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 `Result`:
79 /// let res: Result<usize, ()> = Ok(1);
86 /// let res: Result<usize, ()> = Ok(1);
87 /// res.expect("more helpful message");
89 pub RESULT_UNWRAP_USED,
91 "using `Result.unwrap()`, which might be better handled"
94 declare_clippy_lint! {
95 /// **What it does:** Checks for `.expect()` calls on `Option`s.
97 /// **Why is this bad?** Usually it is better to handle the `None` case. Still,
98 /// for a lot of quick-and-dirty code, `expect` is a good choice, which is why
99 /// this lint is `Allow` by default.
101 /// **Known problems:** None.
105 /// Using expect on an `Option`:
108 /// let opt = Some(1);
109 /// opt.expect("one");
115 /// let opt = Some(1);
118 pub OPTION_EXPECT_USED,
120 "using `Option.expect()`, which might be better handled"
123 declare_clippy_lint! {
124 /// **What it does:** Checks for `.expect()` calls on `Result`s.
126 /// **Why is this bad?** `result.expect()` will let the thread panic on `Err`
127 /// values. Normally, you want to implement more sophisticated error handling,
128 /// and propagate errors upwards with `try!`.
130 /// **Known problems:** None.
133 /// Using expect on an `Result`:
136 /// let res: Result<usize, ()> = Ok(1);
137 /// res.expect("one");
143 /// let res: Result<usize, ()> = Ok(1);
146 pub RESULT_EXPECT_USED,
148 "using `Result.expect()`, which might be better handled"
151 declare_clippy_lint! {
152 /// **What it does:** Checks for methods that should live in a trait
153 /// implementation of a `std` trait (see [llogiq's blog
154 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
155 /// information) instead of an inherent implementation.
157 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
158 /// the code, often with very little cost. Also people seeing a `mul(...)`
160 /// may expect `*` to work equally, so you should have good reason to disappoint
163 /// **Known problems:** None.
169 /// fn add(&self, other: &X) -> X {
174 pub SHOULD_IMPLEMENT_TRAIT,
176 "defining a method that should be implementing a std trait"
179 declare_clippy_lint! {
180 /// **What it does:** Checks for methods with certain name prefixes and which
181 /// doesn't match how self is taken. The actual rules are:
183 /// |Prefix |`self` taken |
184 /// |-------|----------------------|
185 /// |`as_` |`&self` or `&mut self`|
187 /// |`into_`|`self` |
188 /// |`is_` |`&self` or none |
189 /// |`to_` |`&self` |
191 /// **Why is this bad?** Consistency breeds readability. If you follow the
192 /// conventions, your users won't be surprised that they, e.g., need to supply a
193 /// mutable reference to a `as_..` function.
195 /// **Known problems:** None.
200 /// fn as_str(self) -> &str {
205 pub WRONG_SELF_CONVENTION,
207 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
210 declare_clippy_lint! {
211 /// **What it does:** This is the same as
212 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
214 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
216 /// **Known problems:** Actually *renaming* the function may break clients if
217 /// the function is part of the public interface. In that case, be mindful of
218 /// the stability guarantees you've given your users.
224 /// pub fn as_str(self) -> &'a str {
229 pub WRONG_PUB_SELF_CONVENTION,
231 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
234 declare_clippy_lint! {
235 /// **What it does:** Checks for usage of `ok().expect(..)`.
237 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
238 /// directly to get a better error message.
240 /// **Known problems:** The error type needs to implement `Debug`
244 /// x.ok().expect("why did I do this again?")
248 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
251 declare_clippy_lint! {
252 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
254 /// **Why is this bad?** Readability, this can be written more concisely as
255 /// `_.map_or(_, _)`.
257 /// **Known problems:** The order of the arguments is not in execution order
261 /// # let x = Some(1);
262 /// x.map(|a| a + 1).unwrap_or(0);
264 pub OPTION_MAP_UNWRAP_OR,
266 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
269 declare_clippy_lint! {
270 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
272 /// **Why is this bad?** Readability, this can be written more concisely as
273 /// `_.map_or_else(_, _)`.
275 /// **Known problems:** The order of the arguments is not in execution order.
279 /// # let x = Some(1);
280 /// # fn some_function() -> usize { 1 }
281 /// x.map(|a| a + 1).unwrap_or_else(some_function);
283 pub OPTION_MAP_UNWRAP_OR_ELSE,
285 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
288 declare_clippy_lint! {
289 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
291 /// **Why is this bad?** Readability, this can be written more concisely as
292 /// `result.ok().map_or_else(_, _)`.
294 /// **Known problems:** None.
298 /// # let x: Result<usize, ()> = Ok(1);
299 /// # fn some_function(foo: ()) -> usize { 1 }
300 /// x.map(|a| a + 1).unwrap_or_else(some_function);
302 pub RESULT_MAP_UNWRAP_OR_ELSE,
304 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.ok().map_or_else(g, f)`"
307 declare_clippy_lint! {
308 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
310 /// **Why is this bad?** Readability, this can be written more concisely as
313 /// **Known problems:** The order of the arguments is not in execution order.
317 /// opt.map_or(None, |a| a + 1)
319 pub OPTION_MAP_OR_NONE,
321 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
324 declare_clippy_lint! {
325 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
327 /// **Why is this bad?** Readability, this can be written more concisely as
330 /// **Known problems:** None
335 /// let x = Some("foo");
336 /// let _ = x.and_then(|s| Some(s.len()));
339 /// The correct use would be:
342 /// let x = Some("foo");
343 /// let _ = x.map(|s| s.len());
345 pub OPTION_AND_THEN_SOME,
347 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
350 declare_clippy_lint! {
351 /// **What it does:** Checks for usage of `_.filter(_).next()`.
353 /// **Why is this bad?** Readability, this can be written more concisely as
356 /// **Known problems:** None.
360 /// # let vec = vec![1];
361 /// vec.iter().filter(|x| **x == 0).next();
363 /// Could be written as
365 /// # let vec = vec![1];
366 /// vec.iter().find(|x| **x == 0);
370 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
373 declare_clippy_lint! {
374 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
376 /// **Why is this bad?** Readability, this can be written more concisely as a
377 /// single method call.
379 /// **Known problems:**
383 /// let vec = vec![vec![1]];
384 /// vec.iter().map(|x| x.iter()).flatten();
388 "using combinations of `flatten` and `map` which can usually be written as a single method call"
391 declare_clippy_lint! {
392 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
393 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
395 /// **Why is this bad?** Readability, this can be written more concisely as a
396 /// single method call.
398 /// **Known problems:** Often requires a condition + Option/Iterator creation
399 /// inside the closure.
403 /// let vec = vec![1];
404 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
408 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
411 declare_clippy_lint! {
412 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
414 /// **Why is this bad?** Readability, this can be written more concisely as a
415 /// single method call.
417 /// **Known problems:** None
421 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
423 /// Can be written as
426 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
430 "using combination of `filter_map` and `next` which can usually be written as a single method call"
433 declare_clippy_lint! {
434 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
436 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
438 /// **Known problems:** None
442 /// # let iter = vec![vec![0]].into_iter();
443 /// iter.flat_map(|x| x);
445 /// Can be written as
447 /// # let iter = vec![vec![0]].into_iter();
450 pub FLAT_MAP_IDENTITY,
452 "call to `flat_map` where `flatten` is sufficient"
455 declare_clippy_lint! {
456 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
458 /// **Why is this bad?** Readability, this can be written more concisely as a
459 /// single method call.
461 /// **Known problems:** Often requires a condition + Option/Iterator creation
462 /// inside the closure.
466 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
468 /// Can be written as
470 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
474 "using a combination of `find` and `map` can usually be written as a single method call"
477 declare_clippy_lint! {
478 /// **What it does:** Checks for an iterator search (such as `find()`,
479 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
481 /// **Why is this bad?** Readability, this can be written more concisely as
484 /// **Known problems:** None.
488 /// # let vec = vec![1];
489 /// vec.iter().find(|x| **x == 0).is_some();
491 /// Could be written as
493 /// # let vec = vec![1];
494 /// vec.iter().any(|x| *x == 0);
498 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
501 declare_clippy_lint! {
502 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
503 /// if it starts with a given char.
505 /// **Why is this bad?** Readability, this can be written more concisely as
506 /// `_.starts_with(_)`.
508 /// **Known problems:** None.
512 /// let name = "foo";
513 /// if name.chars().next() == Some('_') {};
515 /// Could be written as
517 /// let name = "foo";
518 /// if name.starts_with('_') {};
522 "using `.chars().next()` to check if a string starts with a char"
525 declare_clippy_lint! {
526 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
527 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
528 /// `unwrap_or_default` instead.
530 /// **Why is this bad?** The function will always be called and potentially
531 /// allocate an object acting as the default.
533 /// **Known problems:** If the function has side-effects, not calling it will
534 /// change the semantic of the program, but you shouldn't rely on that anyway.
538 /// # let foo = Some(String::new());
539 /// foo.unwrap_or(String::new());
541 /// this can instead be written:
543 /// # let foo = Some(String::new());
544 /// foo.unwrap_or_else(String::new);
548 /// # let foo = Some(String::new());
549 /// foo.unwrap_or_default();
553 "using any `*or` method with a function call, which suggests `*or_else`"
556 declare_clippy_lint! {
557 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
558 /// etc., and suggests to use `unwrap_or_else` instead
560 /// **Why is this bad?** The function will always be called.
562 /// **Known problems:** If the function has side-effects, not calling it will
563 /// change the semantics of the program, but you shouldn't rely on that anyway.
567 /// # let foo = Some(String::new());
568 /// # let err_code = "418";
569 /// # let err_msg = "I'm a teapot";
570 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
574 /// # let foo = Some(String::new());
575 /// # let err_code = "418";
576 /// # let err_msg = "I'm a teapot";
577 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
579 /// this can instead be written:
581 /// # let foo = Some(String::new());
582 /// # let err_code = "418";
583 /// # let err_msg = "I'm a teapot";
584 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
588 "using any `expect` method with a function call"
591 declare_clippy_lint! {
592 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
594 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
595 /// generics, not for using the `clone` method on a concrete type.
597 /// **Known problems:** None.
605 "using `clone` on a `Copy` type"
608 declare_clippy_lint! {
609 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
610 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
611 /// function syntax instead (e.g., `Rc::clone(foo)`).
613 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
614 /// can obscure the fact that only the pointer is being cloned, not the underlying
619 /// # use std::rc::Rc;
620 /// let x = Rc::new(1);
623 pub CLONE_ON_REF_PTR,
625 "using 'clone' on a ref-counted pointer"
628 declare_clippy_lint! {
629 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
631 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
632 /// cloning the underlying `T`.
634 /// **Known problems:** None.
641 /// let z = y.clone();
642 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
645 pub CLONE_DOUBLE_REF,
647 "using `clone` on `&&T`"
650 declare_clippy_lint! {
651 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
652 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
654 /// **Why is this bad?** This bypasses the specialized implementation of
655 /// `ToString` and instead goes through the more expensive string formatting
658 /// **Known problems:** None.
662 /// // Generic implementation for `T: Display` is used (slow)
663 /// ["foo", "bar"].iter().map(|s| s.to_string());
665 /// // OK, the specialized impl is used
666 /// ["foo", "bar"].iter().map(|&s| s.to_string());
668 pub INEFFICIENT_TO_STRING,
670 "using `to_string` on `&&T` where `T: ToString`"
673 declare_clippy_lint! {
674 /// **What it does:** Checks for `new` not returning `Self`.
676 /// **Why is this bad?** As a convention, `new` methods are used to make a new
677 /// instance of a type.
679 /// **Known problems:** None.
684 /// fn new(..) -> NotAFoo {
690 "not returning `Self` in a `new` method"
693 declare_clippy_lint! {
694 /// **What it does:** Checks for string methods that receive a single-character
695 /// `str` as an argument, e.g., `_.split("x")`.
697 /// **Why is this bad?** Performing these methods using a `char` is faster than
700 /// **Known problems:** Does not catch multi-byte unicode characters.
703 /// `_.split("x")` could be `_.split('x')`
704 pub SINGLE_CHAR_PATTERN,
706 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
709 declare_clippy_lint! {
710 /// **What it does:** Checks for getting the inner pointer of a temporary
713 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
714 /// as the `CString` is alive.
716 /// **Known problems:** None.
720 /// let c_str = CString::new("foo").unwrap().as_ptr();
722 /// call_some_ffi_func(c_str);
725 /// Here `c_str` point to a freed address. The correct use would be:
727 /// let c_str = CString::new("foo").unwrap();
729 /// call_some_ffi_func(c_str.as_ptr());
732 pub TEMPORARY_CSTRING_AS_PTR,
734 "getting the inner pointer of a temporary `CString`"
737 declare_clippy_lint! {
738 /// **What it does:** Checks for use of `.iter().nth()` (and the related
739 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
741 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
744 /// **Known problems:** None.
748 /// let some_vec = vec![0, 1, 2, 3];
749 /// let bad_vec = some_vec.iter().nth(3);
750 /// let bad_slice = &some_vec[..].iter().nth(3);
752 /// The correct use would be:
754 /// let some_vec = vec![0, 1, 2, 3];
755 /// let bad_vec = some_vec.get(3);
756 /// let bad_slice = &some_vec[..].get(3);
760 "using `.iter().nth()` on a standard library type with O(1) element access"
763 declare_clippy_lint! {
764 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
766 /// **Why is this bad?** `.nth(x)` is cleaner
768 /// **Known problems:** None.
772 /// let some_vec = vec![0, 1, 2, 3];
773 /// let bad_vec = some_vec.iter().skip(3).next();
774 /// let bad_slice = &some_vec[..].iter().skip(3).next();
776 /// The correct use would be:
778 /// let some_vec = vec![0, 1, 2, 3];
779 /// let bad_vec = some_vec.iter().nth(3);
780 /// let bad_slice = &some_vec[..].iter().nth(3);
784 "using `.skip(x).next()` on an iterator"
787 declare_clippy_lint! {
788 /// **What it does:** Checks for use of `.get().unwrap()` (or
789 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
791 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
794 /// **Known problems:** Not a replacement for error handling: Using either
795 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
796 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
797 /// temporary placeholder for dealing with the `Option` type, then this does
798 /// not mitigate the need for error handling. If there is a chance that `.get()`
799 /// will be `None` in your program, then it is advisable that the `None` case
800 /// is handled in a future refactor instead of using `.unwrap()` or the Index
805 /// let mut some_vec = vec![0, 1, 2, 3];
806 /// let last = some_vec.get(3).unwrap();
807 /// *some_vec.get_mut(0).unwrap() = 1;
809 /// The correct use would be:
811 /// let mut some_vec = vec![0, 1, 2, 3];
812 /// let last = some_vec[3];
817 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
820 declare_clippy_lint! {
821 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
822 /// `&str` or `String`.
824 /// **Why is this bad?** `.push_str(s)` is clearer
826 /// **Known problems:** None.
831 /// let def = String::from("def");
832 /// let mut s = String::new();
833 /// s.extend(abc.chars());
834 /// s.extend(def.chars());
836 /// The correct use would be:
839 /// let def = String::from("def");
840 /// let mut s = String::new();
842 /// s.push_str(&def);
844 pub STRING_EXTEND_CHARS,
846 "using `x.extend(s.chars())` where s is a `&str` or `String`"
849 declare_clippy_lint! {
850 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
853 /// **Why is this bad?** `.to_vec()` is clearer
855 /// **Known problems:** None.
859 /// let s = [1, 2, 3, 4, 5];
860 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
862 /// The better use would be:
864 /// let s = [1, 2, 3, 4, 5];
865 /// let s2: Vec<isize> = s.to_vec();
867 pub ITER_CLONED_COLLECT,
869 "using `.cloned().collect()` on slice to create a `Vec`"
872 declare_clippy_lint! {
873 /// **What it does:** Checks for usage of `.chars().last()` or
874 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
876 /// **Why is this bad?** Readability, this can be written more concisely as
877 /// `_.ends_with(_)`.
879 /// **Known problems:** None.
883 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
887 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
890 declare_clippy_lint! {
891 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
892 /// types before and after the call are the same.
894 /// **Why is this bad?** The call is unnecessary.
896 /// **Known problems:** None.
900 /// # fn do_stuff(x: &[i32]) {}
901 /// let x: &[i32] = &[1, 2, 3, 4, 5];
902 /// do_stuff(x.as_ref());
904 /// The correct use would be:
906 /// # fn do_stuff(x: &[i32]) {}
907 /// let x: &[i32] = &[1, 2, 3, 4, 5];
912 "using `as_ref` where the types before and after the call are the same"
915 declare_clippy_lint! {
916 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
917 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
918 /// `sum` or `product`.
920 /// **Why is this bad?** Readability.
922 /// **Known problems:** False positive in pattern guards. Will be resolved once
923 /// non-lexical lifetimes are stable.
927 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
929 /// This could be written as:
931 /// let _ = (0..3).any(|x| x > 2);
933 pub UNNECESSARY_FOLD,
935 "using `fold` when a more succinct alternative exists"
938 declare_clippy_lint! {
939 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
940 /// More specifically it checks if the closure provided is only performing one of the
941 /// filter or map operations and suggests the appropriate option.
943 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
944 /// operation is being performed.
946 /// **Known problems:** None
950 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
952 /// As there is no transformation of the argument this could be written as:
954 /// let _ = (0..3).filter(|&x| x > 2);
958 /// let _ = (0..4).filter_map(i32::checked_abs);
960 /// As there is no conditional check on the argument this could be written as:
962 /// let _ = (0..4).map(i32::checked_abs);
964 pub UNNECESSARY_FILTER_MAP,
966 "using `filter_map` when a more succinct alternative exists"
969 declare_clippy_lint! {
970 /// **What it does:** Checks for `into_iter` calls on types which should be replaced by `iter` or
973 /// **Why is this bad?** Arrays and `PathBuf` do not yet have an `into_iter` method which move out
974 /// their content into an iterator. Auto-referencing resolves the `into_iter` call to its reference
975 /// instead, like `<&[T; N] as IntoIterator>::into_iter`, which just iterates over item references
976 /// like calling `iter` would. Furthermore, when the standard library actually
977 /// [implements the `into_iter` method](https://github.com/rust-lang/rust/issues/25725) which moves
978 /// the content out of the array, the original use of `into_iter` got inferred with the wrong type
979 /// and the code will be broken.
981 /// **Known problems:** None
986 /// let _ = [1, 2, 3].into_iter().map(|x| *x).collect::<Vec<u32>>();
988 /// Could be written as:
990 /// let _ = [1, 2, 3].iter().map(|x| *x).collect::<Vec<u32>>();
992 pub INTO_ITER_ON_ARRAY,
994 "using `.into_iter()` on an array"
997 declare_clippy_lint! {
998 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
1001 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
1002 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1003 /// `iter_mut` directly.
1005 /// **Known problems:** None
1010 /// let _ = (&vec![3, 4, 5]).into_iter();
1012 pub INTO_ITER_ON_REF,
1014 "using `.into_iter()` on a reference"
1017 declare_clippy_lint! {
1018 /// **What it does:** Checks for calls to `map` followed by a `count`.
1020 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
1021 /// If the `map` call is intentional, this should be rewritten.
1023 /// **Known problems:** None
1028 /// let _ = (0..3).map(|x| x + 2).count();
1032 "suspicious usage of map"
1035 declare_clippy_lint! {
1036 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1038 /// **Why is this bad?** For most types, this is undefined behavior.
1040 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1041 /// of `MaybeUninit`. There may be other types that allow uninitialized
1042 /// data, but those are not yet rigorously defined.
1047 /// // Beware the UB
1048 /// use std::mem::MaybeUninit;
1050 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1053 /// Note that the following is OK:
1056 /// use std::mem::MaybeUninit;
1058 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1059 /// MaybeUninit::uninit().assume_init()
1062 pub UNINIT_ASSUMED_INIT,
1064 "`MaybeUninit::uninit().assume_init()`"
1067 declare_clippy_lint! {
1068 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1070 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1075 /// # let y: u32 = 0;
1076 /// # let x: u32 = 100;
1077 /// let add = x.checked_add(y).unwrap_or(u32::max_value());
1078 /// let sub = x.checked_sub(y).unwrap_or(u32::min_value());
1081 /// can be written using dedicated methods for saturating addition/subtraction as:
1084 /// # let y: u32 = 0;
1085 /// # let x: u32 = 100;
1086 /// let add = x.saturating_add(y);
1087 /// let sub = x.saturating_sub(y);
1089 pub MANUAL_SATURATING_ARITHMETIC,
1091 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1094 declare_lint_pass!(Methods => [
1099 SHOULD_IMPLEMENT_TRAIT,
1100 WRONG_SELF_CONVENTION,
1101 WRONG_PUB_SELF_CONVENTION,
1103 OPTION_MAP_UNWRAP_OR,
1104 OPTION_MAP_UNWRAP_OR_ELSE,
1105 RESULT_MAP_UNWRAP_OR_ELSE,
1107 OPTION_AND_THEN_SOME,
1115 INEFFICIENT_TO_STRING,
1117 SINGLE_CHAR_PATTERN,
1119 TEMPORARY_CSTRING_AS_PTR,
1129 STRING_EXTEND_CHARS,
1130 ITER_CLONED_COLLECT,
1133 UNNECESSARY_FILTER_MAP,
1137 UNINIT_ASSUMED_INIT,
1138 MANUAL_SATURATING_ARITHMETIC,
1141 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
1142 #[allow(clippy::cognitive_complexity)]
1143 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
1144 if in_macro(expr.span) {
1148 let (method_names, arg_lists, method_spans) = method_calls(expr, 2);
1149 let method_names: Vec<LocalInternedString> = method_names.iter().map(|s| s.as_str()).collect();
1150 let method_names: Vec<&str> = method_names.iter().map(std::convert::AsRef::as_ref).collect();
1152 match method_names.as_slice() {
1153 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1154 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1155 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1156 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1157 ["expect", ..] => lint_expect(cx, expr, arg_lists[0]),
1158 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0]),
1159 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
1160 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1161 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
1162 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1163 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1164 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1165 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1166 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1167 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1168 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1169 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0], method_spans[0]),
1170 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1171 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0], method_spans[1]),
1172 ["is_some", "position"] => {
1173 lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0], method_spans[1])
1175 ["is_some", "rposition"] => {
1176 lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
1178 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1179 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1180 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1182 ["nth", "iter"] => lint_iter_nth(cx, expr, arg_lists[1], false),
1183 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, arg_lists[1], true),
1184 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1185 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1186 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1187 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1188 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0], method_spans[0]),
1189 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1190 ["count", "map"] => lint_suspicious_map(cx, expr),
1191 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1192 ["unwrap_or", arith @ "checked_add"]
1193 | ["unwrap_or", arith @ "checked_sub"]
1194 | ["unwrap_or", arith @ "checked_mul"] => {
1195 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1201 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1202 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1203 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1205 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1206 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1207 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1208 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1210 if args.len() == 1 && method_call.ident.name == sym!(to_string) {
1211 inefficient_to_string::lint(cx, expr, &args[0], self_ty);
1214 match self_ty.kind {
1215 ty::Ref(_, ty, _) if ty.kind == ty::Str => {
1216 for &(method, pos) in &PATTERN_METHODS {
1217 if method_call.ident.name.as_str() == method && args.len() > pos {
1218 lint_single_char_pattern(cx, expr, &args[pos]);
1222 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1223 lint_into_iter(cx, expr, self_ty, *method_span);
1228 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1229 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1231 let mut info = BinaryExprInfo {
1235 eq: op.node == hir::BinOpKind::Eq,
1237 lint_binary_expr_with_method_call(cx, &mut info);
1243 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem) {
1244 if in_external_macro(cx.sess(), impl_item.span) {
1247 let name = impl_item.ident.name.as_str();
1248 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1249 let item = cx.tcx.hir().expect_item(parent);
1250 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1251 let ty = cx.tcx.type_of(def_id);
1253 if let hir::ImplItemKind::Method(ref sig, id) = impl_item.kind;
1254 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1255 if let hir::ItemKind::Impl(_, _, _, _, None, _, _) = item.kind;
1257 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1258 let method_sig = cx.tcx.fn_sig(method_def_id);
1259 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1261 let first_arg_ty = &method_sig.inputs().iter().next();
1263 // check conventions w.r.t. conversion method names and predicates
1264 if let Some(first_arg_ty) = first_arg_ty;
1267 if cx.access_levels.is_exported(impl_item.hir_id) {
1268 // check missing trait implementations
1269 for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1270 if name == method_name &&
1271 sig.decl.inputs.len() == n_args &&
1272 out_type.matches(cx, &sig.decl.output) &&
1273 self_kind.matches(cx, ty, first_arg_ty) {
1274 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1275 "defining a method called `{}` on this type; consider implementing \
1276 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1281 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1283 .find(|(ref conv, _)| conv.check(&name))
1285 if !self_kinds.iter().any(|k| k.matches(cx, ty, first_arg_ty)) {
1286 let lint = if item.vis.node.is_pub() {
1287 WRONG_PUB_SELF_CONVENTION
1289 WRONG_SELF_CONVENTION
1297 "methods called `{}` usually take {}; consider choosing a less \
1302 .map(|k| k.description())
1303 .collect::<Vec<_>>()
1312 if let hir::ImplItemKind::Method(_, _) = impl_item.kind {
1313 let ret_ty = return_ty(cx, impl_item.hir_id);
1315 // walk the return type and check for Self (this does not check associated types)
1316 if ret_ty.walk().any(|inner_type| same_tys(cx, ty, inner_type)) {
1320 // if return type is impl trait, check the associated types
1321 if let ty::Opaque(def_id, _) = ret_ty.kind {
1322 // one of the associated types must be Self
1323 for predicate in &cx.tcx.predicates_of(def_id).predicates {
1325 (Predicate::Projection(poly_projection_predicate), _) => {
1326 let binder = poly_projection_predicate.ty();
1327 let associated_type = binder.skip_binder();
1329 // walk the associated type and check for Self
1330 for inner_type in associated_type.walk() {
1331 if same_tys(cx, ty, inner_type) {
1341 if name == "new" && !same_tys(cx, ret_ty, ty) {
1346 "methods called `new` usually return `Self`",
1353 /// Checks for the `OR_FUN_CALL` lint.
1354 #[allow(clippy::too_many_lines)]
1355 fn lint_or_fun_call<'a, 'tcx>(
1356 cx: &LateContext<'a, 'tcx>,
1360 args: &'tcx [hir::Expr],
1362 // Searches an expression for method calls or function calls that aren't ctors
1363 struct FunCallFinder<'a, 'tcx> {
1364 cx: &'a LateContext<'a, 'tcx>,
1368 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1369 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
1370 let call_found = match &expr.kind {
1371 // ignore enum and struct constructors
1372 hir::ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
1373 hir::ExprKind::MethodCall(..) => true,
1382 intravisit::walk_expr(self, expr);
1386 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
1387 intravisit::NestedVisitorMap::None
1391 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1392 fn check_unwrap_or_default(
1393 cx: &LateContext<'_, '_>,
1396 self_expr: &hir::Expr,
1403 if name == "unwrap_or";
1404 if let hir::ExprKind::Path(ref qpath) = fun.kind;
1405 let path = &*last_path_segment(qpath).ident.as_str();
1406 if ["default", "new"].contains(&path);
1407 let arg_ty = cx.tables.expr_ty(arg);
1408 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1409 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1412 let mut applicability = Applicability::MachineApplicable;
1417 &format!("use of `{}` followed by a call to `{}`", name, path),
1420 "{}.unwrap_or_default()",
1421 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1433 /// Checks for `*or(foo())`.
1434 #[allow(clippy::too_many_arguments)]
1435 fn check_general_case<'a, 'tcx>(
1436 cx: &LateContext<'a, 'tcx>,
1440 self_expr: &hir::Expr,
1441 arg: &'tcx hir::Expr,
1445 // (path, fn_has_argument, methods, suffix)
1446 let know_types: &[(&[_], _, &[_], _)] = &[
1447 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1448 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1449 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1450 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1454 if know_types.iter().any(|k| k.2.contains(&name));
1456 let mut finder = FunCallFinder { cx: &cx, found: false };
1457 if { finder.visit_expr(&arg); finder.found };
1458 if !contains_return(&arg);
1460 let self_ty = cx.tables.expr_ty(self_expr);
1462 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1463 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1465 if poss.contains(&name);
1468 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1469 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1470 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1471 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1473 let span_replace_word = method_span.with_hi(span.hi());
1478 &format!("use of `{}` followed by a function call", name),
1480 format!("{}_{}({})", name, suffix, sugg),
1481 Applicability::HasPlaceholders,
1487 if args.len() == 2 {
1488 match args[1].kind {
1489 hir::ExprKind::Call(ref fun, ref or_args) => {
1490 let or_has_args = !or_args.is_empty();
1491 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1504 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1511 !or_args.is_empty(),
1519 /// Checks for the `EXPECT_FUN_CALL` lint.
1520 #[allow(clippy::too_many_lines)]
1521 fn lint_expect_fun_call(cx: &LateContext<'_, '_>, expr: &hir::Expr, method_span: Span, name: &str, args: &[hir::Expr]) {
1522 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1524 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr) -> &'a hir::Expr {
1525 let mut arg_root = arg;
1527 arg_root = match &arg_root.kind {
1528 hir::ExprKind::AddrOf(_, expr) => expr,
1529 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1530 if call_args.len() == 1
1531 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1533 let arg_type = cx.tables.expr_ty(&call_args[0]);
1534 let base_type = walk_ptrs_ty(arg_type);
1535 base_type.kind == ty::Str || match_type(cx, base_type, &paths::STRING)
1549 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1550 // converted to string.
1551 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr) -> bool {
1552 let arg_ty = cx.tables.expr_ty(arg);
1553 if match_type(cx, arg_ty, &paths::STRING) {
1556 if let ty::Ref(ty::ReStatic, ty, ..) = arg_ty.kind {
1557 if ty.kind == ty::Str {
1564 fn generate_format_arg_snippet(
1565 cx: &LateContext<'_, '_>,
1567 applicability: &mut Applicability,
1570 if let hir::ExprKind::AddrOf(_, ref format_arg) = a.kind;
1571 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.kind;
1572 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.kind;
1577 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1585 fn is_call(node: &hir::ExprKind) -> bool {
1587 hir::ExprKind::AddrOf(_, expr) => {
1590 hir::ExprKind::Call(..)
1591 | hir::ExprKind::MethodCall(..)
1592 // These variants are debatable or require further examination
1593 | hir::ExprKind::Match(..)
1594 | hir::ExprKind::Block{ .. } => true,
1599 if args.len() != 2 || name != "expect" || !is_call(&args[1].kind) {
1603 let receiver_type = cx.tables.expr_ty(&args[0]);
1604 let closure_args = if match_type(cx, receiver_type, &paths::OPTION) {
1606 } else if match_type(cx, receiver_type, &paths::RESULT) {
1612 let arg_root = get_arg_root(cx, &args[1]);
1614 let span_replace_word = method_span.with_hi(expr.span.hi());
1616 let mut applicability = Applicability::MachineApplicable;
1618 //Special handling for `format!` as arg_root
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 {
1622 let fmt_spec = &format_args[0];
1623 let fmt_args = &format_args[1];
1625 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1627 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1629 let sugg = args.join(", ");
1635 &format!("use of `{}` followed by a function call", name),
1637 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 `ok().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 `{2}map_or_else({1}, {0})`",
2245 if is_result { "ok()." } else { "" }
2248 } else if same_span && multiline {
2252 OPTION_MAP_UNWRAP_OR_ELSE
2254 RESULT_MAP_UNWRAP_OR_ELSE
2263 /// lint use of `_.map_or(None, _)` for `Option`s
2264 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
2265 if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
2266 // check if the first non-self argument to map_or() is None
2267 let map_or_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].kind {
2268 match_qpath(qpath, &paths::OPTION_NONE)
2273 if map_or_arg_is_none {
2275 let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
2276 `and_then(f)` instead";
2277 let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
2278 let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
2279 let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
2280 span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
2283 "try using and_then instead",
2285 Applicability::MachineApplicable, // snippet
2292 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2293 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr, args: &[hir::Expr]) {
2294 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2295 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2297 let ty = cx.tables.expr_ty(&args[0]);
2298 if !match_type(cx, ty, &paths::OPTION) {
2302 match args[1].kind {
2303 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2304 let closure_body = cx.tcx.hir().body(body_id);
2305 let closure_expr = remove_blocks(&closure_body.value);
2307 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.kind;
2308 if let hir::ExprKind::Path(ref qpath) = some_expr.kind;
2309 if match_qpath(qpath, &paths::OPTION_SOME);
2310 if some_args.len() == 1;
2312 let inner_expr = &some_args[0];
2314 if contains_return(inner_expr) {
2318 let some_inner_snip = if inner_expr.span.from_expansion() {
2319 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2321 snippet(cx, inner_expr.span, "_")
2324 let closure_args_snip = snippet(cx, closure_args_span, "..");
2325 let option_snip = snippet(cx, args[0].span, "..");
2326 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2329 OPTION_AND_THEN_SOME,
2334 Applicability::MachineApplicable,
2339 // `_.and_then(Some)` case, which is no-op.
2340 hir::ExprKind::Path(ref qpath) => {
2341 if match_qpath(qpath, &paths::OPTION_SOME) {
2342 let option_snip = snippet(cx, args[0].span, "..");
2343 let note = format!("{}", option_snip);
2346 OPTION_AND_THEN_SOME,
2349 "use the expression directly",
2351 Applicability::MachineApplicable,
2359 /// lint use of `filter().next()` for `Iterators`
2360 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2361 // lint if caller of `.filter().next()` is an Iterator
2362 if match_trait_method(cx, expr, &paths::ITERATOR) {
2363 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2364 `.find(p)` instead.";
2365 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2366 if filter_snippet.lines().count() <= 1 {
2367 // add note if not multi-line
2374 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2377 span_lint(cx, FILTER_NEXT, expr.span, msg);
2382 /// lint use of `filter().map()` for `Iterators`
2383 fn lint_filter_map<'a, 'tcx>(
2384 cx: &LateContext<'a, 'tcx>,
2385 expr: &'tcx hir::Expr,
2386 _filter_args: &'tcx [hir::Expr],
2387 _map_args: &'tcx [hir::Expr],
2389 // lint if caller of `.filter().map()` is an Iterator
2390 if match_trait_method(cx, expr, &paths::ITERATOR) {
2391 let msg = "called `filter(p).map(q)` on an `Iterator`. \
2392 This is more succinctly expressed by calling `.filter_map(..)` instead.";
2393 span_lint(cx, FILTER_MAP, expr.span, msg);
2397 /// lint use of `filter_map().next()` for `Iterators`
2398 fn lint_filter_map_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
2399 if match_trait_method(cx, expr, &paths::ITERATOR) {
2400 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2401 `.find_map(p)` instead.";
2402 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2403 if filter_snippet.lines().count() <= 1 {
2410 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2413 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2418 /// lint use of `find().map()` for `Iterators`
2419 fn lint_find_map<'a, 'tcx>(
2420 cx: &LateContext<'a, 'tcx>,
2421 expr: &'tcx hir::Expr,
2422 _find_args: &'tcx [hir::Expr],
2423 map_args: &'tcx [hir::Expr],
2425 // lint if caller of `.filter().map()` is an Iterator
2426 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2427 let msg = "called `find(p).map(q)` on an `Iterator`. \
2428 This is more succinctly expressed by calling `.find_map(..)` instead.";
2429 span_lint(cx, FIND_MAP, expr.span, msg);
2433 /// lint use of `filter().map()` for `Iterators`
2434 fn lint_filter_map_map<'a, 'tcx>(
2435 cx: &LateContext<'a, 'tcx>,
2436 expr: &'tcx hir::Expr,
2437 _filter_args: &'tcx [hir::Expr],
2438 _map_args: &'tcx [hir::Expr],
2440 // lint if caller of `.filter().map()` is an Iterator
2441 if match_trait_method(cx, expr, &paths::ITERATOR) {
2442 let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
2443 This is more succinctly expressed by only calling `.filter_map(..)` instead.";
2444 span_lint(cx, FILTER_MAP, expr.span, msg);
2448 /// lint use of `filter().flat_map()` for `Iterators`
2449 fn lint_filter_flat_map<'a, 'tcx>(
2450 cx: &LateContext<'a, 'tcx>,
2451 expr: &'tcx hir::Expr,
2452 _filter_args: &'tcx [hir::Expr],
2453 _map_args: &'tcx [hir::Expr],
2455 // lint if caller of `.filter().flat_map()` is an Iterator
2456 if match_trait_method(cx, expr, &paths::ITERATOR) {
2457 let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
2458 This is more succinctly expressed by calling `.flat_map(..)` \
2459 and filtering by returning an empty Iterator.";
2460 span_lint(cx, FILTER_MAP, expr.span, msg);
2464 /// lint use of `filter_map().flat_map()` for `Iterators`
2465 fn lint_filter_map_flat_map<'a, 'tcx>(
2466 cx: &LateContext<'a, 'tcx>,
2467 expr: &'tcx hir::Expr,
2468 _filter_args: &'tcx [hir::Expr],
2469 _map_args: &'tcx [hir::Expr],
2471 // lint if caller of `.filter_map().flat_map()` is an Iterator
2472 if match_trait_method(cx, expr, &paths::ITERATOR) {
2473 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
2474 This is more succinctly expressed by calling `.flat_map(..)` \
2475 and filtering by returning an empty Iterator.";
2476 span_lint(cx, FILTER_MAP, expr.span, msg);
2480 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2481 fn lint_flat_map_identity<'a, 'tcx>(
2482 cx: &LateContext<'a, 'tcx>,
2483 expr: &'tcx hir::Expr,
2484 flat_map_args: &'tcx [hir::Expr],
2485 flat_map_span: Span,
2487 if match_trait_method(cx, expr, &paths::ITERATOR) {
2488 let arg_node = &flat_map_args[1].kind;
2490 let apply_lint = |message: &str| {
2494 flat_map_span.with_hi(expr.span.hi()),
2497 "flatten()".to_string(),
2498 Applicability::MachineApplicable,
2503 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2504 let body = cx.tcx.hir().body(*body_id);
2506 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
2507 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
2509 if path.segments.len() == 1;
2510 if path.segments[0].ident.as_str() == binding_ident.as_str();
2513 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2518 if let hir::ExprKind::Path(ref qpath) = arg_node;
2520 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2523 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2529 /// lint searching an Iterator followed by `is_some()`
2530 fn lint_search_is_some<'a, 'tcx>(
2531 cx: &LateContext<'a, 'tcx>,
2532 expr: &'tcx hir::Expr,
2533 search_method: &str,
2534 search_args: &'tcx [hir::Expr],
2535 is_some_args: &'tcx [hir::Expr],
2538 // lint if caller of search is an Iterator
2539 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2541 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2542 expressed by calling `any()`.",
2545 let search_snippet = snippet(cx, search_args[1].span, "..");
2546 if search_snippet.lines().count() <= 1 {
2547 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2548 // suggest `any(|..| *..)` instead of `any(|..| **..)` for `find(|..| **..).is_some()`
2549 let any_search_snippet = if_chain! {
2550 if search_method == "find";
2551 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].kind;
2552 let closure_body = cx.tcx.hir().body(body_id);
2553 if let Some(closure_arg) = closure_body.params.get(0);
2555 if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
2556 Some(search_snippet.replacen('&', "", 1))
2557 } else if let Some(name) = get_arg_name(&closure_arg.pat) {
2558 Some(search_snippet.replace(&format!("*{}", name), &name.as_str()))
2566 // add note if not multi-line
2570 method_span.with_hi(expr.span.hi()),
2575 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2577 Applicability::MachineApplicable,
2580 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2585 /// Used for `lint_binary_expr_with_method_call`.
2586 #[derive(Copy, Clone)]
2587 struct BinaryExprInfo<'a> {
2588 expr: &'a hir::Expr,
2589 chain: &'a hir::Expr,
2590 other: &'a hir::Expr,
2594 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2595 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
2596 macro_rules! lint_with_both_lhs_and_rhs {
2597 ($func:ident, $cx:expr, $info:ident) => {
2598 if !$func($cx, $info) {
2599 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2600 if $func($cx, $info) {
2607 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
2608 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
2609 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
2610 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
2613 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2615 cx: &LateContext<'_, '_>,
2616 info: &BinaryExprInfo<'_>,
2617 chain_methods: &[&str],
2618 lint: &'static Lint,
2622 if let Some(args) = method_chain_args(info.chain, chain_methods);
2623 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.kind;
2624 if arg_char.len() == 1;
2625 if let hir::ExprKind::Path(ref qpath) = fun.kind;
2626 if let Some(segment) = single_segment_path(qpath);
2627 if segment.ident.name == sym!(Some);
2629 let mut applicability = Applicability::MachineApplicable;
2630 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
2632 if self_ty.kind != ty::Str {
2640 &format!("you should use the `{}` method", suggest),
2642 format!("{}{}.{}({})",
2643 if info.eq { "" } else { "!" },
2644 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2646 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
2657 /// Checks for the `CHARS_NEXT_CMP` lint.
2658 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2659 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
2662 /// Checks for the `CHARS_LAST_CMP` lint.
2663 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2664 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
2667 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
2671 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
2672 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
2673 cx: &LateContext<'a, 'tcx>,
2674 info: &BinaryExprInfo<'_>,
2675 chain_methods: &[&str],
2676 lint: &'static Lint,
2680 if let Some(args) = method_chain_args(info.chain, chain_methods);
2681 if let hir::ExprKind::Lit(ref lit) = info.other.kind;
2682 if let ast::LitKind::Char(c) = lit.node;
2684 let mut applicability = Applicability::MachineApplicable;
2689 &format!("you should use the `{}` method", suggest),
2691 format!("{}{}.{}('{}')",
2692 if info.eq { "" } else { "!" },
2693 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
2706 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
2707 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2708 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
2711 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
2712 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
2713 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
2716 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
2720 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
2721 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, _expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
2723 if let hir::ExprKind::Lit(lit) = &arg.kind;
2724 if let ast::LitKind::Str(r, style) = lit.node;
2725 if r.as_str().len() == 1;
2727 let mut applicability = Applicability::MachineApplicable;
2728 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
2729 let ch = if let ast::StrStyle::Raw(nhash) = style {
2730 let nhash = nhash as usize;
2731 // for raw string: r##"a"##
2732 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
2734 // for regular string: "a"
2735 &snip[1..(snip.len() - 1)]
2737 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
2740 SINGLE_CHAR_PATTERN,
2742 "single-character string constant used as pattern",
2743 "try using a char instead",
2751 /// Checks for the `USELESS_ASREF` lint.
2752 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
2753 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
2754 // check if the call is to the actual `AsRef` or `AsMut` trait
2755 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
2756 // check if the type after `as_ref` or `as_mut` is the same as before
2757 let recvr = &as_ref_args[0];
2758 let rcv_ty = cx.tables.expr_ty(recvr);
2759 let res_ty = cx.tables.expr_ty(expr);
2760 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
2761 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
2762 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
2763 // allow the `as_ref` or `as_mut` if it is followed by another method call
2765 if let Some(parent) = get_parent_expr(cx, expr);
2766 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.kind;
2767 if span != &expr.span;
2773 let mut applicability = Applicability::MachineApplicable;
2778 &format!("this call to `{}` does nothing", call_name),
2780 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
2787 fn ty_has_iter_method(
2788 cx: &LateContext<'_, '_>,
2789 self_ref_ty: Ty<'_>,
2790 ) -> Option<(&'static Lint, &'static str, &'static str)> {
2791 has_iter_method(cx, self_ref_ty).map(|ty_name| {
2792 let lint = if ty_name == "array" || ty_name == "PathBuf" {
2797 let mutbl = match self_ref_ty.kind {
2798 ty::Ref(_, _, mutbl) => mutbl,
2799 _ => unreachable!(),
2801 let method_name = match mutbl {
2802 hir::MutImmutable => "iter",
2803 hir::MutMutable => "iter_mut",
2805 (lint, ty_name, method_name)
2809 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr, self_ref_ty: Ty<'_>, method_span: Span) {
2810 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
2813 if let Some((lint, kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
2819 "this .into_iter() call is equivalent to .{}() and will not move the {}",
2823 method_name.to_string(),
2824 Applicability::MachineApplicable,
2829 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
2830 fn lint_maybe_uninit(cx: &LateContext<'_, '_>, expr: &hir::Expr, outer: &hir::Expr) {
2832 if let hir::ExprKind::Call(ref callee, ref args) = expr.kind;
2834 if let hir::ExprKind::Path(ref path) = callee.kind;
2835 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
2836 if !is_maybe_uninit_ty_valid(cx, cx.tables.expr_ty_adjusted(outer));
2840 UNINIT_ASSUMED_INIT,
2842 "this call for this type may be undefined behavior"
2848 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
2850 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
2851 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
2852 ty::Adt(ref adt, _) => {
2853 // needs to be a MaybeUninit
2854 match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT)
2860 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr) {
2865 "this call to `map()` won't have an effect on the call to `count()`",
2866 "make sure you did not confuse `map` with `filter`",
2870 /// Given a `Result<T, E>` type, return its error type (`E`).
2871 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
2873 ty::Adt(_, substs) if match_type(cx, ty, &paths::RESULT) => substs.types().nth(1),
2878 /// This checks whether a given type is known to implement Debug.
2879 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
2881 .get_diagnostic_item(sym::debug_trait)
2882 .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
2887 StartsWith(&'static str),
2891 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
2892 (Convention::Eq("new"), &[SelfKind::No]),
2893 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
2894 (Convention::StartsWith("from_"), &[SelfKind::No]),
2895 (Convention::StartsWith("into_"), &[SelfKind::Value]),
2896 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
2897 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
2898 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
2902 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
2903 ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
2904 ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
2905 ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
2906 ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
2907 ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
2908 ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
2909 ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
2910 ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
2911 ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
2912 ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
2913 ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
2914 ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
2915 ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
2916 ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
2917 ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
2918 ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
2919 ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
2920 ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
2921 ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
2922 ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
2923 ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
2924 ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
2925 ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
2926 ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
2927 ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
2928 ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
2929 ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
2930 ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
2931 ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
2932 ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
2936 const PATTERN_METHODS: [(&str, usize); 17] = [
2944 ("split_terminator", 1),
2945 ("rsplit_terminator", 1),
2950 ("match_indices", 1),
2951 ("rmatch_indices", 1),
2952 ("trim_start_matches", 1),
2953 ("trim_end_matches", 1),
2956 #[derive(Clone, Copy, PartialEq, Debug)]
2965 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2966 fn matches_value(parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2967 if ty == parent_ty {
2969 } else if ty.is_box() {
2970 ty.boxed_ty() == parent_ty
2971 } else if ty.is_rc() || ty.is_arc() {
2972 if let ty::Adt(_, substs) = ty.kind {
2973 substs.types().next().map_or(false, |t| t == parent_ty)
2983 cx: &LateContext<'_, 'a>,
2984 mutability: hir::Mutability,
2988 if let ty::Ref(_, t, m) = ty.kind {
2989 return m == mutability && t == parent_ty;
2992 let trait_path = match mutability {
2993 hir::Mutability::MutImmutable => &paths::ASREF_TRAIT,
2994 hir::Mutability::MutMutable => &paths::ASMUT_TRAIT,
2997 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2999 None => return false,
3001 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
3005 Self::Value => matches_value(parent_ty, ty),
3007 matches_ref(cx, hir::Mutability::MutImmutable, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty)
3009 Self::RefMut => matches_ref(cx, hir::Mutability::MutMutable, parent_ty, ty),
3010 Self::No => ty != parent_ty,
3015 fn description(self) -> &'static str {
3017 Self::Value => "self by value",
3018 Self::Ref => "self by reference",
3019 Self::RefMut => "self by mutable reference",
3020 Self::No => "no self",
3027 fn check(&self, other: &str) -> bool {
3029 Self::Eq(this) => this == other,
3030 Self::StartsWith(this) => other.starts_with(this) && this != other,
3035 impl fmt::Display for Convention {
3036 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
3038 Self::Eq(this) => this.fmt(f),
3039 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
3044 #[derive(Clone, Copy)]
3053 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FunctionRetTy) -> bool {
3054 let is_unit = |ty: &hir::Ty| SpanlessEq::new(cx).eq_ty_kind(&ty.kind, &hir::TyKind::Tup(vec![].into()));
3056 (Self::Unit, &hir::DefaultReturn(_)) => true,
3057 (Self::Unit, &hir::Return(ref ty)) if is_unit(ty) => true,
3058 (Self::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
3059 (Self::Any, &hir::Return(ref ty)) if !is_unit(ty) => true,
3060 (Self::Ref, &hir::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
3066 fn is_bool(ty: &hir::Ty) -> bool {
3067 if let hir::TyKind::Path(ref p) = ty.kind {
3068 match_qpath(p, &["bool"])
3074 // Returns `true` if `expr` contains a return expression
3075 fn contains_return(expr: &hir::Expr) -> bool {
3076 struct RetCallFinder {
3080 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
3081 fn visit_expr(&mut self, expr: &'tcx hir::Expr) {
3085 if let hir::ExprKind::Ret(..) = &expr.kind {
3088 intravisit::walk_expr(self, expr);
3092 fn nested_visit_map<'this>(&'this mut self) -> intravisit::NestedVisitorMap<'this, 'tcx> {
3093 intravisit::NestedVisitorMap::None
3097 let mut visitor = RetCallFinder { found: false };
3098 visitor.visit_expr(expr);