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;
12 use rustc::declare_lint_pass;
14 use rustc::hir::intravisit::{self, Visitor};
15 use rustc::lint::{in_external_macro, LateContext, LateLintPass, Lint, LintArray, LintContext, LintPass};
16 use rustc::ty::{self, Predicate, Ty};
17 use rustc_errors::Applicability;
18 use rustc_session::declare_tool_lint;
20 use syntax::source_map::Span;
21 use syntax::symbol::{sym, Symbol, SymbolStr};
23 use crate::utils::usage::mutated_variables;
25 get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, in_macro, is_copy,
26 is_ctor_or_promotable_const_function, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment,
27 match_def_path, match_qpath, match_trait_method, match_type, match_var, method_calls, method_chain_args, paths,
28 remove_blocks, return_ty, same_tys, single_segment_path, snippet, snippet_with_applicability,
29 snippet_with_macro_callsite, span_help_and_lint, span_lint, span_lint_and_sugg, span_lint_and_then,
30 span_note_and_lint, sugg, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
33 declare_clippy_lint! {
34 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
36 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
37 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
38 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
39 /// `Allow` by default.
41 /// **Known problems:** None.
45 /// Using unwrap on an `Option`:
48 /// let opt = Some(1);
55 /// let opt = Some(1);
56 /// opt.expect("more helpful message");
58 pub OPTION_UNWRAP_USED,
60 "using `Option.unwrap()`, which should at least get a better message using `expect()`"
63 declare_clippy_lint! {
64 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
66 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
67 /// values. Normally, you want to implement more sophisticated error handling,
68 /// and propagate errors upwards with `try!`.
70 /// Even if you want to panic on errors, not all `Error`s implement good
71 /// messages on display. Therefore, it may be beneficial to look at the places
72 /// where they may get displayed. Activate this lint to do just that.
74 /// **Known problems:** None.
77 /// Using unwrap on an `Result`:
80 /// let res: Result<usize, ()> = Ok(1);
87 /// let res: Result<usize, ()> = Ok(1);
88 /// res.expect("more helpful message");
90 pub RESULT_UNWRAP_USED,
92 "using `Result.unwrap()`, which might be better handled"
95 declare_clippy_lint! {
96 /// **What it does:** Checks for `.expect()` calls on `Option`s.
98 /// **Why is this bad?** Usually it is better to handle the `None` case. Still,
99 /// for a lot of quick-and-dirty code, `expect` is a good choice, which is why
100 /// this lint is `Allow` by default.
102 /// **Known problems:** None.
106 /// Using expect on an `Option`:
109 /// let opt = Some(1);
110 /// opt.expect("one");
116 /// let opt = Some(1);
120 pub OPTION_EXPECT_USED,
122 "using `Option.expect()`, which might be better handled"
125 declare_clippy_lint! {
126 /// **What it does:** Checks for `.expect()` calls on `Result`s.
128 /// **Why is this bad?** `result.expect()` will let the thread panic on `Err`
129 /// values. Normally, you want to implement more sophisticated error handling,
130 /// and propagate errors upwards with `try!`.
132 /// **Known problems:** None.
135 /// Using expect on an `Result`:
138 /// let res: Result<usize, ()> = Ok(1);
139 /// res.expect("one");
145 /// let res: Result<usize, ()> = Ok(1);
147 /// # Ok::<(), ()>(())
149 pub RESULT_EXPECT_USED,
151 "using `Result.expect()`, which might be better handled"
154 declare_clippy_lint! {
155 /// **What it does:** Checks for methods that should live in a trait
156 /// implementation of a `std` trait (see [llogiq's blog
157 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
158 /// information) instead of an inherent implementation.
160 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
161 /// the code, often with very little cost. Also people seeing a `mul(...)`
163 /// may expect `*` to work equally, so you should have good reason to disappoint
166 /// **Known problems:** None.
172 /// fn add(&self, other: &X) -> X {
177 pub SHOULD_IMPLEMENT_TRAIT,
179 "defining a method that should be implementing a std trait"
182 declare_clippy_lint! {
183 /// **What it does:** Checks for methods with certain name prefixes and which
184 /// doesn't match how self is taken. The actual rules are:
186 /// |Prefix |`self` taken |
187 /// |-------|----------------------|
188 /// |`as_` |`&self` or `&mut self`|
190 /// |`into_`|`self` |
191 /// |`is_` |`&self` or none |
192 /// |`to_` |`&self` |
194 /// **Why is this bad?** Consistency breeds readability. If you follow the
195 /// conventions, your users won't be surprised that they, e.g., need to supply a
196 /// mutable reference to a `as_..` function.
198 /// **Known problems:** None.
203 /// fn as_str(self) -> &str {
208 pub WRONG_SELF_CONVENTION,
210 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
213 declare_clippy_lint! {
214 /// **What it does:** This is the same as
215 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
217 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
219 /// **Known problems:** Actually *renaming* the function may break clients if
220 /// the function is part of the public interface. In that case, be mindful of
221 /// the stability guarantees you've given your users.
227 /// pub fn as_str(self) -> &'a str {
232 pub WRONG_PUB_SELF_CONVENTION,
234 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
237 declare_clippy_lint! {
238 /// **What it does:** Checks for usage of `ok().expect(..)`.
240 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
241 /// directly to get a better error message.
243 /// **Known problems:** The error type needs to implement `Debug`
247 /// x.ok().expect("why did I do this again?")
251 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
254 declare_clippy_lint! {
255 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
257 /// **Why is this bad?** Readability, this can be written more concisely as
258 /// `_.map_or(_, _)`.
260 /// **Known problems:** The order of the arguments is not in execution order
264 /// # let x = Some(1);
265 /// x.map(|a| a + 1).unwrap_or(0);
267 pub OPTION_MAP_UNWRAP_OR,
269 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
272 declare_clippy_lint! {
273 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
275 /// **Why is this bad?** Readability, this can be written more concisely as
276 /// `_.map_or_else(_, _)`.
278 /// **Known problems:** The order of the arguments is not in execution order.
282 /// # let x = Some(1);
283 /// # fn some_function() -> usize { 1 }
284 /// x.map(|a| a + 1).unwrap_or_else(some_function);
286 pub OPTION_MAP_UNWRAP_OR_ELSE,
288 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
291 declare_clippy_lint! {
292 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
294 /// **Why is this bad?** Readability, this can be written more concisely as
295 /// `result.map_or_else(_, _)`.
297 /// **Known problems:** None.
301 /// # let x: Result<usize, ()> = Ok(1);
302 /// # fn some_function(foo: ()) -> usize { 1 }
303 /// x.map(|a| a + 1).unwrap_or_else(some_function);
305 pub RESULT_MAP_UNWRAP_OR_ELSE,
307 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.map_or_else(g, f)`"
310 declare_clippy_lint! {
311 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
313 /// **Why is this bad?** Readability, this can be written more concisely as
316 /// **Known problems:** The order of the arguments is not in execution order.
320 /// opt.map_or(None, |a| a + 1)
322 pub OPTION_MAP_OR_NONE,
324 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
327 declare_clippy_lint! {
328 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
330 /// **Why is this bad?** Readability, this can be written more concisely as
333 /// **Known problems:** None
338 /// let x = Some("foo");
339 /// let _ = x.and_then(|s| Some(s.len()));
342 /// The correct use would be:
345 /// let x = Some("foo");
346 /// let _ = x.map(|s| s.len());
348 pub OPTION_AND_THEN_SOME,
350 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
353 declare_clippy_lint! {
354 /// **What it does:** Checks for usage of `_.filter(_).next()`.
356 /// **Why is this bad?** Readability, this can be written more concisely as
359 /// **Known problems:** None.
363 /// # let vec = vec![1];
364 /// vec.iter().filter(|x| **x == 0).next();
366 /// Could be written as
368 /// # let vec = vec![1];
369 /// vec.iter().find(|x| **x == 0);
373 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
376 declare_clippy_lint! {
377 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
379 /// **Why is this bad?** Readability, this can be written more concisely as a
380 /// single method call.
382 /// **Known problems:**
386 /// let vec = vec![vec![1]];
387 /// vec.iter().map(|x| x.iter()).flatten();
391 "using combinations of `flatten` and `map` which can usually be written as a single method call"
394 declare_clippy_lint! {
395 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
396 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
398 /// **Why is this bad?** Readability, this can be written more concisely as a
399 /// single method call.
401 /// **Known problems:** Often requires a condition + Option/Iterator creation
402 /// inside the closure.
406 /// let vec = vec![1];
407 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
411 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
414 declare_clippy_lint! {
415 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
417 /// **Why is this bad?** Readability, this can be written more concisely as a
418 /// single method call.
420 /// **Known problems:** None
424 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
426 /// Can be written as
429 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
433 "using combination of `filter_map` and `next` which can usually be written as a single method call"
436 declare_clippy_lint! {
437 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
439 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
441 /// **Known problems:** None
445 /// # let iter = vec![vec![0]].into_iter();
446 /// iter.flat_map(|x| x);
448 /// Can be written as
450 /// # let iter = vec![vec![0]].into_iter();
453 pub FLAT_MAP_IDENTITY,
455 "call to `flat_map` where `flatten` is sufficient"
458 declare_clippy_lint! {
459 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
461 /// **Why is this bad?** Readability, this can be written more concisely as a
462 /// single method call.
464 /// **Known problems:** Often requires a condition + Option/Iterator creation
465 /// inside the closure.
469 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
471 /// Can be written as
473 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
477 "using a combination of `find` and `map` can usually be written as a single method call"
480 declare_clippy_lint! {
481 /// **What it does:** Checks for an iterator search (such as `find()`,
482 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
484 /// **Why is this bad?** Readability, this can be written more concisely as
487 /// **Known problems:** None.
491 /// # let vec = vec![1];
492 /// vec.iter().find(|x| **x == 0).is_some();
494 /// Could be written as
496 /// # let vec = vec![1];
497 /// vec.iter().any(|x| *x == 0);
501 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
504 declare_clippy_lint! {
505 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
506 /// if it starts with a given char.
508 /// **Why is this bad?** Readability, this can be written more concisely as
509 /// `_.starts_with(_)`.
511 /// **Known problems:** None.
515 /// let name = "foo";
516 /// if name.chars().next() == Some('_') {};
518 /// Could be written as
520 /// let name = "foo";
521 /// if name.starts_with('_') {};
525 "using `.chars().next()` to check if a string starts with a char"
528 declare_clippy_lint! {
529 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
530 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
531 /// `unwrap_or_default` instead.
533 /// **Why is this bad?** The function will always be called and potentially
534 /// allocate an object acting as the default.
536 /// **Known problems:** If the function has side-effects, not calling it will
537 /// change the semantic of the program, but you shouldn't rely on that anyway.
541 /// # let foo = Some(String::new());
542 /// foo.unwrap_or(String::new());
544 /// this can instead be written:
546 /// # let foo = Some(String::new());
547 /// foo.unwrap_or_else(String::new);
551 /// # let foo = Some(String::new());
552 /// foo.unwrap_or_default();
556 "using any `*or` method with a function call, which suggests `*or_else`"
559 declare_clippy_lint! {
560 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
561 /// etc., and suggests to use `unwrap_or_else` instead
563 /// **Why is this bad?** The function will always be called.
565 /// **Known problems:** If the function has side-effects, not calling it will
566 /// change the semantics of the program, but you shouldn't rely on that anyway.
570 /// # let foo = Some(String::new());
571 /// # let err_code = "418";
572 /// # let err_msg = "I'm a teapot";
573 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
577 /// # let foo = Some(String::new());
578 /// # let err_code = "418";
579 /// # let err_msg = "I'm a teapot";
580 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
582 /// this can instead be written:
584 /// # let foo = Some(String::new());
585 /// # let err_code = "418";
586 /// # let err_msg = "I'm a teapot";
587 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
591 "using any `expect` method with a function call"
594 declare_clippy_lint! {
595 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
597 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
598 /// generics, not for using the `clone` method on a concrete type.
600 /// **Known problems:** None.
608 "using `clone` on a `Copy` type"
611 declare_clippy_lint! {
612 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
613 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
614 /// function syntax instead (e.g., `Rc::clone(foo)`).
616 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
617 /// can obscure the fact that only the pointer is being cloned, not the underlying
622 /// # use std::rc::Rc;
623 /// let x = Rc::new(1);
626 pub CLONE_ON_REF_PTR,
628 "using 'clone' on a ref-counted pointer"
631 declare_clippy_lint! {
632 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
634 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
635 /// cloning the underlying `T`.
637 /// **Known problems:** None.
644 /// let z = y.clone();
645 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
648 pub CLONE_DOUBLE_REF,
650 "using `clone` on `&&T`"
653 declare_clippy_lint! {
654 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
655 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
657 /// **Why is this bad?** This bypasses the specialized implementation of
658 /// `ToString` and instead goes through the more expensive string formatting
661 /// **Known problems:** None.
665 /// // Generic implementation for `T: Display` is used (slow)
666 /// ["foo", "bar"].iter().map(|s| s.to_string());
668 /// // OK, the specialized impl is used
669 /// ["foo", "bar"].iter().map(|&s| s.to_string());
671 pub INEFFICIENT_TO_STRING,
673 "using `to_string` on `&&T` where `T: ToString`"
676 declare_clippy_lint! {
677 /// **What it does:** Checks for `new` not returning `Self`.
679 /// **Why is this bad?** As a convention, `new` methods are used to make a new
680 /// instance of a type.
682 /// **Known problems:** None.
687 /// fn new(..) -> NotAFoo {
693 "not returning `Self` in a `new` method"
696 declare_clippy_lint! {
697 /// **What it does:** Checks for string methods that receive a single-character
698 /// `str` as an argument, e.g., `_.split("x")`.
700 /// **Why is this bad?** Performing these methods using a `char` is faster than
703 /// **Known problems:** Does not catch multi-byte unicode characters.
706 /// `_.split("x")` could be `_.split('x')`
707 pub SINGLE_CHAR_PATTERN,
709 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
712 declare_clippy_lint! {
713 /// **What it does:** Checks for getting the inner pointer of a temporary
716 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
717 /// as the `CString` is alive.
719 /// **Known problems:** None.
723 /// let c_str = CString::new("foo").unwrap().as_ptr();
725 /// call_some_ffi_func(c_str);
728 /// Here `c_str` point to a freed address. The correct use would be:
730 /// let c_str = CString::new("foo").unwrap();
732 /// call_some_ffi_func(c_str.as_ptr());
735 pub TEMPORARY_CSTRING_AS_PTR,
737 "getting the inner pointer of a temporary `CString`"
740 declare_clippy_lint! {
741 /// **What it does:** Checks for use of `.iter().nth()` (and the related
742 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
744 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
747 /// **Known problems:** None.
751 /// let some_vec = vec![0, 1, 2, 3];
752 /// let bad_vec = some_vec.iter().nth(3);
753 /// let bad_slice = &some_vec[..].iter().nth(3);
755 /// The correct use would be:
757 /// let some_vec = vec![0, 1, 2, 3];
758 /// let bad_vec = some_vec.get(3);
759 /// let bad_slice = &some_vec[..].get(3);
763 "using `.iter().nth()` on a standard library type with O(1) element access"
766 declare_clippy_lint! {
767 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
769 /// **Why is this bad?** `.nth(x)` is cleaner
771 /// **Known problems:** None.
775 /// let some_vec = vec![0, 1, 2, 3];
776 /// let bad_vec = some_vec.iter().skip(3).next();
777 /// let bad_slice = &some_vec[..].iter().skip(3).next();
779 /// The correct use would be:
781 /// let some_vec = vec![0, 1, 2, 3];
782 /// let bad_vec = some_vec.iter().nth(3);
783 /// let bad_slice = &some_vec[..].iter().nth(3);
787 "using `.skip(x).next()` on an iterator"
790 declare_clippy_lint! {
791 /// **What it does:** Checks for use of `.get().unwrap()` (or
792 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
794 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
797 /// **Known problems:** Not a replacement for error handling: Using either
798 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
799 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
800 /// temporary placeholder for dealing with the `Option` type, then this does
801 /// not mitigate the need for error handling. If there is a chance that `.get()`
802 /// will be `None` in your program, then it is advisable that the `None` case
803 /// is handled in a future refactor instead of using `.unwrap()` or the Index
808 /// let mut some_vec = vec![0, 1, 2, 3];
809 /// let last = some_vec.get(3).unwrap();
810 /// *some_vec.get_mut(0).unwrap() = 1;
812 /// The correct use would be:
814 /// let mut some_vec = vec![0, 1, 2, 3];
815 /// let last = some_vec[3];
820 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
823 declare_clippy_lint! {
824 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
825 /// `&str` or `String`.
827 /// **Why is this bad?** `.push_str(s)` is clearer
829 /// **Known problems:** None.
834 /// let def = String::from("def");
835 /// let mut s = String::new();
836 /// s.extend(abc.chars());
837 /// s.extend(def.chars());
839 /// The correct use would be:
842 /// let def = String::from("def");
843 /// let mut s = String::new();
845 /// s.push_str(&def);
847 pub STRING_EXTEND_CHARS,
849 "using `x.extend(s.chars())` where s is a `&str` or `String`"
852 declare_clippy_lint! {
853 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
856 /// **Why is this bad?** `.to_vec()` is clearer
858 /// **Known problems:** None.
862 /// let s = [1, 2, 3, 4, 5];
863 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
865 /// The better use would be:
867 /// let s = [1, 2, 3, 4, 5];
868 /// let s2: Vec<isize> = s.to_vec();
870 pub ITER_CLONED_COLLECT,
872 "using `.cloned().collect()` on slice to create a `Vec`"
875 declare_clippy_lint! {
876 /// **What it does:** Checks for usage of `.chars().last()` or
877 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
879 /// **Why is this bad?** Readability, this can be written more concisely as
880 /// `_.ends_with(_)`.
882 /// **Known problems:** None.
886 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
890 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
893 declare_clippy_lint! {
894 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
895 /// types before and after the call are the same.
897 /// **Why is this bad?** The call is unnecessary.
899 /// **Known problems:** None.
903 /// # fn do_stuff(x: &[i32]) {}
904 /// let x: &[i32] = &[1, 2, 3, 4, 5];
905 /// do_stuff(x.as_ref());
907 /// The correct use would be:
909 /// # fn do_stuff(x: &[i32]) {}
910 /// let x: &[i32] = &[1, 2, 3, 4, 5];
915 "using `as_ref` where the types before and after the call are the same"
918 declare_clippy_lint! {
919 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
920 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
921 /// `sum` or `product`.
923 /// **Why is this bad?** Readability.
925 /// **Known problems:** False positive in pattern guards. Will be resolved once
926 /// non-lexical lifetimes are stable.
930 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
932 /// This could be written as:
934 /// let _ = (0..3).any(|x| x > 2);
936 pub UNNECESSARY_FOLD,
938 "using `fold` when a more succinct alternative exists"
941 declare_clippy_lint! {
942 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
943 /// More specifically it checks if the closure provided is only performing one of the
944 /// filter or map operations and suggests the appropriate option.
946 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
947 /// operation is being performed.
949 /// **Known problems:** None
953 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
955 /// As there is no transformation of the argument this could be written as:
957 /// let _ = (0..3).filter(|&x| x > 2);
961 /// let _ = (0..4).filter_map(|x| Some(x + 1));
963 /// As there is no conditional check on the argument this could be written as:
965 /// let _ = (0..4).map(|x| x + 1);
967 pub UNNECESSARY_FILTER_MAP,
969 "using `filter_map` when a more succinct alternative exists"
972 declare_clippy_lint! {
973 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
976 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
977 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
978 /// `iter_mut` directly.
980 /// **Known problems:** None
985 /// let _ = (&vec![3, 4, 5]).into_iter();
987 pub INTO_ITER_ON_REF,
989 "using `.into_iter()` on a reference"
992 declare_clippy_lint! {
993 /// **What it does:** Checks for calls to `map` followed by a `count`.
995 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
996 /// If the `map` call is intentional, this should be rewritten.
998 /// **Known problems:** None
1003 /// let _ = (0..3).map(|x| x + 2).count();
1007 "suspicious usage of map"
1010 declare_clippy_lint! {
1011 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1013 /// **Why is this bad?** For most types, this is undefined behavior.
1015 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1016 /// of `MaybeUninit`. There may be other types that allow uninitialized
1017 /// data, but those are not yet rigorously defined.
1022 /// // Beware the UB
1023 /// use std::mem::MaybeUninit;
1025 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1028 /// Note that the following is OK:
1031 /// use std::mem::MaybeUninit;
1033 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1034 /// MaybeUninit::uninit().assume_init()
1037 pub UNINIT_ASSUMED_INIT,
1039 "`MaybeUninit::uninit().assume_init()`"
1042 declare_clippy_lint! {
1043 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1045 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1050 /// # let y: u32 = 0;
1051 /// # let x: u32 = 100;
1052 /// let add = x.checked_add(y).unwrap_or(u32::max_value());
1053 /// let sub = x.checked_sub(y).unwrap_or(u32::min_value());
1056 /// can be written using dedicated methods for saturating addition/subtraction as:
1059 /// # let y: u32 = 0;
1060 /// # let x: u32 = 100;
1061 /// let add = x.saturating_add(y);
1062 /// let sub = x.saturating_sub(y);
1064 pub MANUAL_SATURATING_ARITHMETIC,
1066 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1069 declare_clippy_lint! {
1070 /// **What it does:** Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1071 /// zero-sized types
1073 /// **Why is this bad?** This is a no-op, and likely unintended
1075 /// **Known problems:** None
1079 /// unsafe { (&() as *const ()).offset(1) };
1083 "Check for offset calculations on raw pointers to zero-sized types"
1086 declare_lint_pass!(Methods => [
1091 SHOULD_IMPLEMENT_TRAIT,
1092 WRONG_SELF_CONVENTION,
1093 WRONG_PUB_SELF_CONVENTION,
1095 OPTION_MAP_UNWRAP_OR,
1096 OPTION_MAP_UNWRAP_OR_ELSE,
1097 RESULT_MAP_UNWRAP_OR_ELSE,
1099 OPTION_AND_THEN_SOME,
1107 INEFFICIENT_TO_STRING,
1109 SINGLE_CHAR_PATTERN,
1111 TEMPORARY_CSTRING_AS_PTR,
1121 STRING_EXTEND_CHARS,
1122 ITER_CLONED_COLLECT,
1125 UNNECESSARY_FILTER_MAP,
1128 UNINIT_ASSUMED_INIT,
1129 MANUAL_SATURATING_ARITHMETIC,
1133 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
1134 #[allow(clippy::cognitive_complexity)]
1135 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
1136 if in_macro(expr.span) {
1140 let (method_names, arg_lists, method_spans) = method_calls(expr, 2);
1141 let method_names: Vec<SymbolStr> = method_names.iter().map(|s| s.as_str()).collect();
1142 let method_names: Vec<&str> = method_names.iter().map(|s| &**s).collect();
1144 match method_names.as_slice() {
1145 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1146 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1147 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1148 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1149 ["expect", ..] => lint_expect(cx, expr, arg_lists[0]),
1150 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0]),
1151 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
1152 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1153 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
1154 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1155 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1156 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1157 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1158 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1159 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1160 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1161 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0], method_spans[0]),
1162 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1163 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0], method_spans[1]),
1164 ["is_some", "position"] => {
1165 lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0], method_spans[1])
1167 ["is_some", "rposition"] => {
1168 lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
1170 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1171 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1172 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1174 ["nth", "iter"] => lint_iter_nth(cx, expr, arg_lists[1], false),
1175 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, arg_lists[1], true),
1176 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1177 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1178 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1179 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1180 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0], method_spans[0]),
1181 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1182 ["count", "map"] => lint_suspicious_map(cx, expr),
1183 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1184 ["unwrap_or", arith @ "checked_add"]
1185 | ["unwrap_or", arith @ "checked_sub"]
1186 | ["unwrap_or", arith @ "checked_mul"] => {
1187 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1189 ["add"] | ["offset"] | ["sub"] | ["wrapping_offset"] | ["wrapping_add"] | ["wrapping_sub"] => {
1190 check_pointer_offset(cx, expr, arg_lists[0])
1196 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1197 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1198 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1200 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1201 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1202 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1203 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1205 if args.len() == 1 && method_call.ident.name == sym!(to_string) {
1206 inefficient_to_string::lint(cx, expr, &args[0], self_ty);
1209 match self_ty.kind {
1210 ty::Ref(_, ty, _) if ty.kind == ty::Str => {
1211 for &(method, pos) in &PATTERN_METHODS {
1212 if method_call.ident.name.as_str() == method && args.len() > pos {
1213 lint_single_char_pattern(cx, expr, &args[pos]);
1217 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1218 lint_into_iter(cx, expr, self_ty, *method_span);
1223 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1224 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1226 let mut info = BinaryExprInfo {
1230 eq: op.node == hir::BinOpKind::Eq,
1232 lint_binary_expr_with_method_call(cx, &mut info);
1238 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem) {
1239 if in_external_macro(cx.sess(), impl_item.span) {
1242 let name = impl_item.ident.name.as_str();
1243 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1244 let item = cx.tcx.hir().expect_item(parent);
1245 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1246 let ty = cx.tcx.type_of(def_id);
1248 if let hir::ImplItemKind::Method(ref sig, id) = impl_item.kind;
1249 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1250 if let hir::ItemKind::Impl(_, _, _, _, None, _, _) = item.kind;
1252 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1253 let method_sig = cx.tcx.fn_sig(method_def_id);
1254 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1256 let first_arg_ty = &method_sig.inputs().iter().next();
1258 // check conventions w.r.t. conversion method names and predicates
1259 if let Some(first_arg_ty) = first_arg_ty;
1262 if cx.access_levels.is_exported(impl_item.hir_id) {
1263 // check missing trait implementations
1264 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1265 if name == method_name &&
1266 sig.decl.inputs.len() == n_args &&
1267 out_type.matches(cx, &sig.decl.output) &&
1268 self_kind.matches(cx, ty, first_arg_ty) {
1269 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1270 "defining a method called `{}` on this type; consider implementing \
1271 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1276 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1278 .find(|(ref conv, _)| conv.check(&name))
1280 if !self_kinds.iter().any(|k| k.matches(cx, ty, first_arg_ty)) {
1281 let lint = if item.vis.node.is_pub() {
1282 WRONG_PUB_SELF_CONVENTION
1284 WRONG_SELF_CONVENTION
1292 "methods called `{}` usually take {}; consider choosing a less \
1297 .map(|k| k.description())
1298 .collect::<Vec<_>>()
1307 if let hir::ImplItemKind::Method(_, _) = impl_item.kind {
1308 let ret_ty = return_ty(cx, impl_item.hir_id);
1310 // walk the return type and check for Self (this does not check associated types)
1311 if ret_ty.walk().any(|inner_type| same_tys(cx, ty, inner_type)) {
1315 // if return type is impl trait, check the associated types
1316 if let ty::Opaque(def_id, _) = ret_ty.kind {
1317 // one of the associated types must be Self
1318 for predicate in cx.tcx.predicates_of(def_id).predicates {
1320 (Predicate::Projection(poly_projection_predicate), _) => {
1321 let binder = poly_projection_predicate.ty();
1322 let associated_type = binder.skip_binder();
1324 // walk the associated type and check for Self
1325 for inner_type in associated_type.walk() {
1326 if same_tys(cx, ty, inner_type) {
1336 if name == "new" && !same_tys(cx, ret_ty, ty) {
1341 "methods called `new` usually return `Self`",
1348 /// Checks for the `OR_FUN_CALL` lint.
1349 #[allow(clippy::too_many_lines)]
1350 fn lint_or_fun_call<'a, 'tcx>(
1351 cx: &LateContext<'a, 'tcx>,
1355 args: &'tcx [hir::Expr],
1357 // Searches an expression for method calls or function calls that aren't ctors
1358 struct FunCallFinder<'a, 'tcx> {
1359 cx: &'a LateContext<'a, 'tcx>,
1363 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1364 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
1365 let call_found = match &expr.kind {
1366 // ignore enum and struct constructors
1367 hir::ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
1368 hir::ExprKind::MethodCall(..) => true,
1377 intravisit::walk_expr(self, expr);
1381 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1382 intravisit::NestedVisitorMap::None
1386 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1387 fn check_unwrap_or_default(
1388 cx: &LateContext<'_, '_>,
1391 self_expr: &hir::Expr,
1398 if name == "unwrap_or";
1399 if let hir::ExprKind::Path(ref qpath) = fun.kind;
1400 let path = &*last_path_segment(qpath).ident.as_str();
1401 if ["default", "new"].contains(&path);
1402 let arg_ty = cx.tables.expr_ty(arg);
1403 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1404 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1407 let mut applicability = Applicability::MachineApplicable;
1412 &format!("use of `{}` followed by a call to `{}`", name, path),
1415 "{}.unwrap_or_default()",
1416 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1428 /// Checks for `*or(foo())`.
1429 #[allow(clippy::too_many_arguments)]
1430 fn check_general_case<'a, 'tcx>(
1431 cx: &LateContext<'a, 'tcx>,
1435 self_expr: &hir::Expr,
1436 arg: &'tcx hir::Expr,
1440 // (path, fn_has_argument, methods, suffix)
1441 let know_types: &[(&[_], _, &[_], _)] = &[
1442 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1443 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1444 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1445 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1449 if know_types.iter().any(|k| k.2.contains(&name));
1451 let mut finder = FunCallFinder { cx: &cx, found: false };
1452 if { finder.visit_expr(&arg); finder.found };
1453 if !contains_return(&arg);
1455 let self_ty = cx.tables.expr_ty(self_expr);
1457 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1458 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1460 if poss.contains(&name);
1463 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1464 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1465 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1466 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1468 let span_replace_word = method_span.with_hi(span.hi());
1473 &format!("use of `{}` followed by a function call", name),
1475 format!("{}_{}({})", name, suffix, sugg),
1476 Applicability::HasPlaceholders,
1482 if args.len() == 2 {
1483 match args[1].kind {
1484 hir::ExprKind::Call(ref fun, ref or_args) => {
1485 let or_has_args = !or_args.is_empty();
1486 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1499 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1506 !or_args.is_empty(),
1514 /// Checks for the `EXPECT_FUN_CALL` lint.
1515 #[allow(clippy::too_many_lines)]
1516 fn lint_expect_fun_call(cx: &LateContext<'_, '_>, expr: &hir::Expr, method_span: Span, name: &str, args: &[hir::Expr]) {
1517 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1519 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr) -> &'a hir::Expr {
1520 let mut arg_root = arg;
1522 arg_root = match &arg_root.kind {
1523 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr) => expr,
1524 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1525 if call_args.len() == 1
1526 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1528 let arg_type = cx.tables.expr_ty(&call_args[0]);
1529 let base_type = walk_ptrs_ty(arg_type);
1530 base_type.kind == ty::Str || match_type(cx, base_type, &paths::STRING)
1544 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1545 // converted to string.
1546 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr) -> bool {
1547 let arg_ty = cx.tables.expr_ty(arg);
1548 if match_type(cx, arg_ty, &paths::STRING) {
1551 if let ty::Ref(ty::ReStatic, ty, ..) = arg_ty.kind {
1552 if ty.kind == ty::Str {
1559 fn generate_format_arg_snippet(
1560 cx: &LateContext<'_, '_>,
1562 applicability: &mut Applicability,
1565 if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref format_arg) = a.kind;
1566 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.kind;
1567 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.kind;
1572 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1580 fn is_call(node: &hir::ExprKind) -> bool {
1582 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr) => {
1585 hir::ExprKind::Call(..)
1586 | hir::ExprKind::MethodCall(..)
1587 // These variants are debatable or require further examination
1588 | hir::ExprKind::Match(..)
1589 | hir::ExprKind::Block{ .. } => true,
1594 if args.len() != 2 || name != "expect" || !is_call(&args[1].kind) {
1598 let receiver_type = cx.tables.expr_ty_adjusted(&args[0]);
1599 let closure_args = if match_type(cx, receiver_type, &paths::OPTION) {
1601 } else if match_type(cx, receiver_type, &paths::RESULT) {
1607 let arg_root = get_arg_root(cx, &args[1]);
1609 let span_replace_word = method_span.with_hi(expr.span.hi());
1611 let mut applicability = Applicability::MachineApplicable;
1613 //Special handling for `format!` as arg_root
1615 if let hir::ExprKind::Block(block, None) = &arg_root.kind;
1616 if block.stmts.len() == 1;
1617 if let hir::StmtKind::Local(local) = &block.stmts[0].kind;
1618 if let Some(arg_root) = &local.init;
1619 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.kind;
1620 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1;
1621 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].kind;
1623 let fmt_spec = &format_args[0];
1624 let fmt_args = &format_args[1];
1626 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1628 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1630 let sugg = args.join(", ");
1636 &format!("use of `{}` followed by a function call", name),
1638 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
1646 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
1647 if requires_to_string(cx, arg_root) {
1648 arg_root_snippet.to_mut().push_str(".to_string()");
1655 &format!("use of `{}` followed by a function call", name),
1657 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
1662 /// Checks for the `CLONE_ON_COPY` lint.
1663 fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty<'_>) {
1664 let ty = cx.tables.expr_ty(expr);
1665 if let ty::Ref(_, inner, _) = arg_ty.kind {
1666 if let ty::Ref(_, innermost, _) = inner.kind {
1671 "using `clone` on a double-reference; \
1672 this will copy the reference instead of cloning the inner type",
1674 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
1675 let mut ty = innermost;
1677 while let ty::Ref(_, inner, _) = ty.kind {
1681 let refs: String = iter::repeat('&').take(n + 1).collect();
1682 let derefs: String = iter::repeat('*').take(n).collect();
1683 let explicit = format!("{}{}::clone({})", refs, ty, snip);
1686 "try dereferencing it",
1687 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
1688 Applicability::MaybeIncorrect,
1692 "or try being explicit about what type to clone",
1694 Applicability::MaybeIncorrect,
1699 return; // don't report clone_on_copy
1703 if is_copy(cx, ty) {
1705 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1706 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
1707 match &cx.tcx.hir().get(parent) {
1708 hir::Node::Expr(parent) => match parent.kind {
1709 // &*x is a nop, &x.clone() is not
1710 hir::ExprKind::AddrOf(..) |
1711 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1712 hir::ExprKind::MethodCall(..) => return,
1715 hir::Node::Stmt(stmt) => {
1716 if let hir::StmtKind::Local(ref loc) = stmt.kind {
1717 if let hir::PatKind::Ref(..) = loc.pat.kind {
1718 // let ref y = *x borrows x, let ref y = x.clone() does not
1726 // x.clone() might have dereferenced x, possibly through Deref impls
1727 if cx.tables.expr_ty(arg) == ty {
1728 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1730 let deref_count = cx
1732 .expr_adjustments(arg)
1735 if let ty::adjustment::Adjust::Deref(_) = adj.kind {
1742 let derefs: String = iter::repeat('*').take(deref_count).collect();
1743 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
1748 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |db| {
1749 if let Some((text, snip)) = snip {
1750 db.span_suggestion(expr.span, text, snip, Applicability::Unspecified);
1756 fn lint_clone_on_ref_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr) {
1757 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(arg));
1759 if let ty::Adt(_, subst) = obj_ty.kind {
1760 let caller_type = if match_type(cx, obj_ty, &paths::RC) {
1762 } else if match_type(cx, obj_ty, &paths::ARC) {
1764 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
1774 "using '.clone()' on a ref-counted pointer",
1777 "{}::<{}>::clone(&{})",
1780 snippet(cx, arg.span, "_")
1782 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
1787 fn lint_string_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1789 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
1790 let target = &arglists[0][0];
1791 let self_ty = walk_ptrs_ty(cx.tables.expr_ty(target));
1792 let ref_str = if self_ty.kind == ty::Str {
1794 } else if match_type(cx, self_ty, &paths::STRING) {
1800 let mut applicability = Applicability::MachineApplicable;
1803 STRING_EXTEND_CHARS,
1805 "calling `.extend(_.chars())`",
1808 "{}.push_str({}{})",
1809 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
1811 snippet_with_applicability(cx, target.span, "_", &mut applicability)
1818 fn lint_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1819 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&args[0]));
1820 if match_type(cx, obj_ty, &paths::STRING) {
1821 lint_string_extend(cx, expr, args);
1825 fn lint_cstring_as_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, source: &hir::Expr, unwrap: &hir::Expr) {
1827 let source_type = cx.tables.expr_ty(source);
1828 if let ty::Adt(def, substs) = source_type.kind;
1829 if match_def_path(cx, def.did, &paths::RESULT);
1830 if match_type(cx, substs.type_at(0), &paths::CSTRING);
1834 TEMPORARY_CSTRING_AS_PTR,
1836 "you are getting the inner pointer of a temporary `CString`",
1838 db.note("that pointer will be invalid outside this expression");
1839 db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
1845 fn lint_iter_cloned_collect<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr]) {
1847 if is_type_diagnostic_item(cx, cx.tables.expr_ty(expr), Symbol::intern("vec_type"));
1848 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0]));
1849 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite());
1854 ITER_CLONED_COLLECT,
1856 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
1859 ".to_vec()".to_string(),
1860 Applicability::MachineApplicable,
1866 fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args: &[hir::Expr], fold_span: Span) {
1867 fn check_fold_with_op(
1868 cx: &LateContext<'_, '_>,
1870 fold_args: &[hir::Expr],
1873 replacement_method_name: &str,
1874 replacement_has_args: bool,
1877 // Extract the body of the closure passed to fold
1878 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
1879 let closure_body = cx.tcx.hir().body(body_id);
1880 let closure_expr = remove_blocks(&closure_body.value);
1882 // Check if the closure body is of the form `acc <op> some_expr(x)`
1883 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
1884 if bin_op.node == op;
1886 // Extract the names of the two arguments to the closure
1887 if let Some(first_arg_ident) = get_arg_name(&closure_body.params[0].pat);
1888 if let Some(second_arg_ident) = get_arg_name(&closure_body.params[1].pat);
1890 if match_var(&*left_expr, first_arg_ident);
1891 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
1894 let mut applicability = Applicability::MachineApplicable;
1895 let sugg = if replacement_has_args {
1897 "{replacement}(|{s}| {r})",
1898 replacement = replacement_method_name,
1899 s = second_arg_ident,
1900 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
1905 replacement = replacement_method_name,
1912 fold_span.with_hi(expr.span.hi()),
1913 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
1914 "this `.fold` can be written more succinctly using another method",
1923 // Check that this is a call to Iterator::fold rather than just some function called fold
1924 if !match_trait_method(cx, expr, &paths::ITERATOR) {
1929 fold_args.len() == 3,
1930 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
1933 // Check if the first argument to .fold is a suitable literal
1934 if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
1936 ast::LitKind::Bool(false) => {
1937 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
1939 ast::LitKind::Bool(true) => {
1940 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
1942 ast::LitKind::Int(0, _) => {
1943 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
1945 ast::LitKind::Int(1, _) => {
1946 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
1953 fn lint_iter_nth<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr], is_mut: bool) {
1954 let mut_str = if is_mut { "_mut" } else { "" };
1955 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
1957 } else if is_type_diagnostic_item(cx, cx.tables.expr_ty(&iter_args[0]), Symbol::intern("vec_type")) {
1959 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
1962 return; // caller is not a type that we want to lint
1970 "called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
1971 mut_str, caller_type
1976 fn lint_get_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, get_args: &'tcx [hir::Expr], is_mut: bool) {
1977 // Note: we don't want to lint `get_mut().unwrap` for `HashMap` or `BTreeMap`,
1978 // because they do not implement `IndexMut`
1979 let mut applicability = Applicability::MachineApplicable;
1980 let expr_ty = cx.tables.expr_ty(&get_args[0]);
1981 let get_args_str = if get_args.len() > 1 {
1982 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
1984 return; // not linting on a .get().unwrap() chain or variant
1987 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
1988 needs_ref = get_args_str.parse::<usize>().is_ok();
1990 } else if is_type_diagnostic_item(cx, expr_ty, Symbol::intern("vec_type")) {
1991 needs_ref = get_args_str.parse::<usize>().is_ok();
1993 } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
1994 needs_ref = get_args_str.parse::<usize>().is_ok();
1996 } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
1999 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
2003 return; // caller is not a type that we want to lint
2006 let mut span = expr.span;
2008 // Handle the case where the result is immediately dereferenced
2009 // by not requiring ref and pulling the dereference into the
2013 if let Some(parent) = get_parent_expr(cx, expr);
2014 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.kind;
2021 let mut_str = if is_mut { "_mut" } else { "" };
2022 let borrow_str = if !needs_ref {
2035 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
2036 mut_str, caller_type
2042 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
2049 fn lint_iter_skip_next(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2050 // lint if caller of skip is an Iterator
2051 if match_trait_method(cx, expr, &paths::ITERATOR) {
2056 "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`",
2061 fn derefs_to_slice<'a, 'tcx>(
2062 cx: &LateContext<'a, 'tcx>,
2063 expr: &'tcx hir::Expr,
2065 ) -> Option<&'tcx hir::Expr> {
2066 fn may_slice<'a>(cx: &LateContext<'_, 'a>, ty: Ty<'a>) -> bool {
2068 ty::Slice(_) => true,
2069 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
2070 ty::Adt(..) => is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")),
2071 ty::Array(_, size) => size.eval_usize(cx.tcx, cx.param_env) < 32,
2072 ty::Ref(_, inner, _) => may_slice(cx, inner),
2077 if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.kind {
2078 if path.ident.name == sym!(iter) && may_slice(cx, cx.tables.expr_ty(&args[0])) {
2085 ty::Slice(_) => Some(expr),
2086 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
2087 ty::Ref(_, inner, _) => {
2088 if may_slice(cx, inner) {
2099 /// lint use of `unwrap()` for `Option`s and `Result`s
2100 fn lint_unwrap(cx: &LateContext<'_, '_>, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
2101 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&unwrap_args[0]));
2103 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
2104 Some((OPTION_UNWRAP_USED, "an Option", "None"))
2105 } else if match_type(cx, obj_ty, &paths::RESULT) {
2106 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
2111 if let Some((lint, kind, none_value)) = mess {
2117 "used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
2118 using expect() to provide a better panic \
2126 /// lint use of `expect()` for `Option`s and `Result`s
2127 fn lint_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, expect_args: &[hir::Expr]) {
2128 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&expect_args[0]));
2130 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
2131 Some((OPTION_EXPECT_USED, "an Option", "None"))
2132 } else if match_type(cx, obj_ty, &paths::RESULT) {
2133 Some((RESULT_EXPECT_USED, "a Result", "Err"))
2138 if let Some((lint, kind, none_value)) = mess {
2144 "used expect() on {} value. If this value is an {} it will panic",
2151 /// lint use of `ok().expect()` for `Result`s
2152 fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, ok_args: &[hir::Expr]) {
2154 // lint if the caller of `ok()` is a `Result`
2155 if match_type(cx, cx.tables.expr_ty(&ok_args[0]), &paths::RESULT);
2156 let result_type = cx.tables.expr_ty(&ok_args[0]);
2157 if let Some(error_type) = get_error_type(cx, result_type);
2158 if has_debug_impl(error_type, cx);
2165 "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`",
2171 /// lint use of `map().flatten()` for `Iterators`
2172 fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_args: &'tcx [hir::Expr]) {
2173 // lint if caller of `.map().flatten()` is an Iterator
2174 if match_trait_method(cx, expr, &paths::ITERATOR) {
2175 let msg = "called `map(..).flatten()` on an `Iterator`. \
2176 This is more succinctly expressed by calling `.flat_map(..)`";
2177 let self_snippet = snippet(cx, map_args[0].span, "..");
2178 let func_snippet = snippet(cx, map_args[1].span, "..");
2179 let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
2180 span_lint_and_then(cx, MAP_FLATTEN, expr.span, msg, |db| {
2183 "try using flat_map instead",
2185 Applicability::MachineApplicable,
2191 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2192 fn lint_map_unwrap_or_else<'a, 'tcx>(
2193 cx: &LateContext<'a, 'tcx>,
2194 expr: &'tcx hir::Expr,
2195 map_args: &'tcx [hir::Expr],
2196 unwrap_args: &'tcx [hir::Expr],
2198 // lint if the caller of `map()` is an `Option`
2199 let is_option = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION);
2200 let is_result = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::RESULT);
2202 if is_option || is_result {
2203 // Don't make a suggestion that may fail to compile due to mutably borrowing
2204 // the same variable twice.
2205 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2206 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2207 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2208 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2216 let msg = if is_option {
2217 "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
2218 `map_or_else(g, f)` instead"
2220 "called `map(f).unwrap_or_else(g)` on a Result value. This can be done more directly by calling \
2221 `.map_or_else(g, f)` instead"
2223 // get snippets for args to map() and unwrap_or_else()
2224 let map_snippet = snippet(cx, map_args[1].span, "..");
2225 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2226 // lint, with note if neither arg is > 1 line and both map() and
2227 // unwrap_or_else() have the same span
2228 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2229 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2230 if same_span && !multiline {
2234 OPTION_MAP_UNWRAP_OR_ELSE
2236 RESULT_MAP_UNWRAP_OR_ELSE
2242 "replace `map({0}).unwrap_or_else({1})` with `map_or_else({1}, {0})`",
2243 map_snippet, unwrap_snippet,
2246 } else if same_span && multiline {
2250 OPTION_MAP_UNWRAP_OR_ELSE
2252 RESULT_MAP_UNWRAP_OR_ELSE
2261 /// lint use of `_.map_or(None, _)` for `Option`s
2262 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
2263 if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
2264 // check if the first non-self argument to map_or() is None
2265 let map_or_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].kind {
2266 match_qpath(qpath, &paths::OPTION_NONE)
2271 if map_or_arg_is_none {
2273 let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
2274 `and_then(f)` instead";
2275 let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
2276 let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
2277 let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
2278 span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
2281 "try using and_then instead",
2283 Applicability::MachineApplicable, // snippet
2290 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2291 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
2292 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2293 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2295 let ty = cx.tables.expr_ty(&args[0]);
2296 if !match_type(cx, ty, &paths::OPTION) {
2300 match args[1].kind {
2301 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2302 let closure_body = cx.tcx.hir().body(body_id);
2303 let closure_expr = remove_blocks(&closure_body.value);
2305 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.kind;
2306 if let hir::ExprKind::Path(ref qpath) = some_expr.kind;
2307 if match_qpath(qpath, &paths::OPTION_SOME);
2308 if some_args.len() == 1;
2310 let inner_expr = &some_args[0];
2312 if contains_return(inner_expr) {
2316 let some_inner_snip = if inner_expr.span.from_expansion() {
2317 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2319 snippet(cx, inner_expr.span, "_")
2322 let closure_args_snip = snippet(cx, closure_args_span, "..");
2323 let option_snip = snippet(cx, args[0].span, "..");
2324 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2327 OPTION_AND_THEN_SOME,
2332 Applicability::MachineApplicable,
2337 // `_.and_then(Some)` case, which is no-op.
2338 hir::ExprKind::Path(ref qpath) => {
2339 if match_qpath(qpath, &paths::OPTION_SOME) {
2340 let option_snip = snippet(cx, args[0].span, "..");
2341 let note = format!("{}", option_snip);
2344 OPTION_AND_THEN_SOME,
2347 "use the expression directly",
2349 Applicability::MachineApplicable,
2357 /// lint use of `filter().next()` for `Iterators`
2358 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2359 // lint if caller of `.filter().next()` is an Iterator
2360 if match_trait_method(cx, expr, &paths::ITERATOR) {
2361 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2362 `.find(p)` instead.";
2363 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2364 if filter_snippet.lines().count() <= 1 {
2365 // add note if not multi-line
2372 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2375 span_lint(cx, FILTER_NEXT, expr.span, msg);
2380 /// lint use of `filter().map()` for `Iterators`
2381 fn lint_filter_map<'a, 'tcx>(
2382 cx: &LateContext<'a, 'tcx>,
2383 expr: &'tcx hir::Expr,
2384 _filter_args: &'tcx [hir::Expr],
2385 _map_args: &'tcx [hir::Expr],
2387 // lint if caller of `.filter().map()` is an Iterator
2388 if match_trait_method(cx, expr, &paths::ITERATOR) {
2389 let msg = "called `filter(p).map(q)` on an `Iterator`. \
2390 This is more succinctly expressed by calling `.filter_map(..)` instead.";
2391 span_lint(cx, FILTER_MAP, expr.span, msg);
2395 /// lint use of `filter_map().next()` for `Iterators`
2396 fn lint_filter_map_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2397 if match_trait_method(cx, expr, &paths::ITERATOR) {
2398 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2399 `.find_map(p)` instead.";
2400 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2401 if filter_snippet.lines().count() <= 1 {
2408 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2411 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2416 /// lint use of `find().map()` for `Iterators`
2417 fn lint_find_map<'a, 'tcx>(
2418 cx: &LateContext<'a, 'tcx>,
2419 expr: &'tcx hir::Expr,
2420 _find_args: &'tcx [hir::Expr],
2421 map_args: &'tcx [hir::Expr],
2423 // lint if caller of `.filter().map()` is an Iterator
2424 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2425 let msg = "called `find(p).map(q)` on an `Iterator`. \
2426 This is more succinctly expressed by calling `.find_map(..)` instead.";
2427 span_lint(cx, FIND_MAP, expr.span, msg);
2431 /// lint use of `filter_map().map()` for `Iterators`
2432 fn lint_filter_map_map<'a, 'tcx>(
2433 cx: &LateContext<'a, 'tcx>,
2434 expr: &'tcx hir::Expr,
2435 _filter_args: &'tcx [hir::Expr],
2436 _map_args: &'tcx [hir::Expr],
2438 // lint if caller of `.filter().map()` is an Iterator
2439 if match_trait_method(cx, expr, &paths::ITERATOR) {
2440 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
2441 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
2442 span_lint(cx, FILTER_MAP, expr.span, msg);
2446 /// lint use of `filter().flat_map()` for `Iterators`
2447 fn lint_filter_flat_map<'a, 'tcx>(
2448 cx: &LateContext<'a, 'tcx>,
2449 expr: &'tcx hir::Expr,
2450 _filter_args: &'tcx [hir::Expr],
2451 _map_args: &'tcx [hir::Expr],
2453 // lint if caller of `.filter().flat_map()` is an Iterator
2454 if match_trait_method(cx, expr, &paths::ITERATOR) {
2455 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
2456 This is more succinctly expressed by calling `.flat_map(..)` \
2457 and filtering by returning an empty Iterator.";
2458 span_lint(cx, FILTER_MAP, expr.span, msg);
2462 /// lint use of `filter_map().flat_map()` for `Iterators`
2463 fn lint_filter_map_flat_map<'a, 'tcx>(
2464 cx: &LateContext<'a, 'tcx>,
2465 expr: &'tcx hir::Expr,
2466 _filter_args: &'tcx [hir::Expr],
2467 _map_args: &'tcx [hir::Expr],
2469 // lint if caller of `.filter_map().flat_map()` is an Iterator
2470 if match_trait_method(cx, expr, &paths::ITERATOR) {
2471 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
2472 This is more succinctly expressed by calling `.flat_map(..)` \
2473 and filtering by returning an empty Iterator.";
2474 span_lint(cx, FILTER_MAP, expr.span, msg);
2478 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2479 fn lint_flat_map_identity<'a, 'tcx>(
2480 cx: &LateContext<'a, 'tcx>,
2481 expr: &'tcx hir::Expr,
2482 flat_map_args: &'tcx [hir::Expr],
2483 flat_map_span: Span,
2485 if match_trait_method(cx, expr, &paths::ITERATOR) {
2486 let arg_node = &flat_map_args[1].kind;
2488 let apply_lint = |message: &str| {
2492 flat_map_span.with_hi(expr.span.hi()),
2495 "flatten()".to_string(),
2496 Applicability::MachineApplicable,
2501 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2502 let body = cx.tcx.hir().body(*body_id);
2504 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
2505 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
2507 if path.segments.len() == 1;
2508 if path.segments[0].ident.as_str() == binding_ident.as_str();
2511 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2516 if let hir::ExprKind::Path(ref qpath) = arg_node;
2518 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2521 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2527 /// lint searching an Iterator followed by `is_some()`
2528 fn lint_search_is_some<'a, 'tcx>(
2529 cx: &LateContext<'a, 'tcx>,
2530 expr: &'tcx hir::Expr,
2531 search_method: &str,
2532 search_args: &'tcx [hir::Expr],
2533 is_some_args: &'tcx [hir::Expr],
2536 // lint if caller of search is an Iterator
2537 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2539 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2540 expressed by calling `any()`.",
2543 let search_snippet = snippet(cx, search_args[1].span, "..");
2544 if search_snippet.lines().count() <= 1 {
2545 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2546 // suggest `any(|..| *..)` instead of `any(|..| **..)` for `find(|..| **..).is_some()`
2547 let any_search_snippet = if_chain! {
2548 if search_method == "find";
2549 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].kind;
2550 let closure_body = cx.tcx.hir().body(body_id);
2551 if let Some(closure_arg) = closure_body.params.get(0);
2553 if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
2554 Some(search_snippet.replacen('&', "", 1))
2555 } else if let Some(name) = get_arg_name(&closure_arg.pat) {
2556 Some(search_snippet.replace(&format!("*{}", name), &name.as_str()))
2564 // add note if not multi-line
2568 method_span.with_hi(expr.span.hi()),
2573 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2575 Applicability::MachineApplicable,
2578 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2583 /// Used for `lint_binary_expr_with_method_call`.
2584 #[derive(Copy, Clone)]
2585 struct BinaryExprInfo<'a> {
2586 expr: &'a hir::Expr,
2587 chain: &'a hir::Expr,
2588 other: &'a hir::Expr,
2592 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2593 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
2594 macro_rules! lint_with_both_lhs_and_rhs {
2595 ($func:ident, $cx:expr, $info:ident) => {
2596 if !$func($cx, $info) {
2597 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2598 if $func($cx, $info) {
2605 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
2606 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
2607 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
2608 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
2611 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2613 cx: &LateContext<'_, '_>,
2614 info: &BinaryExprInfo<'_>,
2615 chain_methods: &[&str],
2616 lint: &'static Lint,
2620 if let Some(args) = method_chain_args(info.chain, chain_methods);
2621 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.kind;
2622 if arg_char.len() == 1;
2623 if let hir::ExprKind::Path(ref qpath) = fun.kind;
2624 if let Some(segment) = single_segment_path(qpath);
2625 if segment.ident.name == sym!(Some);
2627 let mut applicability = Applicability::MachineApplicable;
2628 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
2630 if self_ty.kind != ty::Str {
2638 &format!("you should use the `{}` method", suggest),
2640 format!("{}{}.{}({})",
2641 if info.eq { "" } else { "!" },
2642 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2644 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
2655 /// Checks for the `CHARS_NEXT_CMP` lint.
2656 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2657 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
2660 /// Checks for the `CHARS_LAST_CMP` lint.
2661 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2662 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
2665 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
2669 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
2670 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
2671 cx: &LateContext<'a, 'tcx>,
2672 info: &BinaryExprInfo<'_>,
2673 chain_methods: &[&str],
2674 lint: &'static Lint,
2678 if let Some(args) = method_chain_args(info.chain, chain_methods);
2679 if let hir::ExprKind::Lit(ref lit) = info.other.kind;
2680 if let ast::LitKind::Char(c) = lit.node;
2682 let mut applicability = Applicability::MachineApplicable;
2687 &format!("you should use the `{}` method", suggest),
2689 format!("{}{}.{}('{}')",
2690 if info.eq { "" } else { "!" },
2691 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2704 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
2705 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2706 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
2709 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
2710 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2711 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
2714 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
2718 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
2719 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
2721 if let hir::ExprKind::Lit(lit) = &arg.kind;
2722 if let ast::LitKind::Str(r, style) = lit.node;
2723 if r.as_str().len() == 1;
2725 let mut applicability = Applicability::MachineApplicable;
2726 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
2727 let ch = if let ast::StrStyle::Raw(nhash) = style {
2728 let nhash = nhash as usize;
2729 // for raw string: r##"a"##
2730 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
2732 // for regular string: "a"
2733 &snip[1..(snip.len() - 1)]
2735 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
2738 SINGLE_CHAR_PATTERN,
2740 "single-character string constant used as pattern",
2741 "try using a char instead",
2749 /// Checks for the `USELESS_ASREF` lint.
2750 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
2751 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
2752 // check if the call is to the actual `AsRef` or `AsMut` trait
2753 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
2754 // check if the type after `as_ref` or `as_mut` is the same as before
2755 let recvr = &as_ref_args[0];
2756 let rcv_ty = cx.tables.expr_ty(recvr);
2757 let res_ty = cx.tables.expr_ty(expr);
2758 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
2759 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
2760 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
2761 // allow the `as_ref` or `as_mut` if it is followed by another method call
2763 if let Some(parent) = get_parent_expr(cx, expr);
2764 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.kind;
2765 if span != &expr.span;
2771 let mut applicability = Applicability::MachineApplicable;
2776 &format!("this call to `{}` does nothing", call_name),
2778 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
2785 fn ty_has_iter_method(cx: &LateContext<'_, '_>, self_ref_ty: Ty<'_>) -> Option<(&'static str, &'static str)> {
2786 has_iter_method(cx, self_ref_ty).map(|ty_name| {
2787 let mutbl = match self_ref_ty.kind {
2788 ty::Ref(_, _, mutbl) => mutbl,
2789 _ => unreachable!(),
2791 let method_name = match mutbl {
2792 hir::Mutability::Immutable => "iter",
2793 hir::Mutability::Mutable => "iter_mut",
2795 (ty_name, method_name)
2799 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr, self_ref_ty: Ty<'_>, method_span: Span) {
2800 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
2803 if let Some((kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
2809 "this .into_iter() call is equivalent to .{}() and will not move the {}",
2813 method_name.to_string(),
2814 Applicability::MachineApplicable,
2819 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
2820 fn lint_maybe_uninit(cx: &LateContext<'_, '_>, expr: &hir::Expr, outer: &hir::Expr) {
2822 if let hir::ExprKind::Call(ref callee, ref args) = expr.kind;
2824 if let hir::ExprKind::Path(ref path) = callee.kind;
2825 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
2826 if !is_maybe_uninit_ty_valid(cx, cx.tables.expr_ty_adjusted(outer));
2830 UNINIT_ASSUMED_INIT,
2832 "this call for this type may be undefined behavior"
2838 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
2840 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
2841 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
2842 ty::Adt(ref adt, _) => {
2843 // needs to be a MaybeUninit
2844 match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT)
2850 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2855 "this call to `map()` won't have an effect on the call to `count()`",
2856 "make sure you did not confuse `map` with `filter`",
2860 /// Given a `Result<T, E>` type, return its error type (`E`).
2861 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
2863 ty::Adt(_, substs) if match_type(cx, ty, &paths::RESULT) => substs.types().nth(1),
2868 /// This checks whether a given type is known to implement Debug.
2869 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
2871 .get_diagnostic_item(sym::debug_trait)
2872 .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
2877 StartsWith(&'static str),
2881 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
2882 (Convention::Eq("new"), &[SelfKind::No]),
2883 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
2884 (Convention::StartsWith("from_"), &[SelfKind::No]),
2885 (Convention::StartsWith("into_"), &[SelfKind::Value]),
2886 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
2887 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
2888 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
2892 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
2893 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
2894 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
2895 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
2896 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
2897 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
2898 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
2899 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
2900 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
2901 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
2902 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
2903 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
2904 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
2905 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
2906 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
2907 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
2908 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
2909 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
2910 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
2911 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
2912 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
2913 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
2914 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
2915 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
2916 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
2917 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
2918 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
2919 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
2920 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
2921 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
2922 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
2926 const PATTERN_METHODS: [(&str, usize); 17] = [
2934 ("split_terminator", 1),
2935 ("rsplit_terminator", 1),
2940 ("match_indices", 1),
2941 ("rmatch_indices", 1),
2942 ("trim_start_matches", 1),
2943 ("trim_end_matches", 1),
2946 #[derive(Clone, Copy, PartialEq, Debug)]
2955 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2956 fn matches_value(parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2957 if ty == parent_ty {
2959 } else if ty.is_box() {
2960 ty.boxed_ty() == parent_ty
2961 } else if ty.is_rc() || ty.is_arc() {
2962 if let ty::Adt(_, substs) = ty.kind {
2963 substs.types().next().map_or(false, |t| t == parent_ty)
2973 cx: &LateContext<'_, 'a>,
2974 mutability: hir::Mutability,
2978 if let ty::Ref(_, t, m) = ty.kind {
2979 return m == mutability && t == parent_ty;
2982 let trait_path = match mutability {
2983 hir::Mutability::Immutable => &paths::ASREF_TRAIT,
2984 hir::Mutability::Mutable => &paths::ASMUT_TRAIT,
2987 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2989 None => return false,
2991 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2995 Self::Value => matches_value(parent_ty, ty),
2997 matches_ref(cx, hir::Mutability::Immutable, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty)
2999 Self::RefMut => matches_ref(cx, hir::Mutability::Mutable, parent_ty, ty),
3000 Self::No => ty != parent_ty,
3005 fn description(self) -> &'static str {
3007 Self::Value => "self by value",
3008 Self::Ref => "self by reference",
3009 Self::RefMut => "self by mutable reference",
3010 Self::No => "no self",
3017 fn check(&self, other: &str) -> bool {
3019 Self::Eq(this) => this == other,
3020 Self::StartsWith(this) => other.starts_with(this) && this != other,
3025 impl fmt::Display for Convention {
3026 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
3028 Self::Eq(this) => this.fmt(f),
3029 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
3034 #[derive(Clone, Copy)]
3043 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FunctionRetTy) -> bool {
3044 let is_unit = |ty: &hir::Ty| SpanlessEq::new(cx).eq_ty_kind(&ty.kind, &hir::TyKind::Tup(vec![].into()));
3046 (Self::Unit, &hir::DefaultReturn(_)) => true,
3047 (Self::Unit, &hir::Return(ref ty)) if is_unit(ty) => true,
3048 (Self::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
3049 (Self::Any, &hir::Return(ref ty)) if !is_unit(ty) => true,
3050 (Self::Ref, &hir::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
3056 fn is_bool(ty: &hir::Ty) -> bool {
3057 if let hir::TyKind::Path(ref p) = ty.kind {
3058 match_qpath(p, &["bool"])
3064 // Returns `true` if `expr` contains a return expression
3065 fn contains_return(expr: &hir::Expr) -> bool {
3066 struct RetCallFinder {
3070 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
3071 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
3075 if let hir::ExprKind::Ret(..) = &expr.kind {
3078 intravisit::walk_expr(self, expr);
3082 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
3083 intravisit::NestedVisitorMap::None
3087 let mut visitor = RetCallFinder { found: false };
3088 visitor.visit_expr(expr);
3092 fn check_pointer_offset(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
3095 if let ty::RawPtr(ty::TypeAndMut { ref ty, .. }) = cx.tables.expr_ty(&args[0]).kind;
3096 if let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty));
3099 span_lint(cx, ZST_OFFSET, expr.span, "offset calculation on zero-sized value");