1 mod inefficient_to_string;
2 mod manual_saturating_arithmetic;
3 mod option_map_unwrap_or;
4 mod unnecessary_filter_map;
10 use if_chain::if_chain;
12 use rustc_errors::Applicability;
14 use rustc_hir::intravisit::{self, Visitor};
15 use rustc_lint::{LateContext, LateLintPass, Lint, LintContext};
16 use rustc_middle::hir::map::Map;
17 use rustc_middle::lint::in_external_macro;
18 use rustc_middle::ty::subst::GenericArgKind;
19 use rustc_middle::ty::{self, Predicate, Ty};
20 use rustc_session::{declare_lint_pass, declare_tool_lint};
21 use rustc_span::source_map::Span;
22 use rustc_span::symbol::{sym, SymbolStr};
24 use crate::consts::{constant, Constant};
25 use crate::utils::usage::mutated_variables;
27 get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, implements_trait, in_macro, is_copy,
28 is_ctor_or_promotable_const_function, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment,
29 match_def_path, match_qpath, match_trait_method, match_type, match_var, method_calls, method_chain_args, paths,
30 remove_blocks, return_ty, same_tys, single_segment_path, snippet, snippet_with_applicability,
31 snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_note, span_lint_and_sugg,
32 span_lint_and_then, sugg, walk_ptrs_ty, walk_ptrs_ty_depth, SpanlessEq,
35 declare_clippy_lint! {
36 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
38 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
39 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
40 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
41 /// `Allow` by default.
43 /// **Known problems:** None.
47 /// Using unwrap on an `Option`:
50 /// let opt = Some(1);
57 /// let opt = Some(1);
58 /// opt.expect("more helpful message");
60 pub OPTION_UNWRAP_USED,
62 "using `Option.unwrap()`, which should at least get a better message using `expect()`"
65 declare_clippy_lint! {
66 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
68 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
69 /// values. Normally, you want to implement more sophisticated error handling,
70 /// and propagate errors upwards with `?` operator.
72 /// Even if you want to panic on errors, not all `Error`s implement good
73 /// messages on display. Therefore, it may be beneficial to look at the places
74 /// where they may get displayed. Activate this lint to do just that.
76 /// **Known problems:** None.
79 /// Using unwrap on an `Result`:
82 /// let res: Result<usize, ()> = Ok(1);
89 /// let res: Result<usize, ()> = Ok(1);
90 /// res.expect("more helpful message");
92 pub RESULT_UNWRAP_USED,
94 "using `Result.unwrap()`, which might be better handled"
97 declare_clippy_lint! {
98 /// **What it does:** Checks for `.expect()` calls on `Option`s.
100 /// **Why is this bad?** Usually it is better to handle the `None` case. Still,
101 /// for a lot of quick-and-dirty code, `expect` is a good choice, which is why
102 /// this lint is `Allow` by default.
104 /// **Known problems:** None.
108 /// Using expect on an `Option`:
111 /// let opt = Some(1);
112 /// opt.expect("one");
118 /// let opt = Some(1);
121 pub OPTION_EXPECT_USED,
123 "using `Option.expect()`, which might be better handled"
126 declare_clippy_lint! {
127 /// **What it does:** Checks for `.expect()` calls on `Result`s.
129 /// **Why is this bad?** `result.expect()` will let the thread panic on `Err`
130 /// values. Normally, you want to implement more sophisticated error handling,
131 /// and propagate errors upwards with `?` operator.
133 /// **Known problems:** None.
136 /// Using expect on an `Result`:
139 /// let res: Result<usize, ()> = Ok(1);
140 /// res.expect("one");
146 /// let res: Result<usize, ()> = Ok(1);
148 /// # Ok::<(), ()>(())
150 pub RESULT_EXPECT_USED,
152 "using `Result.expect()`, which might be better handled"
155 declare_clippy_lint! {
156 /// **What it does:** Checks for methods that should live in a trait
157 /// implementation of a `std` trait (see [llogiq's blog
158 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
159 /// information) instead of an inherent implementation.
161 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
162 /// the code, often with very little cost. Also people seeing a `mul(...)`
164 /// may expect `*` to work equally, so you should have good reason to disappoint
167 /// **Known problems:** None.
173 /// fn add(&self, other: &X) -> X {
179 pub SHOULD_IMPLEMENT_TRAIT,
181 "defining a method that should be implementing a std trait"
184 declare_clippy_lint! {
185 /// **What it does:** Checks for methods with certain name prefixes and which
186 /// doesn't match how self is taken. The actual rules are:
188 /// |Prefix |`self` taken |
189 /// |-------|----------------------|
190 /// |`as_` |`&self` or `&mut self`|
192 /// |`into_`|`self` |
193 /// |`is_` |`&self` or none |
194 /// |`to_` |`&self` |
196 /// **Why is this bad?** Consistency breeds readability. If you follow the
197 /// conventions, your users won't be surprised that they, e.g., need to supply a
198 /// mutable reference to a `as_..` function.
200 /// **Known problems:** None.
206 /// fn as_str(self) -> &'static str {
212 pub WRONG_SELF_CONVENTION,
214 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
217 declare_clippy_lint! {
218 /// **What it does:** This is the same as
219 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
221 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
223 /// **Known problems:** Actually *renaming* the function may break clients if
224 /// the function is part of the public interface. In that case, be mindful of
225 /// the stability guarantees you've given your users.
231 /// pub fn as_str(self) -> &'a str {
236 pub WRONG_PUB_SELF_CONVENTION,
238 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
241 declare_clippy_lint! {
242 /// **What it does:** Checks for usage of `ok().expect(..)`.
244 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
245 /// directly to get a better error message.
247 /// **Known problems:** The error type needs to implement `Debug`
251 /// # let x = Ok::<_, ()>(());
252 /// x.ok().expect("why did I do this again?")
256 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
259 declare_clippy_lint! {
260 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
262 /// **Why is this bad?** Readability, this can be written more concisely as
263 /// `_.map_or(_, _)`.
265 /// **Known problems:** The order of the arguments is not in execution order
269 /// # let x = Some(1);
270 /// x.map(|a| a + 1).unwrap_or(0);
272 pub OPTION_MAP_UNWRAP_OR,
274 "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as `map_or(a, f)`"
277 declare_clippy_lint! {
278 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
280 /// **Why is this bad?** Readability, this can be written more concisely as
281 /// `_.map_or_else(_, _)`.
283 /// **Known problems:** The order of the arguments is not in execution order.
287 /// # let x = Some(1);
288 /// # fn some_function() -> usize { 1 }
289 /// x.map(|a| a + 1).unwrap_or_else(some_function);
291 pub OPTION_MAP_UNWRAP_OR_ELSE,
293 "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `map_or_else(g, f)`"
296 declare_clippy_lint! {
297 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
299 /// **Why is this bad?** Readability, this can be written more concisely as
300 /// `result.map_or_else(_, _)`.
302 /// **Known problems:** None.
306 /// # let x: Result<usize, ()> = Ok(1);
307 /// # fn some_function(foo: ()) -> usize { 1 }
308 /// x.map(|a| a + 1).unwrap_or_else(some_function);
310 pub RESULT_MAP_UNWRAP_OR_ELSE,
312 "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as `.map_or_else(g, f)`"
315 declare_clippy_lint! {
316 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
318 /// **Why is this bad?** Readability, this can be written more concisely as
321 /// **Known problems:** The order of the arguments is not in execution order.
325 /// # let opt = Some(1);
326 /// opt.map_or(None, |a| Some(a + 1))
329 pub OPTION_MAP_OR_NONE,
331 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
334 declare_clippy_lint! {
335 /// **What it does:** Checks for usage of `_.map_or(None, Some)`.
337 /// **Why is this bad?** Readability, this can be written more concisely as
340 /// **Known problems:** None.
346 /// # let r: Result<u32, &str> = Ok(1);
347 /// assert_eq!(Some(1), r.map_or(None, Some));
352 /// # let r: Result<u32, &str> = Ok(1);
353 /// assert_eq!(Some(1), r.ok());
355 pub RESULT_MAP_OR_INTO_OPTION,
357 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
360 declare_clippy_lint! {
361 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`.
363 /// **Why is this bad?** Readability, this can be written more concisely as
366 /// **Known problems:** None
371 /// let x = Some("foo");
372 /// let _ = x.and_then(|s| Some(s.len()));
375 /// The correct use would be:
378 /// let x = Some("foo");
379 /// let _ = x.map(|s| s.len());
381 pub OPTION_AND_THEN_SOME,
383 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
386 declare_clippy_lint! {
387 /// **What it does:** Checks for usage of `_.filter(_).next()`.
389 /// **Why is this bad?** Readability, this can be written more concisely as
392 /// **Known problems:** None.
396 /// # let vec = vec![1];
397 /// vec.iter().filter(|x| **x == 0).next();
399 /// Could be written as
401 /// # let vec = vec![1];
402 /// vec.iter().find(|x| **x == 0);
406 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
409 declare_clippy_lint! {
410 /// **What it does:** Checks for usage of `_.skip_while(condition).next()`.
412 /// **Why is this bad?** Readability, this can be written more concisely as
413 /// `_.find(!condition)`.
415 /// **Known problems:** None.
419 /// # let vec = vec![1];
420 /// vec.iter().skip_while(|x| **x == 0).next();
422 /// Could be written as
424 /// # let vec = vec![1];
425 /// vec.iter().find(|x| **x != 0);
429 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
432 declare_clippy_lint! {
433 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
435 /// **Why is this bad?** Readability, this can be written more concisely as a
436 /// single method call.
438 /// **Known problems:**
442 /// let vec = vec![vec![1]];
443 /// vec.iter().map(|x| x.iter()).flatten();
447 "using combinations of `flatten` and `map` which can usually be written as a single method call"
450 declare_clippy_lint! {
451 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
452 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
454 /// **Why is this bad?** Readability, this can be written more concisely as a
455 /// single method call.
457 /// **Known problems:** Often requires a condition + Option/Iterator creation
458 /// inside the closure.
462 /// let vec = vec![1];
463 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
467 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
470 declare_clippy_lint! {
471 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
473 /// **Why is this bad?** Readability, this can be written more concisely as a
474 /// single method call.
476 /// **Known problems:** None
480 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
482 /// Can be written as
485 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
489 "using combination of `filter_map` and `next` which can usually be written as a single method call"
492 declare_clippy_lint! {
493 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
495 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
497 /// **Known problems:** None
501 /// # let iter = vec![vec![0]].into_iter();
502 /// iter.flat_map(|x| x);
504 /// Can be written as
506 /// # let iter = vec![vec![0]].into_iter();
509 pub FLAT_MAP_IDENTITY,
511 "call to `flat_map` where `flatten` is sufficient"
514 declare_clippy_lint! {
515 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
517 /// **Why is this bad?** Readability, this can be written more concisely as a
518 /// single method call.
520 /// **Known problems:** Often requires a condition + Option/Iterator creation
521 /// inside the closure.
525 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
527 /// Can be written as
529 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
533 "using a combination of `find` and `map` can usually be written as a single method call"
536 declare_clippy_lint! {
537 /// **What it does:** Checks for an iterator search (such as `find()`,
538 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
540 /// **Why is this bad?** Readability, this can be written more concisely as
543 /// **Known problems:** None.
547 /// # let vec = vec![1];
548 /// vec.iter().find(|x| **x == 0).is_some();
550 /// Could be written as
552 /// # let vec = vec![1];
553 /// vec.iter().any(|x| *x == 0);
557 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
560 declare_clippy_lint! {
561 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
562 /// if it starts with a given char.
564 /// **Why is this bad?** Readability, this can be written more concisely as
565 /// `_.starts_with(_)`.
567 /// **Known problems:** None.
571 /// let name = "foo";
572 /// if name.chars().next() == Some('_') {};
574 /// Could be written as
576 /// let name = "foo";
577 /// if name.starts_with('_') {};
581 "using `.chars().next()` to check if a string starts with a char"
584 declare_clippy_lint! {
585 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
586 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
587 /// `unwrap_or_default` instead.
589 /// **Why is this bad?** The function will always be called and potentially
590 /// allocate an object acting as the default.
592 /// **Known problems:** If the function has side-effects, not calling it will
593 /// change the semantic of the program, but you shouldn't rely on that anyway.
597 /// # let foo = Some(String::new());
598 /// foo.unwrap_or(String::new());
600 /// this can instead be written:
602 /// # let foo = Some(String::new());
603 /// foo.unwrap_or_else(String::new);
607 /// # let foo = Some(String::new());
608 /// foo.unwrap_or_default();
612 "using any `*or` method with a function call, which suggests `*or_else`"
615 declare_clippy_lint! {
616 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
617 /// etc., and suggests to use `unwrap_or_else` instead
619 /// **Why is this bad?** The function will always be called.
621 /// **Known problems:** If the function has side-effects, not calling it will
622 /// change the semantics of the program, but you shouldn't rely on that anyway.
626 /// # let foo = Some(String::new());
627 /// # let err_code = "418";
628 /// # let err_msg = "I'm a teapot";
629 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
633 /// # let foo = Some(String::new());
634 /// # let err_code = "418";
635 /// # let err_msg = "I'm a teapot";
636 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
638 /// this can instead be written:
640 /// # let foo = Some(String::new());
641 /// # let err_code = "418";
642 /// # let err_msg = "I'm a teapot";
643 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
647 "using any `expect` method with a function call"
650 declare_clippy_lint! {
651 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
653 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
654 /// generics, not for using the `clone` method on a concrete type.
656 /// **Known problems:** None.
664 "using `clone` on a `Copy` type"
667 declare_clippy_lint! {
668 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
669 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
670 /// function syntax instead (e.g., `Rc::clone(foo)`).
672 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
673 /// can obscure the fact that only the pointer is being cloned, not the underlying
678 /// # use std::rc::Rc;
679 /// let x = Rc::new(1);
682 pub CLONE_ON_REF_PTR,
684 "using 'clone' on a ref-counted pointer"
687 declare_clippy_lint! {
688 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
690 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
691 /// cloning the underlying `T`.
693 /// **Known problems:** None.
700 /// let z = y.clone();
701 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
704 pub CLONE_DOUBLE_REF,
706 "using `clone` on `&&T`"
709 declare_clippy_lint! {
710 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
711 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
713 /// **Why is this bad?** This bypasses the specialized implementation of
714 /// `ToString` and instead goes through the more expensive string formatting
717 /// **Known problems:** None.
721 /// // Generic implementation for `T: Display` is used (slow)
722 /// ["foo", "bar"].iter().map(|s| s.to_string());
724 /// // OK, the specialized impl is used
725 /// ["foo", "bar"].iter().map(|&s| s.to_string());
727 pub INEFFICIENT_TO_STRING,
729 "using `to_string` on `&&T` where `T: ToString`"
732 declare_clippy_lint! {
733 /// **What it does:** Checks for `new` not returning a type that contains `Self`.
735 /// **Why is this bad?** As a convention, `new` methods are used to make a new
736 /// instance of a type.
738 /// **Known problems:** None.
743 /// # struct NotAFoo;
745 /// fn new() -> NotAFoo {
753 /// # struct FooError;
755 /// // Good. Return type contains `Self`
756 /// fn new() -> Result<Foo, FooError> {
766 /// // Bad. The type name must contain `Self`.
767 /// fn new() -> Bar {
774 "not returning type containing `Self` in a `new` method"
777 declare_clippy_lint! {
778 /// **What it does:** Checks for string methods that receive a single-character
779 /// `str` as an argument, e.g., `_.split("x")`.
781 /// **Why is this bad?** Performing these methods using a `char` is faster than
784 /// **Known problems:** Does not catch multi-byte unicode characters.
787 /// `_.split("x")` could be `_.split('x')`
788 pub SINGLE_CHAR_PATTERN,
790 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
793 declare_clippy_lint! {
794 /// **What it does:** Checks for getting the inner pointer of a temporary
797 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
798 /// as the `CString` is alive.
800 /// **Known problems:** None.
804 /// # use std::ffi::CString;
805 /// # fn call_some_ffi_func(_: *const i8) {}
807 /// let c_str = CString::new("foo").unwrap().as_ptr();
809 /// call_some_ffi_func(c_str);
812 /// Here `c_str` point to a freed address. The correct use would be:
814 /// # use std::ffi::CString;
815 /// # fn call_some_ffi_func(_: *const i8) {}
817 /// let c_str = CString::new("foo").unwrap();
819 /// call_some_ffi_func(c_str.as_ptr());
822 pub TEMPORARY_CSTRING_AS_PTR,
824 "getting the inner pointer of a temporary `CString`"
827 declare_clippy_lint! {
828 /// **What it does:** Checks for calling `.step_by(0)` on iterators which panics.
830 /// **Why is this bad?** This very much looks like an oversight. Use `panic!()` instead if you
831 /// actually intend to panic.
833 /// **Known problems:** None.
836 /// ```rust,should_panic
837 /// for x in (0..100).step_by(0) {
841 pub ITERATOR_STEP_BY_ZERO,
843 "using `Iterator::step_by(0)`, which will panic at runtime"
846 declare_clippy_lint! {
847 /// **What it does:** Checks for the use of `iter.nth(0)`.
849 /// **Why is this bad?** `iter.next()` is equivalent to
850 /// `iter.nth(0)`, as they both consume the next element,
851 /// but is more readable.
853 /// **Known problems:** None.
858 /// # use std::collections::HashSet;
860 /// # let mut s = HashSet::new();
862 /// let x = s.iter().nth(0);
865 /// # let mut s = HashSet::new();
867 /// let x = s.iter().next();
871 "replace `iter.nth(0)` with `iter.next()`"
874 declare_clippy_lint! {
875 /// **What it does:** Checks for use of `.iter().nth()` (and the related
876 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
878 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
881 /// **Known problems:** None.
885 /// let some_vec = vec![0, 1, 2, 3];
886 /// let bad_vec = some_vec.iter().nth(3);
887 /// let bad_slice = &some_vec[..].iter().nth(3);
889 /// The correct use would be:
891 /// let some_vec = vec![0, 1, 2, 3];
892 /// let bad_vec = some_vec.get(3);
893 /// let bad_slice = &some_vec[..].get(3);
897 "using `.iter().nth()` on a standard library type with O(1) element access"
900 declare_clippy_lint! {
901 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
903 /// **Why is this bad?** `.nth(x)` is cleaner
905 /// **Known problems:** None.
909 /// let some_vec = vec![0, 1, 2, 3];
910 /// let bad_vec = some_vec.iter().skip(3).next();
911 /// let bad_slice = &some_vec[..].iter().skip(3).next();
913 /// The correct use would be:
915 /// let some_vec = vec![0, 1, 2, 3];
916 /// let bad_vec = some_vec.iter().nth(3);
917 /// let bad_slice = &some_vec[..].iter().nth(3);
921 "using `.skip(x).next()` on an iterator"
924 declare_clippy_lint! {
925 /// **What it does:** Checks for use of `.get().unwrap()` (or
926 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
928 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
931 /// **Known problems:** Not a replacement for error handling: Using either
932 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
933 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
934 /// temporary placeholder for dealing with the `Option` type, then this does
935 /// not mitigate the need for error handling. If there is a chance that `.get()`
936 /// will be `None` in your program, then it is advisable that the `None` case
937 /// is handled in a future refactor instead of using `.unwrap()` or the Index
942 /// let mut some_vec = vec![0, 1, 2, 3];
943 /// let last = some_vec.get(3).unwrap();
944 /// *some_vec.get_mut(0).unwrap() = 1;
946 /// The correct use would be:
948 /// let mut some_vec = vec![0, 1, 2, 3];
949 /// let last = some_vec[3];
954 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
957 declare_clippy_lint! {
958 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
959 /// `&str` or `String`.
961 /// **Why is this bad?** `.push_str(s)` is clearer
963 /// **Known problems:** None.
968 /// let def = String::from("def");
969 /// let mut s = String::new();
970 /// s.extend(abc.chars());
971 /// s.extend(def.chars());
973 /// The correct use would be:
976 /// let def = String::from("def");
977 /// let mut s = String::new();
979 /// s.push_str(&def);
981 pub STRING_EXTEND_CHARS,
983 "using `x.extend(s.chars())` where s is a `&str` or `String`"
986 declare_clippy_lint! {
987 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
990 /// **Why is this bad?** `.to_vec()` is clearer
992 /// **Known problems:** None.
996 /// let s = [1, 2, 3, 4, 5];
997 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
999 /// The better use would be:
1001 /// let s = [1, 2, 3, 4, 5];
1002 /// let s2: Vec<isize> = s.to_vec();
1004 pub ITER_CLONED_COLLECT,
1006 "using `.cloned().collect()` on slice to create a `Vec`"
1009 declare_clippy_lint! {
1010 /// **What it does:** Checks for usage of `.chars().last()` or
1011 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
1013 /// **Why is this bad?** Readability, this can be written more concisely as
1014 /// `_.ends_with(_)`.
1016 /// **Known problems:** None.
1020 /// # let name = "_";
1021 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
1026 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1029 declare_clippy_lint! {
1030 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
1031 /// types before and after the call are the same.
1033 /// **Why is this bad?** The call is unnecessary.
1035 /// **Known problems:** None.
1039 /// # fn do_stuff(x: &[i32]) {}
1040 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1041 /// do_stuff(x.as_ref());
1043 /// The correct use would be:
1045 /// # fn do_stuff(x: &[i32]) {}
1046 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1051 "using `as_ref` where the types before and after the call are the same"
1054 declare_clippy_lint! {
1055 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
1056 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1057 /// `sum` or `product`.
1059 /// **Why is this bad?** Readability.
1061 /// **Known problems:** False positive in pattern guards. Will be resolved once
1062 /// non-lexical lifetimes are stable.
1066 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1068 /// This could be written as:
1070 /// let _ = (0..3).any(|x| x > 2);
1072 pub UNNECESSARY_FOLD,
1074 "using `fold` when a more succinct alternative exists"
1077 declare_clippy_lint! {
1078 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1079 /// More specifically it checks if the closure provided is only performing one of the
1080 /// filter or map operations and suggests the appropriate option.
1082 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
1083 /// operation is being performed.
1085 /// **Known problems:** None
1089 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1091 /// As there is no transformation of the argument this could be written as:
1093 /// let _ = (0..3).filter(|&x| x > 2);
1097 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1099 /// As there is no conditional check on the argument this could be written as:
1101 /// let _ = (0..4).map(|x| x + 1);
1103 pub UNNECESSARY_FILTER_MAP,
1105 "using `filter_map` when a more succinct alternative exists"
1108 declare_clippy_lint! {
1109 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
1112 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
1113 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1114 /// `iter_mut` directly.
1116 /// **Known problems:** None
1121 /// let _ = (&vec![3, 4, 5]).into_iter();
1123 pub INTO_ITER_ON_REF,
1125 "using `.into_iter()` on a reference"
1128 declare_clippy_lint! {
1129 /// **What it does:** Checks for calls to `map` followed by a `count`.
1131 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
1132 /// If the `map` call is intentional, this should be rewritten. Or, if you intend to
1133 /// drive the iterator to completion, you can just use `for_each` instead.
1135 /// **Known problems:** None
1140 /// let _ = (0..3).map(|x| x + 2).count();
1144 "suspicious usage of map"
1147 declare_clippy_lint! {
1148 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1150 /// **Why is this bad?** For most types, this is undefined behavior.
1152 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1153 /// of `MaybeUninit`. There may be other types that allow uninitialized
1154 /// data, but those are not yet rigorously defined.
1159 /// // Beware the UB
1160 /// use std::mem::MaybeUninit;
1162 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1165 /// Note that the following is OK:
1168 /// use std::mem::MaybeUninit;
1170 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1171 /// MaybeUninit::uninit().assume_init()
1174 pub UNINIT_ASSUMED_INIT,
1176 "`MaybeUninit::uninit().assume_init()`"
1179 declare_clippy_lint! {
1180 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1182 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1187 /// # let y: u32 = 0;
1188 /// # let x: u32 = 100;
1189 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1190 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1193 /// can be written using dedicated methods for saturating addition/subtraction as:
1196 /// # let y: u32 = 0;
1197 /// # let x: u32 = 100;
1198 /// let add = x.saturating_add(y);
1199 /// let sub = x.saturating_sub(y);
1201 pub MANUAL_SATURATING_ARITHMETIC,
1203 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1206 declare_clippy_lint! {
1207 /// **What it does:** Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1208 /// zero-sized types
1210 /// **Why is this bad?** This is a no-op, and likely unintended
1212 /// **Known problems:** None
1216 /// unsafe { (&() as *const ()).offset(1) };
1220 "Check for offset calculations on raw pointers to zero-sized types"
1223 declare_clippy_lint! {
1224 /// **What it does:** Checks for `FileType::is_file()`.
1226 /// **Why is this bad?** When people testing a file type with `FileType::is_file`
1227 /// they are testing whether a path is something they can get bytes from. But
1228 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1229 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1235 /// let metadata = std::fs::metadata("foo.txt")?;
1236 /// let filetype = metadata.file_type();
1238 /// if filetype.is_file() {
1241 /// # Ok::<_, std::io::Error>(())
1245 /// should be written as:
1249 /// let metadata = std::fs::metadata("foo.txt")?;
1250 /// let filetype = metadata.file_type();
1252 /// if !filetype.is_dir() {
1255 /// # Ok::<_, std::io::Error>(())
1258 pub FILETYPE_IS_FILE,
1260 "`FileType::is_file` is not recommended to test for readable file type"
1263 declare_clippy_lint! {
1264 /// **What it does:** Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1266 /// **Why is this bad?** Readability, this can be written more concisely as a
1267 /// single method call.
1269 /// **Known problems:** None.
1273 /// # let opt = Some("".to_string());
1274 /// opt.as_ref().map(String::as_str)
1277 /// Can be written as
1279 /// # let opt = Some("".to_string());
1283 pub OPTION_AS_REF_DEREF,
1285 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1288 declare_lint_pass!(Methods => [
1293 SHOULD_IMPLEMENT_TRAIT,
1294 WRONG_SELF_CONVENTION,
1295 WRONG_PUB_SELF_CONVENTION,
1297 OPTION_MAP_UNWRAP_OR,
1298 OPTION_MAP_UNWRAP_OR_ELSE,
1299 RESULT_MAP_UNWRAP_OR_ELSE,
1300 RESULT_MAP_OR_INTO_OPTION,
1302 OPTION_AND_THEN_SOME,
1310 INEFFICIENT_TO_STRING,
1312 SINGLE_CHAR_PATTERN,
1314 TEMPORARY_CSTRING_AS_PTR,
1322 ITERATOR_STEP_BY_ZERO,
1327 STRING_EXTEND_CHARS,
1328 ITER_CLONED_COLLECT,
1331 UNNECESSARY_FILTER_MAP,
1334 UNINIT_ASSUMED_INIT,
1335 MANUAL_SATURATING_ARITHMETIC,
1338 OPTION_AS_REF_DEREF,
1341 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Methods {
1342 #[allow(clippy::too_many_lines)]
1343 fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'_>) {
1344 if in_macro(expr.span) {
1348 let (method_names, arg_lists, method_spans) = method_calls(expr, 2);
1349 let method_names: Vec<SymbolStr> = method_names.iter().map(|s| s.as_str()).collect();
1350 let method_names: Vec<&str> = method_names.iter().map(|s| &**s).collect();
1352 match method_names.as_slice() {
1353 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1354 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1355 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1356 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1357 ["expect", ..] => lint_expect(cx, expr, arg_lists[0]),
1358 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0], method_spans[1]),
1359 ["unwrap_or_else", "map"] => lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]),
1360 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1361 ["and_then", ..] => lint_option_and_then_some(cx, expr, arg_lists[0]),
1362 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1363 ["next", "skip_while"] => lint_skip_while_next(cx, expr, arg_lists[1]),
1364 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1365 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1366 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1367 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1368 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1369 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1370 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0], method_spans[0]),
1371 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1372 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0], method_spans[1]),
1373 ["is_some", "position"] => {
1374 lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0], method_spans[1])
1376 ["is_some", "rposition"] => {
1377 lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
1379 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1380 ["as_ptr", "unwrap"] | ["as_ptr", "expect"] => {
1381 lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0])
1383 ["nth", "iter"] => lint_iter_nth(cx, expr, &arg_lists, false),
1384 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, &arg_lists, true),
1385 ["nth", ..] => lint_iter_nth_zero(cx, expr, arg_lists[0]),
1386 ["step_by", ..] => lint_step_by(cx, expr, arg_lists[0]),
1387 ["next", "skip"] => lint_iter_skip_next(cx, expr),
1388 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1389 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1390 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1391 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0], method_spans[0]),
1392 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1393 ["count", "map"] => lint_suspicious_map(cx, expr),
1394 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1395 ["unwrap_or", arith @ "checked_add"]
1396 | ["unwrap_or", arith @ "checked_sub"]
1397 | ["unwrap_or", arith @ "checked_mul"] => {
1398 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1400 ["add"] | ["offset"] | ["sub"] | ["wrapping_offset"] | ["wrapping_add"] | ["wrapping_sub"] => {
1401 check_pointer_offset(cx, expr, arg_lists[0])
1403 ["is_file", ..] => lint_filetype_is_file(cx, expr, arg_lists[0]),
1404 ["map", "as_ref"] => lint_option_as_ref_deref(cx, expr, arg_lists[1], arg_lists[0], false),
1405 ["map", "as_mut"] => lint_option_as_ref_deref(cx, expr, arg_lists[1], arg_lists[0], true),
1410 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args) => {
1411 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1412 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1414 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
1415 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1416 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1417 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1419 if args.len() == 1 && method_call.ident.name == sym!(to_string) {
1420 inefficient_to_string::lint(cx, expr, &args[0], self_ty);
1423 match self_ty.kind {
1424 ty::Ref(_, ty, _) if ty.kind == ty::Str => {
1425 for &(method, pos) in &PATTERN_METHODS {
1426 if method_call.ident.name.as_str() == method && args.len() > pos {
1427 lint_single_char_pattern(cx, expr, &args[pos]);
1431 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1432 lint_into_iter(cx, expr, self_ty, *method_span);
1437 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1438 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1440 let mut info = BinaryExprInfo {
1444 eq: op.node == hir::BinOpKind::Eq,
1446 lint_binary_expr_with_method_call(cx, &mut info);
1452 fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1453 if in_external_macro(cx.sess(), impl_item.span) {
1456 let name = impl_item.ident.name.as_str();
1457 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1458 let item = cx.tcx.hir().expect_item(parent);
1459 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1460 let self_ty = cx.tcx.type_of(def_id);
1462 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1463 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1464 if let hir::ItemKind::Impl{ of_trait: None, .. } = item.kind;
1466 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1467 let method_sig = cx.tcx.fn_sig(method_def_id);
1468 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1470 let first_arg_ty = &method_sig.inputs().iter().next();
1472 // check conventions w.r.t. conversion method names and predicates
1473 if let Some(first_arg_ty) = first_arg_ty;
1476 if cx.access_levels.is_exported(impl_item.hir_id) {
1477 // check missing trait implementations
1478 for &(method_name, n_args, fn_header, self_kind, out_type, trait_name) in &TRAIT_METHODS {
1479 if name == method_name &&
1480 sig.decl.inputs.len() == n_args &&
1481 out_type.matches(cx, &sig.decl.output) &&
1482 self_kind.matches(cx, self_ty, first_arg_ty) &&
1483 fn_header_equals(*fn_header, sig.header) {
1484 span_lint(cx, SHOULD_IMPLEMENT_TRAIT, impl_item.span, &format!(
1485 "defining a method called `{}` on this type; consider implementing \
1486 the `{}` trait or choosing a less ambiguous name", name, trait_name));
1491 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1493 .find(|(ref conv, _)| conv.check(&name))
1495 if !self_kinds.iter().any(|k| k.matches(cx, self_ty, first_arg_ty)) {
1496 let lint = if item.vis.node.is_pub() {
1497 WRONG_PUB_SELF_CONVENTION
1499 WRONG_SELF_CONVENTION
1507 "methods called `{}` usually take {}; consider choosing a less \
1512 .map(|k| k.description())
1513 .collect::<Vec<_>>()
1522 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
1523 let ret_ty = return_ty(cx, impl_item.hir_id);
1525 let contains_self_ty = |ty: Ty<'tcx>| {
1526 ty.walk().any(|inner| match inner.unpack() {
1527 GenericArgKind::Type(inner_ty) => same_tys(cx, self_ty, inner_ty),
1529 GenericArgKind::Lifetime(_) | GenericArgKind::Const(_) => false,
1533 // walk the return type and check for Self (this does not check associated types)
1534 if contains_self_ty(ret_ty) {
1538 // if return type is impl trait, check the associated types
1539 if let ty::Opaque(def_id, _) = ret_ty.kind {
1540 // one of the associated types must be Self
1541 for predicate in cx.tcx.predicates_of(def_id).predicates {
1543 (Predicate::Projection(poly_projection_predicate), _) => {
1544 let binder = poly_projection_predicate.ty();
1545 let associated_type = binder.skip_binder();
1547 // walk the associated type and check for Self
1548 if contains_self_ty(associated_type) {
1557 if name == "new" && !same_tys(cx, ret_ty, self_ty) {
1562 "methods called `new` usually return `Self`",
1569 /// Checks for the `OR_FUN_CALL` lint.
1570 #[allow(clippy::too_many_lines)]
1571 fn lint_or_fun_call<'a, 'tcx>(
1572 cx: &LateContext<'a, 'tcx>,
1573 expr: &hir::Expr<'_>,
1576 args: &'tcx [hir::Expr<'_>],
1578 // Searches an expression for method calls or function calls that aren't ctors
1579 struct FunCallFinder<'a, 'tcx> {
1580 cx: &'a LateContext<'a, 'tcx>,
1584 impl<'a, 'tcx> intravisit::Visitor<'tcx> for FunCallFinder<'a, 'tcx> {
1585 type Map = Map<'tcx>;
1587 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
1588 let call_found = match &expr.kind {
1589 // ignore enum and struct constructors
1590 hir::ExprKind::Call(..) => !is_ctor_or_promotable_const_function(self.cx, expr),
1591 hir::ExprKind::MethodCall(..) => true,
1600 intravisit::walk_expr(self, expr);
1604 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
1605 intravisit::NestedVisitorMap::None
1609 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1610 fn check_unwrap_or_default(
1611 cx: &LateContext<'_, '_>,
1613 fun: &hir::Expr<'_>,
1614 self_expr: &hir::Expr<'_>,
1615 arg: &hir::Expr<'_>,
1621 if name == "unwrap_or";
1622 if let hir::ExprKind::Path(ref qpath) = fun.kind;
1623 let path = &*last_path_segment(qpath).ident.as_str();
1624 if ["default", "new"].contains(&path);
1625 let arg_ty = cx.tables.expr_ty(arg);
1626 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1627 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1630 let mut applicability = Applicability::MachineApplicable;
1635 &format!("use of `{}` followed by a call to `{}`", name, path),
1638 "{}.unwrap_or_default()",
1639 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1651 /// Checks for `*or(foo())`.
1652 #[allow(clippy::too_many_arguments)]
1653 fn check_general_case<'a, 'tcx>(
1654 cx: &LateContext<'a, 'tcx>,
1658 self_expr: &hir::Expr<'_>,
1659 arg: &'tcx hir::Expr<'_>,
1663 // (path, fn_has_argument, methods, suffix)
1664 let know_types: &[(&[_], _, &[_], _)] = &[
1665 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1666 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1667 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1668 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1672 if know_types.iter().any(|k| k.2.contains(&name));
1674 let mut finder = FunCallFinder { cx: &cx, found: false };
1675 if { finder.visit_expr(&arg); finder.found };
1676 if !contains_return(&arg);
1678 let self_ty = cx.tables.expr_ty(self_expr);
1680 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1681 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1683 if poss.contains(&name);
1686 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1687 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1688 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1689 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1691 let span_replace_word = method_span.with_hi(span.hi());
1696 &format!("use of `{}` followed by a function call", name),
1698 format!("{}_{}({})", name, suffix, sugg),
1699 Applicability::HasPlaceholders,
1705 if args.len() == 2 {
1706 match args[1].kind {
1707 hir::ExprKind::Call(ref fun, ref or_args) => {
1708 let or_has_args = !or_args.is_empty();
1709 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1722 hir::ExprKind::MethodCall(_, span, ref or_args) => check_general_case(
1729 !or_args.is_empty(),
1737 /// Checks for the `EXPECT_FUN_CALL` lint.
1738 #[allow(clippy::too_many_lines)]
1739 fn lint_expect_fun_call(
1740 cx: &LateContext<'_, '_>,
1741 expr: &hir::Expr<'_>,
1744 args: &[hir::Expr<'_>],
1746 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1748 fn get_arg_root<'a>(cx: &LateContext<'_, '_>, arg: &'a hir::Expr<'a>) -> &'a hir::Expr<'a> {
1749 let mut arg_root = arg;
1751 arg_root = match &arg_root.kind {
1752 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr) => expr,
1753 hir::ExprKind::MethodCall(method_name, _, call_args) => {
1754 if call_args.len() == 1
1755 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1757 let arg_type = cx.tables.expr_ty(&call_args[0]);
1758 let base_type = walk_ptrs_ty(arg_type);
1759 base_type.kind == ty::Str || is_type_diagnostic_item(cx, base_type, sym!(string_type))
1773 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1774 // converted to string.
1775 fn requires_to_string(cx: &LateContext<'_, '_>, arg: &hir::Expr<'_>) -> bool {
1776 let arg_ty = cx.tables.expr_ty(arg);
1777 if is_type_diagnostic_item(cx, arg_ty, sym!(string_type)) {
1780 if let ty::Ref(_, ty, ..) = arg_ty.kind {
1781 if ty.kind == ty::Str && can_be_static_str(cx, arg) {
1788 // Check if an expression could have type `&'static str`, knowing that it
1789 // has type `&str` for some lifetime.
1790 fn can_be_static_str(cx: &LateContext<'_, '_>, arg: &hir::Expr<'_>) -> bool {
1792 hir::ExprKind::Lit(_) => true,
1793 hir::ExprKind::Call(fun, _) => {
1794 if let hir::ExprKind::Path(ref p) = fun.kind {
1795 match cx.tables.qpath_res(p, fun.hir_id) {
1796 hir::def::Res::Def(hir::def::DefKind::Fn, def_id)
1797 | hir::def::Res::Def(hir::def::DefKind::AssocFn, def_id) => matches!(
1798 cx.tcx.fn_sig(def_id).output().skip_binder().kind,
1799 ty::Ref(ty::ReStatic, ..)
1807 hir::ExprKind::MethodCall(..) => cx.tables.type_dependent_def_id(arg.hir_id).map_or(false, |method_id| {
1809 cx.tcx.fn_sig(method_id).output().skip_binder().kind,
1810 ty::Ref(ty::ReStatic, ..)
1813 hir::ExprKind::Path(ref p) => match cx.tables.qpath_res(p, arg.hir_id) {
1814 hir::def::Res::Def(hir::def::DefKind::Const | hir::def::DefKind::Static, _) => true,
1821 fn generate_format_arg_snippet(
1822 cx: &LateContext<'_, '_>,
1824 applicability: &mut Applicability,
1827 if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref format_arg) = a.kind;
1828 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.kind;
1829 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.kind;
1834 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1842 fn is_call(node: &hir::ExprKind<'_>) -> bool {
1844 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr) => {
1847 hir::ExprKind::Call(..)
1848 | hir::ExprKind::MethodCall(..)
1849 // These variants are debatable or require further examination
1850 | hir::ExprKind::Match(..)
1851 | hir::ExprKind::Block{ .. } => true,
1856 if args.len() != 2 || name != "expect" || !is_call(&args[1].kind) {
1860 let receiver_type = cx.tables.expr_ty_adjusted(&args[0]);
1861 let closure_args = if is_type_diagnostic_item(cx, receiver_type, sym!(option_type)) {
1863 } else if is_type_diagnostic_item(cx, receiver_type, sym!(result_type)) {
1869 let arg_root = get_arg_root(cx, &args[1]);
1871 let span_replace_word = method_span.with_hi(expr.span.hi());
1873 let mut applicability = Applicability::MachineApplicable;
1875 //Special handling for `format!` as arg_root
1877 if let hir::ExprKind::Block(block, None) = &arg_root.kind;
1878 if block.stmts.len() == 1;
1879 if let hir::StmtKind::Local(local) = &block.stmts[0].kind;
1880 if let Some(arg_root) = &local.init;
1881 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.kind;
1882 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1;
1883 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].kind;
1885 let fmt_spec = &format_args[0];
1886 let fmt_args = &format_args[1];
1888 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
1890 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
1892 let sugg = args.join(", ");
1898 &format!("use of `{}` followed by a function call", name),
1900 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
1908 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
1909 if requires_to_string(cx, arg_root) {
1910 arg_root_snippet.to_mut().push_str(".to_string()");
1917 &format!("use of `{}` followed by a function call", name),
1919 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
1924 /// Checks for the `CLONE_ON_COPY` lint.
1925 fn lint_clone_on_copy(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, arg: &hir::Expr<'_>, arg_ty: Ty<'_>) {
1926 let ty = cx.tables.expr_ty(expr);
1927 if let ty::Ref(_, inner, _) = arg_ty.kind {
1928 if let ty::Ref(_, innermost, _) = inner.kind {
1933 "using `clone` on a double-reference; \
1934 this will copy the reference instead of cloning the inner type",
1936 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
1937 let mut ty = innermost;
1939 while let ty::Ref(_, inner, _) = ty.kind {
1943 let refs: String = iter::repeat('&').take(n + 1).collect();
1944 let derefs: String = iter::repeat('*').take(n).collect();
1945 let explicit = format!("<{}{}>::clone({})", refs, ty, snip);
1946 diag.span_suggestion(
1948 "try dereferencing it",
1949 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
1950 Applicability::MaybeIncorrect,
1952 diag.span_suggestion(
1954 "or try being explicit if you are sure, that you want to clone a reference",
1956 Applicability::MaybeIncorrect,
1961 return; // don't report clone_on_copy
1965 if is_copy(cx, ty) {
1967 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1968 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
1969 match &cx.tcx.hir().get(parent) {
1970 hir::Node::Expr(parent) => match parent.kind {
1971 // &*x is a nop, &x.clone() is not
1972 hir::ExprKind::AddrOf(..) => return,
1973 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1974 hir::ExprKind::MethodCall(_, _, parent_args) if expr.hir_id == parent_args[0].hir_id => return,
1978 hir::Node::Stmt(stmt) => {
1979 if let hir::StmtKind::Local(ref loc) = stmt.kind {
1980 if let hir::PatKind::Ref(..) = loc.pat.kind {
1981 // let ref y = *x borrows x, let ref y = x.clone() does not
1989 // x.clone() might have dereferenced x, possibly through Deref impls
1990 if cx.tables.expr_ty(arg) == ty {
1991 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1993 let deref_count = cx
1995 .expr_adjustments(arg)
1998 if let ty::adjustment::Adjust::Deref(_) = adj.kind {
2005 let derefs: String = iter::repeat('*').take(deref_count).collect();
2006 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
2011 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |diag| {
2012 if let Some((text, snip)) = snip {
2013 diag.span_suggestion(expr.span, text, snip, Applicability::Unspecified);
2019 fn lint_clone_on_ref_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, arg: &hir::Expr<'_>) {
2020 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(arg));
2022 if let ty::Adt(_, subst) = obj_ty.kind {
2023 let caller_type = if is_type_diagnostic_item(cx, obj_ty, sym::Rc) {
2025 } else if is_type_diagnostic_item(cx, obj_ty, sym::Arc) {
2027 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
2037 "using `.clone()` on a ref-counted pointer",
2040 "{}::<{}>::clone(&{})",
2043 snippet(cx, arg.span, "_")
2045 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
2050 fn lint_string_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
2052 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
2053 let target = &arglists[0][0];
2054 let self_ty = walk_ptrs_ty(cx.tables.expr_ty(target));
2055 let ref_str = if self_ty.kind == ty::Str {
2057 } else if is_type_diagnostic_item(cx, self_ty, sym!(string_type)) {
2063 let mut applicability = Applicability::MachineApplicable;
2066 STRING_EXTEND_CHARS,
2068 "calling `.extend(_.chars())`",
2071 "{}.push_str({}{})",
2072 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
2074 snippet_with_applicability(cx, target.span, "_", &mut applicability)
2081 fn lint_extend(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
2082 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&args[0]));
2083 if is_type_diagnostic_item(cx, obj_ty, sym!(string_type)) {
2084 lint_string_extend(cx, expr, args);
2088 fn lint_cstring_as_ptr(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, source: &hir::Expr<'_>, unwrap: &hir::Expr<'_>) {
2090 let source_type = cx.tables.expr_ty(source);
2091 if let ty::Adt(def, substs) = source_type.kind;
2092 if cx.tcx.is_diagnostic_item(sym!(result_type), def.did);
2093 if match_type(cx, substs.type_at(0), &paths::CSTRING);
2097 TEMPORARY_CSTRING_AS_PTR,
2099 "you are getting the inner pointer of a temporary `CString`",
2101 diag.note("that pointer will be invalid outside this expression");
2102 diag.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
2108 fn lint_iter_cloned_collect<'a, 'tcx>(
2109 cx: &LateContext<'a, 'tcx>,
2110 expr: &hir::Expr<'_>,
2111 iter_args: &'tcx [hir::Expr<'_>],
2114 if is_type_diagnostic_item(cx, cx.tables.expr_ty(expr), sym!(vec_type));
2115 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0]));
2116 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite());
2121 ITER_CLONED_COLLECT,
2123 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
2126 ".to_vec()".to_string(),
2127 Applicability::MachineApplicable,
2133 fn lint_unnecessary_fold(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, fold_args: &[hir::Expr<'_>], fold_span: Span) {
2134 fn check_fold_with_op(
2135 cx: &LateContext<'_, '_>,
2136 expr: &hir::Expr<'_>,
2137 fold_args: &[hir::Expr<'_>],
2140 replacement_method_name: &str,
2141 replacement_has_args: bool,
2144 // Extract the body of the closure passed to fold
2145 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
2146 let closure_body = cx.tcx.hir().body(body_id);
2147 let closure_expr = remove_blocks(&closure_body.value);
2149 // Check if the closure body is of the form `acc <op> some_expr(x)`
2150 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
2151 if bin_op.node == op;
2153 // Extract the names of the two arguments to the closure
2154 if let Some(first_arg_ident) = get_arg_name(&closure_body.params[0].pat);
2155 if let Some(second_arg_ident) = get_arg_name(&closure_body.params[1].pat);
2157 if match_var(&*left_expr, first_arg_ident);
2158 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
2161 let mut applicability = Applicability::MachineApplicable;
2162 let sugg = if replacement_has_args {
2164 "{replacement}(|{s}| {r})",
2165 replacement = replacement_method_name,
2166 s = second_arg_ident,
2167 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
2172 replacement = replacement_method_name,
2179 fold_span.with_hi(expr.span.hi()),
2180 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
2181 "this `.fold` can be written more succinctly using another method",
2190 // Check that this is a call to Iterator::fold rather than just some function called fold
2191 if !match_trait_method(cx, expr, &paths::ITERATOR) {
2196 fold_args.len() == 3,
2197 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
2200 // Check if the first argument to .fold is a suitable literal
2201 if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
2203 ast::LitKind::Bool(false) => {
2204 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
2206 ast::LitKind::Bool(true) => {
2207 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
2209 ast::LitKind::Int(0, _) => {
2210 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
2212 ast::LitKind::Int(1, _) => {
2213 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
2220 fn lint_step_by<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr<'_>, args: &'tcx [hir::Expr<'_>]) {
2221 if match_trait_method(cx, expr, &paths::ITERATOR) {
2222 if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &args[1]) {
2225 ITERATOR_STEP_BY_ZERO,
2227 "Iterator::step_by(0) will panic at runtime",
2233 fn lint_iter_nth<'a, 'tcx>(
2234 cx: &LateContext<'a, 'tcx>,
2235 expr: &hir::Expr<'_>,
2236 nth_and_iter_args: &[&'tcx [hir::Expr<'tcx>]],
2239 let iter_args = nth_and_iter_args[1];
2240 let mut_str = if is_mut { "_mut" } else { "" };
2241 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
2243 } else if is_type_diagnostic_item(cx, cx.tables.expr_ty(&iter_args[0]), sym!(vec_type)) {
2245 } else if is_type_diagnostic_item(cx, cx.tables.expr_ty(&iter_args[0]), sym!(vecdeque_type)) {
2248 let nth_args = nth_and_iter_args[0];
2249 lint_iter_nth_zero(cx, expr, &nth_args);
2250 return; // caller is not a type that we want to lint
2257 &format!("called `.iter{0}().nth()` on a {1}", mut_str, caller_type),
2259 &format!("calling `.get{}()` is both faster and more readable", mut_str),
2263 fn lint_iter_nth_zero<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &hir::Expr<'_>, nth_args: &'tcx [hir::Expr<'_>]) {
2265 if match_trait_method(cx, expr, &paths::ITERATOR);
2266 if let Some((Constant::Int(0), _)) = constant(cx, cx.tables, &nth_args[1]);
2268 let mut applicability = Applicability::MachineApplicable;
2273 "called `.nth(0)` on a `std::iter::Iterator`",
2275 format!("{}.next()", snippet_with_applicability(cx, nth_args[0].span, "..", &mut applicability)),
2282 fn lint_get_unwrap<'a, 'tcx>(
2283 cx: &LateContext<'a, 'tcx>,
2284 expr: &hir::Expr<'_>,
2285 get_args: &'tcx [hir::Expr<'_>],
2288 // Note: we don't want to lint `get_mut().unwrap` for `HashMap` or `BTreeMap`,
2289 // because they do not implement `IndexMut`
2290 let mut applicability = Applicability::MachineApplicable;
2291 let expr_ty = cx.tables.expr_ty(&get_args[0]);
2292 let get_args_str = if get_args.len() > 1 {
2293 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
2295 return; // not linting on a .get().unwrap() chain or variant
2298 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
2299 needs_ref = get_args_str.parse::<usize>().is_ok();
2301 } else if is_type_diagnostic_item(cx, expr_ty, sym!(vec_type)) {
2302 needs_ref = get_args_str.parse::<usize>().is_ok();
2304 } else if is_type_diagnostic_item(cx, expr_ty, sym!(vecdeque_type)) {
2305 needs_ref = get_args_str.parse::<usize>().is_ok();
2307 } else if !is_mut && is_type_diagnostic_item(cx, expr_ty, sym!(hashmap_type)) {
2310 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
2314 return; // caller is not a type that we want to lint
2317 let mut span = expr.span;
2319 // Handle the case where the result is immediately dereferenced
2320 // by not requiring ref and pulling the dereference into the
2324 if let Some(parent) = get_parent_expr(cx, expr);
2325 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.kind;
2332 let mut_str = if is_mut { "_mut" } else { "" };
2333 let borrow_str = if !needs_ref {
2346 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
2347 mut_str, caller_type
2353 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
2360 fn lint_iter_skip_next(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>) {
2361 // lint if caller of skip is an Iterator
2362 if match_trait_method(cx, expr, &paths::ITERATOR) {
2367 "called `skip(x).next()` on an iterator",
2369 "this is more succinctly expressed by calling `nth(x)`",
2374 fn derefs_to_slice<'a, 'tcx>(
2375 cx: &LateContext<'a, 'tcx>,
2376 expr: &'tcx hir::Expr<'tcx>,
2378 ) -> Option<&'tcx hir::Expr<'tcx>> {
2379 fn may_slice<'a>(cx: &LateContext<'_, 'a>, ty: Ty<'a>) -> bool {
2381 ty::Slice(_) => true,
2382 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
2383 ty::Adt(..) => is_type_diagnostic_item(cx, ty, sym!(vec_type)),
2384 ty::Array(_, size) => {
2385 if let Some(size) = size.try_eval_usize(cx.tcx, cx.param_env) {
2391 ty::Ref(_, inner, _) => may_slice(cx, inner),
2396 if let hir::ExprKind::MethodCall(ref path, _, ref args) = expr.kind {
2397 if path.ident.name == sym!(iter) && may_slice(cx, cx.tables.expr_ty(&args[0])) {
2404 ty::Slice(_) => Some(expr),
2405 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
2406 ty::Ref(_, inner, _) => {
2407 if may_slice(cx, inner) {
2418 /// lint use of `unwrap()` for `Option`s and `Result`s
2419 fn lint_unwrap(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, unwrap_args: &[hir::Expr<'_>]) {
2420 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&unwrap_args[0]));
2422 let mess = if is_type_diagnostic_item(cx, obj_ty, sym!(option_type)) {
2423 Some((OPTION_UNWRAP_USED, "an Option", "None"))
2424 } else if is_type_diagnostic_item(cx, obj_ty, sym!(result_type)) {
2425 Some((RESULT_UNWRAP_USED, "a Result", "Err"))
2430 if let Some((lint, kind, none_value)) = mess {
2435 &format!("used `unwrap()` on `{}` value", kind,),
2438 "if you don't want to handle the `{}` case gracefully, consider \
2439 using `expect()` to provide a better panic message",
2446 /// lint use of `expect()` for `Option`s and `Result`s
2447 fn lint_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, expect_args: &[hir::Expr<'_>]) {
2448 let obj_ty = walk_ptrs_ty(cx.tables.expr_ty(&expect_args[0]));
2450 let mess = if is_type_diagnostic_item(cx, obj_ty, sym!(option_type)) {
2451 Some((OPTION_EXPECT_USED, "an Option", "None"))
2452 } else if is_type_diagnostic_item(cx, obj_ty, sym!(result_type)) {
2453 Some((RESULT_EXPECT_USED, "a Result", "Err"))
2458 if let Some((lint, kind, none_value)) = mess {
2463 &format!("used `expect()` on `{}` value", kind,),
2465 &format!("if this value is an `{}`, it will panic", none_value,),
2470 /// lint use of `ok().expect()` for `Result`s
2471 fn lint_ok_expect(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, ok_args: &[hir::Expr<'_>]) {
2473 // lint if the caller of `ok()` is a `Result`
2474 if is_type_diagnostic_item(cx, cx.tables.expr_ty(&ok_args[0]), sym!(result_type));
2475 let result_type = cx.tables.expr_ty(&ok_args[0]);
2476 if let Some(error_type) = get_error_type(cx, result_type);
2477 if has_debug_impl(error_type, cx);
2484 "called `ok().expect()` on a `Result` value",
2486 "you can call `expect()` directly on the `Result`",
2492 /// lint use of `map().flatten()` for `Iterators` and 'Options'
2493 fn lint_map_flatten<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr<'_>, map_args: &'tcx [hir::Expr<'_>]) {
2494 // lint if caller of `.map().flatten()` is an Iterator
2495 if match_trait_method(cx, expr, &paths::ITERATOR) {
2496 let msg = "called `map(..).flatten()` on an `Iterator`. \
2497 This is more succinctly expressed by calling `.flat_map(..)`";
2498 let self_snippet = snippet(cx, map_args[0].span, "..");
2499 let func_snippet = snippet(cx, map_args[1].span, "..");
2500 let hint = format!("{0}.flat_map({1})", self_snippet, func_snippet);
2506 "try using `flat_map` instead",
2508 Applicability::MachineApplicable,
2512 // lint if caller of `.map().flatten()` is an Option
2513 if is_type_diagnostic_item(cx, cx.tables.expr_ty(&map_args[0]), sym!(option_type)) {
2514 let msg = "called `map(..).flatten()` on an `Option`. \
2515 This is more succinctly expressed by calling `.and_then(..)`";
2516 let self_snippet = snippet(cx, map_args[0].span, "..");
2517 let func_snippet = snippet(cx, map_args[1].span, "..");
2518 let hint = format!("{0}.and_then({1})", self_snippet, func_snippet);
2524 "try using `and_then` instead",
2526 Applicability::MachineApplicable,
2531 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2532 fn lint_map_unwrap_or_else<'a, 'tcx>(
2533 cx: &LateContext<'a, 'tcx>,
2534 expr: &'tcx hir::Expr<'_>,
2535 map_args: &'tcx [hir::Expr<'_>],
2536 unwrap_args: &'tcx [hir::Expr<'_>],
2538 // lint if the caller of `map()` is an `Option`
2539 let is_option = is_type_diagnostic_item(cx, cx.tables.expr_ty(&map_args[0]), sym!(option_type));
2540 let is_result = is_type_diagnostic_item(cx, cx.tables.expr_ty(&map_args[0]), sym!(result_type));
2542 if is_option || is_result {
2543 // Don't make a suggestion that may fail to compile due to mutably borrowing
2544 // the same variable twice.
2545 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2546 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2547 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2548 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2556 let msg = if is_option {
2557 "called `map(f).unwrap_or_else(g)` on an `Option` value. This can be done more directly by calling \
2558 `map_or_else(g, f)` instead"
2560 "called `map(f).unwrap_or_else(g)` on a `Result` value. This can be done more directly by calling \
2561 `.map_or_else(g, f)` instead"
2563 // get snippets for args to map() and unwrap_or_else()
2564 let map_snippet = snippet(cx, map_args[1].span, "..");
2565 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2566 // lint, with note if neither arg is > 1 line and both map() and
2567 // unwrap_or_else() have the same span
2568 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2569 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2570 if same_span && !multiline {
2574 OPTION_MAP_UNWRAP_OR_ELSE
2576 RESULT_MAP_UNWRAP_OR_ELSE
2582 "replace `map({0}).unwrap_or_else({1})` with `map_or_else({1}, {0})`",
2583 map_snippet, unwrap_snippet,
2586 } else if same_span && multiline {
2590 OPTION_MAP_UNWRAP_OR_ELSE
2592 RESULT_MAP_UNWRAP_OR_ELSE
2601 /// lint use of `_.map_or(None, _)` for `Option`s and `Result`s
2602 fn lint_map_or_none<'a, 'tcx>(
2603 cx: &LateContext<'a, 'tcx>,
2604 expr: &'tcx hir::Expr<'_>,
2605 map_or_args: &'tcx [hir::Expr<'_>],
2607 let is_option = is_type_diagnostic_item(cx, cx.tables.expr_ty(&map_or_args[0]), sym!(option_type));
2608 let is_result = is_type_diagnostic_item(cx, cx.tables.expr_ty(&map_or_args[0]), sym!(result_type));
2610 // There are two variants of this `map_or` lint:
2611 // (1) using `map_or` as an adapter from `Result<T,E>` to `Option<T>`
2612 // (2) using `map_or` as a combinator instead of `and_then`
2614 // (For this lint) we don't care if any other type calls `map_or`
2615 if !is_option && !is_result {
2619 let (lint_name, msg, instead, hint) = {
2620 let default_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].kind {
2621 match_qpath(qpath, &paths::OPTION_NONE)
2626 if !default_arg_is_none {
2631 let f_arg_is_some = if let hir::ExprKind::Path(ref qpath) = map_or_args[2].kind {
2632 match_qpath(qpath, &paths::OPTION_SOME)
2638 let self_snippet = snippet(cx, map_or_args[0].span, "..");
2639 let func_snippet = snippet(cx, map_or_args[2].span, "..");
2640 let msg = "called `map_or(None, f)` on an `Option` value. This can be done more directly by calling \
2641 `and_then(f)` instead";
2645 "try using `and_then` instead",
2646 format!("{0}.and_then({1})", self_snippet, func_snippet),
2648 } else if f_arg_is_some {
2649 let msg = "called `map_or(None, Some)` on a `Result` value. This can be done more directly by calling \
2651 let self_snippet = snippet(cx, map_or_args[0].span, "..");
2653 RESULT_MAP_OR_INTO_OPTION,
2655 "try using `ok` instead",
2656 format!("{0}.ok()", self_snippet),
2671 Applicability::MachineApplicable,
2675 /// Lint use of `_.and_then(|x| Some(y))` for `Option`s
2676 fn lint_option_and_then_some(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
2677 const LINT_MSG: &str = "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`";
2678 const NO_OP_MSG: &str = "using `Option.and_then(Some)`, which is a no-op";
2680 let ty = cx.tables.expr_ty(&args[0]);
2681 if !is_type_diagnostic_item(cx, ty, sym!(option_type)) {
2685 match args[1].kind {
2686 hir::ExprKind::Closure(_, _, body_id, closure_args_span, _) => {
2687 let closure_body = cx.tcx.hir().body(body_id);
2688 let closure_expr = remove_blocks(&closure_body.value);
2690 if let hir::ExprKind::Call(ref some_expr, ref some_args) = closure_expr.kind;
2691 if let hir::ExprKind::Path(ref qpath) = some_expr.kind;
2692 if match_qpath(qpath, &paths::OPTION_SOME);
2693 if some_args.len() == 1;
2695 let inner_expr = &some_args[0];
2697 if contains_return(inner_expr) {
2701 let some_inner_snip = if inner_expr.span.from_expansion() {
2702 snippet_with_macro_callsite(cx, inner_expr.span, "_")
2704 snippet(cx, inner_expr.span, "_")
2707 let closure_args_snip = snippet(cx, closure_args_span, "..");
2708 let option_snip = snippet(cx, args[0].span, "..");
2709 let note = format!("{}.map({} {})", option_snip, closure_args_snip, some_inner_snip);
2712 OPTION_AND_THEN_SOME,
2717 Applicability::MachineApplicable,
2722 // `_.and_then(Some)` case, which is no-op.
2723 hir::ExprKind::Path(ref qpath) => {
2724 if match_qpath(qpath, &paths::OPTION_SOME) {
2725 let option_snip = snippet(cx, args[0].span, "..");
2726 let note = format!("{}", option_snip);
2729 OPTION_AND_THEN_SOME,
2732 "use the expression directly",
2734 Applicability::MachineApplicable,
2742 /// lint use of `filter().next()` for `Iterators`
2743 fn lint_filter_next<'a, 'tcx>(
2744 cx: &LateContext<'a, 'tcx>,
2745 expr: &'tcx hir::Expr<'_>,
2746 filter_args: &'tcx [hir::Expr<'_>],
2748 // lint if caller of `.filter().next()` is an Iterator
2749 if match_trait_method(cx, expr, &paths::ITERATOR) {
2750 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2751 `.find(p)` instead.";
2752 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2753 if filter_snippet.lines().count() <= 1 {
2754 // add note if not multi-line
2761 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2764 span_lint(cx, FILTER_NEXT, expr.span, msg);
2769 /// lint use of `skip_while().next()` for `Iterators`
2770 fn lint_skip_while_next<'a, 'tcx>(
2771 cx: &LateContext<'a, 'tcx>,
2772 expr: &'tcx hir::Expr<'_>,
2773 _skip_while_args: &'tcx [hir::Expr<'_>],
2775 // lint if caller of `.skip_while().next()` is an Iterator
2776 if match_trait_method(cx, expr, &paths::ITERATOR) {
2781 "called `skip_while(p).next()` on an `Iterator`",
2783 "this is more succinctly expressed by calling `.find(!p)` instead",
2788 /// lint use of `filter().map()` for `Iterators`
2789 fn lint_filter_map<'a, 'tcx>(
2790 cx: &LateContext<'a, 'tcx>,
2791 expr: &'tcx hir::Expr<'_>,
2792 _filter_args: &'tcx [hir::Expr<'_>],
2793 _map_args: &'tcx [hir::Expr<'_>],
2795 // lint if caller of `.filter().map()` is an Iterator
2796 if match_trait_method(cx, expr, &paths::ITERATOR) {
2797 let msg = "called `filter(p).map(q)` on an `Iterator`";
2798 let hint = "this is more succinctly expressed by calling `.filter_map(..)` instead";
2799 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2803 /// lint use of `filter_map().next()` for `Iterators`
2804 fn lint_filter_map_next<'a, 'tcx>(
2805 cx: &LateContext<'a, 'tcx>,
2806 expr: &'tcx hir::Expr<'_>,
2807 filter_args: &'tcx [hir::Expr<'_>],
2809 if match_trait_method(cx, expr, &paths::ITERATOR) {
2810 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2811 `.find_map(p)` instead.";
2812 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2813 if filter_snippet.lines().count() <= 1 {
2820 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2823 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2828 /// lint use of `find().map()` for `Iterators`
2829 fn lint_find_map<'a, 'tcx>(
2830 cx: &LateContext<'a, 'tcx>,
2831 expr: &'tcx hir::Expr<'_>,
2832 _find_args: &'tcx [hir::Expr<'_>],
2833 map_args: &'tcx [hir::Expr<'_>],
2835 // lint if caller of `.filter().map()` is an Iterator
2836 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2837 let msg = "called `find(p).map(q)` on an `Iterator`";
2838 let hint = "this is more succinctly expressed by calling `.find_map(..)` instead";
2839 span_lint_and_help(cx, FIND_MAP, expr.span, msg, None, hint);
2843 /// lint use of `filter_map().map()` for `Iterators`
2844 fn lint_filter_map_map<'a, 'tcx>(
2845 cx: &LateContext<'a, 'tcx>,
2846 expr: &'tcx hir::Expr<'_>,
2847 _filter_args: &'tcx [hir::Expr<'_>],
2848 _map_args: &'tcx [hir::Expr<'_>],
2850 // lint if caller of `.filter().map()` is an Iterator
2851 if match_trait_method(cx, expr, &paths::ITERATOR) {
2852 let msg = "called `filter_map(p).map(q)` on an `Iterator`";
2853 let hint = "this is more succinctly expressed by only calling `.filter_map(..)` instead";
2854 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2858 /// lint use of `filter().flat_map()` for `Iterators`
2859 fn lint_filter_flat_map<'a, 'tcx>(
2860 cx: &LateContext<'a, 'tcx>,
2861 expr: &'tcx hir::Expr<'_>,
2862 _filter_args: &'tcx [hir::Expr<'_>],
2863 _map_args: &'tcx [hir::Expr<'_>],
2865 // lint if caller of `.filter().flat_map()` is an Iterator
2866 if match_trait_method(cx, expr, &paths::ITERATOR) {
2867 let msg = "called `filter(p).flat_map(q)` on an `Iterator`";
2868 let hint = "this is more succinctly expressed by calling `.flat_map(..)` \
2869 and filtering by returning `iter::empty()`";
2870 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2874 /// lint use of `filter_map().flat_map()` for `Iterators`
2875 fn lint_filter_map_flat_map<'a, 'tcx>(
2876 cx: &LateContext<'a, 'tcx>,
2877 expr: &'tcx hir::Expr<'_>,
2878 _filter_args: &'tcx [hir::Expr<'_>],
2879 _map_args: &'tcx [hir::Expr<'_>],
2881 // lint if caller of `.filter_map().flat_map()` is an Iterator
2882 if match_trait_method(cx, expr, &paths::ITERATOR) {
2883 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`";
2884 let hint = "this is more succinctly expressed by calling `.flat_map(..)` \
2885 and filtering by returning `iter::empty()`";
2886 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2890 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2891 fn lint_flat_map_identity<'a, 'tcx>(
2892 cx: &LateContext<'a, 'tcx>,
2893 expr: &'tcx hir::Expr<'_>,
2894 flat_map_args: &'tcx [hir::Expr<'_>],
2895 flat_map_span: Span,
2897 if match_trait_method(cx, expr, &paths::ITERATOR) {
2898 let arg_node = &flat_map_args[1].kind;
2900 let apply_lint = |message: &str| {
2904 flat_map_span.with_hi(expr.span.hi()),
2907 "flatten()".to_string(),
2908 Applicability::MachineApplicable,
2913 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
2914 let body = cx.tcx.hir().body(*body_id);
2916 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
2917 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
2919 if path.segments.len() == 1;
2920 if path.segments[0].ident.as_str() == binding_ident.as_str();
2923 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
2928 if let hir::ExprKind::Path(ref qpath) = arg_node;
2930 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
2933 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
2939 /// lint searching an Iterator followed by `is_some()`
2940 fn lint_search_is_some<'a, 'tcx>(
2941 cx: &LateContext<'a, 'tcx>,
2942 expr: &'tcx hir::Expr<'_>,
2943 search_method: &str,
2944 search_args: &'tcx [hir::Expr<'_>],
2945 is_some_args: &'tcx [hir::Expr<'_>],
2948 // lint if caller of search is an Iterator
2949 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
2951 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
2952 expressed by calling `any()`.",
2955 let search_snippet = snippet(cx, search_args[1].span, "..");
2956 if search_snippet.lines().count() <= 1 {
2957 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
2958 // suggest `any(|..| *..)` instead of `any(|..| **..)` for `find(|..| **..).is_some()`
2959 let any_search_snippet = if_chain! {
2960 if search_method == "find";
2961 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].kind;
2962 let closure_body = cx.tcx.hir().body(body_id);
2963 if let Some(closure_arg) = closure_body.params.get(0);
2965 if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
2966 Some(search_snippet.replacen('&', "", 1))
2967 } else if let Some(name) = get_arg_name(&closure_arg.pat) {
2968 Some(search_snippet.replace(&format!("*{}", name), &name.as_str()))
2976 // add note if not multi-line
2980 method_span.with_hi(expr.span.hi()),
2985 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
2987 Applicability::MachineApplicable,
2990 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
2995 /// Used for `lint_binary_expr_with_method_call`.
2996 #[derive(Copy, Clone)]
2997 struct BinaryExprInfo<'a> {
2998 expr: &'a hir::Expr<'a>,
2999 chain: &'a hir::Expr<'a>,
3000 other: &'a hir::Expr<'a>,
3004 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
3005 fn lint_binary_expr_with_method_call(cx: &LateContext<'_, '_>, info: &mut BinaryExprInfo<'_>) {
3006 macro_rules! lint_with_both_lhs_and_rhs {
3007 ($func:ident, $cx:expr, $info:ident) => {
3008 if !$func($cx, $info) {
3009 ::std::mem::swap(&mut $info.chain, &mut $info.other);
3010 if $func($cx, $info) {
3017 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
3018 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
3019 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
3020 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
3023 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
3025 cx: &LateContext<'_, '_>,
3026 info: &BinaryExprInfo<'_>,
3027 chain_methods: &[&str],
3028 lint: &'static Lint,
3032 if let Some(args) = method_chain_args(info.chain, chain_methods);
3033 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.kind;
3034 if arg_char.len() == 1;
3035 if let hir::ExprKind::Path(ref qpath) = fun.kind;
3036 if let Some(segment) = single_segment_path(qpath);
3037 if segment.ident.name == sym!(Some);
3039 let mut applicability = Applicability::MachineApplicable;
3040 let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
3042 if self_ty.kind != ty::Str {
3050 &format!("you should use the `{}` method", suggest),
3052 format!("{}{}.{}({})",
3053 if info.eq { "" } else { "!" },
3054 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
3056 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
3067 /// Checks for the `CHARS_NEXT_CMP` lint.
3068 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3069 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
3072 /// Checks for the `CHARS_LAST_CMP` lint.
3073 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3074 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
3077 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
3081 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
3082 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
3083 cx: &LateContext<'a, 'tcx>,
3084 info: &BinaryExprInfo<'_>,
3085 chain_methods: &[&str],
3086 lint: &'static Lint,
3090 if let Some(args) = method_chain_args(info.chain, chain_methods);
3091 if let hir::ExprKind::Lit(ref lit) = info.other.kind;
3092 if let ast::LitKind::Char(c) = lit.node;
3094 let mut applicability = Applicability::MachineApplicable;
3099 &format!("you should use the `{}` method", suggest),
3101 format!("{}{}.{}('{}')",
3102 if info.eq { "" } else { "!" },
3103 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
3116 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
3117 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3118 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
3121 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
3122 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3123 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
3126 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
3130 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
3131 fn lint_single_char_pattern<'a, 'tcx>(
3132 cx: &LateContext<'a, 'tcx>,
3133 _expr: &'tcx hir::Expr<'_>,
3134 arg: &'tcx hir::Expr<'_>,
3137 if let hir::ExprKind::Lit(lit) = &arg.kind;
3138 if let ast::LitKind::Str(r, style) = lit.node;
3139 if r.as_str().len() == 1;
3141 let mut applicability = Applicability::MachineApplicable;
3142 let snip = snippet_with_applicability(cx, arg.span, "..", &mut applicability);
3143 let ch = if let ast::StrStyle::Raw(nhash) = style {
3144 let nhash = nhash as usize;
3145 // for raw string: r##"a"##
3146 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
3148 // for regular string: "a"
3149 &snip[1..(snip.len() - 1)]
3151 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
3154 SINGLE_CHAR_PATTERN,
3156 "single-character string constant used as pattern",
3157 "try using a `char` instead",
3165 /// Checks for the `USELESS_ASREF` lint.
3166 fn lint_asref(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, call_name: &str, as_ref_args: &[hir::Expr<'_>]) {
3167 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
3168 // check if the call is to the actual `AsRef` or `AsMut` trait
3169 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
3170 // check if the type after `as_ref` or `as_mut` is the same as before
3171 let recvr = &as_ref_args[0];
3172 let rcv_ty = cx.tables.expr_ty(recvr);
3173 let res_ty = cx.tables.expr_ty(expr);
3174 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
3175 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
3176 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
3177 // allow the `as_ref` or `as_mut` if it is followed by another method call
3179 if let Some(parent) = get_parent_expr(cx, expr);
3180 if let hir::ExprKind::MethodCall(_, ref span, _) = parent.kind;
3181 if span != &expr.span;
3187 let mut applicability = Applicability::MachineApplicable;
3192 &format!("this call to `{}` does nothing", call_name),
3194 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
3201 fn ty_has_iter_method(cx: &LateContext<'_, '_>, self_ref_ty: Ty<'_>) -> Option<(&'static str, &'static str)> {
3202 has_iter_method(cx, self_ref_ty).map(|ty_name| {
3203 let mutbl = match self_ref_ty.kind {
3204 ty::Ref(_, _, mutbl) => mutbl,
3205 _ => unreachable!(),
3207 let method_name = match mutbl {
3208 hir::Mutability::Not => "iter",
3209 hir::Mutability::Mut => "iter_mut",
3211 (ty_name, method_name)
3215 fn lint_into_iter(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, self_ref_ty: Ty<'_>, method_span: Span) {
3216 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
3219 if let Some((kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
3225 "this `.into_iter()` call is equivalent to `.{}()` and will not move the `{}`",
3229 method_name.to_string(),
3230 Applicability::MachineApplicable,
3235 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
3236 fn lint_maybe_uninit(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, outer: &hir::Expr<'_>) {
3238 if let hir::ExprKind::Call(ref callee, ref args) = expr.kind;
3240 if let hir::ExprKind::Path(ref path) = callee.kind;
3241 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
3242 if !is_maybe_uninit_ty_valid(cx, cx.tables.expr_ty_adjusted(outer));
3246 UNINIT_ASSUMED_INIT,
3248 "this call for this type may be undefined behavior"
3254 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_, '_>, ty: Ty<'_>) -> bool {
3256 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
3257 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
3258 ty::Adt(ref adt, _) => match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT),
3263 fn lint_suspicious_map(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>) {
3268 "this call to `map()` won't have an effect on the call to `count()`",
3270 "make sure you did not confuse `map` with `filter` or `for_each`",
3274 /// lint use of `_.as_ref().map(Deref::deref)` for `Option`s
3275 fn lint_option_as_ref_deref<'a, 'tcx>(
3276 cx: &LateContext<'a, 'tcx>,
3277 expr: &hir::Expr<'_>,
3278 as_ref_args: &[hir::Expr<'_>],
3279 map_args: &[hir::Expr<'_>],
3282 let same_mutability = |m| (is_mut && m == &hir::Mutability::Mut) || (!is_mut && m == &hir::Mutability::Not);
3284 let option_ty = cx.tables.expr_ty(&as_ref_args[0]);
3285 if !is_type_diagnostic_item(cx, option_ty, sym!(option_type)) {
3289 let deref_aliases: [&[&str]; 9] = [
3290 &paths::DEREF_TRAIT_METHOD,
3291 &paths::DEREF_MUT_TRAIT_METHOD,
3292 &paths::CSTRING_AS_C_STR,
3293 &paths::OS_STRING_AS_OS_STR,
3294 &paths::PATH_BUF_AS_PATH,
3295 &paths::STRING_AS_STR,
3296 &paths::STRING_AS_MUT_STR,
3297 &paths::VEC_AS_SLICE,
3298 &paths::VEC_AS_MUT_SLICE,
3301 let is_deref = match map_args[1].kind {
3302 hir::ExprKind::Path(ref expr_qpath) => deref_aliases.iter().any(|path| match_qpath(expr_qpath, path)),
3303 hir::ExprKind::Closure(_, _, body_id, _, _) => {
3304 let closure_body = cx.tcx.hir().body(body_id);
3305 let closure_expr = remove_blocks(&closure_body.value);
3307 match &closure_expr.kind {
3308 hir::ExprKind::MethodCall(_, _, args) => {
3311 if let hir::ExprKind::Path(qpath) = &args[0].kind;
3312 if let hir::def::Res::Local(local_id) = cx.tables.qpath_res(qpath, args[0].hir_id);
3313 if closure_body.params[0].pat.hir_id == local_id;
3314 let adj = cx.tables.expr_adjustments(&args[0]).iter().map(|x| &x.kind).collect::<Box<[_]>>();
3315 if let [ty::adjustment::Adjust::Deref(None), ty::adjustment::Adjust::Borrow(_)] = *adj;
3317 let method_did = cx.tables.type_dependent_def_id(closure_expr.hir_id).unwrap();
3318 deref_aliases.iter().any(|path| match_def_path(cx, method_did, path))
3324 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, m, ref inner) if same_mutability(m) => {
3326 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner1) = inner.kind;
3327 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner2) = inner1.kind;
3328 if let hir::ExprKind::Path(ref qpath) = inner2.kind;
3329 if let hir::def::Res::Local(local_id) = cx.tables.qpath_res(qpath, inner2.hir_id);
3331 closure_body.params[0].pat.hir_id == local_id
3344 let current_method = if is_mut {
3345 format!(".as_mut().map({})", snippet(cx, map_args[1].span, ".."))
3347 format!(".as_ref().map({})", snippet(cx, map_args[1].span, ".."))
3349 let method_hint = if is_mut { "as_deref_mut" } else { "as_deref" };
3350 let hint = format!("{}.{}()", snippet(cx, as_ref_args[0].span, ".."), method_hint);
3351 let suggestion = format!("try using {} instead", method_hint);
3354 "called `{0}` on an Option value. This can be done more directly \
3355 by calling `{1}` instead",
3356 current_method, hint
3360 OPTION_AS_REF_DEREF,
3365 Applicability::MachineApplicable,
3370 /// Given a `Result<T, E>` type, return its error type (`E`).
3371 fn get_error_type<'a>(cx: &LateContext<'_, '_>, ty: Ty<'a>) -> Option<Ty<'a>> {
3373 ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym!(result_type)) => substs.types().nth(1),
3378 /// This checks whether a given type is known to implement Debug.
3379 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
3381 .get_diagnostic_item(sym::debug_trait)
3382 .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
3387 StartsWith(&'static str),
3391 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
3392 (Convention::Eq("new"), &[SelfKind::No]),
3393 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
3394 (Convention::StartsWith("from_"), &[SelfKind::No]),
3395 (Convention::StartsWith("into_"), &[SelfKind::Value]),
3396 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
3397 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
3398 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
3401 const FN_HEADER: hir::FnHeader = hir::FnHeader {
3402 unsafety: hir::Unsafety::Normal,
3403 constness: hir::Constness::NotConst,
3404 asyncness: hir::IsAsync::NotAsync,
3405 abi: rustc_target::spec::abi::Abi::Rust,
3409 const TRAIT_METHODS: [(&str, usize, &hir::FnHeader, SelfKind, OutType, &str); 30] = [
3410 ("add", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Add"),
3411 ("as_mut", 1, &FN_HEADER, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
3412 ("as_ref", 1, &FN_HEADER, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
3413 ("bitand", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
3414 ("bitor", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
3415 ("bitxor", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
3416 ("borrow", 1, &FN_HEADER, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
3417 ("borrow_mut", 1, &FN_HEADER, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
3418 ("clone", 1, &FN_HEADER, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
3419 ("cmp", 2, &FN_HEADER, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
3420 ("default", 0, &FN_HEADER, SelfKind::No, OutType::Any, "std::default::Default"),
3421 ("deref", 1, &FN_HEADER, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
3422 ("deref_mut", 1, &FN_HEADER, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
3423 ("div", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Div"),
3424 ("drop", 1, &FN_HEADER, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
3425 ("eq", 2, &FN_HEADER, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
3426 ("from_iter", 1, &FN_HEADER, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
3427 ("from_str", 1, &FN_HEADER, SelfKind::No, OutType::Any, "std::str::FromStr"),
3428 ("hash", 2, &FN_HEADER, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
3429 ("index", 2, &FN_HEADER, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
3430 ("index_mut", 2, &FN_HEADER, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
3431 ("into_iter", 1, &FN_HEADER, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
3432 ("mul", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Mul"),
3433 ("neg", 1, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Neg"),
3434 ("next", 1, &FN_HEADER, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
3435 ("not", 1, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Not"),
3436 ("rem", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Rem"),
3437 ("shl", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Shl"),
3438 ("shr", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Shr"),
3439 ("sub", 2, &FN_HEADER, SelfKind::Value, OutType::Any, "std::ops::Sub"),
3443 const PATTERN_METHODS: [(&str, usize); 17] = [
3451 ("split_terminator", 1),
3452 ("rsplit_terminator", 1),
3457 ("match_indices", 1),
3458 ("rmatch_indices", 1),
3459 ("trim_start_matches", 1),
3460 ("trim_end_matches", 1),
3463 #[derive(Clone, Copy, PartialEq, Debug)]
3472 fn matches<'a>(self, cx: &LateContext<'_, 'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
3473 fn matches_value<'a>(cx: &LateContext<'_, 'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
3474 if ty == parent_ty {
3476 } else if ty.is_box() {
3477 ty.boxed_ty() == parent_ty
3478 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
3479 if let ty::Adt(_, substs) = ty.kind {
3480 substs.types().next().map_or(false, |t| t == parent_ty)
3490 cx: &LateContext<'_, 'a>,
3491 mutability: hir::Mutability,
3495 if let ty::Ref(_, t, m) = ty.kind {
3496 return m == mutability && t == parent_ty;
3499 let trait_path = match mutability {
3500 hir::Mutability::Not => &paths::ASREF_TRAIT,
3501 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
3504 let trait_def_id = match get_trait_def_id(cx, trait_path) {
3506 None => return false,
3508 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
3512 Self::Value => matches_value(cx, parent_ty, ty),
3513 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
3514 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
3515 Self::No => ty != parent_ty,
3520 fn description(self) -> &'static str {
3522 Self::Value => "self by value",
3523 Self::Ref => "self by reference",
3524 Self::RefMut => "self by mutable reference",
3525 Self::No => "no self",
3532 fn check(&self, other: &str) -> bool {
3534 Self::Eq(this) => this == other,
3535 Self::StartsWith(this) => other.starts_with(this) && this != other,
3540 impl fmt::Display for Convention {
3541 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
3543 Self::Eq(this) => this.fmt(f),
3544 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
3549 #[derive(Clone, Copy)]
3558 fn matches(self, cx: &LateContext<'_, '_>, ty: &hir::FnRetTy<'_>) -> bool {
3559 let is_unit = |ty: &hir::Ty<'_>| SpanlessEq::new(cx).eq_ty_kind(&ty.kind, &hir::TyKind::Tup(&[]));
3561 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
3562 (Self::Unit, &hir::FnRetTy::Return(ref ty)) if is_unit(ty) => true,
3563 (Self::Bool, &hir::FnRetTy::Return(ref ty)) if is_bool(ty) => true,
3564 (Self::Any, &hir::FnRetTy::Return(ref ty)) if !is_unit(ty) => true,
3565 (Self::Ref, &hir::FnRetTy::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
3571 fn is_bool(ty: &hir::Ty<'_>) -> bool {
3572 if let hir::TyKind::Path(ref p) = ty.kind {
3573 match_qpath(p, &["bool"])
3579 // Returns `true` if `expr` contains a return expression
3580 fn contains_return(expr: &hir::Expr<'_>) -> bool {
3581 struct RetCallFinder {
3585 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
3586 type Map = Map<'tcx>;
3588 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
3592 if let hir::ExprKind::Ret(..) = &expr.kind {
3595 intravisit::walk_expr(self, expr);
3599 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
3600 intravisit::NestedVisitorMap::None
3604 let mut visitor = RetCallFinder { found: false };
3605 visitor.visit_expr(expr);
3609 fn check_pointer_offset(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
3612 if let ty::RawPtr(ty::TypeAndMut { ref ty, .. }) = cx.tables.expr_ty(&args[0]).kind;
3613 if let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty));
3616 span_lint(cx, ZST_OFFSET, expr.span, "offset calculation on zero-sized value");
3621 fn lint_filetype_is_file(cx: &LateContext<'_, '_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
3622 let ty = cx.tables.expr_ty(&args[0]);
3624 if !match_type(cx, ty, &paths::FILE_TYPE) {
3630 let lint_unary: &str;
3631 let help_unary: &str;
3633 if let Some(parent) = get_parent_expr(cx, expr);
3634 if let hir::ExprKind::Unary(op, _) = parent.kind;
3635 if op == hir::UnOp::UnNot;
3648 let lint_msg = format!("`{}FileType::is_file()` only {} regular files", lint_unary, verb);
3649 let help_msg = format!("use `{}FileType::is_dir()` instead", help_unary);
3650 span_lint_and_help(cx, FILETYPE_IS_FILE, span, &lint_msg, None, &help_msg);
3653 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
3654 expected.constness == actual.constness
3655 && expected.unsafety == actual.unsafety
3656 && expected.asyncness == actual.asyncness