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;
14 mod extend_with_drain;
17 mod filter_map_identity;
20 mod flat_map_identity;
22 mod from_iter_instead_of_collect;
25 mod inefficient_to_string;
28 mod iter_cloned_collect;
34 mod iterator_step_by_zero;
35 mod manual_saturating_arithmetic;
36 mod manual_str_repeat;
37 mod map_collect_result_unit;
42 mod option_as_ref_deref;
43 mod option_map_or_none;
44 mod option_map_unwrap_or;
47 mod single_char_add_str;
48 mod single_char_insert_string;
49 mod single_char_pattern;
50 mod single_char_push_string;
52 mod string_extend_chars;
54 mod suspicious_splitn;
55 mod uninit_assumed_init;
56 mod unnecessary_filter_map;
58 mod unnecessary_lazy_eval;
59 mod unwrap_or_else_default;
63 mod wrong_self_convention;
66 use bind_instead_of_map::BindInsteadOfMap;
67 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
68 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
69 use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
70 use if_chain::if_chain;
72 use rustc_hir::def::Res;
73 use rustc_hir::{Expr, ExprKind, PrimTy, QPath, TraitItem, TraitItemKind};
74 use rustc_lint::{LateContext, LateLintPass, LintContext};
75 use rustc_middle::lint::in_external_macro;
76 use rustc_middle::ty::{self, TraitRef, Ty, TyS};
77 use rustc_semver::RustcVersion;
78 use rustc_session::{declare_tool_lint, impl_lint_pass};
79 use rustc_span::symbol::SymbolStr;
80 use rustc_span::{sym, Span};
81 use rustc_typeck::hir_ty_to_ty;
83 declare_clippy_lint! {
85 /// Checks for usages of `cloned()` on an `Iterator` or `Option` where
86 /// `copied()` could be used instead.
88 /// ### Why is this bad?
89 /// `copied()` is better because it guarantees that the type being cloned
90 /// implements `Copy`.
94 /// [1, 2, 3].iter().cloned();
98 /// [1, 2, 3].iter().copied();
100 pub CLONED_INSTEAD_OF_COPIED,
102 "used `cloned` where `copied` could be used instead"
105 declare_clippy_lint! {
107 /// Checks for usages of `Iterator::flat_map()` where `filter_map()` could be
110 /// ### Why is this bad?
111 /// When applicable, `filter_map()` is more clear since it shows that
112 /// `Option` is used to produce 0 or 1 items.
116 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().flat_map(|x| x.parse().ok()).collect();
120 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().filter_map(|x| x.parse().ok()).collect();
124 "used `flat_map` where `filter_map` could be used instead"
127 declare_clippy_lint! {
129 /// Checks for `.unwrap()` calls on `Option`s and on `Result`s.
131 /// ### Why is this bad?
132 /// It is better to handle the `None` or `Err` case,
133 /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
134 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
135 /// `Allow` by default.
137 /// `result.unwrap()` will let the thread panic on `Err` values.
138 /// Normally, you want to implement more sophisticated error handling,
139 /// and propagate errors upwards with `?` operator.
141 /// Even if you want to panic on errors, not all `Error`s implement good
142 /// messages on display. Therefore, it may be beneficial to look at the places
143 /// where they may get displayed. Activate this lint to do just that.
147 /// # let opt = Some(1);
153 /// opt.expect("more helpful message");
159 /// # let res: Result<usize, ()> = Ok(1);
165 /// res.expect("more helpful message");
169 "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
172 declare_clippy_lint! {
174 /// Checks for `.expect()` calls on `Option`s and `Result`s.
176 /// ### Why is this bad?
177 /// Usually it is better to handle the `None` or `Err` case.
178 /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
179 /// this lint is `Allow` by default.
181 /// `result.expect()` will let the thread panic on `Err`
182 /// values. Normally, you want to implement more sophisticated error handling,
183 /// and propagate errors upwards with `?` operator.
187 /// # let opt = Some(1);
190 /// opt.expect("one");
193 /// let opt = Some(1);
200 /// # let res: Result<usize, ()> = Ok(1);
203 /// res.expect("one");
207 /// # Ok::<(), ()>(())
211 "using `.expect()` on `Result` or `Option`, which might be better handled"
214 declare_clippy_lint! {
216 /// Checks for methods that should live in a trait
217 /// implementation of a `std` trait (see [llogiq's blog
218 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
219 /// information) instead of an inherent implementation.
221 /// ### Why is this bad?
222 /// Implementing the traits improve ergonomics for users of
223 /// the code, often with very little cost. Also people seeing a `mul(...)`
225 /// may expect `*` to work equally, so you should have good reason to disappoint
232 /// fn add(&self, other: &X) -> X {
238 pub SHOULD_IMPLEMENT_TRAIT,
240 "defining a method that should be implementing a std trait"
243 declare_clippy_lint! {
245 /// Checks for methods with certain name prefixes and which
246 /// doesn't match how self is taken. The actual rules are:
248 /// |Prefix |Postfix |`self` taken | `self` type |
249 /// |-------|------------|-----------------------|--------------|
250 /// |`as_` | none |`&self` or `&mut self` | any |
251 /// |`from_`| none | none | any |
252 /// |`into_`| none |`self` | any |
253 /// |`is_` | none |`&self` or none | any |
254 /// |`to_` | `_mut` |`&mut self` | any |
255 /// |`to_` | not `_mut` |`self` | `Copy` |
256 /// |`to_` | not `_mut` |`&self` | not `Copy` |
258 /// Note: Clippy doesn't trigger methods with `to_` prefix in:
259 /// - Traits definition.
260 /// Clippy can not tell if a type that implements a trait is `Copy` or not.
261 /// - Traits implementation, when `&self` is taken.
262 /// The method signature is controlled by the trait and often `&self` is required for all types that implement the trait
263 /// (see e.g. the `std::string::ToString` trait).
265 /// Please find more info here:
266 /// https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
268 /// ### Why is this bad?
269 /// Consistency breeds readability. If you follow the
270 /// conventions, your users won't be surprised that they, e.g., need to supply a
271 /// mutable reference to a `as_..` function.
277 /// fn as_str(self) -> &'static str {
283 pub WRONG_SELF_CONVENTION,
285 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
288 declare_clippy_lint! {
290 /// Checks for usage of `ok().expect(..)`.
292 /// ### Why is this bad?
293 /// Because you usually call `expect()` on the `Result`
294 /// directly to get a better error message.
296 /// ### Known problems
297 /// The error type needs to implement `Debug`
301 /// # let x = Ok::<_, ()>(());
304 /// x.ok().expect("why did I do this again?");
307 /// x.expect("why did I do this again?");
311 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
314 declare_clippy_lint! {
316 /// Checks for usages of `_.unwrap_or_else(Default::default)` on `Option` and
319 /// ### Why is this bad?
320 /// Readability, these can be written as `_.unwrap_or_default`, which is
321 /// simpler and more concise.
325 /// # let x = Some(1);
328 /// x.unwrap_or_else(Default::default);
329 /// x.unwrap_or_else(u32::default);
332 /// x.unwrap_or_default();
334 pub UNWRAP_OR_ELSE_DEFAULT,
336 "using `.unwrap_or_else(Default::default)`, which is more succinctly expressed as `.unwrap_or_default()`"
339 declare_clippy_lint! {
341 /// Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
342 /// `result.map(_).unwrap_or_else(_)`.
344 /// ### Why is this bad?
345 /// Readability, these can be written more concisely (resp.) as
346 /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
348 /// ### Known problems
349 /// The order of the arguments is not in execution order
353 /// # let x = Some(1);
356 /// x.map(|a| a + 1).unwrap_or(0);
359 /// x.map_or(0, |a| a + 1);
365 /// # let x: Result<usize, ()> = Ok(1);
366 /// # fn some_function(foo: ()) -> usize { 1 }
369 /// x.map(|a| a + 1).unwrap_or_else(some_function);
372 /// x.map_or_else(some_function, |a| a + 1);
376 "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)`"
379 declare_clippy_lint! {
381 /// Checks for usage of `_.map_or(None, _)`.
383 /// ### Why is this bad?
384 /// Readability, this can be written more concisely as
387 /// ### Known problems
388 /// The order of the arguments is not in execution order.
392 /// # let opt = Some(1);
395 /// opt.map_or(None, |a| Some(a + 1));
398 /// opt.and_then(|a| Some(a + 1));
400 pub OPTION_MAP_OR_NONE,
402 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
405 declare_clippy_lint! {
407 /// Checks for usage of `_.map_or(None, Some)`.
409 /// ### Why is this bad?
410 /// Readability, this can be written more concisely as
416 /// # let r: Result<u32, &str> = Ok(1);
417 /// assert_eq!(Some(1), r.map_or(None, Some));
422 /// # let r: Result<u32, &str> = Ok(1);
423 /// assert_eq!(Some(1), r.ok());
425 pub RESULT_MAP_OR_INTO_OPTION,
427 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
430 declare_clippy_lint! {
432 /// Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
433 /// `_.or_else(|x| Err(y))`.
435 /// ### Why is this bad?
436 /// Readability, this can be written more concisely as
437 /// `_.map(|x| y)` or `_.map_err(|x| y)`.
441 /// # fn opt() -> Option<&'static str> { Some("42") }
442 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
443 /// let _ = opt().and_then(|s| Some(s.len()));
444 /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
445 /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
448 /// The correct use would be:
451 /// # fn opt() -> Option<&'static str> { Some("42") }
452 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
453 /// let _ = opt().map(|s| s.len());
454 /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
455 /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
457 pub BIND_INSTEAD_OF_MAP,
459 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
462 declare_clippy_lint! {
464 /// Checks for usage of `_.filter(_).next()`.
466 /// ### Why is this bad?
467 /// Readability, this can be written more concisely as
472 /// # let vec = vec![1];
473 /// vec.iter().filter(|x| **x == 0).next();
475 /// Could be written as
477 /// # let vec = vec![1];
478 /// vec.iter().find(|x| **x == 0);
482 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
485 declare_clippy_lint! {
487 /// Checks for usage of `_.skip_while(condition).next()`.
489 /// ### Why is this bad?
490 /// Readability, this can be written more concisely as
491 /// `_.find(!condition)`.
495 /// # let vec = vec![1];
496 /// vec.iter().skip_while(|x| **x == 0).next();
498 /// Could be written as
500 /// # let vec = vec![1];
501 /// vec.iter().find(|x| **x != 0);
505 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
508 declare_clippy_lint! {
510 /// Checks for usage of `_.map(_).flatten(_)` on `Iterator` and `Option`
512 /// ### Why is this bad?
513 /// Readability, this can be written more concisely as
518 /// let vec = vec![vec![1]];
521 /// vec.iter().map(|x| x.iter()).flatten();
524 /// vec.iter().flat_map(|x| x.iter());
528 "using combinations of `flatten` and `map` which can usually be written as a single method call"
531 declare_clippy_lint! {
533 /// Checks for usage of `_.filter(_).map(_)` that can be written more simply
534 /// as `filter_map(_)`.
536 /// ### Why is this bad?
537 /// Redundant code in the `filter` and `map` operations is poor style and
544 /// .filter(|n| n.checked_add(1).is_some())
545 /// .map(|n| n.checked_add(1).unwrap());
550 /// (0_i32..10).filter_map(|n| n.checked_add(1));
552 pub MANUAL_FILTER_MAP,
554 "using `_.filter(_).map(_)` in a way that can be written more simply as `filter_map(_)`"
557 declare_clippy_lint! {
559 /// Checks for usage of `_.find(_).map(_)` that can be written more simply
560 /// as `find_map(_)`.
562 /// ### Why is this bad?
563 /// Redundant code in the `find` and `map` operations is poor style and
570 /// .find(|n| n.checked_add(1).is_some())
571 /// .map(|n| n.checked_add(1).unwrap());
576 /// (0_i32..10).find_map(|n| n.checked_add(1));
580 "using `_.find(_).map(_)` in a way that can be written more simply as `find_map(_)`"
583 declare_clippy_lint! {
585 /// Checks for usage of `_.filter_map(_).next()`.
587 /// ### Why is this bad?
588 /// Readability, this can be written more concisely as
593 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
595 /// Can be written as
598 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
602 "using combination of `filter_map` and `next` which can usually be written as a single method call"
605 declare_clippy_lint! {
607 /// Checks for usage of `flat_map(|x| x)`.
609 /// ### Why is this bad?
610 /// Readability, this can be written more concisely by using `flatten`.
614 /// # let iter = vec![vec![0]].into_iter();
615 /// iter.flat_map(|x| x);
617 /// Can be written as
619 /// # let iter = vec![vec![0]].into_iter();
622 pub FLAT_MAP_IDENTITY,
624 "call to `flat_map` where `flatten` is sufficient"
627 declare_clippy_lint! {
629 /// Checks for an iterator or string search (such as `find()`,
630 /// `position()`, or `rposition()`) followed by a call to `is_some()` or `is_none()`.
632 /// ### Why is this bad?
633 /// Readability, this can be written more concisely as:
634 /// * `_.any(_)`, or `_.contains(_)` for `is_some()`,
635 /// * `!_.any(_)`, or `!_.contains(_)` for `is_none()`.
639 /// let vec = vec![1];
640 /// vec.iter().find(|x| **x == 0).is_some();
642 /// let _ = "hello world".find("world").is_none();
644 /// Could be written as
646 /// let vec = vec![1];
647 /// vec.iter().any(|x| *x == 0);
649 /// let _ = !"hello world".contains("world");
653 "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()`)"
656 declare_clippy_lint! {
658 /// Checks for usage of `.chars().next()` on a `str` to check
659 /// if it starts with a given char.
661 /// ### Why is this bad?
662 /// Readability, this can be written more concisely as
663 /// `_.starts_with(_)`.
667 /// let name = "foo";
668 /// if name.chars().next() == Some('_') {};
670 /// Could be written as
672 /// let name = "foo";
673 /// if name.starts_with('_') {};
677 "using `.chars().next()` to check if a string starts with a char"
680 declare_clippy_lint! {
682 /// Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
683 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
684 /// `unwrap_or_default` instead.
686 /// ### Why is this bad?
687 /// The function will always be called and potentially
688 /// allocate an object acting as the default.
690 /// ### Known problems
691 /// If the function has side-effects, not calling it will
692 /// change the semantic of the program, but you shouldn't rely on that anyway.
696 /// # let foo = Some(String::new());
697 /// foo.unwrap_or(String::new());
699 /// this can instead be written:
701 /// # let foo = Some(String::new());
702 /// foo.unwrap_or_else(String::new);
706 /// # let foo = Some(String::new());
707 /// foo.unwrap_or_default();
711 "using any `*or` method with a function call, which suggests `*or_else`"
714 declare_clippy_lint! {
716 /// Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
717 /// etc., and suggests to use `unwrap_or_else` instead
719 /// ### Why is this bad?
720 /// The function will always be called.
722 /// ### Known problems
723 /// If the function has side-effects, not calling it will
724 /// change the semantics of the program, but you shouldn't rely on that anyway.
728 /// # let foo = Some(String::new());
729 /// # let err_code = "418";
730 /// # let err_msg = "I'm a teapot";
731 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
735 /// # let foo = Some(String::new());
736 /// # let err_code = "418";
737 /// # let err_msg = "I'm a teapot";
738 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
740 /// this can instead be written:
742 /// # let foo = Some(String::new());
743 /// # let err_code = "418";
744 /// # let err_msg = "I'm a teapot";
745 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
749 "using any `expect` method with a function call"
752 declare_clippy_lint! {
754 /// Checks for usage of `.clone()` on a `Copy` type.
756 /// ### Why is this bad?
757 /// The only reason `Copy` types implement `Clone` is for
758 /// generics, not for using the `clone` method on a concrete type.
766 "using `clone` on a `Copy` type"
769 declare_clippy_lint! {
771 /// Checks for usage of `.clone()` on a ref-counted pointer,
772 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
773 /// function syntax instead (e.g., `Rc::clone(foo)`).
775 /// ### Why is this bad?
776 /// Calling '.clone()' on an Rc, Arc, or Weak
777 /// can obscure the fact that only the pointer is being cloned, not the underlying
782 /// # use std::rc::Rc;
783 /// let x = Rc::new(1);
791 pub CLONE_ON_REF_PTR,
793 "using 'clone' on a ref-counted pointer"
796 declare_clippy_lint! {
798 /// Checks for usage of `.clone()` on an `&&T`.
800 /// ### Why is this bad?
801 /// Cloning an `&&T` copies the inner `&T`, instead of
802 /// cloning the underlying `T`.
809 /// let z = y.clone();
810 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
813 pub CLONE_DOUBLE_REF,
815 "using `clone` on `&&T`"
818 declare_clippy_lint! {
820 /// Checks for usage of `.to_string()` on an `&&T` where
821 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
823 /// ### Why is this bad?
824 /// This bypasses the specialized implementation of
825 /// `ToString` and instead goes through the more expensive string formatting
830 /// // Generic implementation for `T: Display` is used (slow)
831 /// ["foo", "bar"].iter().map(|s| s.to_string());
833 /// // OK, the specialized impl is used
834 /// ["foo", "bar"].iter().map(|&s| s.to_string());
836 pub INEFFICIENT_TO_STRING,
838 "using `to_string` on `&&T` where `T: ToString`"
841 declare_clippy_lint! {
843 /// Checks for `new` not returning a type that contains `Self`.
845 /// ### Why is this bad?
846 /// As a convention, `new` methods are used to make a new
847 /// instance of a type.
850 /// In an impl block:
853 /// # struct NotAFoo;
855 /// fn new() -> NotAFoo {
865 /// // Bad. The type name must contain `Self`
866 /// fn new() -> Bar {
874 /// # struct FooError;
876 /// // Good. Return type contains `Self`
877 /// fn new() -> Result<Foo, FooError> {
883 /// Or in a trait definition:
885 /// pub trait Trait {
886 /// // Bad. The type name must contain `Self`
892 /// pub trait Trait {
893 /// // Good. Return type contains `Self`
894 /// fn new() -> Self;
899 "not returning type containing `Self` in a `new` method"
902 declare_clippy_lint! {
904 /// Checks for string methods that receive a single-character
905 /// `str` as an argument, e.g., `_.split("x")`.
907 /// ### Why is this bad?
908 /// Performing these methods using a `char` is faster than
911 /// ### Known problems
912 /// Does not catch multi-byte unicode characters.
921 pub SINGLE_CHAR_PATTERN,
923 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
926 declare_clippy_lint! {
928 /// Checks for calling `.step_by(0)` on iterators which panics.
930 /// ### Why is this bad?
931 /// This very much looks like an oversight. Use `panic!()` instead if you
932 /// actually intend to panic.
935 /// ```rust,should_panic
936 /// for x in (0..100).step_by(0) {
940 pub ITERATOR_STEP_BY_ZERO,
942 "using `Iterator::step_by(0)`, which will panic at runtime"
945 declare_clippy_lint! {
947 /// Checks for indirect collection of populated `Option`
949 /// ### Why is this bad?
950 /// `Option` is like a collection of 0-1 things, so `flatten`
951 /// automatically does this without suspicious-looking `unwrap` calls.
955 /// let _ = std::iter::empty::<Option<i32>>().filter(Option::is_some).map(Option::unwrap);
959 /// let _ = std::iter::empty::<Option<i32>>().flatten();
961 pub OPTION_FILTER_MAP,
963 "filtering `Option` for `Some` then force-unwrapping, which can be one type-safe operation"
966 declare_clippy_lint! {
968 /// Checks for the use of `iter.nth(0)`.
970 /// ### Why is this bad?
971 /// `iter.next()` is equivalent to
972 /// `iter.nth(0)`, as they both consume the next element,
973 /// but is more readable.
977 /// # use std::collections::HashSet;
979 /// # let mut s = HashSet::new();
981 /// let x = s.iter().nth(0);
984 /// # let mut s = HashSet::new();
986 /// let x = s.iter().next();
990 "replace `iter.nth(0)` with `iter.next()`"
993 declare_clippy_lint! {
995 /// Checks for use of `.iter().nth()` (and the related
996 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
998 /// ### Why is this bad?
999 /// `.get()` and `.get_mut()` are more efficient and more
1004 /// let some_vec = vec![0, 1, 2, 3];
1005 /// let bad_vec = some_vec.iter().nth(3);
1006 /// let bad_slice = &some_vec[..].iter().nth(3);
1008 /// The correct use would be:
1010 /// let some_vec = vec![0, 1, 2, 3];
1011 /// let bad_vec = some_vec.get(3);
1012 /// let bad_slice = &some_vec[..].get(3);
1016 "using `.iter().nth()` on a standard library type with O(1) element access"
1019 declare_clippy_lint! {
1020 /// ### What it does
1021 /// Checks for use of `.skip(x).next()` on iterators.
1023 /// ### Why is this bad?
1024 /// `.nth(x)` is cleaner
1028 /// let some_vec = vec![0, 1, 2, 3];
1029 /// let bad_vec = some_vec.iter().skip(3).next();
1030 /// let bad_slice = &some_vec[..].iter().skip(3).next();
1032 /// The correct use would be:
1034 /// let some_vec = vec![0, 1, 2, 3];
1035 /// let bad_vec = some_vec.iter().nth(3);
1036 /// let bad_slice = &some_vec[..].iter().nth(3);
1040 "using `.skip(x).next()` on an iterator"
1043 declare_clippy_lint! {
1044 /// ### What it does
1045 /// Checks for use of `.get().unwrap()` (or
1046 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
1048 /// ### Why is this bad?
1049 /// Using the Index trait (`[]`) is more clear and more
1052 /// ### Known problems
1053 /// Not a replacement for error handling: Using either
1054 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
1055 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
1056 /// temporary placeholder for dealing with the `Option` type, then this does
1057 /// not mitigate the need for error handling. If there is a chance that `.get()`
1058 /// will be `None` in your program, then it is advisable that the `None` case
1059 /// is handled in a future refactor instead of using `.unwrap()` or the Index
1064 /// let mut some_vec = vec![0, 1, 2, 3];
1065 /// let last = some_vec.get(3).unwrap();
1066 /// *some_vec.get_mut(0).unwrap() = 1;
1068 /// The correct use would be:
1070 /// let mut some_vec = vec![0, 1, 2, 3];
1071 /// let last = some_vec[3];
1072 /// some_vec[0] = 1;
1076 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
1079 declare_clippy_lint! {
1080 /// ### What it does
1081 /// Checks for occurrences where one vector gets extended instead of append
1083 /// ### Why is this bad?
1084 /// Using `append` instead of `extend` is more concise and faster
1088 /// let mut a = vec![1, 2, 3];
1089 /// let mut b = vec![4, 5, 6];
1092 /// a.extend(b.drain(..));
1095 /// a.append(&mut b);
1097 pub EXTEND_WITH_DRAIN,
1099 "using vec.append(&mut vec) to move the full range of a vecor to another"
1102 declare_clippy_lint! {
1103 /// ### What it does
1104 /// Checks for the use of `.extend(s.chars())` where s is a
1105 /// `&str` or `String`.
1107 /// ### Why is this bad?
1108 /// `.push_str(s)` is clearer
1112 /// let abc = "abc";
1113 /// let def = String::from("def");
1114 /// let mut s = String::new();
1115 /// s.extend(abc.chars());
1116 /// s.extend(def.chars());
1118 /// The correct use would be:
1120 /// let abc = "abc";
1121 /// let def = String::from("def");
1122 /// let mut s = String::new();
1123 /// s.push_str(abc);
1124 /// s.push_str(&def);
1126 pub STRING_EXTEND_CHARS,
1128 "using `x.extend(s.chars())` where s is a `&str` or `String`"
1131 declare_clippy_lint! {
1132 /// ### What it does
1133 /// Checks for the use of `.cloned().collect()` on slice to
1136 /// ### Why is this bad?
1137 /// `.to_vec()` is clearer
1141 /// let s = [1, 2, 3, 4, 5];
1142 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1144 /// The better use would be:
1146 /// let s = [1, 2, 3, 4, 5];
1147 /// let s2: Vec<isize> = s.to_vec();
1149 pub ITER_CLONED_COLLECT,
1151 "using `.cloned().collect()` on slice to create a `Vec`"
1154 declare_clippy_lint! {
1155 /// ### What it does
1156 /// Checks for usage of `_.chars().last()` or
1157 /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1159 /// ### Why is this bad?
1160 /// Readability, this can be written more concisely as
1161 /// `_.ends_with(_)`.
1165 /// # let name = "_";
1168 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1171 /// name.ends_with('_') || name.ends_with('-');
1175 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1178 declare_clippy_lint! {
1179 /// ### What it does
1180 /// Checks for usage of `.as_ref()` or `.as_mut()` where the
1181 /// types before and after the call are the same.
1183 /// ### Why is this bad?
1184 /// The call is unnecessary.
1188 /// # fn do_stuff(x: &[i32]) {}
1189 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1190 /// do_stuff(x.as_ref());
1192 /// The correct use would be:
1194 /// # fn do_stuff(x: &[i32]) {}
1195 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1200 "using `as_ref` where the types before and after the call are the same"
1203 declare_clippy_lint! {
1204 /// ### What it does
1205 /// Checks for using `fold` when a more succinct alternative exists.
1206 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1207 /// `sum` or `product`.
1209 /// ### Why is this bad?
1214 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1216 /// This could be written as:
1218 /// let _ = (0..3).any(|x| x > 2);
1220 pub UNNECESSARY_FOLD,
1222 "using `fold` when a more succinct alternative exists"
1225 declare_clippy_lint! {
1226 /// ### What it does
1227 /// Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1228 /// More specifically it checks if the closure provided is only performing one of the
1229 /// filter or map operations and suggests the appropriate option.
1231 /// ### Why is this bad?
1232 /// Complexity. The intent is also clearer if only a single
1233 /// operation is being performed.
1237 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1239 /// // As there is no transformation of the argument this could be written as:
1240 /// let _ = (0..3).filter(|&x| x > 2);
1244 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1246 /// // As there is no conditional check on the argument this could be written as:
1247 /// let _ = (0..4).map(|x| x + 1);
1249 pub UNNECESSARY_FILTER_MAP,
1251 "using `filter_map` when a more succinct alternative exists"
1254 declare_clippy_lint! {
1255 /// ### What it does
1256 /// Checks for `into_iter` calls on references which should be replaced by `iter`
1259 /// ### Why is this bad?
1260 /// Readability. Calling `into_iter` on a reference will not move out its
1261 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1262 /// `iter_mut` directly.
1267 /// let _ = (&vec![3, 4, 5]).into_iter();
1270 /// let _ = (&vec![3, 4, 5]).iter();
1272 pub INTO_ITER_ON_REF,
1274 "using `.into_iter()` on a reference"
1277 declare_clippy_lint! {
1278 /// ### What it does
1279 /// Checks for calls to `map` followed by a `count`.
1281 /// ### Why is this bad?
1282 /// It looks suspicious. Maybe `map` was confused with `filter`.
1283 /// If the `map` call is intentional, this should be rewritten. Or, if you intend to
1284 /// drive the iterator to completion, you can just use `for_each` instead.
1288 /// let _ = (0..3).map(|x| x + 2).count();
1292 "suspicious usage of map"
1295 declare_clippy_lint! {
1296 /// ### What it does
1297 /// Checks for `MaybeUninit::uninit().assume_init()`.
1299 /// ### Why is this bad?
1300 /// For most types, this is undefined behavior.
1302 /// ### Known problems
1303 /// For now, we accept empty tuples and tuples / arrays
1304 /// of `MaybeUninit`. There may be other types that allow uninitialized
1305 /// data, but those are not yet rigorously defined.
1309 /// // Beware the UB
1310 /// use std::mem::MaybeUninit;
1312 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1315 /// Note that the following is OK:
1318 /// use std::mem::MaybeUninit;
1320 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1321 /// MaybeUninit::uninit().assume_init()
1324 pub UNINIT_ASSUMED_INIT,
1326 "`MaybeUninit::uninit().assume_init()`"
1329 declare_clippy_lint! {
1330 /// ### What it does
1331 /// Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1333 /// ### Why is this bad?
1334 /// These can be written simply with `saturating_add/sub` methods.
1338 /// # let y: u32 = 0;
1339 /// # let x: u32 = 100;
1340 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1341 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1344 /// can be written using dedicated methods for saturating addition/subtraction as:
1347 /// # let y: u32 = 0;
1348 /// # let x: u32 = 100;
1349 /// let add = x.saturating_add(y);
1350 /// let sub = x.saturating_sub(y);
1352 pub MANUAL_SATURATING_ARITHMETIC,
1354 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1357 declare_clippy_lint! {
1358 /// ### What it does
1359 /// Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1360 /// zero-sized types
1362 /// ### Why is this bad?
1363 /// This is a no-op, and likely unintended
1367 /// unsafe { (&() as *const ()).offset(1) };
1371 "Check for offset calculations on raw pointers to zero-sized types"
1374 declare_clippy_lint! {
1375 /// ### What it does
1376 /// Checks for `FileType::is_file()`.
1378 /// ### Why is this bad?
1379 /// When people testing a file type with `FileType::is_file`
1380 /// they are testing whether a path is something they can get bytes from. But
1381 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1382 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1387 /// let metadata = std::fs::metadata("foo.txt")?;
1388 /// let filetype = metadata.file_type();
1390 /// if filetype.is_file() {
1393 /// # Ok::<_, std::io::Error>(())
1397 /// should be written as:
1401 /// let metadata = std::fs::metadata("foo.txt")?;
1402 /// let filetype = metadata.file_type();
1404 /// if !filetype.is_dir() {
1407 /// # Ok::<_, std::io::Error>(())
1410 pub FILETYPE_IS_FILE,
1412 "`FileType::is_file` is not recommended to test for readable file type"
1415 declare_clippy_lint! {
1416 /// ### What it does
1417 /// Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1419 /// ### Why is this bad?
1420 /// Readability, this can be written more concisely as
1425 /// # let opt = Some("".to_string());
1426 /// opt.as_ref().map(String::as_str)
1429 /// Can be written as
1431 /// # let opt = Some("".to_string());
1435 pub OPTION_AS_REF_DEREF,
1437 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1440 declare_clippy_lint! {
1441 /// ### What it does
1442 /// Checks for usage of `iter().next()` on a Slice or an Array
1444 /// ### Why is this bad?
1445 /// These can be shortened into `.get()`
1449 /// # let a = [1, 2, 3];
1450 /// # let b = vec![1, 2, 3];
1451 /// a[2..].iter().next();
1452 /// b.iter().next();
1454 /// should be written as:
1456 /// # let a = [1, 2, 3];
1457 /// # let b = vec![1, 2, 3];
1461 pub ITER_NEXT_SLICE,
1463 "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1466 declare_clippy_lint! {
1467 /// ### What it does
1468 /// Warns when using `push_str`/`insert_str` with a single-character string literal
1469 /// where `push`/`insert` with a `char` would work fine.
1471 /// ### Why is this bad?
1472 /// It's less clear that we are pushing a single character.
1476 /// let mut string = String::new();
1477 /// string.insert_str(0, "R");
1478 /// string.push_str("R");
1480 /// Could be written as
1482 /// let mut string = String::new();
1483 /// string.insert(0, 'R');
1484 /// string.push('R');
1486 pub SINGLE_CHAR_ADD_STR,
1488 "`push_str()` or `insert_str()` used with a single-character string literal as parameter"
1491 declare_clippy_lint! {
1492 /// ### What it does
1493 /// As the counterpart to `or_fun_call`, this lint looks for unnecessary
1494 /// lazily evaluated closures on `Option` and `Result`.
1496 /// This lint suggests changing the following functions, when eager evaluation results in
1498 /// - `unwrap_or_else` to `unwrap_or`
1499 /// - `and_then` to `and`
1500 /// - `or_else` to `or`
1501 /// - `get_or_insert_with` to `get_or_insert`
1502 /// - `ok_or_else` to `ok_or`
1504 /// ### Why is this bad?
1505 /// Using eager evaluation is shorter and simpler in some cases.
1507 /// ### Known problems
1508 /// It is possible, but not recommended for `Deref` and `Index` to have
1509 /// side effects. Eagerly evaluating them can change the semantics of the program.
1513 /// // example code where clippy issues a warning
1514 /// let opt: Option<u32> = None;
1516 /// opt.unwrap_or_else(|| 42);
1520 /// let opt: Option<u32> = None;
1522 /// opt.unwrap_or(42);
1524 pub UNNECESSARY_LAZY_EVALUATIONS,
1526 "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1529 declare_clippy_lint! {
1530 /// ### What it does
1531 /// Checks for usage of `_.map(_).collect::<Result<(), _>()`.
1533 /// ### Why is this bad?
1534 /// Using `try_for_each` instead is more readable and idiomatic.
1538 /// (0..3).map(|t| Err(t)).collect::<Result<(), _>>();
1542 /// (0..3).try_for_each(|t| Err(t));
1544 pub MAP_COLLECT_RESULT_UNIT,
1546 "using `.map(_).collect::<Result<(),_>()`, which can be replaced with `try_for_each`"
1549 declare_clippy_lint! {
1550 /// ### What it does
1551 /// Checks for `from_iter()` function calls on types that implement the `FromIterator`
1554 /// ### Why is this bad?
1555 /// It is recommended style to use collect. See
1556 /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
1560 /// use std::iter::FromIterator;
1562 /// let five_fives = std::iter::repeat(5).take(5);
1564 /// let v = Vec::from_iter(five_fives);
1566 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1570 /// let five_fives = std::iter::repeat(5).take(5);
1572 /// let v: Vec<i32> = five_fives.collect();
1574 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1576 pub FROM_ITER_INSTEAD_OF_COLLECT,
1578 "use `.collect()` instead of `::from_iter()`"
1581 declare_clippy_lint! {
1582 /// ### What it does
1583 /// Checks for usage of `inspect().for_each()`.
1585 /// ### Why is this bad?
1586 /// It is the same as performing the computation
1587 /// inside `inspect` at the beginning of the closure in `for_each`.
1591 /// [1,2,3,4,5].iter()
1592 /// .inspect(|&x| println!("inspect the number: {}", x))
1593 /// .for_each(|&x| {
1594 /// assert!(x >= 0);
1597 /// Can be written as
1599 /// [1,2,3,4,5].iter()
1600 /// .for_each(|&x| {
1601 /// println!("inspect the number: {}", x);
1602 /// assert!(x >= 0);
1605 pub INSPECT_FOR_EACH,
1607 "using `.inspect().for_each()`, which can be replaced with `.for_each()`"
1610 declare_clippy_lint! {
1611 /// ### What it does
1612 /// Checks for usage of `filter_map(|x| x)`.
1614 /// ### Why is this bad?
1615 /// Readability, this can be written more concisely by using `flatten`.
1619 /// # let iter = vec![Some(1)].into_iter();
1620 /// iter.filter_map(|x| x);
1624 /// # let iter = vec![Some(1)].into_iter();
1627 pub FILTER_MAP_IDENTITY,
1629 "call to `filter_map` where `flatten` is sufficient"
1632 declare_clippy_lint! {
1633 /// ### What it does
1634 /// Checks for instances of `map(f)` where `f` is the identity function.
1636 /// ### Why is this bad?
1637 /// It can be written more concisely without the call to `map`.
1641 /// let x = [1, 2, 3];
1642 /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
1646 /// let x = [1, 2, 3];
1647 /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
1651 "using iterator.map(|x| x)"
1654 declare_clippy_lint! {
1655 /// ### What it does
1656 /// Checks for the use of `.bytes().nth()`.
1658 /// ### Why is this bad?
1659 /// `.as_bytes().get()` is more efficient and more
1665 /// let _ = "Hello".bytes().nth(3);
1668 /// let _ = "Hello".as_bytes().get(3);
1672 "replace `.bytes().nth()` with `.as_bytes().get()`"
1675 declare_clippy_lint! {
1676 /// ### What it does
1677 /// Checks for the usage of `_.to_owned()`, `vec.to_vec()`, or similar when calling `_.clone()` would be clearer.
1679 /// ### Why is this bad?
1680 /// These methods do the same thing as `_.clone()` but may be confusing as
1681 /// to why we are calling `to_vec` on something that is already a `Vec` or calling `to_owned` on something that is already owned.
1685 /// let a = vec![1, 2, 3];
1686 /// let b = a.to_vec();
1687 /// let c = a.to_owned();
1691 /// let a = vec![1, 2, 3];
1692 /// let b = a.clone();
1693 /// let c = a.clone();
1697 "implicitly cloning a value by invoking a function on its dereferenced type"
1700 declare_clippy_lint! {
1701 /// ### What it does
1702 /// Checks for the use of `.iter().count()`.
1704 /// ### Why is this bad?
1705 /// `.len()` is more efficient and more
1711 /// let some_vec = vec![0, 1, 2, 3];
1712 /// let _ = some_vec.iter().count();
1713 /// let _ = &some_vec[..].iter().count();
1716 /// let some_vec = vec![0, 1, 2, 3];
1717 /// let _ = some_vec.len();
1718 /// let _ = &some_vec[..].len();
1722 "replace `.iter().count()` with `.len()`"
1725 declare_clippy_lint! {
1726 /// ### What it does
1727 /// Checks for calls to [`splitn`]
1728 /// (https://doc.rust-lang.org/std/primitive.str.html#method.splitn) and
1729 /// related functions with either zero or one splits.
1731 /// ### Why is this bad?
1732 /// These calls don't actually split the value and are
1733 /// likely to be intended as a different number.
1739 /// for x in s.splitn(1, ":") {
1745 /// for x in s.splitn(2, ":") {
1749 pub SUSPICIOUS_SPLITN,
1751 "checks for `.splitn(0, ..)` and `.splitn(1, ..)`"
1754 declare_clippy_lint! {
1755 /// ### What it does
1756 /// Checks for manual implementations of `str::repeat`
1758 /// ### Why is this bad?
1759 /// These are both harder to read, as well as less performant.
1764 /// let x: String = std::iter::repeat('x').take(10).collect();
1767 /// let x: String = "x".repeat(10);
1769 pub MANUAL_STR_REPEAT,
1771 "manual implementation of `str::repeat`"
1774 pub struct Methods {
1775 avoid_breaking_exported_api: bool,
1776 msrv: Option<RustcVersion>,
1781 pub fn new(avoid_breaking_exported_api: bool, msrv: Option<RustcVersion>) -> Self {
1783 avoid_breaking_exported_api,
1789 impl_lint_pass!(Methods => [
1792 SHOULD_IMPLEMENT_TRAIT,
1793 WRONG_SELF_CONVENTION,
1795 UNWRAP_OR_ELSE_DEFAULT,
1797 RESULT_MAP_OR_INTO_OPTION,
1799 BIND_INSTEAD_OF_MAP,
1807 CLONED_INSTEAD_OF_COPIED,
1809 INEFFICIENT_TO_STRING,
1811 SINGLE_CHAR_PATTERN,
1812 SINGLE_CHAR_ADD_STR,
1816 FILTER_MAP_IDENTITY,
1824 ITERATOR_STEP_BY_ZERO,
1832 STRING_EXTEND_CHARS,
1833 ITER_CLONED_COLLECT,
1836 UNNECESSARY_FILTER_MAP,
1839 UNINIT_ASSUMED_INIT,
1840 MANUAL_SATURATING_ARITHMETIC,
1843 OPTION_AS_REF_DEREF,
1844 UNNECESSARY_LAZY_EVALUATIONS,
1845 MAP_COLLECT_RESULT_UNIT,
1846 FROM_ITER_INSTEAD_OF_COLLECT,
1854 /// Extracts a method call name, args, and `Span` of the method name.
1855 fn method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(SymbolStr, &'tcx [hir::Expr<'tcx>], Span)> {
1856 if let ExprKind::MethodCall(path, span, args, _) = recv.kind {
1857 if !args.iter().any(|e| e.span.from_expansion()) {
1858 return Some((path.ident.name.as_str(), args, span));
1864 /// Same as `method_call` but the `SymbolStr` is dereferenced into a temporary `&str`
1865 macro_rules! method_call {
1869 .map(|&(ref name, args, span)| (&**name, args, span))
1873 impl<'tcx> LateLintPass<'tcx> for Methods {
1874 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1875 if in_macro(expr.span) {
1879 check_methods(cx, expr, self.msrv.as_ref());
1882 hir::ExprKind::Call(func, args) => {
1883 from_iter_instead_of_collect::check(cx, expr, args, func);
1885 hir::ExprKind::MethodCall(method_call, ref method_span, args, _) => {
1886 or_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1887 expect_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1888 clone_on_copy::check(cx, expr, method_call.ident.name, args);
1889 clone_on_ref_ptr::check(cx, expr, method_call.ident.name, args);
1890 inefficient_to_string::check(cx, expr, method_call.ident.name, args);
1891 single_char_add_str::check(cx, expr, args);
1892 into_iter_on_ref::check(cx, expr, *method_span, method_call.ident.name, args);
1893 single_char_pattern::check(cx, expr, method_call.ident.name, args);
1895 hir::ExprKind::Binary(op, lhs, rhs) if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne => {
1896 let mut info = BinaryExprInfo {
1900 eq: op.node == hir::BinOpKind::Eq,
1902 lint_binary_expr_with_method_call(cx, &mut info);
1908 #[allow(clippy::too_many_lines)]
1909 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1910 if in_external_macro(cx.sess(), impl_item.span) {
1913 let name = impl_item.ident.name.as_str();
1914 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
1915 let item = cx.tcx.hir().expect_item(parent);
1916 let self_ty = cx.tcx.type_of(item.def_id);
1918 let implements_trait = matches!(item.kind, hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }));
1920 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1921 if let Some(first_arg) = iter_input_pats(sig.decl, cx.tcx.hir().body(id)).next();
1923 let method_sig = cx.tcx.fn_sig(impl_item.def_id);
1924 let method_sig = cx.tcx.erase_late_bound_regions(method_sig);
1926 let first_arg_ty = &method_sig.inputs().iter().next();
1928 // check conventions w.r.t. conversion method names and predicates
1929 if let Some(first_arg_ty) = first_arg_ty;
1932 // if this impl block implements a trait, lint in trait definition instead
1933 if !implements_trait && cx.access_levels.is_exported(impl_item.hir_id()) {
1934 // check missing trait implementations
1935 for method_config in &TRAIT_METHODS {
1936 if name == method_config.method_name &&
1937 sig.decl.inputs.len() == method_config.param_count &&
1938 method_config.output_type.matches(&sig.decl.output) &&
1939 method_config.self_kind.matches(cx, self_ty, first_arg_ty) &&
1940 fn_header_equals(method_config.fn_header, sig.header) &&
1941 method_config.lifetime_param_cond(impl_item)
1945 SHOULD_IMPLEMENT_TRAIT,
1948 "method `{}` can be confused for the standard trait method `{}::{}`",
1949 method_config.method_name,
1950 method_config.trait_name,
1951 method_config.method_name
1955 "consider implementing the trait `{}` or choosing a less ambiguous method name",
1956 method_config.trait_name
1963 if sig.decl.implicit_self.has_implicit_self()
1964 && !(self.avoid_breaking_exported_api
1965 && cx.access_levels.is_exported(impl_item.hir_id()))
1967 wrong_self_convention::check(
1980 // if this impl block implements a trait, lint in trait definition instead
1981 if implements_trait {
1985 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
1986 let ret_ty = return_ty(cx, impl_item.hir_id());
1988 // walk the return type and check for Self (this does not check associated types)
1989 if let Some(self_adt) = self_ty.ty_adt_def() {
1990 if contains_adt_constructor(ret_ty, self_adt) {
1993 } else if contains_ty(ret_ty, self_ty) {
1997 // if return type is impl trait, check the associated types
1998 if let ty::Opaque(def_id, _) = *ret_ty.kind() {
1999 // one of the associated types must be Self
2000 for &(predicate, _span) in cx.tcx.explicit_item_bounds(def_id) {
2001 if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
2002 // walk the associated type and check for Self
2003 if let Some(self_adt) = self_ty.ty_adt_def() {
2004 if contains_adt_constructor(projection_predicate.ty, self_adt) {
2007 } else if contains_ty(projection_predicate.ty, self_ty) {
2014 if name == "new" && !TyS::same_type(ret_ty, self_ty) {
2019 "methods called `new` usually return `Self`",
2025 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
2026 if in_external_macro(cx.tcx.sess, item.span) {
2031 if let TraitItemKind::Fn(ref sig, _) = item.kind;
2032 if sig.decl.implicit_self.has_implicit_self();
2033 if let Some(first_arg_ty) = sig.decl.inputs.iter().next();
2036 let first_arg_span = first_arg_ty.span;
2037 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
2038 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
2039 wrong_self_convention::check(
2041 &item.ident.name.as_str(),
2052 if item.ident.name == sym::new;
2053 if let TraitItemKind::Fn(_, _) = item.kind;
2054 let ret_ty = return_ty(cx, item.hir_id());
2055 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
2056 if !contains_ty(ret_ty, self_ty);
2063 "methods called `new` usually return `Self`",
2069 extract_msrv_attr!(LateContext);
2072 #[allow(clippy::too_many_lines)]
2073 fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>) {
2074 if let Some((name, [recv, args @ ..], span)) = method_call!(expr) {
2075 match (name, args) {
2076 ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
2077 zst_offset::check(cx, expr, recv);
2079 ("and_then", [arg]) => {
2080 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::check(cx, expr, recv, arg);
2081 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::check(cx, expr, recv, arg);
2082 if !biom_option_linted && !biom_result_linted {
2083 unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
2086 ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
2087 ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
2088 ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
2089 ("cloned", []) => cloned_instead_of_copied::check(cx, expr, recv, span, msrv),
2090 ("collect", []) => match method_call!(recv) {
2091 Some(("cloned", [recv2], _)) => iter_cloned_collect::check(cx, expr, recv2),
2092 Some(("map", [m_recv, m_arg], _)) => {
2093 map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
2095 Some(("take", [take_self_arg, take_arg], _)) => {
2096 if meets_msrv(msrv, &msrvs::STR_REPEAT) {
2097 manual_str_repeat::check(cx, expr, recv, take_self_arg, take_arg);
2102 ("count", []) => match method_call!(recv) {
2103 Some((name @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
2104 iter_count::check(cx, expr, recv2, name);
2106 Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
2109 ("expect", [_]) => match method_call!(recv) {
2110 Some(("ok", [recv], _)) => ok_expect::check(cx, expr, recv),
2111 _ => expect_used::check(cx, expr, recv),
2113 ("extend", [arg]) => {
2114 string_extend_chars::check(cx, expr, recv, arg);
2115 extend_with_drain::check(cx, expr, recv, arg);
2117 ("filter_map", [arg]) => {
2118 unnecessary_filter_map::check(cx, expr, arg);
2119 filter_map_identity::check(cx, expr, arg, span);
2121 ("flat_map", [arg]) => {
2122 flat_map_identity::check(cx, expr, arg, span);
2123 flat_map_option::check(cx, expr, arg, span);
2125 ("flatten", []) => {
2126 if let Some(("map", [recv, map_arg], _)) = method_call!(recv) {
2127 map_flatten::check(cx, expr, recv, map_arg);
2130 ("fold", [init, acc]) => unnecessary_fold::check(cx, expr, init, acc, span),
2131 ("for_each", [_]) => {
2132 if let Some(("inspect", [_, _], span2)) = method_call!(recv) {
2133 inspect_for_each::check(cx, expr, span2);
2136 ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
2137 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
2138 ("is_none", []) => check_is_some_is_none(cx, expr, recv, false),
2139 ("is_some", []) => check_is_some_is_none(cx, expr, recv, true),
2140 ("map", [m_arg]) => {
2141 if let Some((name, [recv2, args @ ..], span2)) = method_call!(recv) {
2142 match (name, args) {
2143 ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, msrv),
2144 ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, msrv),
2145 ("filter", [f_arg]) => {
2146 filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, false);
2148 ("find", [f_arg]) => filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, true),
2152 map_identity::check(cx, expr, recv, m_arg, span);
2154 ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
2156 if let Some((name, [recv, args @ ..], _)) = method_call!(recv) {
2157 match (name, args) {
2158 ("filter", [arg]) => filter_next::check(cx, expr, recv, arg),
2159 ("filter_map", [arg]) => filter_map_next::check(cx, expr, recv, arg, msrv),
2160 ("iter", []) => iter_next_slice::check(cx, expr, recv),
2161 ("skip", [arg]) => iter_skip_next::check(cx, expr, recv, arg),
2162 ("skip_while", [_]) => skip_while_next::check(cx, expr),
2167 ("nth", [n_arg]) => match method_call!(recv) {
2168 Some(("bytes", [recv2], _)) => bytes_nth::check(cx, expr, recv2, n_arg),
2169 Some(("iter", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
2170 Some(("iter_mut", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
2171 _ => iter_nth_zero::check(cx, expr, recv, n_arg),
2173 ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
2174 ("or_else", [arg]) => {
2175 if !bind_instead_of_map::ResultOrElseErrInfo::check(cx, expr, recv, arg) {
2176 unnecessary_lazy_eval::check(cx, expr, recv, arg, "or");
2179 ("splitn" | "splitn_mut" | "rsplitn" | "rsplitn_mut", [count_arg, _]) => {
2180 suspicious_splitn::check(cx, name, expr, recv, count_arg);
2182 ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
2183 ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
2184 implicit_clone::check(cx, name, expr, recv, span);
2186 ("unwrap", []) => match method_call!(recv) {
2187 Some(("get", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, false),
2188 Some(("get_mut", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, true),
2189 _ => unwrap_used::check(cx, expr, recv),
2191 ("unwrap_or", [u_arg]) => match method_call!(recv) {
2192 Some((arith @ ("checked_add" | "checked_sub" | "checked_mul"), [lhs, rhs], _)) => {
2193 manual_saturating_arithmetic::check(cx, expr, lhs, rhs, u_arg, &arith["checked_".len()..]);
2195 Some(("map", [m_recv, m_arg], span)) => {
2196 option_map_unwrap_or::check(cx, expr, m_recv, m_arg, recv, u_arg, span);
2200 ("unwrap_or_else", [u_arg]) => match method_call!(recv) {
2201 Some(("map", [recv, map_arg], _)) if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, msrv) => {},
2203 unwrap_or_else_default::check(cx, expr, recv, u_arg);
2204 unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or");
2212 fn check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool) {
2213 if let Some((name @ ("find" | "position" | "rposition"), [f_recv, arg], span)) = method_call!(recv) {
2214 search_is_some::check(cx, expr, name, is_some, f_recv, arg, recv, span);
2218 /// Used for `lint_binary_expr_with_method_call`.
2219 #[derive(Copy, Clone)]
2220 struct BinaryExprInfo<'a> {
2221 expr: &'a hir::Expr<'a>,
2222 chain: &'a hir::Expr<'a>,
2223 other: &'a hir::Expr<'a>,
2227 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2228 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
2229 macro_rules! lint_with_both_lhs_and_rhs {
2230 ($func:expr, $cx:expr, $info:ident) => {
2231 if !$func($cx, $info) {
2232 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2233 if $func($cx, $info) {
2240 lint_with_both_lhs_and_rhs!(chars_next_cmp::check, cx, info);
2241 lint_with_both_lhs_and_rhs!(chars_last_cmp::check, cx, info);
2242 lint_with_both_lhs_and_rhs!(chars_next_cmp_with_unwrap::check, cx, info);
2243 lint_with_both_lhs_and_rhs!(chars_last_cmp_with_unwrap::check, cx, info);
2246 const FN_HEADER: hir::FnHeader = hir::FnHeader {
2247 unsafety: hir::Unsafety::Normal,
2248 constness: hir::Constness::NotConst,
2249 asyncness: hir::IsAsync::NotAsync,
2250 abi: rustc_target::spec::abi::Abi::Rust,
2253 struct ShouldImplTraitCase {
2254 trait_name: &'static str,
2255 method_name: &'static str,
2257 fn_header: hir::FnHeader,
2258 // implicit self kind expected (none, self, &self, ...)
2259 self_kind: SelfKind,
2260 // checks against the output type
2261 output_type: OutType,
2262 // certain methods with explicit lifetimes can't implement the equivalent trait method
2263 lint_explicit_lifetime: bool,
2265 impl ShouldImplTraitCase {
2267 trait_name: &'static str,
2268 method_name: &'static str,
2270 fn_header: hir::FnHeader,
2271 self_kind: SelfKind,
2272 output_type: OutType,
2273 lint_explicit_lifetime: bool,
2274 ) -> ShouldImplTraitCase {
2275 ShouldImplTraitCase {
2282 lint_explicit_lifetime,
2286 fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
2287 self.lint_explicit_lifetime
2288 || !impl_item.generics.params.iter().any(|p| {
2291 hir::GenericParamKind::Lifetime {
2292 kind: hir::LifetimeParamKind::Explicit
2300 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
2301 ShouldImplTraitCase::new("std::ops::Add", "add", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2302 ShouldImplTraitCase::new("std::convert::AsMut", "as_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2303 ShouldImplTraitCase::new("std::convert::AsRef", "as_ref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2304 ShouldImplTraitCase::new("std::ops::BitAnd", "bitand", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2305 ShouldImplTraitCase::new("std::ops::BitOr", "bitor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2306 ShouldImplTraitCase::new("std::ops::BitXor", "bitxor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2307 ShouldImplTraitCase::new("std::borrow::Borrow", "borrow", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2308 ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2309 ShouldImplTraitCase::new("std::clone::Clone", "clone", 1, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2310 ShouldImplTraitCase::new("std::cmp::Ord", "cmp", 2, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2311 // FIXME: default doesn't work
2312 ShouldImplTraitCase::new("std::default::Default", "default", 0, FN_HEADER, SelfKind::No, OutType::Any, true),
2313 ShouldImplTraitCase::new("std::ops::Deref", "deref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2314 ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2315 ShouldImplTraitCase::new("std::ops::Div", "div", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2316 ShouldImplTraitCase::new("std::ops::Drop", "drop", 1, FN_HEADER, SelfKind::RefMut, OutType::Unit, true),
2317 ShouldImplTraitCase::new("std::cmp::PartialEq", "eq", 2, FN_HEADER, SelfKind::Ref, OutType::Bool, true),
2318 ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2319 ShouldImplTraitCase::new("std::str::FromStr", "from_str", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2320 ShouldImplTraitCase::new("std::hash::Hash", "hash", 2, FN_HEADER, SelfKind::Ref, OutType::Unit, true),
2321 ShouldImplTraitCase::new("std::ops::Index", "index", 2, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2322 ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut", 2, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2323 ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2324 ShouldImplTraitCase::new("std::ops::Mul", "mul", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2325 ShouldImplTraitCase::new("std::ops::Neg", "neg", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2326 ShouldImplTraitCase::new("std::iter::Iterator", "next", 1, FN_HEADER, SelfKind::RefMut, OutType::Any, false),
2327 ShouldImplTraitCase::new("std::ops::Not", "not", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2328 ShouldImplTraitCase::new("std::ops::Rem", "rem", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2329 ShouldImplTraitCase::new("std::ops::Shl", "shl", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2330 ShouldImplTraitCase::new("std::ops::Shr", "shr", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2331 ShouldImplTraitCase::new("std::ops::Sub", "sub", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2334 #[derive(Clone, Copy, PartialEq, Debug)]
2343 fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2344 fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2345 if ty == parent_ty {
2347 } else if ty.is_box() {
2348 ty.boxed_ty() == parent_ty
2349 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
2350 if let ty::Adt(_, substs) = ty.kind() {
2351 substs.types().next().map_or(false, |t| t == parent_ty)
2360 fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2361 if let ty::Ref(_, t, m) = *ty.kind() {
2362 return m == mutability && t == parent_ty;
2365 let trait_path = match mutability {
2366 hir::Mutability::Not => &paths::ASREF_TRAIT,
2367 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
2370 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2372 None => return false,
2374 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2378 Self::Value => matches_value(cx, parent_ty, ty),
2379 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
2380 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
2381 Self::No => ty != parent_ty,
2386 fn description(self) -> &'static str {
2388 Self::Value => "`self` by value",
2389 Self::Ref => "`self` by reference",
2390 Self::RefMut => "`self` by mutable reference",
2391 Self::No => "no `self`",
2396 #[derive(Clone, Copy)]
2405 fn matches(self, ty: &hir::FnRetTy<'_>) -> bool {
2406 let is_unit = |ty: &hir::Ty<'_>| matches!(ty.kind, hir::TyKind::Tup(&[]));
2408 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
2409 (Self::Unit, &hir::FnRetTy::Return(ty)) if is_unit(ty) => true,
2410 (Self::Bool, &hir::FnRetTy::Return(ty)) if is_bool(ty) => true,
2411 (Self::Any, &hir::FnRetTy::Return(ty)) if !is_unit(ty) => true,
2412 (Self::Ref, &hir::FnRetTy::Return(ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
2418 fn is_bool(ty: &hir::Ty<'_>) -> bool {
2419 if let hir::TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
2420 matches!(path.res, Res::PrimTy(PrimTy::Bool))
2426 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
2427 expected.constness == actual.constness
2428 && expected.unsafety == actual.unsafety
2429 && expected.asyncness == actual.asyncness