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;
62 mod wrong_self_convention;
65 use bind_instead_of_map::BindInsteadOfMap;
66 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
67 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
68 use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
69 use if_chain::if_chain;
71 use rustc_hir::def::Res;
72 use rustc_hir::{Expr, ExprKind, PrimTy, QPath, TraitItem, TraitItemKind};
73 use rustc_lint::{LateContext, LateLintPass, LintContext};
74 use rustc_middle::lint::in_external_macro;
75 use rustc_middle::ty::{self, TraitRef, Ty, TyS};
76 use rustc_semver::RustcVersion;
77 use rustc_session::{declare_tool_lint, impl_lint_pass};
78 use rustc_span::symbol::SymbolStr;
79 use rustc_span::{sym, Span};
80 use rustc_typeck::hir_ty_to_ty;
82 declare_clippy_lint! {
84 /// Checks for usages of `cloned()` on an `Iterator` or `Option` where
85 /// `copied()` could be used instead.
87 /// ### Why is this bad?
88 /// `copied()` is better because it guarantees that the type being cloned
89 /// implements `Copy`.
93 /// [1, 2, 3].iter().cloned();
97 /// [1, 2, 3].iter().copied();
99 pub CLONED_INSTEAD_OF_COPIED,
101 "used `cloned` where `copied` could be used instead"
104 declare_clippy_lint! {
106 /// Checks for usages of `Iterator::flat_map()` where `filter_map()` could be
109 /// ### Why is this bad?
110 /// When applicable, `filter_map()` is more clear since it shows that
111 /// `Option` is used to produce 0 or 1 items.
115 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().flat_map(|x| x.parse().ok()).collect();
119 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().filter_map(|x| x.parse().ok()).collect();
123 "used `flat_map` where `filter_map` could be used instead"
126 declare_clippy_lint! {
128 /// Checks for `.unwrap()` calls on `Option`s and on `Result`s.
130 /// ### Why is this bad?
131 /// It is better to handle the `None` or `Err` case,
132 /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
133 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
134 /// `Allow` by default.
136 /// `result.unwrap()` will let the thread panic on `Err` values.
137 /// Normally, you want to implement more sophisticated error handling,
138 /// and propagate errors upwards with `?` operator.
140 /// Even if you want to panic on errors, not all `Error`s implement good
141 /// messages on display. Therefore, it may be beneficial to look at the places
142 /// where they may get displayed. Activate this lint to do just that.
146 /// # let opt = Some(1);
152 /// opt.expect("more helpful message");
158 /// # let res: Result<usize, ()> = Ok(1);
164 /// res.expect("more helpful message");
168 "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
171 declare_clippy_lint! {
173 /// Checks for `.expect()` calls on `Option`s and `Result`s.
175 /// ### Why is this bad?
176 /// Usually it is better to handle the `None` or `Err` case.
177 /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
178 /// this lint is `Allow` by default.
180 /// `result.expect()` will let the thread panic on `Err`
181 /// values. Normally, you want to implement more sophisticated error handling,
182 /// and propagate errors upwards with `?` operator.
186 /// # let opt = Some(1);
189 /// opt.expect("one");
192 /// let opt = Some(1);
199 /// # let res: Result<usize, ()> = Ok(1);
202 /// res.expect("one");
206 /// # Ok::<(), ()>(())
210 "using `.expect()` on `Result` or `Option`, which might be better handled"
213 declare_clippy_lint! {
215 /// Checks for methods that should live in a trait
216 /// implementation of a `std` trait (see [llogiq's blog
217 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
218 /// information) instead of an inherent implementation.
220 /// ### Why is this bad?
221 /// Implementing the traits improve ergonomics for users of
222 /// the code, often with very little cost. Also people seeing a `mul(...)`
224 /// may expect `*` to work equally, so you should have good reason to disappoint
231 /// fn add(&self, other: &X) -> X {
237 pub SHOULD_IMPLEMENT_TRAIT,
239 "defining a method that should be implementing a std trait"
242 declare_clippy_lint! {
244 /// Checks for methods with certain name prefixes and which
245 /// doesn't match how self is taken. The actual rules are:
247 /// |Prefix |Postfix |`self` taken | `self` type |
248 /// |-------|------------|-----------------------|--------------|
249 /// |`as_` | none |`&self` or `&mut self` | any |
250 /// |`from_`| none | none | any |
251 /// |`into_`| none |`self` | any |
252 /// |`is_` | none |`&self` or none | any |
253 /// |`to_` | `_mut` |`&mut self` | any |
254 /// |`to_` | not `_mut` |`self` | `Copy` |
255 /// |`to_` | not `_mut` |`&self` | not `Copy` |
257 /// Note: Clippy doesn't trigger methods with `to_` prefix in:
258 /// - Traits definition.
259 /// Clippy can not tell if a type that implements a trait is `Copy` or not.
260 /// - Traits implementation, when `&self` is taken.
261 /// The method signature is controlled by the trait and often `&self` is required for all types that implement the trait
262 /// (see e.g. the `std::string::ToString` trait).
264 /// Please find more info here:
265 /// https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
267 /// ### Why is this bad?
268 /// Consistency breeds readability. If you follow the
269 /// conventions, your users won't be surprised that they, e.g., need to supply a
270 /// mutable reference to a `as_..` function.
276 /// fn as_str(self) -> &'static str {
282 pub WRONG_SELF_CONVENTION,
284 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
287 declare_clippy_lint! {
289 /// Checks for usage of `ok().expect(..)`.
291 /// ### Why is this bad?
292 /// Because you usually call `expect()` on the `Result`
293 /// directly to get a better error message.
295 /// ### Known problems
296 /// The error type needs to implement `Debug`
300 /// # let x = Ok::<_, ()>(());
303 /// x.ok().expect("why did I do this again?");
306 /// x.expect("why did I do this again?");
310 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
313 declare_clippy_lint! {
315 /// Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
316 /// `result.map(_).unwrap_or_else(_)`.
318 /// ### Why is this bad?
319 /// Readability, these can be written more concisely (resp.) as
320 /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
322 /// ### Known problems
323 /// The order of the arguments is not in execution order
327 /// # let x = Some(1);
330 /// x.map(|a| a + 1).unwrap_or(0);
333 /// x.map_or(0, |a| a + 1);
339 /// # let x: Result<usize, ()> = Ok(1);
340 /// # fn some_function(foo: ()) -> usize { 1 }
343 /// x.map(|a| a + 1).unwrap_or_else(some_function);
346 /// x.map_or_else(some_function, |a| a + 1);
350 "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)`"
353 declare_clippy_lint! {
355 /// Checks for usage of `_.map_or(None, _)`.
357 /// ### Why is this bad?
358 /// Readability, this can be written more concisely as
361 /// ### Known problems
362 /// The order of the arguments is not in execution order.
366 /// # let opt = Some(1);
369 /// opt.map_or(None, |a| Some(a + 1));
372 /// opt.and_then(|a| Some(a + 1));
374 pub OPTION_MAP_OR_NONE,
376 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
379 declare_clippy_lint! {
381 /// Checks for usage of `_.map_or(None, Some)`.
383 /// ### Why is this bad?
384 /// Readability, this can be written more concisely as
390 /// # let r: Result<u32, &str> = Ok(1);
391 /// assert_eq!(Some(1), r.map_or(None, Some));
396 /// # let r: Result<u32, &str> = Ok(1);
397 /// assert_eq!(Some(1), r.ok());
399 pub RESULT_MAP_OR_INTO_OPTION,
401 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
404 declare_clippy_lint! {
406 /// Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
407 /// `_.or_else(|x| Err(y))`.
409 /// ### Why is this bad?
410 /// Readability, this can be written more concisely as
411 /// `_.map(|x| y)` or `_.map_err(|x| y)`.
415 /// # fn opt() -> Option<&'static str> { Some("42") }
416 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
417 /// let _ = opt().and_then(|s| Some(s.len()));
418 /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
419 /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
422 /// The correct use would be:
425 /// # fn opt() -> Option<&'static str> { Some("42") }
426 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
427 /// let _ = opt().map(|s| s.len());
428 /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
429 /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
431 pub BIND_INSTEAD_OF_MAP,
433 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
436 declare_clippy_lint! {
438 /// Checks for usage of `_.filter(_).next()`.
440 /// ### Why is this bad?
441 /// Readability, this can be written more concisely as
446 /// # let vec = vec![1];
447 /// vec.iter().filter(|x| **x == 0).next();
449 /// Could be written as
451 /// # let vec = vec![1];
452 /// vec.iter().find(|x| **x == 0);
456 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
459 declare_clippy_lint! {
461 /// Checks for usage of `_.skip_while(condition).next()`.
463 /// ### Why is this bad?
464 /// Readability, this can be written more concisely as
465 /// `_.find(!condition)`.
469 /// # let vec = vec![1];
470 /// vec.iter().skip_while(|x| **x == 0).next();
472 /// Could be written as
474 /// # let vec = vec![1];
475 /// vec.iter().find(|x| **x != 0);
479 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
482 declare_clippy_lint! {
484 /// Checks for usage of `_.map(_).flatten(_)` on `Iterator` and `Option`
486 /// ### Why is this bad?
487 /// Readability, this can be written more concisely as
492 /// let vec = vec![vec![1]];
495 /// vec.iter().map(|x| x.iter()).flatten();
498 /// vec.iter().flat_map(|x| x.iter());
502 "using combinations of `flatten` and `map` which can usually be written as a single method call"
505 declare_clippy_lint! {
507 /// Checks for usage of `_.filter(_).map(_)` that can be written more simply
508 /// as `filter_map(_)`.
510 /// ### Why is this bad?
511 /// Redundant code in the `filter` and `map` operations is poor style and
518 /// .filter(|n| n.checked_add(1).is_some())
519 /// .map(|n| n.checked_add(1).unwrap());
524 /// (0_i32..10).filter_map(|n| n.checked_add(1));
526 pub MANUAL_FILTER_MAP,
528 "using `_.filter(_).map(_)` in a way that can be written more simply as `filter_map(_)`"
531 declare_clippy_lint! {
533 /// Checks for usage of `_.find(_).map(_)` that can be written more simply
534 /// as `find_map(_)`.
536 /// ### Why is this bad?
537 /// Redundant code in the `find` and `map` operations is poor style and
544 /// .find(|n| n.checked_add(1).is_some())
545 /// .map(|n| n.checked_add(1).unwrap());
550 /// (0_i32..10).find_map(|n| n.checked_add(1));
554 "using `_.find(_).map(_)` in a way that can be written more simply as `find_map(_)`"
557 declare_clippy_lint! {
559 /// Checks for usage of `_.filter_map(_).next()`.
561 /// ### Why is this bad?
562 /// Readability, this can be written more concisely as
567 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
569 /// Can be written as
572 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
576 "using combination of `filter_map` and `next` which can usually be written as a single method call"
579 declare_clippy_lint! {
581 /// Checks for usage of `flat_map(|x| x)`.
583 /// ### Why is this bad?
584 /// Readability, this can be written more concisely by using `flatten`.
588 /// # let iter = vec![vec![0]].into_iter();
589 /// iter.flat_map(|x| x);
591 /// Can be written as
593 /// # let iter = vec![vec![0]].into_iter();
596 pub FLAT_MAP_IDENTITY,
598 "call to `flat_map` where `flatten` is sufficient"
601 declare_clippy_lint! {
603 /// Checks for an iterator or string search (such as `find()`,
604 /// `position()`, or `rposition()`) followed by a call to `is_some()` or `is_none()`.
606 /// ### Why is this bad?
607 /// Readability, this can be written more concisely as:
608 /// * `_.any(_)`, or `_.contains(_)` for `is_some()`,
609 /// * `!_.any(_)`, or `!_.contains(_)` for `is_none()`.
613 /// let vec = vec![1];
614 /// vec.iter().find(|x| **x == 0).is_some();
616 /// let _ = "hello world".find("world").is_none();
618 /// Could be written as
620 /// let vec = vec![1];
621 /// vec.iter().any(|x| *x == 0);
623 /// let _ = !"hello world".contains("world");
627 "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()`)"
630 declare_clippy_lint! {
632 /// Checks for usage of `.chars().next()` on a `str` to check
633 /// if it starts with a given char.
635 /// ### Why is this bad?
636 /// Readability, this can be written more concisely as
637 /// `_.starts_with(_)`.
641 /// let name = "foo";
642 /// if name.chars().next() == Some('_') {};
644 /// Could be written as
646 /// let name = "foo";
647 /// if name.starts_with('_') {};
651 "using `.chars().next()` to check if a string starts with a char"
654 declare_clippy_lint! {
656 /// Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
657 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
658 /// `unwrap_or_default` instead.
660 /// ### Why is this bad?
661 /// The function will always be called and potentially
662 /// allocate an object acting as the default.
664 /// ### Known problems
665 /// If the function has side-effects, not calling it will
666 /// change the semantic of the program, but you shouldn't rely on that anyway.
670 /// # let foo = Some(String::new());
671 /// foo.unwrap_or(String::new());
673 /// this can instead be written:
675 /// # let foo = Some(String::new());
676 /// foo.unwrap_or_else(String::new);
680 /// # let foo = Some(String::new());
681 /// foo.unwrap_or_default();
685 "using any `*or` method with a function call, which suggests `*or_else`"
688 declare_clippy_lint! {
690 /// Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
691 /// etc., and suggests to use `unwrap_or_else` instead
693 /// ### Why is this bad?
694 /// The function will always be called.
696 /// ### Known problems
697 /// If the function has side-effects, not calling it will
698 /// change the semantics of the program, but you shouldn't rely on that anyway.
702 /// # let foo = Some(String::new());
703 /// # let err_code = "418";
704 /// # let err_msg = "I'm a teapot";
705 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
709 /// # let foo = Some(String::new());
710 /// # let err_code = "418";
711 /// # let err_msg = "I'm a teapot";
712 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
714 /// this can instead be written:
716 /// # let foo = Some(String::new());
717 /// # let err_code = "418";
718 /// # let err_msg = "I'm a teapot";
719 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
723 "using any `expect` method with a function call"
726 declare_clippy_lint! {
728 /// Checks for usage of `.clone()` on a `Copy` type.
730 /// ### Why is this bad?
731 /// The only reason `Copy` types implement `Clone` is for
732 /// generics, not for using the `clone` method on a concrete type.
740 "using `clone` on a `Copy` type"
743 declare_clippy_lint! {
745 /// Checks for usage of `.clone()` on a ref-counted pointer,
746 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
747 /// function syntax instead (e.g., `Rc::clone(foo)`).
749 /// ### Why is this bad?
750 /// Calling '.clone()' on an Rc, Arc, or Weak
751 /// can obscure the fact that only the pointer is being cloned, not the underlying
756 /// # use std::rc::Rc;
757 /// let x = Rc::new(1);
765 pub CLONE_ON_REF_PTR,
767 "using 'clone' on a ref-counted pointer"
770 declare_clippy_lint! {
772 /// Checks for usage of `.clone()` on an `&&T`.
774 /// ### Why is this bad?
775 /// Cloning an `&&T` copies the inner `&T`, instead of
776 /// cloning the underlying `T`.
783 /// let z = y.clone();
784 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
787 pub CLONE_DOUBLE_REF,
789 "using `clone` on `&&T`"
792 declare_clippy_lint! {
794 /// Checks for usage of `.to_string()` on an `&&T` where
795 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
797 /// ### Why is this bad?
798 /// This bypasses the specialized implementation of
799 /// `ToString` and instead goes through the more expensive string formatting
804 /// // Generic implementation for `T: Display` is used (slow)
805 /// ["foo", "bar"].iter().map(|s| s.to_string());
807 /// // OK, the specialized impl is used
808 /// ["foo", "bar"].iter().map(|&s| s.to_string());
810 pub INEFFICIENT_TO_STRING,
812 "using `to_string` on `&&T` where `T: ToString`"
815 declare_clippy_lint! {
817 /// Checks for `new` not returning a type that contains `Self`.
819 /// ### Why is this bad?
820 /// As a convention, `new` methods are used to make a new
821 /// instance of a type.
824 /// In an impl block:
827 /// # struct NotAFoo;
829 /// fn new() -> NotAFoo {
839 /// // Bad. The type name must contain `Self`
840 /// fn new() -> Bar {
848 /// # struct FooError;
850 /// // Good. Return type contains `Self`
851 /// fn new() -> Result<Foo, FooError> {
857 /// Or in a trait definition:
859 /// pub trait Trait {
860 /// // Bad. The type name must contain `Self`
866 /// pub trait Trait {
867 /// // Good. Return type contains `Self`
868 /// fn new() -> Self;
873 "not returning type containing `Self` in a `new` method"
876 declare_clippy_lint! {
878 /// Checks for string methods that receive a single-character
879 /// `str` as an argument, e.g., `_.split("x")`.
881 /// ### Why is this bad?
882 /// Performing these methods using a `char` is faster than
885 /// ### Known problems
886 /// Does not catch multi-byte unicode characters.
895 pub SINGLE_CHAR_PATTERN,
897 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
900 declare_clippy_lint! {
902 /// Checks for calling `.step_by(0)` on iterators which panics.
904 /// ### Why is this bad?
905 /// This very much looks like an oversight. Use `panic!()` instead if you
906 /// actually intend to panic.
909 /// ```rust,should_panic
910 /// for x in (0..100).step_by(0) {
914 pub ITERATOR_STEP_BY_ZERO,
916 "using `Iterator::step_by(0)`, which will panic at runtime"
919 declare_clippy_lint! {
921 /// Checks for indirect collection of populated `Option`
923 /// ### Why is this bad?
924 /// `Option` is like a collection of 0-1 things, so `flatten`
925 /// automatically does this without suspicious-looking `unwrap` calls.
929 /// let _ = std::iter::empty::<Option<i32>>().filter(Option::is_some).map(Option::unwrap);
933 /// let _ = std::iter::empty::<Option<i32>>().flatten();
935 pub OPTION_FILTER_MAP,
937 "filtering `Option` for `Some` then force-unwrapping, which can be one type-safe operation"
940 declare_clippy_lint! {
942 /// Checks for the use of `iter.nth(0)`.
944 /// ### Why is this bad?
945 /// `iter.next()` is equivalent to
946 /// `iter.nth(0)`, as they both consume the next element,
947 /// but is more readable.
951 /// # use std::collections::HashSet;
953 /// # let mut s = HashSet::new();
955 /// let x = s.iter().nth(0);
958 /// # let mut s = HashSet::new();
960 /// let x = s.iter().next();
964 "replace `iter.nth(0)` with `iter.next()`"
967 declare_clippy_lint! {
969 /// Checks for use of `.iter().nth()` (and the related
970 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
972 /// ### Why is this bad?
973 /// `.get()` and `.get_mut()` are more efficient and more
978 /// let some_vec = vec![0, 1, 2, 3];
979 /// let bad_vec = some_vec.iter().nth(3);
980 /// let bad_slice = &some_vec[..].iter().nth(3);
982 /// The correct use would be:
984 /// let some_vec = vec![0, 1, 2, 3];
985 /// let bad_vec = some_vec.get(3);
986 /// let bad_slice = &some_vec[..].get(3);
990 "using `.iter().nth()` on a standard library type with O(1) element access"
993 declare_clippy_lint! {
995 /// Checks for use of `.skip(x).next()` on iterators.
997 /// ### Why is this bad?
998 /// `.nth(x)` is cleaner
1002 /// let some_vec = vec![0, 1, 2, 3];
1003 /// let bad_vec = some_vec.iter().skip(3).next();
1004 /// let bad_slice = &some_vec[..].iter().skip(3).next();
1006 /// The correct use would be:
1008 /// let some_vec = vec![0, 1, 2, 3];
1009 /// let bad_vec = some_vec.iter().nth(3);
1010 /// let bad_slice = &some_vec[..].iter().nth(3);
1014 "using `.skip(x).next()` on an iterator"
1017 declare_clippy_lint! {
1018 /// ### What it does
1019 /// Checks for use of `.get().unwrap()` (or
1020 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
1022 /// ### Why is this bad?
1023 /// Using the Index trait (`[]`) is more clear and more
1026 /// ### Known problems
1027 /// Not a replacement for error handling: Using either
1028 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
1029 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
1030 /// temporary placeholder for dealing with the `Option` type, then this does
1031 /// not mitigate the need for error handling. If there is a chance that `.get()`
1032 /// will be `None` in your program, then it is advisable that the `None` case
1033 /// is handled in a future refactor instead of using `.unwrap()` or the Index
1038 /// let mut some_vec = vec![0, 1, 2, 3];
1039 /// let last = some_vec.get(3).unwrap();
1040 /// *some_vec.get_mut(0).unwrap() = 1;
1042 /// The correct use would be:
1044 /// let mut some_vec = vec![0, 1, 2, 3];
1045 /// let last = some_vec[3];
1046 /// some_vec[0] = 1;
1050 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
1053 declare_clippy_lint! {
1054 /// ### What it does
1055 /// Checks for occurrences where one vector gets extended instead of append
1057 /// ### Why is this bad?
1058 /// Using `append` instead of `extend` is more concise and faster
1062 /// let mut a = vec![1, 2, 3];
1063 /// let mut b = vec![4, 5, 6];
1066 /// a.extend(b.drain(..));
1069 /// a.append(&mut b);
1071 pub EXTEND_WITH_DRAIN,
1073 "using vec.append(&mut vec) to move the full range of a vecor to another"
1076 declare_clippy_lint! {
1077 /// ### What it does
1078 /// Checks for the use of `.extend(s.chars())` where s is a
1079 /// `&str` or `String`.
1081 /// ### Why is this bad?
1082 /// `.push_str(s)` is clearer
1086 /// let abc = "abc";
1087 /// let def = String::from("def");
1088 /// let mut s = String::new();
1089 /// s.extend(abc.chars());
1090 /// s.extend(def.chars());
1092 /// The correct use would be:
1094 /// let abc = "abc";
1095 /// let def = String::from("def");
1096 /// let mut s = String::new();
1097 /// s.push_str(abc);
1098 /// s.push_str(&def);
1100 pub STRING_EXTEND_CHARS,
1102 "using `x.extend(s.chars())` where s is a `&str` or `String`"
1105 declare_clippy_lint! {
1106 /// ### What it does
1107 /// Checks for the use of `.cloned().collect()` on slice to
1110 /// ### Why is this bad?
1111 /// `.to_vec()` is clearer
1115 /// let s = [1, 2, 3, 4, 5];
1116 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1118 /// The better use would be:
1120 /// let s = [1, 2, 3, 4, 5];
1121 /// let s2: Vec<isize> = s.to_vec();
1123 pub ITER_CLONED_COLLECT,
1125 "using `.cloned().collect()` on slice to create a `Vec`"
1128 declare_clippy_lint! {
1129 /// ### What it does
1130 /// Checks for usage of `_.chars().last()` or
1131 /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1133 /// ### Why is this bad?
1134 /// Readability, this can be written more concisely as
1135 /// `_.ends_with(_)`.
1139 /// # let name = "_";
1142 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1145 /// name.ends_with('_') || name.ends_with('-');
1149 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1152 declare_clippy_lint! {
1153 /// ### What it does
1154 /// Checks for usage of `.as_ref()` or `.as_mut()` where the
1155 /// types before and after the call are the same.
1157 /// ### Why is this bad?
1158 /// The call is unnecessary.
1162 /// # fn do_stuff(x: &[i32]) {}
1163 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1164 /// do_stuff(x.as_ref());
1166 /// The correct use would be:
1168 /// # fn do_stuff(x: &[i32]) {}
1169 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1174 "using `as_ref` where the types before and after the call are the same"
1177 declare_clippy_lint! {
1178 /// ### What it does
1179 /// Checks for using `fold` when a more succinct alternative exists.
1180 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1181 /// `sum` or `product`.
1183 /// ### Why is this bad?
1188 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1190 /// This could be written as:
1192 /// let _ = (0..3).any(|x| x > 2);
1194 pub UNNECESSARY_FOLD,
1196 "using `fold` when a more succinct alternative exists"
1199 declare_clippy_lint! {
1200 /// ### What it does
1201 /// Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1202 /// More specifically it checks if the closure provided is only performing one of the
1203 /// filter or map operations and suggests the appropriate option.
1205 /// ### Why is this bad?
1206 /// Complexity. The intent is also clearer if only a single
1207 /// operation is being performed.
1211 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1213 /// // As there is no transformation of the argument this could be written as:
1214 /// let _ = (0..3).filter(|&x| x > 2);
1218 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1220 /// // As there is no conditional check on the argument this could be written as:
1221 /// let _ = (0..4).map(|x| x + 1);
1223 pub UNNECESSARY_FILTER_MAP,
1225 "using `filter_map` when a more succinct alternative exists"
1228 declare_clippy_lint! {
1229 /// ### What it does
1230 /// Checks for `into_iter` calls on references which should be replaced by `iter`
1233 /// ### Why is this bad?
1234 /// Readability. Calling `into_iter` on a reference will not move out its
1235 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1236 /// `iter_mut` directly.
1241 /// let _ = (&vec![3, 4, 5]).into_iter();
1244 /// let _ = (&vec![3, 4, 5]).iter();
1246 pub INTO_ITER_ON_REF,
1248 "using `.into_iter()` on a reference"
1251 declare_clippy_lint! {
1252 /// ### What it does
1253 /// Checks for calls to `map` followed by a `count`.
1255 /// ### Why is this bad?
1256 /// It looks suspicious. Maybe `map` was confused with `filter`.
1257 /// If the `map` call is intentional, this should be rewritten. Or, if you intend to
1258 /// drive the iterator to completion, you can just use `for_each` instead.
1262 /// let _ = (0..3).map(|x| x + 2).count();
1266 "suspicious usage of map"
1269 declare_clippy_lint! {
1270 /// ### What it does
1271 /// Checks for `MaybeUninit::uninit().assume_init()`.
1273 /// ### Why is this bad?
1274 /// For most types, this is undefined behavior.
1276 /// ### Known problems
1277 /// For now, we accept empty tuples and tuples / arrays
1278 /// of `MaybeUninit`. There may be other types that allow uninitialized
1279 /// data, but those are not yet rigorously defined.
1283 /// // Beware the UB
1284 /// use std::mem::MaybeUninit;
1286 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1289 /// Note that the following is OK:
1292 /// use std::mem::MaybeUninit;
1294 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1295 /// MaybeUninit::uninit().assume_init()
1298 pub UNINIT_ASSUMED_INIT,
1300 "`MaybeUninit::uninit().assume_init()`"
1303 declare_clippy_lint! {
1304 /// ### What it does
1305 /// Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1307 /// ### Why is this bad?
1308 /// These can be written simply with `saturating_add/sub` methods.
1312 /// # let y: u32 = 0;
1313 /// # let x: u32 = 100;
1314 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1315 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1318 /// can be written using dedicated methods for saturating addition/subtraction as:
1321 /// # let y: u32 = 0;
1322 /// # let x: u32 = 100;
1323 /// let add = x.saturating_add(y);
1324 /// let sub = x.saturating_sub(y);
1326 pub MANUAL_SATURATING_ARITHMETIC,
1328 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1331 declare_clippy_lint! {
1332 /// ### What it does
1333 /// Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1334 /// zero-sized types
1336 /// ### Why is this bad?
1337 /// This is a no-op, and likely unintended
1341 /// unsafe { (&() as *const ()).offset(1) };
1345 "Check for offset calculations on raw pointers to zero-sized types"
1348 declare_clippy_lint! {
1349 /// ### What it does
1350 /// Checks for `FileType::is_file()`.
1352 /// ### Why is this bad?
1353 /// When people testing a file type with `FileType::is_file`
1354 /// they are testing whether a path is something they can get bytes from. But
1355 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1356 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1361 /// let metadata = std::fs::metadata("foo.txt")?;
1362 /// let filetype = metadata.file_type();
1364 /// if filetype.is_file() {
1367 /// # Ok::<_, std::io::Error>(())
1371 /// should be written as:
1375 /// let metadata = std::fs::metadata("foo.txt")?;
1376 /// let filetype = metadata.file_type();
1378 /// if !filetype.is_dir() {
1381 /// # Ok::<_, std::io::Error>(())
1384 pub FILETYPE_IS_FILE,
1386 "`FileType::is_file` is not recommended to test for readable file type"
1389 declare_clippy_lint! {
1390 /// ### What it does
1391 /// Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1393 /// ### Why is this bad?
1394 /// Readability, this can be written more concisely as
1399 /// # let opt = Some("".to_string());
1400 /// opt.as_ref().map(String::as_str)
1403 /// Can be written as
1405 /// # let opt = Some("".to_string());
1409 pub OPTION_AS_REF_DEREF,
1411 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1414 declare_clippy_lint! {
1415 /// ### What it does
1416 /// Checks for usage of `iter().next()` on a Slice or an Array
1418 /// ### Why is this bad?
1419 /// These can be shortened into `.get()`
1423 /// # let a = [1, 2, 3];
1424 /// # let b = vec![1, 2, 3];
1425 /// a[2..].iter().next();
1426 /// b.iter().next();
1428 /// should be written as:
1430 /// # let a = [1, 2, 3];
1431 /// # let b = vec![1, 2, 3];
1435 pub ITER_NEXT_SLICE,
1437 "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1440 declare_clippy_lint! {
1441 /// ### What it does
1442 /// Warns when using `push_str`/`insert_str` with a single-character string literal
1443 /// where `push`/`insert` with a `char` would work fine.
1445 /// ### Why is this bad?
1446 /// It's less clear that we are pushing a single character.
1450 /// let mut string = String::new();
1451 /// string.insert_str(0, "R");
1452 /// string.push_str("R");
1454 /// Could be written as
1456 /// let mut string = String::new();
1457 /// string.insert(0, 'R');
1458 /// string.push('R');
1460 pub SINGLE_CHAR_ADD_STR,
1462 "`push_str()` or `insert_str()` used with a single-character string literal as parameter"
1465 declare_clippy_lint! {
1466 /// ### What it does
1467 /// As the counterpart to `or_fun_call`, this lint looks for unnecessary
1468 /// lazily evaluated closures on `Option` and `Result`.
1470 /// This lint suggests changing the following functions, when eager evaluation results in
1472 /// - `unwrap_or_else` to `unwrap_or`
1473 /// - `and_then` to `and`
1474 /// - `or_else` to `or`
1475 /// - `get_or_insert_with` to `get_or_insert`
1476 /// - `ok_or_else` to `ok_or`
1478 /// ### Why is this bad?
1479 /// Using eager evaluation is shorter and simpler in some cases.
1481 /// ### Known problems
1482 /// It is possible, but not recommended for `Deref` and `Index` to have
1483 /// side effects. Eagerly evaluating them can change the semantics of the program.
1487 /// // example code where clippy issues a warning
1488 /// let opt: Option<u32> = None;
1490 /// opt.unwrap_or_else(|| 42);
1494 /// let opt: Option<u32> = None;
1496 /// opt.unwrap_or(42);
1498 pub UNNECESSARY_LAZY_EVALUATIONS,
1500 "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1503 declare_clippy_lint! {
1504 /// ### What it does
1505 /// Checks for usage of `_.map(_).collect::<Result<(), _>()`.
1507 /// ### Why is this bad?
1508 /// Using `try_for_each` instead is more readable and idiomatic.
1512 /// (0..3).map(|t| Err(t)).collect::<Result<(), _>>();
1516 /// (0..3).try_for_each(|t| Err(t));
1518 pub MAP_COLLECT_RESULT_UNIT,
1520 "using `.map(_).collect::<Result<(),_>()`, which can be replaced with `try_for_each`"
1523 declare_clippy_lint! {
1524 /// ### What it does
1525 /// Checks for `from_iter()` function calls on types that implement the `FromIterator`
1528 /// ### Why is this bad?
1529 /// It is recommended style to use collect. See
1530 /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
1534 /// use std::iter::FromIterator;
1536 /// let five_fives = std::iter::repeat(5).take(5);
1538 /// let v = Vec::from_iter(five_fives);
1540 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1544 /// let five_fives = std::iter::repeat(5).take(5);
1546 /// let v: Vec<i32> = five_fives.collect();
1548 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1550 pub FROM_ITER_INSTEAD_OF_COLLECT,
1552 "use `.collect()` instead of `::from_iter()`"
1555 declare_clippy_lint! {
1556 /// ### What it does
1557 /// Checks for usage of `inspect().for_each()`.
1559 /// ### Why is this bad?
1560 /// It is the same as performing the computation
1561 /// inside `inspect` at the beginning of the closure in `for_each`.
1565 /// [1,2,3,4,5].iter()
1566 /// .inspect(|&x| println!("inspect the number: {}", x))
1567 /// .for_each(|&x| {
1568 /// assert!(x >= 0);
1571 /// Can be written as
1573 /// [1,2,3,4,5].iter()
1574 /// .for_each(|&x| {
1575 /// println!("inspect the number: {}", x);
1576 /// assert!(x >= 0);
1579 pub INSPECT_FOR_EACH,
1581 "using `.inspect().for_each()`, which can be replaced with `.for_each()`"
1584 declare_clippy_lint! {
1585 /// ### What it does
1586 /// Checks for usage of `filter_map(|x| x)`.
1588 /// ### Why is this bad?
1589 /// Readability, this can be written more concisely by using `flatten`.
1593 /// # let iter = vec![Some(1)].into_iter();
1594 /// iter.filter_map(|x| x);
1598 /// # let iter = vec![Some(1)].into_iter();
1601 pub FILTER_MAP_IDENTITY,
1603 "call to `filter_map` where `flatten` is sufficient"
1606 declare_clippy_lint! {
1607 /// ### What it does
1608 /// Checks for instances of `map(f)` where `f` is the identity function.
1610 /// ### Why is this bad?
1611 /// It can be written more concisely without the call to `map`.
1615 /// let x = [1, 2, 3];
1616 /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
1620 /// let x = [1, 2, 3];
1621 /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
1625 "using iterator.map(|x| x)"
1628 declare_clippy_lint! {
1629 /// ### What it does
1630 /// Checks for the use of `.bytes().nth()`.
1632 /// ### Why is this bad?
1633 /// `.as_bytes().get()` is more efficient and more
1639 /// let _ = "Hello".bytes().nth(3);
1642 /// let _ = "Hello".as_bytes().get(3);
1646 "replace `.bytes().nth()` with `.as_bytes().get()`"
1649 declare_clippy_lint! {
1650 /// ### What it does
1651 /// Checks for the usage of `_.to_owned()`, `vec.to_vec()`, or similar when calling `_.clone()` would be clearer.
1653 /// ### Why is this bad?
1654 /// These methods do the same thing as `_.clone()` but may be confusing as
1655 /// to why we are calling `to_vec` on something that is already a `Vec` or calling `to_owned` on something that is already owned.
1659 /// let a = vec![1, 2, 3];
1660 /// let b = a.to_vec();
1661 /// let c = a.to_owned();
1665 /// let a = vec![1, 2, 3];
1666 /// let b = a.clone();
1667 /// let c = a.clone();
1671 "implicitly cloning a value by invoking a function on its dereferenced type"
1674 declare_clippy_lint! {
1675 /// ### What it does
1676 /// Checks for the use of `.iter().count()`.
1678 /// ### Why is this bad?
1679 /// `.len()` is more efficient and more
1685 /// let some_vec = vec![0, 1, 2, 3];
1686 /// let _ = some_vec.iter().count();
1687 /// let _ = &some_vec[..].iter().count();
1690 /// let some_vec = vec![0, 1, 2, 3];
1691 /// let _ = some_vec.len();
1692 /// let _ = &some_vec[..].len();
1696 "replace `.iter().count()` with `.len()`"
1699 declare_clippy_lint! {
1700 /// ### What it does
1701 /// Checks for calls to [`splitn`]
1702 /// (https://doc.rust-lang.org/std/primitive.str.html#method.splitn) and
1703 /// related functions with either zero or one splits.
1705 /// ### Why is this bad?
1706 /// These calls don't actually split the value and are
1707 /// likely to be intended as a different number.
1713 /// for x in s.splitn(1, ":") {
1719 /// for x in s.splitn(2, ":") {
1723 pub SUSPICIOUS_SPLITN,
1725 "checks for `.splitn(0, ..)` and `.splitn(1, ..)`"
1728 declare_clippy_lint! {
1729 /// ### What it does
1730 /// Checks for manual implementations of `str::repeat`
1732 /// ### Why is this bad?
1733 /// These are both harder to read, as well as less performant.
1738 /// let x: String = std::iter::repeat('x').take(10).collect();
1741 /// let x: String = "x".repeat(10);
1743 pub MANUAL_STR_REPEAT,
1745 "manual implementation of `str::repeat`"
1748 pub struct Methods {
1749 avoid_breaking_exported_api: bool,
1750 msrv: Option<RustcVersion>,
1755 pub fn new(avoid_breaking_exported_api: bool, msrv: Option<RustcVersion>) -> Self {
1757 avoid_breaking_exported_api,
1763 impl_lint_pass!(Methods => [
1766 SHOULD_IMPLEMENT_TRAIT,
1767 WRONG_SELF_CONVENTION,
1770 RESULT_MAP_OR_INTO_OPTION,
1772 BIND_INSTEAD_OF_MAP,
1780 CLONED_INSTEAD_OF_COPIED,
1782 INEFFICIENT_TO_STRING,
1784 SINGLE_CHAR_PATTERN,
1785 SINGLE_CHAR_ADD_STR,
1789 FILTER_MAP_IDENTITY,
1797 ITERATOR_STEP_BY_ZERO,
1805 STRING_EXTEND_CHARS,
1806 ITER_CLONED_COLLECT,
1809 UNNECESSARY_FILTER_MAP,
1812 UNINIT_ASSUMED_INIT,
1813 MANUAL_SATURATING_ARITHMETIC,
1816 OPTION_AS_REF_DEREF,
1817 UNNECESSARY_LAZY_EVALUATIONS,
1818 MAP_COLLECT_RESULT_UNIT,
1819 FROM_ITER_INSTEAD_OF_COLLECT,
1827 /// Extracts a method call name, args, and `Span` of the method name.
1828 fn method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(SymbolStr, &'tcx [hir::Expr<'tcx>], Span)> {
1829 if let ExprKind::MethodCall(path, span, args, _) = recv.kind {
1830 if !args.iter().any(|e| e.span.from_expansion()) {
1831 return Some((path.ident.name.as_str(), args, span));
1837 /// Same as `method_call` but the `SymbolStr` is dereferenced into a temporary `&str`
1838 macro_rules! method_call {
1842 .map(|&(ref name, args, span)| (&**name, args, span))
1846 impl<'tcx> LateLintPass<'tcx> for Methods {
1847 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1848 if in_macro(expr.span) {
1852 check_methods(cx, expr, self.msrv.as_ref());
1855 hir::ExprKind::Call(func, args) => {
1856 from_iter_instead_of_collect::check(cx, expr, args, func);
1858 hir::ExprKind::MethodCall(method_call, ref method_span, args, _) => {
1859 or_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1860 expect_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1861 clone_on_copy::check(cx, expr, method_call.ident.name, args);
1862 clone_on_ref_ptr::check(cx, expr, method_call.ident.name, args);
1863 inefficient_to_string::check(cx, expr, method_call.ident.name, args);
1864 single_char_add_str::check(cx, expr, args);
1865 into_iter_on_ref::check(cx, expr, *method_span, method_call.ident.name, args);
1866 single_char_pattern::check(cx, expr, method_call.ident.name, args);
1868 hir::ExprKind::Binary(op, lhs, rhs) if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne => {
1869 let mut info = BinaryExprInfo {
1873 eq: op.node == hir::BinOpKind::Eq,
1875 lint_binary_expr_with_method_call(cx, &mut info);
1881 #[allow(clippy::too_many_lines)]
1882 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1883 if in_external_macro(cx.sess(), impl_item.span) {
1886 let name = impl_item.ident.name.as_str();
1887 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
1888 let item = cx.tcx.hir().expect_item(parent);
1889 let self_ty = cx.tcx.type_of(item.def_id);
1891 let implements_trait = matches!(item.kind, hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }));
1893 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1894 if let Some(first_arg) = iter_input_pats(sig.decl, cx.tcx.hir().body(id)).next();
1896 let method_sig = cx.tcx.fn_sig(impl_item.def_id);
1897 let method_sig = cx.tcx.erase_late_bound_regions(method_sig);
1899 let first_arg_ty = &method_sig.inputs().iter().next();
1901 // check conventions w.r.t. conversion method names and predicates
1902 if let Some(first_arg_ty) = first_arg_ty;
1905 // if this impl block implements a trait, lint in trait definition instead
1906 if !implements_trait && cx.access_levels.is_exported(impl_item.def_id) {
1907 // check missing trait implementations
1908 for method_config in &TRAIT_METHODS {
1909 if name == method_config.method_name &&
1910 sig.decl.inputs.len() == method_config.param_count &&
1911 method_config.output_type.matches(&sig.decl.output) &&
1912 method_config.self_kind.matches(cx, self_ty, first_arg_ty) &&
1913 fn_header_equals(method_config.fn_header, sig.header) &&
1914 method_config.lifetime_param_cond(impl_item)
1918 SHOULD_IMPLEMENT_TRAIT,
1921 "method `{}` can be confused for the standard trait method `{}::{}`",
1922 method_config.method_name,
1923 method_config.trait_name,
1924 method_config.method_name
1928 "consider implementing the trait `{}` or choosing a less ambiguous method name",
1929 method_config.trait_name
1936 if sig.decl.implicit_self.has_implicit_self()
1937 && !(self.avoid_breaking_exported_api
1938 && cx.access_levels.is_exported(impl_item.def_id))
1940 wrong_self_convention::check(
1953 // if this impl block implements a trait, lint in trait definition instead
1954 if implements_trait {
1958 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
1959 let ret_ty = return_ty(cx, impl_item.hir_id());
1961 // walk the return type and check for Self (this does not check associated types)
1962 if let Some(self_adt) = self_ty.ty_adt_def() {
1963 if contains_adt_constructor(ret_ty, self_adt) {
1966 } else if contains_ty(ret_ty, self_ty) {
1970 // if return type is impl trait, check the associated types
1971 if let ty::Opaque(def_id, _) = *ret_ty.kind() {
1972 // one of the associated types must be Self
1973 for &(predicate, _span) in cx.tcx.explicit_item_bounds(def_id) {
1974 if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
1975 // walk the associated type and check for Self
1976 if let Some(self_adt) = self_ty.ty_adt_def() {
1977 if contains_adt_constructor(projection_predicate.ty, self_adt) {
1980 } else if contains_ty(projection_predicate.ty, self_ty) {
1987 if name == "new" && !TyS::same_type(ret_ty, self_ty) {
1992 "methods called `new` usually return `Self`",
1998 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1999 if in_external_macro(cx.tcx.sess, item.span) {
2004 if let TraitItemKind::Fn(ref sig, _) = item.kind;
2005 if sig.decl.implicit_self.has_implicit_self();
2006 if let Some(first_arg_ty) = sig.decl.inputs.iter().next();
2009 let first_arg_span = first_arg_ty.span;
2010 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
2011 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
2012 wrong_self_convention::check(
2014 &item.ident.name.as_str(),
2025 if item.ident.name == sym::new;
2026 if let TraitItemKind::Fn(_, _) = item.kind;
2027 let ret_ty = return_ty(cx, item.hir_id());
2028 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
2029 if !contains_ty(ret_ty, self_ty);
2036 "methods called `new` usually return `Self`",
2042 extract_msrv_attr!(LateContext);
2045 #[allow(clippy::too_many_lines)]
2046 fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>) {
2047 if let Some((name, [recv, args @ ..], span)) = method_call!(expr) {
2048 match (name, args) {
2049 ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
2050 zst_offset::check(cx, expr, recv);
2052 ("and_then", [arg]) => {
2053 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::check(cx, expr, recv, arg);
2054 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::check(cx, expr, recv, arg);
2055 if !biom_option_linted && !biom_result_linted {
2056 unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
2059 ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
2060 ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
2061 ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
2062 ("cloned", []) => cloned_instead_of_copied::check(cx, expr, recv, span, msrv),
2063 ("collect", []) => match method_call!(recv) {
2064 Some(("cloned", [recv2], _)) => iter_cloned_collect::check(cx, expr, recv2),
2065 Some(("map", [m_recv, m_arg], _)) => {
2066 map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
2068 Some(("take", [take_self_arg, take_arg], _)) => {
2069 if meets_msrv(msrv, &msrvs::STR_REPEAT) {
2070 manual_str_repeat::check(cx, expr, recv, take_self_arg, take_arg);
2075 ("count", []) => match method_call!(recv) {
2076 Some((name @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
2077 iter_count::check(cx, expr, recv2, name);
2079 Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
2082 ("expect", [_]) => match method_call!(recv) {
2083 Some(("ok", [recv], _)) => ok_expect::check(cx, expr, recv),
2084 _ => expect_used::check(cx, expr, recv),
2086 ("extend", [arg]) => {
2087 string_extend_chars::check(cx, expr, recv, arg);
2088 extend_with_drain::check(cx, expr, recv, arg);
2090 ("filter_map", [arg]) => {
2091 unnecessary_filter_map::check(cx, expr, arg);
2092 filter_map_identity::check(cx, expr, arg, span);
2094 ("flat_map", [arg]) => {
2095 flat_map_identity::check(cx, expr, arg, span);
2096 flat_map_option::check(cx, expr, arg, span);
2098 ("flatten", []) => {
2099 if let Some(("map", [recv, map_arg], _)) = method_call!(recv) {
2100 map_flatten::check(cx, expr, recv, map_arg);
2103 ("fold", [init, acc]) => unnecessary_fold::check(cx, expr, init, acc, span),
2104 ("for_each", [_]) => {
2105 if let Some(("inspect", [_, _], span2)) = method_call!(recv) {
2106 inspect_for_each::check(cx, expr, span2);
2109 ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
2110 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
2111 ("is_none", []) => check_is_some_is_none(cx, expr, recv, false),
2112 ("is_some", []) => check_is_some_is_none(cx, expr, recv, true),
2113 ("map", [m_arg]) => {
2114 if let Some((name, [recv2, args @ ..], span2)) = method_call!(recv) {
2115 match (name, args) {
2116 ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, msrv),
2117 ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, msrv),
2118 ("filter", [f_arg]) => {
2119 filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, false);
2121 ("find", [f_arg]) => filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, true),
2125 map_identity::check(cx, expr, recv, m_arg, span);
2127 ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
2129 if let Some((name, [recv, args @ ..], _)) = method_call!(recv) {
2130 match (name, args) {
2131 ("filter", [arg]) => filter_next::check(cx, expr, recv, arg),
2132 ("filter_map", [arg]) => filter_map_next::check(cx, expr, recv, arg, msrv),
2133 ("iter", []) => iter_next_slice::check(cx, expr, recv),
2134 ("skip", [arg]) => iter_skip_next::check(cx, expr, recv, arg),
2135 ("skip_while", [_]) => skip_while_next::check(cx, expr),
2140 ("nth", [n_arg]) => match method_call!(recv) {
2141 Some(("bytes", [recv2], _)) => bytes_nth::check(cx, expr, recv2, n_arg),
2142 Some(("iter", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
2143 Some(("iter_mut", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
2144 _ => iter_nth_zero::check(cx, expr, recv, n_arg),
2146 ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
2147 ("or_else", [arg]) => {
2148 if !bind_instead_of_map::ResultOrElseErrInfo::check(cx, expr, recv, arg) {
2149 unnecessary_lazy_eval::check(cx, expr, recv, arg, "or");
2152 ("splitn" | "splitn_mut" | "rsplitn" | "rsplitn_mut", [count_arg, _]) => {
2153 suspicious_splitn::check(cx, name, expr, recv, count_arg);
2155 ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
2156 ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
2157 implicit_clone::check(cx, name, expr, recv, span);
2159 ("unwrap", []) => match method_call!(recv) {
2160 Some(("get", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, false),
2161 Some(("get_mut", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, true),
2162 _ => unwrap_used::check(cx, expr, recv),
2164 ("unwrap_or", [u_arg]) => match method_call!(recv) {
2165 Some((arith @ ("checked_add" | "checked_sub" | "checked_mul"), [lhs, rhs], _)) => {
2166 manual_saturating_arithmetic::check(cx, expr, lhs, rhs, u_arg, &arith["checked_".len()..]);
2168 Some(("map", [m_recv, m_arg], span)) => {
2169 option_map_unwrap_or::check(cx, expr, m_recv, m_arg, recv, u_arg, span);
2173 ("unwrap_or_else", [u_arg]) => match method_call!(recv) {
2174 Some(("map", [recv, map_arg], _)) if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, msrv) => {},
2175 _ => unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or"),
2182 fn check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool) {
2183 if let Some((name @ ("find" | "position" | "rposition"), [f_recv, arg], span)) = method_call!(recv) {
2184 search_is_some::check(cx, expr, name, is_some, f_recv, arg, recv, span);
2188 /// Used for `lint_binary_expr_with_method_call`.
2189 #[derive(Copy, Clone)]
2190 struct BinaryExprInfo<'a> {
2191 expr: &'a hir::Expr<'a>,
2192 chain: &'a hir::Expr<'a>,
2193 other: &'a hir::Expr<'a>,
2197 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2198 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
2199 macro_rules! lint_with_both_lhs_and_rhs {
2200 ($func:expr, $cx:expr, $info:ident) => {
2201 if !$func($cx, $info) {
2202 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2203 if $func($cx, $info) {
2210 lint_with_both_lhs_and_rhs!(chars_next_cmp::check, cx, info);
2211 lint_with_both_lhs_and_rhs!(chars_last_cmp::check, cx, info);
2212 lint_with_both_lhs_and_rhs!(chars_next_cmp_with_unwrap::check, cx, info);
2213 lint_with_both_lhs_and_rhs!(chars_last_cmp_with_unwrap::check, cx, info);
2216 const FN_HEADER: hir::FnHeader = hir::FnHeader {
2217 unsafety: hir::Unsafety::Normal,
2218 constness: hir::Constness::NotConst,
2219 asyncness: hir::IsAsync::NotAsync,
2220 abi: rustc_target::spec::abi::Abi::Rust,
2223 struct ShouldImplTraitCase {
2224 trait_name: &'static str,
2225 method_name: &'static str,
2227 fn_header: hir::FnHeader,
2228 // implicit self kind expected (none, self, &self, ...)
2229 self_kind: SelfKind,
2230 // checks against the output type
2231 output_type: OutType,
2232 // certain methods with explicit lifetimes can't implement the equivalent trait method
2233 lint_explicit_lifetime: bool,
2235 impl ShouldImplTraitCase {
2237 trait_name: &'static str,
2238 method_name: &'static str,
2240 fn_header: hir::FnHeader,
2241 self_kind: SelfKind,
2242 output_type: OutType,
2243 lint_explicit_lifetime: bool,
2244 ) -> ShouldImplTraitCase {
2245 ShouldImplTraitCase {
2252 lint_explicit_lifetime,
2256 fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
2257 self.lint_explicit_lifetime
2258 || !impl_item.generics.params.iter().any(|p| {
2261 hir::GenericParamKind::Lifetime {
2262 kind: hir::LifetimeParamKind::Explicit
2270 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
2271 ShouldImplTraitCase::new("std::ops::Add", "add", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2272 ShouldImplTraitCase::new("std::convert::AsMut", "as_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2273 ShouldImplTraitCase::new("std::convert::AsRef", "as_ref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2274 ShouldImplTraitCase::new("std::ops::BitAnd", "bitand", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2275 ShouldImplTraitCase::new("std::ops::BitOr", "bitor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2276 ShouldImplTraitCase::new("std::ops::BitXor", "bitxor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2277 ShouldImplTraitCase::new("std::borrow::Borrow", "borrow", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2278 ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2279 ShouldImplTraitCase::new("std::clone::Clone", "clone", 1, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2280 ShouldImplTraitCase::new("std::cmp::Ord", "cmp", 2, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2281 // FIXME: default doesn't work
2282 ShouldImplTraitCase::new("std::default::Default", "default", 0, FN_HEADER, SelfKind::No, OutType::Any, true),
2283 ShouldImplTraitCase::new("std::ops::Deref", "deref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2284 ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2285 ShouldImplTraitCase::new("std::ops::Div", "div", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2286 ShouldImplTraitCase::new("std::ops::Drop", "drop", 1, FN_HEADER, SelfKind::RefMut, OutType::Unit, true),
2287 ShouldImplTraitCase::new("std::cmp::PartialEq", "eq", 2, FN_HEADER, SelfKind::Ref, OutType::Bool, true),
2288 ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2289 ShouldImplTraitCase::new("std::str::FromStr", "from_str", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2290 ShouldImplTraitCase::new("std::hash::Hash", "hash", 2, FN_HEADER, SelfKind::Ref, OutType::Unit, true),
2291 ShouldImplTraitCase::new("std::ops::Index", "index", 2, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2292 ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut", 2, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2293 ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2294 ShouldImplTraitCase::new("std::ops::Mul", "mul", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2295 ShouldImplTraitCase::new("std::ops::Neg", "neg", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2296 ShouldImplTraitCase::new("std::iter::Iterator", "next", 1, FN_HEADER, SelfKind::RefMut, OutType::Any, false),
2297 ShouldImplTraitCase::new("std::ops::Not", "not", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2298 ShouldImplTraitCase::new("std::ops::Rem", "rem", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2299 ShouldImplTraitCase::new("std::ops::Shl", "shl", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2300 ShouldImplTraitCase::new("std::ops::Shr", "shr", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2301 ShouldImplTraitCase::new("std::ops::Sub", "sub", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2304 #[derive(Clone, Copy, PartialEq, Debug)]
2313 fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2314 fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2315 if ty == parent_ty {
2317 } else if ty.is_box() {
2318 ty.boxed_ty() == parent_ty
2319 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
2320 if let ty::Adt(_, substs) = ty.kind() {
2321 substs.types().next().map_or(false, |t| t == parent_ty)
2330 fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2331 if let ty::Ref(_, t, m) = *ty.kind() {
2332 return m == mutability && t == parent_ty;
2335 let trait_path = match mutability {
2336 hir::Mutability::Not => &paths::ASREF_TRAIT,
2337 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
2340 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2342 None => return false,
2344 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2348 Self::Value => matches_value(cx, parent_ty, ty),
2349 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
2350 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
2351 Self::No => ty != parent_ty,
2356 fn description(self) -> &'static str {
2358 Self::Value => "`self` by value",
2359 Self::Ref => "`self` by reference",
2360 Self::RefMut => "`self` by mutable reference",
2361 Self::No => "no `self`",
2366 #[derive(Clone, Copy)]
2375 fn matches(self, ty: &hir::FnRetTy<'_>) -> bool {
2376 let is_unit = |ty: &hir::Ty<'_>| matches!(ty.kind, hir::TyKind::Tup(&[]));
2378 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
2379 (Self::Unit, &hir::FnRetTy::Return(ty)) if is_unit(ty) => true,
2380 (Self::Bool, &hir::FnRetTy::Return(ty)) if is_bool(ty) => true,
2381 (Self::Any, &hir::FnRetTy::Return(ty)) if !is_unit(ty) => true,
2382 (Self::Ref, &hir::FnRetTy::Return(ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
2388 fn is_bool(ty: &hir::Ty<'_>) -> bool {
2389 if let hir::TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
2390 matches!(path.res, Res::PrimTy(PrimTy::Bool))
2396 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
2397 expected.constness == actual.constness
2398 && expected.unsafety == actual.unsafety
2399 && expected.asyncness == actual.asyncness