1 mod option_map_unwrap_or;
2 mod unnecessary_filter_map;
8 use if_chain::if_chain;
11 use rustc::hir::intravisit::{self, Visitor};
12 use rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
13 use rustc::ty::{self, Predicate, Ty};
14 use rustc::{declare_lint_pass, declare_tool_lint};
15 use rustc_errors::Applicability;
17 use syntax::source_map::Span;
18 use syntax::symbol::LocalInternedString;
20 use crate::utils::sugg;
21 use crate::utils::usage::mutated_variables;
23 get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, in_macro, is_copy,
24 is_ctor_function, is_expn_of, iter_input_pats, last_path_segment, match_def_path, match_qpath, match_trait_method,
25 match_type, match_var, method_calls, method_chain_args, remove_blocks, return_ty, same_tys, single_segment_path,
26 snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_sugg,
27 span_lint_and_then, span_note_and_lint, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
29 use crate::utils::{paths, span_help_and_lint};
31 declare_clippy_lint! {
32 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
34 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
35 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
36 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
37 /// `Allow` by default.
39 /// **Known problems:** None.
43 /// Using unwrap on an `Option`:
46 /// let opt = Some(1);
53 /// let opt = Some(1);
54 /// opt.expect("more helpful message");
56 pub OPTION_UNWRAP_USED,
58 "using `Option.unwrap()`, which should at least get a better message using `expect()`"
61 declare_clippy_lint! {
62 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
64 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
65 /// values. Normally, you want to implement more sophisticated error handling,
66 /// and propagate errors upwards with `try!`.
68 /// Even if you want to panic on errors, not all `Error`s implement good
69 /// messages on display. Therefore, it may be beneficial to look at the places
70 /// where they may get displayed. Activate this lint to do just that.
72 /// **Known problems:** None.
75 /// Using unwrap on an `Option`:
78 /// let res: Result<usize, ()> = Ok(1);
85 /// let res: Result<usize, ()> = Ok(1);
86 /// res.expect("more helpful message");
88 pub RESULT_UNWRAP_USED,
90 "using `Result.unwrap()`, which might be better handled"
93 declare_clippy_lint! {
94 /// **What it does:** Checks for methods that should live in a trait
95 /// implementation of a `std` trait (see [llogiq's blog
96 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
97 /// information) instead of an inherent implementation.
99 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
100 /// the code, often with very little cost. Also people seeing a `mul(...)`
102 /// may expect `*` to work equally, so you should have good reason to disappoint
105 /// **Known problems:** None.
111 /// fn add(&self, other: &X) -> X {
116 pub SHOULD_IMPLEMENT_TRAIT,
118 "defining a method that should be implementing a std trait"
121 declare_clippy_lint! {
122 /// **What it does:** Checks for methods with certain name prefixes and which
123 /// doesn't match how self is taken. The actual rules are:
125 /// |Prefix |`self` taken |
126 /// |-------|----------------------|
127 /// |`as_` |`&self` or `&mut self`|
129 /// |`into_`|`self` |
130 /// |`is_` |`&self` or none |
131 /// |`to_` |`&self` |
133 /// **Why is this bad?** Consistency breeds readability. If you follow the
134 /// conventions, your users won't be surprised that they, e.g., need to supply a
135 /// mutable reference to a `as_..` function.
137 /// **Known problems:** None.
142 /// fn as_str(self) -> &str {
147 pub WRONG_SELF_CONVENTION,
149 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
152 declare_clippy_lint! {
153 /// **What it does:** This is the same as
154 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
156 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
158 /// **Known problems:** Actually *renaming* the function may break clients if
159 /// the function is part of the public interface. In that case, be mindful of
160 /// the stability guarantees you've given your users.
166 /// pub fn as_str(self) -> &'a str {
171 pub WRONG_PUB_SELF_CONVENTION,
173 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
176 declare_clippy_lint! {
177 /// **What it does:** Checks for usage of `ok().expect(..)`.
179 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
180 /// directly to get a better error message.
182 /// **Known problems:** The error type needs to implement `Debug`
186 /// x.ok().expect("why did I do this again?")
190 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
193 declare_clippy_lint! {
194 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
196 /// **Why is this bad?** Readability, this can be written more concisely as
197 /// `_.map_or(_, _)`.
199 /// **Known problems:** The order of the arguments is not in execution order
203 /// # let x = Some(1);
204 /// x.map(|a| a + 1).unwrap_or(0);
206 pub OPTION_MAP_UNWRAP_OR,
208 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
211 declare_clippy_lint! {
212 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
214 /// **Why is this bad?** Readability, this can be written more concisely as
215 /// `_.map_or_else(_, _)`.
217 /// **Known problems:** The order of the arguments is not in execution order.
221 /// # let x = Some(1);
222 /// # fn some_function() -> usize { 1 }
223 /// x.map(|a| a + 1).unwrap_or_else(some_function);
225 pub OPTION_MAP_UNWRAP_OR_ELSE,
227 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
230 declare_clippy_lint! {
231 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
233 /// **Why is this bad?** Readability, this can be written more concisely as
234 /// `result.ok().map_or_else(_, _)`.
236 /// **Known problems:** None.
240 /// # let x: Result<usize, ()> = Ok(1);
241 /// # fn some_function(foo: ()) -> usize { 1 }
242 /// x.map(|a| a + 1).unwrap_or_else(some_function);
244 pub RESULT_MAP_UNWRAP_OR_ELSE,
246 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.ok().map_or_else(g, f)`"
249 declare_clippy_lint! {
250 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
252 /// **Why is this bad?** Readability, this can be written more concisely as
255 /// **Known problems:** The order of the arguments is not in execution order.
259 /// opt.map_or(None, |a| a + 1)
261 pub OPTION_MAP_OR_NONE,
263 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
266 declare_clippy_lint! {
267 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
269 /// **Why is this bad?** Readability, this can be written more concisely as
272 /// **Known problems:** None
277 /// let x = Some("foo");
278 /// let _ = x.and_then(|s| Some(s.len()));
281 /// The correct use would be:
284 /// let x = Some("foo");
285 /// let _ = x.map(|s| s.len());
287 pub OPTION_AND_THEN_SOME,
289 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
292 declare_clippy_lint! {
293 /// **What it does:** Checks for usage of `_.filter(_).next()`.
295 /// **Why is this bad?** Readability, this can be written more concisely as
298 /// **Known problems:** None.
302 /// # let vec = vec![1];
303 /// vec.iter().filter(|x| **x == 0).next();
307 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
310 declare_clippy_lint! {
311 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
313 /// **Why is this bad?** Readability, this can be written more concisely as a
314 /// single method call.
316 /// **Known problems:**
320 /// let vec = vec![vec![1]];
321 /// vec.iter().map(|x| x.iter()).flatten();
325 "using combinations of `flatten` and `map` which can usually be written as a single method call"
328 declare_clippy_lint! {
329 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
330 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
332 /// **Why is this bad?** Readability, this can be written more concisely as a
333 /// single method call.
335 /// **Known problems:** Often requires a condition + Option/Iterator creation
336 /// inside the closure.
340 /// let vec = vec![1];
341 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
345 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
348 declare_clippy_lint! {
349 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
351 /// **Why is this bad?** Readability, this can be written more concisely as a
352 /// single method call.
354 /// **Known problems:** None
358 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
360 /// Can be written as
363 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
367 "using combination of `filter_map` and `next` which can usually be written as a single method call"
370 declare_clippy_lint! {
371 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
373 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
375 /// **Known problems:** None
379 /// # let iter = vec![vec![0]].into_iter();
380 /// iter.flat_map(|x| x);
382 /// Can be written as
384 /// # let iter = vec![vec![0]].into_iter();
387 pub FLAT_MAP_IDENTITY,
389 "call to `flat_map` where `flatten` is sufficient"
392 declare_clippy_lint! {
393 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
395 /// **Why is this bad?** Readability, this can be written more concisely as a
396 /// single method call.
398 /// **Known problems:** Often requires a condition + Option/Iterator creation
399 /// inside the closure.
403 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
405 /// Can be written as
407 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
411 "using a combination of `find` and `map` can usually be written as a single method call"
414 declare_clippy_lint! {
415 /// **What it does:** Checks for an iterator search (such as `find()`,
416 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
418 /// **Why is this bad?** Readability, this can be written more concisely as
421 /// **Known problems:** None.
425 /// # let vec = vec![1];
426 /// vec.iter().find(|x| **x == 0).is_some();
430 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
433 declare_clippy_lint! {
434 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
435 /// if it starts with a given char.
437 /// **Why is this bad?** Readability, this can be written more concisely as
438 /// `_.starts_with(_)`.
440 /// **Known problems:** None.
444 /// let name = "foo";
445 /// name.chars().next() == Some('_');
449 "using `.chars().next()` to check if a string starts with a char"
452 declare_clippy_lint! {
453 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
454 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
455 /// `unwrap_or_default` instead.
457 /// **Why is this bad?** The function will always be called and potentially
458 /// allocate an object acting as the default.
460 /// **Known problems:** If the function has side-effects, not calling it will
461 /// change the semantic of the program, but you shouldn't rely on that anyway.
465 /// # let foo = Some(String::new());
466 /// foo.unwrap_or(String::new());
468 /// this can instead be written:
470 /// # let foo = Some(String::new());
471 /// foo.unwrap_or_else(String::new);
475 /// # let foo = Some(String::new());
476 /// foo.unwrap_or_default();
480 "using any `*or` method with a function call, which suggests `*or_else`"
483 declare_clippy_lint! {
484 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
485 /// etc., and suggests to use `unwrap_or_else` instead
487 /// **Why is this bad?** The function will always be called.
489 /// **Known problems:** If the function has side-effects, not calling it will
490 /// change the semantics of the program, but you shouldn't rely on that anyway.
494 /// # let foo = Some(String::new());
495 /// # let err_code = "418";
496 /// # let err_msg = "I'm a teapot";
497 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
501 /// # let foo = Some(String::new());
502 /// # let err_code = "418";
503 /// # let err_msg = "I'm a teapot";
504 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
506 /// this can instead be written:
508 /// # let foo = Some(String::new());
509 /// # let err_code = "418";
510 /// # let err_msg = "I'm a teapot";
511 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
515 "using any `expect` method with a function call"
518 declare_clippy_lint! {
519 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
521 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
522 /// generics, not for using the `clone` method on a concrete type.
524 /// **Known problems:** None.
532 "using `clone` on a `Copy` type"
535 declare_clippy_lint! {
536 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
537 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
538 /// function syntax instead (e.g., `Rc::clone(foo)`).
540 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
541 /// can obscure the fact that only the pointer is being cloned, not the underlying
546 /// # use std::rc::Rc;
547 /// let x = Rc::new(1);
550 pub CLONE_ON_REF_PTR,
552 "using 'clone' on a ref-counted pointer"
555 declare_clippy_lint! {
556 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
558 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
559 /// cloning the underlying `T`.
561 /// **Known problems:** None.
568 /// let z = y.clone();
569 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
572 pub CLONE_DOUBLE_REF,
574 "using `clone` on `&&T`"
577 declare_clippy_lint! {
578 /// **What it does:** Checks for `new` not returning `Self`.
580 /// **Why is this bad?** As a convention, `new` methods are used to make a new
581 /// instance of a type.
583 /// **Known problems:** None.
588 /// fn new(..) -> NotAFoo {
594 "not returning `Self` in a `new` method"
597 declare_clippy_lint! {
598 /// **What it does:** Checks for string methods that receive a single-character
599 /// `str` as an argument, e.g., `_.split("x")`.
601 /// **Why is this bad?** Performing these methods using a `char` is faster than
604 /// **Known problems:** Does not catch multi-byte unicode characters.
607 /// `_.split("x")` could be `_.split('x')`
608 pub SINGLE_CHAR_PATTERN,
610 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
613 declare_clippy_lint! {
614 /// **What it does:** Checks for getting the inner pointer of a temporary
617 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
618 /// as the `CString` is alive.
620 /// **Known problems:** None.
624 /// let c_str = CString::new("foo").unwrap().as_ptr();
626 /// call_some_ffi_func(c_str);
629 /// Here `c_str` point to a freed address. The correct use would be:
631 /// let c_str = CString::new("foo").unwrap();
633 /// call_some_ffi_func(c_str.as_ptr());
636 pub TEMPORARY_CSTRING_AS_PTR,
638 "getting the inner pointer of a temporary `CString`"
641 declare_clippy_lint! {
642 /// **What it does:** Checks for use of `.iter().nth()` (and the related
643 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
645 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
648 /// **Known problems:** None.
652 /// let some_vec = vec![0, 1, 2, 3];
653 /// let bad_vec = some_vec.iter().nth(3);
654 /// let bad_slice = &some_vec[..].iter().nth(3);
656 /// The correct use would be:
658 /// let some_vec = vec![0, 1, 2, 3];
659 /// let bad_vec = some_vec.get(3);
660 /// let bad_slice = &some_vec[..].get(3);
664 "using `.iter().nth()` on a standard library type with O(1) element access"
667 declare_clippy_lint! {
668 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
670 /// **Why is this bad?** `.nth(x)` is cleaner
672 /// **Known problems:** None.
676 /// let some_vec = vec![0, 1, 2, 3];
677 /// let bad_vec = some_vec.iter().skip(3).next();
678 /// let bad_slice = &some_vec[..].iter().skip(3).next();
680 /// The correct use would be:
682 /// let some_vec = vec![0, 1, 2, 3];
683 /// let bad_vec = some_vec.iter().nth(3);
684 /// let bad_slice = &some_vec[..].iter().nth(3);
688 "using `.skip(x).next()` on an iterator"
691 declare_clippy_lint! {
692 /// **What it does:** Checks for use of `.get().unwrap()` (or
693 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
695 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
698 /// **Known problems:** Not a replacement for error handling: Using either
699 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
700 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
701 /// temporary placeholder for dealing with the `Option` type, then this does
702 /// not mitigate the need for error handling. If there is a chance that `.get()`
703 /// will be `None` in your program, then it is advisable that the `None` case
704 /// is handled in a future refactor instead of using `.unwrap()` or the Index
709 /// let mut some_vec = vec![0, 1, 2, 3];
710 /// let last = some_vec.get(3).unwrap();
711 /// *some_vec.get_mut(0).unwrap() = 1;
713 /// The correct use would be:
715 /// let mut some_vec = vec![0, 1, 2, 3];
716 /// let last = some_vec[3];
721 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
724 declare_clippy_lint! {
725 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
726 /// `&str` or `String`.
728 /// **Why is this bad?** `.push_str(s)` is clearer
730 /// **Known problems:** None.
735 /// let def = String::from("def");
736 /// let mut s = String::new();
737 /// s.extend(abc.chars());
738 /// s.extend(def.chars());
740 /// The correct use would be:
743 /// let def = String::from("def");
744 /// let mut s = String::new();
746 /// s.push_str(&def);
748 pub STRING_EXTEND_CHARS,
750 "using `x.extend(s.chars())` where s is a `&str` or `String`"
753 declare_clippy_lint! {
754 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
757 /// **Why is this bad?** `.to_vec()` is clearer
759 /// **Known problems:** None.
763 /// let s = [1, 2, 3, 4, 5];
764 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
766 /// The better use would be:
768 /// let s = [1, 2, 3, 4, 5];
769 /// let s2: Vec<isize> = s.to_vec();
771 pub ITER_CLONED_COLLECT,
773 "using `.cloned().collect()` on slice to create a `Vec`"
776 declare_clippy_lint! {
777 /// **What it does:** Checks for usage of `.chars().last()` or
778 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
780 /// **Why is this bad?** Readability, this can be written more concisely as
781 /// `_.ends_with(_)`.
783 /// **Known problems:** None.
787 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
791 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
794 declare_clippy_lint! {
795 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
796 /// types before and after the call are the same.
798 /// **Why is this bad?** The call is unnecessary.
800 /// **Known problems:** None.
804 /// # fn do_stuff(x: &[i32]) {}
805 /// let x: &[i32] = &[1, 2, 3, 4, 5];
806 /// do_stuff(x.as_ref());
808 /// The correct use would be:
810 /// # fn do_stuff(x: &[i32]) {}
811 /// let x: &[i32] = &[1, 2, 3, 4, 5];
816 "using `as_ref` where the types before and after the call are the same"
819 declare_clippy_lint! {
820 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
821 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
822 /// `sum` or `product`.
824 /// **Why is this bad?** Readability.
826 /// **Known problems:** False positive in pattern guards. Will be resolved once
827 /// non-lexical lifetimes are stable.
831 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
833 /// This could be written as:
835 /// let _ = (0..3).any(|x| x > 2);
837 pub UNNECESSARY_FOLD,
839 "using `fold` when a more succinct alternative exists"
842 declare_clippy_lint! {
843 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
844 /// More specifically it checks if the closure provided is only performing one of the
845 /// filter or map operations and suggests the appropriate option.
847 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
848 /// operation is being performed.
850 /// **Known problems:** None
854 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
856 /// As there is no transformation of the argument this could be written as:
858 /// let _ = (0..3).filter(|&x| x > 2);
862 /// let _ = (0..4).filter_map(i32::checked_abs);
864 /// As there is no conditional check on the argument this could be written as:
866 /// let _ = (0..4).map(i32::checked_abs);
868 pub UNNECESSARY_FILTER_MAP,
870 "using `filter_map` when a more succinct alternative exists"
873 declare_clippy_lint! {
874 /// **What it does:** Checks for `into_iter` calls on types which should be replaced by `iter` or
877 /// **Why is this bad?** Arrays and `PathBuf` do not yet have an `into_iter` method which move out
878 /// their content into an iterator. Auto-referencing resolves the `into_iter` call to its reference
879 /// instead, like `<&[T; N] as IntoIterator>::into_iter`, which just iterates over item references
880 /// like calling `iter` would. Furthermore, when the standard library actually
881 /// [implements the `into_iter` method](https://github.com/rust-lang/rust/issues/25725) which moves
882 /// the content out of the array, the original use of `into_iter` got inferred with the wrong type
883 /// and the code will be broken.
885 /// **Known problems:** None
890 /// let _ = [1, 2, 3].into_iter().map(|x| *x).collect::<Vec<u32>>();
892 pub INTO_ITER_ON_ARRAY,
894 "using `.into_iter()` on an array"
897 declare_clippy_lint! {
898 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
901 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
902 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
903 /// `iter_mut` directly.
905 /// **Known problems:** None
910 /// let _ = (&vec![3, 4, 5]).into_iter();
912 pub INTO_ITER_ON_REF,
914 "using `.into_iter()` on a reference"
917 declare_clippy_lint! {
918 /// **What it does:** Checks for calls to `map` followed by a `count`.
920 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
921 /// If the `map` call is intentional, this should be rewritten.
923 /// **Known problems:** None
928 /// let _ = (0..3).map(|x| x + 2).count();
932 "suspicious usage of map"
935 declare_lint_pass!(Methods => [
938 SHOULD_IMPLEMENT_TRAIT,
939 WRONG_SELF_CONVENTION,
940 WRONG_PUB_SELF_CONVENTION,
942 OPTION_MAP_UNWRAP_OR,
943 OPTION_MAP_UNWRAP_OR_ELSE,
944 RESULT_MAP_UNWRAP_OR_ELSE,
946 OPTION_AND_THEN_SOME,
957 TEMPORARY_CSTRING_AS_PTR,
971 UNNECESSARY_FILTER_MAP,
977 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
978 #[allow(clippy::cognitive_complexity)]
979 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
980 if in_macro(expr.span) {
984 let (method_names, arg_lists) = method_calls(expr, 2);
985 let method_names: Vec<LocalInternedString> = method_names.iter().map(|s| s.as_str()).collect();
986 let method_names: Vec<&str> = method_names.iter().map(std::convert::AsRef::as_ref).collect();
988 match method_names.as_slice() {
989 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
990 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
991 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
992 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
993 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0]),
994 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
995 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
996 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
997 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
998 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
999 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1000 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1001 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1002 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1003 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1004 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0]),
1005 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1006 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0]),
1007 ["is_some", "position"] => lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0]),
1008 ["is_some", "rposition"] => lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0]),
1009 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1010 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1011 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1013 ["nth", "iter"] => lint_iter_nth(cx, expr, arg_lists[1], false),
1014 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, arg_lists[1], true),
1015 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1016 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1017 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1018 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1019 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0]),
1020 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1021 ["count", "map"] => lint_suspicious_map(cx, expr),
1026 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1027 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1028 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1030 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1031 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1032 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1033 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1037 ty::Ref(_, ty, _) if ty.sty == ty::Str => {
1038 for &(method, pos) in &PATTERN_METHODS {
1039 if method_call.ident.name.as_str() == method && args.len() > pos {
1040 lint_single_char_pattern(cx, expr, &args[pos]);
1044 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1045 lint_into_iter(cx, expr, self_ty, *method_span);
1050 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1051 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1053 let mut info = BinaryExprInfo {
1057 eq: op.node == hir::BinOpKind::Eq,
1059 lint_binary_expr_with_method_call(cx, &mut info);
1065 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem) {
1066 if in_external_macro(cx.sess(), impl_item.span) {
1069 let name = impl_item.ident.name.as_str();
1070 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1071 let item = cx.tcx.hir().expect_item(parent);
1072 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1073 let ty = cx.tcx.type_of(def_id);
1075 if let hir::ImplItemKind::Method(ref sig, id) = impl_item.node;
1076 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1077 if let hir::ItemKind::Impl(_, _, _, _, None, _, _) = item.node;
1079 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1080 let method_sig = cx.tcx.fn_sig(method_def_id);
1081 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1083 let first_arg_ty = &method_sig.inputs().iter().next();
1085 // check conventions w.r.t. conversion method names and predicates
1086 if let Some(first_arg_ty) = first_arg_ty;
1089 if cx.access_levels.is_exported(impl_item.hir_id) {
1090 // check missing trait implementations
1091 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1092 if name == method_name &&
1093 sig.decl.inputs.len() == n_args &&
1094 out_type.matches(cx, &sig.decl.output) &&
1095 self_kind.matches(cx, ty, first_arg_ty) {
1096 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1097 "defining a method called `{}` on this type; consider implementing \
1098 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1103 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1105 .find(|(ref conv, _)| conv.check(&name))
1107 if !self_kinds.iter().any(|k| k.matches(cx, ty, first_arg_ty)) {
1108 let lint = if item.vis.node.is_pub() {
1109 WRONG_PUB_SELF_CONVENTION
1111 WRONG_SELF_CONVENTION
1119 "methods called `{}` usually take {}; consider choosing a less \
1124 .map(|k| k.description())
1125 .collect::<Vec<_>>()
1134 if let hir::ImplItemKind::Method(_, _) = impl_item.node {
1135 let ret_ty = return_ty(cx, impl_item.hir_id);
1137 // walk the return type and check for Self (this does not check associated types)
1138 if ret_ty.walk().any(|inner_type| same_tys(cx, ty, inner_type)) {
1142 // if return type is impl trait, check the associated types
1143 if let ty::Opaque(def_id, _) = ret_ty.sty {
1144 // one of the associated types must be Self
1145 for predicate in &cx.tcx.predicates_of(def_id).predicates {
1147 (Predicate::Projection(poly_projection_predicate), _) => {
1148 let binder = poly_projection_predicate.ty();
1149 let associated_type = binder.skip_binder();
1151 // walk the associated type and check for Self
1152 for inner_type in associated_type.walk() {
1153 if same_tys(cx, ty, inner_type) {
1163 if name == "new" && !same_tys(cx, ret_ty, ty) {
1168 "methods called `new` usually return `Self`",
1175 /// Checks for the `OR_FUN_CALL` lint.
1176 #[allow(clippy::too_many_lines)]
1177 fn lint_or_fun_call<'a, 'tcx>(
1178 cx: &LateContext<'a, 'tcx>,
1182 args: &'tcx [hir::Expr],
1184 // Searches an expression for method calls or function calls that aren't ctors
1185 struct FunCallFinder<'a, 'tcx> {
1186 cx: &'a LateContext<'a, 'tcx>,
1190 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1191 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
1192 let call_found = match &expr.node {
1193 // ignore enum and struct constructors
1194 hir::ExprKind::Call(..) => !is_ctor_function(self.cx, expr),
1195 hir::ExprKind::MethodCall(..) => true,
1200 // don't lint for constant values
1201 let owner_def = self.cx.tcx.hir().get_parent_did(expr.hir_id);
1202 let promotable = self
1205 .rvalue_promotable_map(owner_def)
1206 .contains(&expr.hir_id.local_id);
1213 intravisit::walk_expr(self, expr);
1217 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1218 intravisit::NestedVisitorMap::None
1222 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1223 fn check_unwrap_or_default(
1224 cx: &LateContext<'_, '_>,
1227 self_expr: &hir::Expr,
1236 if name == "unwrap_or" {
1237 if let hir::ExprKind::Path(ref qpath) = fun.node {
1238 let path = &*last_path_segment(qpath).ident.as_str();
1240 if ["default", "new"].contains(&path) {
1241 let arg_ty = cx.tables.expr_ty(arg);
1242 let default_trait_id = if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT) {
1248 if implements_trait(cx, arg_ty, default_trait_id, &[]) {
1249 let mut applicability = Applicability::MachineApplicable;
1254 &format!("use of `{}` followed by a call to `{}`", name, path),
1257 "{}.unwrap_or_default()",
1258 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1271 /// Checks for `*or(foo())`.
1272 #[allow(clippy::too_many_arguments)]
1273 fn check_general_case<'a, 'tcx>(
1274 cx: &LateContext<'a, 'tcx>,
1278 self_expr: &hir::Expr,
1279 arg: &'tcx hir::Expr,
1283 // (path, fn_has_argument, methods, suffix)
1284 let know_types: &[(&[_], _, &[_], _)] = &[
1285 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1286 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1287 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1288 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1291 // early check if the name is one we care about
1292 if know_types.iter().all(|k| !k.2.contains(&name)) {
1296 let mut finder = FunCallFinder { cx: &cx, found: false };
1297 finder.visit_expr(&arg);
1302 let self_ty = cx.tables.expr_ty(self_expr);
1304 let (fn_has_arguments, poss, suffix) = if let Some(&(_, fn_has_arguments, poss, suffix)) =
1305 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0))
1307 (fn_has_arguments, poss, suffix)
1312 if !poss.contains(&name) {
1316 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1317 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1318 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1319 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1321 let span_replace_word = method_span.with_hi(span.hi());
1326 &format!("use of `{}` followed by a function call", name),
1328 format!("{}_{}({})", name, suffix, sugg),
1329 Applicability::HasPlaceholders,
1333 if args.len() == 2 {
1334 match args[1].node {
1335 hir::ExprKind::Call(ref fun, ref or_args) => {
1336 let or_has_args = !or_args.is_empty();
1337 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1350 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1357 !or_args.is_empty(),
1365 /// Checks for the `EXPECT_FUN_CALL` lint.
1366 #[allow(clippy::too_many_lines)]
1367 fn lint_expect_fun_call(cx: &LateContext<'_, '_>, expr: &hir::Expr, method_span: Span, name: &str, args: &[hir::Expr]) {
1368 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1370 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr) -> &'a hir::Expr {
1371 let mut arg_root = arg;
1373 arg_root = match &arg_root.node {
1374 hir::ExprKind::AddrOf(_, expr) => expr,
1375 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1376 if call_args.len() == 1
1377 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1379 let arg_type = cx.tables.expr_ty(&call_args[0]);
1380 let base_type = walk_ptrs_ty(arg_type);
1381 base_type.sty == ty::Str || match_type(cx, base_type, &paths::STRING)
1395 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1396 // converted to string.
1397 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr) -> bool {
1398 let arg_ty = cx.tables.expr_ty(arg);
1399 if match_type(cx, arg_ty, &paths::STRING) {
1402 if let ty::Ref(ty::ReStatic, ty, ..) = arg_ty.sty {
1403 if ty.sty == ty::Str {
1410 fn generate_format_arg_snippet(
1411 cx: &LateContext<'_, '_>,
1413 applicability: &mut Applicability,
1415 if let hir::ExprKind::AddrOf(_, ref format_arg) = a.node {
1416 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.node {
1417 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.node {
1418 return format_arg_expr_tup
1420 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1429 fn is_call(node: &hir::ExprKind) -> bool {
1431 hir::ExprKind::AddrOf(_, expr) => {
1434 hir::ExprKind::Call(..)
1435 | hir::ExprKind::MethodCall(..)
1436 // These variants are debatable or require further examination
1437 | hir::ExprKind::Match(..)
1438 | hir::ExprKind::Block{ .. } => true,
1443 if args.len() != 2 || name != "expect" || !is_call(&args[1].node) {
1447 let receiver_type = cx.tables.expr_ty(&args[0]);
1448 let closure_args = if match_type(cx, receiver_type, &paths::OPTION) {
1450 } else if match_type(cx, receiver_type, &paths::RESULT) {
1456 let arg_root = get_arg_root(cx, &args[1]);
1458 let span_replace_word = method_span.with_hi(expr.span.hi());
1460 let mut applicability = Applicability::MachineApplicable;
1462 //Special handling for `format!` as arg_root
1463 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.node {
1464 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1 {
1465 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].node {
1466 let fmt_spec = &format_args[0];
1467 let fmt_args = &format_args[1];
1469 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1471 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1473 let sugg = args.join(", ");
1479 &format!("use of `{}` followed by a function call", name),
1481 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
1490 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
1491 if requires_to_string(cx, arg_root) {
1492 arg_root_snippet.to_mut().push_str(".to_string()");
1499 &format!("use of `{}` followed by a function call", name),
1501 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
1506 /// Checks for the `CLONE_ON_COPY` lint.
1507 fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty<'_>) {
1508 let ty = cx.tables.expr_ty(expr);
1509 if let ty::Ref(_, inner, _) = arg_ty.sty {
1510 if let ty::Ref(_, innermost, _) = inner.sty {
1515 "using `clone` on a double-reference; \
1516 this will copy the reference instead of cloning the inner type",
1518 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
1519 let mut ty = innermost;
1521 while let ty::Ref(_, inner, _) = ty.sty {
1525 let refs: String = iter::repeat('&').take(n + 1).collect();
1526 let derefs: String = iter::repeat('*').take(n).collect();
1527 let explicit = format!("{}{}::clone({})", refs, ty, snip);
1530 "try dereferencing it",
1531 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
1532 Applicability::MaybeIncorrect,
1536 "or try being explicit about what type to clone",
1538 Applicability::MaybeIncorrect,
1543 return; // don't report clone_on_copy
1547 if is_copy(cx, ty) {
1549 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1550 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
1551 match &cx.tcx.hir().get(parent) {
1552 hir::Node::Expr(parent) => match parent.node {
1553 // &*x is a nop, &x.clone() is not
1554 hir::ExprKind::AddrOf(..) |
1555 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1556 hir::ExprKind::MethodCall(..) => return,
1559 hir::Node::Stmt(stmt) => {
1560 if let hir::StmtKind::Local(ref loc) = stmt.node {
1561 if let hir::PatKind::Ref(..) = loc.pat.node {
1562 // let ref y = *x borrows x, let ref y = x.clone() does not
1570 // x.clone() might have dereferenced x, possibly through Deref impls
1571 if cx.tables.expr_ty(arg) == ty {
1572 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1574 let deref_count = cx
1576 .expr_adjustments(arg)
1579 if let ty::adjustment::Adjust::Deref(_) = adj.kind {
1586 let derefs: String = iter::repeat('*').take(deref_count).collect();
1587 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
1592 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |db| {
1593 if let Some((text, snip)) = snip {
1594 db.span_suggestion(expr.span, text, snip, Applicability::Unspecified);
1600 fn lint_clone_on_ref_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr) {
1601 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(arg));
1603 if let ty::Adt(_, subst) = obj_ty.sty {
1604 let caller_type = if match_type(cx, obj_ty, &paths::RC) {
1606 } else if match_type(cx, obj_ty, &paths::ARC) {
1608 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
1618 "using '.clone()' on a ref-counted pointer",
1621 "{}::<{}>::clone(&{})",
1624 snippet(cx, arg.span, "_")
1626 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
1631 fn lint_string_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1633 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
1634 let target = &arglists[0][0];
1635 let self_ty = walk_ptrs_ty(cx.tables.expr_ty(target));
1636 let ref_str = if self_ty.sty == ty::Str {
1638 } else if match_type(cx, self_ty, &paths::STRING) {
1644 let mut applicability = Applicability::MachineApplicable;
1647 STRING_EXTEND_CHARS,
1649 "calling `.extend(_.chars())`",
1652 "{}.push_str({}{})",
1653 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
1655 snippet_with_applicability(cx, target.span, "_", &mut applicability)
1662 fn lint_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1663 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&args[0]));
1664 if match_type(cx, obj_ty, &paths::STRING) {
1665 lint_string_extend(cx, expr, args);
1669 fn lint_cstring_as_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, source: &hir::Expr, unwrap: &hir::Expr) {
1671 let source_type = cx.tables.expr_ty(source);
1672 if let ty::Adt(def, substs) = source_type.sty;
1673 if match_def_path(cx, def.did, &paths::RESULT);
1674 if match_type(cx, substs.type_at(0), &paths::CSTRING);
1678 TEMPORARY_CSTRING_AS_PTR,
1680 "you are getting the inner pointer of a temporary `CString`",
1682 db.note("that pointer will be invalid outside this expression");
1683 db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
1689 fn lint_iter_cloned_collect<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr]) {
1690 if match_type(cx, cx.tables.expr_ty(expr), &paths::VEC) {
1691 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])) {
1692 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite()) {
1695 ITER_CLONED_COLLECT,
1697 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
1700 ".to_vec()".to_string(),
1701 Applicability::MachineApplicable,
1708 fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args: &[hir::Expr]) {
1709 fn check_fold_with_op(
1710 cx: &LateContext<'_, '_>,
1712 fold_args: &[hir::Expr],
1714 replacement_method_name: &str,
1715 replacement_has_args: bool,
1718 // Extract the body of the closure passed to fold
1719 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].node;
1720 let closure_body = cx.tcx.hir().body(body_id);
1721 let closure_expr = remove_blocks(&closure_body.value);
1723 // Check if the closure body is of the form `acc <op> some_expr(x)`
1724 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.node;
1725 if bin_op.node == op;
1727 // Extract the names of the two arguments to the closure
1728 if let Some(first_arg_ident) = get_arg_name(&closure_body.arguments[0].pat);
1729 if let Some(second_arg_ident) = get_arg_name(&closure_body.arguments[1].pat);
1731 if match_var(&*left_expr, first_arg_ident);
1732 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
1734 if let hir::ExprKind::MethodCall(_, span, _) = &expr.node;
1737 let mut applicability = Applicability::MachineApplicable;
1738 let sugg = if replacement_has_args {
1740 "{replacement}(|{s}| {r})",
1741 replacement = replacement_method_name,
1742 s = second_arg_ident,
1743 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
1748 replacement = replacement_method_name,
1755 span.with_hi(expr.span.hi()),
1756 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
1757 "this `.fold` can be written more succinctly using another method",
1766 // Check that this is a call to Iterator::fold rather than just some function called fold
1767 if !match_trait_method(cx, expr, &paths::ITERATOR) {
1772 fold_args.len() == 3,
1773 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
1776 // Check if the first argument to .fold is a suitable literal
1777 if let hir::ExprKind::Lit(ref lit) = fold_args[1].node {
1779 ast::LitKind::Bool(false) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::Or, "any", true),
1780 ast::LitKind::Bool(true) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::And, "all", true),
1781 ast::LitKind::Int(0, _) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::Add, "sum", false),
1782 ast::LitKind::Int(1, _) => check_fold_with_op(cx, expr, fold_args, hir::BinOpKind::Mul, "product", false),
1788 fn lint_iter_nth<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr], is_mut: bool) {
1789 let mut_str = if is_mut { "_mut" } else { "" };
1790 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
1792 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC) {
1794 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
1797 return; // caller is not a type that we want to lint
1805 "called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
1806 mut_str, caller_type
1811 fn lint_get_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, get_args: &'tcx [hir::Expr], is_mut: bool) {
1812 // Note: we don't want to lint `get_mut().unwrap` for HashMap or BTreeMap,
1813 // because they do not implement `IndexMut`
1814 let mut applicability = Applicability::MachineApplicable;
1815 let expr_ty = cx.tables.expr_ty(&get_args[0]);
1816 let get_args_str = if get_args.len() > 1 {
1817 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
1819 return; // not linting on a .get().unwrap() chain or variant
1822 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
1823 needs_ref = get_args_str.parse::<usize>().is_ok();
1825 } else if match_type(cx, expr_ty, &paths::VEC) {
1826 needs_ref = get_args_str.parse::<usize>().is_ok();
1828 } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
1829 needs_ref = get_args_str.parse::<usize>().is_ok();
1831 } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
1834 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
1838 return; // caller is not a type that we want to lint
1841 let mut span = expr.span;
1843 // Handle the case where the result is immediately dereferenced
1844 // by not requiring ref and pulling the dereference into the
1848 if let Some(parent) = get_parent_expr(cx, expr);
1849 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.node;
1856 let mut_str = if is_mut { "_mut" } else { "" };
1857 let borrow_str = if !needs_ref {
1870 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
1871 mut_str, caller_type
1877 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
1884 fn lint_iter_skip_next(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
1885 // lint if caller of skip is an Iterator
1886 if match_trait_method(cx, expr, &paths::ITERATOR) {
1891 "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`",
1896 fn derefs_to_slice<'a, 'tcx>(
1897 cx: &LateContext<'a, 'tcx>,
1898 expr: &'tcx hir::Expr,
1900 ) -> Option<&'tcx hir::Expr> {
1901 fn may_slice<'a>(cx: &LateContext<'_, 'a>, ty: Ty<'a>) -> bool {
1903 ty::Slice(_) => true,
1904 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
1905 ty::Adt(..) => match_type(cx, ty, &paths::VEC),
1906 ty::Array(_, size) => size.eval_usize(cx.tcx, cx.param_env) < 32,
1907 ty::Ref(_, inner, _) => may_slice(cx, inner),
1912 if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.node {
1913 if path.ident.name == sym!(iter) && may_slice(cx, cx.tables.expr_ty(&args[0])) {
1920 ty::Slice(_) => Some(expr),
1921 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
1922 ty::Ref(_, inner, _) => {
1923 if may_slice(cx, inner) {
1934 /// lint use of `unwrap()` for `Option`s and `Result`s
1935 fn lint_unwrap(cx: &LateContext<'_, '_>, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
1936 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&unwrap_args[0]));
1938 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
1939 Some((OPTION_UNWRAP_USED, "an Option", "None"))
1940 } else if match_type(cx, obj_ty, &paths::RESULT) {
1941 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
1946 if let Some((lint, kind, none_value)) = mess {
1952 "used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
1953 using expect() to provide a better panic \
1961 /// lint use of `ok().expect()` for `Result`s
1962 fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, ok_args: &[hir::Expr]) {
1963 // lint if the caller of `ok()` is a `Result`
1964 if match_type(cx, cx.tables.expr_ty(&ok_args[0]), &paths::RESULT) {
1965 let result_type = cx.tables.expr_ty(&ok_args[0]);
1966 if let Some(error_type) = get_error_type(cx, result_type) {
1967 if has_debug_impl(error_type, cx) {
1972 "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`",
1979 /// lint use of `map().flatten()` for `Iterators`
1980 fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_args: &'tcx [hir::Expr]) {
1981 // lint if caller of `.map().flatten()` is an Iterator
1982 if match_trait_method(cx, expr, &paths::ITERATOR) {
1983 let msg = "called `map(..).flatten()` on an `Iterator`. \
1984 This is more succinctly expressed by calling `.flat_map(..)`";
1985 let self_snippet = snippet(cx, map_args[0].span, "..");
1986 let func_snippet = snippet(cx, map_args[1].span, "..");
1987 let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
1988 span_lint_and_then(cx, MAP_FLATTEN, expr.span, msg, |db| {
1991 "try using flat_map instead",
1993 Applicability::MachineApplicable,
1999 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2000 fn lint_map_unwrap_or_else<'a, 'tcx>(
2001 cx: &LateContext<'a, 'tcx>,
2002 expr: &'tcx hir::Expr,
2003 map_args: &'tcx [hir::Expr],
2004 unwrap_args: &'tcx [hir::Expr],
2006 // lint if the caller of `map()` is an `Option`
2007 let is_option = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION);
2008 let is_result = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::RESULT);
2010 if is_option || is_result {
2011 // Don't make a suggestion that may fail to compile due to mutably borrowing
2012 // the same variable twice.
2013 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2014 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2015 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2016 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2024 let msg = if is_option {
2025 "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
2026 `map_or_else(g, f)` instead"
2028 "called `map(f).unwrap_or_else(g)` on a Result value. This can be done more directly by calling \
2029 `ok().map_or_else(g, f)` instead"
2031 // get snippets for args to map() and unwrap_or_else()
2032 let map_snippet = snippet(cx, map_args[1].span, "..");
2033 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2034 // lint, with note if neither arg is > 1 line and both map() and
2035 // unwrap_or_else() have the same span
2036 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2037 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2038 if same_span && !multiline {
2042 OPTION_MAP_UNWRAP_OR_ELSE
2044 RESULT_MAP_UNWRAP_OR_ELSE
2050 "replace `map({0}).unwrap_or_else({1})` with `{2}map_or_else({1}, {0})`",
2053 if is_result { "ok()." } else { "" }
2056 } else if same_span && multiline {
2060 OPTION_MAP_UNWRAP_OR_ELSE
2062 RESULT_MAP_UNWRAP_OR_ELSE
2071 /// lint use of `_.map_or(None, _)` for `Option`s
2072 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
2073 if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
2074 // check if the first non-self argument to map_or() is None
2075 let map_or_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].node {
2076 match_qpath(qpath, &paths::OPTION_NONE)
2081 if map_or_arg_is_none {
2083 let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
2084 `and_then(f)` instead";
2085 let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
2086 let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
2087 let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
2088 span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
2091 "try using and_then instead",
2093 Applicability::MachineApplicable, // snippet
2100 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2101 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
2102 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2103 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2105 // Searches an return expressions in `y` in `_.and_then(|x| Some(y))`, which we don't lint
2106 struct RetCallFinder {
2110 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
2111 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
2115 if let hir::ExprKind::Ret(..) = &expr.node {
2118 intravisit::walk_expr(self, expr);
2122 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
2123 intravisit::NestedVisitorMap::None
2127 let ty = cx.tables.expr_ty(&args[0]);
2128 if !match_type(cx, ty, &paths::OPTION) {
2132 match args[1].node {
2133 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2134 let closure_body = cx.tcx.hir().body(body_id);
2135 let closure_expr = remove_blocks(&closure_body.value);
2137 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.node;
2138 if let hir::ExprKind::Path(ref qpath) = some_expr.node;
2139 if match_qpath(qpath, &paths::OPTION_SOME);
2140 if some_args.len() == 1;
2142 let inner_expr = &some_args[0];
2144 let mut finder = RetCallFinder { found: false };
2145 finder.visit_expr(inner_expr);
2150 let some_inner_snip = if inner_expr.span.from_expansion() {
2151 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2153 snippet(cx, inner_expr.span, "_")
2156 let closure_args_snip = snippet(cx, closure_args_span, "..");
2157 let option_snip = snippet(cx, args[0].span, "..");
2158 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2161 OPTION_AND_THEN_SOME,
2166 Applicability::MachineApplicable,
2171 // `_.and_then(Some)` case, which is no-op.
2172 hir::ExprKind::Path(ref qpath) => {
2173 if match_qpath(qpath, &paths::OPTION_SOME) {
2174 let option_snip = snippet(cx, args[0].span, "..");
2175 let note = format!("{}", option_snip);
2178 OPTION_AND_THEN_SOME,
2181 "use the expression directly",
2183 Applicability::MachineApplicable,
2191 /// lint use of `filter().next()` for `Iterators`
2192 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2193 // lint if caller of `.filter().next()` is an Iterator
2194 if match_trait_method(cx, expr, &paths::ITERATOR) {
2195 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2196 `.find(p)` instead.";
2197 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2198 if filter_snippet.lines().count() <= 1 {
2199 // add note if not multi-line
2206 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2209 span_lint(cx, FILTER_NEXT, expr.span, msg);
2214 /// lint use of `filter().map()` for `Iterators`
2215 fn lint_filter_map<'a, 'tcx>(
2216 cx: &LateContext<'a, 'tcx>,
2217 expr: &'tcx hir::Expr,
2218 _filter_args: &'tcx [hir::Expr],
2219 _map_args: &'tcx [hir::Expr],
2221 // lint if caller of `.filter().map()` is an Iterator
2222 if match_trait_method(cx, expr, &paths::ITERATOR) {
2223 let msg = "called `filter(p).map(q)` on an `Iterator`. \
2224 This is more succinctly expressed by calling `.filter_map(..)` instead.";
2225 span_lint(cx, FILTER_MAP, expr.span, msg);
2229 /// lint use of `filter_map().next()` for `Iterators`
2230 fn lint_filter_map_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2231 if match_trait_method(cx, expr, &paths::ITERATOR) {
2232 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2233 `.find_map(p)` instead.";
2234 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2235 if filter_snippet.lines().count() <= 1 {
2242 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2245 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2250 /// lint use of `find().map()` for `Iterators`
2251 fn lint_find_map<'a, 'tcx>(
2252 cx: &LateContext<'a, 'tcx>,
2253 expr: &'tcx hir::Expr,
2254 _find_args: &'tcx [hir::Expr],
2255 map_args: &'tcx [hir::Expr],
2257 // lint if caller of `.filter().map()` is an Iterator
2258 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2259 let msg = "called `find(p).map(q)` on an `Iterator`. \
2260 This is more succinctly expressed by calling `.find_map(..)` instead.";
2261 span_lint(cx, FIND_MAP, expr.span, msg);
2265 /// lint use of `filter().map()` for `Iterators`
2266 fn lint_filter_map_map<'a, 'tcx>(
2267 cx: &LateContext<'a, 'tcx>,
2268 expr: &'tcx hir::Expr,
2269 _filter_args: &'tcx [hir::Expr],
2270 _map_args: &'tcx [hir::Expr],
2272 // lint if caller of `.filter().map()` is an Iterator
2273 if match_trait_method(cx, expr, &paths::ITERATOR) {
2274 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
2275 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
2276 span_lint(cx, FILTER_MAP, expr.span, msg);
2280 /// lint use of `filter().flat_map()` for `Iterators`
2281 fn lint_filter_flat_map<'a, 'tcx>(
2282 cx: &LateContext<'a, 'tcx>,
2283 expr: &'tcx hir::Expr,
2284 _filter_args: &'tcx [hir::Expr],
2285 _map_args: &'tcx [hir::Expr],
2287 // lint if caller of `.filter().flat_map()` is an Iterator
2288 if match_trait_method(cx, expr, &paths::ITERATOR) {
2289 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
2290 This is more succinctly expressed by calling `.flat_map(..)` \
2291 and filtering by returning an empty Iterator.";
2292 span_lint(cx, FILTER_MAP, expr.span, msg);
2296 /// lint use of `filter_map().flat_map()` for `Iterators`
2297 fn lint_filter_map_flat_map<'a, 'tcx>(
2298 cx: &LateContext<'a, 'tcx>,
2299 expr: &'tcx hir::Expr,
2300 _filter_args: &'tcx [hir::Expr],
2301 _map_args: &'tcx [hir::Expr],
2303 // lint if caller of `.filter_map().flat_map()` is an Iterator
2304 if match_trait_method(cx, expr, &paths::ITERATOR) {
2305 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
2306 This is more succinctly expressed by calling `.flat_map(..)` \
2307 and filtering by returning an empty Iterator.";
2308 span_lint(cx, FILTER_MAP, expr.span, msg);
2312 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2313 fn lint_flat_map_identity<'a, 'tcx>(
2314 cx: &LateContext<'a, 'tcx>,
2315 expr: &'tcx hir::Expr,
2316 flat_map_args: &'tcx [hir::Expr],
2318 if match_trait_method(cx, expr, &paths::ITERATOR) {
2319 let arg_node = &flat_map_args[1].node;
2321 let apply_lint = |message: &str| {
2322 if let hir::ExprKind::MethodCall(_, span, _) = &expr.node {
2326 span.with_hi(expr.span.hi()),
2329 "flatten()".to_string(),
2330 Applicability::MachineApplicable,
2336 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2337 let body = cx.tcx.hir().body(*body_id);
2339 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.arguments[0].pat.node;
2340 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.node;
2342 if path.segments.len() == 1;
2343 if path.segments[0].ident.as_str() == binding_ident.as_str();
2346 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2351 if let hir::ExprKind::Path(ref qpath) = arg_node;
2353 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2356 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2362 /// lint searching an Iterator followed by `is_some()`
2363 fn lint_search_is_some<'a, 'tcx>(
2364 cx: &LateContext<'a, 'tcx>,
2365 expr: &'tcx hir::Expr,
2366 search_method: &str,
2367 search_args: &'tcx [hir::Expr],
2368 is_some_args: &'tcx [hir::Expr],
2370 // lint if caller of search is an Iterator
2371 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2373 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2374 expressed by calling `any()`.",
2377 let search_snippet = snippet(cx, search_args[1].span, "..");
2378 if search_snippet.lines().count() <= 1 {
2379 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2380 let any_search_snippet = if_chain! {
2381 if search_method == "find";
2382 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].node;
2383 let closure_body = cx.tcx.hir().body(body_id);
2384 if let Some(closure_arg) = closure_body.arguments.get(0);
2385 if let hir::PatKind::Ref(..) = closure_arg.pat.node;
2387 Some(search_snippet.replacen('&', "", 1))
2392 // add note if not multi-line
2400 "replace `{0}({1}).is_some()` with `any({2})`",
2403 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2407 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2412 /// Used for `lint_binary_expr_with_method_call`.
2413 #[derive(Copy, Clone)]
2414 struct BinaryExprInfo<'a> {
2415 expr: &'a hir::Expr,
2416 chain: &'a hir::Expr,
2417 other: &'a hir::Expr,
2421 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2422 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
2423 macro_rules! lint_with_both_lhs_and_rhs {
2424 ($func:ident, $cx:expr, $info:ident) => {
2425 if !$func($cx, $info) {
2426 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2427 if $func($cx, $info) {
2434 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
2435 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
2436 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
2437 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
2440 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2442 cx: &LateContext<'_, '_>,
2443 info: &BinaryExprInfo<'_>,
2444 chain_methods: &[&str],
2445 lint: &'static Lint,
2449 if let Some(args) = method_chain_args(info.chain, chain_methods);
2450 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.node;
2451 if arg_char.len() == 1;
2452 if let hir::ExprKind::Path(ref qpath) = fun.node;
2453 if let Some(segment) = single_segment_path(qpath);
2454 if segment.ident.name == sym!(Some);
2456 let mut applicability = Applicability::MachineApplicable;
2457 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
2459 if self_ty.sty != ty::Str {
2467 &format!("you should use the `{}` method", suggest),
2469 format!("{}{}.{}({})",
2470 if info.eq { "" } else { "!" },
2471 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2473 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
2484 /// Checks for the `CHARS_NEXT_CMP` lint.
2485 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2486 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
2489 /// Checks for the `CHARS_LAST_CMP` lint.
2490 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2491 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
2494 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
2498 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
2499 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
2500 cx: &LateContext<'a, 'tcx>,
2501 info: &BinaryExprInfo<'_>,
2502 chain_methods: &[&str],
2503 lint: &'static Lint,
2507 if let Some(args) = method_chain_args(info.chain, chain_methods);
2508 if let hir::ExprKind::Lit(ref lit) = info.other.node;
2509 if let ast::LitKind::Char(c) = lit.node;
2511 let mut applicability = Applicability::MachineApplicable;
2516 &format!("you should use the `{}` method", suggest),
2518 format!("{}{}.{}('{}')",
2519 if info.eq { "" } else { "!" },
2520 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2533 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
2534 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2535 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
2538 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
2539 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2540 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
2543 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
2547 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
2548 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
2550 if let hir::ExprKind::Lit(lit) = &arg.node;
2551 if let ast::LitKind::Str(r, style) = lit.node;
2552 if r.as_str().len() == 1;
2554 let mut applicability = Applicability::MachineApplicable;
2555 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
2556 let ch = if let ast::StrStyle::Raw(nhash) = style {
2557 let nhash = nhash as usize;
2558 // for raw string: r##"a"##
2559 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
2561 // for regular string: "a"
2562 &snip[1..(snip.len() - 1)]
2564 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
2567 SINGLE_CHAR_PATTERN,
2569 "single-character string constant used as pattern",
2570 "try using a char instead",
2578 /// Checks for the `USELESS_ASREF` lint.
2579 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
2580 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
2581 // check if the call is to the actual `AsRef` or `AsMut` trait
2582 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
2583 // check if the type after `as_ref` or `as_mut` is the same as before
2584 let recvr = &as_ref_args[0];
2585 let rcv_ty = cx.tables.expr_ty(recvr);
2586 let res_ty = cx.tables.expr_ty(expr);
2587 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
2588 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
2589 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
2590 // allow the `as_ref` or `as_mut` if it is followed by another method call
2592 if let Some(parent) = get_parent_expr(cx, expr);
2593 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.node;
2594 if span != &expr.span;
2600 let mut applicability = Applicability::MachineApplicable;
2605 &format!("this call to `{}` does nothing", call_name),
2607 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
2614 fn ty_has_iter_method(
2615 cx: &LateContext<'_, '_>,
2616 self_ref_ty: Ty<'_>,
2617 ) -> Option<(&'static Lint, &'static str, &'static str)> {
2618 if let Some(ty_name) = has_iter_method(cx, self_ref_ty) {
2619 let lint = if ty_name == "array" || ty_name == "PathBuf" {
2624 let mutbl = match self_ref_ty.sty {
2625 ty::Ref(_, _, mutbl) => mutbl,
2626 _ => unreachable!(),
2628 let method_name = match mutbl {
2629 hir::MutImmutable => "iter",
2630 hir::MutMutable => "iter_mut",
2632 Some((lint, ty_name, method_name))
2638 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr, self_ref_ty: Ty<'_>, method_span: Span) {
2639 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
2642 if let Some((lint, kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
2648 "this .into_iter() call is equivalent to .{}() and will not move the {}",
2652 method_name.to_string(),
2653 Applicability::MachineApplicable,
2658 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2663 "this call to `map()` won't have an effect on the call to `count()`",
2664 "make sure you did not confuse `map` with `filter`",
2668 /// Given a `Result<T, E>` type, return its error type (`E`).
2669 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
2670 if let ty::Adt(_, substs) = ty.sty {
2671 if match_type(cx, ty, &paths::RESULT) {
2672 substs.types().nth(1)
2681 /// This checks whether a given type is known to implement Debug.
2682 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
2683 match cx.tcx.lang_items().debug_trait() {
2684 Some(debug) => implements_trait(cx, ty, debug, &[]),
2691 StartsWith(&'static str),
2695 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
2696 (Convention::Eq("new"), &[SelfKind::No]),
2697 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
2698 (Convention::StartsWith("from_"), &[SelfKind::No]),
2699 (Convention::StartsWith("into_"), &[SelfKind::Value]),
2700 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
2701 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
2702 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
2706 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
2707 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
2708 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
2709 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
2710 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
2711 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
2712 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
2713 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
2714 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
2715 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
2716 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
2717 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
2718 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
2719 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
2720 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
2721 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
2722 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
2723 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
2724 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
2725 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
2726 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
2727 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
2728 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
2729 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
2730 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
2731 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
2732 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
2733 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
2734 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
2735 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
2736 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
2740 const PATTERN_METHODS: [(&str, usize); 17] = [
2748 ("split_terminator", 1),
2749 ("rsplit_terminator", 1),
2754 ("match_indices", 1),
2755 ("rmatch_indices", 1),
2756 ("trim_start_matches", 1),
2757 ("trim_end_matches", 1),
2760 #[derive(Clone, Copy, PartialEq, Debug)]
2769 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2770 fn matches_value(parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2771 if ty == parent_ty {
2773 } else if ty.is_box() {
2774 ty.boxed_ty() == parent_ty
2775 } else if ty.is_rc() || ty.is_arc() {
2776 if let ty::Adt(_, substs) = ty.sty {
2777 substs.types().next().map_or(false, |t| t == parent_ty)
2787 cx: &LateContext<'_, 'a>,
2788 mutability: hir::Mutability,
2792 if let ty::Ref(_, t, m) = ty.sty {
2793 return m == mutability && t == parent_ty;
2796 let trait_path = match mutability {
2797 hir::Mutability::MutImmutable => &paths::ASREF_TRAIT,
2798 hir::Mutability::MutMutable => &paths::ASMUT_TRAIT,
2801 let trait_def_id = get_trait_def_id(cx, trait_path).expect("trait def id not found");
2802 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2806 Self::Value => matches_value(parent_ty, ty),
2808 matches_ref(cx, hir::Mutability::MutImmutable, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty)
2810 Self::RefMut => matches_ref(cx, hir::Mutability::MutMutable, parent_ty, ty),
2811 Self::No => ty != parent_ty,
2815 fn description(self) -> &'static str {
2817 Self::Value => "self by value",
2818 Self::Ref => "self by reference",
2819 Self::RefMut => "self by mutable reference",
2820 Self::No => "no self",
2826 fn check(&self, other: &str) -> bool {
2828 Self::Eq(this) => this == other,
2829 Self::StartsWith(this) => other.starts_with(this) && this != other,
2834 impl fmt::Display for Convention {
2835 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
2837 Self::Eq(this) => this.fmt(f),
2838 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
2843 #[derive(Clone, Copy)]
2852 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FunctionRetTy) -> bool {
2853 let is_unit = |ty: &hir::Ty| SpanlessEq::new(cx).eq_ty_kind(&ty.node, &hir::TyKind::Tup(vec![].into()));
2855 (Self::Unit, &hir::DefaultReturn(_)) => true,
2856 (Self::Unit, &hir::Return(ref ty)) if is_unit(ty) => true,
2857 (Self::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
2858 (Self::Any, &hir::Return(ref ty)) if !is_unit(ty) => true,
2859 (Self::Ref, &hir::Return(ref ty)) => matches!(ty.node, hir::TyKind::Rptr(_, _)),
2865 fn is_bool(ty: &hir::Ty) -> bool {
2866 if let hir::TyKind::Path(ref p) = ty.node {
2867 match_qpath(p, &["bool"])