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, LocalInternedString, Symbol};
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 `Option`:
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 methods that should live in a trait
96 /// implementation of a `std` trait (see [llogiq's blog
97 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
98 /// information) instead of an inherent implementation.
100 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
101 /// the code, often with very little cost. Also people seeing a `mul(...)`
103 /// may expect `*` to work equally, so you should have good reason to disappoint
106 /// **Known problems:** None.
112 /// fn add(&self, other: &X) -> X {
117 pub SHOULD_IMPLEMENT_TRAIT,
119 "defining a method that should be implementing a std trait"
122 declare_clippy_lint! {
123 /// **What it does:** Checks for methods with certain name prefixes and which
124 /// doesn't match how self is taken. The actual rules are:
126 /// |Prefix |`self` taken |
127 /// |-------|----------------------|
128 /// |`as_` |`&self` or `&mut self`|
130 /// |`into_`|`self` |
131 /// |`is_` |`&self` or none |
132 /// |`to_` |`&self` |
134 /// **Why is this bad?** Consistency breeds readability. If you follow the
135 /// conventions, your users won't be surprised that they, e.g., need to supply a
136 /// mutable reference to a `as_..` function.
138 /// **Known problems:** None.
143 /// fn as_str(self) -> &str {
148 pub WRONG_SELF_CONVENTION,
150 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
153 declare_clippy_lint! {
154 /// **What it does:** This is the same as
155 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
157 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
159 /// **Known problems:** Actually *renaming* the function may break clients if
160 /// the function is part of the public interface. In that case, be mindful of
161 /// the stability guarantees you've given your users.
167 /// pub fn as_str(self) -> &'a str {
172 pub WRONG_PUB_SELF_CONVENTION,
174 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
177 declare_clippy_lint! {
178 /// **What it does:** Checks for usage of `ok().expect(..)`.
180 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
181 /// directly to get a better error message.
183 /// **Known problems:** The error type needs to implement `Debug`
187 /// x.ok().expect("why did I do this again?")
191 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
194 declare_clippy_lint! {
195 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
197 /// **Why is this bad?** Readability, this can be written more concisely as
198 /// `_.map_or(_, _)`.
200 /// **Known problems:** The order of the arguments is not in execution order
204 /// # let x = Some(1);
205 /// x.map(|a| a + 1).unwrap_or(0);
207 pub OPTION_MAP_UNWRAP_OR,
209 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
212 declare_clippy_lint! {
213 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
215 /// **Why is this bad?** Readability, this can be written more concisely as
216 /// `_.map_or_else(_, _)`.
218 /// **Known problems:** The order of the arguments is not in execution order.
222 /// # let x = Some(1);
223 /// # fn some_function() -> usize { 1 }
224 /// x.map(|a| a + 1).unwrap_or_else(some_function);
226 pub OPTION_MAP_UNWRAP_OR_ELSE,
228 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
231 declare_clippy_lint! {
232 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
234 /// **Why is this bad?** Readability, this can be written more concisely as
235 /// `result.ok().map_or_else(_, _)`.
237 /// **Known problems:** None.
241 /// # let x: Result<usize, ()> = Ok(1);
242 /// # fn some_function(foo: ()) -> usize { 1 }
243 /// x.map(|a| a + 1).unwrap_or_else(some_function);
245 pub RESULT_MAP_UNWRAP_OR_ELSE,
247 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.ok().map_or_else(g, f)`"
250 declare_clippy_lint! {
251 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
253 /// **Why is this bad?** Readability, this can be written more concisely as
256 /// **Known problems:** The order of the arguments is not in execution order.
260 /// opt.map_or(None, |a| a + 1)
262 pub OPTION_MAP_OR_NONE,
264 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
267 declare_clippy_lint! {
268 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
270 /// **Why is this bad?** Readability, this can be written more concisely as
273 /// **Known problems:** None
278 /// let x = Some("foo");
279 /// let _ = x.and_then(|s| Some(s.len()));
282 /// The correct use would be:
285 /// let x = Some("foo");
286 /// let _ = x.map(|s| s.len());
288 pub OPTION_AND_THEN_SOME,
290 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
293 declare_clippy_lint! {
294 /// **What it does:** Checks for usage of `_.filter(_).next()`.
296 /// **Why is this bad?** Readability, this can be written more concisely as
299 /// **Known problems:** None.
303 /// # let vec = vec![1];
304 /// vec.iter().filter(|x| **x == 0).next();
306 /// Could be written as
308 /// # let vec = vec![1];
309 /// vec.iter().find(|x| **x == 0);
313 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
316 declare_clippy_lint! {
317 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
319 /// **Why is this bad?** Readability, this can be written more concisely as a
320 /// single method call.
322 /// **Known problems:**
326 /// let vec = vec![vec![1]];
327 /// vec.iter().map(|x| x.iter()).flatten();
331 "using combinations of `flatten` and `map` which can usually be written as a single method call"
334 declare_clippy_lint! {
335 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
336 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
338 /// **Why is this bad?** Readability, this can be written more concisely as a
339 /// single method call.
341 /// **Known problems:** Often requires a condition + Option/Iterator creation
342 /// inside the closure.
346 /// let vec = vec![1];
347 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
351 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
354 declare_clippy_lint! {
355 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
357 /// **Why is this bad?** Readability, this can be written more concisely as a
358 /// single method call.
360 /// **Known problems:** None
364 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
366 /// Can be written as
369 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
373 "using combination of `filter_map` and `next` which can usually be written as a single method call"
376 declare_clippy_lint! {
377 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
379 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
381 /// **Known problems:** None
385 /// # let iter = vec![vec![0]].into_iter();
386 /// iter.flat_map(|x| x);
388 /// Can be written as
390 /// # let iter = vec![vec![0]].into_iter();
393 pub FLAT_MAP_IDENTITY,
395 "call to `flat_map` where `flatten` is sufficient"
398 declare_clippy_lint! {
399 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
401 /// **Why is this bad?** Readability, this can be written more concisely as a
402 /// single method call.
404 /// **Known problems:** Often requires a condition + Option/Iterator creation
405 /// inside the closure.
409 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
411 /// Can be written as
413 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
417 "using a combination of `find` and `map` can usually be written as a single method call"
420 declare_clippy_lint! {
421 /// **What it does:** Checks for an iterator search (such as `find()`,
422 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
424 /// **Why is this bad?** Readability, this can be written more concisely as
427 /// **Known problems:** None.
431 /// # let vec = vec![1];
432 /// vec.iter().find(|x| **x == 0).is_some();
434 /// Could be written as
436 /// # let vec = vec![1];
437 /// vec.iter().any(|x| *x == 0);
441 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
444 declare_clippy_lint! {
445 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
446 /// if it starts with a given char.
448 /// **Why is this bad?** Readability, this can be written more concisely as
449 /// `_.starts_with(_)`.
451 /// **Known problems:** None.
455 /// let name = "foo";
456 /// if name.chars().next() == Some('_') {};
458 /// Could be written as
460 /// let name = "foo";
461 /// if name.starts_with('_') {};
465 "using `.chars().next()` to check if a string starts with a char"
468 declare_clippy_lint! {
469 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
470 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
471 /// `unwrap_or_default` instead.
473 /// **Why is this bad?** The function will always be called and potentially
474 /// allocate an object acting as the default.
476 /// **Known problems:** If the function has side-effects, not calling it will
477 /// change the semantic of the program, but you shouldn't rely on that anyway.
481 /// # let foo = Some(String::new());
482 /// foo.unwrap_or(String::new());
484 /// this can instead be written:
486 /// # let foo = Some(String::new());
487 /// foo.unwrap_or_else(String::new);
491 /// # let foo = Some(String::new());
492 /// foo.unwrap_or_default();
496 "using any `*or` method with a function call, which suggests `*or_else`"
499 declare_clippy_lint! {
500 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
501 /// etc., and suggests to use `unwrap_or_else` instead
503 /// **Why is this bad?** The function will always be called.
505 /// **Known problems:** If the function has side-effects, not calling it will
506 /// change the semantics of the program, but you shouldn't rely on that anyway.
510 /// # let foo = Some(String::new());
511 /// # let err_code = "418";
512 /// # let err_msg = "I'm a teapot";
513 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
517 /// # let foo = Some(String::new());
518 /// # let err_code = "418";
519 /// # let err_msg = "I'm a teapot";
520 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
522 /// this can instead be written:
524 /// # let foo = Some(String::new());
525 /// # let err_code = "418";
526 /// # let err_msg = "I'm a teapot";
527 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
531 "using any `expect` method with a function call"
534 declare_clippy_lint! {
535 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
537 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
538 /// generics, not for using the `clone` method on a concrete type.
540 /// **Known problems:** None.
548 "using `clone` on a `Copy` type"
551 declare_clippy_lint! {
552 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
553 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
554 /// function syntax instead (e.g., `Rc::clone(foo)`).
556 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
557 /// can obscure the fact that only the pointer is being cloned, not the underlying
562 /// # use std::rc::Rc;
563 /// let x = Rc::new(1);
566 pub CLONE_ON_REF_PTR,
568 "using 'clone' on a ref-counted pointer"
571 declare_clippy_lint! {
572 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
574 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
575 /// cloning the underlying `T`.
577 /// **Known problems:** None.
584 /// let z = y.clone();
585 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
588 pub CLONE_DOUBLE_REF,
590 "using `clone` on `&&T`"
593 declare_clippy_lint! {
594 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
595 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
597 /// **Why is this bad?** This bypasses the specialized implementation of
598 /// `ToString` and instead goes through the more expensive string formatting
601 /// **Known problems:** None.
605 /// // Generic implementation for `T: Display` is used (slow)
606 /// ["foo", "bar"].iter().map(|s| s.to_string());
608 /// // OK, the specialized impl is used
609 /// ["foo", "bar"].iter().map(|&s| s.to_string());
611 pub INEFFICIENT_TO_STRING,
613 "using `to_string` on `&&T` where `T: ToString`"
616 declare_clippy_lint! {
617 /// **What it does:** Checks for `new` not returning `Self`.
619 /// **Why is this bad?** As a convention, `new` methods are used to make a new
620 /// instance of a type.
622 /// **Known problems:** None.
627 /// fn new(..) -> NotAFoo {
633 "not returning `Self` in a `new` method"
636 declare_clippy_lint! {
637 /// **What it does:** Checks for string methods that receive a single-character
638 /// `str` as an argument, e.g., `_.split("x")`.
640 /// **Why is this bad?** Performing these methods using a `char` is faster than
643 /// **Known problems:** Does not catch multi-byte unicode characters.
646 /// `_.split("x")` could be `_.split('x')`
647 pub SINGLE_CHAR_PATTERN,
649 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
652 declare_clippy_lint! {
653 /// **What it does:** Checks for getting the inner pointer of a temporary
656 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
657 /// as the `CString` is alive.
659 /// **Known problems:** None.
663 /// let c_str = CString::new("foo").unwrap().as_ptr();
665 /// call_some_ffi_func(c_str);
668 /// Here `c_str` point to a freed address. The correct use would be:
670 /// let c_str = CString::new("foo").unwrap();
672 /// call_some_ffi_func(c_str.as_ptr());
675 pub TEMPORARY_CSTRING_AS_PTR,
677 "getting the inner pointer of a temporary `CString`"
680 declare_clippy_lint! {
681 /// **What it does:** Checks for use of `.iter().nth()` (and the related
682 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
684 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
687 /// **Known problems:** None.
691 /// let some_vec = vec![0, 1, 2, 3];
692 /// let bad_vec = some_vec.iter().nth(3);
693 /// let bad_slice = &some_vec[..].iter().nth(3);
695 /// The correct use would be:
697 /// let some_vec = vec![0, 1, 2, 3];
698 /// let bad_vec = some_vec.get(3);
699 /// let bad_slice = &some_vec[..].get(3);
703 "using `.iter().nth()` on a standard library type with O(1) element access"
706 declare_clippy_lint! {
707 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
709 /// **Why is this bad?** `.nth(x)` is cleaner
711 /// **Known problems:** None.
715 /// let some_vec = vec![0, 1, 2, 3];
716 /// let bad_vec = some_vec.iter().skip(3).next();
717 /// let bad_slice = &some_vec[..].iter().skip(3).next();
719 /// The correct use would be:
721 /// let some_vec = vec![0, 1, 2, 3];
722 /// let bad_vec = some_vec.iter().nth(3);
723 /// let bad_slice = &some_vec[..].iter().nth(3);
727 "using `.skip(x).next()` on an iterator"
730 declare_clippy_lint! {
731 /// **What it does:** Checks for use of `.get().unwrap()` (or
732 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
734 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
737 /// **Known problems:** Not a replacement for error handling: Using either
738 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
739 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
740 /// temporary placeholder for dealing with the `Option` type, then this does
741 /// not mitigate the need for error handling. If there is a chance that `.get()`
742 /// will be `None` in your program, then it is advisable that the `None` case
743 /// is handled in a future refactor instead of using `.unwrap()` or the Index
748 /// let mut some_vec = vec![0, 1, 2, 3];
749 /// let last = some_vec.get(3).unwrap();
750 /// *some_vec.get_mut(0).unwrap() = 1;
752 /// The correct use would be:
754 /// let mut some_vec = vec![0, 1, 2, 3];
755 /// let last = some_vec[3];
760 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
763 declare_clippy_lint! {
764 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
765 /// `&str` or `String`.
767 /// **Why is this bad?** `.push_str(s)` is clearer
769 /// **Known problems:** None.
774 /// let def = String::from("def");
775 /// let mut s = String::new();
776 /// s.extend(abc.chars());
777 /// s.extend(def.chars());
779 /// The correct use would be:
782 /// let def = String::from("def");
783 /// let mut s = String::new();
785 /// s.push_str(&def);
787 pub STRING_EXTEND_CHARS,
789 "using `x.extend(s.chars())` where s is a `&str` or `String`"
792 declare_clippy_lint! {
793 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
796 /// **Why is this bad?** `.to_vec()` is clearer
798 /// **Known problems:** None.
802 /// let s = [1, 2, 3, 4, 5];
803 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
805 /// The better use would be:
807 /// let s = [1, 2, 3, 4, 5];
808 /// let s2: Vec<isize> = s.to_vec();
810 pub ITER_CLONED_COLLECT,
812 "using `.cloned().collect()` on slice to create a `Vec`"
815 declare_clippy_lint! {
816 /// **What it does:** Checks for usage of `.chars().last()` or
817 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
819 /// **Why is this bad?** Readability, this can be written more concisely as
820 /// `_.ends_with(_)`.
822 /// **Known problems:** None.
826 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
830 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
833 declare_clippy_lint! {
834 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
835 /// types before and after the call are the same.
837 /// **Why is this bad?** The call is unnecessary.
839 /// **Known problems:** None.
843 /// # fn do_stuff(x: &[i32]) {}
844 /// let x: &[i32] = &[1, 2, 3, 4, 5];
845 /// do_stuff(x.as_ref());
847 /// The correct use would be:
849 /// # fn do_stuff(x: &[i32]) {}
850 /// let x: &[i32] = &[1, 2, 3, 4, 5];
855 "using `as_ref` where the types before and after the call are the same"
858 declare_clippy_lint! {
859 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
860 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
861 /// `sum` or `product`.
863 /// **Why is this bad?** Readability.
865 /// **Known problems:** False positive in pattern guards. Will be resolved once
866 /// non-lexical lifetimes are stable.
870 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
872 /// This could be written as:
874 /// let _ = (0..3).any(|x| x > 2);
876 pub UNNECESSARY_FOLD,
878 "using `fold` when a more succinct alternative exists"
881 declare_clippy_lint! {
882 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
883 /// More specifically it checks if the closure provided is only performing one of the
884 /// filter or map operations and suggests the appropriate option.
886 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
887 /// operation is being performed.
889 /// **Known problems:** None
893 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
895 /// As there is no transformation of the argument this could be written as:
897 /// let _ = (0..3).filter(|&x| x > 2);
901 /// let _ = (0..4).filter_map(i32::checked_abs);
903 /// As there is no conditional check on the argument this could be written as:
905 /// let _ = (0..4).map(i32::checked_abs);
907 pub UNNECESSARY_FILTER_MAP,
909 "using `filter_map` when a more succinct alternative exists"
912 declare_clippy_lint! {
913 /// **What it does:** Checks for `into_iter` calls on types which should be replaced by `iter` or
916 /// **Why is this bad?** Arrays and `PathBuf` do not yet have an `into_iter` method which move out
917 /// their content into an iterator. Auto-referencing resolves the `into_iter` call to its reference
918 /// instead, like `<&[T; N] as IntoIterator>::into_iter`, which just iterates over item references
919 /// like calling `iter` would. Furthermore, when the standard library actually
920 /// [implements the `into_iter` method](https://github.com/rust-lang/rust/issues/25725) which moves
921 /// the content out of the array, the original use of `into_iter` got inferred with the wrong type
922 /// and the code will be broken.
924 /// **Known problems:** None
929 /// let _ = [1, 2, 3].into_iter().map(|x| *x).collect::<Vec<u32>>();
931 /// Could be written as:
933 /// let _ = [1, 2, 3].iter().map(|x| *x).collect::<Vec<u32>>();
935 pub INTO_ITER_ON_ARRAY,
937 "using `.into_iter()` on an array"
940 declare_clippy_lint! {
941 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
944 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
945 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
946 /// `iter_mut` directly.
948 /// **Known problems:** None
953 /// let _ = (&vec![3, 4, 5]).into_iter();
955 pub INTO_ITER_ON_REF,
957 "using `.into_iter()` on a reference"
960 declare_clippy_lint! {
961 /// **What it does:** Checks for calls to `map` followed by a `count`.
963 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
964 /// If the `map` call is intentional, this should be rewritten.
966 /// **Known problems:** None
971 /// let _ = (0..3).map(|x| x + 2).count();
975 "suspicious usage of map"
978 declare_clippy_lint! {
979 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
981 /// **Why is this bad?** For most types, this is undefined behavior.
983 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
984 /// of `MaybeUninit`. There may be other types that allow uninitialized
985 /// data, but those are not yet rigorously defined.
991 /// use std::mem::MaybeUninit;
993 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
996 /// Note that the following is OK:
999 /// use std::mem::MaybeUninit;
1001 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1002 /// MaybeUninit::uninit().assume_init()
1005 pub UNINIT_ASSUMED_INIT,
1007 "`MaybeUninit::uninit().assume_init()`"
1010 declare_clippy_lint! {
1011 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1013 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1018 /// # let y: u32 = 0;
1019 /// # let x: u32 = 100;
1020 /// let add = x.checked_add(y).unwrap_or(u32::max_value());
1021 /// let sub = x.checked_sub(y).unwrap_or(u32::min_value());
1024 /// can be written using dedicated methods for saturating addition/subtraction as:
1027 /// # let y: u32 = 0;
1028 /// # let x: u32 = 100;
1029 /// let add = x.saturating_add(y);
1030 /// let sub = x.saturating_sub(y);
1032 pub MANUAL_SATURATING_ARITHMETIC,
1034 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1037 declare_lint_pass!(Methods => [
1040 SHOULD_IMPLEMENT_TRAIT,
1041 WRONG_SELF_CONVENTION,
1042 WRONG_PUB_SELF_CONVENTION,
1044 OPTION_MAP_UNWRAP_OR,
1045 OPTION_MAP_UNWRAP_OR_ELSE,
1046 RESULT_MAP_UNWRAP_OR_ELSE,
1048 OPTION_AND_THEN_SOME,
1056 INEFFICIENT_TO_STRING,
1058 SINGLE_CHAR_PATTERN,
1060 TEMPORARY_CSTRING_AS_PTR,
1070 STRING_EXTEND_CHARS,
1071 ITER_CLONED_COLLECT,
1074 UNNECESSARY_FILTER_MAP,
1078 UNINIT_ASSUMED_INIT,
1079 MANUAL_SATURATING_ARITHMETIC,
1082 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
1083 #[allow(clippy::cognitive_complexity)]
1084 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
1085 if in_macro(expr.span) {
1089 let (method_names, arg_lists, method_spans) = method_calls(expr, 2);
1090 let method_names: Vec<LocalInternedString> = method_names.iter().map(|s| s.as_str()).collect();
1091 let method_names: Vec<&str> = method_names.iter().map(std::convert::AsRef::as_ref).collect();
1093 match method_names.as_slice() {
1094 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1095 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1096 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1097 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1098 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0]),
1099 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
1100 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1101 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
1102 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1103 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1104 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1105 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1106 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1107 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1108 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1109 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0], method_spans[0]),
1110 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1111 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0], method_spans[1]),
1112 ["is_some", "position"] => {
1113 lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0], method_spans[1])
1115 ["is_some", "rposition"] => {
1116 lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
1118 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1119 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1120 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1122 ["nth", "iter"] => lint_iter_nth(cx, expr, arg_lists[1], false),
1123 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, arg_lists[1], true),
1124 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1125 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1126 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1127 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1128 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0], method_spans[0]),
1129 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1130 ["count", "map"] => lint_suspicious_map(cx, expr),
1131 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1132 ["unwrap_or", arith @ "checked_add"]
1133 | ["unwrap_or", arith @ "checked_sub"]
1134 | ["unwrap_or", arith @ "checked_mul"] => {
1135 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1141 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1142 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1143 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1145 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1146 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1147 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1148 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1150 if args.len() == 1 && method_call.ident.name == sym!(to_string) {
1151 inefficient_to_string::lint(cx, expr, &args[0], self_ty);
1154 match self_ty.kind {
1155 ty::Ref(_, ty, _) if ty.kind == ty::Str => {
1156 for &(method, pos) in &PATTERN_METHODS {
1157 if method_call.ident.name.as_str() == method && args.len() > pos {
1158 lint_single_char_pattern(cx, expr, &args[pos]);
1162 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1163 lint_into_iter(cx, expr, self_ty, *method_span);
1168 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1169 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1171 let mut info = BinaryExprInfo {
1175 eq: op.node == hir::BinOpKind::Eq,
1177 lint_binary_expr_with_method_call(cx, &mut info);
1183 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem) {
1184 if in_external_macro(cx.sess(), impl_item.span) {
1187 let name = impl_item.ident.name.as_str();
1188 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1189 let item = cx.tcx.hir().expect_item(parent);
1190 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1191 let ty = cx.tcx.type_of(def_id);
1193 if let hir::ImplItemKind::Method(ref sig, id) = impl_item.kind;
1194 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1195 if let hir::ItemKind::Impl(_, _, _, _, None, _, _) = item.kind;
1197 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1198 let method_sig = cx.tcx.fn_sig(method_def_id);
1199 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1201 let first_arg_ty = &method_sig.inputs().iter().next();
1203 // check conventions w.r.t. conversion method names and predicates
1204 if let Some(first_arg_ty) = first_arg_ty;
1207 if cx.access_levels.is_exported(impl_item.hir_id) {
1208 // check missing trait implementations
1209 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1210 if name == method_name &&
1211 sig.decl.inputs.len() == n_args &&
1212 out_type.matches(cx, &sig.decl.output) &&
1213 self_kind.matches(cx, ty, first_arg_ty) {
1214 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1215 "defining a method called `{}` on this type; consider implementing \
1216 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1221 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1223 .find(|(ref conv, _)| conv.check(&name))
1225 if !self_kinds.iter().any(|k| k.matches(cx, ty, first_arg_ty)) {
1226 let lint = if item.vis.node.is_pub() {
1227 WRONG_PUB_SELF_CONVENTION
1229 WRONG_SELF_CONVENTION
1237 "methods called `{}` usually take {}; consider choosing a less \
1242 .map(|k| k.description())
1243 .collect::<Vec<_>>()
1252 if let hir::ImplItemKind::Method(_, _) = impl_item.kind {
1253 let ret_ty = return_ty(cx, impl_item.hir_id);
1255 // walk the return type and check for Self (this does not check associated types)
1256 if ret_ty.walk().any(|inner_type| same_tys(cx, ty, inner_type)) {
1260 // if return type is impl trait, check the associated types
1261 if let ty::Opaque(def_id, _) = ret_ty.kind {
1262 // one of the associated types must be Self
1263 for predicate in &cx.tcx.predicates_of(def_id).predicates {
1265 (Predicate::Projection(poly_projection_predicate), _) => {
1266 let binder = poly_projection_predicate.ty();
1267 let associated_type = binder.skip_binder();
1269 // walk the associated type and check for Self
1270 for inner_type in associated_type.walk() {
1271 if same_tys(cx, ty, inner_type) {
1281 if name == "new" && !same_tys(cx, ret_ty, ty) {
1286 "methods called `new` usually return `Self`",
1293 /// Checks for the `OR_FUN_CALL` lint.
1294 #[allow(clippy::too_many_lines)]
1295 fn lint_or_fun_call<'a, 'tcx>(
1296 cx: &LateContext<'a, 'tcx>,
1300 args: &'tcx [hir::Expr],
1302 // Searches an expression for method calls or function calls that aren't ctors
1303 struct FunCallFinder<'a, 'tcx> {
1304 cx: &'a LateContext<'a, 'tcx>,
1308 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1309 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
1310 let call_found = match &expr.kind {
1311 // ignore enum and struct constructors
1312 hir::ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
1313 hir::ExprKind::MethodCall(..) => true,
1322 intravisit::walk_expr(self, expr);
1326 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1327 intravisit::NestedVisitorMap::None
1331 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1332 fn check_unwrap_or_default(
1333 cx: &LateContext<'_, '_>,
1336 self_expr: &hir::Expr,
1343 if name == "unwrap_or";
1344 if let hir::ExprKind::Path(ref qpath) = fun.kind;
1345 let path = &*last_path_segment(qpath).ident.as_str();
1346 if ["default", "new"].contains(&path);
1347 let arg_ty = cx.tables.expr_ty(arg);
1348 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1349 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1352 let mut applicability = Applicability::MachineApplicable;
1357 &format!("use of `{}` followed by a call to `{}`", name, path),
1360 "{}.unwrap_or_default()",
1361 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1373 /// Checks for `*or(foo())`.
1374 #[allow(clippy::too_many_arguments)]
1375 fn check_general_case<'a, 'tcx>(
1376 cx: &LateContext<'a, 'tcx>,
1380 self_expr: &hir::Expr,
1381 arg: &'tcx hir::Expr,
1385 // (path, fn_has_argument, methods, suffix)
1386 let know_types: &[(&[_], _, &[_], _)] = &[
1387 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1388 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1389 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1390 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1394 if know_types.iter().any(|k| k.2.contains(&name));
1396 let mut finder = FunCallFinder { cx: &cx, found: false };
1397 if { finder.visit_expr(&arg); finder.found };
1398 if !contains_return(&arg);
1400 let self_ty = cx.tables.expr_ty(self_expr);
1402 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1403 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1405 if poss.contains(&name);
1408 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1409 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1410 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1411 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1413 let span_replace_word = method_span.with_hi(span.hi());
1418 &format!("use of `{}` followed by a function call", name),
1420 format!("{}_{}({})", name, suffix, sugg),
1421 Applicability::HasPlaceholders,
1427 if args.len() == 2 {
1428 match args[1].kind {
1429 hir::ExprKind::Call(ref fun, ref or_args) => {
1430 let or_has_args = !or_args.is_empty();
1431 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1444 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1451 !or_args.is_empty(),
1459 /// Checks for the `EXPECT_FUN_CALL` lint.
1460 #[allow(clippy::too_many_lines)]
1461 fn lint_expect_fun_call(cx: &LateContext<'_, '_>, expr: &hir::Expr, method_span: Span, name: &str, args: &[hir::Expr]) {
1462 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1464 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr) -> &'a hir::Expr {
1465 let mut arg_root = arg;
1467 arg_root = match &arg_root.kind {
1468 hir::ExprKind::AddrOf(_, expr) => expr,
1469 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1470 if call_args.len() == 1
1471 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1473 let arg_type = cx.tables.expr_ty(&call_args[0]);
1474 let base_type = walk_ptrs_ty(arg_type);
1475 base_type.kind == ty::Str || match_type(cx, base_type, &paths::STRING)
1489 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1490 // converted to string.
1491 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr) -> bool {
1492 let arg_ty = cx.tables.expr_ty(arg);
1493 if match_type(cx, arg_ty, &paths::STRING) {
1496 if let ty::Ref(ty::ReStatic, ty, ..) = arg_ty.kind {
1497 if ty.kind == ty::Str {
1504 fn generate_format_arg_snippet(
1505 cx: &LateContext<'_, '_>,
1507 applicability: &mut Applicability,
1510 if let hir::ExprKind::AddrOf(_, ref format_arg) = a.kind;
1511 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.kind;
1512 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.kind;
1517 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1525 fn is_call(node: &hir::ExprKind) -> bool {
1527 hir::ExprKind::AddrOf(_, expr) => {
1530 hir::ExprKind::Call(..)
1531 | hir::ExprKind::MethodCall(..)
1532 // These variants are debatable or require further examination
1533 | hir::ExprKind::Match(..)
1534 | hir::ExprKind::Block{ .. } => true,
1539 if args.len() != 2 || name != "expect" || !is_call(&args[1].kind) {
1543 let receiver_type = cx.tables.expr_ty(&args[0]);
1544 let closure_args = if match_type(cx, receiver_type, &paths::OPTION) {
1546 } else if match_type(cx, receiver_type, &paths::RESULT) {
1552 let arg_root = get_arg_root(cx, &args[1]);
1554 let span_replace_word = method_span.with_hi(expr.span.hi());
1556 let mut applicability = Applicability::MachineApplicable;
1558 //Special handling for `format!` as arg_root
1559 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.kind {
1560 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1 {
1561 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].kind {
1562 let fmt_spec = &format_args[0];
1563 let fmt_args = &format_args[1];
1565 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1567 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1569 let sugg = args.join(", ");
1575 &format!("use of `{}` followed by a function call", name),
1577 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
1586 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
1587 if requires_to_string(cx, arg_root) {
1588 arg_root_snippet.to_mut().push_str(".to_string()");
1595 &format!("use of `{}` followed by a function call", name),
1597 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
1602 /// Checks for the `CLONE_ON_COPY` lint.
1603 fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty<'_>) {
1604 let ty = cx.tables.expr_ty(expr);
1605 if let ty::Ref(_, inner, _) = arg_ty.kind {
1606 if let ty::Ref(_, innermost, _) = inner.kind {
1611 "using `clone` on a double-reference; \
1612 this will copy the reference instead of cloning the inner type",
1614 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
1615 let mut ty = innermost;
1617 while let ty::Ref(_, inner, _) = ty.kind {
1621 let refs: String = iter::repeat('&').take(n + 1).collect();
1622 let derefs: String = iter::repeat('*').take(n).collect();
1623 let explicit = format!("{}{}::clone({})", refs, ty, snip);
1626 "try dereferencing it",
1627 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
1628 Applicability::MaybeIncorrect,
1632 "or try being explicit about what type to clone",
1634 Applicability::MaybeIncorrect,
1639 return; // don't report clone_on_copy
1643 if is_copy(cx, ty) {
1645 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1646 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
1647 match &cx.tcx.hir().get(parent) {
1648 hir::Node::Expr(parent) => match parent.kind {
1649 // &*x is a nop, &x.clone() is not
1650 hir::ExprKind::AddrOf(..) |
1651 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1652 hir::ExprKind::MethodCall(..) => return,
1655 hir::Node::Stmt(stmt) => {
1656 if let hir::StmtKind::Local(ref loc) = stmt.kind {
1657 if let hir::PatKind::Ref(..) = loc.pat.kind {
1658 // let ref y = *x borrows x, let ref y = x.clone() does not
1666 // x.clone() might have dereferenced x, possibly through Deref impls
1667 if cx.tables.expr_ty(arg) == ty {
1668 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1670 let deref_count = cx
1672 .expr_adjustments(arg)
1675 if let ty::adjustment::Adjust::Deref(_) = adj.kind {
1682 let derefs: String = iter::repeat('*').take(deref_count).collect();
1683 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
1688 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |db| {
1689 if let Some((text, snip)) = snip {
1690 db.span_suggestion(expr.span, text, snip, Applicability::Unspecified);
1696 fn lint_clone_on_ref_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, arg: &hir::Expr) {
1697 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(arg));
1699 if let ty::Adt(_, subst) = obj_ty.kind {
1700 let caller_type = if match_type(cx, obj_ty, &paths::RC) {
1702 } else if match_type(cx, obj_ty, &paths::ARC) {
1704 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
1714 "using '.clone()' on a ref-counted pointer",
1717 "{}::<{}>::clone(&{})",
1720 snippet(cx, arg.span, "_")
1722 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
1727 fn lint_string_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1729 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
1730 let target = &arglists[0][0];
1731 let self_ty = walk_ptrs_ty(cx.tables.expr_ty(target));
1732 let ref_str = if self_ty.kind == ty::Str {
1734 } else if match_type(cx, self_ty, &paths::STRING) {
1740 let mut applicability = Applicability::MachineApplicable;
1743 STRING_EXTEND_CHARS,
1745 "calling `.extend(_.chars())`",
1748 "{}.push_str({}{})",
1749 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
1751 snippet_with_applicability(cx, target.span, "_", &mut applicability)
1758 fn lint_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
1759 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&args[0]));
1760 if match_type(cx, obj_ty, &paths::STRING) {
1761 lint_string_extend(cx, expr, args);
1765 fn lint_cstring_as_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr, source: &hir::Expr, unwrap: &hir::Expr) {
1767 let source_type = cx.tables.expr_ty(source);
1768 if let ty::Adt(def, substs) = source_type.kind;
1769 if match_def_path(cx, def.did, &paths::RESULT);
1770 if match_type(cx, substs.type_at(0), &paths::CSTRING);
1774 TEMPORARY_CSTRING_AS_PTR,
1776 "you are getting the inner pointer of a temporary `CString`",
1778 db.note("that pointer will be invalid outside this expression");
1779 db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
1785 fn lint_iter_cloned_collect<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr]) {
1787 if is_type_diagnostic_item(cx, cx.tables.expr_ty(expr), Symbol::intern("vec_type"));
1788 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0]));
1789 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite());
1794 ITER_CLONED_COLLECT,
1796 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
1799 ".to_vec()".to_string(),
1800 Applicability::MachineApplicable,
1806 fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr, fold_args: &[hir::Expr], fold_span: Span) {
1807 fn check_fold_with_op(
1808 cx: &LateContext<'_, '_>,
1810 fold_args: &[hir::Expr],
1813 replacement_method_name: &str,
1814 replacement_has_args: bool,
1817 // Extract the body of the closure passed to fold
1818 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
1819 let closure_body = cx.tcx.hir().body(body_id);
1820 let closure_expr = remove_blocks(&closure_body.value);
1822 // Check if the closure body is of the form `acc <op> some_expr(x)`
1823 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
1824 if bin_op.node == op;
1826 // Extract the names of the two arguments to the closure
1827 if let Some(first_arg_ident) = get_arg_name(&closure_body.params[0].pat);
1828 if let Some(second_arg_ident) = get_arg_name(&closure_body.params[1].pat);
1830 if match_var(&*left_expr, first_arg_ident);
1831 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
1834 let mut applicability = Applicability::MachineApplicable;
1835 let sugg = if replacement_has_args {
1837 "{replacement}(|{s}| {r})",
1838 replacement = replacement_method_name,
1839 s = second_arg_ident,
1840 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
1845 replacement = replacement_method_name,
1852 fold_span.with_hi(expr.span.hi()),
1853 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
1854 "this `.fold` can be written more succinctly using another method",
1863 // Check that this is a call to Iterator::fold rather than just some function called fold
1864 if !match_trait_method(cx, expr, &paths::ITERATOR) {
1869 fold_args.len() == 3,
1870 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
1873 // Check if the first argument to .fold is a suitable literal
1874 if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
1876 ast::LitKind::Bool(false) => {
1877 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
1879 ast::LitKind::Bool(true) => {
1880 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
1882 ast::LitKind::Int(0, _) => {
1883 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
1885 ast::LitKind::Int(1, _) => {
1886 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
1893 fn lint_iter_nth<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, iter_args: &'tcx [hir::Expr], is_mut: bool) {
1894 let mut_str = if is_mut { "_mut" } else { "" };
1895 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
1897 } else if is_type_diagnostic_item(cx, cx.tables.expr_ty(&iter_args[0]), Symbol::intern("vec_type")) {
1899 } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
1902 return; // caller is not a type that we want to lint
1910 "called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
1911 mut_str, caller_type
1916 fn lint_get_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr, get_args: &'tcx [hir::Expr], is_mut: bool) {
1917 // Note: we don't want to lint `get_mut().unwrap` for `HashMap` or `BTreeMap`,
1918 // because they do not implement `IndexMut`
1919 let mut applicability = Applicability::MachineApplicable;
1920 let expr_ty = cx.tables.expr_ty(&get_args[0]);
1921 let get_args_str = if get_args.len() > 1 {
1922 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
1924 return; // not linting on a .get().unwrap() chain or variant
1927 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
1928 needs_ref = get_args_str.parse::<usize>().is_ok();
1930 } else if is_type_diagnostic_item(cx, expr_ty, Symbol::intern("vec_type")) {
1931 needs_ref = get_args_str.parse::<usize>().is_ok();
1933 } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
1934 needs_ref = get_args_str.parse::<usize>().is_ok();
1936 } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
1939 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
1943 return; // caller is not a type that we want to lint
1946 let mut span = expr.span;
1948 // Handle the case where the result is immediately dereferenced
1949 // by not requiring ref and pulling the dereference into the
1953 if let Some(parent) = get_parent_expr(cx, expr);
1954 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.kind;
1961 let mut_str = if is_mut { "_mut" } else { "" };
1962 let borrow_str = if !needs_ref {
1975 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
1976 mut_str, caller_type
1982 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
1989 fn lint_iter_skip_next(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
1990 // lint if caller of skip is an Iterator
1991 if match_trait_method(cx, expr, &paths::ITERATOR) {
1996 "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`",
2001 fn derefs_to_slice<'a, 'tcx>(
2002 cx: &LateContext<'a, 'tcx>,
2003 expr: &'tcx hir::Expr,
2005 ) -> Option<&'tcx hir::Expr> {
2006 fn may_slice<'a>(cx: &LateContext<'_, 'a>, ty: Ty<'a>) -> bool {
2008 ty::Slice(_) => true,
2009 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
2010 ty::Adt(..) => is_type_diagnostic_item(cx, ty, Symbol::intern("vec_type")),
2011 ty::Array(_, size) => size.eval_usize(cx.tcx, cx.param_env) < 32,
2012 ty::Ref(_, inner, _) => may_slice(cx, inner),
2017 if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.kind {
2018 if path.ident.name == sym!(iter) && may_slice(cx, cx.tables.expr_ty(&args[0])) {
2025 ty::Slice(_) => Some(expr),
2026 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
2027 ty::Ref(_, inner, _) => {
2028 if may_slice(cx, inner) {
2039 /// lint use of `unwrap()` for `Option`s and `Result`s
2040 fn lint_unwrap(cx: &LateContext<'_, '_>, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
2041 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&unwrap_args[0]));
2043 let mess = if match_type(cx, obj_ty, &paths::OPTION) {
2044 Some((OPTION_UNWRAP_USED, "an Option", "None"))
2045 } else if match_type(cx, obj_ty, &paths::RESULT) {
2046 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
2051 if let Some((lint, kind, none_value)) = mess {
2057 "used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
2058 using expect() to provide a better panic \
2066 /// lint use of `ok().expect()` for `Result`s
2067 fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr, ok_args: &[hir::Expr]) {
2069 // lint if the caller of `ok()` is a `Result`
2070 if match_type(cx, cx.tables.expr_ty(&ok_args[0]), &paths::RESULT);
2071 let result_type = cx.tables.expr_ty(&ok_args[0]);
2072 if let Some(error_type) = get_error_type(cx, result_type);
2073 if has_debug_impl(error_type, cx);
2080 "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`",
2086 /// lint use of `map().flatten()` for `Iterators`
2087 fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_args: &'tcx [hir::Expr]) {
2088 // lint if caller of `.map().flatten()` is an Iterator
2089 if match_trait_method(cx, expr, &paths::ITERATOR) {
2090 let msg = "called `map(..).flatten()` on an `Iterator`. \
2091 This is more succinctly expressed by calling `.flat_map(..)`";
2092 let self_snippet = snippet(cx, map_args[0].span, "..");
2093 let func_snippet = snippet(cx, map_args[1].span, "..");
2094 let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
2095 span_lint_and_then(cx, MAP_FLATTEN, expr.span, msg, |db| {
2098 "try using flat_map instead",
2100 Applicability::MachineApplicable,
2106 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2107 fn lint_map_unwrap_or_else<'a, 'tcx>(
2108 cx: &LateContext<'a, 'tcx>,
2109 expr: &'tcx hir::Expr,
2110 map_args: &'tcx [hir::Expr],
2111 unwrap_args: &'tcx [hir::Expr],
2113 // lint if the caller of `map()` is an `Option`
2114 let is_option = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION);
2115 let is_result = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::RESULT);
2117 if is_option || is_result {
2118 // Don't make a suggestion that may fail to compile due to mutably borrowing
2119 // the same variable twice.
2120 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2121 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2122 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2123 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2131 let msg = if is_option {
2132 "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
2133 `map_or_else(g, f)` instead"
2135 "called `map(f).unwrap_or_else(g)` on a Result value. This can be done more directly by calling \
2136 `ok().map_or_else(g, f)` instead"
2138 // get snippets for args to map() and unwrap_or_else()
2139 let map_snippet = snippet(cx, map_args[1].span, "..");
2140 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2141 // lint, with note if neither arg is > 1 line and both map() and
2142 // unwrap_or_else() have the same span
2143 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2144 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2145 if same_span && !multiline {
2149 OPTION_MAP_UNWRAP_OR_ELSE
2151 RESULT_MAP_UNWRAP_OR_ELSE
2157 "replace `map({0}).unwrap_or_else({1})` with `{2}map_or_else({1}, {0})`",
2160 if is_result { "ok()." } else { "" }
2163 } else if same_span && multiline {
2167 OPTION_MAP_UNWRAP_OR_ELSE
2169 RESULT_MAP_UNWRAP_OR_ELSE
2178 /// lint use of `_.map_or(None, _)` for `Option`s
2179 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
2180 if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
2181 // check if the first non-self argument to map_or() is None
2182 let map_or_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].kind {
2183 match_qpath(qpath, &paths::OPTION_NONE)
2188 if map_or_arg_is_none {
2190 let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
2191 `and_then(f)` instead";
2192 let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
2193 let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
2194 let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
2195 span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
2198 "try using and_then instead",
2200 Applicability::MachineApplicable, // snippet
2207 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2208 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
2209 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2210 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2212 let ty = cx.tables.expr_ty(&args[0]);
2213 if !match_type(cx, ty, &paths::OPTION) {
2217 match args[1].kind {
2218 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2219 let closure_body = cx.tcx.hir().body(body_id);
2220 let closure_expr = remove_blocks(&closure_body.value);
2222 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.kind;
2223 if let hir::ExprKind::Path(ref qpath) = some_expr.kind;
2224 if match_qpath(qpath, &paths::OPTION_SOME);
2225 if some_args.len() == 1;
2227 let inner_expr = &some_args[0];
2229 if contains_return(inner_expr) {
2233 let some_inner_snip = if inner_expr.span.from_expansion() {
2234 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2236 snippet(cx, inner_expr.span, "_")
2239 let closure_args_snip = snippet(cx, closure_args_span, "..");
2240 let option_snip = snippet(cx, args[0].span, "..");
2241 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2244 OPTION_AND_THEN_SOME,
2249 Applicability::MachineApplicable,
2254 // `_.and_then(Some)` case, which is no-op.
2255 hir::ExprKind::Path(ref qpath) => {
2256 if match_qpath(qpath, &paths::OPTION_SOME) {
2257 let option_snip = snippet(cx, args[0].span, "..");
2258 let note = format!("{}", option_snip);
2261 OPTION_AND_THEN_SOME,
2264 "use the expression directly",
2266 Applicability::MachineApplicable,
2274 /// lint use of `filter().next()` for `Iterators`
2275 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2276 // lint if caller of `.filter().next()` is an Iterator
2277 if match_trait_method(cx, expr, &paths::ITERATOR) {
2278 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2279 `.find(p)` instead.";
2280 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2281 if filter_snippet.lines().count() <= 1 {
2282 // add note if not multi-line
2289 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2292 span_lint(cx, FILTER_NEXT, expr.span, msg);
2297 /// lint use of `filter().map()` for `Iterators`
2298 fn lint_filter_map<'a, 'tcx>(
2299 cx: &LateContext<'a, 'tcx>,
2300 expr: &'tcx hir::Expr,
2301 _filter_args: &'tcx [hir::Expr],
2302 _map_args: &'tcx [hir::Expr],
2304 // lint if caller of `.filter().map()` is an Iterator
2305 if match_trait_method(cx, expr, &paths::ITERATOR) {
2306 let msg = "called `filter(p).map(q)` on an `Iterator`. \
2307 This is more succinctly expressed by calling `.filter_map(..)` instead.";
2308 span_lint(cx, FILTER_MAP, expr.span, msg);
2312 /// lint use of `filter_map().next()` for `Iterators`
2313 fn lint_filter_map_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2314 if match_trait_method(cx, expr, &paths::ITERATOR) {
2315 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2316 `.find_map(p)` instead.";
2317 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2318 if filter_snippet.lines().count() <= 1 {
2325 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2328 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2333 /// lint use of `find().map()` for `Iterators`
2334 fn lint_find_map<'a, 'tcx>(
2335 cx: &LateContext<'a, 'tcx>,
2336 expr: &'tcx hir::Expr,
2337 _find_args: &'tcx [hir::Expr],
2338 map_args: &'tcx [hir::Expr],
2340 // lint if caller of `.filter().map()` is an Iterator
2341 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2342 let msg = "called `find(p).map(q)` on an `Iterator`. \
2343 This is more succinctly expressed by calling `.find_map(..)` instead.";
2344 span_lint(cx, FIND_MAP, expr.span, msg);
2348 /// lint use of `filter().map()` for `Iterators`
2349 fn lint_filter_map_map<'a, 'tcx>(
2350 cx: &LateContext<'a, 'tcx>,
2351 expr: &'tcx hir::Expr,
2352 _filter_args: &'tcx [hir::Expr],
2353 _map_args: &'tcx [hir::Expr],
2355 // lint if caller of `.filter().map()` is an Iterator
2356 if match_trait_method(cx, expr, &paths::ITERATOR) {
2357 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
2358 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
2359 span_lint(cx, FILTER_MAP, expr.span, msg);
2363 /// lint use of `filter().flat_map()` for `Iterators`
2364 fn lint_filter_flat_map<'a, 'tcx>(
2365 cx: &LateContext<'a, 'tcx>,
2366 expr: &'tcx hir::Expr,
2367 _filter_args: &'tcx [hir::Expr],
2368 _map_args: &'tcx [hir::Expr],
2370 // lint if caller of `.filter().flat_map()` is an Iterator
2371 if match_trait_method(cx, expr, &paths::ITERATOR) {
2372 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
2373 This is more succinctly expressed by calling `.flat_map(..)` \
2374 and filtering by returning an empty Iterator.";
2375 span_lint(cx, FILTER_MAP, expr.span, msg);
2379 /// lint use of `filter_map().flat_map()` for `Iterators`
2380 fn lint_filter_map_flat_map<'a, 'tcx>(
2381 cx: &LateContext<'a, 'tcx>,
2382 expr: &'tcx hir::Expr,
2383 _filter_args: &'tcx [hir::Expr],
2384 _map_args: &'tcx [hir::Expr],
2386 // lint if caller of `.filter_map().flat_map()` is an Iterator
2387 if match_trait_method(cx, expr, &paths::ITERATOR) {
2388 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
2389 This is more succinctly expressed by calling `.flat_map(..)` \
2390 and filtering by returning an empty Iterator.";
2391 span_lint(cx, FILTER_MAP, expr.span, msg);
2395 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2396 fn lint_flat_map_identity<'a, 'tcx>(
2397 cx: &LateContext<'a, 'tcx>,
2398 expr: &'tcx hir::Expr,
2399 flat_map_args: &'tcx [hir::Expr],
2400 flat_map_span: Span,
2402 if match_trait_method(cx, expr, &paths::ITERATOR) {
2403 let arg_node = &flat_map_args[1].kind;
2405 let apply_lint = |message: &str| {
2409 flat_map_span.with_hi(expr.span.hi()),
2412 "flatten()".to_string(),
2413 Applicability::MachineApplicable,
2418 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2419 let body = cx.tcx.hir().body(*body_id);
2421 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
2422 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
2424 if path.segments.len() == 1;
2425 if path.segments[0].ident.as_str() == binding_ident.as_str();
2428 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2433 if let hir::ExprKind::Path(ref qpath) = arg_node;
2435 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2438 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2444 /// lint searching an Iterator followed by `is_some()`
2445 fn lint_search_is_some<'a, 'tcx>(
2446 cx: &LateContext<'a, 'tcx>,
2447 expr: &'tcx hir::Expr,
2448 search_method: &str,
2449 search_args: &'tcx [hir::Expr],
2450 is_some_args: &'tcx [hir::Expr],
2453 // lint if caller of search is an Iterator
2454 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2456 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2457 expressed by calling `any()`.",
2460 let search_snippet = snippet(cx, search_args[1].span, "..");
2461 if search_snippet.lines().count() <= 1 {
2462 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2463 // suggest `any(|..| *..)` instead of `any(|..| **..)` for `find(|..| **..).is_some()`
2464 let any_search_snippet = if_chain! {
2465 if search_method == "find";
2466 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].kind;
2467 let closure_body = cx.tcx.hir().body(body_id);
2468 if let Some(closure_arg) = closure_body.params.get(0);
2470 if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
2471 Some(search_snippet.replacen('&', "", 1))
2472 } else if let Some(name) = get_arg_name(&closure_arg.pat) {
2473 Some(search_snippet.replace(&format!("*{}", name), &name.as_str()))
2481 // add note if not multi-line
2485 method_span.with_hi(expr.span.hi()),
2490 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2492 Applicability::MachineApplicable,
2495 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2500 /// Used for `lint_binary_expr_with_method_call`.
2501 #[derive(Copy, Clone)]
2502 struct BinaryExprInfo<'a> {
2503 expr: &'a hir::Expr,
2504 chain: &'a hir::Expr,
2505 other: &'a hir::Expr,
2509 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2510 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
2511 macro_rules! lint_with_both_lhs_and_rhs {
2512 ($func:ident, $cx:expr, $info:ident) => {
2513 if !$func($cx, $info) {
2514 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2515 if $func($cx, $info) {
2522 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
2523 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
2524 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
2525 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
2528 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2530 cx: &LateContext<'_, '_>,
2531 info: &BinaryExprInfo<'_>,
2532 chain_methods: &[&str],
2533 lint: &'static Lint,
2537 if let Some(args) = method_chain_args(info.chain, chain_methods);
2538 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.kind;
2539 if arg_char.len() == 1;
2540 if let hir::ExprKind::Path(ref qpath) = fun.kind;
2541 if let Some(segment) = single_segment_path(qpath);
2542 if segment.ident.name == sym!(Some);
2544 let mut applicability = Applicability::MachineApplicable;
2545 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
2547 if self_ty.kind != ty::Str {
2555 &format!("you should use the `{}` method", suggest),
2557 format!("{}{}.{}({})",
2558 if info.eq { "" } else { "!" },
2559 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2561 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
2572 /// Checks for the `CHARS_NEXT_CMP` lint.
2573 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2574 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
2577 /// Checks for the `CHARS_LAST_CMP` lint.
2578 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2579 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
2582 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
2586 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
2587 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
2588 cx: &LateContext<'a, 'tcx>,
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::Lit(ref lit) = info.other.kind;
2597 if let ast::LitKind::Char(c) = lit.node;
2599 let mut applicability = Applicability::MachineApplicable;
2604 &format!("you should use the `{}` method", suggest),
2606 format!("{}{}.{}('{}')",
2607 if info.eq { "" } else { "!" },
2608 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2621 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
2622 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2623 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
2626 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
2627 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2628 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
2631 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
2635 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
2636 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
2638 if let hir::ExprKind::Lit(lit) = &arg.kind;
2639 if let ast::LitKind::Str(r, style) = lit.node;
2640 if r.as_str().len() == 1;
2642 let mut applicability = Applicability::MachineApplicable;
2643 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
2644 let ch = if let ast::StrStyle::Raw(nhash) = style {
2645 let nhash = nhash as usize;
2646 // for raw string: r##"a"##
2647 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
2649 // for regular string: "a"
2650 &snip[1..(snip.len() - 1)]
2652 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
2655 SINGLE_CHAR_PATTERN,
2657 "single-character string constant used as pattern",
2658 "try using a char instead",
2666 /// Checks for the `USELESS_ASREF` lint.
2667 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
2668 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
2669 // check if the call is to the actual `AsRef` or `AsMut` trait
2670 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
2671 // check if the type after `as_ref` or `as_mut` is the same as before
2672 let recvr = &as_ref_args[0];
2673 let rcv_ty = cx.tables.expr_ty(recvr);
2674 let res_ty = cx.tables.expr_ty(expr);
2675 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
2676 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
2677 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
2678 // allow the `as_ref` or `as_mut` if it is followed by another method call
2680 if let Some(parent) = get_parent_expr(cx, expr);
2681 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.kind;
2682 if span != &expr.span;
2688 let mut applicability = Applicability::MachineApplicable;
2693 &format!("this call to `{}` does nothing", call_name),
2695 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
2702 fn ty_has_iter_method(
2703 cx: &LateContext<'_, '_>,
2704 self_ref_ty: Ty<'_>,
2705 ) -> Option<(&'static Lint, &'static str, &'static str)> {
2706 has_iter_method(cx, self_ref_ty).map(|ty_name| {
2707 let lint = if ty_name == "array" || ty_name == "PathBuf" {
2712 let mutbl = match self_ref_ty.kind {
2713 ty::Ref(_, _, mutbl) => mutbl,
2714 _ => unreachable!(),
2716 let method_name = match mutbl {
2717 hir::MutImmutable => "iter",
2718 hir::MutMutable => "iter_mut",
2720 (lint, ty_name, method_name)
2724 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr, self_ref_ty: Ty<'_>, method_span: Span) {
2725 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
2728 if let Some((lint, kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
2734 "this .into_iter() call is equivalent to .{}() and will not move the {}",
2738 method_name.to_string(),
2739 Applicability::MachineApplicable,
2744 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
2745 fn lint_maybe_uninit(cx: &LateContext<'_, '_>, expr: &hir::Expr, outer: &hir::Expr) {
2747 if let hir::ExprKind::Call(ref callee, ref args) = expr.kind;
2749 if let hir::ExprKind::Path(ref path) = callee.kind;
2750 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
2751 if !is_maybe_uninit_ty_valid(cx, cx.tables.expr_ty_adjusted(outer));
2755 UNINIT_ASSUMED_INIT,
2757 "this call for this type may be undefined behavior"
2763 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
2765 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
2766 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
2767 ty::Adt(ref adt, _) => {
2768 // needs to be a MaybeUninit
2769 match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT)
2775 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2780 "this call to `map()` won't have an effect on the call to `count()`",
2781 "make sure you did not confuse `map` with `filter`",
2785 /// Given a `Result<T, E>` type, return its error type (`E`).
2786 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
2788 ty::Adt(_, substs) if match_type(cx, ty, &paths::RESULT) => substs.types().nth(1),
2793 /// This checks whether a given type is known to implement Debug.
2794 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
2796 .get_diagnostic_item(sym::debug_trait)
2797 .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
2802 StartsWith(&'static str),
2806 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
2807 (Convention::Eq("new"), &[SelfKind::No]),
2808 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
2809 (Convention::StartsWith("from_"), &[SelfKind::No]),
2810 (Convention::StartsWith("into_"), &[SelfKind::Value]),
2811 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
2812 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
2813 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
2817 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
2818 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
2819 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
2820 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
2821 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
2822 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
2823 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
2824 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
2825 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
2826 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
2827 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
2828 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
2829 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
2830 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
2831 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
2832 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
2833 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
2834 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
2835 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
2836 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
2837 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
2838 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
2839 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
2840 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
2841 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
2842 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
2843 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
2844 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
2845 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
2846 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
2847 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
2851 const PATTERN_METHODS: [(&str, usize); 17] = [
2859 ("split_terminator", 1),
2860 ("rsplit_terminator", 1),
2865 ("match_indices", 1),
2866 ("rmatch_indices", 1),
2867 ("trim_start_matches", 1),
2868 ("trim_end_matches", 1),
2871 #[derive(Clone, Copy, PartialEq, Debug)]
2880 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2881 fn matches_value(parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2882 if ty == parent_ty {
2884 } else if ty.is_box() {
2885 ty.boxed_ty() == parent_ty
2886 } else if ty.is_rc() || ty.is_arc() {
2887 if let ty::Adt(_, substs) = ty.kind {
2888 substs.types().next().map_or(false, |t| t == parent_ty)
2898 cx: &LateContext<'_, 'a>,
2899 mutability: hir::Mutability,
2903 if let ty::Ref(_, t, m) = ty.kind {
2904 return m == mutability && t == parent_ty;
2907 let trait_path = match mutability {
2908 hir::Mutability::MutImmutable => &paths::ASREF_TRAIT,
2909 hir::Mutability::MutMutable => &paths::ASMUT_TRAIT,
2912 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2914 None => return false,
2916 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2920 Self::Value => matches_value(parent_ty, ty),
2922 matches_ref(cx, hir::Mutability::MutImmutable, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty)
2924 Self::RefMut => matches_ref(cx, hir::Mutability::MutMutable, parent_ty, ty),
2925 Self::No => ty != parent_ty,
2930 fn description(self) -> &'static str {
2932 Self::Value => "self by value",
2933 Self::Ref => "self by reference",
2934 Self::RefMut => "self by mutable reference",
2935 Self::No => "no self",
2942 fn check(&self, other: &str) -> bool {
2944 Self::Eq(this) => this == other,
2945 Self::StartsWith(this) => other.starts_with(this) && this != other,
2950 impl fmt::Display for Convention {
2951 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
2953 Self::Eq(this) => this.fmt(f),
2954 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
2959 #[derive(Clone, Copy)]
2968 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FunctionRetTy) -> bool {
2969 let is_unit = |ty: &hir::Ty| SpanlessEq::new(cx).eq_ty_kind(&ty.kind, &hir::TyKind::Tup(vec![].into()));
2971 (Self::Unit, &hir::DefaultReturn(_)) => true,
2972 (Self::Unit, &hir::Return(ref ty)) if is_unit(ty) => true,
2973 (Self::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
2974 (Self::Any, &hir::Return(ref ty)) if !is_unit(ty) => true,
2975 (Self::Ref, &hir::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
2981 fn is_bool(ty: &hir::Ty) -> bool {
2982 if let hir::TyKind::Path(ref p) = ty.kind {
2983 match_qpath(p, &["bool"])
2989 // Returns `true` if `expr` contains a return expression
2990 fn contains_return(expr: &hir::Expr) -> bool {
2991 struct RetCallFinder {
2995 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
2996 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
3000 if let hir::ExprKind::Ret(..) = &expr.kind {
3003 intravisit::walk_expr(self, expr);
3007 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
3008 intravisit::NestedVisitorMap::None
3012 let mut visitor = RetCallFinder { found: false };
3013 visitor.visit_expr(expr);