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;
16 mod filter_map_flat_map;
17 mod filter_map_identity;
21 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 map_collect_result_unit;
40 mod option_as_ref_deref;
41 mod option_map_or_none;
42 mod option_map_unwrap_or;
45 mod single_char_add_str;
46 mod single_char_insert_string;
47 mod single_char_pattern;
48 mod single_char_push_string;
50 mod string_extend_chars;
52 mod uninit_assumed_init;
53 mod unnecessary_filter_map;
55 mod unnecessary_lazy_eval;
59 mod wrong_self_convention;
62 use bind_instead_of_map::BindInsteadOfMap;
63 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
64 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
65 use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, paths, return_ty};
66 use if_chain::if_chain;
68 use rustc_hir::def::Res;
69 use rustc_hir::{Expr, ExprKind, PrimTy, QPath, TraitItem, TraitItemKind};
70 use rustc_lint::{LateContext, LateLintPass, LintContext};
71 use rustc_middle::lint::in_external_macro;
72 use rustc_middle::ty::{self, TraitRef, Ty, TyS};
73 use rustc_semver::RustcVersion;
74 use rustc_session::{declare_tool_lint, impl_lint_pass};
75 use rustc_span::symbol::SymbolStr;
76 use rustc_span::{sym, Span};
77 use rustc_typeck::hir_ty_to_ty;
79 declare_clippy_lint! {
80 /// **What it does:** Checks for `.unwrap()` calls on `Option`s and on `Result`s.
82 /// **Why is this bad?** It is better to handle the `None` or `Err` case,
83 /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
84 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
85 /// `Allow` by default.
87 /// `result.unwrap()` will let the thread panic on `Err` values.
88 /// Normally, you want to implement more sophisticated error handling,
89 /// and propagate errors upwards with `?` operator.
91 /// Even if you want to panic on errors, not all `Error`s implement good
92 /// messages on display. Therefore, it may be beneficial to look at the places
93 /// where they may get displayed. Activate this lint to do just that.
95 /// **Known problems:** None.
99 /// # let opt = Some(1);
105 /// opt.expect("more helpful message");
111 /// # let res: Result<usize, ()> = Ok(1);
117 /// res.expect("more helpful message");
121 "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
124 declare_clippy_lint! {
125 /// **What it does:** Checks for `.expect()` calls on `Option`s and `Result`s.
127 /// **Why is this bad?** Usually it is better to handle the `None` or `Err` case.
128 /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
129 /// this lint is `Allow` by default.
131 /// `result.expect()` will let the thread panic on `Err`
132 /// values. Normally, you want to implement more sophisticated error handling,
133 /// and propagate errors upwards with `?` operator.
135 /// **Known problems:** None.
139 /// # let opt = Some(1);
142 /// opt.expect("one");
145 /// let opt = Some(1);
152 /// # let res: Result<usize, ()> = Ok(1);
155 /// res.expect("one");
159 /// # Ok::<(), ()>(())
163 "using `.expect()` on `Result` or `Option`, which might be better handled"
166 declare_clippy_lint! {
167 /// **What it does:** Checks for methods that should live in a trait
168 /// implementation of a `std` trait (see [llogiq's blog
169 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
170 /// information) instead of an inherent implementation.
172 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
173 /// the code, often with very little cost. Also people seeing a `mul(...)`
175 /// may expect `*` to work equally, so you should have good reason to disappoint
178 /// **Known problems:** None.
184 /// fn add(&self, other: &X) -> X {
190 pub SHOULD_IMPLEMENT_TRAIT,
192 "defining a method that should be implementing a std trait"
195 declare_clippy_lint! {
196 /// **What it does:** Checks for methods with certain name prefixes and which
197 /// doesn't match how self is taken. The actual rules are:
199 /// |Prefix |Postfix |`self` taken | `self` type |
200 /// |-------|------------|-----------------------|--------------|
201 /// |`as_` | none |`&self` or `&mut self` | any |
202 /// |`from_`| none | none | any |
203 /// |`into_`| none |`self` | any |
204 /// |`is_` | none |`&self` or none | any |
205 /// |`to_` | `_mut` |`&mut self` | any |
206 /// |`to_` | not `_mut` |`self` | `Copy` |
207 /// |`to_` | not `_mut` |`&self` | not `Copy` |
209 /// Please find more info here:
210 /// https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
212 /// **Why is this bad?** Consistency breeds readability. If you follow the
213 /// conventions, your users won't be surprised that they, e.g., need to supply a
214 /// mutable reference to a `as_..` function.
216 /// **Known problems:** None.
222 /// fn as_str(self) -> &'static str {
228 pub WRONG_SELF_CONVENTION,
230 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
233 declare_clippy_lint! {
234 /// **What it does:** This is the same as
235 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
237 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
239 /// **Known problems:** Actually *renaming* the function may break clients if
240 /// the function is part of the public interface. In that case, be mindful of
241 /// the stability guarantees you've given your users.
247 /// pub fn as_str(self) -> &'a str {
252 pub WRONG_PUB_SELF_CONVENTION,
254 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
257 declare_clippy_lint! {
258 /// **What it does:** Checks for usage of `ok().expect(..)`.
260 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
261 /// directly to get a better error message.
263 /// **Known problems:** The error type needs to implement `Debug`
267 /// # let x = Ok::<_, ()>(());
270 /// x.ok().expect("why did I do this again?");
273 /// x.expect("why did I do this again?");
277 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
280 declare_clippy_lint! {
281 /// **What it does:** Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
282 /// `result.map(_).unwrap_or_else(_)`.
284 /// **Why is this bad?** Readability, these can be written more concisely (resp.) as
285 /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
287 /// **Known problems:** The order of the arguments is not in execution order
291 /// # let x = Some(1);
294 /// x.map(|a| a + 1).unwrap_or(0);
297 /// x.map_or(0, |a| a + 1);
303 /// # let x: Result<usize, ()> = Ok(1);
304 /// # fn some_function(foo: ()) -> usize { 1 }
307 /// x.map(|a| a + 1).unwrap_or_else(some_function);
310 /// x.map_or_else(some_function, |a| a + 1);
314 "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)`"
317 declare_clippy_lint! {
318 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
320 /// **Why is this bad?** Readability, this can be written more concisely as
323 /// **Known problems:** The order of the arguments is not in execution order.
327 /// # let opt = Some(1);
330 /// opt.map_or(None, |a| Some(a + 1));
333 /// opt.and_then(|a| Some(a + 1));
335 pub OPTION_MAP_OR_NONE,
337 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
340 declare_clippy_lint! {
341 /// **What it does:** Checks for usage of `_.map_or(None, Some)`.
343 /// **Why is this bad?** Readability, this can be written more concisely as
346 /// **Known problems:** None.
352 /// # let r: Result<u32, &str> = Ok(1);
353 /// assert_eq!(Some(1), r.map_or(None, Some));
358 /// # let r: Result<u32, &str> = Ok(1);
359 /// assert_eq!(Some(1), r.ok());
361 pub RESULT_MAP_OR_INTO_OPTION,
363 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
366 declare_clippy_lint! {
367 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
368 /// `_.or_else(|x| Err(y))`.
370 /// **Why is this bad?** Readability, this can be written more concisely as
371 /// `_.map(|x| y)` or `_.map_err(|x| y)`.
373 /// **Known problems:** None
378 /// # fn opt() -> Option<&'static str> { Some("42") }
379 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
380 /// let _ = opt().and_then(|s| Some(s.len()));
381 /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
382 /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
385 /// The correct use would be:
388 /// # fn opt() -> Option<&'static str> { Some("42") }
389 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
390 /// let _ = opt().map(|s| s.len());
391 /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
392 /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
394 pub BIND_INSTEAD_OF_MAP,
396 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
399 declare_clippy_lint! {
400 /// **What it does:** Checks for usage of `_.filter(_).next()`.
402 /// **Why is this bad?** Readability, this can be written more concisely as
405 /// **Known problems:** None.
409 /// # let vec = vec![1];
410 /// vec.iter().filter(|x| **x == 0).next();
412 /// Could be written as
414 /// # let vec = vec![1];
415 /// vec.iter().find(|x| **x == 0);
419 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
422 declare_clippy_lint! {
423 /// **What it does:** Checks for usage of `_.skip_while(condition).next()`.
425 /// **Why is this bad?** Readability, this can be written more concisely as
426 /// `_.find(!condition)`.
428 /// **Known problems:** None.
432 /// # let vec = vec![1];
433 /// vec.iter().skip_while(|x| **x == 0).next();
435 /// Could be written as
437 /// # let vec = vec![1];
438 /// vec.iter().find(|x| **x != 0);
442 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
445 declare_clippy_lint! {
446 /// **What it does:** Checks for usage of `_.map(_).flatten(_)` on `Iterator` and `Option`
448 /// **Why is this bad?** Readability, this can be written more concisely as
451 /// **Known problems:**
455 /// let vec = vec![vec![1]];
458 /// vec.iter().map(|x| x.iter()).flatten();
461 /// vec.iter().flat_map(|x| x.iter());
465 "using combinations of `flatten` and `map` which can usually be written as a single method call"
468 declare_clippy_lint! {
469 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
470 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
472 /// **Why is this bad?** Readability, this can be written more concisely as
473 /// `_.filter_map(_)`.
475 /// **Known problems:** Often requires a condition + Option/Iterator creation
476 /// inside the closure.
480 /// let vec = vec![1];
483 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
486 /// vec.iter().filter_map(|x| if *x == 0 {
494 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
497 declare_clippy_lint! {
498 /// **What it does:** Checks for usage of `_.filter(_).map(_)` that can be written more simply
499 /// as `filter_map(_)`.
501 /// **Why is this bad?** Redundant code in the `filter` and `map` operations is poor style and
504 /// **Known problems:** None.
510 /// .filter(|n| n.checked_add(1).is_some())
511 /// .map(|n| n.checked_add(1).unwrap());
516 /// (0_i32..10).filter_map(|n| n.checked_add(1));
518 pub MANUAL_FILTER_MAP,
520 "using `_.filter(_).map(_)` in a way that can be written more simply as `filter_map(_)`"
523 declare_clippy_lint! {
524 /// **What it does:** Checks for usage of `_.find(_).map(_)` that can be written more simply
525 /// as `find_map(_)`.
527 /// **Why is this bad?** Redundant code in the `find` and `map` operations is poor style and
530 /// **Known problems:** None.
536 /// .find(|n| n.checked_add(1).is_some())
537 /// .map(|n| n.checked_add(1).unwrap());
542 /// (0_i32..10).find_map(|n| n.checked_add(1));
546 "using `_.find(_).map(_)` in a way that can be written more simply as `find_map(_)`"
549 declare_clippy_lint! {
550 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
552 /// **Why is this bad?** Readability, this can be written more concisely as
555 /// **Known problems:** None
559 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
561 /// Can be written as
564 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
568 "using combination of `filter_map` and `next` which can usually be written as a single method call"
571 declare_clippy_lint! {
572 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
574 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
576 /// **Known problems:** None
580 /// # let iter = vec![vec![0]].into_iter();
581 /// iter.flat_map(|x| x);
583 /// Can be written as
585 /// # let iter = vec![vec![0]].into_iter();
588 pub FLAT_MAP_IDENTITY,
590 "call to `flat_map` where `flatten` is sufficient"
593 declare_clippy_lint! {
594 /// **What it does:** Checks for an iterator or string search (such as `find()`,
595 /// `position()`, or `rposition()`) followed by a call to `is_some()` or `is_none()`.
597 /// **Why is this bad?** Readability, this can be written more concisely as:
598 /// * `_.any(_)`, or `_.contains(_)` for `is_some()`,
599 /// * `!_.any(_)`, or `!_.contains(_)` for `is_none()`.
601 /// **Known problems:** None.
605 /// let vec = vec![1];
606 /// vec.iter().find(|x| **x == 0).is_some();
608 /// let _ = "hello world".find("world").is_none();
610 /// Could be written as
612 /// let vec = vec![1];
613 /// vec.iter().any(|x| *x == 0);
615 /// let _ = !"hello world".contains("world");
619 "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()`)"
622 declare_clippy_lint! {
623 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
624 /// if it starts with a given char.
626 /// **Why is this bad?** Readability, this can be written more concisely as
627 /// `_.starts_with(_)`.
629 /// **Known problems:** None.
633 /// let name = "foo";
634 /// if name.chars().next() == Some('_') {};
636 /// Could be written as
638 /// let name = "foo";
639 /// if name.starts_with('_') {};
643 "using `.chars().next()` to check if a string starts with a char"
646 declare_clippy_lint! {
647 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
648 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
649 /// `unwrap_or_default` instead.
651 /// **Why is this bad?** The function will always be called and potentially
652 /// allocate an object acting as the default.
654 /// **Known problems:** If the function has side-effects, not calling it will
655 /// change the semantic of the program, but you shouldn't rely on that anyway.
659 /// # let foo = Some(String::new());
660 /// foo.unwrap_or(String::new());
662 /// this can instead be written:
664 /// # let foo = Some(String::new());
665 /// foo.unwrap_or_else(String::new);
669 /// # let foo = Some(String::new());
670 /// foo.unwrap_or_default();
674 "using any `*or` method with a function call, which suggests `*or_else`"
677 declare_clippy_lint! {
678 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
679 /// etc., and suggests to use `unwrap_or_else` instead
681 /// **Why is this bad?** The function will always be called.
683 /// **Known problems:** If the function has side-effects, not calling it will
684 /// change the semantics of the program, but you shouldn't rely on that anyway.
688 /// # let foo = Some(String::new());
689 /// # let err_code = "418";
690 /// # let err_msg = "I'm a teapot";
691 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
695 /// # let foo = Some(String::new());
696 /// # let err_code = "418";
697 /// # let err_msg = "I'm a teapot";
698 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
700 /// this can instead be written:
702 /// # let foo = Some(String::new());
703 /// # let err_code = "418";
704 /// # let err_msg = "I'm a teapot";
705 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
709 "using any `expect` method with a function call"
712 declare_clippy_lint! {
713 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
715 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
716 /// generics, not for using the `clone` method on a concrete type.
718 /// **Known problems:** None.
726 "using `clone` on a `Copy` type"
729 declare_clippy_lint! {
730 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
731 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
732 /// function syntax instead (e.g., `Rc::clone(foo)`).
734 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
735 /// can obscure the fact that only the pointer is being cloned, not the underlying
740 /// # use std::rc::Rc;
741 /// let x = Rc::new(1);
749 pub CLONE_ON_REF_PTR,
751 "using 'clone' on a ref-counted pointer"
754 declare_clippy_lint! {
755 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
757 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
758 /// cloning the underlying `T`.
760 /// **Known problems:** None.
767 /// let z = y.clone();
768 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
771 pub CLONE_DOUBLE_REF,
773 "using `clone` on `&&T`"
776 declare_clippy_lint! {
777 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
778 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
780 /// **Why is this bad?** This bypasses the specialized implementation of
781 /// `ToString` and instead goes through the more expensive string formatting
784 /// **Known problems:** None.
788 /// // Generic implementation for `T: Display` is used (slow)
789 /// ["foo", "bar"].iter().map(|s| s.to_string());
791 /// // OK, the specialized impl is used
792 /// ["foo", "bar"].iter().map(|&s| s.to_string());
794 pub INEFFICIENT_TO_STRING,
796 "using `to_string` on `&&T` where `T: ToString`"
799 declare_clippy_lint! {
800 /// **What it does:** Checks for `new` not returning a type that contains `Self`.
802 /// **Why is this bad?** As a convention, `new` methods are used to make a new
803 /// instance of a type.
805 /// **Known problems:** None.
808 /// In an impl block:
811 /// # struct NotAFoo;
813 /// fn new() -> NotAFoo {
823 /// // Bad. The type name must contain `Self`
824 /// fn new() -> Bar {
832 /// # struct FooError;
834 /// // Good. Return type contains `Self`
835 /// fn new() -> Result<Foo, FooError> {
841 /// Or in a trait definition:
843 /// pub trait Trait {
844 /// // Bad. The type name must contain `Self`
850 /// pub trait Trait {
851 /// // Good. Return type contains `Self`
852 /// fn new() -> Self;
857 "not returning type containing `Self` in a `new` method"
860 declare_clippy_lint! {
861 /// **What it does:** Checks for string methods that receive a single-character
862 /// `str` as an argument, e.g., `_.split("x")`.
864 /// **Why is this bad?** Performing these methods using a `char` is faster than
867 /// **Known problems:** Does not catch multi-byte unicode characters.
876 pub SINGLE_CHAR_PATTERN,
878 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
881 declare_clippy_lint! {
882 /// **What it does:** Checks for calling `.step_by(0)` on iterators which panics.
884 /// **Why is this bad?** This very much looks like an oversight. Use `panic!()` instead if you
885 /// actually intend to panic.
887 /// **Known problems:** None.
890 /// ```rust,should_panic
891 /// for x in (0..100).step_by(0) {
895 pub ITERATOR_STEP_BY_ZERO,
897 "using `Iterator::step_by(0)`, which will panic at runtime"
900 declare_clippy_lint! {
901 /// **What it does:** Checks for indirect collection of populated `Option`
903 /// **Why is this bad?** `Option` is like a collection of 0-1 things, so `flatten`
904 /// automatically does this without suspicious-looking `unwrap` calls.
906 /// **Known problems:** None.
911 /// let _ = std::iter::empty::<Option<i32>>().filter(Option::is_some).map(Option::unwrap);
915 /// let _ = std::iter::empty::<Option<i32>>().flatten();
917 pub OPTION_FILTER_MAP,
919 "filtering `Option` for `Some` then force-unwrapping, which can be one type-safe operation"
922 declare_clippy_lint! {
923 /// **What it does:** Checks for the use of `iter.nth(0)`.
925 /// **Why is this bad?** `iter.next()` is equivalent to
926 /// `iter.nth(0)`, as they both consume the next element,
927 /// but is more readable.
929 /// **Known problems:** None.
934 /// # use std::collections::HashSet;
936 /// # let mut s = HashSet::new();
938 /// let x = s.iter().nth(0);
941 /// # let mut s = HashSet::new();
943 /// let x = s.iter().next();
947 "replace `iter.nth(0)` with `iter.next()`"
950 declare_clippy_lint! {
951 /// **What it does:** Checks for use of `.iter().nth()` (and the related
952 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
954 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
957 /// **Known problems:** None.
961 /// let some_vec = vec![0, 1, 2, 3];
962 /// let bad_vec = some_vec.iter().nth(3);
963 /// let bad_slice = &some_vec[..].iter().nth(3);
965 /// The correct use would be:
967 /// let some_vec = vec![0, 1, 2, 3];
968 /// let bad_vec = some_vec.get(3);
969 /// let bad_slice = &some_vec[..].get(3);
973 "using `.iter().nth()` on a standard library type with O(1) element access"
976 declare_clippy_lint! {
977 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
979 /// **Why is this bad?** `.nth(x)` is cleaner
981 /// **Known problems:** None.
985 /// let some_vec = vec![0, 1, 2, 3];
986 /// let bad_vec = some_vec.iter().skip(3).next();
987 /// let bad_slice = &some_vec[..].iter().skip(3).next();
989 /// The correct use would be:
991 /// let some_vec = vec![0, 1, 2, 3];
992 /// let bad_vec = some_vec.iter().nth(3);
993 /// let bad_slice = &some_vec[..].iter().nth(3);
997 "using `.skip(x).next()` on an iterator"
1000 declare_clippy_lint! {
1001 /// **What it does:** Checks for use of `.get().unwrap()` (or
1002 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
1004 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
1007 /// **Known problems:** Not a replacement for error handling: Using either
1008 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
1009 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
1010 /// temporary placeholder for dealing with the `Option` type, then this does
1011 /// not mitigate the need for error handling. If there is a chance that `.get()`
1012 /// will be `None` in your program, then it is advisable that the `None` case
1013 /// is handled in a future refactor instead of using `.unwrap()` or the Index
1018 /// let mut some_vec = vec![0, 1, 2, 3];
1019 /// let last = some_vec.get(3).unwrap();
1020 /// *some_vec.get_mut(0).unwrap() = 1;
1022 /// The correct use would be:
1024 /// let mut some_vec = vec![0, 1, 2, 3];
1025 /// let last = some_vec[3];
1026 /// some_vec[0] = 1;
1030 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
1033 declare_clippy_lint! {
1034 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
1035 /// `&str` or `String`.
1037 /// **Why is this bad?** `.push_str(s)` is clearer
1039 /// **Known problems:** None.
1043 /// let abc = "abc";
1044 /// let def = String::from("def");
1045 /// let mut s = String::new();
1046 /// s.extend(abc.chars());
1047 /// s.extend(def.chars());
1049 /// The correct use would be:
1051 /// let abc = "abc";
1052 /// let def = String::from("def");
1053 /// let mut s = String::new();
1054 /// s.push_str(abc);
1055 /// s.push_str(&def);
1057 pub STRING_EXTEND_CHARS,
1059 "using `x.extend(s.chars())` where s is a `&str` or `String`"
1062 declare_clippy_lint! {
1063 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
1066 /// **Why is this bad?** `.to_vec()` is clearer
1068 /// **Known problems:** None.
1072 /// let s = [1, 2, 3, 4, 5];
1073 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1075 /// The better use would be:
1077 /// let s = [1, 2, 3, 4, 5];
1078 /// let s2: Vec<isize> = s.to_vec();
1080 pub ITER_CLONED_COLLECT,
1082 "using `.cloned().collect()` on slice to create a `Vec`"
1085 declare_clippy_lint! {
1086 /// **What it does:** Checks for usage of `_.chars().last()` or
1087 /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1089 /// **Why is this bad?** Readability, this can be written more concisely as
1090 /// `_.ends_with(_)`.
1092 /// **Known problems:** None.
1096 /// # let name = "_";
1099 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1102 /// name.ends_with('_') || name.ends_with('-');
1106 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1109 declare_clippy_lint! {
1110 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
1111 /// types before and after the call are the same.
1113 /// **Why is this bad?** The call is unnecessary.
1115 /// **Known problems:** None.
1119 /// # fn do_stuff(x: &[i32]) {}
1120 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1121 /// do_stuff(x.as_ref());
1123 /// The correct use would be:
1125 /// # fn do_stuff(x: &[i32]) {}
1126 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1131 "using `as_ref` where the types before and after the call are the same"
1134 declare_clippy_lint! {
1135 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
1136 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1137 /// `sum` or `product`.
1139 /// **Why is this bad?** Readability.
1141 /// **Known problems:** None.
1145 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1147 /// This could be written as:
1149 /// let _ = (0..3).any(|x| x > 2);
1151 pub UNNECESSARY_FOLD,
1153 "using `fold` when a more succinct alternative exists"
1156 declare_clippy_lint! {
1157 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1158 /// More specifically it checks if the closure provided is only performing one of the
1159 /// filter or map operations and suggests the appropriate option.
1161 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
1162 /// operation is being performed.
1164 /// **Known problems:** None
1168 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1170 /// // As there is no transformation of the argument this could be written as:
1171 /// let _ = (0..3).filter(|&x| x > 2);
1175 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1177 /// // As there is no conditional check on the argument this could be written as:
1178 /// let _ = (0..4).map(|x| x + 1);
1180 pub UNNECESSARY_FILTER_MAP,
1182 "using `filter_map` when a more succinct alternative exists"
1185 declare_clippy_lint! {
1186 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
1189 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
1190 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1191 /// `iter_mut` directly.
1193 /// **Known problems:** None
1199 /// let _ = (&vec![3, 4, 5]).into_iter();
1202 /// let _ = (&vec![3, 4, 5]).iter();
1204 pub INTO_ITER_ON_REF,
1206 "using `.into_iter()` on a reference"
1209 declare_clippy_lint! {
1210 /// **What it does:** Checks for calls to `map` followed by a `count`.
1212 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
1213 /// If the `map` call is intentional, this should be rewritten. Or, if you intend to
1214 /// drive the iterator to completion, you can just use `for_each` instead.
1216 /// **Known problems:** None
1221 /// let _ = (0..3).map(|x| x + 2).count();
1225 "suspicious usage of map"
1228 declare_clippy_lint! {
1229 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1231 /// **Why is this bad?** For most types, this is undefined behavior.
1233 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1234 /// of `MaybeUninit`. There may be other types that allow uninitialized
1235 /// data, but those are not yet rigorously defined.
1240 /// // Beware the UB
1241 /// use std::mem::MaybeUninit;
1243 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1246 /// Note that the following is OK:
1249 /// use std::mem::MaybeUninit;
1251 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1252 /// MaybeUninit::uninit().assume_init()
1255 pub UNINIT_ASSUMED_INIT,
1257 "`MaybeUninit::uninit().assume_init()`"
1260 declare_clippy_lint! {
1261 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1263 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1268 /// # let y: u32 = 0;
1269 /// # let x: u32 = 100;
1270 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1271 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1274 /// can be written using dedicated methods for saturating addition/subtraction as:
1277 /// # let y: u32 = 0;
1278 /// # let x: u32 = 100;
1279 /// let add = x.saturating_add(y);
1280 /// let sub = x.saturating_sub(y);
1282 pub MANUAL_SATURATING_ARITHMETIC,
1284 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1287 declare_clippy_lint! {
1288 /// **What it does:** Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1289 /// zero-sized types
1291 /// **Why is this bad?** This is a no-op, and likely unintended
1293 /// **Known problems:** None
1297 /// unsafe { (&() as *const ()).offset(1) };
1301 "Check for offset calculations on raw pointers to zero-sized types"
1304 declare_clippy_lint! {
1305 /// **What it does:** Checks for `FileType::is_file()`.
1307 /// **Why is this bad?** When people testing a file type with `FileType::is_file`
1308 /// they are testing whether a path is something they can get bytes from. But
1309 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1310 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1316 /// let metadata = std::fs::metadata("foo.txt")?;
1317 /// let filetype = metadata.file_type();
1319 /// if filetype.is_file() {
1322 /// # Ok::<_, std::io::Error>(())
1326 /// should be written as:
1330 /// let metadata = std::fs::metadata("foo.txt")?;
1331 /// let filetype = metadata.file_type();
1333 /// if !filetype.is_dir() {
1336 /// # Ok::<_, std::io::Error>(())
1339 pub FILETYPE_IS_FILE,
1341 "`FileType::is_file` is not recommended to test for readable file type"
1344 declare_clippy_lint! {
1345 /// **What it does:** Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1347 /// **Why is this bad?** Readability, this can be written more concisely as
1350 /// **Known problems:** None.
1354 /// # let opt = Some("".to_string());
1355 /// opt.as_ref().map(String::as_str)
1358 /// Can be written as
1360 /// # let opt = Some("".to_string());
1364 pub OPTION_AS_REF_DEREF,
1366 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1369 declare_clippy_lint! {
1370 /// **What it does:** Checks for usage of `iter().next()` on a Slice or an Array
1372 /// **Why is this bad?** These can be shortened into `.get()`
1374 /// **Known problems:** None.
1378 /// # let a = [1, 2, 3];
1379 /// # let b = vec![1, 2, 3];
1380 /// a[2..].iter().next();
1381 /// b.iter().next();
1383 /// should be written as:
1385 /// # let a = [1, 2, 3];
1386 /// # let b = vec![1, 2, 3];
1390 pub ITER_NEXT_SLICE,
1392 "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1395 declare_clippy_lint! {
1396 /// **What it does:** Warns when using `push_str`/`insert_str` with a single-character string literal
1397 /// where `push`/`insert` with a `char` would work fine.
1399 /// **Why is this bad?** It's less clear that we are pushing a single character.
1401 /// **Known problems:** None
1405 /// let mut string = String::new();
1406 /// string.insert_str(0, "R");
1407 /// string.push_str("R");
1409 /// Could be written as
1411 /// let mut string = String::new();
1412 /// string.insert(0, 'R');
1413 /// string.push('R');
1415 pub SINGLE_CHAR_ADD_STR,
1417 "`push_str()` or `insert_str()` used with a single-character string literal as parameter"
1420 declare_clippy_lint! {
1421 /// **What it does:** As the counterpart to `or_fun_call`, this lint looks for unnecessary
1422 /// lazily evaluated closures on `Option` and `Result`.
1424 /// This lint suggests changing the following functions, when eager evaluation results in
1426 /// - `unwrap_or_else` to `unwrap_or`
1427 /// - `and_then` to `and`
1428 /// - `or_else` to `or`
1429 /// - `get_or_insert_with` to `get_or_insert`
1430 /// - `ok_or_else` to `ok_or`
1432 /// **Why is this bad?** Using eager evaluation is shorter and simpler in some cases.
1434 /// **Known problems:** It is possible, but not recommended for `Deref` and `Index` to have
1435 /// side effects. Eagerly evaluating them can change the semantics of the program.
1440 /// // example code where clippy issues a warning
1441 /// let opt: Option<u32> = None;
1443 /// opt.unwrap_or_else(|| 42);
1447 /// let opt: Option<u32> = None;
1449 /// opt.unwrap_or(42);
1451 pub UNNECESSARY_LAZY_EVALUATIONS,
1453 "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1456 declare_clippy_lint! {
1457 /// **What it does:** Checks for usage of `_.map(_).collect::<Result<(), _>()`.
1459 /// **Why is this bad?** Using `try_for_each` instead is more readable and idiomatic.
1461 /// **Known problems:** None
1466 /// (0..3).map(|t| Err(t)).collect::<Result<(), _>>();
1470 /// (0..3).try_for_each(|t| Err(t));
1472 pub MAP_COLLECT_RESULT_UNIT,
1474 "using `.map(_).collect::<Result<(),_>()`, which can be replaced with `try_for_each`"
1477 declare_clippy_lint! {
1478 /// **What it does:** Checks for `from_iter()` function calls on types that implement the `FromIterator`
1481 /// **Why is this bad?** It is recommended style to use collect. See
1482 /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
1484 /// **Known problems:** None.
1489 /// use std::iter::FromIterator;
1491 /// let five_fives = std::iter::repeat(5).take(5);
1493 /// let v = Vec::from_iter(five_fives);
1495 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1499 /// let five_fives = std::iter::repeat(5).take(5);
1501 /// let v: Vec<i32> = five_fives.collect();
1503 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1505 pub FROM_ITER_INSTEAD_OF_COLLECT,
1507 "use `.collect()` instead of `::from_iter()`"
1510 declare_clippy_lint! {
1511 /// **What it does:** Checks for usage of `inspect().for_each()`.
1513 /// **Why is this bad?** It is the same as performing the computation
1514 /// inside `inspect` at the beginning of the closure in `for_each`.
1516 /// **Known problems:** None.
1521 /// [1,2,3,4,5].iter()
1522 /// .inspect(|&x| println!("inspect the number: {}", x))
1523 /// .for_each(|&x| {
1524 /// assert!(x >= 0);
1527 /// Can be written as
1529 /// [1,2,3,4,5].iter()
1530 /// .for_each(|&x| {
1531 /// println!("inspect the number: {}", x);
1532 /// assert!(x >= 0);
1535 pub INSPECT_FOR_EACH,
1537 "using `.inspect().for_each()`, which can be replaced with `.for_each()`"
1540 declare_clippy_lint! {
1541 /// **What it does:** Checks for usage of `filter_map(|x| x)`.
1543 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
1545 /// **Known problems:** None.
1550 /// # let iter = vec![Some(1)].into_iter();
1551 /// iter.filter_map(|x| x);
1555 /// # let iter = vec![Some(1)].into_iter();
1558 pub FILTER_MAP_IDENTITY,
1560 "call to `filter_map` where `flatten` is sufficient"
1563 declare_clippy_lint! {
1564 /// **What it does:** Checks for the use of `.bytes().nth()`.
1566 /// **Why is this bad?** `.as_bytes().get()` is more efficient and more
1569 /// **Known problems:** None.
1575 /// let _ = "Hello".bytes().nth(3);
1578 /// let _ = "Hello".as_bytes().get(3);
1582 "replace `.bytes().nth()` with `.as_bytes().get()`"
1585 declare_clippy_lint! {
1586 /// **What it does:** Checks for the usage of `_.to_owned()`, `vec.to_vec()`, or similar when calling `_.clone()` would be clearer.
1588 /// **Why is this bad?** These methods do the same thing as `_.clone()` but may be confusing as
1589 /// to why we are calling `to_vec` on something that is already a `Vec` or calling `to_owned` on something that is already owned.
1591 /// **Known problems:** None.
1596 /// let a = vec![1, 2, 3];
1597 /// let b = a.to_vec();
1598 /// let c = a.to_owned();
1602 /// let a = vec![1, 2, 3];
1603 /// let b = a.clone();
1604 /// let c = a.clone();
1608 "implicitly cloning a value by invoking a function on its dereferenced type"
1611 declare_clippy_lint! {
1612 /// **What it does:** Checks for the use of `.iter().count()`.
1614 /// **Why is this bad?** `.len()` is more efficient and more
1617 /// **Known problems:** None.
1623 /// let some_vec = vec![0, 1, 2, 3];
1624 /// let _ = some_vec.iter().count();
1625 /// let _ = &some_vec[..].iter().count();
1628 /// let some_vec = vec![0, 1, 2, 3];
1629 /// let _ = some_vec.len();
1630 /// let _ = &some_vec[..].len();
1634 "replace `.iter().count()` with `.len()`"
1637 pub struct Methods {
1638 msrv: Option<RustcVersion>,
1643 pub fn new(msrv: Option<RustcVersion>) -> Self {
1648 impl_lint_pass!(Methods => [
1651 SHOULD_IMPLEMENT_TRAIT,
1652 WRONG_SELF_CONVENTION,
1653 WRONG_PUB_SELF_CONVENTION,
1656 RESULT_MAP_OR_INTO_OPTION,
1658 BIND_INSTEAD_OF_MAP,
1666 INEFFICIENT_TO_STRING,
1668 SINGLE_CHAR_PATTERN,
1669 SINGLE_CHAR_ADD_STR,
1674 FILTER_MAP_IDENTITY,
1681 ITERATOR_STEP_BY_ZERO,
1689 STRING_EXTEND_CHARS,
1690 ITER_CLONED_COLLECT,
1693 UNNECESSARY_FILTER_MAP,
1696 UNINIT_ASSUMED_INIT,
1697 MANUAL_SATURATING_ARITHMETIC,
1700 OPTION_AS_REF_DEREF,
1701 UNNECESSARY_LAZY_EVALUATIONS,
1702 MAP_COLLECT_RESULT_UNIT,
1703 FROM_ITER_INSTEAD_OF_COLLECT,
1708 /// Extracts a method call name, args, and `Span` of the method name.
1709 fn method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(SymbolStr, &'tcx [hir::Expr<'tcx>], Span)> {
1710 if let ExprKind::MethodCall(path, span, args, _) = recv.kind {
1711 if !args.iter().any(|e| e.span.from_expansion()) {
1712 return Some((path.ident.name.as_str(), args, span));
1718 /// Same as `method_call` but the `SymbolStr` is dereferenced into a temporary `&str`
1719 macro_rules! method_call {
1723 .map(|&(ref name, args, span)| (&**name, args, span))
1727 impl<'tcx> LateLintPass<'tcx> for Methods {
1728 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1729 if in_macro(expr.span) {
1733 check_methods(cx, expr, self.msrv.as_ref());
1736 hir::ExprKind::Call(ref func, ref args) => {
1737 from_iter_instead_of_collect::check(cx, expr, args, &func.kind);
1739 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args, _) => {
1740 or_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1741 expect_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1742 clone_on_copy::check(cx, expr, method_call.ident.name, args);
1743 clone_on_ref_ptr::check(cx, expr, method_call.ident.name, args);
1744 inefficient_to_string::check(cx, expr, method_call.ident.name, args);
1745 single_char_add_str::check(cx, expr, args);
1746 into_iter_on_ref::check(cx, expr, *method_span, method_call.ident.name, args);
1747 single_char_pattern::check(cx, expr, method_call.ident.name, args);
1749 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1750 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1752 let mut info = BinaryExprInfo {
1756 eq: op.node == hir::BinOpKind::Eq,
1758 lint_binary_expr_with_method_call(cx, &mut info);
1764 #[allow(clippy::too_many_lines)]
1765 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1766 if in_external_macro(cx.sess(), impl_item.span) {
1769 let name = impl_item.ident.name.as_str();
1770 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
1771 let item = cx.tcx.hir().expect_item(parent);
1772 let self_ty = cx.tcx.type_of(item.def_id);
1774 let implements_trait = matches!(item.kind, hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }));
1777 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1778 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1780 let method_sig = cx.tcx.fn_sig(impl_item.def_id);
1781 let method_sig = cx.tcx.erase_late_bound_regions(method_sig);
1783 let first_arg_ty = &method_sig.inputs().iter().next();
1785 // check conventions w.r.t. conversion method names and predicates
1786 if let Some(first_arg_ty) = first_arg_ty;
1789 // if this impl block implements a trait, lint in trait definition instead
1790 if !implements_trait && cx.access_levels.is_exported(impl_item.hir_id()) {
1791 // check missing trait implementations
1792 for method_config in &TRAIT_METHODS {
1793 if name == method_config.method_name &&
1794 sig.decl.inputs.len() == method_config.param_count &&
1795 method_config.output_type.matches(&sig.decl.output) &&
1796 method_config.self_kind.matches(cx, self_ty, first_arg_ty) &&
1797 fn_header_equals(method_config.fn_header, sig.header) &&
1798 method_config.lifetime_param_cond(&impl_item)
1802 SHOULD_IMPLEMENT_TRAIT,
1805 "method `{}` can be confused for the standard trait method `{}::{}`",
1806 method_config.method_name,
1807 method_config.trait_name,
1808 method_config.method_name
1812 "consider implementing the trait `{}` or choosing a less ambiguous method name",
1813 method_config.trait_name
1820 wrong_self_convention::check(
1823 item.vis.node.is_pub(),
1832 // if this impl block implements a trait, lint in trait definition instead
1833 if implements_trait {
1837 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
1838 let ret_ty = return_ty(cx, impl_item.hir_id());
1840 // walk the return type and check for Self (this does not check associated types)
1841 if let Some(self_adt) = self_ty.ty_adt_def() {
1842 if contains_adt_constructor(ret_ty, self_adt) {
1845 } else if contains_ty(ret_ty, self_ty) {
1849 // if return type is impl trait, check the associated types
1850 if let ty::Opaque(def_id, _) = *ret_ty.kind() {
1851 // one of the associated types must be Self
1852 for &(predicate, _span) in cx.tcx.explicit_item_bounds(def_id) {
1853 if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
1854 // walk the associated type and check for Self
1855 if let Some(self_adt) = self_ty.ty_adt_def() {
1856 if contains_adt_constructor(projection_predicate.ty, self_adt) {
1859 } else if contains_ty(projection_predicate.ty, self_ty) {
1866 if name == "new" && !TyS::same_type(ret_ty, self_ty) {
1871 "methods called `new` usually return `Self`",
1877 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1878 if in_external_macro(cx.tcx.sess, item.span) {
1883 if let TraitItemKind::Fn(ref sig, _) = item.kind;
1884 if let Some(first_arg_ty) = sig.decl.inputs.iter().next();
1885 let first_arg_span = first_arg_ty.span;
1886 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
1887 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
1890 wrong_self_convention::check(
1892 &item.ident.name.as_str(),
1903 if item.ident.name == sym::new;
1904 if let TraitItemKind::Fn(_, _) = item.kind;
1905 let ret_ty = return_ty(cx, item.hir_id());
1906 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
1907 if !contains_ty(ret_ty, self_ty);
1914 "methods called `new` usually return `Self`",
1920 extract_msrv_attr!(LateContext);
1923 #[allow(clippy::too_many_lines)]
1924 fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>) {
1925 if let Some((name, [recv, args @ ..], span)) = method_call!(expr) {
1926 match (name, args) {
1927 ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [recv, _]) => {
1928 zst_offset::check(cx, expr, recv)
1930 ("and_then", [arg]) => {
1931 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::check(cx, expr, recv, arg);
1932 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::check(cx, expr, recv, arg);
1933 if !biom_option_linted && !biom_result_linted {
1934 unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
1937 ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
1938 ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
1939 ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
1940 ("collect", []) => match method_call!(recv) {
1941 Some(("cloned", [recv2], _)) => iter_cloned_collect::check(cx, expr, recv2),
1942 Some(("map", [m_recv, m_arg], _)) => {
1943 map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
1947 ("count", []) => match method_call!(recv) {
1948 Some((name @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
1949 iter_count::check(cx, expr, recv2, name);
1951 Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
1954 ("expect", [_]) => match method_call!(recv) {
1955 Some(("ok", [recv], _)) => ok_expect::check(cx, expr, recv),
1956 _ => expect_used::check(cx, expr, recv),
1958 ("extend", [arg]) => string_extend_chars::check(cx, expr, recv, arg),
1959 ("filter_map", [arg]) => {
1960 unnecessary_filter_map::check(cx, expr, arg);
1961 filter_map_identity::check(cx, expr, arg, span);
1963 ("flat_map", [flm_arg]) => match method_call!(recv) {
1964 Some(("filter", [_, _], _)) => filter_flat_map::check(cx, expr),
1965 Some(("filter_map", [_, _], _)) => filter_map_flat_map::check(cx, expr),
1966 _ => flat_map_identity::check(cx, expr, flm_arg, span),
1968 ("flatten", []) => {
1969 if let Some(("map", [recv, map_arg], _)) = method_call!(recv) {
1970 map_flatten::check(cx, expr, recv, map_arg);
1973 ("fold", [init, acc]) => unnecessary_fold::check(cx, expr, init, acc, span),
1974 ("for_each", [_]) => {
1975 if let Some(("inspect", [_, _], span2)) = method_call!(recv) {
1976 inspect_for_each::check(cx, expr, span2);
1979 ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
1980 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
1981 ("is_none", []) => check_is_some_is_none(cx, expr, recv, false),
1982 ("is_some", []) => check_is_some_is_none(cx, expr, recv, true),
1983 ("map", [m_arg]) => {
1984 if let Some((name, [recv2, args @ ..], span2)) = method_call!(recv) {
1985 match (name, args) {
1986 ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, msrv),
1987 ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, msrv),
1988 ("filter", [f_arg]) => {
1989 filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, false)
1991 ("filter_map", [_]) => filter_map_map::check(cx, expr),
1992 ("find", [f_arg]) => filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, true),
1997 ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
1999 if let Some((name, [recv, args @ ..], _)) = method_call!(recv) {
2000 match (name, args) {
2001 ("filter", [arg]) => filter_next::check(cx, expr, recv, arg),
2002 ("filter_map", [arg]) => filter_map_next::check(cx, expr, recv, arg, msrv),
2003 ("iter", []) => iter_next_slice::check(cx, expr, recv),
2004 ("skip", [arg]) => iter_skip_next::check(cx, expr, recv, arg),
2005 ("skip_while", [_]) => skip_while_next::check(cx, expr),
2010 ("nth", [n_arg]) => match method_call!(recv) {
2011 Some(("bytes", [recv2], _)) => bytes_nth::check(cx, expr, recv2, n_arg),
2012 Some(("iter", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
2013 Some(("iter_mut", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
2014 _ => iter_nth_zero::check(cx, expr, recv, n_arg),
2016 ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
2017 ("or_else", [arg]) => {
2018 if !bind_instead_of_map::ResultOrElseErrInfo::check(cx, expr, recv, arg) {
2019 unnecessary_lazy_eval::check(cx, expr, recv, arg, "or");
2022 ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
2023 ("to_os_string", []) => implicit_clone::check(cx, expr, sym::OsStr),
2024 ("to_owned", []) => implicit_clone::check(cx, expr, sym::ToOwned),
2025 ("to_path_buf", []) => implicit_clone::check(cx, expr, sym::Path),
2026 ("to_vec", []) => implicit_clone::check(cx, expr, sym::slice),
2027 ("unwrap", []) => match method_call!(recv) {
2028 Some(("get", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, false),
2029 Some(("get_mut", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, true),
2030 _ => unwrap_used::check(cx, expr, recv),
2032 ("unwrap_or", [u_arg]) => match method_call!(recv) {
2033 Some((arith @ ("checked_add" | "checked_sub" | "checked_mul"), [lhs, rhs], _)) => {
2034 manual_saturating_arithmetic::check(cx, expr, lhs, rhs, u_arg, &arith["checked_".len()..]);
2036 Some(("map", [m_recv, m_arg], span)) => {
2037 option_map_unwrap_or::check(cx, expr, m_recv, m_arg, recv, u_arg, span)
2041 ("unwrap_or_else", [u_arg]) => match method_call!(recv) {
2042 Some(("map", [recv, map_arg], _)) if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, msrv) => {},
2043 _ => unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or"),
2050 fn check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool) {
2051 if let Some((name @ ("find" | "position" | "rposition"), [f_recv, arg], span)) = method_call!(recv) {
2052 search_is_some::check(cx, expr, name, is_some, f_recv, arg, recv, span)
2056 /// Used for `lint_binary_expr_with_method_call`.
2057 #[derive(Copy, Clone)]
2058 struct BinaryExprInfo<'a> {
2059 expr: &'a hir::Expr<'a>,
2060 chain: &'a hir::Expr<'a>,
2061 other: &'a hir::Expr<'a>,
2065 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2066 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
2067 macro_rules! lint_with_both_lhs_and_rhs {
2068 ($func:expr, $cx:expr, $info:ident) => {
2069 if !$func($cx, $info) {
2070 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2071 if $func($cx, $info) {
2078 lint_with_both_lhs_and_rhs!(chars_next_cmp::check, cx, info);
2079 lint_with_both_lhs_and_rhs!(chars_last_cmp::check, cx, info);
2080 lint_with_both_lhs_and_rhs!(chars_next_cmp_with_unwrap::check, cx, info);
2081 lint_with_both_lhs_and_rhs!(chars_last_cmp_with_unwrap::check, cx, info);
2084 const FN_HEADER: hir::FnHeader = hir::FnHeader {
2085 unsafety: hir::Unsafety::Normal,
2086 constness: hir::Constness::NotConst,
2087 asyncness: hir::IsAsync::NotAsync,
2088 abi: rustc_target::spec::abi::Abi::Rust,
2091 struct ShouldImplTraitCase {
2092 trait_name: &'static str,
2093 method_name: &'static str,
2095 fn_header: hir::FnHeader,
2096 // implicit self kind expected (none, self, &self, ...)
2097 self_kind: SelfKind,
2098 // checks against the output type
2099 output_type: OutType,
2100 // certain methods with explicit lifetimes can't implement the equivalent trait method
2101 lint_explicit_lifetime: bool,
2103 impl ShouldImplTraitCase {
2105 trait_name: &'static str,
2106 method_name: &'static str,
2108 fn_header: hir::FnHeader,
2109 self_kind: SelfKind,
2110 output_type: OutType,
2111 lint_explicit_lifetime: bool,
2112 ) -> ShouldImplTraitCase {
2113 ShouldImplTraitCase {
2120 lint_explicit_lifetime,
2124 fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
2125 self.lint_explicit_lifetime
2126 || !impl_item.generics.params.iter().any(|p| {
2129 hir::GenericParamKind::Lifetime {
2130 kind: hir::LifetimeParamKind::Explicit
2138 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
2139 ShouldImplTraitCase::new("std::ops::Add", "add", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2140 ShouldImplTraitCase::new("std::convert::AsMut", "as_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2141 ShouldImplTraitCase::new("std::convert::AsRef", "as_ref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2142 ShouldImplTraitCase::new("std::ops::BitAnd", "bitand", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2143 ShouldImplTraitCase::new("std::ops::BitOr", "bitor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2144 ShouldImplTraitCase::new("std::ops::BitXor", "bitxor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2145 ShouldImplTraitCase::new("std::borrow::Borrow", "borrow", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2146 ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2147 ShouldImplTraitCase::new("std::clone::Clone", "clone", 1, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2148 ShouldImplTraitCase::new("std::cmp::Ord", "cmp", 2, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2149 // FIXME: default doesn't work
2150 ShouldImplTraitCase::new("std::default::Default", "default", 0, FN_HEADER, SelfKind::No, OutType::Any, true),
2151 ShouldImplTraitCase::new("std::ops::Deref", "deref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2152 ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2153 ShouldImplTraitCase::new("std::ops::Div", "div", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2154 ShouldImplTraitCase::new("std::ops::Drop", "drop", 1, FN_HEADER, SelfKind::RefMut, OutType::Unit, true),
2155 ShouldImplTraitCase::new("std::cmp::PartialEq", "eq", 2, FN_HEADER, SelfKind::Ref, OutType::Bool, true),
2156 ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2157 ShouldImplTraitCase::new("std::str::FromStr", "from_str", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2158 ShouldImplTraitCase::new("std::hash::Hash", "hash", 2, FN_HEADER, SelfKind::Ref, OutType::Unit, true),
2159 ShouldImplTraitCase::new("std::ops::Index", "index", 2, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2160 ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut", 2, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2161 ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2162 ShouldImplTraitCase::new("std::ops::Mul", "mul", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2163 ShouldImplTraitCase::new("std::ops::Neg", "neg", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2164 ShouldImplTraitCase::new("std::iter::Iterator", "next", 1, FN_HEADER, SelfKind::RefMut, OutType::Any, false),
2165 ShouldImplTraitCase::new("std::ops::Not", "not", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2166 ShouldImplTraitCase::new("std::ops::Rem", "rem", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2167 ShouldImplTraitCase::new("std::ops::Shl", "shl", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2168 ShouldImplTraitCase::new("std::ops::Shr", "shr", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2169 ShouldImplTraitCase::new("std::ops::Sub", "sub", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2173 const PATTERN_METHODS: [(&str, usize); 17] = [
2181 ("split_terminator", 1),
2182 ("rsplit_terminator", 1),
2187 ("match_indices", 1),
2188 ("rmatch_indices", 1),
2189 ("trim_start_matches", 1),
2190 ("trim_end_matches", 1),
2193 #[derive(Clone, Copy, PartialEq, Debug)]
2202 fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2203 fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2204 if ty == parent_ty {
2206 } else if ty.is_box() {
2207 ty.boxed_ty() == parent_ty
2208 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
2209 if let ty::Adt(_, substs) = ty.kind() {
2210 substs.types().next().map_or(false, |t| t == parent_ty)
2219 fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2220 if let ty::Ref(_, t, m) = *ty.kind() {
2221 return m == mutability && t == parent_ty;
2224 let trait_path = match mutability {
2225 hir::Mutability::Not => &paths::ASREF_TRAIT,
2226 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
2229 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2231 None => return false,
2233 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2237 Self::Value => matches_value(cx, parent_ty, ty),
2238 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
2239 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
2240 Self::No => ty != parent_ty,
2245 fn description(self) -> &'static str {
2247 Self::Value => "`self` by value",
2248 Self::Ref => "`self` by reference",
2249 Self::RefMut => "`self` by mutable reference",
2250 Self::No => "no `self`",
2255 #[derive(Clone, Copy)]
2264 fn matches(self, ty: &hir::FnRetTy<'_>) -> bool {
2265 let is_unit = |ty: &hir::Ty<'_>| matches!(ty.kind, hir::TyKind::Tup(&[]));
2267 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
2268 (Self::Unit, &hir::FnRetTy::Return(ref ty)) if is_unit(ty) => true,
2269 (Self::Bool, &hir::FnRetTy::Return(ref ty)) if is_bool(ty) => true,
2270 (Self::Any, &hir::FnRetTy::Return(ref ty)) if !is_unit(ty) => true,
2271 (Self::Ref, &hir::FnRetTy::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
2277 fn is_bool(ty: &hir::Ty<'_>) -> bool {
2278 if let hir::TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
2279 matches!(path.res, Res::PrimTy(PrimTy::Bool))
2285 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
2286 expected.constness == actual.constness
2287 && expected.unsafety == actual.unsafety
2288 && expected.asyncness == actual.asyncness