1 mod inefficient_to_string;
2 mod manual_saturating_arithmetic;
3 mod option_map_unwrap_or;
4 mod unnecessary_filter_map;
10 use if_chain::if_chain;
13 use rustc::hir::intravisit::{self, Visitor};
14 use rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
15 use rustc::ty::{self, Predicate, Ty};
16 use rustc::{declare_lint_pass, declare_tool_lint};
17 use rustc_errors::Applicability;
19 use syntax::source_map::Span;
20 use syntax::symbol::{sym, Symbol, SymbolStr};
22 use crate::utils::usage::mutated_variables;
24 get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, in_macro, is_copy,
25 is_ctor_or_promotable_const_function, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment,
26 match_def_path, match_qpath, match_trait_method, match_type, match_var, method_calls, method_chain_args, paths,
27 remove_blocks, return_ty, same_tys, single_segment_path, snippet, snippet_with_applicability,
28 snippet_with_macro_callsite, span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then,
29 span_note_and_lint, sugg, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
32 declare_clippy_lint! {
33 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
35 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
36 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
37 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
38 /// `Allow` by default.
40 /// **Known problems:** None.
44 /// Using unwrap on an `Option`:
47 /// let opt = Some(1);
54 /// let opt = Some(1);
55 /// opt.expect("more helpful message");
57 pub OPTION_UNWRAP_USED,
59 "using `Option.unwrap()`, which should at least get a better message using `expect()`"
62 declare_clippy_lint! {
63 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
65 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
66 /// values. Normally, you want to implement more sophisticated error handling,
67 /// and propagate errors upwards with `try!`.
69 /// Even if you want to panic on errors, not all `Error`s implement good
70 /// messages on display. Therefore, it may be beneficial to look at the places
71 /// where they may get displayed. Activate this lint to do just that.
73 /// **Known problems:** None.
76 /// Using unwrap on an `Result`:
79 /// let res: Result<usize, ()> = Ok(1);
86 /// let res: Result<usize, ()> = Ok(1);
87 /// res.expect("more helpful message");
89 pub RESULT_UNWRAP_USED,
91 "using `Result.unwrap()`, which might be better handled"
94 declare_clippy_lint! {
95 /// **What it does:** Checks for `.expect()` calls on `Option`s.
97 /// **Why is this bad?** Usually it is better to handle the `None` case. Still,
98 /// for a lot of quick-and-dirty code, `expect` is a good choice, which is why
99 /// this lint is `Allow` by default.
101 /// **Known problems:** None.
105 /// Using expect on an `Option`:
108 /// let opt = Some(1);
109 /// opt.expect("one");
115 /// let opt = Some(1);
119 pub OPTION_EXPECT_USED,
121 "using `Option.expect()`, which might be better handled"
124 declare_clippy_lint! {
125 /// **What it does:** Checks for `.expect()` calls on `Result`s.
127 /// **Why is this bad?** `result.expect()` will let the thread panic on `Err`
128 /// values. Normally, you want to implement more sophisticated error handling,
129 /// and propagate errors upwards with `try!`.
131 /// **Known problems:** None.
134 /// Using expect on an `Result`:
137 /// let res: Result<usize, ()> = Ok(1);
138 /// res.expect("one");
144 /// let res: Result<usize, ()> = Ok(1);
146 /// # Ok::<(), ()>(())
148 pub RESULT_EXPECT_USED,
150 "using `Result.expect()`, which might be better handled"
153 declare_clippy_lint! {
154 /// **What it does:** Checks for methods that should live in a trait
155 /// implementation of a `std` trait (see [llogiq's blog
156 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
157 /// information) instead of an inherent implementation.
159 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
160 /// the code, often with very little cost. Also people seeing a `mul(...)`
162 /// may expect `*` to work equally, so you should have good reason to disappoint
165 /// **Known problems:** None.
171 /// fn add(&self, other: &X) -> X {
176 pub SHOULD_IMPLEMENT_TRAIT,
178 "defining a method that should be implementing a std trait"
181 declare_clippy_lint! {
182 /// **What it does:** Checks for methods with certain name prefixes and which
183 /// doesn't match how self is taken. The actual rules are:
185 /// |Prefix |`self` taken |
186 /// |-------|----------------------|
187 /// |`as_` |`&self` or `&mut self`|
189 /// |`into_`|`self` |
190 /// |`is_` |`&self` or none |
191 /// |`to_` |`&self` |
193 /// **Why is this bad?** Consistency breeds readability. If you follow the
194 /// conventions, your users won't be surprised that they, e.g., need to supply a
195 /// mutable reference to a `as_..` function.
197 /// **Known problems:** None.
202 /// fn as_str(self) -> &str {
207 pub WRONG_SELF_CONVENTION,
209 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
212 declare_clippy_lint! {
213 /// **What it does:** This is the same as
214 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
216 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
218 /// **Known problems:** Actually *renaming* the function may break clients if
219 /// the function is part of the public interface. In that case, be mindful of
220 /// the stability guarantees you've given your users.
226 /// pub fn as_str(self) -> &'a str {
231 pub WRONG_PUB_SELF_CONVENTION,
233 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
236 declare_clippy_lint! {
237 /// **What it does:** Checks for usage of `ok().expect(..)`.
239 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
240 /// directly to get a better error message.
242 /// **Known problems:** The error type needs to implement `Debug`
246 /// x.ok().expect("why did I do this again?")
250 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
253 declare_clippy_lint! {
254 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
256 /// **Why is this bad?** Readability, this can be written more concisely as
257 /// `_.map_or(_, _)`.
259 /// **Known problems:** The order of the arguments is not in execution order
263 /// # let x = Some(1);
264 /// x.map(|a| a + 1).unwrap_or(0);
266 pub OPTION_MAP_UNWRAP_OR,
268 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
271 declare_clippy_lint! {
272 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
274 /// **Why is this bad?** Readability, this can be written more concisely as
275 /// `_.map_or_else(_, _)`.
277 /// **Known problems:** The order of the arguments is not in execution order.
281 /// # let x = Some(1);
282 /// # fn some_function() -> usize { 1 }
283 /// x.map(|a| a + 1).unwrap_or_else(some_function);
285 pub OPTION_MAP_UNWRAP_OR_ELSE,
287 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
290 declare_clippy_lint! {
291 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
293 /// **Why is this bad?** Readability, this can be written more concisely as
294 /// `result.ok().map_or_else(_, _)`.
296 /// **Known problems:** None.
300 /// # let x: Result<usize, ()> = Ok(1);
301 /// # fn some_function(foo: ()) -> usize { 1 }
302 /// x.map(|a| a + 1).unwrap_or_else(some_function);
304 pub RESULT_MAP_UNWRAP_OR_ELSE,
306 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.ok().map_or_else(g, f)`"
309 declare_clippy_lint! {
310 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
312 /// **Why is this bad?** Readability, this can be written more concisely as
315 /// **Known problems:** The order of the arguments is not in execution order.
319 /// opt.map_or(None, |a| a + 1)
321 pub OPTION_MAP_OR_NONE,
323 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
326 declare_clippy_lint! {
327 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
329 /// **Why is this bad?** Readability, this can be written more concisely as
332 /// **Known problems:** None
337 /// let x = Some("foo");
338 /// let _ = x.and_then(|s| Some(s.len()));
341 /// The correct use would be:
344 /// let x = Some("foo");
345 /// let _ = x.map(|s| s.len());
347 pub OPTION_AND_THEN_SOME,
349 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
352 declare_clippy_lint! {
353 /// **What it does:** Checks for usage of `_.filter(_).next()`.
355 /// **Why is this bad?** Readability, this can be written more concisely as
358 /// **Known problems:** None.
362 /// # let vec = vec![1];
363 /// vec.iter().filter(|x| **x == 0).next();
365 /// Could be written as
367 /// # let vec = vec![1];
368 /// vec.iter().find(|x| **x == 0);
372 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
375 declare_clippy_lint! {
376 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
378 /// **Why is this bad?** Readability, this can be written more concisely as a
379 /// single method call.
381 /// **Known problems:**
385 /// let vec = vec![vec![1]];
386 /// vec.iter().map(|x| x.iter()).flatten();
390 "using combinations of `flatten` and `map` which can usually be written as a single method call"
393 declare_clippy_lint! {
394 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
395 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
397 /// **Why is this bad?** Readability, this can be written more concisely as a
398 /// single method call.
400 /// **Known problems:** Often requires a condition + Option/Iterator creation
401 /// inside the closure.
405 /// let vec = vec![1];
406 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
410 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
413 declare_clippy_lint! {
414 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
416 /// **Why is this bad?** Readability, this can be written more concisely as a
417 /// single method call.
419 /// **Known problems:** None
423 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
425 /// Can be written as
428 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
432 "using combination of `filter_map` and `next` which can usually be written as a single method call"
435 declare_clippy_lint! {
436 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
438 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
440 /// **Known problems:** None
444 /// # let iter = vec![vec![0]].into_iter();
445 /// iter.flat_map(|x| x);
447 /// Can be written as
449 /// # let iter = vec![vec![0]].into_iter();
452 pub FLAT_MAP_IDENTITY,
454 "call to `flat_map` where `flatten` is sufficient"
457 declare_clippy_lint! {
458 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
460 /// **Why is this bad?** Readability, this can be written more concisely as a
461 /// single method call.
463 /// **Known problems:** Often requires a condition + Option/Iterator creation
464 /// inside the closure.
468 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
470 /// Can be written as
472 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
476 "using a combination of `find` and `map` can usually be written as a single method call"
479 declare_clippy_lint! {
480 /// **What it does:** Checks for an iterator search (such as `find()`,
481 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
483 /// **Why is this bad?** Readability, this can be written more concisely as
486 /// **Known problems:** None.
490 /// # let vec = vec![1];
491 /// vec.iter().find(|x| **x == 0).is_some();
493 /// Could be written as
495 /// # let vec = vec![1];
496 /// vec.iter().any(|x| *x == 0);
500 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
503 declare_clippy_lint! {
504 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
505 /// if it starts with a given char.
507 /// **Why is this bad?** Readability, this can be written more concisely as
508 /// `_.starts_with(_)`.
510 /// **Known problems:** None.
514 /// let name = "foo";
515 /// if name.chars().next() == Some('_') {};
517 /// Could be written as
519 /// let name = "foo";
520 /// if name.starts_with('_') {};
524 "using `.chars().next()` to check if a string starts with a char"
527 declare_clippy_lint! {
528 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
529 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
530 /// `unwrap_or_default` instead.
532 /// **Why is this bad?** The function will always be called and potentially
533 /// allocate an object acting as the default.
535 /// **Known problems:** If the function has side-effects, not calling it will
536 /// change the semantic of the program, but you shouldn't rely on that anyway.
540 /// # let foo = Some(String::new());
541 /// foo.unwrap_or(String::new());
543 /// this can instead be written:
545 /// # let foo = Some(String::new());
546 /// foo.unwrap_or_else(String::new);
550 /// # let foo = Some(String::new());
551 /// foo.unwrap_or_default();
555 "using any `*or` method with a function call, which suggests `*or_else`"
558 declare_clippy_lint! {
559 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
560 /// etc., and suggests to use `unwrap_or_else` instead
562 /// **Why is this bad?** The function will always be called.
564 /// **Known problems:** If the function has side-effects, not calling it will
565 /// change the semantics of the program, but you shouldn't rely on that anyway.
569 /// # let foo = Some(String::new());
570 /// # let err_code = "418";
571 /// # let err_msg = "I'm a teapot";
572 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
576 /// # let foo = Some(String::new());
577 /// # let err_code = "418";
578 /// # let err_msg = "I'm a teapot";
579 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
581 /// this can instead be written:
583 /// # let foo = Some(String::new());
584 /// # let err_code = "418";
585 /// # let err_msg = "I'm a teapot";
586 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
590 "using any `expect` method with a function call"
593 declare_clippy_lint! {
594 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
596 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
597 /// generics, not for using the `clone` method on a concrete type.
599 /// **Known problems:** None.
607 "using `clone` on a `Copy` type"
610 declare_clippy_lint! {
611 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
612 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
613 /// function syntax instead (e.g., `Rc::clone(foo)`).
615 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
616 /// can obscure the fact that only the pointer is being cloned, not the underlying
621 /// # use std::rc::Rc;
622 /// let x = Rc::new(1);
625 pub CLONE_ON_REF_PTR,
627 "using 'clone' on a ref-counted pointer"
630 declare_clippy_lint! {
631 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
633 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
634 /// cloning the underlying `T`.
636 /// **Known problems:** None.
643 /// let z = y.clone();
644 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
647 pub CLONE_DOUBLE_REF,
649 "using `clone` on `&&T`"
652 declare_clippy_lint! {
653 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
654 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
656 /// **Why is this bad?** This bypasses the specialized implementation of
657 /// `ToString` and instead goes through the more expensive string formatting
660 /// **Known problems:** None.
664 /// // Generic implementation for `T: Display` is used (slow)
665 /// ["foo", "bar"].iter().map(|s| s.to_string());
667 /// // OK, the specialized impl is used
668 /// ["foo", "bar"].iter().map(|&s| s.to_string());
670 pub INEFFICIENT_TO_STRING,
672 "using `to_string` on `&&T` where `T: ToString`"
675 declare_clippy_lint! {
676 /// **What it does:** Checks for `new` not returning `Self`.
678 /// **Why is this bad?** As a convention, `new` methods are used to make a new
679 /// instance of a type.
681 /// **Known problems:** None.
686 /// fn new(..) -> NotAFoo {
692 "not returning `Self` in a `new` method"
695 declare_clippy_lint! {
696 /// **What it does:** Checks for string methods that receive a single-character
697 /// `str` as an argument, e.g., `_.split("x")`.
699 /// **Why is this bad?** Performing these methods using a `char` is faster than
702 /// **Known problems:** Does not catch multi-byte unicode characters.
705 /// `_.split("x")` could be `_.split('x')`
706 pub SINGLE_CHAR_PATTERN,
708 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
711 declare_clippy_lint! {
712 /// **What it does:** Checks for getting the inner pointer of a temporary
715 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
716 /// as the `CString` is alive.
718 /// **Known problems:** None.
722 /// let c_str = CString::new("foo").unwrap().as_ptr();
724 /// call_some_ffi_func(c_str);
727 /// Here `c_str` point to a freed address. The correct use would be:
729 /// let c_str = CString::new("foo").unwrap();
731 /// call_some_ffi_func(c_str.as_ptr());
734 pub TEMPORARY_CSTRING_AS_PTR,
736 "getting the inner pointer of a temporary `CString`"
739 declare_clippy_lint! {
740 /// **What it does:** Checks for use of `.iter().nth()` (and the related
741 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
743 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
746 /// **Known problems:** None.
750 /// let some_vec = vec![0, 1, 2, 3];
751 /// let bad_vec = some_vec.iter().nth(3);
752 /// let bad_slice = &some_vec[..].iter().nth(3);
754 /// The correct use would be:
756 /// let some_vec = vec![0, 1, 2, 3];
757 /// let bad_vec = some_vec.get(3);
758 /// let bad_slice = &some_vec[..].get(3);
762 "using `.iter().nth()` on a standard library type with O(1) element access"
765 declare_clippy_lint! {
766 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
768 /// **Why is this bad?** `.nth(x)` is cleaner
770 /// **Known problems:** None.
774 /// let some_vec = vec![0, 1, 2, 3];
775 /// let bad_vec = some_vec.iter().skip(3).next();
776 /// let bad_slice = &some_vec[..].iter().skip(3).next();
778 /// The correct use would be:
780 /// let some_vec = vec![0, 1, 2, 3];
781 /// let bad_vec = some_vec.iter().nth(3);
782 /// let bad_slice = &some_vec[..].iter().nth(3);
786 "using `.skip(x).next()` on an iterator"
789 declare_clippy_lint! {
790 /// **What it does:** Checks for use of `.get().unwrap()` (or
791 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
793 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
796 /// **Known problems:** Not a replacement for error handling: Using either
797 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
798 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
799 /// temporary placeholder for dealing with the `Option` type, then this does
800 /// not mitigate the need for error handling. If there is a chance that `.get()`
801 /// will be `None` in your program, then it is advisable that the `None` case
802 /// is handled in a future refactor instead of using `.unwrap()` or the Index
807 /// let mut some_vec = vec![0, 1, 2, 3];
808 /// let last = some_vec.get(3).unwrap();
809 /// *some_vec.get_mut(0).unwrap() = 1;
811 /// The correct use would be:
813 /// let mut some_vec = vec![0, 1, 2, 3];
814 /// let last = some_vec[3];
819 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
822 declare_clippy_lint! {
823 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
824 /// `&str` or `String`.
826 /// **Why is this bad?** `.push_str(s)` is clearer
828 /// **Known problems:** None.
833 /// let def = String::from("def");
834 /// let mut s = String::new();
835 /// s.extend(abc.chars());
836 /// s.extend(def.chars());
838 /// The correct use would be:
841 /// let def = String::from("def");
842 /// let mut s = String::new();
844 /// s.push_str(&def);
846 pub STRING_EXTEND_CHARS,
848 "using `x.extend(s.chars())` where s is a `&str` or `String`"
851 declare_clippy_lint! {
852 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
855 /// **Why is this bad?** `.to_vec()` is clearer
857 /// **Known problems:** None.
861 /// let s = [1, 2, 3, 4, 5];
862 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
864 /// The better use would be:
866 /// let s = [1, 2, 3, 4, 5];
867 /// let s2: Vec<isize> = s.to_vec();
869 pub ITER_CLONED_COLLECT,
871 "using `.cloned().collect()` on slice to create a `Vec`"
874 declare_clippy_lint! {
875 /// **What it does:** Checks for usage of `.chars().last()` or
876 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
878 /// **Why is this bad?** Readability, this can be written more concisely as
879 /// `_.ends_with(_)`.
881 /// **Known problems:** None.
885 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
889 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
892 declare_clippy_lint! {
893 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
894 /// types before and after the call are the same.
896 /// **Why is this bad?** The call is unnecessary.
898 /// **Known problems:** None.
902 /// # fn do_stuff(x: &[i32]) {}
903 /// let x: &[i32] = &[1, 2, 3, 4, 5];
904 /// do_stuff(x.as_ref());
906 /// The correct use would be:
908 /// # fn do_stuff(x: &[i32]) {}
909 /// let x: &[i32] = &[1, 2, 3, 4, 5];
914 "using `as_ref` where the types before and after the call are the same"
917 declare_clippy_lint! {
918 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
919 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
920 /// `sum` or `product`.
922 /// **Why is this bad?** Readability.
924 /// **Known problems:** False positive in pattern guards. Will be resolved once
925 /// non-lexical lifetimes are stable.
929 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
931 /// This could be written as:
933 /// let _ = (0..3).any(|x| x > 2);
935 pub UNNECESSARY_FOLD,
937 "using `fold` when a more succinct alternative exists"
940 declare_clippy_lint! {
941 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
942 /// More specifically it checks if the closure provided is only performing one of the
943 /// filter or map operations and suggests the appropriate option.
945 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
946 /// operation is being performed.
948 /// **Known problems:** None
952 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
954 /// As there is no transformation of the argument this could be written as:
956 /// let _ = (0..3).filter(|&x| x > 2);
960 /// let _ = (0..4).filter_map(i32::checked_abs);
962 /// As there is no conditional check on the argument this could be written as:
964 /// let _ = (0..4).map(i32::checked_abs);
966 pub UNNECESSARY_FILTER_MAP,
968 "using `filter_map` when a more succinct alternative exists"
971 declare_clippy_lint! {
972 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
975 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
976 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
977 /// `iter_mut` directly.
979 /// **Known problems:** None
984 /// let _ = (&vec![3, 4, 5]).into_iter();
986 pub INTO_ITER_ON_REF,
988 "using `.into_iter()` on a reference"
991 declare_clippy_lint! {
992 /// **What it does:** Checks for calls to `map` followed by a `count`.
994 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
995 /// If the `map` call is intentional, this should be rewritten.
997 /// **Known problems:** None
1002 /// let _ = (0..3).map(|x| x + 2).count();
1006 "suspicious usage of map"
1009 declare_clippy_lint! {
1010 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1012 /// **Why is this bad?** For most types, this is undefined behavior.
1014 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1015 /// of `MaybeUninit`. There may be other types that allow uninitialized
1016 /// data, but those are not yet rigorously defined.
1021 /// // Beware the UB
1022 /// use std::mem::MaybeUninit;
1024 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1027 /// Note that the following is OK:
1030 /// use std::mem::MaybeUninit;
1032 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1033 /// MaybeUninit::uninit().assume_init()
1036 pub UNINIT_ASSUMED_INIT,
1038 "`MaybeUninit::uninit().assume_init()`"
1041 declare_clippy_lint! {
1042 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1044 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1049 /// # let y: u32 = 0;
1050 /// # let x: u32 = 100;
1051 /// let add = x.checked_add(y).unwrap_or(u32::max_value());
1052 /// let sub = x.checked_sub(y).unwrap_or(u32::min_value());
1055 /// can be written using dedicated methods for saturating addition/subtraction as:
1058 /// # let y: u32 = 0;
1059 /// # let x: u32 = 100;
1060 /// let add = x.saturating_add(y);
1061 /// let sub = x.saturating_sub(y);
1063 pub MANUAL_SATURATING_ARITHMETIC,
1065 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1068 declare_lint_pass!(Methods => [
1073 SHOULD_IMPLEMENT_TRAIT,
1074 WRONG_SELF_CONVENTION,
1075 WRONG_PUB_SELF_CONVENTION,
1077 OPTION_MAP_UNWRAP_OR,
1078 OPTION_MAP_UNWRAP_OR_ELSE,
1079 RESULT_MAP_UNWRAP_OR_ELSE,
1081 OPTION_AND_THEN_SOME,
1089 INEFFICIENT_TO_STRING,
1091 SINGLE_CHAR_PATTERN,
1093 TEMPORARY_CSTRING_AS_PTR,
1103 STRING_EXTEND_CHARS,
1104 ITER_CLONED_COLLECT,
1107 UNNECESSARY_FILTER_MAP,
1110 UNINIT_ASSUMED_INIT,
1111 MANUAL_SATURATING_ARITHMETIC,
1114 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
1115 #[allow(clippy::cognitive_complexity)]
1116 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
1117 if in_macro(expr.span) {
1121 let (method_names, arg_lists, method_spans) = method_calls(expr, 2);
1122 let method_names: Vec<SymbolStr> = method_names.iter().map(|s| s.as_str()).collect();
1123 let method_names: Vec<&str> = method_names.iter().map(|s| &**s).collect();
1125 match method_names.as_slice() {
1126 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1127 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1128 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1129 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1130 ["expect", ..] => lint_expect(cx, expr, arg_lists[0]),
1131 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0]),
1132 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
1133 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1134 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
1135 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1136 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1137 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1138 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1139 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1140 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1141 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1142 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0], method_spans[0]),
1143 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1144 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0], method_spans[1]),
1145 ["is_some", "position"] => {
1146 lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0], method_spans[1])
1148 ["is_some", "rposition"] => {
1149 lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
1151 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1152 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1153 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1155 ["nth", "iter"] => lint_iter_nth(cx, expr, arg_lists[1], false),
1156 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, arg_lists[1], true),
1157 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1158 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1159 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1160 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1161 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0], method_spans[0]),
1162 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1163 ["count", "map"] => lint_suspicious_map(cx, expr),
1164 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1165 ["unwrap_or", arith @ "checked_add"]
1166 | ["unwrap_or", arith @ "checked_sub"]
1167 | ["unwrap_or", arith @ "checked_mul"] => {
1168 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1174 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1175 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1176 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1178 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1179 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1180 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1181 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1183 if args.len() == 1 && method_call.ident.name == sym!(to_string) {
1184 inefficient_to_string::lint(cx, expr, &args[0], self_ty);
1187 match self_ty.kind {
1188 ty::Ref(_, ty, _) if ty.kind == ty::Str => {
1189 for &(method, pos) in &PATTERN_METHODS {
1190 if method_call.ident.name.as_str() == method && args.len() > pos {
1191 lint_single_char_pattern(cx, expr, &args[pos]);
1195 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1196 lint_into_iter(cx, expr, self_ty, *method_span);
1201 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1202 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1204 let mut info = BinaryExprInfo {
1208 eq: op.node == hir::BinOpKind::Eq,
1210 lint_binary_expr_with_method_call(cx, &mut info);
1216 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem) {
1217 if in_external_macro(cx.sess(), impl_item.span) {
1220 let name = impl_item.ident.name.as_str();
1221 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1222 let item = cx.tcx.hir().expect_item(parent);
1223 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1224 let ty = cx.tcx.type_of(def_id);
1226 if let hir::ImplItemKind::Method(ref sig, id) = impl_item.kind;
1227 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1228 if let hir::ItemKind::Impl(_, _, _, _, None, _, _) = item.kind;
1230 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1231 let method_sig = cx.tcx.fn_sig(method_def_id);
1232 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1234 let first_arg_ty = &method_sig.inputs().iter().next();
1236 // check conventions w.r.t. conversion method names and predicates
1237 if let Some(first_arg_ty) = first_arg_ty;
1240 if cx.access_levels.is_exported(impl_item.hir_id) {
1241 // check missing trait implementations
1242 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1243 if name == method_name &&
1244 sig.decl.inputs.len() == n_args &&
1245 out_type.matches(cx, &sig.decl.output) &&
1246 self_kind.matches(cx, ty, first_arg_ty) {
1247 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1248 "defining a method called `{}` on this type; consider implementing \
1249 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1254 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1256 .find(|(ref conv, _)| conv.check(&name))
1258 if !self_kinds.iter().any(|k| k.matches(cx, ty, first_arg_ty)) {
1259 let lint = if item.vis.node.is_pub() {
1260 WRONG_PUB_SELF_CONVENTION
1262 WRONG_SELF_CONVENTION
1270 "methods called `{}` usually take {}; consider choosing a less \
1275 .map(|k| k.description())
1276 .collect::<Vec<_>>()
1285 if let hir::ImplItemKind::Method(_, _) = impl_item.kind {
1286 let ret_ty = return_ty(cx, impl_item.hir_id);
1288 // walk the return type and check for Self (this does not check associated types)
1289 if ret_ty.walk().any(|inner_type| same_tys(cx, ty, inner_type)) {
1293 // if return type is impl trait, check the associated types
1294 if let ty::Opaque(def_id, _) = ret_ty.kind {
1295 // one of the associated types must be Self
1296 for predicate in cx.tcx.predicates_of(def_id).predicates {
1298 (Predicate::Projection(poly_projection_predicate), _) => {
1299 let binder = poly_projection_predicate.ty();
1300 let associated_type = binder.skip_binder();
1302 // walk the associated type and check for Self
1303 for inner_type in associated_type.walk() {
1304 if same_tys(cx, ty, inner_type) {
1314 if name == "new" && !same_tys(cx, ret_ty, ty) {
1319 "methods called `new` usually return `Self`",
1326 /// Checks for the `OR_FUN_CALL` lint.
1327 #[allow(clippy::too_many_lines)]
1328 fn lint_or_fun_call<'a, 'tcx>(
1329 cx: &LateContext<'a, 'tcx>,
1333 args: &'tcx [hir::Expr],
1335 // Searches an expression for method calls or function calls that aren't ctors
1336 struct FunCallFinder<'a, 'tcx> {
1337 cx: &'a LateContext<'a, 'tcx>,
1341 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1342 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
1343 let call_found = match &expr.kind {
1344 // ignore enum and struct constructors
1345 hir::ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
1346 hir::ExprKind::MethodCall(..) => true,
1355 intravisit::walk_expr(self, expr);
1359 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1360 intravisit::NestedVisitorMap::None
1364 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1365 fn check_unwrap_or_default(
1366 cx: &LateContext<'_, '_>,
1369 self_expr: &hir::Expr,
1376 if name == "unwrap_or";
1377 if let hir::ExprKind::Path(ref qpath) = fun.kind;
1378 let path = &*last_path_segment(qpath).ident.as_str();
1379 if ["default", "new"].contains(&path);
1380 let arg_ty = cx.tables.expr_ty(arg);
1381 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1382 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1385 let mut applicability = Applicability::MachineApplicable;
1390 &format!("use of `{}` followed by a call to `{}`", name, path),
1393 "{}.unwrap_or_default()",
1394 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1406 /// Checks for `*or(foo())`.
1407 #[allow(clippy::too_many_arguments)]
1408 fn check_general_case<'a, 'tcx>(
1409 cx: &LateContext<'a, 'tcx>,
1413 self_expr: &hir::Expr,
1414 arg: &'tcx hir::Expr,
1418 // (path, fn_has_argument, methods, suffix)
1419 let know_types: &[(&[_], _, &[_], _)] = &[
1420 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1421 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1422 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1423 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1427 if know_types.iter().any(|k| k.2.contains(&name));
1429 let mut finder = FunCallFinder { cx: &cx, found: false };
1430 if { finder.visit_expr(&arg); finder.found };
1431 if !contains_return(&arg);
1433 let self_ty = cx.tables.expr_ty(self_expr);
1435 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1436 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1438 if poss.contains(&name);
1441 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1442 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1443 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1444 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1446 let span_replace_word = method_span.with_hi(span.hi());
1451 &format!("use of `{}` followed by a function call", name),
1453 format!("{}_{}({})", name, suffix, sugg),
1454 Applicability::HasPlaceholders,
1460 if args.len() == 2 {
1461 match args[1].kind {
1462 hir::ExprKind::Call(ref fun, ref or_args) => {
1463 let or_has_args = !or_args.is_empty();
1464 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1477 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1484 !or_args.is_empty(),
1492 /// Checks for the `EXPECT_FUN_CALL` lint.
1493 #[allow(clippy::too_many_lines)]
1494 fn lint_expect_fun_call(cx: &LateContext<'_, '_>, expr: &hir::Expr, method_span: Span, name: &str, args: &[hir::Expr]) {
1495 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1497 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr) -> &'a hir::Expr {
1498 let mut arg_root = arg;
1500 arg_root = match &arg_root.kind {
1501 hir::ExprKind::AddrOf(_, expr) => expr,
1502 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1503 if call_args.len() == 1
1504 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1506 let arg_type = cx.tables.expr_ty(&call_args[0]);
1507 let base_type = walk_ptrs_ty(arg_type);
1508 base_type.kind == ty::Str || match_type(cx, base_type, &paths::STRING)
1522 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1523 // converted to string.
1524 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr) -> bool {
1525 let arg_ty = cx.tables.expr_ty(arg);
1526 if match_type(cx, arg_ty, &paths::STRING) {
1529 if let ty::Ref(ty::ReStatic, ty, ..) = arg_ty.kind {
1530 if ty.kind == ty::Str {
1537 fn generate_format_arg_snippet(
1538 cx: &LateContext<'_, '_>,
1540 applicability: &mut Applicability,
1543 if let hir::ExprKind::AddrOf(_, ref format_arg) = a.kind;
1544 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.kind;
1545 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.kind;
1550 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1558 fn is_call(node: &hir::ExprKind) -> bool {
1560 hir::ExprKind::AddrOf(_, expr) => {
1563 hir::ExprKind::Call(..)
1564 | hir::ExprKind::MethodCall(..)
1565 // These variants are debatable or require further examination
1566 | hir::ExprKind::Match(..)
1567 | hir::ExprKind::Block{ .. } => true,
1572 if args.len() != 2 || name != "expect" || !is_call(&args[1].kind) {
1576 let receiver_type = cx.tables.expr_ty(&args[0]);
1577 let closure_args = if match_type(cx, receiver_type, &paths::OPTION) {
1579 } else if match_type(cx, receiver_type, &paths::RESULT) {
1585 let arg_root = get_arg_root(cx, &args[1]);
1587 let span_replace_word = method_span.with_hi(expr.span.hi());
1589 let mut applicability = Applicability::MachineApplicable;
1591 //Special handling for `format!` as arg_root
1592 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.kind {
1593 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1 {
1594 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].kind {
1595 let fmt_spec = &format_args[0];
1596 let fmt_args = &format_args[1];
1598 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1600 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1602 let sugg = args.join(", ");
1608 &format!("use of `{}` followed by a function call", name),
1610 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
1619 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
1620 if requires_to_string(cx, arg_root) {
1621 arg_root_snippet.to_mut().push_str(".to_string()");
1628 &format!("use of `{}` followed by a function call", name),
1630 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
1635 /// Checks for the `CLONE_ON_COPY` lint.
1636 fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty<'_>) {
1637 let ty = cx.tables.expr_ty(expr);
1638 if let ty::Ref(_, inner, _) = arg_ty.kind {
1639 if let ty::Ref(_, innermost, _) = inner.kind {
1644 "using `clone` on a double-reference; \
1645 this will copy the reference instead of cloning the inner type",
1647 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
1648 let mut ty = innermost;
1650 while let ty::Ref(_, inner, _) = ty.kind {
1654 let refs: String = iter::repeat('&').take(n + 1).collect();
1655 let derefs: String = iter::repeat('*').take(n).collect();
1656 let explicit = format!("{}{}::clone({})", refs, ty, snip);
1659 "try dereferencing it",
1660 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
1661 Applicability::MaybeIncorrect,
1665 "or try being explicit about what type to clone",
1667 Applicability::MaybeIncorrect,
1672 return; // don't report clone_on_copy
1676 if is_copy(cx, ty) {
1678 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1679 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
1680 match &cx.tcx.hir().get(parent) {
1681 hir::Node::Expr(parent) => match parent.kind {
1682 // &*x is a nop, &x.clone() is not
1683 hir::ExprKind::AddrOf(..) |
1684 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1685 hir::ExprKind::MethodCall(..) => return,
1688 hir::Node::Stmt(stmt) => {
1689 if let hir::StmtKind::Local(ref loc) = stmt.kind {
1690 if let hir::PatKind::Ref(..) = loc.pat.kind {
1691 // let ref y = *x borrows x, let ref y = x.clone() does not
1699 // x.clone() might have dereferenced x, possibly through Deref impls
1700 if cx.tables.expr_ty(arg) == ty {
1701 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1703 let deref_count = cx
1705 .expr_adjustments(arg)
1708 if let ty::adjustment::Adjust::Deref(_) = adj.kind {
1715 let derefs: String = iter::repeat('*').take(deref_count).collect();
1716 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
1721 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |db| {
1722 if let Some((text, snip)) = snip {
1723 db.span_suggestion(expr.span, text, snip, Applicability::Unspecified);
1729 fn lint_clone_on_ref_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr) {
1730 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(arg));
1732 if let ty::Adt(_, subst) = obj_ty.kind {
1733 let caller_type = if match_type(cx, obj_ty, &paths::RC) {
1735 } else if match_type(cx, obj_ty, &paths::ARC) {
1737 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
1747 "using '.clone()' on a ref-counted pointer",
1750 "{}::<{}>::clone(&{})",
1753 snippet(cx, arg.span, "_")
1755 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
1760 fn lint_string_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1762 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
1763 let target = &arglists[0][0];
1764 let self_ty = walk_ptrs_ty(cx.tables.expr_ty(target));
1765 let ref_str = if self_ty.kind == ty::Str {
1767 } else if match_type(cx, self_ty, &paths::STRING) {
1773 let mut applicability = Applicability::MachineApplicable;
1776 STRING_EXTEND_CHARS,
1778 "calling `.extend(_.chars())`",
1781 "{}.push_str({}{})",
1782 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
1784 snippet_with_applicability(cx, target.span, "_", &mut applicability)
1791 fn lint_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1792 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&args[0]));
1793 if match_type(cx, obj_ty, &paths::STRING) {
1794 lint_string_extend(cx, expr, args);
1798 fn lint_cstring_as_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, source: &hir::Expr, unwrap: &hir::Expr) {
1800 let source_type = cx.tables.expr_ty(source);
1801 if let ty::Adt(def, substs) = source_type.kind;
1802 if match_def_path(cx, def.did, &paths::RESULT);
1803 if match_type(cx, substs.type_at(0), &paths::CSTRING);
1807 TEMPORARY_CSTRING_AS_PTR,
1809 "you are getting the inner pointer of a temporary `CString`",
1811 db.note("that pointer will be invalid outside this expression");
1812 db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
1818 fn lint_iter_cloned_collect<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr]) {
1820 if is_type_diagnostic_item(cx, cx.tables.expr_ty(expr), Symbol::intern("vec_type"));
1821 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0]));
1822 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite());
1827 ITER_CLONED_COLLECT,
1829 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
1832 ".to_vec()".to_string(),
1833 Applicability::MachineApplicable,
1839 fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args: &[hir::Expr], fold_span: Span) {
1840 fn check_fold_with_op(
1841 cx: &LateContext<'_, '_>,
1843 fold_args: &[hir::Expr],
1846 replacement_method_name: &str,
1847 replacement_has_args: bool,
1850 // Extract the body of the closure passed to fold
1851 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
1852 let closure_body = cx.tcx.hir().body(body_id);
1853 let closure_expr = remove_blocks(&closure_body.value);
1855 // Check if the closure body is of the form `acc <op> some_expr(x)`
1856 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
1857 if bin_op.node == op;
1859 // Extract the names of the two arguments to the closure
1860 if let Some(first_arg_ident) = get_arg_name(&closure_body.params[0].pat);
1861 if let Some(second_arg_ident) = get_arg_name(&closure_body.params[1].pat);
1863 if match_var(&*left_expr, first_arg_ident);
1864 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
1867 let mut applicability = Applicability::MachineApplicable;
1868 let sugg = if replacement_has_args {
1870 "{replacement}(|{s}| {r})",
1871 replacement = replacement_method_name,
1872 s = second_arg_ident,
1873 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
1878 replacement = replacement_method_name,
1885 fold_span.with_hi(expr.span.hi()),
1886 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
1887 "this `.fold` can be written more succinctly using another method",
1896 // Check that this is a call to Iterator::fold rather than just some function called fold
1897 if !match_trait_method(cx, expr, &paths::ITERATOR) {
1902 fold_args.len() == 3,
1903 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
1906 // Check if the first argument to .fold is a suitable literal
1907 if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
1909 ast::LitKind::Bool(false) => {
1910 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
1912 ast::LitKind::Bool(true) => {
1913 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
1915 ast::LitKind::Int(0, _) => {
1916 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
1918 ast::LitKind::Int(1, _) => {
1919 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
1926 fn lint_iter_nth<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr], is_mut: bool) {
1927 let mut_str = if is_mut { "_mut" } else { "" };
1928 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
1930 } else if is_type_diagnostic_item(cx, cx.tables.expr_ty(&iter_args[0]), Symbol::intern("vec_type")) {
1932 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
1935 return; // caller is not a type that we want to lint
1943 "called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
1944 mut_str, caller_type
1949 fn lint_get_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, get_args: &'tcx [hir::Expr], is_mut: bool) {
1950 // Note: we don't want to lint `get_mut().unwrap` for `HashMap` or `BTreeMap`,
1951 // because they do not implement `IndexMut`
1952 let mut applicability = Applicability::MachineApplicable;
1953 let expr_ty = cx.tables.expr_ty(&get_args[0]);
1954 let get_args_str = if get_args.len() > 1 {
1955 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
1957 return; // not linting on a .get().unwrap() chain or variant
1960 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
1961 needs_ref = get_args_str.parse::<usize>().is_ok();
1963 } else if is_type_diagnostic_item(cx, expr_ty, Symbol::intern("vec_type")) {
1964 needs_ref = get_args_str.parse::<usize>().is_ok();
1966 } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
1967 needs_ref = get_args_str.parse::<usize>().is_ok();
1969 } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
1972 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
1976 return; // caller is not a type that we want to lint
1979 let mut span = expr.span;
1981 // Handle the case where the result is immediately dereferenced
1982 // by not requiring ref and pulling the dereference into the
1986 if let Some(parent) = get_parent_expr(cx, expr);
1987 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.kind;
1994 let mut_str = if is_mut { "_mut" } else { "" };
1995 let borrow_str = if !needs_ref {
2008 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
2009 mut_str, caller_type
2015 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
2022 fn lint_iter_skip_next(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2023 // lint if caller of skip is an Iterator
2024 if match_trait_method(cx, expr, &paths::ITERATOR) {
2029 "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`",
2034 fn derefs_to_slice<'a, 'tcx>(
2035 cx: &LateContext<'a, 'tcx>,
2036 expr: &'tcx hir::Expr,
2038 ) -> Option<&'tcx hir::Expr> {
2039 fn may_slice<'a>(cx: &LateContext<'_, 'a>, ty: Ty<'a>) -> bool {
2041 ty::Slice(_) => true,
2042 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
2043 ty::Adt(..) => is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")),
2044 ty::Array(_, size) => size.eval_usize(cx.tcx, cx.param_env) < 32,
2045 ty::Ref(_, inner, _) => may_slice(cx, inner),
2050 if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.kind {
2051 if path.ident.name == sym!(iter) && may_slice(cx, cx.tables.expr_ty(&args[0])) {
2058 ty::Slice(_) => Some(expr),
2059 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
2060 ty::Ref(_, inner, _) => {
2061 if may_slice(cx, inner) {
2072 /// lint use of `unwrap()` for `Option`s and `Result`s
2073 fn lint_unwrap(cx: &LateContext<'_, '_>, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
2074 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&unwrap_args[0]));
2076 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
2077 Some((OPTION_UNWRAP_USED, "an Option", "None"))
2078 } else if match_type(cx, obj_ty, &paths::RESULT) {
2079 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
2084 if let Some((lint, kind, none_value)) = mess {
2090 "used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
2091 using expect() to provide a better panic \
2099 /// lint use of `expect()` for `Option`s and `Result`s
2100 fn lint_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, expect_args: &[hir::Expr]) {
2101 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&expect_args[0]));
2103 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
2104 Some((OPTION_EXPECT_USED, "an Option", "None"))
2105 } else if match_type(cx, obj_ty, &paths::RESULT) {
2106 Some((RESULT_EXPECT_USED, "a Result", "Err"))
2111 if let Some((lint, kind, none_value)) = mess {
2117 "used expect() on {} value. If this value is an {} it will panic",
2124 /// lint use of `ok().expect()` for `Result`s
2125 fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, ok_args: &[hir::Expr]) {
2127 // lint if the caller of `ok()` is a `Result`
2128 if match_type(cx, cx.tables.expr_ty(&ok_args[0]), &paths::RESULT);
2129 let result_type = cx.tables.expr_ty(&ok_args[0]);
2130 if let Some(error_type) = get_error_type(cx, result_type);
2131 if has_debug_impl(error_type, cx);
2138 "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`",
2144 /// lint use of `map().flatten()` for `Iterators`
2145 fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_args: &'tcx [hir::Expr]) {
2146 // lint if caller of `.map().flatten()` is an Iterator
2147 if match_trait_method(cx, expr, &paths::ITERATOR) {
2148 let msg = "called `map(..).flatten()` on an `Iterator`. \
2149 This is more succinctly expressed by calling `.flat_map(..)`";
2150 let self_snippet = snippet(cx, map_args[0].span, "..");
2151 let func_snippet = snippet(cx, map_args[1].span, "..");
2152 let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
2153 span_lint_and_then(cx, MAP_FLATTEN, expr.span, msg, |db| {
2156 "try using flat_map instead",
2158 Applicability::MachineApplicable,
2164 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2165 fn lint_map_unwrap_or_else<'a, 'tcx>(
2166 cx: &LateContext<'a, 'tcx>,
2167 expr: &'tcx hir::Expr,
2168 map_args: &'tcx [hir::Expr],
2169 unwrap_args: &'tcx [hir::Expr],
2171 // lint if the caller of `map()` is an `Option`
2172 let is_option = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION);
2173 let is_result = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::RESULT);
2175 if is_option || is_result {
2176 // Don't make a suggestion that may fail to compile due to mutably borrowing
2177 // the same variable twice.
2178 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2179 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2180 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2181 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2189 let msg = if is_option {
2190 "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
2191 `map_or_else(g, f)` instead"
2193 "called `map(f).unwrap_or_else(g)` on a Result value. This can be done more directly by calling \
2194 `ok().map_or_else(g, f)` instead"
2196 // get snippets for args to map() and unwrap_or_else()
2197 let map_snippet = snippet(cx, map_args[1].span, "..");
2198 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2199 // lint, with note if neither arg is > 1 line and both map() and
2200 // unwrap_or_else() have the same span
2201 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2202 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2203 if same_span && !multiline {
2207 OPTION_MAP_UNWRAP_OR_ELSE
2209 RESULT_MAP_UNWRAP_OR_ELSE
2215 "replace `map({0}).unwrap_or_else({1})` with `{2}map_or_else({1}, {0})`",
2218 if is_result { "ok()." } else { "" }
2221 } else if same_span && multiline {
2225 OPTION_MAP_UNWRAP_OR_ELSE
2227 RESULT_MAP_UNWRAP_OR_ELSE
2236 /// lint use of `_.map_or(None, _)` for `Option`s
2237 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
2238 if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
2239 // check if the first non-self argument to map_or() is None
2240 let map_or_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].kind {
2241 match_qpath(qpath, &paths::OPTION_NONE)
2246 if map_or_arg_is_none {
2248 let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
2249 `and_then(f)` instead";
2250 let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
2251 let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
2252 let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
2253 span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
2256 "try using and_then instead",
2258 Applicability::MachineApplicable, // snippet
2265 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2266 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
2267 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2268 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2270 let ty = cx.tables.expr_ty(&args[0]);
2271 if !match_type(cx, ty, &paths::OPTION) {
2275 match args[1].kind {
2276 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2277 let closure_body = cx.tcx.hir().body(body_id);
2278 let closure_expr = remove_blocks(&closure_body.value);
2280 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.kind;
2281 if let hir::ExprKind::Path(ref qpath) = some_expr.kind;
2282 if match_qpath(qpath, &paths::OPTION_SOME);
2283 if some_args.len() == 1;
2285 let inner_expr = &some_args[0];
2287 if contains_return(inner_expr) {
2291 let some_inner_snip = if inner_expr.span.from_expansion() {
2292 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2294 snippet(cx, inner_expr.span, "_")
2297 let closure_args_snip = snippet(cx, closure_args_span, "..");
2298 let option_snip = snippet(cx, args[0].span, "..");
2299 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2302 OPTION_AND_THEN_SOME,
2307 Applicability::MachineApplicable,
2312 // `_.and_then(Some)` case, which is no-op.
2313 hir::ExprKind::Path(ref qpath) => {
2314 if match_qpath(qpath, &paths::OPTION_SOME) {
2315 let option_snip = snippet(cx, args[0].span, "..");
2316 let note = format!("{}", option_snip);
2319 OPTION_AND_THEN_SOME,
2322 "use the expression directly",
2324 Applicability::MachineApplicable,
2332 /// lint use of `filter().next()` for `Iterators`
2333 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2334 // lint if caller of `.filter().next()` is an Iterator
2335 if match_trait_method(cx, expr, &paths::ITERATOR) {
2336 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2337 `.find(p)` instead.";
2338 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2339 if filter_snippet.lines().count() <= 1 {
2340 // add note if not multi-line
2347 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2350 span_lint(cx, FILTER_NEXT, expr.span, msg);
2355 /// lint use of `filter().map()` for `Iterators`
2356 fn lint_filter_map<'a, 'tcx>(
2357 cx: &LateContext<'a, 'tcx>,
2358 expr: &'tcx hir::Expr,
2359 _filter_args: &'tcx [hir::Expr],
2360 _map_args: &'tcx [hir::Expr],
2362 // lint if caller of `.filter().map()` is an Iterator
2363 if match_trait_method(cx, expr, &paths::ITERATOR) {
2364 let msg = "called `filter(p).map(q)` on an `Iterator`. \
2365 This is more succinctly expressed by calling `.filter_map(..)` instead.";
2366 span_lint(cx, FILTER_MAP, expr.span, msg);
2370 /// lint use of `filter_map().next()` for `Iterators`
2371 fn lint_filter_map_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2372 if match_trait_method(cx, expr, &paths::ITERATOR) {
2373 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2374 `.find_map(p)` instead.";
2375 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2376 if filter_snippet.lines().count() <= 1 {
2383 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2386 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2391 /// lint use of `find().map()` for `Iterators`
2392 fn lint_find_map<'a, 'tcx>(
2393 cx: &LateContext<'a, 'tcx>,
2394 expr: &'tcx hir::Expr,
2395 _find_args: &'tcx [hir::Expr],
2396 map_args: &'tcx [hir::Expr],
2398 // lint if caller of `.filter().map()` is an Iterator
2399 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2400 let msg = "called `find(p).map(q)` on an `Iterator`. \
2401 This is more succinctly expressed by calling `.find_map(..)` instead.";
2402 span_lint(cx, FIND_MAP, expr.span, msg);
2406 /// lint use of `filter().map()` for `Iterators`
2407 fn lint_filter_map_map<'a, 'tcx>(
2408 cx: &LateContext<'a, 'tcx>,
2409 expr: &'tcx hir::Expr,
2410 _filter_args: &'tcx [hir::Expr],
2411 _map_args: &'tcx [hir::Expr],
2413 // lint if caller of `.filter().map()` is an Iterator
2414 if match_trait_method(cx, expr, &paths::ITERATOR) {
2415 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
2416 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
2417 span_lint(cx, FILTER_MAP, expr.span, msg);
2421 /// lint use of `filter().flat_map()` for `Iterators`
2422 fn lint_filter_flat_map<'a, 'tcx>(
2423 cx: &LateContext<'a, 'tcx>,
2424 expr: &'tcx hir::Expr,
2425 _filter_args: &'tcx [hir::Expr],
2426 _map_args: &'tcx [hir::Expr],
2428 // lint if caller of `.filter().flat_map()` is an Iterator
2429 if match_trait_method(cx, expr, &paths::ITERATOR) {
2430 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
2431 This is more succinctly expressed by calling `.flat_map(..)` \
2432 and filtering by returning an empty Iterator.";
2433 span_lint(cx, FILTER_MAP, expr.span, msg);
2437 /// lint use of `filter_map().flat_map()` for `Iterators`
2438 fn lint_filter_map_flat_map<'a, 'tcx>(
2439 cx: &LateContext<'a, 'tcx>,
2440 expr: &'tcx hir::Expr,
2441 _filter_args: &'tcx [hir::Expr],
2442 _map_args: &'tcx [hir::Expr],
2444 // lint if caller of `.filter_map().flat_map()` is an Iterator
2445 if match_trait_method(cx, expr, &paths::ITERATOR) {
2446 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
2447 This is more succinctly expressed by calling `.flat_map(..)` \
2448 and filtering by returning an empty Iterator.";
2449 span_lint(cx, FILTER_MAP, expr.span, msg);
2453 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2454 fn lint_flat_map_identity<'a, 'tcx>(
2455 cx: &LateContext<'a, 'tcx>,
2456 expr: &'tcx hir::Expr,
2457 flat_map_args: &'tcx [hir::Expr],
2458 flat_map_span: Span,
2460 if match_trait_method(cx, expr, &paths::ITERATOR) {
2461 let arg_node = &flat_map_args[1].kind;
2463 let apply_lint = |message: &str| {
2467 flat_map_span.with_hi(expr.span.hi()),
2470 "flatten()".to_string(),
2471 Applicability::MachineApplicable,
2476 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2477 let body = cx.tcx.hir().body(*body_id);
2479 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
2480 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
2482 if path.segments.len() == 1;
2483 if path.segments[0].ident.as_str() == binding_ident.as_str();
2486 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2491 if let hir::ExprKind::Path(ref qpath) = arg_node;
2493 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2496 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2502 /// lint searching an Iterator followed by `is_some()`
2503 fn lint_search_is_some<'a, 'tcx>(
2504 cx: &LateContext<'a, 'tcx>,
2505 expr: &'tcx hir::Expr,
2506 search_method: &str,
2507 search_args: &'tcx [hir::Expr],
2508 is_some_args: &'tcx [hir::Expr],
2511 // lint if caller of search is an Iterator
2512 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2514 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2515 expressed by calling `any()`.",
2518 let search_snippet = snippet(cx, search_args[1].span, "..");
2519 if search_snippet.lines().count() <= 1 {
2520 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2521 // suggest `any(|..| *..)` instead of `any(|..| **..)` for `find(|..| **..).is_some()`
2522 let any_search_snippet = if_chain! {
2523 if search_method == "find";
2524 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].kind;
2525 let closure_body = cx.tcx.hir().body(body_id);
2526 if let Some(closure_arg) = closure_body.params.get(0);
2528 if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
2529 Some(search_snippet.replacen('&', "", 1))
2530 } else if let Some(name) = get_arg_name(&closure_arg.pat) {
2531 Some(search_snippet.replace(&format!("*{}", name), &name.as_str()))
2539 // add note if not multi-line
2543 method_span.with_hi(expr.span.hi()),
2548 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2550 Applicability::MachineApplicable,
2553 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2558 /// Used for `lint_binary_expr_with_method_call`.
2559 #[derive(Copy, Clone)]
2560 struct BinaryExprInfo<'a> {
2561 expr: &'a hir::Expr,
2562 chain: &'a hir::Expr,
2563 other: &'a hir::Expr,
2567 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2568 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
2569 macro_rules! lint_with_both_lhs_and_rhs {
2570 ($func:ident, $cx:expr, $info:ident) => {
2571 if !$func($cx, $info) {
2572 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2573 if $func($cx, $info) {
2580 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
2581 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
2582 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
2583 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
2586 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2588 cx: &LateContext<'_, '_>,
2589 info: &BinaryExprInfo<'_>,
2590 chain_methods: &[&str],
2591 lint: &'static Lint,
2595 if let Some(args) = method_chain_args(info.chain, chain_methods);
2596 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.kind;
2597 if arg_char.len() == 1;
2598 if let hir::ExprKind::Path(ref qpath) = fun.kind;
2599 if let Some(segment) = single_segment_path(qpath);
2600 if segment.ident.name == sym!(Some);
2602 let mut applicability = Applicability::MachineApplicable;
2603 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
2605 if self_ty.kind != ty::Str {
2613 &format!("you should use the `{}` method", suggest),
2615 format!("{}{}.{}({})",
2616 if info.eq { "" } else { "!" },
2617 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2619 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
2630 /// Checks for the `CHARS_NEXT_CMP` lint.
2631 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2632 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
2635 /// Checks for the `CHARS_LAST_CMP` lint.
2636 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2637 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
2640 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
2644 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
2645 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
2646 cx: &LateContext<'a, 'tcx>,
2647 info: &BinaryExprInfo<'_>,
2648 chain_methods: &[&str],
2649 lint: &'static Lint,
2653 if let Some(args) = method_chain_args(info.chain, chain_methods);
2654 if let hir::ExprKind::Lit(ref lit) = info.other.kind;
2655 if let ast::LitKind::Char(c) = lit.node;
2657 let mut applicability = Applicability::MachineApplicable;
2662 &format!("you should use the `{}` method", suggest),
2664 format!("{}{}.{}('{}')",
2665 if info.eq { "" } else { "!" },
2666 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2679 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
2680 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2681 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
2684 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
2685 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2686 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
2689 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
2693 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
2694 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
2696 if let hir::ExprKind::Lit(lit) = &arg.kind;
2697 if let ast::LitKind::Str(r, style) = lit.node;
2698 if r.as_str().len() == 1;
2700 let mut applicability = Applicability::MachineApplicable;
2701 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
2702 let ch = if let ast::StrStyle::Raw(nhash) = style {
2703 let nhash = nhash as usize;
2704 // for raw string: r##"a"##
2705 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
2707 // for regular string: "a"
2708 &snip[1..(snip.len() - 1)]
2710 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
2713 SINGLE_CHAR_PATTERN,
2715 "single-character string constant used as pattern",
2716 "try using a char instead",
2724 /// Checks for the `USELESS_ASREF` lint.
2725 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
2726 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
2727 // check if the call is to the actual `AsRef` or `AsMut` trait
2728 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
2729 // check if the type after `as_ref` or `as_mut` is the same as before
2730 let recvr = &as_ref_args[0];
2731 let rcv_ty = cx.tables.expr_ty(recvr);
2732 let res_ty = cx.tables.expr_ty(expr);
2733 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
2734 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
2735 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
2736 // allow the `as_ref` or `as_mut` if it is followed by another method call
2738 if let Some(parent) = get_parent_expr(cx, expr);
2739 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.kind;
2740 if span != &expr.span;
2746 let mut applicability = Applicability::MachineApplicable;
2751 &format!("this call to `{}` does nothing", call_name),
2753 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
2760 fn ty_has_iter_method(cx: &LateContext<'_, '_>, self_ref_ty: Ty<'_>) -> Option<(&'static str, &'static str)> {
2761 has_iter_method(cx, self_ref_ty).map(|ty_name| {
2762 let mutbl = match self_ref_ty.kind {
2763 ty::Ref(_, _, mutbl) => mutbl,
2764 _ => unreachable!(),
2766 let method_name = match mutbl {
2767 hir::MutImmutable => "iter",
2768 hir::MutMutable => "iter_mut",
2770 (ty_name, method_name)
2774 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr, self_ref_ty: Ty<'_>, method_span: Span) {
2775 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
2778 if let Some((kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
2784 "this .into_iter() call is equivalent to .{}() and will not move the {}",
2788 method_name.to_string(),
2789 Applicability::MachineApplicable,
2794 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
2795 fn lint_maybe_uninit(cx: &LateContext<'_, '_>, expr: &hir::Expr, outer: &hir::Expr) {
2797 if let hir::ExprKind::Call(ref callee, ref args) = expr.kind;
2799 if let hir::ExprKind::Path(ref path) = callee.kind;
2800 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
2801 if !is_maybe_uninit_ty_valid(cx, cx.tables.expr_ty_adjusted(outer));
2805 UNINIT_ASSUMED_INIT,
2807 "this call for this type may be undefined behavior"
2813 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
2815 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
2816 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
2817 ty::Adt(ref adt, _) => {
2818 // needs to be a MaybeUninit
2819 match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT)
2825 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2830 "this call to `map()` won't have an effect on the call to `count()`",
2831 "make sure you did not confuse `map` with `filter`",
2835 /// Given a `Result<T, E>` type, return its error type (`E`).
2836 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
2838 ty::Adt(_, substs) if match_type(cx, ty, &paths::RESULT) => substs.types().nth(1),
2843 /// This checks whether a given type is known to implement Debug.
2844 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
2846 .get_diagnostic_item(sym::debug_trait)
2847 .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
2852 StartsWith(&'static str),
2856 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
2857 (Convention::Eq("new"), &[SelfKind::No]),
2858 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
2859 (Convention::StartsWith("from_"), &[SelfKind::No]),
2860 (Convention::StartsWith("into_"), &[SelfKind::Value]),
2861 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
2862 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
2863 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
2867 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
2868 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
2869 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
2870 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
2871 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
2872 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
2873 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
2874 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
2875 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
2876 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
2877 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
2878 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
2879 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
2880 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
2881 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
2882 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
2883 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
2884 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
2885 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
2886 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
2887 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
2888 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
2889 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
2890 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
2891 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
2892 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
2893 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
2894 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
2895 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
2896 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
2897 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
2901 const PATTERN_METHODS: [(&str, usize); 17] = [
2909 ("split_terminator", 1),
2910 ("rsplit_terminator", 1),
2915 ("match_indices", 1),
2916 ("rmatch_indices", 1),
2917 ("trim_start_matches", 1),
2918 ("trim_end_matches", 1),
2921 #[derive(Clone, Copy, PartialEq, Debug)]
2930 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2931 fn matches_value(parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2932 if ty == parent_ty {
2934 } else if ty.is_box() {
2935 ty.boxed_ty() == parent_ty
2936 } else if ty.is_rc() || ty.is_arc() {
2937 if let ty::Adt(_, substs) = ty.kind {
2938 substs.types().next().map_or(false, |t| t == parent_ty)
2948 cx: &LateContext<'_, 'a>,
2949 mutability: hir::Mutability,
2953 if let ty::Ref(_, t, m) = ty.kind {
2954 return m == mutability && t == parent_ty;
2957 let trait_path = match mutability {
2958 hir::Mutability::MutImmutable => &paths::ASREF_TRAIT,
2959 hir::Mutability::MutMutable => &paths::ASMUT_TRAIT,
2962 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2964 None => return false,
2966 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2970 Self::Value => matches_value(parent_ty, ty),
2972 matches_ref(cx, hir::Mutability::MutImmutable, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty)
2974 Self::RefMut => matches_ref(cx, hir::Mutability::MutMutable, parent_ty, ty),
2975 Self::No => ty != parent_ty,
2980 fn description(self) -> &'static str {
2982 Self::Value => "self by value",
2983 Self::Ref => "self by reference",
2984 Self::RefMut => "self by mutable reference",
2985 Self::No => "no self",
2992 fn check(&self, other: &str) -> bool {
2994 Self::Eq(this) => this == other,
2995 Self::StartsWith(this) => other.starts_with(this) && this != other,
3000 impl fmt::Display for Convention {
3001 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
3003 Self::Eq(this) => this.fmt(f),
3004 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
3009 #[derive(Clone, Copy)]
3018 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FunctionRetTy) -> bool {
3019 let is_unit = |ty: &hir::Ty| SpanlessEq::new(cx).eq_ty_kind(&ty.kind, &hir::TyKind::Tup(vec![].into()));
3021 (Self::Unit, &hir::DefaultReturn(_)) => true,
3022 (Self::Unit, &hir::Return(ref ty)) if is_unit(ty) => true,
3023 (Self::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
3024 (Self::Any, &hir::Return(ref ty)) if !is_unit(ty) => true,
3025 (Self::Ref, &hir::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
3031 fn is_bool(ty: &hir::Ty) -> bool {
3032 if let hir::TyKind::Path(ref p) = ty.kind {
3033 match_qpath(p, &["bool"])
3039 // Returns `true` if `expr` contains a return expression
3040 fn contains_return(expr: &hir::Expr) -> bool {
3041 struct RetCallFinder {
3045 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
3046 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
3050 if let hir::ExprKind::Ret(..) = &expr.kind {
3053 intravisit::walk_expr(self, expr);
3057 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
3058 intravisit::NestedVisitorMap::None
3062 let mut visitor = RetCallFinder { found: false };
3063 visitor.visit_expr(expr);