not `Copy` |
295 /// Note: Clippy doesn't trigger methods with `to_` prefix in:
296 /// - Traits definition.
297 /// Clippy can not tell if a type that implements a trait is `Copy` or not.
298 /// - Traits implementation, when `&self` is taken.
299 /// The method signature is controlled by the trait and often `&self` is required for all types that implement the trait
300 /// (see e.g. the `std::string::ToString` trait).
302 /// Clippy allows `Pin<&Self>` and `Pin<&mut Self>` if `&self` and `&mut self` is required.
304 /// Please find more info here:
305 /// https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
307 /// ### Why is this bad?
308 /// Consistency breeds readability. If you follow the
309 /// conventions, your users won't be surprised that they, e.g., need to supply a
310 /// mutable reference to a `as_..` function.
316 /// fn as_str(self) -> &'static str {
322 #[clippy::version = "pre 1.29.0"]
323 pub WRONG_SELF_CONVENTION,
325 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
328 declare_clippy_lint! {
330 /// Checks for usage of `ok().expect(..)`.
332 /// ### Why is this bad?
333 /// Because you usually call `expect()` on the `Result`
334 /// directly to get a better error message.
336 /// ### Known problems
337 /// The error type needs to implement `Debug`
341 /// # let x = Ok::<_, ()>(());
342 /// x.ok().expect("why did I do this again?");
347 /// # let x = Ok::<_, ()>(());
348 /// x.expect("why did I do this again?");
350 #[clippy::version = "pre 1.29.0"]
353 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
356 declare_clippy_lint! {
358 /// Checks for `.err().expect()` calls on the `Result` type.
360 /// ### Why is this bad?
361 /// `.expect_err()` can be called directly to avoid the extra type conversion from `err()`.
365 /// let x: Result<u32, &str> = Ok(10);
366 /// x.err().expect("Testing err().expect()");
370 /// let x: Result<u32, &str> = Ok(10);
371 /// x.expect_err("Testing expect_err");
373 #[clippy::version = "1.62.0"]
376 r#"using `.err().expect("")` when `.expect_err("")` can be used"#
379 declare_clippy_lint! {
381 /// Checks for usages of `_.unwrap_or_else(Default::default)` on `Option` and
384 /// ### Why is this bad?
385 /// Readability, these can be written as `_.unwrap_or_default`, which is
386 /// simpler and more concise.
390 /// # let x = Some(1);
391 /// x.unwrap_or_else(Default::default);
392 /// x.unwrap_or_else(u32::default);
397 /// # let x = Some(1);
398 /// x.unwrap_or_default();
400 #[clippy::version = "1.56.0"]
401 pub UNWRAP_OR_ELSE_DEFAULT,
403 "using `.unwrap_or_else(Default::default)`, which is more succinctly expressed as `.unwrap_or_default()`"
406 declare_clippy_lint! {
408 /// Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
409 /// `result.map(_).unwrap_or_else(_)`.
411 /// ### Why is this bad?
412 /// Readability, these can be written more concisely (resp.) as
413 /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
415 /// ### Known problems
416 /// The order of the arguments is not in execution order
420 /// # let option = Some(1);
421 /// # let result: Result<usize, ()> = Ok(1);
422 /// # fn some_function(foo: ()) -> usize { 1 }
423 /// option.map(|a| a + 1).unwrap_or(0);
424 /// result.map(|a| a + 1).unwrap_or_else(some_function);
429 /// # let option = Some(1);
430 /// # let result: Result<usize, ()> = Ok(1);
431 /// # fn some_function(foo: ()) -> usize { 1 }
432 /// option.map_or(0, |a| a + 1);
433 /// result.map_or_else(some_function, |a| a + 1);
435 #[clippy::version = "1.45.0"]
438 "using `.map(f).unwrap_or(a)` or `.map(f).unwrap_or_else(func)`, which are more succinctly expressed as `map_or(a, f)` or `map_or_else(a, f)`"
441 declare_clippy_lint! {
443 /// Checks for usage of `_.map_or(None, _)`.
445 /// ### Why is this bad?
446 /// Readability, this can be written more concisely as
449 /// ### Known problems
450 /// The order of the arguments is not in execution order.
454 /// # let opt = Some(1);
455 /// opt.map_or(None, |a| Some(a + 1));
460 /// # let opt = Some(1);
461 /// opt.and_then(|a| Some(a + 1));
463 #[clippy::version = "pre 1.29.0"]
464 pub OPTION_MAP_OR_NONE,
466 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
469 declare_clippy_lint! {
471 /// Checks for usage of `_.map_or(None, Some)`.
473 /// ### Why is this bad?
474 /// Readability, this can be written more concisely as
479 /// # let r: Result<u32, &str> = Ok(1);
480 /// assert_eq!(Some(1), r.map_or(None, Some));
485 /// # let r: Result<u32, &str> = Ok(1);
486 /// assert_eq!(Some(1), r.ok());
488 #[clippy::version = "1.44.0"]
489 pub RESULT_MAP_OR_INTO_OPTION,
491 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
494 declare_clippy_lint! {
496 /// Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
497 /// `_.or_else(|x| Err(y))`.
499 /// ### Why is this bad?
500 /// Readability, this can be written more concisely as
501 /// `_.map(|x| y)` or `_.map_err(|x| y)`.
505 /// # fn opt() -> Option<&'static str> { Some("42") }
506 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
507 /// let _ = opt().and_then(|s| Some(s.len()));
508 /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
509 /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
512 /// The correct use would be:
515 /// # fn opt() -> Option<&'static str> { Some("42") }
516 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
517 /// let _ = opt().map(|s| s.len());
518 /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
519 /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
521 #[clippy::version = "1.45.0"]
522 pub BIND_INSTEAD_OF_MAP,
524 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
527 declare_clippy_lint! {
529 /// Checks for usage of `_.filter(_).next()`.
531 /// ### Why is this bad?
532 /// Readability, this can be written more concisely as
537 /// # let vec = vec![1];
538 /// vec.iter().filter(|x| **x == 0).next();
543 /// # let vec = vec![1];
544 /// vec.iter().find(|x| **x == 0);
546 #[clippy::version = "pre 1.29.0"]
549 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
552 declare_clippy_lint! {
554 /// Checks for usage of `_.skip_while(condition).next()`.
556 /// ### Why is this bad?
557 /// Readability, this can be written more concisely as
558 /// `_.find(!condition)`.
562 /// # let vec = vec![1];
563 /// vec.iter().skip_while(|x| **x == 0).next();
568 /// # let vec = vec![1];
569 /// vec.iter().find(|x| **x != 0);
571 #[clippy::version = "1.42.0"]
574 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
577 declare_clippy_lint! {
579 /// Checks for usage of `_.map(_).flatten(_)` on `Iterator` and `Option`
581 /// ### Why is this bad?
582 /// Readability, this can be written more concisely as
583 /// `_.flat_map(_)` for `Iterator` or `_.and_then(_)` for `Option`
587 /// let vec = vec![vec![1]];
588 /// let opt = Some(5);
590 /// vec.iter().map(|x| x.iter()).flatten();
591 /// opt.map(|x| Some(x * 2)).flatten();
596 /// # let vec = vec![vec![1]];
597 /// # let opt = Some(5);
598 /// vec.iter().flat_map(|x| x.iter());
599 /// opt.and_then(|x| Some(x * 2));
601 #[clippy::version = "1.31.0"]
604 "using combinations of `flatten` and `map` which can usually be written as a single method call"
607 declare_clippy_lint! {
609 /// Checks for usage of `_.filter(_).map(_)` that can be written more simply
610 /// as `filter_map(_)`.
612 /// ### Why is this bad?
613 /// Redundant code in the `filter` and `map` operations is poor style and
618 /// # #![allow(unused)]
620 /// .filter(|n| n.checked_add(1).is_some())
621 /// .map(|n| n.checked_add(1).unwrap());
626 /// # #[allow(unused)]
627 /// (0_i32..10).filter_map(|n| n.checked_add(1));
629 #[clippy::version = "1.51.0"]
630 pub MANUAL_FILTER_MAP,
632 "using `_.filter(_).map(_)` in a way that can be written more simply as `filter_map(_)`"
635 declare_clippy_lint! {
637 /// Checks for usage of `_.find(_).map(_)` that can be written more simply
638 /// as `find_map(_)`.
640 /// ### Why is this bad?
641 /// Redundant code in the `find` and `map` operations is poor style and
647 /// .find(|n| n.checked_add(1).is_some())
648 /// .map(|n| n.checked_add(1).unwrap());
653 /// (0_i32..10).find_map(|n| n.checked_add(1));
655 #[clippy::version = "1.51.0"]
658 "using `_.find(_).map(_)` in a way that can be written more simply as `find_map(_)`"
661 declare_clippy_lint! {
663 /// Checks for usage of `_.filter_map(_).next()`.
665 /// ### Why is this bad?
666 /// Readability, this can be written more concisely as
671 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
673 /// Can be written as
676 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
678 #[clippy::version = "1.36.0"]
681 "using combination of `filter_map` and `next` which can usually be written as a single method call"
684 declare_clippy_lint! {
686 /// Checks for usage of `flat_map(|x| x)`.
688 /// ### Why is this bad?
689 /// Readability, this can be written more concisely by using `flatten`.
693 /// # let iter = vec![vec![0]].into_iter();
694 /// iter.flat_map(|x| x);
696 /// Can be written as
698 /// # let iter = vec![vec![0]].into_iter();
701 #[clippy::version = "1.39.0"]
702 pub FLAT_MAP_IDENTITY,
704 "call to `flat_map` where `flatten` is sufficient"
707 declare_clippy_lint! {
709 /// Checks for an iterator or string search (such as `find()`,
710 /// `position()`, or `rposition()`) followed by a call to `is_some()` or `is_none()`.
712 /// ### Why is this bad?
713 /// Readability, this can be written more concisely as:
714 /// * `_.any(_)`, or `_.contains(_)` for `is_some()`,
715 /// * `!_.any(_)`, or `!_.contains(_)` for `is_none()`.
719 /// # #![allow(unused)]
720 /// let vec = vec![1];
721 /// vec.iter().find(|x| **x == 0).is_some();
723 /// "hello world".find("world").is_none();
728 /// let vec = vec![1];
729 /// vec.iter().any(|x| *x == 0);
731 /// # #[allow(unused)]
732 /// !"hello world".contains("world");
734 #[clippy::version = "pre 1.29.0"]
737 "using an iterator or string search followed by `is_some()` or `is_none()`, which is more succinctly expressed as a call to `any()` or `contains()` (with negation in case of `is_none()`)"
740 declare_clippy_lint! {
742 /// Checks for usage of `.chars().next()` on a `str` to check
743 /// if it starts with a given char.
745 /// ### Why is this bad?
746 /// Readability, this can be written more concisely as
747 /// `_.starts_with(_)`.
751 /// let name = "foo";
752 /// if name.chars().next() == Some('_') {};
757 /// let name = "foo";
758 /// if name.starts_with('_') {};
760 #[clippy::version = "pre 1.29.0"]
763 "using `.chars().next()` to check if a string starts with a char"
766 declare_clippy_lint! {
768 /// Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
769 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
770 /// `unwrap_or_default` instead.
772 /// ### Why is this bad?
773 /// The function will always be called and potentially
774 /// allocate an object acting as the default.
776 /// ### Known problems
777 /// If the function has side-effects, not calling it will
778 /// change the semantic of the program, but you shouldn't rely on that anyway.
782 /// # let foo = Some(String::new());
783 /// foo.unwrap_or(String::new());
788 /// # let foo = Some(String::new());
789 /// foo.unwrap_or_else(String::new);
793 /// # let foo = Some(String::new());
794 /// foo.unwrap_or_default();
796 #[clippy::version = "pre 1.29.0"]
799 "using any `*or` method with a function call, which suggests `*or_else`"
802 declare_clippy_lint! {
804 /// Checks for `.or(…).unwrap()` calls to Options and Results.
806 /// ### Why is this bad?
807 /// You should use `.unwrap_or(…)` instead for clarity.
811 /// # let fallback = "fallback";
813 /// # type Error = &'static str;
814 /// # let result: Result<&str, Error> = Err("error");
815 /// let value = result.or::<Error>(Ok(fallback)).unwrap();
818 /// # let option: Option<&str> = None;
819 /// let value = option.or(Some(fallback)).unwrap();
823 /// # let fallback = "fallback";
825 /// # let result: Result<&str, &str> = Err("error");
826 /// let value = result.unwrap_or(fallback);
829 /// # let option: Option<&str> = None;
830 /// let value = option.unwrap_or(fallback);
832 #[clippy::version = "1.61.0"]
835 "checks for `.or(…).unwrap()` calls to Options and Results."
838 declare_clippy_lint! {
840 /// Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
841 /// etc., and suggests to use `unwrap_or_else` instead
843 /// ### Why is this bad?
844 /// The function will always be called.
846 /// ### Known problems
847 /// If the function has side-effects, not calling it will
848 /// change the semantics of the program, but you shouldn't rely on that anyway.
852 /// # let foo = Some(String::new());
853 /// # let err_code = "418";
854 /// # let err_msg = "I'm a teapot";
855 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
859 /// # let foo = Some(String::new());
860 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
865 /// # let foo = Some(String::new());
866 /// # let err_code = "418";
867 /// # let err_msg = "I'm a teapot";
868 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
870 #[clippy::version = "pre 1.29.0"]
873 "using any `expect` method with a function call"
876 declare_clippy_lint! {
878 /// Checks for usage of `.clone()` on a `Copy` type.
880 /// ### Why is this bad?
881 /// The only reason `Copy` types implement `Clone` is for
882 /// generics, not for using the `clone` method on a concrete type.
888 #[clippy::version = "pre 1.29.0"]
891 "using `clone` on a `Copy` type"
894 declare_clippy_lint! {
896 /// Checks for usage of `.clone()` on a ref-counted pointer,
897 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
898 /// function syntax instead (e.g., `Rc::clone(foo)`).
900 /// ### Why is this bad?
901 /// Calling '.clone()' on an Rc, Arc, or Weak
902 /// can obscure the fact that only the pointer is being cloned, not the underlying
907 /// # use std::rc::Rc;
908 /// let x = Rc::new(1);
915 /// # use std::rc::Rc;
916 /// # let x = Rc::new(1);
919 #[clippy::version = "pre 1.29.0"]
920 pub CLONE_ON_REF_PTR,
922 "using 'clone' on a ref-counted pointer"
925 declare_clippy_lint! {
927 /// Checks for usage of `.clone()` on an `&&T`.
929 /// ### Why is this bad?
930 /// Cloning an `&&T` copies the inner `&T`, instead of
931 /// cloning the underlying `T`.
938 /// let z = y.clone();
939 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
942 #[clippy::version = "pre 1.29.0"]
943 pub CLONE_DOUBLE_REF,
945 "using `clone` on `&&T`"
948 declare_clippy_lint! {
950 /// Checks for usage of `.to_string()` on an `&&T` where
951 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
953 /// ### Why is this bad?
954 /// This bypasses the specialized implementation of
955 /// `ToString` and instead goes through the more expensive string formatting
960 /// // Generic implementation for `T: Display` is used (slow)
961 /// ["foo", "bar"].iter().map(|s| s.to_string());
963 /// // OK, the specialized impl is used
964 /// ["foo", "bar"].iter().map(|&s| s.to_string());
966 #[clippy::version = "1.40.0"]
967 pub INEFFICIENT_TO_STRING,
969 "using `to_string` on `&&T` where `T: ToString`"
972 declare_clippy_lint! {
974 /// Checks for `new` not returning a type that contains `Self`.
976 /// ### Why is this bad?
977 /// As a convention, `new` methods are used to make a new
978 /// instance of a type.
981 /// In an impl block:
984 /// # struct NotAFoo;
986 /// fn new() -> NotAFoo {
996 /// // Bad. The type name must contain `Self`
997 /// fn new() -> Bar {
1005 /// # struct FooError;
1007 /// // Good. Return type contains `Self`
1008 /// fn new() -> Result<Foo, FooError> {
1014 /// Or in a trait definition:
1016 /// pub trait Trait {
1017 /// // Bad. The type name must contain `Self`
1023 /// pub trait Trait {
1024 /// // Good. Return type contains `Self`
1025 /// fn new() -> Self;
1028 #[clippy::version = "pre 1.29.0"]
1029 pub NEW_RET_NO_SELF,
1031 "not returning type containing `Self` in a `new` method"
1034 declare_clippy_lint! {
1035 /// ### What it does
1036 /// Checks for string methods that receive a single-character
1037 /// `str` as an argument, e.g., `_.split("x")`.
1039 /// ### Why is this bad?
1040 /// Performing these methods using a `char` is faster than
1043 /// ### Known problems
1044 /// Does not catch multi-byte unicode characters.
1055 #[clippy::version = "pre 1.29.0"]
1056 pub SINGLE_CHAR_PATTERN,
1058 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
1061 declare_clippy_lint! {
1062 /// ### What it does
1063 /// Checks for calling `.step_by(0)` on iterators which panics.
1065 /// ### Why is this bad?
1066 /// This very much looks like an oversight. Use `panic!()` instead if you
1067 /// actually intend to panic.
1070 /// ```rust,should_panic
1071 /// for x in (0..100).step_by(0) {
1075 #[clippy::version = "pre 1.29.0"]
1076 pub ITERATOR_STEP_BY_ZERO,
1078 "using `Iterator::step_by(0)`, which will panic at runtime"
1081 declare_clippy_lint! {
1082 /// ### What it does
1083 /// Checks for indirect collection of populated `Option`
1085 /// ### Why is this bad?
1086 /// `Option` is like a collection of 0-1 things, so `flatten`
1087 /// automatically does this without suspicious-looking `unwrap` calls.
1091 /// let _ = std::iter::empty::<Option<i32>>().filter(Option::is_some).map(Option::unwrap);
1095 /// let _ = std::iter::empty::<Option<i32>>().flatten();
1097 #[clippy::version = "1.53.0"]
1098 pub OPTION_FILTER_MAP,
1100 "filtering `Option` for `Some` then force-unwrapping, which can be one type-safe operation"
1103 declare_clippy_lint! {
1104 /// ### What it does
1105 /// Checks for the use of `iter.nth(0)`.
1107 /// ### Why is this bad?
1108 /// `iter.next()` is equivalent to
1109 /// `iter.nth(0)`, as they both consume the next element,
1110 /// but is more readable.
1114 /// # use std::collections::HashSet;
1115 /// # let mut s = HashSet::new();
1117 /// let x = s.iter().nth(0);
1122 /// # use std::collections::HashSet;
1123 /// # let mut s = HashSet::new();
1125 /// let x = s.iter().next();
1127 #[clippy::version = "1.42.0"]
1130 "replace `iter.nth(0)` with `iter.next()`"
1133 declare_clippy_lint! {
1134 /// ### What it does
1135 /// Checks for use of `.iter().nth()` (and the related
1136 /// `.iter_mut().nth()`) on standard library types with *O*(1) element access.
1138 /// ### Why is this bad?
1139 /// `.get()` and `.get_mut()` are more efficient and more
1144 /// let some_vec = vec![0, 1, 2, 3];
1145 /// let bad_vec = some_vec.iter().nth(3);
1146 /// let bad_slice = &some_vec[..].iter().nth(3);
1148 /// The correct use would be:
1150 /// let some_vec = vec![0, 1, 2, 3];
1151 /// let bad_vec = some_vec.get(3);
1152 /// let bad_slice = &some_vec[..].get(3);
1154 #[clippy::version = "pre 1.29.0"]
1157 "using `.iter().nth()` on a standard library type with O(1) element access"
1160 declare_clippy_lint! {
1161 /// ### What it does
1162 /// Checks for use of `.skip(x).next()` on iterators.
1164 /// ### Why is this bad?
1165 /// `.nth(x)` is cleaner
1169 /// let some_vec = vec![0, 1, 2, 3];
1170 /// let bad_vec = some_vec.iter().skip(3).next();
1171 /// let bad_slice = &some_vec[..].iter().skip(3).next();
1173 /// The correct use would be:
1175 /// let some_vec = vec![0, 1, 2, 3];
1176 /// let bad_vec = some_vec.iter().nth(3);
1177 /// let bad_slice = &some_vec[..].iter().nth(3);
1179 #[clippy::version = "pre 1.29.0"]
1182 "using `.skip(x).next()` on an iterator"
1185 declare_clippy_lint! {
1186 /// ### What it does
1187 /// Checks for use of `.drain(..)` on `Vec` and `VecDeque` for iteration.
1189 /// ### Why is this bad?
1190 /// `.into_iter()` is simpler with better performance.
1194 /// # use std::collections::HashSet;
1195 /// let mut foo = vec![0, 1, 2, 3];
1196 /// let bar: HashSet<usize> = foo.drain(..).collect();
1200 /// # use std::collections::HashSet;
1201 /// let foo = vec![0, 1, 2, 3];
1202 /// let bar: HashSet<usize> = foo.into_iter().collect();
1204 #[clippy::version = "1.61.0"]
1205 pub ITER_WITH_DRAIN,
1207 "replace `.drain(..)` with `.into_iter()`"
1210 declare_clippy_lint! {
1211 /// ### What it does
1212 /// Checks for using `x.get(x.len() - 1)` instead of
1215 /// ### Why is this bad?
1216 /// Using `x.last()` is easier to read and has the same
1219 /// Note that using `x[x.len() - 1]` is semantically different from
1220 /// `x.last()`. Indexing into the array will panic on out-of-bounds
1221 /// accesses, while `x.get()` and `x.last()` will return `None`.
1223 /// There is another lint (get_unwrap) that covers the case of using
1224 /// `x.get(index).unwrap()` instead of `x[index]`.
1228 /// let x = vec![2, 3, 5];
1229 /// let last_element = x.get(x.len() - 1);
1234 /// let x = vec![2, 3, 5];
1235 /// let last_element = x.last();
1237 #[clippy::version = "1.37.0"]
1238 pub GET_LAST_WITH_LEN,
1240 "Using `x.get(x.len() - 1)` when `x.last()` is correct and simpler"
1243 declare_clippy_lint! {
1244 /// ### What it does
1245 /// Checks for use of `.get().unwrap()` (or
1246 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
1248 /// ### Why is this bad?
1249 /// Using the Index trait (`[]`) is more clear and more
1252 /// ### Known problems
1253 /// Not a replacement for error handling: Using either
1254 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
1255 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
1256 /// temporary placeholder for dealing with the `Option` type, then this does
1257 /// not mitigate the need for error handling. If there is a chance that `.get()`
1258 /// will be `None` in your program, then it is advisable that the `None` case
1259 /// is handled in a future refactor instead of using `.unwrap()` or the Index
1264 /// let mut some_vec = vec![0, 1, 2, 3];
1265 /// let last = some_vec.get(3).unwrap();
1266 /// *some_vec.get_mut(0).unwrap() = 1;
1268 /// The correct use would be:
1270 /// let mut some_vec = vec![0, 1, 2, 3];
1271 /// let last = some_vec[3];
1272 /// some_vec[0] = 1;
1274 #[clippy::version = "pre 1.29.0"]
1277 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
1280 declare_clippy_lint! {
1281 /// ### What it does
1282 /// Checks for occurrences where one vector gets extended instead of append
1284 /// ### Why is this bad?
1285 /// Using `append` instead of `extend` is more concise and faster
1289 /// let mut a = vec![1, 2, 3];
1290 /// let mut b = vec![4, 5, 6];
1292 /// a.extend(b.drain(..));
1297 /// let mut a = vec![1, 2, 3];
1298 /// let mut b = vec![4, 5, 6];
1300 /// a.append(&mut b);
1302 #[clippy::version = "1.55.0"]
1303 pub EXTEND_WITH_DRAIN,
1305 "using vec.append(&mut vec) to move the full range of a vector to another"
1308 declare_clippy_lint! {
1309 /// ### What it does
1310 /// Checks for the use of `.extend(s.chars())` where s is a
1311 /// `&str` or `String`.
1313 /// ### Why is this bad?
1314 /// `.push_str(s)` is clearer
1318 /// let abc = "abc";
1319 /// let def = String::from("def");
1320 /// let mut s = String::new();
1321 /// s.extend(abc.chars());
1322 /// s.extend(def.chars());
1324 /// The correct use would be:
1326 /// let abc = "abc";
1327 /// let def = String::from("def");
1328 /// let mut s = String::new();
1329 /// s.push_str(abc);
1330 /// s.push_str(&def);
1332 #[clippy::version = "pre 1.29.0"]
1333 pub STRING_EXTEND_CHARS,
1335 "using `x.extend(s.chars())` where s is a `&str` or `String`"
1338 declare_clippy_lint! {
1339 /// ### What it does
1340 /// Checks for the use of `.cloned().collect()` on slice to
1343 /// ### Why is this bad?
1344 /// `.to_vec()` is clearer
1348 /// let s = [1, 2, 3, 4, 5];
1349 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1351 /// The better use would be:
1353 /// let s = [1, 2, 3, 4, 5];
1354 /// let s2: Vec<isize> = s.to_vec();
1356 #[clippy::version = "pre 1.29.0"]
1357 pub ITER_CLONED_COLLECT,
1359 "using `.cloned().collect()` on slice to create a `Vec`"
1362 declare_clippy_lint! {
1363 /// ### What it does
1364 /// Checks for usage of `_.chars().last()` or
1365 /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1367 /// ### Why is this bad?
1368 /// Readability, this can be written more concisely as
1369 /// `_.ends_with(_)`.
1373 /// # let name = "_";
1374 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1379 /// # let name = "_";
1380 /// name.ends_with('_') || name.ends_with('-');
1382 #[clippy::version = "pre 1.29.0"]
1385 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1388 declare_clippy_lint! {
1389 /// ### What it does
1390 /// Checks for usage of `.as_ref()` or `.as_mut()` where the
1391 /// types before and after the call are the same.
1393 /// ### Why is this bad?
1394 /// The call is unnecessary.
1398 /// # fn do_stuff(x: &[i32]) {}
1399 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1400 /// do_stuff(x.as_ref());
1402 /// The correct use would be:
1404 /// # fn do_stuff(x: &[i32]) {}
1405 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1408 #[clippy::version = "pre 1.29.0"]
1411 "using `as_ref` where the types before and after the call are the same"
1414 declare_clippy_lint! {
1415 /// ### What it does
1416 /// Checks for using `fold` when a more succinct alternative exists.
1417 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1418 /// `sum` or `product`.
1420 /// ### Why is this bad?
1425 /// # #[allow(unused)]
1426 /// (0..3).fold(false, |acc, x| acc || x > 2);
1431 /// (0..3).any(|x| x > 2);
1433 #[clippy::version = "pre 1.29.0"]
1434 pub UNNECESSARY_FOLD,
1436 "using `fold` when a more succinct alternative exists"
1439 declare_clippy_lint! {
1440 /// ### What it does
1441 /// Checks for `filter_map` calls that could be replaced by `filter` or `map`.
1442 /// More specifically it checks if the closure provided is only performing one of the
1443 /// filter or map operations and suggests the appropriate option.
1445 /// ### Why is this bad?
1446 /// Complexity. The intent is also clearer if only a single
1447 /// operation is being performed.
1451 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1453 /// // As there is no transformation of the argument this could be written as:
1454 /// let _ = (0..3).filter(|&x| x > 2);
1458 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1460 /// // As there is no conditional check on the argument this could be written as:
1461 /// let _ = (0..4).map(|x| x + 1);
1463 #[clippy::version = "1.31.0"]
1464 pub UNNECESSARY_FILTER_MAP,
1466 "using `filter_map` when a more succinct alternative exists"
1469 declare_clippy_lint! {
1470 /// ### What it does
1471 /// Checks for `find_map` calls that could be replaced by `find` or `map`. More
1472 /// specifically it checks if the closure provided is only performing one of the
1473 /// find or map operations and suggests the appropriate option.
1475 /// ### Why is this bad?
1476 /// Complexity. The intent is also clearer if only a single
1477 /// operation is being performed.
1481 /// let _ = (0..3).find_map(|x| if x > 2 { Some(x) } else { None });
1483 /// // As there is no transformation of the argument this could be written as:
1484 /// let _ = (0..3).find(|&x| x > 2);
1488 /// let _ = (0..4).find_map(|x| Some(x + 1));
1490 /// // As there is no conditional check on the argument this could be written as:
1491 /// let _ = (0..4).map(|x| x + 1).next();
1493 #[clippy::version = "1.61.0"]
1494 pub UNNECESSARY_FIND_MAP,
1496 "using `find_map` when a more succinct alternative exists"
1499 declare_clippy_lint! {
1500 /// ### What it does
1501 /// Checks for `into_iter` calls on references which should be replaced by `iter`
1504 /// ### Why is this bad?
1505 /// Readability. Calling `into_iter` on a reference will not move out its
1506 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1507 /// `iter_mut` directly.
1511 /// # let vec = vec![3, 4, 5];
1512 /// (&vec).into_iter();
1517 /// # let vec = vec![3, 4, 5];
1520 #[clippy::version = "1.32.0"]
1521 pub INTO_ITER_ON_REF,
1523 "using `.into_iter()` on a reference"
1526 declare_clippy_lint! {
1527 /// ### What it does
1528 /// Checks for calls to `map` followed by a `count`.
1530 /// ### Why is this bad?
1531 /// It looks suspicious. Maybe `map` was confused with `filter`.
1532 /// If the `map` call is intentional, this should be rewritten
1533 /// using `inspect`. Or, if you intend to drive the iterator to
1534 /// completion, you can just use `for_each` instead.
1538 /// let _ = (0..3).map(|x| x + 2).count();
1540 #[clippy::version = "1.39.0"]
1543 "suspicious usage of map"
1546 declare_clippy_lint! {
1547 /// ### What it does
1548 /// Checks for `MaybeUninit::uninit().assume_init()`.
1550 /// ### Why is this bad?
1551 /// For most types, this is undefined behavior.
1553 /// ### Known problems
1554 /// For now, we accept empty tuples and tuples / arrays
1555 /// of `MaybeUninit`. There may be other types that allow uninitialized
1556 /// data, but those are not yet rigorously defined.
1560 /// // Beware the UB
1561 /// use std::mem::MaybeUninit;
1563 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1566 /// Note that the following is OK:
1569 /// use std::mem::MaybeUninit;
1571 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1572 /// MaybeUninit::uninit().assume_init()
1575 #[clippy::version = "1.39.0"]
1576 pub UNINIT_ASSUMED_INIT,
1578 "`MaybeUninit::uninit().assume_init()`"
1581 declare_clippy_lint! {
1582 /// ### What it does
1583 /// Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1585 /// ### Why is this bad?
1586 /// These can be written simply with `saturating_add/sub` methods.
1590 /// # let y: u32 = 0;
1591 /// # let x: u32 = 100;
1592 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1593 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1596 /// can be written using dedicated methods for saturating addition/subtraction as:
1599 /// # let y: u32 = 0;
1600 /// # let x: u32 = 100;
1601 /// let add = x.saturating_add(y);
1602 /// let sub = x.saturating_sub(y);
1604 #[clippy::version = "1.39.0"]
1605 pub MANUAL_SATURATING_ARITHMETIC,
1607 "`.checked_add/sub(x).unwrap_or(MAX/MIN)`"
1610 declare_clippy_lint! {
1611 /// ### What it does
1612 /// Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1613 /// zero-sized types
1615 /// ### Why is this bad?
1616 /// This is a no-op, and likely unintended
1620 /// unsafe { (&() as *const ()).offset(1) };
1622 #[clippy::version = "1.41.0"]
1625 "Check for offset calculations on raw pointers to zero-sized types"
1628 declare_clippy_lint! {
1629 /// ### What it does
1630 /// Checks for `FileType::is_file()`.
1632 /// ### Why is this bad?
1633 /// When people testing a file type with `FileType::is_file`
1634 /// they are testing whether a path is something they can get bytes from. But
1635 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1636 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1641 /// let metadata = std::fs::metadata("foo.txt")?;
1642 /// let filetype = metadata.file_type();
1644 /// if filetype.is_file() {
1647 /// # Ok::<_, std::io::Error>(())
1651 /// should be written as:
1655 /// let metadata = std::fs::metadata("foo.txt")?;
1656 /// let filetype = metadata.file_type();
1658 /// if !filetype.is_dir() {
1661 /// # Ok::<_, std::io::Error>(())
1664 #[clippy::version = "1.42.0"]
1665 pub FILETYPE_IS_FILE,
1667 "`FileType::is_file` is not recommended to test for readable file type"
1670 declare_clippy_lint! {
1671 /// ### What it does
1672 /// Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1674 /// ### Why is this bad?
1675 /// Readability, this can be written more concisely as
1680 /// # let opt = Some("".to_string());
1681 /// opt.as_ref().map(String::as_str)
1684 /// Can be written as
1686 /// # let opt = Some("".to_string());
1690 #[clippy::version = "1.42.0"]
1691 pub OPTION_AS_REF_DEREF,
1693 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1696 declare_clippy_lint! {
1697 /// ### What it does
1698 /// Checks for usage of `iter().next()` on a Slice or an Array
1700 /// ### Why is this bad?
1701 /// These can be shortened into `.get()`
1705 /// # let a = [1, 2, 3];
1706 /// # let b = vec![1, 2, 3];
1707 /// a[2..].iter().next();
1708 /// b.iter().next();
1710 /// should be written as:
1712 /// # let a = [1, 2, 3];
1713 /// # let b = vec![1, 2, 3];
1717 #[clippy::version = "1.46.0"]
1718 pub ITER_NEXT_SLICE,
1720 "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1723 declare_clippy_lint! {
1724 /// ### What it does
1725 /// Warns when using `push_str`/`insert_str` with a single-character string literal
1726 /// where `push`/`insert` with a `char` would work fine.
1728 /// ### Why is this bad?
1729 /// It's less clear that we are pushing a single character.
1733 /// # let mut string = String::new();
1734 /// string.insert_str(0, "R");
1735 /// string.push_str("R");
1740 /// # let mut string = String::new();
1741 /// string.insert(0, 'R');
1742 /// string.push('R');
1744 #[clippy::version = "1.49.0"]
1745 pub SINGLE_CHAR_ADD_STR,
1747 "`push_str()` or `insert_str()` used with a single-character string literal as parameter"
1750 declare_clippy_lint! {
1751 /// ### What it does
1752 /// As the counterpart to `or_fun_call`, this lint looks for unnecessary
1753 /// lazily evaluated closures on `Option` and `Result`.
1755 /// This lint suggests changing the following functions, when eager evaluation results in
1757 /// - `unwrap_or_else` to `unwrap_or`
1758 /// - `and_then` to `and`
1759 /// - `or_else` to `or`
1760 /// - `get_or_insert_with` to `get_or_insert`
1761 /// - `ok_or_else` to `ok_or`
1763 /// ### Why is this bad?
1764 /// Using eager evaluation is shorter and simpler in some cases.
1766 /// ### Known problems
1767 /// It is possible, but not recommended for `Deref` and `Index` to have
1768 /// side effects. Eagerly evaluating them can change the semantics of the program.
1772 /// // example code where clippy issues a warning
1773 /// let opt: Option<u32> = None;
1775 /// opt.unwrap_or_else(|| 42);
1779 /// let opt: Option<u32> = None;
1781 /// opt.unwrap_or(42);
1783 #[clippy::version = "1.48.0"]
1784 pub UNNECESSARY_LAZY_EVALUATIONS,
1786 "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1789 declare_clippy_lint! {
1790 /// ### What it does
1791 /// Checks for usage of `_.map(_).collect::<Result<(), _>()`.
1793 /// ### Why is this bad?
1794 /// Using `try_for_each` instead is more readable and idiomatic.
1798 /// (0..3).map(|t| Err(t)).collect::<Result<(), _>>();
1802 /// (0..3).try_for_each(|t| Err(t));
1804 #[clippy::version = "1.49.0"]
1805 pub MAP_COLLECT_RESULT_UNIT,
1807 "using `.map(_).collect::<Result<(),_>()`, which can be replaced with `try_for_each`"
1810 declare_clippy_lint! {
1811 /// ### What it does
1812 /// Checks for `from_iter()` function calls on types that implement the `FromIterator`
1815 /// ### Why is this bad?
1816 /// It is recommended style to use collect. See
1817 /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
1821 /// let five_fives = std::iter::repeat(5).take(5);
1823 /// let v = Vec::from_iter(five_fives);
1825 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1829 /// let five_fives = std::iter::repeat(5).take(5);
1831 /// let v: Vec<i32> = five_fives.collect();
1833 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1835 #[clippy::version = "1.49.0"]
1836 pub FROM_ITER_INSTEAD_OF_COLLECT,
1838 "use `.collect()` instead of `::from_iter()`"
1841 declare_clippy_lint! {
1842 /// ### What it does
1843 /// Checks for usage of `inspect().for_each()`.
1845 /// ### Why is this bad?
1846 /// It is the same as performing the computation
1847 /// inside `inspect` at the beginning of the closure in `for_each`.
1851 /// [1,2,3,4,5].iter()
1852 /// .inspect(|&x| println!("inspect the number: {}", x))
1853 /// .for_each(|&x| {
1854 /// assert!(x >= 0);
1857 /// Can be written as
1859 /// [1,2,3,4,5].iter()
1860 /// .for_each(|&x| {
1861 /// println!("inspect the number: {}", x);
1862 /// assert!(x >= 0);
1865 #[clippy::version = "1.51.0"]
1866 pub INSPECT_FOR_EACH,
1868 "using `.inspect().for_each()`, which can be replaced with `.for_each()`"
1871 declare_clippy_lint! {
1872 /// ### What it does
1873 /// Checks for usage of `filter_map(|x| x)`.
1875 /// ### Why is this bad?
1876 /// Readability, this can be written more concisely by using `flatten`.
1880 /// # let iter = vec![Some(1)].into_iter();
1881 /// iter.filter_map(|x| x);
1885 /// # let iter = vec![Some(1)].into_iter();
1888 #[clippy::version = "1.52.0"]
1889 pub FILTER_MAP_IDENTITY,
1891 "call to `filter_map` where `flatten` is sufficient"
1894 declare_clippy_lint! {
1895 /// ### What it does
1896 /// Checks for instances of `map(f)` where `f` is the identity function.
1898 /// ### Why is this bad?
1899 /// It can be written more concisely without the call to `map`.
1903 /// let x = [1, 2, 3];
1904 /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
1908 /// let x = [1, 2, 3];
1909 /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
1911 #[clippy::version = "1.47.0"]
1914 "using iterator.map(|x| x)"
1917 declare_clippy_lint! {
1918 /// ### What it does
1919 /// Checks for the use of `.bytes().nth()`.
1921 /// ### Why is this bad?
1922 /// `.as_bytes().get()` is more efficient and more
1927 /// # #[allow(unused)]
1928 /// "Hello".bytes().nth(3);
1933 /// # #[allow(unused)]
1934 /// "Hello".as_bytes().get(3);
1936 #[clippy::version = "1.52.0"]
1939 "replace `.bytes().nth()` with `.as_bytes().get()`"
1942 declare_clippy_lint! {
1943 /// ### What it does
1944 /// Checks for the usage of `_.to_owned()`, `vec.to_vec()`, or similar when calling `_.clone()` would be clearer.
1946 /// ### Why is this bad?
1947 /// These methods do the same thing as `_.clone()` but may be confusing as
1948 /// to why we are calling `to_vec` on something that is already a `Vec` or calling `to_owned` on something that is already owned.
1952 /// let a = vec![1, 2, 3];
1953 /// let b = a.to_vec();
1954 /// let c = a.to_owned();
1958 /// let a = vec![1, 2, 3];
1959 /// let b = a.clone();
1960 /// let c = a.clone();
1962 #[clippy::version = "1.52.0"]
1965 "implicitly cloning a value by invoking a function on its dereferenced type"
1968 declare_clippy_lint! {
1969 /// ### What it does
1970 /// Checks for the use of `.iter().count()`.
1972 /// ### Why is this bad?
1973 /// `.len()` is more efficient and more
1978 /// # #![allow(unused)]
1979 /// let some_vec = vec![0, 1, 2, 3];
1981 /// some_vec.iter().count();
1982 /// &some_vec[..].iter().count();
1987 /// let some_vec = vec![0, 1, 2, 3];
1990 /// &some_vec[..].len();
1992 #[clippy::version = "1.52.0"]
1995 "replace `.iter().count()` with `.len()`"
1998 declare_clippy_lint! {
1999 /// ### What it does
2000 /// Checks for calls to [`splitn`]
2001 /// (https://doc.rust-lang.org/std/primitive.str.html#method.splitn) and
2002 /// related functions with either zero or one splits.
2004 /// ### Why is this bad?
2005 /// These calls don't actually split the value and are
2006 /// likely to be intended as a different number.
2011 /// for x in s.splitn(1, ":") {
2019 /// for x in s.splitn(2, ":") {
2023 #[clippy::version = "1.54.0"]
2024 pub SUSPICIOUS_SPLITN,
2026 "checks for `.splitn(0, ..)` and `.splitn(1, ..)`"
2029 declare_clippy_lint! {
2030 /// ### What it does
2031 /// Checks for manual implementations of `str::repeat`
2033 /// ### Why is this bad?
2034 /// These are both harder to read, as well as less performant.
2038 /// let x: String = std::iter::repeat('x').take(10).collect();
2043 /// let x: String = "x".repeat(10);
2045 #[clippy::version = "1.54.0"]
2046 pub MANUAL_STR_REPEAT,
2048 "manual implementation of `str::repeat`"
2051 declare_clippy_lint! {
2052 /// ### What it does
2053 /// Checks for usages of `str::splitn(2, _)`
2055 /// ### Why is this bad?
2056 /// `split_once` is both clearer in intent and slightly more efficient.
2060 /// let s = "key=value=add";
2061 /// let (key, value) = s.splitn(2, '=').next_tuple()?;
2062 /// let value = s.splitn(2, '=').nth(1)?;
2064 /// let mut parts = s.splitn(2, '=');
2065 /// let key = parts.next()?;
2066 /// let value = parts.next()?;
2071 /// let s = "key=value=add";
2072 /// let (key, value) = s.split_once('=')?;
2073 /// let value = s.split_once('=')?.1;
2075 /// let (key, value) = s.split_once('=')?;
2079 /// The multiple statement variant currently only detects `iter.next()?`/`iter.next().unwrap()`
2080 /// in two separate `let` statements that immediately follow the `splitn()`
2081 #[clippy::version = "1.57.0"]
2082 pub MANUAL_SPLIT_ONCE,
2084 "replace `.splitn(2, pat)` with `.split_once(pat)`"
2087 declare_clippy_lint! {
2088 /// ### What it does
2089 /// Checks for usages of `str::splitn` (or `str::rsplitn`) where using `str::split` would be the same.
2090 /// ### Why is this bad?
2091 /// The function `split` is simpler and there is no performance difference in these cases, considering
2092 /// that both functions return a lazy iterator.
2095 /// let str = "key=value=add";
2096 /// let _ = str.splitn(3, '=').next().unwrap();
2101 /// let str = "key=value=add";
2102 /// let _ = str.split('=').next().unwrap();
2104 #[clippy::version = "1.59.0"]
2105 pub NEEDLESS_SPLITN,
2107 "usages of `str::splitn` that can be replaced with `str::split`"
2110 declare_clippy_lint! {
2111 /// ### What it does
2112 /// Checks for unnecessary calls to [`ToOwned::to_owned`](https://doc.rust-lang.org/std/borrow/trait.ToOwned.html#tymethod.to_owned)
2113 /// and other `to_owned`-like functions.
2115 /// ### Why is this bad?
2116 /// The unnecessary calls result in useless allocations.
2118 /// ### Known problems
2119 /// `unnecessary_to_owned` can falsely trigger if `IntoIterator::into_iter` is applied to an
2120 /// owned copy of a resource and the resource is later used mutably. See
2121 /// [#8148](https://github.com/rust-lang/rust-clippy/issues/8148).
2125 /// let path = std::path::Path::new("x");
2126 /// foo(&path.to_string_lossy().to_string());
2127 /// fn foo(s: &str) {}
2131 /// let path = std::path::Path::new("x");
2132 /// foo(&path.to_string_lossy());
2133 /// fn foo(s: &str) {}
2135 #[clippy::version = "1.59.0"]
2136 pub UNNECESSARY_TO_OWNED,
2138 "unnecessary calls to `to_owned`-like functions"
2141 declare_clippy_lint! {
2142 /// ### What it does
2143 /// Checks for use of `.collect::<Vec<String>>().join("")` on iterators.
2145 /// ### Why is this bad?
2146 /// `.collect::<String>()` is more concise and might be more performant
2150 /// let vector = vec!["hello", "world"];
2151 /// let output = vector.iter().map(|item| item.to_uppercase()).collect::<Vec<String>>().join("");
2152 /// println!("{}", output);
2154 /// The correct use would be:
2156 /// let vector = vec!["hello", "world"];
2157 /// let output = vector.iter().map(|item| item.to_uppercase()).collect::<String>();
2158 /// println!("{}", output);
2160 /// ### Known problems
2161 /// While `.collect::<String>()` is sometimes more performant, there are cases where
2162 /// using `.collect::<String>()` over `.collect::<Vec<String>>().join("")`
2163 /// will prevent loop unrolling and will result in a negative performance impact.
2165 /// Additionally, differences have been observed between aarch64 and x86_64 assembly output,
2166 /// with aarch64 tending to producing faster assembly in more cases when using `.collect::<String>()`
2167 #[clippy::version = "1.61.0"]
2168 pub UNNECESSARY_JOIN,
2170 "using `.collect::<Vec<String>>().join(\"\")` on an iterator"
2173 declare_clippy_lint! {
2174 /// ### What it does
2175 /// Checks for no-op uses of `Option::{as_deref, as_deref_mut}`,
2176 /// for example, `Option<&T>::as_deref()` returns the same type.
2178 /// ### Why is this bad?
2179 /// Redundant code and improving readability.
2183 /// let a = Some(&1);
2184 /// let b = a.as_deref(); // goes from Option<&i32> to Option<&i32>
2189 /// let a = Some(&1);
2192 #[clippy::version = "1.57.0"]
2193 pub NEEDLESS_OPTION_AS_DEREF,
2195 "no-op use of `deref` or `deref_mut` method to `Option`."
2198 declare_clippy_lint! {
2199 /// ### What it does
2200 /// Finds usages of [`char::is_digit`](https://doc.rust-lang.org/stable/std/primitive.char.html#method.is_digit) that
2201 /// can be replaced with [`is_ascii_digit`](https://doc.rust-lang.org/stable/std/primitive.char.html#method.is_ascii_digit) or
2202 /// [`is_ascii_hexdigit`](https://doc.rust-lang.org/stable/std/primitive.char.html#method.is_ascii_hexdigit).
2204 /// ### Why is this bad?
2205 /// `is_digit(..)` is slower and requires specifying the radix.
2209 /// let c: char = '6';
2215 /// let c: char = '6';
2216 /// c.is_ascii_digit();
2217 /// c.is_ascii_hexdigit();
2219 #[clippy::version = "1.62.0"]
2220 pub IS_DIGIT_ASCII_RADIX,
2222 "use of `char::is_digit(..)` with literal radix of 10 or 16"
2225 declare_clippy_lint! {
2226 /// ### What it does
2227 /// Checks for calling `take` function after `as_ref`.
2229 /// ### Why is this bad?
2230 /// Redundant code. `take` writes `None` to its argument.
2231 /// In this case the modification is useless as it's a temporary that cannot be read from afterwards.
2235 /// let x = Some(3);
2236 /// x.as_ref().take();
2240 /// let x = Some(3);
2243 #[clippy::version = "1.62.0"]
2244 pub NEEDLESS_OPTION_TAKE,
2246 "using `.as_ref().take()` on a temporary value"
2249 declare_clippy_lint! {
2250 /// ### What it does
2251 /// Checks for `replace` statements which have no effect.
2253 /// ### Why is this bad?
2254 /// It's either a mistake or confusing.
2258 /// "1234".replace("12", "12");
2259 /// "1234".replacen("12", "12", 1);
2261 #[clippy::version = "1.62.0"]
2262 pub NO_EFFECT_REPLACE,
2264 "replace with no effect"
2267 declare_clippy_lint! {
2268 /// ### What it does
2269 /// Checks for usages of `.then_some(..).unwrap_or(..)`
2271 /// ### Why is this bad?
2272 /// This can be written more clearly with `if .. else ..`
2275 /// This lint currently only looks for usages of
2276 /// `.then_some(..).unwrap_or(..)`, but will be expanded
2277 /// to account for similar patterns.
2282 /// x.then_some("a").unwrap_or("b");
2287 /// if x { "a" } else { "b" };
2289 #[clippy::version = "1.64.0"]
2290 pub OBFUSCATED_IF_ELSE,
2292 "use of `.then_some(..).unwrap_or(..)` can be written \
2293 more clearly with `if .. else ..`"
2296 pub struct Methods {
2297 avoid_breaking_exported_api: bool,
2298 msrv: Option<RustcVersion>,
2299 allow_expect_in_tests: bool,
2300 allow_unwrap_in_tests: bool,
2306 avoid_breaking_exported_api: bool,
2307 msrv: Option<RustcVersion>,
2308 allow_expect_in_tests: bool,
2309 allow_unwrap_in_tests: bool,
2312 avoid_breaking_exported_api,
2314 allow_expect_in_tests,
2315 allow_unwrap_in_tests,
2320 impl_lint_pass!(Methods => [
2323 SHOULD_IMPLEMENT_TRAIT,
2324 WRONG_SELF_CONVENTION,
2326 UNWRAP_OR_ELSE_DEFAULT,
2328 RESULT_MAP_OR_INTO_OPTION,
2330 BIND_INSTEAD_OF_MAP,
2339 ITER_OVEREAGER_CLONED,
2340 CLONED_INSTEAD_OF_COPIED,
2342 INEFFICIENT_TO_STRING,
2344 SINGLE_CHAR_PATTERN,
2345 SINGLE_CHAR_ADD_STR,
2349 FILTER_MAP_IDENTITY,
2357 ITERATOR_STEP_BY_ZERO,
2366 STRING_EXTEND_CHARS,
2367 ITER_CLONED_COLLECT,
2371 UNNECESSARY_FILTER_MAP,
2372 UNNECESSARY_FIND_MAP,
2375 UNINIT_ASSUMED_INIT,
2376 MANUAL_SATURATING_ARITHMETIC,
2379 OPTION_AS_REF_DEREF,
2380 UNNECESSARY_LAZY_EVALUATIONS,
2381 MAP_COLLECT_RESULT_UNIT,
2382 FROM_ITER_INSTEAD_OF_COLLECT,
2390 UNNECESSARY_TO_OWNED,
2393 NEEDLESS_OPTION_AS_DEREF,
2394 IS_DIGIT_ASCII_RADIX,
2395 NEEDLESS_OPTION_TAKE,
2400 /// Extracts a method call name, args, and `Span` of the method name.
2401 fn method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(&'tcx str, &'tcx [hir::Expr<'tcx>], Span)> {
2402 if let ExprKind::MethodCall(path, args, _) = recv.kind {
2403 if !args.iter().any(|e| e.span.from_expansion()) {
2404 let name = path.ident.name.as_str();
2405 return Some((name, args, path.ident.span));
2411 impl<'tcx> LateLintPass<'tcx> for Methods {
2412 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
2413 if expr.span.from_expansion() {
2417 self.check_methods(cx, expr);
2420 hir::ExprKind::Call(func, args) => {
2421 from_iter_instead_of_collect::check(cx, expr, args, func);
2423 hir::ExprKind::MethodCall(method_call, args, _) => {
2424 let method_span = method_call.ident.span;
2425 or_fun_call::check(cx, expr, method_span, method_call.ident.as_str(), args);
2426 expect_fun_call::check(cx, expr, method_span, method_call.ident.as_str(), args);
2427 clone_on_copy::check(cx, expr, method_call.ident.name, args);
2428 clone_on_ref_ptr::check(cx, expr, method_call.ident.name, args);
2429 inefficient_to_string::check(cx, expr, method_call.ident.name, args);
2430 single_char_add_str::check(cx, expr, args);
2431 into_iter_on_ref::check(cx, expr, method_span, method_call.ident.name, args);
2432 single_char_pattern::check(cx, expr, method_call.ident.name, args);
2433 unnecessary_to_owned::check(cx, expr, method_call.ident.name, args, self.msrv);
2435 hir::ExprKind::Binary(op, lhs, rhs) if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne => {
2436 let mut info = BinaryExprInfo {
2440 eq: op.node == hir::BinOpKind::Eq,
2442 lint_binary_expr_with_method_call(cx, &mut info);
2448 #[allow(clippy::too_many_lines)]
2449 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
2450 if in_external_macro(cx.sess(), impl_item.span) {
2453 let name = impl_item.ident.name.as_str();
2454 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
2455 let item = cx.tcx.hir().expect_item(parent);
2456 let self_ty = cx.tcx.type_of(item.def_id);
2458 let implements_trait = matches!(item.kind, hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }));
2460 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
2461 if let Some(first_arg) = iter_input_pats(sig.decl, cx.tcx.hir().body(id)).next();
2463 let method_sig = cx.tcx.fn_sig(impl_item.def_id);
2464 let method_sig = cx.tcx.erase_late_bound_regions(method_sig);
2466 let first_arg_ty = method_sig.inputs().iter().next();
2468 // check conventions w.r.t. conversion method names and predicates
2469 if let Some(first_arg_ty) = first_arg_ty;
2472 // if this impl block implements a trait, lint in trait definition instead
2473 if !implements_trait && cx.access_levels.is_exported(impl_item.def_id) {
2474 // check missing trait implementations
2475 for method_config in &TRAIT_METHODS {
2476 if name == method_config.method_name &&
2477 sig.decl.inputs.len() == method_config.param_count &&
2478 method_config.output_type.matches(&sig.decl.output) &&
2479 method_config.self_kind.matches(cx, self_ty, *first_arg_ty) &&
2480 fn_header_equals(method_config.fn_header, sig.header) &&
2481 method_config.lifetime_param_cond(impl_item)
2485 SHOULD_IMPLEMENT_TRAIT,
2488 "method `{}` can be confused for the standard trait method `{}::{}`",
2489 method_config.method_name,
2490 method_config.trait_name,
2491 method_config.method_name
2495 "consider implementing the trait `{}` or choosing a less ambiguous method name",
2496 method_config.trait_name
2503 if sig.decl.implicit_self.has_implicit_self()
2504 && !(self.avoid_breaking_exported_api
2505 && cx.access_levels.is_exported(impl_item.def_id))
2507 wrong_self_convention::check(
2520 // if this impl block implements a trait, lint in trait definition instead
2521 if implements_trait {
2525 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
2526 let ret_ty = return_ty(cx, impl_item.hir_id());
2528 // walk the return type and check for Self (this does not check associated types)
2529 if let Some(self_adt) = self_ty.ty_adt_def() {
2530 if contains_adt_constructor(ret_ty, self_adt) {
2533 } else if contains_ty(ret_ty, self_ty) {
2537 // if return type is impl trait, check the associated types
2538 if let ty::Opaque(def_id, _) = *ret_ty.kind() {
2539 // one of the associated types must be Self
2540 for &(predicate, _span) in cx.tcx.explicit_item_bounds(def_id) {
2541 if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
2542 let assoc_ty = match projection_predicate.term {
2543 ty::Term::Ty(ty) => ty,
2544 ty::Term::Const(_c) => continue,
2546 // walk the associated type and check for Self
2547 if let Some(self_adt) = self_ty.ty_adt_def() {
2548 if contains_adt_constructor(assoc_ty, self_adt) {
2551 } else if contains_ty(assoc_ty, self_ty) {
2558 if name == "new" && ret_ty != self_ty {
2563 "methods called `new` usually return `Self`",
2569 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
2570 if in_external_macro(cx.tcx.sess, item.span) {
2575 if let TraitItemKind::Fn(ref sig, _) = item.kind;
2576 if sig.decl.implicit_self.has_implicit_self();
2577 if let Some(first_arg_ty) = sig.decl.inputs.iter().next();
2580 let first_arg_span = first_arg_ty.span;
2581 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
2582 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty().skip_binder();
2583 wrong_self_convention::check(
2585 item.ident.name.as_str(),
2596 if item.ident.name == sym::new;
2597 if let TraitItemKind::Fn(_, _) = item.kind;
2598 let ret_ty = return_ty(cx, item.hir_id());
2599 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty().skip_binder();
2600 if !contains_ty(ret_ty, self_ty);
2607 "methods called `new` usually return `Self`",
2613 extract_msrv_attr!(LateContext);
2617 #[allow(clippy::too_many_lines)]
2618 fn check_methods<'tcx>(&self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2619 if let Some((name, [recv, args @ ..], span)) = method_call(expr) {
2620 match (name, args) {
2621 ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
2622 zst_offset::check(cx, expr, recv);
2624 ("and_then", [arg]) => {
2625 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::check(cx, expr, recv, arg);
2626 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::check(cx, expr, recv, arg);
2627 if !biom_option_linted && !biom_result_linted {
2628 unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
2631 ("as_deref" | "as_deref_mut", []) => {
2632 needless_option_as_deref::check(cx, expr, recv, name);
2634 ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
2635 ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
2636 ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
2637 ("cloned", []) => cloned_instead_of_copied::check(cx, expr, recv, span, self.msrv),
2638 ("collect", []) => match method_call(recv) {
2639 Some((name @ ("cloned" | "copied"), [recv2], _)) => {
2640 iter_cloned_collect::check(cx, name, expr, recv2);
2642 Some(("map", [m_recv, m_arg], _)) => {
2643 map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
2645 Some(("take", [take_self_arg, take_arg], _)) => {
2646 if meets_msrv(self.msrv, msrvs::STR_REPEAT) {
2647 manual_str_repeat::check(cx, expr, recv, take_self_arg, take_arg);
2652 ("count", []) => match method_call(recv) {
2653 Some(("cloned", [recv2], _)) => iter_overeager_cloned::check(cx, expr, recv, recv2, true, false),
2654 Some((name2 @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
2655 iter_count::check(cx, expr, recv2, name2);
2657 Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
2660 ("drain", [arg]) => {
2661 iter_with_drain::check(cx, expr, recv, span, arg);
2663 ("expect", [_]) => match method_call(recv) {
2664 Some(("ok", [recv], _)) => ok_expect::check(cx, expr, recv),
2665 Some(("err", [recv], err_span)) => err_expect::check(cx, expr, recv, self.msrv, span, err_span),
2666 _ => expect_used::check(cx, expr, recv, self.allow_expect_in_tests),
2668 ("extend", [arg]) => {
2669 string_extend_chars::check(cx, expr, recv, arg);
2670 extend_with_drain::check(cx, expr, recv, arg);
2672 ("filter_map", [arg]) => {
2673 unnecessary_filter_map::check(cx, expr, arg, name);
2674 filter_map_identity::check(cx, expr, arg, span);
2676 ("find_map", [arg]) => {
2677 unnecessary_filter_map::check(cx, expr, arg, name);
2679 ("flat_map", [arg]) => {
2680 flat_map_identity::check(cx, expr, arg, span);
2681 flat_map_option::check(cx, expr, arg, span);
2683 ("flatten", []) => match method_call(recv) {
2684 Some(("map", [recv, map_arg], map_span)) => map_flatten::check(cx, expr, recv, map_arg, map_span),
2685 Some(("cloned", [recv2], _)) => iter_overeager_cloned::check(cx, expr, recv, recv2, false, true),
2688 ("fold", [init, acc]) => unnecessary_fold::check(cx, expr, init, acc, span),
2689 ("for_each", [_]) => {
2690 if let Some(("inspect", [_, _], span2)) = method_call(recv) {
2691 inspect_for_each::check(cx, expr, span2);
2694 ("get", [arg]) => get_last_with_len::check(cx, expr, recv, arg),
2695 ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
2696 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
2697 ("is_digit", [radix]) => is_digit_ascii_radix::check(cx, expr, recv, radix, self.msrv),
2698 ("is_none", []) => check_is_some_is_none(cx, expr, recv, false),
2699 ("is_some", []) => check_is_some_is_none(cx, expr, recv, true),
2700 ("join", [join_arg]) => {
2701 if let Some(("collect", _, span)) = method_call(recv) {
2702 unnecessary_join::check(cx, expr, recv, join_arg, span);
2705 ("last", []) | ("skip", [_]) => {
2706 if let Some((name2, [recv2, args2 @ ..], _span2)) = method_call(recv) {
2707 if let ("cloned", []) = (name2, args2) {
2708 iter_overeager_cloned::check(cx, expr, recv, recv2, false, false);
2712 (name @ ("map" | "map_err"), [m_arg]) => {
2713 if let Some((name, [recv2, args @ ..], span2)) = method_call(recv) {
2714 match (name, args) {
2715 ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, self.msrv),
2716 ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, self.msrv),
2717 ("filter", [f_arg]) => {
2718 filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, false);
2720 ("find", [f_arg]) => {
2721 filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, true);
2726 map_identity::check(cx, expr, recv, m_arg, name, span);
2728 ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
2730 if let Some((name2, [recv2, args2 @ ..], _)) = method_call(recv) {
2731 match (name2, args2) {
2732 ("cloned", []) => iter_overeager_cloned::check(cx, expr, recv, recv2, false, false),
2733 ("filter", [arg]) => filter_next::check(cx, expr, recv2, arg),
2734 ("filter_map", [arg]) => filter_map_next::check(cx, expr, recv2, arg, self.msrv),
2735 ("iter", []) => iter_next_slice::check(cx, expr, recv2),
2736 ("skip", [arg]) => iter_skip_next::check(cx, expr, recv2, arg),
2737 ("skip_while", [_]) => skip_while_next::check(cx, expr),
2742 ("nth", [n_arg]) => match method_call(recv) {
2743 Some(("bytes", [recv2], _)) => bytes_nth::check(cx, expr, recv2, n_arg),
2744 Some(("cloned", [recv2], _)) => iter_overeager_cloned::check(cx, expr, recv, recv2, false, false),
2745 Some(("iter", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
2746 Some(("iter_mut", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
2747 _ => iter_nth_zero::check(cx, expr, recv, n_arg),
2749 ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
2750 ("or_else", [arg]) => {
2751 if !bind_instead_of_map::ResultOrElseErrInfo::check(cx, expr, recv, arg) {
2752 unnecessary_lazy_eval::check(cx, expr, recv, arg, "or");
2755 ("splitn" | "rsplitn", [count_arg, pat_arg]) => {
2756 if let Some((Constant::Int(count), _)) = constant(cx, cx.typeck_results(), count_arg) {
2757 suspicious_splitn::check(cx, name, expr, recv, count);
2758 str_splitn::check(cx, name, expr, recv, pat_arg, count, self.msrv);
2761 ("splitn_mut" | "rsplitn_mut", [count_arg, _]) => {
2762 if let Some((Constant::Int(count), _)) = constant(cx, cx.typeck_results(), count_arg) {
2763 suspicious_splitn::check(cx, name, expr, recv, count);
2766 ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
2767 ("take", [_arg]) => {
2768 if let Some((name2, [recv2, args2 @ ..], _span2)) = method_call(recv) {
2769 if let ("cloned", []) = (name2, args2) {
2770 iter_overeager_cloned::check(cx, expr, recv, recv2, false, false);
2774 ("take", []) => needless_option_take::check(cx, expr, recv),
2775 ("then", [arg]) => {
2776 if !meets_msrv(self.msrv, msrvs::BOOL_THEN_SOME) {
2779 unnecessary_lazy_eval::check(cx, expr, recv, arg, "then_some");
2781 ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
2782 implicit_clone::check(cx, name, expr, recv);
2785 match method_call(recv) {
2786 Some(("get", [recv, get_arg], _)) => {
2787 get_unwrap::check(cx, expr, recv, get_arg, false);
2789 Some(("get_mut", [recv, get_arg], _)) => {
2790 get_unwrap::check(cx, expr, recv, get_arg, true);
2792 Some(("or", [recv, or_arg], or_span)) => {
2793 or_then_unwrap::check(cx, expr, recv, or_arg, or_span);
2797 unwrap_used::check(cx, expr, recv, self.allow_unwrap_in_tests);
2799 ("unwrap_or", [u_arg]) => match method_call(recv) {
2800 Some((arith @ ("checked_add" | "checked_sub" | "checked_mul"), [lhs, rhs], _)) => {
2801 manual_saturating_arithmetic::check(cx, expr, lhs, rhs, u_arg, &arith["checked_".len()..]);
2803 Some(("map", [m_recv, m_arg], span)) => {
2804 option_map_unwrap_or::check(cx, expr, m_recv, m_arg, recv, u_arg, span);
2806 Some(("then_some", [t_recv, t_arg], _)) => {
2807 obfuscated_if_else::check(cx, expr, t_recv, t_arg, u_arg);
2811 ("unwrap_or_else", [u_arg]) => match method_call(recv) {
2812 Some(("map", [recv, map_arg], _))
2813 if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, self.msrv) => {},
2815 unwrap_or_else_default::check(cx, expr, recv, u_arg);
2816 unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or");
2819 ("replace" | "replacen", [arg1, arg2] | [arg1, arg2, _]) => {
2820 no_effect_replace::check(cx, expr, arg1, arg2);
2828 fn check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool) {
2829 if let Some((name @ ("find" | "position" | "rposition"), [f_recv, arg], span)) = method_call(recv) {
2830 search_is_some::check(cx, expr, name, is_some, f_recv, arg, recv, span);
2834 /// Used for `lint_binary_expr_with_method_call`.
2835 #[derive(Copy, Clone)]
2836 struct BinaryExprInfo<'a> {
2837 expr: &'a hir::Expr<'a>,
2838 chain: &'a hir::Expr<'a>,
2839 other: &'a hir::Expr<'a>,
2843 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2844 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
2845 macro_rules! lint_with_both_lhs_and_rhs {
2846 ($func:expr, $cx:expr, $info:ident) => {
2847 if !$func($cx, $info) {
2848 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2849 if $func($cx, $info) {
2856 lint_with_both_lhs_and_rhs!(chars_next_cmp::check, cx, info);
2857 lint_with_both_lhs_and_rhs!(chars_last_cmp::check, cx, info);
2858 lint_with_both_lhs_and_rhs!(chars_next_cmp_with_unwrap::check, cx, info);
2859 lint_with_both_lhs_and_rhs!(chars_last_cmp_with_unwrap::check, cx, info);
2862 const FN_HEADER: hir::FnHeader = hir::FnHeader {
2863 unsafety: hir::Unsafety::Normal,
2864 constness: hir::Constness::NotConst,
2865 asyncness: hir::IsAsync::NotAsync,
2866 abi: rustc_target::spec::abi::Abi::Rust,
2869 struct ShouldImplTraitCase {
2870 trait_name: &'static str,
2871 method_name: &'static str,
2873 fn_header: hir::FnHeader,
2874 // implicit self kind expected (none, self, &self, ...)
2875 self_kind: SelfKind,
2876 // checks against the output type
2877 output_type: OutType,
2878 // certain methods with explicit lifetimes can't implement the equivalent trait method
2879 lint_explicit_lifetime: bool,
2881 impl ShouldImplTraitCase {
2883 trait_name: &'static str,
2884 method_name: &'static str,
2886 fn_header: hir::FnHeader,
2887 self_kind: SelfKind,
2888 output_type: OutType,
2889 lint_explicit_lifetime: bool,
2890 ) -> ShouldImplTraitCase {
2891 ShouldImplTraitCase {
2898 lint_explicit_lifetime,
2902 fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
2903 self.lint_explicit_lifetime
2904 || !impl_item.generics.params.iter().any(|p| {
2907 hir::GenericParamKind::Lifetime {
2908 kind: hir::LifetimeParamKind::Explicit
2916 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
2917 ShouldImplTraitCase::new("std::ops::Add", "add", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2918 ShouldImplTraitCase::new("std::convert::AsMut", "as_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2919 ShouldImplTraitCase::new("std::convert::AsRef", "as_ref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2920 ShouldImplTraitCase::new("std::ops::BitAnd", "bitand", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2921 ShouldImplTraitCase::new("std::ops::BitOr", "bitor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2922 ShouldImplTraitCase::new("std::ops::BitXor", "bitxor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2923 ShouldImplTraitCase::new("std::borrow::Borrow", "borrow", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2924 ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2925 ShouldImplTraitCase::new("std::clone::Clone", "clone", 1, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2926 ShouldImplTraitCase::new("std::cmp::Ord", "cmp", 2, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2927 // FIXME: default doesn't work
2928 ShouldImplTraitCase::new("std::default::Default", "default", 0, FN_HEADER, SelfKind::No, OutType::Any, true),
2929 ShouldImplTraitCase::new("std::ops::Deref", "deref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2930 ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2931 ShouldImplTraitCase::new("std::ops::Div", "div", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2932 ShouldImplTraitCase::new("std::ops::Drop", "drop", 1, FN_HEADER, SelfKind::RefMut, OutType::Unit, true),
2933 ShouldImplTraitCase::new("std::cmp::PartialEq", "eq", 2, FN_HEADER, SelfKind::Ref, OutType::Bool, true),
2934 ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2935 ShouldImplTraitCase::new("std::str::FromStr", "from_str", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2936 ShouldImplTraitCase::new("std::hash::Hash", "hash", 2, FN_HEADER, SelfKind::Ref, OutType::Unit, true),
2937 ShouldImplTraitCase::new("std::ops::Index", "index", 2, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2938 ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut", 2, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2939 ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2940 ShouldImplTraitCase::new("std::ops::Mul", "mul", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2941 ShouldImplTraitCase::new("std::ops::Neg", "neg", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2942 ShouldImplTraitCase::new("std::iter::Iterator", "next", 1, FN_HEADER, SelfKind::RefMut, OutType::Any, false),
2943 ShouldImplTraitCase::new("std::ops::Not", "not", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2944 ShouldImplTraitCase::new("std::ops::Rem", "rem", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2945 ShouldImplTraitCase::new("std::ops::Shl", "shl", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2946 ShouldImplTraitCase::new("std::ops::Shr", "shr", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2947 ShouldImplTraitCase::new("std::ops::Sub", "sub", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2950 #[derive(Clone, Copy, PartialEq, Eq, Debug)]
2959 fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2960 fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2961 if ty == parent_ty {
2963 } else if ty.is_box() {
2964 ty.boxed_ty() == parent_ty
2965 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
2966 if let ty::Adt(_, substs) = ty.kind() {
2967 substs.types().next().map_or(false, |t| t == parent_ty)
2976 fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2977 if let ty::Ref(_, t, m) = *ty.kind() {
2978 return m == mutability && t == parent_ty;
2981 let trait_path = match mutability {
2982 hir::Mutability::Not => &paths::ASREF_TRAIT,
2983 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
2986 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2988 None => return false,
2990 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2993 fn matches_none<'a>(cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2994 !matches_value(cx, parent_ty, ty)
2995 && !matches_ref(cx, hir::Mutability::Not, parent_ty, ty)
2996 && !matches_ref(cx, hir::Mutability::Mut, parent_ty, ty)
3000 Self::Value => matches_value(cx, parent_ty, ty),
3001 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
3002 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
3003 Self::No => matches_none(cx, parent_ty, ty),
3008 fn description(self) -> &'static str {
3010 Self::Value => "`self` by value",
3011 Self::Ref => "`self` by reference",
3012 Self::RefMut => "`self` by mutable reference",
3013 Self::No => "no `self`",
3018 #[derive(Clone, Copy)]
3027 fn matches(self, ty: &hir::FnRetTy<'_>) -> bool {
3028 let is_unit = |ty: &hir::Ty<'_>| matches!(ty.kind, hir::TyKind::Tup(&[]));
3030 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
3031 (Self::Unit, &hir::FnRetTy::Return(ty)) if is_unit(ty) => true,
3032 (Self::Bool, &hir::FnRetTy::Return(ty)) if is_bool(ty) => true,
3033 (Self::Any, &hir::FnRetTy::Return(ty)) if !is_unit(ty) => true,
3034 (Self::Ref, &hir::FnRetTy::Return(ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
3040 fn is_bool(ty: &hir::Ty<'_>) -> bool {
3041 if let hir::TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
3042 matches!(path.res, Res::PrimTy(PrimTy::Bool))
3048 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
3049 expected.constness == actual.constness
3050 && expected.unsafety == actual.unsafety
3051 && expected.asyncness == actual.asyncness