1 mod bind_instead_of_map;
2 mod inefficient_to_string;
3 mod manual_saturating_arithmetic;
4 mod option_map_unwrap_or;
5 mod unnecessary_filter_map;
6 mod unnecessary_lazy_eval;
12 use bind_instead_of_map::BindInsteadOfMap;
13 use if_chain::if_chain;
15 use rustc_errors::Applicability;
17 use rustc_hir::intravisit::{self, Visitor};
18 use rustc_hir::{TraitItem, TraitItemKind};
19 use rustc_lint::{LateContext, LateLintPass, Lint, LintContext};
20 use rustc_middle::hir::map::Map;
21 use rustc_middle::lint::in_external_macro;
22 use rustc_middle::ty::{self, TraitRef, Ty, TyS};
23 use rustc_session::{declare_lint_pass, declare_tool_lint};
24 use rustc_span::source_map::Span;
25 use rustc_span::symbol::{sym, SymbolStr};
27 use crate::consts::{constant, Constant};
28 use crate::utils::eager_or_lazy::is_lazyness_candidate;
29 use crate::utils::usage::mutated_variables;
31 contains_ty, get_arg_name, get_parent_expr, get_trait_def_id, has_iter_method, higher, implements_trait, in_macro,
32 is_copy, is_expn_of, is_type_diagnostic_item, iter_input_pats, last_path_segment, match_def_path, match_qpath,
33 match_trait_method, match_type, match_var, method_calls, method_chain_args, paths, remove_blocks, return_ty,
34 single_segment_path, snippet, snippet_with_applicability, snippet_with_macro_callsite, span_lint,
35 span_lint_and_help, span_lint_and_note, span_lint_and_sugg, span_lint_and_then, sugg, walk_ptrs_ty_depth,
39 declare_clippy_lint! {
40 /// **What it does:** Checks for `.unwrap()` calls on `Option`s and on `Result`s.
42 /// **Why is this bad?** It is better to handle the `None` or `Err` case,
43 /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
44 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
45 /// `Allow` by default.
47 /// `result.unwrap()` will let the thread panic on `Err` values.
48 /// Normally, you want to implement more sophisticated error handling,
49 /// and propagate errors upwards with `?` operator.
51 /// Even if you want to panic on errors, not all `Error`s implement good
52 /// messages on display. Therefore, it may be beneficial to look at the places
53 /// where they may get displayed. Activate this lint to do just that.
55 /// **Known problems:** None.
59 /// # let opt = Some(1);
65 /// opt.expect("more helpful message");
71 /// # let res: Result<usize, ()> = Ok(1);
77 /// res.expect("more helpful message");
81 "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
84 declare_clippy_lint! {
85 /// **What it does:** Checks for `.expect()` calls on `Option`s and `Result`s.
87 /// **Why is this bad?** Usually it is better to handle the `None` or `Err` case.
88 /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
89 /// this lint is `Allow` by default.
91 /// `result.expect()` will let the thread panic on `Err`
92 /// values. Normally, you want to implement more sophisticated error handling,
93 /// and propagate errors upwards with `?` operator.
95 /// **Known problems:** None.
99 /// # let opt = Some(1);
102 /// opt.expect("one");
105 /// let opt = Some(1);
112 /// # let res: Result<usize, ()> = Ok(1);
115 /// res.expect("one");
119 /// # Ok::<(), ()>(())
123 "using `.expect()` on `Result` or `Option`, which might be better handled"
126 declare_clippy_lint! {
127 /// **What it does:** Checks for methods that should live in a trait
128 /// implementation of a `std` trait (see [llogiq's blog
129 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
130 /// information) instead of an inherent implementation.
132 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
133 /// the code, often with very little cost. Also people seeing a `mul(...)`
135 /// may expect `*` to work equally, so you should have good reason to disappoint
138 /// **Known problems:** None.
144 /// fn add(&self, other: &X) -> X {
150 pub SHOULD_IMPLEMENT_TRAIT,
152 "defining a method that should be implementing a std trait"
155 declare_clippy_lint! {
156 /// **What it does:** Checks for methods with certain name prefixes and which
157 /// doesn't match how self is taken. The actual rules are:
159 /// |Prefix |`self` taken |
160 /// |-------|----------------------|
161 /// |`as_` |`&self` or `&mut self`|
163 /// |`into_`|`self` |
164 /// |`is_` |`&self` or none |
165 /// |`to_` |`&self` |
167 /// **Why is this bad?** Consistency breeds readability. If you follow the
168 /// conventions, your users won't be surprised that they, e.g., need to supply a
169 /// mutable reference to a `as_..` function.
171 /// **Known problems:** None.
177 /// fn as_str(self) -> &'static str {
183 pub WRONG_SELF_CONVENTION,
185 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
188 declare_clippy_lint! {
189 /// **What it does:** This is the same as
190 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
192 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
194 /// **Known problems:** Actually *renaming* the function may break clients if
195 /// the function is part of the public interface. In that case, be mindful of
196 /// the stability guarantees you've given your users.
202 /// pub fn as_str(self) -> &'a str {
207 pub WRONG_PUB_SELF_CONVENTION,
209 "defining a public method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
212 declare_clippy_lint! {
213 /// **What it does:** Checks for usage of `ok().expect(..)`.
215 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
216 /// directly to get a better error message.
218 /// **Known problems:** The error type needs to implement `Debug`
222 /// # let x = Ok::<_, ()>(());
225 /// x.ok().expect("why did I do this again?");
228 /// x.expect("why did I do this again?");
232 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
235 declare_clippy_lint! {
236 /// **What it does:** Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
237 /// `result.map(_).unwrap_or_else(_)`.
239 /// **Why is this bad?** Readability, these can be written more concisely (resp.) as
240 /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
242 /// **Known problems:** The order of the arguments is not in execution order
246 /// # let x = Some(1);
249 /// x.map(|a| a + 1).unwrap_or(0);
252 /// x.map_or(0, |a| a + 1);
258 /// # let x: Result<usize, ()> = Ok(1);
259 /// # fn some_function(foo: ()) -> usize { 1 }
262 /// x.map(|a| a + 1).unwrap_or_else(some_function);
265 /// x.map_or_else(some_function, |a| a + 1);
269 "using `.map(f).unwrap_or(a)` or `.map(f).unwrap_or_else(func)`, which are more succinctly expressed as `map_or(a, f)` or `map_or_else(a, f)`"
272 declare_clippy_lint! {
273 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
275 /// **Why is this bad?** Readability, this can be written more concisely as
278 /// **Known problems:** The order of the arguments is not in execution order.
282 /// # let opt = Some(1);
285 /// opt.map_or(None, |a| Some(a + 1));
288 /// opt.and_then(|a| Some(a + 1));
290 pub OPTION_MAP_OR_NONE,
292 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
295 declare_clippy_lint! {
296 /// **What it does:** Checks for usage of `_.map_or(None, Some)`.
298 /// **Why is this bad?** Readability, this can be written more concisely as
301 /// **Known problems:** None.
307 /// # let r: Result<u32, &str> = Ok(1);
308 /// assert_eq!(Some(1), r.map_or(None, Some));
313 /// # let r: Result<u32, &str> = Ok(1);
314 /// assert_eq!(Some(1), r.ok());
316 pub RESULT_MAP_OR_INTO_OPTION,
318 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
321 declare_clippy_lint! {
322 /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
323 /// `_.or_else(|x| Err(y))`.
325 /// **Why is this bad?** Readability, this can be written more concisely as
326 /// `_.map(|x| y)` or `_.map_err(|x| y)`.
328 /// **Known problems:** None
333 /// # fn opt() -> Option<&'static str> { Some("42") }
334 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
335 /// let _ = opt().and_then(|s| Some(s.len()));
336 /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
337 /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
340 /// The correct use would be:
343 /// # fn opt() -> Option<&'static str> { Some("42") }
344 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
345 /// let _ = opt().map(|s| s.len());
346 /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
347 /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
349 pub BIND_INSTEAD_OF_MAP,
351 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
354 declare_clippy_lint! {
355 /// **What it does:** Checks for usage of `_.filter(_).next()`.
357 /// **Why is this bad?** Readability, this can be written more concisely as
360 /// **Known problems:** None.
364 /// # let vec = vec![1];
365 /// vec.iter().filter(|x| **x == 0).next();
367 /// Could be written as
369 /// # let vec = vec![1];
370 /// vec.iter().find(|x| **x == 0);
374 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
377 declare_clippy_lint! {
378 /// **What it does:** Checks for usage of `_.skip_while(condition).next()`.
380 /// **Why is this bad?** Readability, this can be written more concisely as
381 /// `_.find(!condition)`.
383 /// **Known problems:** None.
387 /// # let vec = vec![1];
388 /// vec.iter().skip_while(|x| **x == 0).next();
390 /// Could be written as
392 /// # let vec = vec![1];
393 /// vec.iter().find(|x| **x != 0);
397 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
400 declare_clippy_lint! {
401 /// **What it does:** Checks for usage of `_.map(_).flatten(_)`,
403 /// **Why is this bad?** Readability, this can be written more concisely as a
404 /// single method call using `_.flat_map(_)`
406 /// **Known problems:**
410 /// let vec = vec![vec![1]];
413 /// vec.iter().map(|x| x.iter()).flatten();
416 /// vec.iter().flat_map(|x| x.iter());
420 "using combinations of `flatten` and `map` which can usually be written as a single method call"
423 declare_clippy_lint! {
424 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
425 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
427 /// **Why is this bad?** Readability, this can be written more concisely as a
428 /// single method call.
430 /// **Known problems:** Often requires a condition + Option/Iterator creation
431 /// inside the closure.
435 /// let vec = vec![1];
438 /// vec.iter().filter(|x| **x == 0).map(|x| *x * 2);
441 /// vec.iter().filter_map(|x| if *x == 0 {
449 "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can usually be written as a single method call"
452 declare_clippy_lint! {
453 /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
455 /// **Why is this bad?** Readability, this can be written more concisely as a
456 /// single method call.
458 /// **Known problems:** None
462 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
464 /// Can be written as
467 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
471 "using combination of `filter_map` and `next` which can usually be written as a single method call"
474 declare_clippy_lint! {
475 /// **What it does:** Checks for usage of `flat_map(|x| x)`.
477 /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
479 /// **Known problems:** None
483 /// # let iter = vec![vec![0]].into_iter();
484 /// iter.flat_map(|x| x);
486 /// Can be written as
488 /// # let iter = vec![vec![0]].into_iter();
491 pub FLAT_MAP_IDENTITY,
493 "call to `flat_map` where `flatten` is sufficient"
496 declare_clippy_lint! {
497 /// **What it does:** Checks for usage of `_.find(_).map(_)`.
499 /// **Why is this bad?** Readability, this can be written more concisely as a
500 /// single method call.
502 /// **Known problems:** Often requires a condition + Option/Iterator creation
503 /// inside the closure.
507 /// (0..3).find(|x| *x == 2).map(|x| x * 2);
509 /// Can be written as
511 /// (0..3).find_map(|x| if x == 2 { Some(x * 2) } else { None });
515 "using a combination of `find` and `map` can usually be written as a single method call"
518 declare_clippy_lint! {
519 /// **What it does:** Checks for an iterator search (such as `find()`,
520 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
522 /// **Why is this bad?** Readability, this can be written more concisely as
525 /// **Known problems:** None.
529 /// # let vec = vec![1];
530 /// vec.iter().find(|x| **x == 0).is_some();
532 /// Could be written as
534 /// # let vec = vec![1];
535 /// vec.iter().any(|x| *x == 0);
539 "using an iterator search followed by `is_some()`, which is more succinctly expressed as a call to `any()`"
542 declare_clippy_lint! {
543 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
544 /// if it starts with a given char.
546 /// **Why is this bad?** Readability, this can be written more concisely as
547 /// `_.starts_with(_)`.
549 /// **Known problems:** None.
553 /// let name = "foo";
554 /// if name.chars().next() == Some('_') {};
556 /// Could be written as
558 /// let name = "foo";
559 /// if name.starts_with('_') {};
563 "using `.chars().next()` to check if a string starts with a char"
566 declare_clippy_lint! {
567 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
568 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
569 /// `unwrap_or_default` instead.
571 /// **Why is this bad?** The function will always be called and potentially
572 /// allocate an object acting as the default.
574 /// **Known problems:** If the function has side-effects, not calling it will
575 /// change the semantic of the program, but you shouldn't rely on that anyway.
579 /// # let foo = Some(String::new());
580 /// foo.unwrap_or(String::new());
582 /// this can instead be written:
584 /// # let foo = Some(String::new());
585 /// foo.unwrap_or_else(String::new);
589 /// # let foo = Some(String::new());
590 /// foo.unwrap_or_default();
594 "using any `*or` method with a function call, which suggests `*or_else`"
597 declare_clippy_lint! {
598 /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
599 /// etc., and suggests to use `unwrap_or_else` instead
601 /// **Why is this bad?** The function will always be called.
603 /// **Known problems:** If the function has side-effects, not calling it will
604 /// change the semantics of the program, but you shouldn't rely on that anyway.
608 /// # let foo = Some(String::new());
609 /// # let err_code = "418";
610 /// # let err_msg = "I'm a teapot";
611 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
615 /// # let foo = Some(String::new());
616 /// # let err_code = "418";
617 /// # let err_msg = "I'm a teapot";
618 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
620 /// this can instead be written:
622 /// # let foo = Some(String::new());
623 /// # let err_code = "418";
624 /// # let err_msg = "I'm a teapot";
625 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
629 "using any `expect` method with a function call"
632 declare_clippy_lint! {
633 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
635 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
636 /// generics, not for using the `clone` method on a concrete type.
638 /// **Known problems:** None.
646 "using `clone` on a `Copy` type"
649 declare_clippy_lint! {
650 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
651 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
652 /// function syntax instead (e.g., `Rc::clone(foo)`).
654 /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
655 /// can obscure the fact that only the pointer is being cloned, not the underlying
660 /// # use std::rc::Rc;
661 /// let x = Rc::new(1);
669 pub CLONE_ON_REF_PTR,
671 "using 'clone' on a ref-counted pointer"
674 declare_clippy_lint! {
675 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
677 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
678 /// cloning the underlying `T`.
680 /// **Known problems:** None.
687 /// let z = y.clone();
688 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
691 pub CLONE_DOUBLE_REF,
693 "using `clone` on `&&T`"
696 declare_clippy_lint! {
697 /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
698 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
700 /// **Why is this bad?** This bypasses the specialized implementation of
701 /// `ToString` and instead goes through the more expensive string formatting
704 /// **Known problems:** None.
708 /// // Generic implementation for `T: Display` is used (slow)
709 /// ["foo", "bar"].iter().map(|s| s.to_string());
711 /// // OK, the specialized impl is used
712 /// ["foo", "bar"].iter().map(|&s| s.to_string());
714 pub INEFFICIENT_TO_STRING,
716 "using `to_string` on `&&T` where `T: ToString`"
719 declare_clippy_lint! {
720 /// **What it does:** Checks for `new` not returning a type that contains `Self`.
722 /// **Why is this bad?** As a convention, `new` methods are used to make a new
723 /// instance of a type.
725 /// **Known problems:** None.
728 /// In an impl block:
731 /// # struct NotAFoo;
733 /// fn new() -> NotAFoo {
743 /// // Bad. The type name must contain `Self`
744 /// fn new() -> Bar {
752 /// # struct FooError;
754 /// // Good. Return type contains `Self`
755 /// fn new() -> Result<Foo, FooError> {
761 /// Or in a trait definition:
763 /// pub trait Trait {
764 /// // Bad. The type name must contain `Self`
770 /// pub trait Trait {
771 /// // Good. Return type contains `Self`
772 /// fn new() -> Self;
777 "not returning type containing `Self` in a `new` method"
780 declare_clippy_lint! {
781 /// **What it does:** Checks for string methods that receive a single-character
782 /// `str` as an argument, e.g., `_.split("x")`.
784 /// **Why is this bad?** Performing these methods using a `char` is faster than
787 /// **Known problems:** Does not catch multi-byte unicode characters.
796 pub SINGLE_CHAR_PATTERN,
798 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
801 declare_clippy_lint! {
802 /// **What it does:** Checks for getting the inner pointer of a temporary
805 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
806 /// as the `CString` is alive.
808 /// **Known problems:** None.
812 /// # use std::ffi::CString;
813 /// # fn call_some_ffi_func(_: *const i8) {}
815 /// let c_str = CString::new("foo").unwrap().as_ptr();
817 /// call_some_ffi_func(c_str);
820 /// Here `c_str` points to a freed address. The correct use would be:
822 /// # use std::ffi::CString;
823 /// # fn call_some_ffi_func(_: *const i8) {}
825 /// let c_str = CString::new("foo").unwrap();
827 /// call_some_ffi_func(c_str.as_ptr());
830 pub TEMPORARY_CSTRING_AS_PTR,
832 "getting the inner pointer of a temporary `CString`"
835 declare_clippy_lint! {
836 /// **What it does:** Checks for calling `.step_by(0)` on iterators which panics.
838 /// **Why is this bad?** This very much looks like an oversight. Use `panic!()` instead if you
839 /// actually intend to panic.
841 /// **Known problems:** None.
844 /// ```rust,should_panic
845 /// for x in (0..100).step_by(0) {
849 pub ITERATOR_STEP_BY_ZERO,
851 "using `Iterator::step_by(0)`, which will panic at runtime"
854 declare_clippy_lint! {
855 /// **What it does:** Checks for the use of `iter.nth(0)`.
857 /// **Why is this bad?** `iter.next()` is equivalent to
858 /// `iter.nth(0)`, as they both consume the next element,
859 /// but is more readable.
861 /// **Known problems:** None.
866 /// # use std::collections::HashSet;
868 /// # let mut s = HashSet::new();
870 /// let x = s.iter().nth(0);
873 /// # let mut s = HashSet::new();
875 /// let x = s.iter().next();
879 "replace `iter.nth(0)` with `iter.next()`"
882 declare_clippy_lint! {
883 /// **What it does:** Checks for use of `.iter().nth()` (and the related
884 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
886 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
889 /// **Known problems:** None.
893 /// let some_vec = vec![0, 1, 2, 3];
894 /// let bad_vec = some_vec.iter().nth(3);
895 /// let bad_slice = &some_vec[..].iter().nth(3);
897 /// The correct use would be:
899 /// let some_vec = vec![0, 1, 2, 3];
900 /// let bad_vec = some_vec.get(3);
901 /// let bad_slice = &some_vec[..].get(3);
905 "using `.iter().nth()` on a standard library type with O(1) element access"
908 declare_clippy_lint! {
909 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
911 /// **Why is this bad?** `.nth(x)` is cleaner
913 /// **Known problems:** None.
917 /// let some_vec = vec![0, 1, 2, 3];
918 /// let bad_vec = some_vec.iter().skip(3).next();
919 /// let bad_slice = &some_vec[..].iter().skip(3).next();
921 /// The correct use would be:
923 /// let some_vec = vec![0, 1, 2, 3];
924 /// let bad_vec = some_vec.iter().nth(3);
925 /// let bad_slice = &some_vec[..].iter().nth(3);
929 "using `.skip(x).next()` on an iterator"
932 declare_clippy_lint! {
933 /// **What it does:** Checks for use of `.get().unwrap()` (or
934 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
936 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
939 /// **Known problems:** Not a replacement for error handling: Using either
940 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
941 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
942 /// temporary placeholder for dealing with the `Option` type, then this does
943 /// not mitigate the need for error handling. If there is a chance that `.get()`
944 /// will be `None` in your program, then it is advisable that the `None` case
945 /// is handled in a future refactor instead of using `.unwrap()` or the Index
950 /// let mut some_vec = vec![0, 1, 2, 3];
951 /// let last = some_vec.get(3).unwrap();
952 /// *some_vec.get_mut(0).unwrap() = 1;
954 /// The correct use would be:
956 /// let mut some_vec = vec![0, 1, 2, 3];
957 /// let last = some_vec[3];
962 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
965 declare_clippy_lint! {
966 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
967 /// `&str` or `String`.
969 /// **Why is this bad?** `.push_str(s)` is clearer
971 /// **Known problems:** None.
976 /// let def = String::from("def");
977 /// let mut s = String::new();
978 /// s.extend(abc.chars());
979 /// s.extend(def.chars());
981 /// The correct use would be:
984 /// let def = String::from("def");
985 /// let mut s = String::new();
987 /// s.push_str(&def);
989 pub STRING_EXTEND_CHARS,
991 "using `x.extend(s.chars())` where s is a `&str` or `String`"
994 declare_clippy_lint! {
995 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
998 /// **Why is this bad?** `.to_vec()` is clearer
1000 /// **Known problems:** None.
1004 /// let s = [1, 2, 3, 4, 5];
1005 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1007 /// The better use would be:
1009 /// let s = [1, 2, 3, 4, 5];
1010 /// let s2: Vec<isize> = s.to_vec();
1012 pub ITER_CLONED_COLLECT,
1014 "using `.cloned().collect()` on slice to create a `Vec`"
1017 declare_clippy_lint! {
1018 /// **What it does:** Checks for usage of `_.chars().last()` or
1019 /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1021 /// **Why is this bad?** Readability, this can be written more concisely as
1022 /// `_.ends_with(_)`.
1024 /// **Known problems:** None.
1028 /// # let name = "_";
1031 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1034 /// name.ends_with('_') || name.ends_with('-');
1038 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1041 declare_clippy_lint! {
1042 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
1043 /// types before and after the call are the same.
1045 /// **Why is this bad?** The call is unnecessary.
1047 /// **Known problems:** None.
1051 /// # fn do_stuff(x: &[i32]) {}
1052 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1053 /// do_stuff(x.as_ref());
1055 /// The correct use would be:
1057 /// # fn do_stuff(x: &[i32]) {}
1058 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1063 "using `as_ref` where the types before and after the call are the same"
1066 declare_clippy_lint! {
1067 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
1068 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1069 /// `sum` or `product`.
1071 /// **Why is this bad?** Readability.
1073 /// **Known problems:** None.
1077 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1079 /// This could be written as:
1081 /// let _ = (0..3).any(|x| x > 2);
1083 pub UNNECESSARY_FOLD,
1085 "using `fold` when a more succinct alternative exists"
1088 declare_clippy_lint! {
1089 /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1090 /// More specifically it checks if the closure provided is only performing one of the
1091 /// filter or map operations and suggests the appropriate option.
1093 /// **Why is this bad?** Complexity. The intent is also clearer if only a single
1094 /// operation is being performed.
1096 /// **Known problems:** None
1100 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1102 /// // As there is no transformation of the argument this could be written as:
1103 /// let _ = (0..3).filter(|&x| x > 2);
1107 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1109 /// // As there is no conditional check on the argument this could be written as:
1110 /// let _ = (0..4).map(|x| x + 1);
1112 pub UNNECESSARY_FILTER_MAP,
1114 "using `filter_map` when a more succinct alternative exists"
1117 declare_clippy_lint! {
1118 /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
1121 /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
1122 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1123 /// `iter_mut` directly.
1125 /// **Known problems:** None
1131 /// let _ = (&vec![3, 4, 5]).into_iter();
1134 /// let _ = (&vec![3, 4, 5]).iter();
1136 pub INTO_ITER_ON_REF,
1138 "using `.into_iter()` on a reference"
1141 declare_clippy_lint! {
1142 /// **What it does:** Checks for calls to `map` followed by a `count`.
1144 /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
1145 /// If the `map` call is intentional, this should be rewritten. Or, if you intend to
1146 /// drive the iterator to completion, you can just use `for_each` instead.
1148 /// **Known problems:** None
1153 /// let _ = (0..3).map(|x| x + 2).count();
1157 "suspicious usage of map"
1160 declare_clippy_lint! {
1161 /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1163 /// **Why is this bad?** For most types, this is undefined behavior.
1165 /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1166 /// of `MaybeUninit`. There may be other types that allow uninitialized
1167 /// data, but those are not yet rigorously defined.
1172 /// // Beware the UB
1173 /// use std::mem::MaybeUninit;
1175 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1178 /// Note that the following is OK:
1181 /// use std::mem::MaybeUninit;
1183 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1184 /// MaybeUninit::uninit().assume_init()
1187 pub UNINIT_ASSUMED_INIT,
1189 "`MaybeUninit::uninit().assume_init()`"
1192 declare_clippy_lint! {
1193 /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1195 /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1200 /// # let y: u32 = 0;
1201 /// # let x: u32 = 100;
1202 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1203 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1206 /// can be written using dedicated methods for saturating addition/subtraction as:
1209 /// # let y: u32 = 0;
1210 /// # let x: u32 = 100;
1211 /// let add = x.saturating_add(y);
1212 /// let sub = x.saturating_sub(y);
1214 pub MANUAL_SATURATING_ARITHMETIC,
1216 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1219 declare_clippy_lint! {
1220 /// **What it does:** Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1221 /// zero-sized types
1223 /// **Why is this bad?** This is a no-op, and likely unintended
1225 /// **Known problems:** None
1229 /// unsafe { (&() as *const ()).offset(1) };
1233 "Check for offset calculations on raw pointers to zero-sized types"
1236 declare_clippy_lint! {
1237 /// **What it does:** Checks for `FileType::is_file()`.
1239 /// **Why is this bad?** When people testing a file type with `FileType::is_file`
1240 /// they are testing whether a path is something they can get bytes from. But
1241 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1242 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1248 /// let metadata = std::fs::metadata("foo.txt")?;
1249 /// let filetype = metadata.file_type();
1251 /// if filetype.is_file() {
1254 /// # Ok::<_, std::io::Error>(())
1258 /// should be written as:
1262 /// let metadata = std::fs::metadata("foo.txt")?;
1263 /// let filetype = metadata.file_type();
1265 /// if !filetype.is_dir() {
1268 /// # Ok::<_, std::io::Error>(())
1271 pub FILETYPE_IS_FILE,
1273 "`FileType::is_file` is not recommended to test for readable file type"
1276 declare_clippy_lint! {
1277 /// **What it does:** Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1279 /// **Why is this bad?** Readability, this can be written more concisely as a
1280 /// single method call.
1282 /// **Known problems:** None.
1286 /// # let opt = Some("".to_string());
1287 /// opt.as_ref().map(String::as_str)
1290 /// Can be written as
1292 /// # let opt = Some("".to_string());
1296 pub OPTION_AS_REF_DEREF,
1298 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1301 declare_clippy_lint! {
1302 /// **What it does:** Checks for usage of `iter().next()` on a Slice or an Array
1304 /// **Why is this bad?** These can be shortened into `.get()`
1306 /// **Known problems:** None.
1310 /// # let a = [1, 2, 3];
1311 /// # let b = vec![1, 2, 3];
1312 /// a[2..].iter().next();
1313 /// b.iter().next();
1315 /// should be written as:
1317 /// # let a = [1, 2, 3];
1318 /// # let b = vec![1, 2, 3];
1322 pub ITER_NEXT_SLICE,
1324 "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1327 declare_clippy_lint! {
1328 /// **What it does:** Warns when using `push_str` with a single-character string literal,
1329 /// and `push` with a `char` would work fine.
1331 /// **Why is this bad?** It's less clear that we are pushing a single character.
1333 /// **Known problems:** None
1337 /// let mut string = String::new();
1338 /// string.push_str("R");
1340 /// Could be written as
1342 /// let mut string = String::new();
1343 /// string.push('R');
1345 pub SINGLE_CHAR_PUSH_STR,
1347 "`push_str()` used with a single-character string literal as parameter"
1350 declare_clippy_lint! {
1351 /// **What it does:** As the counterpart to `or_fun_call`, this lint looks for unnecessary
1352 /// lazily evaluated closures on `Option` and `Result`.
1354 /// This lint suggests changing the following functions, when eager evaluation results in
1356 /// - `unwrap_or_else` to `unwrap_or`
1357 /// - `and_then` to `and`
1358 /// - `or_else` to `or`
1359 /// - `get_or_insert_with` to `get_or_insert`
1360 /// - `ok_or_else` to `ok_or`
1362 /// **Why is this bad?** Using eager evaluation is shorter and simpler in some cases.
1364 /// **Known problems:** It is possible, but not recommended for `Deref` and `Index` to have
1365 /// side effects. Eagerly evaluating them can change the semantics of the program.
1370 /// // example code where clippy issues a warning
1371 /// let opt: Option<u32> = None;
1373 /// opt.unwrap_or_else(|| 42);
1377 /// let opt: Option<u32> = None;
1379 /// opt.unwrap_or(42);
1381 pub UNNECESSARY_LAZY_EVALUATIONS,
1383 "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1386 declare_lint_pass!(Methods => [
1389 SHOULD_IMPLEMENT_TRAIT,
1390 WRONG_SELF_CONVENTION,
1391 WRONG_PUB_SELF_CONVENTION,
1394 RESULT_MAP_OR_INTO_OPTION,
1396 BIND_INSTEAD_OF_MAP,
1404 INEFFICIENT_TO_STRING,
1406 SINGLE_CHAR_PATTERN,
1407 SINGLE_CHAR_PUSH_STR,
1409 TEMPORARY_CSTRING_AS_PTR,
1417 ITERATOR_STEP_BY_ZERO,
1423 STRING_EXTEND_CHARS,
1424 ITER_CLONED_COLLECT,
1427 UNNECESSARY_FILTER_MAP,
1430 UNINIT_ASSUMED_INIT,
1431 MANUAL_SATURATING_ARITHMETIC,
1434 OPTION_AS_REF_DEREF,
1435 UNNECESSARY_LAZY_EVALUATIONS,
1438 impl<'tcx> LateLintPass<'tcx> for Methods {
1439 #[allow(clippy::too_many_lines)]
1440 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1441 if in_macro(expr.span) {
1445 let (method_names, arg_lists, method_spans) = method_calls(expr, 2);
1446 let method_names: Vec<SymbolStr> = method_names.iter().map(|s| s.as_str()).collect();
1447 let method_names: Vec<&str> = method_names.iter().map(|s| &**s).collect();
1449 match method_names.as_slice() {
1450 ["unwrap", "get"] => lint_get_unwrap(cx, expr, arg_lists[1], false),
1451 ["unwrap", "get_mut"] => lint_get_unwrap(cx, expr, arg_lists[1], true),
1452 ["unwrap", ..] => lint_unwrap(cx, expr, arg_lists[0]),
1453 ["expect", "ok"] => lint_ok_expect(cx, expr, arg_lists[1]),
1454 ["expect", ..] => lint_expect(cx, expr, arg_lists[0]),
1455 ["unwrap_or", "map"] => option_map_unwrap_or::lint(cx, expr, arg_lists[1], arg_lists[0], method_spans[1]),
1456 ["unwrap_or_else", "map"] => {
1457 if !lint_map_unwrap_or_else(cx, expr, arg_lists[1], arg_lists[0]) {
1458 unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "unwrap_or");
1461 ["map_or", ..] => lint_map_or_none(cx, expr, arg_lists[0]),
1462 ["and_then", ..] => {
1463 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::lint(cx, expr, arg_lists[0]);
1464 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::lint(cx, expr, arg_lists[0]);
1465 if !biom_option_linted && !biom_result_linted {
1466 unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "and");
1469 ["or_else", ..] => {
1470 if !bind_instead_of_map::ResultOrElseErrInfo::lint(cx, expr, arg_lists[0]) {
1471 unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "or");
1474 ["next", "filter"] => lint_filter_next(cx, expr, arg_lists[1]),
1475 ["next", "skip_while"] => lint_skip_while_next(cx, expr, arg_lists[1]),
1476 ["next", "iter"] => lint_iter_next(cx, expr, arg_lists[1]),
1477 ["map", "filter"] => lint_filter_map(cx, expr, arg_lists[1], arg_lists[0]),
1478 ["map", "filter_map"] => lint_filter_map_map(cx, expr, arg_lists[1], arg_lists[0]),
1479 ["next", "filter_map"] => lint_filter_map_next(cx, expr, arg_lists[1]),
1480 ["map", "find"] => lint_find_map(cx, expr, arg_lists[1], arg_lists[0]),
1481 ["flat_map", "filter"] => lint_filter_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1482 ["flat_map", "filter_map"] => lint_filter_map_flat_map(cx, expr, arg_lists[1], arg_lists[0]),
1483 ["flat_map", ..] => lint_flat_map_identity(cx, expr, arg_lists[0], method_spans[0]),
1484 ["flatten", "map"] => lint_map_flatten(cx, expr, arg_lists[1]),
1485 ["is_some", "find"] => lint_search_is_some(cx, expr, "find", arg_lists[1], arg_lists[0], method_spans[1]),
1486 ["is_some", "position"] => {
1487 lint_search_is_some(cx, expr, "position", arg_lists[1], arg_lists[0], method_spans[1])
1489 ["is_some", "rposition"] => {
1490 lint_search_is_some(cx, expr, "rposition", arg_lists[1], arg_lists[0], method_spans[1])
1492 ["extend", ..] => lint_extend(cx, expr, arg_lists[0]),
1493 ["as_ptr", "unwrap" | "expect"] => lint_cstring_as_ptr(cx, expr, &arg_lists[1][0], &arg_lists[0][0]),
1494 ["nth", "iter"] => lint_iter_nth(cx, expr, &arg_lists, false),
1495 ["nth", "iter_mut"] => lint_iter_nth(cx, expr, &arg_lists, true),
1496 ["nth", ..] => lint_iter_nth_zero(cx, expr, arg_lists[0]),
1497 ["step_by", ..] => lint_step_by(cx, expr, arg_lists[0]),
1498 ["next", "skip"] => lint_iter_skip_next(cx, expr, arg_lists[1]),
1499 ["collect", "cloned"] => lint_iter_cloned_collect(cx, expr, arg_lists[1]),
1500 ["as_ref"] => lint_asref(cx, expr, "as_ref", arg_lists[0]),
1501 ["as_mut"] => lint_asref(cx, expr, "as_mut", arg_lists[0]),
1502 ["fold", ..] => lint_unnecessary_fold(cx, expr, arg_lists[0], method_spans[0]),
1503 ["filter_map", ..] => unnecessary_filter_map::lint(cx, expr, arg_lists[0]),
1504 ["count", "map"] => lint_suspicious_map(cx, expr),
1505 ["assume_init"] => lint_maybe_uninit(cx, &arg_lists[0][0], expr),
1506 ["unwrap_or", arith @ ("checked_add" | "checked_sub" | "checked_mul")] => {
1507 manual_saturating_arithmetic::lint(cx, expr, &arg_lists, &arith["checked_".len()..])
1509 ["add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub"] => {
1510 check_pointer_offset(cx, expr, arg_lists[0])
1512 ["is_file", ..] => lint_filetype_is_file(cx, expr, arg_lists[0]),
1513 ["map", "as_ref"] => lint_option_as_ref_deref(cx, expr, arg_lists[1], arg_lists[0], false),
1514 ["map", "as_mut"] => lint_option_as_ref_deref(cx, expr, arg_lists[1], arg_lists[0], true),
1515 ["unwrap_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "unwrap_or"),
1516 ["get_or_insert_with", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "get_or_insert"),
1517 ["ok_or_else", ..] => unnecessary_lazy_eval::lint(cx, expr, arg_lists[0], "ok_or"),
1522 hir::ExprKind::MethodCall(ref method_call, ref method_span, ref args, _) => {
1523 lint_or_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1524 lint_expect_fun_call(cx, expr, *method_span, &method_call.ident.as_str(), args);
1526 let self_ty = cx.typeck_results().expr_ty_adjusted(&args[0]);
1527 if args.len() == 1 && method_call.ident.name == sym!(clone) {
1528 lint_clone_on_copy(cx, expr, &args[0], self_ty);
1529 lint_clone_on_ref_ptr(cx, expr, &args[0]);
1531 if args.len() == 1 && method_call.ident.name == sym!(to_string) {
1532 inefficient_to_string::lint(cx, expr, &args[0], self_ty);
1535 if let Some(fn_def_id) = cx.typeck_results().type_dependent_def_id(expr.hir_id) {
1536 if match_def_path(cx, fn_def_id, &paths::PUSH_STR) {
1537 lint_single_char_push_string(cx, expr, args);
1541 match self_ty.kind() {
1542 ty::Ref(_, ty, _) if *ty.kind() == ty::Str => {
1543 for &(method, pos) in &PATTERN_METHODS {
1544 if method_call.ident.name.as_str() == method && args.len() > pos {
1545 lint_single_char_pattern(cx, expr, &args[pos]);
1549 ty::Ref(..) if method_call.ident.name == sym!(into_iter) => {
1550 lint_into_iter(cx, expr, self_ty, *method_span);
1555 hir::ExprKind::Binary(op, ref lhs, ref rhs)
1556 if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne =>
1558 let mut info = BinaryExprInfo {
1562 eq: op.node == hir::BinOpKind::Eq,
1564 lint_binary_expr_with_method_call(cx, &mut info);
1570 #[allow(clippy::too_many_lines)]
1571 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1572 if in_external_macro(cx.sess(), impl_item.span) {
1575 let name = impl_item.ident.name.as_str();
1576 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id);
1577 let item = cx.tcx.hir().expect_item(parent);
1578 let def_id = cx.tcx.hir().local_def_id(item.hir_id);
1579 let self_ty = cx.tcx.type_of(def_id);
1581 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1582 if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir().body(id)).next();
1583 if let hir::ItemKind::Impl{ of_trait: None, .. } = item.kind;
1585 let method_def_id = cx.tcx.hir().local_def_id(impl_item.hir_id);
1586 let method_sig = cx.tcx.fn_sig(method_def_id);
1587 let method_sig = cx.tcx.erase_late_bound_regions(&method_sig);
1589 let first_arg_ty = &method_sig.inputs().iter().next();
1591 // check conventions w.r.t. conversion method names and predicates
1592 if let Some(first_arg_ty) = first_arg_ty;
1595 if cx.access_levels.is_exported(impl_item.hir_id) {
1596 // check missing trait implementations
1597 for method_config in &TRAIT_METHODS {
1598 if name == method_config.method_name &&
1599 sig.decl.inputs.len() == method_config.param_count &&
1600 method_config.output_type.matches(cx, &sig.decl.output) &&
1601 method_config.self_kind.matches(cx, self_ty, first_arg_ty) &&
1602 fn_header_equals(method_config.fn_header, sig.header) &&
1603 method_config.lifetime_param_cond(&impl_item)
1607 SHOULD_IMPLEMENT_TRAIT,
1610 "method `{}` can be confused for the standard trait method `{}::{}`",
1611 method_config.method_name,
1612 method_config.trait_name,
1613 method_config.method_name
1617 "consider implementing the trait `{}` or choosing a less ambiguous method name",
1618 method_config.trait_name
1625 if let Some((ref conv, self_kinds)) = &CONVENTIONS
1627 .find(|(ref conv, _)| conv.check(&name))
1629 if !self_kinds.iter().any(|k| k.matches(cx, self_ty, first_arg_ty)) {
1630 let lint = if item.vis.node.is_pub() {
1631 WRONG_PUB_SELF_CONVENTION
1633 WRONG_SELF_CONVENTION
1640 &format!("methods called `{}` usually take {}; consider choosing a less ambiguous name",
1644 .map(|k| k.description())
1645 .collect::<Vec<_>>()
1654 // if this impl block implements a trait, lint in trait definition instead
1655 if let hir::ItemKind::Impl { of_trait: Some(_), .. } = item.kind {
1659 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
1660 let ret_ty = return_ty(cx, impl_item.hir_id);
1662 // walk the return type and check for Self (this does not check associated types)
1663 if contains_ty(ret_ty, self_ty) {
1667 // if return type is impl trait, check the associated types
1668 if let ty::Opaque(def_id, _) = *ret_ty.kind() {
1669 // one of the associated types must be Self
1670 for &(predicate, _span) in cx.tcx.predicates_of(def_id).predicates {
1671 if let ty::PredicateAtom::Projection(projection_predicate) = predicate.skip_binders() {
1672 // walk the associated type and check for Self
1673 if contains_ty(projection_predicate.ty, self_ty) {
1680 if name == "new" && !TyS::same_type(ret_ty, self_ty) {
1685 "methods called `new` usually return `Self`",
1691 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1693 if !in_external_macro(cx.tcx.sess, item.span);
1694 if item.ident.name == sym!(new);
1695 if let TraitItemKind::Fn(_, _) = item.kind;
1696 let ret_ty = return_ty(cx, item.hir_id);
1697 let self_ty = TraitRef::identity(cx.tcx, item.hir_id.owner.to_def_id()).self_ty();
1698 if !contains_ty(ret_ty, self_ty);
1705 "methods called `new` usually return `Self`",
1712 /// Checks for the `OR_FUN_CALL` lint.
1713 #[allow(clippy::too_many_lines)]
1714 fn lint_or_fun_call<'tcx>(
1715 cx: &LateContext<'tcx>,
1716 expr: &hir::Expr<'_>,
1719 args: &'tcx [hir::Expr<'_>],
1721 /// Checks for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
1722 fn check_unwrap_or_default(
1723 cx: &LateContext<'_>,
1725 fun: &hir::Expr<'_>,
1726 self_expr: &hir::Expr<'_>,
1727 arg: &hir::Expr<'_>,
1733 if name == "unwrap_or";
1734 if let hir::ExprKind::Path(ref qpath) = fun.kind;
1735 let path = &*last_path_segment(qpath).ident.as_str();
1736 if ["default", "new"].contains(&path);
1737 let arg_ty = cx.typeck_results().expr_ty(arg);
1738 if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT);
1739 if implements_trait(cx, arg_ty, default_trait_id, &[]);
1742 let mut applicability = Applicability::MachineApplicable;
1747 &format!("use of `{}` followed by a call to `{}`", name, path),
1750 "{}.unwrap_or_default()",
1751 snippet_with_applicability(cx, self_expr.span, "_", &mut applicability)
1763 /// Checks for `*or(foo())`.
1764 #[allow(clippy::too_many_arguments)]
1765 fn check_general_case<'tcx>(
1766 cx: &LateContext<'tcx>,
1770 self_expr: &hir::Expr<'_>,
1771 arg: &'tcx hir::Expr<'_>,
1775 if let hir::ExprKind::MethodCall(ref path, _, ref args, _) = &arg.kind {
1776 if path.ident.as_str() == "len" {
1777 let ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
1780 ty::Slice(_) | ty::Array(_, _) => return,
1784 if is_type_diagnostic_item(cx, ty, sym!(vec_type)) {
1790 // (path, fn_has_argument, methods, suffix)
1791 let know_types: &[(&[_], _, &[_], _)] = &[
1792 (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
1793 (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
1794 (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
1795 (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
1799 if know_types.iter().any(|k| k.2.contains(&name));
1801 if is_lazyness_candidate(cx, arg);
1802 if !contains_return(&arg);
1804 let self_ty = cx.typeck_results().expr_ty(self_expr);
1806 if let Some(&(_, fn_has_arguments, poss, suffix)) =
1807 know_types.iter().find(|&&i| match_type(cx, self_ty, i.0));
1809 if poss.contains(&name);
1812 let sugg: Cow<'_, _> = match (fn_has_arguments, !or_has_args) {
1813 (true, _) => format!("|_| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1814 (false, false) => format!("|| {}", snippet_with_macro_callsite(cx, arg.span, "..")).into(),
1815 (false, true) => snippet_with_macro_callsite(cx, fun_span, ".."),
1817 let span_replace_word = method_span.with_hi(span.hi());
1822 &format!("use of `{}` followed by a function call", name),
1824 format!("{}_{}({})", name, suffix, sugg),
1825 Applicability::HasPlaceholders,
1831 if args.len() == 2 {
1832 match args[1].kind {
1833 hir::ExprKind::Call(ref fun, ref or_args) => {
1834 let or_has_args = !or_args.is_empty();
1835 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
1848 hir::ExprKind::MethodCall(_, span, ref or_args, _) => check_general_case(
1855 !or_args.is_empty(),
1863 /// Checks for the `EXPECT_FUN_CALL` lint.
1864 #[allow(clippy::too_many_lines)]
1865 fn lint_expect_fun_call(
1866 cx: &LateContext<'_>,
1867 expr: &hir::Expr<'_>,
1870 args: &[hir::Expr<'_>],
1872 // Strip `&`, `as_ref()` and `as_str()` off `arg` until we're left with either a `String` or
1874 fn get_arg_root<'a>(cx: &LateContext<'_>, arg: &'a hir::Expr<'a>) -> &'a hir::Expr<'a> {
1875 let mut arg_root = arg;
1877 arg_root = match &arg_root.kind {
1878 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr) => expr,
1879 hir::ExprKind::MethodCall(method_name, _, call_args, _) => {
1880 if call_args.len() == 1
1881 && (method_name.ident.name == sym!(as_str) || method_name.ident.name == sym!(as_ref))
1883 let arg_type = cx.typeck_results().expr_ty(&call_args[0]);
1884 let base_type = arg_type.peel_refs();
1885 *base_type.kind() == ty::Str || is_type_diagnostic_item(cx, base_type, sym!(string_type))
1899 // Only `&'static str` or `String` can be used directly in the `panic!`. Other types should be
1900 // converted to string.
1901 fn requires_to_string(cx: &LateContext<'_>, arg: &hir::Expr<'_>) -> bool {
1902 let arg_ty = cx.typeck_results().expr_ty(arg);
1903 if is_type_diagnostic_item(cx, arg_ty, sym!(string_type)) {
1906 if let ty::Ref(_, ty, ..) = arg_ty.kind() {
1907 if *ty.kind() == ty::Str && can_be_static_str(cx, arg) {
1914 // Check if an expression could have type `&'static str`, knowing that it
1915 // has type `&str` for some lifetime.
1916 fn can_be_static_str(cx: &LateContext<'_>, arg: &hir::Expr<'_>) -> bool {
1918 hir::ExprKind::Lit(_) => true,
1919 hir::ExprKind::Call(fun, _) => {
1920 if let hir::ExprKind::Path(ref p) = fun.kind {
1921 match cx.qpath_res(p, fun.hir_id) {
1922 hir::def::Res::Def(hir::def::DefKind::Fn | hir::def::DefKind::AssocFn, def_id) => matches!(
1923 cx.tcx.fn_sig(def_id).output().skip_binder().kind(),
1924 ty::Ref(ty::ReStatic, ..)
1932 hir::ExprKind::MethodCall(..) => {
1934 .type_dependent_def_id(arg.hir_id)
1935 .map_or(false, |method_id| {
1937 cx.tcx.fn_sig(method_id).output().skip_binder().kind(),
1938 ty::Ref(ty::ReStatic, ..)
1942 hir::ExprKind::Path(ref p) => matches!(
1943 cx.qpath_res(p, arg.hir_id),
1944 hir::def::Res::Def(hir::def::DefKind::Const | hir::def::DefKind::Static, _)
1950 fn generate_format_arg_snippet(
1951 cx: &LateContext<'_>,
1953 applicability: &mut Applicability,
1956 if let hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, ref format_arg) = a.kind;
1957 if let hir::ExprKind::Match(ref format_arg_expr, _, _) = format_arg.kind;
1958 if let hir::ExprKind::Tup(ref format_arg_expr_tup) = format_arg_expr.kind;
1963 .map(|a| snippet_with_applicability(cx, a.span, "..", applicability).into_owned())
1971 fn is_call(node: &hir::ExprKind<'_>) -> bool {
1973 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, _, expr) => {
1976 hir::ExprKind::Call(..)
1977 | hir::ExprKind::MethodCall(..)
1978 // These variants are debatable or require further examination
1979 | hir::ExprKind::Match(..)
1980 | hir::ExprKind::Block{ .. } => true,
1985 if args.len() != 2 || name != "expect" || !is_call(&args[1].kind) {
1989 let receiver_type = cx.typeck_results().expr_ty_adjusted(&args[0]);
1990 let closure_args = if is_type_diagnostic_item(cx, receiver_type, sym!(option_type)) {
1992 } else if is_type_diagnostic_item(cx, receiver_type, sym!(result_type)) {
1998 let arg_root = get_arg_root(cx, &args[1]);
2000 let span_replace_word = method_span.with_hi(expr.span.hi());
2002 let mut applicability = Applicability::MachineApplicable;
2004 //Special handling for `format!` as arg_root
2006 if let hir::ExprKind::Block(block, None) = &arg_root.kind;
2007 if block.stmts.len() == 1;
2008 if let hir::StmtKind::Local(local) = &block.stmts[0].kind;
2009 if let Some(arg_root) = &local.init;
2010 if let hir::ExprKind::Call(ref inner_fun, ref inner_args) = arg_root.kind;
2011 if is_expn_of(inner_fun.span, "format").is_some() && inner_args.len() == 1;
2012 if let hir::ExprKind::Call(_, format_args) = &inner_args[0].kind;
2014 let fmt_spec = &format_args[0];
2015 let fmt_args = &format_args[1];
2017 let mut args = vec![snippet(cx, fmt_spec.span, "..").into_owned()];
2019 args.extend(generate_format_arg_snippet(cx, fmt_args, &mut applicability));
2021 let sugg = args.join(", ");
2027 &format!("use of `{}` followed by a function call", name),
2029 format!("unwrap_or_else({} panic!({}))", closure_args, sugg),
2037 let mut arg_root_snippet: Cow<'_, _> = snippet_with_applicability(cx, arg_root.span, "..", &mut applicability);
2038 if requires_to_string(cx, arg_root) {
2039 arg_root_snippet.to_mut().push_str(".to_string()");
2046 &format!("use of `{}` followed by a function call", name),
2048 format!("unwrap_or_else({} {{ panic!({}) }})", closure_args, arg_root_snippet),
2053 /// Checks for the `CLONE_ON_COPY` lint.
2054 fn lint_clone_on_copy(cx: &LateContext<'_>, expr: &hir::Expr<'_>, arg: &hir::Expr<'_>, arg_ty: Ty<'_>) {
2055 let ty = cx.typeck_results().expr_ty(expr);
2056 if let ty::Ref(_, inner, _) = arg_ty.kind() {
2057 if let ty::Ref(_, innermost, _) = inner.kind() {
2062 "using `clone` on a double-reference; \
2063 this will copy the reference instead of cloning the inner type",
2065 if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
2066 let mut ty = innermost;
2068 while let ty::Ref(_, inner, _) = ty.kind() {
2072 let refs: String = iter::repeat('&').take(n + 1).collect();
2073 let derefs: String = iter::repeat('*').take(n).collect();
2074 let explicit = format!("<{}{}>::clone({})", refs, ty, snip);
2075 diag.span_suggestion(
2077 "try dereferencing it",
2078 format!("{}({}{}).clone()", refs, derefs, snip.deref()),
2079 Applicability::MaybeIncorrect,
2081 diag.span_suggestion(
2083 "or try being explicit if you are sure, that you want to clone a reference",
2085 Applicability::MaybeIncorrect,
2090 return; // don't report clone_on_copy
2094 if is_copy(cx, ty) {
2096 if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
2097 let parent = cx.tcx.hir().get_parent_node(expr.hir_id);
2098 match &cx.tcx.hir().get(parent) {
2099 hir::Node::Expr(parent) => match parent.kind {
2100 // &*x is a nop, &x.clone() is not
2101 hir::ExprKind::AddrOf(..) => return,
2102 // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
2103 hir::ExprKind::MethodCall(_, _, parent_args, _) if expr.hir_id == parent_args[0].hir_id => {
2109 hir::Node::Stmt(stmt) => {
2110 if let hir::StmtKind::Local(ref loc) = stmt.kind {
2111 if let hir::PatKind::Ref(..) = loc.pat.kind {
2112 // let ref y = *x borrows x, let ref y = x.clone() does not
2120 // x.clone() might have dereferenced x, possibly through Deref impls
2121 if cx.typeck_results().expr_ty(arg) == ty {
2122 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
2124 let deref_count = cx
2126 .expr_adjustments(arg)
2128 .filter(|adj| matches!(adj.kind, ty::adjustment::Adjust::Deref(_)))
2130 let derefs: String = iter::repeat('*').take(deref_count).collect();
2131 snip = Some(("try dereferencing it", format!("{}{}", derefs, snippet)));
2136 span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |diag| {
2137 if let Some((text, snip)) = snip {
2138 diag.span_suggestion(expr.span, text, snip, Applicability::MachineApplicable);
2144 fn lint_clone_on_ref_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>, arg: &hir::Expr<'_>) {
2145 let obj_ty = cx.typeck_results().expr_ty(arg).peel_refs();
2147 if let ty::Adt(_, subst) = obj_ty.kind() {
2148 let caller_type = if is_type_diagnostic_item(cx, obj_ty, sym::Rc) {
2150 } else if is_type_diagnostic_item(cx, obj_ty, sym::Arc) {
2152 } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
2158 let snippet = snippet_with_macro_callsite(cx, arg.span, "_");
2164 "using `.clone()` on a ref-counted pointer",
2166 format!("{}::<{}>::clone(&{})", caller_type, subst.type_at(0), snippet),
2167 Applicability::Unspecified, // Sometimes unnecessary ::<_> after Rc/Arc/Weak
2172 fn lint_string_extend(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
2174 if let Some(arglists) = method_chain_args(arg, &["chars"]) {
2175 let target = &arglists[0][0];
2176 let self_ty = cx.typeck_results().expr_ty(target).peel_refs();
2177 let ref_str = if *self_ty.kind() == ty::Str {
2179 } else if is_type_diagnostic_item(cx, self_ty, sym!(string_type)) {
2185 let mut applicability = Applicability::MachineApplicable;
2188 STRING_EXTEND_CHARS,
2190 "calling `.extend(_.chars())`",
2193 "{}.push_str({}{})",
2194 snippet_with_applicability(cx, args[0].span, "_", &mut applicability),
2196 snippet_with_applicability(cx, target.span, "_", &mut applicability)
2203 fn lint_extend(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
2204 let obj_ty = cx.typeck_results().expr_ty(&args[0]).peel_refs();
2205 if is_type_diagnostic_item(cx, obj_ty, sym!(string_type)) {
2206 lint_string_extend(cx, expr, args);
2210 fn lint_cstring_as_ptr(cx: &LateContext<'_>, expr: &hir::Expr<'_>, source: &hir::Expr<'_>, unwrap: &hir::Expr<'_>) {
2212 let source_type = cx.typeck_results().expr_ty(source);
2213 if let ty::Adt(def, substs) = source_type.kind();
2214 if cx.tcx.is_diagnostic_item(sym!(result_type), def.did);
2215 if match_type(cx, substs.type_at(0), &paths::CSTRING);
2219 TEMPORARY_CSTRING_AS_PTR,
2221 "you are getting the inner pointer of a temporary `CString`",
2223 diag.note("that pointer will be invalid outside this expression");
2224 diag.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
2230 fn lint_iter_cloned_collect<'tcx>(cx: &LateContext<'tcx>, expr: &hir::Expr<'_>, iter_args: &'tcx [hir::Expr<'_>]) {
2232 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(expr), sym!(vec_type));
2233 if let Some(slice) = derefs_to_slice(cx, &iter_args[0], cx.typeck_results().expr_ty(&iter_args[0]));
2234 if let Some(to_replace) = expr.span.trim_start(slice.span.source_callsite());
2239 ITER_CLONED_COLLECT,
2241 "called `iter().cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
2244 ".to_vec()".to_string(),
2245 Applicability::MachineApplicable,
2251 fn lint_unnecessary_fold(cx: &LateContext<'_>, expr: &hir::Expr<'_>, fold_args: &[hir::Expr<'_>], fold_span: Span) {
2252 fn check_fold_with_op(
2253 cx: &LateContext<'_>,
2254 expr: &hir::Expr<'_>,
2255 fold_args: &[hir::Expr<'_>],
2258 replacement_method_name: &str,
2259 replacement_has_args: bool,
2262 // Extract the body of the closure passed to fold
2263 if let hir::ExprKind::Closure(_, _, body_id, _, _) = fold_args[2].kind;
2264 let closure_body = cx.tcx.hir().body(body_id);
2265 let closure_expr = remove_blocks(&closure_body.value);
2267 // Check if the closure body is of the form `acc <op> some_expr(x)`
2268 if let hir::ExprKind::Binary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.kind;
2269 if bin_op.node == op;
2271 // Extract the names of the two arguments to the closure
2272 if let Some(first_arg_ident) = get_arg_name(&closure_body.params[0].pat);
2273 if let Some(second_arg_ident) = get_arg_name(&closure_body.params[1].pat);
2275 if match_var(&*left_expr, first_arg_ident);
2276 if replacement_has_args || match_var(&*right_expr, second_arg_ident);
2279 let mut applicability = Applicability::MachineApplicable;
2280 let sugg = if replacement_has_args {
2282 "{replacement}(|{s}| {r})",
2283 replacement = replacement_method_name,
2284 s = second_arg_ident,
2285 r = snippet_with_applicability(cx, right_expr.span, "EXPR", &mut applicability),
2290 replacement = replacement_method_name,
2297 fold_span.with_hi(expr.span.hi()),
2298 // TODO #2371 don't suggest e.g., .any(|x| f(x)) if we can suggest .any(f)
2299 "this `.fold` can be written more succinctly using another method",
2308 // Check that this is a call to Iterator::fold rather than just some function called fold
2309 if !match_trait_method(cx, expr, &paths::ITERATOR) {
2314 fold_args.len() == 3,
2315 "Expected fold_args to have three entries - the receiver, the initial value and the closure"
2318 // Check if the first argument to .fold is a suitable literal
2319 if let hir::ExprKind::Lit(ref lit) = fold_args[1].kind {
2321 ast::LitKind::Bool(false) => {
2322 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Or, "any", true)
2324 ast::LitKind::Bool(true) => {
2325 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::And, "all", true)
2327 ast::LitKind::Int(0, _) => {
2328 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Add, "sum", false)
2330 ast::LitKind::Int(1, _) => {
2331 check_fold_with_op(cx, expr, fold_args, fold_span, hir::BinOpKind::Mul, "product", false)
2338 fn lint_step_by<'tcx>(cx: &LateContext<'tcx>, expr: &hir::Expr<'_>, args: &'tcx [hir::Expr<'_>]) {
2339 if match_trait_method(cx, expr, &paths::ITERATOR) {
2340 if let Some((Constant::Int(0), _)) = constant(cx, cx.typeck_results(), &args[1]) {
2343 ITERATOR_STEP_BY_ZERO,
2345 "Iterator::step_by(0) will panic at runtime",
2351 fn lint_iter_next<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, iter_args: &'tcx [hir::Expr<'_>]) {
2352 let caller_expr = &iter_args[0];
2354 // Skip lint if the `iter().next()` expression is a for loop argument,
2355 // since it is already covered by `&loops::ITER_NEXT_LOOP`
2356 let mut parent_expr_opt = get_parent_expr(cx, expr);
2357 while let Some(parent_expr) = parent_expr_opt {
2358 if higher::for_loop(parent_expr).is_some() {
2361 parent_expr_opt = get_parent_expr(cx, parent_expr);
2364 if derefs_to_slice(cx, caller_expr, cx.typeck_results().expr_ty(caller_expr)).is_some() {
2365 // caller is a Slice
2367 if let hir::ExprKind::Index(ref caller_var, ref index_expr) = &caller_expr.kind;
2368 if let Some(higher::Range { start: Some(start_expr), end: None, limits: ast::RangeLimits::HalfOpen })
2369 = higher::range(index_expr);
2370 if let hir::ExprKind::Lit(ref start_lit) = &start_expr.kind;
2371 if let ast::LitKind::Int(start_idx, _) = start_lit.node;
2373 let mut applicability = Applicability::MachineApplicable;
2378 "using `.iter().next()` on a Slice without end index",
2380 format!("{}.get({})", snippet_with_applicability(cx, caller_var.span, "..", &mut applicability), start_idx),
2385 } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(caller_expr), sym!(vec_type))
2387 &cx.typeck_results().expr_ty(caller_expr).peel_refs().kind(),
2391 // caller is a Vec or an Array
2392 let mut applicability = Applicability::MachineApplicable;
2397 "using `.iter().next()` on an array",
2401 snippet_with_applicability(cx, caller_expr.span, "..", &mut applicability)
2408 fn lint_iter_nth<'tcx>(
2409 cx: &LateContext<'tcx>,
2410 expr: &hir::Expr<'_>,
2411 nth_and_iter_args: &[&'tcx [hir::Expr<'tcx>]],
2414 let iter_args = nth_and_iter_args[1];
2415 let mut_str = if is_mut { "_mut" } else { "" };
2416 let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.typeck_results().expr_ty(&iter_args[0])).is_some() {
2418 } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&iter_args[0]), sym!(vec_type)) {
2420 } else if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&iter_args[0]), sym!(vecdeque_type)) {
2423 let nth_args = nth_and_iter_args[0];
2424 lint_iter_nth_zero(cx, expr, &nth_args);
2425 return; // caller is not a type that we want to lint
2432 &format!("called `.iter{0}().nth()` on a {1}", mut_str, caller_type),
2434 &format!("calling `.get{}()` is both faster and more readable", mut_str),
2438 fn lint_iter_nth_zero<'tcx>(cx: &LateContext<'tcx>, expr: &hir::Expr<'_>, nth_args: &'tcx [hir::Expr<'_>]) {
2440 if match_trait_method(cx, expr, &paths::ITERATOR);
2441 if let Some((Constant::Int(0), _)) = constant(cx, cx.typeck_results(), &nth_args[1]);
2443 let mut applicability = Applicability::MachineApplicable;
2448 "called `.nth(0)` on a `std::iter::Iterator`, when `.next()` is equivalent",
2449 "try calling `.next()` instead of `.nth(0)`",
2450 format!("{}.next()", snippet_with_applicability(cx, nth_args[0].span, "..", &mut applicability)),
2457 fn lint_get_unwrap<'tcx>(cx: &LateContext<'tcx>, expr: &hir::Expr<'_>, get_args: &'tcx [hir::Expr<'_>], is_mut: bool) {
2458 // Note: we don't want to lint `get_mut().unwrap` for `HashMap` or `BTreeMap`,
2459 // because they do not implement `IndexMut`
2460 let mut applicability = Applicability::MachineApplicable;
2461 let expr_ty = cx.typeck_results().expr_ty(&get_args[0]);
2462 let get_args_str = if get_args.len() > 1 {
2463 snippet_with_applicability(cx, get_args[1].span, "_", &mut applicability)
2465 return; // not linting on a .get().unwrap() chain or variant
2468 let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
2469 needs_ref = get_args_str.parse::<usize>().is_ok();
2471 } else if is_type_diagnostic_item(cx, expr_ty, sym!(vec_type)) {
2472 needs_ref = get_args_str.parse::<usize>().is_ok();
2474 } else if is_type_diagnostic_item(cx, expr_ty, sym!(vecdeque_type)) {
2475 needs_ref = get_args_str.parse::<usize>().is_ok();
2477 } else if !is_mut && is_type_diagnostic_item(cx, expr_ty, sym!(hashmap_type)) {
2480 } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
2484 return; // caller is not a type that we want to lint
2487 let mut span = expr.span;
2489 // Handle the case where the result is immediately dereferenced
2490 // by not requiring ref and pulling the dereference into the
2494 if let Some(parent) = get_parent_expr(cx, expr);
2495 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, _) = parent.kind;
2502 let mut_str = if is_mut { "_mut" } else { "" };
2503 let borrow_str = if !needs_ref {
2516 "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
2517 mut_str, caller_type
2523 snippet_with_applicability(cx, get_args[0].span, "_", &mut applicability),
2530 fn lint_iter_skip_next(cx: &LateContext<'_>, expr: &hir::Expr<'_>, skip_args: &[hir::Expr<'_>]) {
2531 // lint if caller of skip is an Iterator
2532 if match_trait_method(cx, expr, &paths::ITERATOR) {
2533 if let [caller, n] = skip_args {
2534 let hint = format!(".nth({})", snippet(cx, n.span, ".."));
2538 expr.span.trim_start(caller.span).unwrap(),
2539 "called `skip(x).next()` on an iterator",
2540 "use `nth` instead",
2542 Applicability::MachineApplicable,
2548 fn derefs_to_slice<'tcx>(
2549 cx: &LateContext<'tcx>,
2550 expr: &'tcx hir::Expr<'tcx>,
2552 ) -> Option<&'tcx hir::Expr<'tcx>> {
2553 fn may_slice<'a>(cx: &LateContext<'a>, ty: Ty<'a>) -> bool {
2555 ty::Slice(_) => true,
2556 ty::Adt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
2557 ty::Adt(..) => is_type_diagnostic_item(cx, ty, sym!(vec_type)),
2558 ty::Array(_, size) => size
2559 .try_eval_usize(cx.tcx, cx.param_env)
2560 .map_or(false, |size| size < 32),
2561 ty::Ref(_, inner, _) => may_slice(cx, inner),
2566 if let hir::ExprKind::MethodCall(ref path, _, ref args, _) = expr.kind {
2567 if path.ident.name == sym!(iter) && may_slice(cx, cx.typeck_results().expr_ty(&args[0])) {
2574 ty::Slice(_) => Some(expr),
2575 ty::Adt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => Some(expr),
2576 ty::Ref(_, inner, _) => {
2577 if may_slice(cx, inner) {
2588 /// lint use of `unwrap()` for `Option`s and `Result`s
2589 fn lint_unwrap(cx: &LateContext<'_>, expr: &hir::Expr<'_>, unwrap_args: &[hir::Expr<'_>]) {
2590 let obj_ty = cx.typeck_results().expr_ty(&unwrap_args[0]).peel_refs();
2592 let mess = if is_type_diagnostic_item(cx, obj_ty, sym!(option_type)) {
2593 Some((UNWRAP_USED, "an Option", "None"))
2594 } else if is_type_diagnostic_item(cx, obj_ty, sym!(result_type)) {
2595 Some((UNWRAP_USED, "a Result", "Err"))
2600 if let Some((lint, kind, none_value)) = mess {
2605 &format!("used `unwrap()` on `{}` value", kind,),
2608 "if you don't want to handle the `{}` case gracefully, consider \
2609 using `expect()` to provide a better panic message",
2616 /// lint use of `expect()` for `Option`s and `Result`s
2617 fn lint_expect(cx: &LateContext<'_>, expr: &hir::Expr<'_>, expect_args: &[hir::Expr<'_>]) {
2618 let obj_ty = cx.typeck_results().expr_ty(&expect_args[0]).peel_refs();
2620 let mess = if is_type_diagnostic_item(cx, obj_ty, sym!(option_type)) {
2621 Some((EXPECT_USED, "an Option", "None"))
2622 } else if is_type_diagnostic_item(cx, obj_ty, sym!(result_type)) {
2623 Some((EXPECT_USED, "a Result", "Err"))
2628 if let Some((lint, kind, none_value)) = mess {
2633 &format!("used `expect()` on `{}` value", kind,),
2635 &format!("if this value is an `{}`, it will panic", none_value,),
2640 /// lint use of `ok().expect()` for `Result`s
2641 fn lint_ok_expect(cx: &LateContext<'_>, expr: &hir::Expr<'_>, ok_args: &[hir::Expr<'_>]) {
2643 // lint if the caller of `ok()` is a `Result`
2644 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&ok_args[0]), sym!(result_type));
2645 let result_type = cx.typeck_results().expr_ty(&ok_args[0]);
2646 if let Some(error_type) = get_error_type(cx, result_type);
2647 if has_debug_impl(error_type, cx);
2654 "called `ok().expect()` on a `Result` value",
2656 "you can call `expect()` directly on the `Result`",
2662 /// lint use of `map().flatten()` for `Iterators` and 'Options'
2663 fn lint_map_flatten<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, map_args: &'tcx [hir::Expr<'_>]) {
2664 // lint if caller of `.map().flatten()` is an Iterator
2665 if match_trait_method(cx, expr, &paths::ITERATOR) {
2666 let map_closure_ty = cx.typeck_results().expr_ty(&map_args[1]);
2667 let is_map_to_option = match map_closure_ty.kind() {
2668 ty::Closure(_, _) | ty::FnDef(_, _) | ty::FnPtr(_) => {
2669 let map_closure_sig = match map_closure_ty.kind() {
2670 ty::Closure(_, substs) => substs.as_closure().sig(),
2671 _ => map_closure_ty.fn_sig(cx.tcx),
2673 let map_closure_return_ty = cx.tcx.erase_late_bound_regions(&map_closure_sig.output());
2674 is_type_diagnostic_item(cx, map_closure_return_ty, sym!(option_type))
2679 let method_to_use = if is_map_to_option {
2680 // `(...).map(...)` has type `impl Iterator<Item=Option<...>>
2683 // `(...).map(...)` has type `impl Iterator<Item=impl Iterator<...>>
2686 let func_snippet = snippet(cx, map_args[1].span, "..");
2687 let hint = format!(".{0}({1})", method_to_use, func_snippet);
2691 expr.span.with_lo(map_args[0].span.hi()),
2692 "called `map(..).flatten()` on an `Iterator`",
2693 &format!("try using `{}` instead", method_to_use),
2695 Applicability::MachineApplicable,
2699 // lint if caller of `.map().flatten()` is an Option
2700 if is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&map_args[0]), sym!(option_type)) {
2701 let func_snippet = snippet(cx, map_args[1].span, "..");
2702 let hint = format!(".and_then({})", func_snippet);
2706 expr.span.with_lo(map_args[0].span.hi()),
2707 "called `map(..).flatten()` on an `Option`",
2708 "try using `and_then` instead",
2710 Applicability::MachineApplicable,
2715 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
2716 /// Return true if lint triggered
2717 fn lint_map_unwrap_or_else<'tcx>(
2718 cx: &LateContext<'tcx>,
2719 expr: &'tcx hir::Expr<'_>,
2720 map_args: &'tcx [hir::Expr<'_>],
2721 unwrap_args: &'tcx [hir::Expr<'_>],
2723 // lint if the caller of `map()` is an `Option`
2724 let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&map_args[0]), sym!(option_type));
2725 let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&map_args[0]), sym!(result_type));
2727 if is_option || is_result {
2728 // Don't make a suggestion that may fail to compile due to mutably borrowing
2729 // the same variable twice.
2730 let map_mutated_vars = mutated_variables(&map_args[0], cx);
2731 let unwrap_mutated_vars = mutated_variables(&unwrap_args[1], cx);
2732 if let (Some(map_mutated_vars), Some(unwrap_mutated_vars)) = (map_mutated_vars, unwrap_mutated_vars) {
2733 if map_mutated_vars.intersection(&unwrap_mutated_vars).next().is_some() {
2741 let msg = if is_option {
2742 "called `map(f).unwrap_or_else(g)` on an `Option` value. This can be done more directly by calling \
2743 `map_or_else(g, f)` instead"
2745 "called `map(f).unwrap_or_else(g)` on a `Result` value. This can be done more directly by calling \
2746 `.map_or_else(g, f)` instead"
2748 // get snippets for args to map() and unwrap_or_else()
2749 let map_snippet = snippet(cx, map_args[1].span, "..");
2750 let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
2751 // lint, with note if neither arg is > 1 line and both map() and
2752 // unwrap_or_else() have the same span
2753 let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
2754 let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
2755 if same_span && !multiline {
2763 "replace `map({0}).unwrap_or_else({1})` with `map_or_else({1}, {0})`",
2764 map_snippet, unwrap_snippet,
2768 } else if same_span && multiline {
2769 span_lint(cx, MAP_UNWRAP_OR, expr.span, msg);
2777 /// lint use of `_.map_or(None, _)` for `Option`s and `Result`s
2778 fn lint_map_or_none<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, map_or_args: &'tcx [hir::Expr<'_>]) {
2779 let is_option = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&map_or_args[0]), sym!(option_type));
2780 let is_result = is_type_diagnostic_item(cx, cx.typeck_results().expr_ty(&map_or_args[0]), sym!(result_type));
2782 // There are two variants of this `map_or` lint:
2783 // (1) using `map_or` as an adapter from `Result<T,E>` to `Option<T>`
2784 // (2) using `map_or` as a combinator instead of `and_then`
2786 // (For this lint) we don't care if any other type calls `map_or`
2787 if !is_option && !is_result {
2791 let (lint_name, msg, instead, hint) = {
2792 let default_arg_is_none = if let hir::ExprKind::Path(ref qpath) = map_or_args[1].kind {
2793 match_qpath(qpath, &paths::OPTION_NONE)
2798 if !default_arg_is_none {
2803 let f_arg_is_some = if let hir::ExprKind::Path(ref qpath) = map_or_args[2].kind {
2804 match_qpath(qpath, &paths::OPTION_SOME)
2810 let self_snippet = snippet(cx, map_or_args[0].span, "..");
2811 let func_snippet = snippet(cx, map_or_args[2].span, "..");
2812 let msg = "called `map_or(None, f)` on an `Option` value. This can be done more directly by calling \
2813 `and_then(f)` instead";
2817 "try using `and_then` instead",
2818 format!("{0}.and_then({1})", self_snippet, func_snippet),
2820 } else if f_arg_is_some {
2821 let msg = "called `map_or(None, Some)` on a `Result` value. This can be done more directly by calling \
2823 let self_snippet = snippet(cx, map_or_args[0].span, "..");
2825 RESULT_MAP_OR_INTO_OPTION,
2827 "try using `ok` instead",
2828 format!("{0}.ok()", self_snippet),
2843 Applicability::MachineApplicable,
2847 /// lint use of `filter().next()` for `Iterators`
2848 fn lint_filter_next<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, filter_args: &'tcx [hir::Expr<'_>]) {
2849 // lint if caller of `.filter().next()` is an Iterator
2850 if match_trait_method(cx, expr, &paths::ITERATOR) {
2851 let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2852 `.find(p)` instead.";
2853 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2854 if filter_snippet.lines().count() <= 1 {
2855 // add note if not multi-line
2862 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
2865 span_lint(cx, FILTER_NEXT, expr.span, msg);
2870 /// lint use of `skip_while().next()` for `Iterators`
2871 fn lint_skip_while_next<'tcx>(
2872 cx: &LateContext<'tcx>,
2873 expr: &'tcx hir::Expr<'_>,
2874 _skip_while_args: &'tcx [hir::Expr<'_>],
2876 // lint if caller of `.skip_while().next()` is an Iterator
2877 if match_trait_method(cx, expr, &paths::ITERATOR) {
2882 "called `skip_while(p).next()` on an `Iterator`",
2884 "this is more succinctly expressed by calling `.find(!p)` instead",
2889 /// lint use of `filter().map()` for `Iterators`
2890 fn lint_filter_map<'tcx>(
2891 cx: &LateContext<'tcx>,
2892 expr: &'tcx hir::Expr<'_>,
2893 _filter_args: &'tcx [hir::Expr<'_>],
2894 _map_args: &'tcx [hir::Expr<'_>],
2896 // lint if caller of `.filter().map()` is an Iterator
2897 if match_trait_method(cx, expr, &paths::ITERATOR) {
2898 let msg = "called `filter(p).map(q)` on an `Iterator`";
2899 let hint = "this is more succinctly expressed by calling `.filter_map(..)` instead";
2900 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2904 /// lint use of `filter_map().next()` for `Iterators`
2905 fn lint_filter_map_next<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>, filter_args: &'tcx [hir::Expr<'_>]) {
2906 if match_trait_method(cx, expr, &paths::ITERATOR) {
2907 let msg = "called `filter_map(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
2908 `.find_map(p)` instead.";
2909 let filter_snippet = snippet(cx, filter_args[1].span, "..");
2910 if filter_snippet.lines().count() <= 1 {
2917 &format!("replace `filter_map({0}).next()` with `find_map({0})`", filter_snippet),
2920 span_lint(cx, FILTER_MAP_NEXT, expr.span, msg);
2925 /// lint use of `find().map()` for `Iterators`
2926 fn lint_find_map<'tcx>(
2927 cx: &LateContext<'tcx>,
2928 expr: &'tcx hir::Expr<'_>,
2929 _find_args: &'tcx [hir::Expr<'_>],
2930 map_args: &'tcx [hir::Expr<'_>],
2932 // lint if caller of `.filter().map()` is an Iterator
2933 if match_trait_method(cx, &map_args[0], &paths::ITERATOR) {
2934 let msg = "called `find(p).map(q)` on an `Iterator`";
2935 let hint = "this is more succinctly expressed by calling `.find_map(..)` instead";
2936 span_lint_and_help(cx, FIND_MAP, expr.span, msg, None, hint);
2940 /// lint use of `filter_map().map()` for `Iterators`
2941 fn lint_filter_map_map<'tcx>(
2942 cx: &LateContext<'tcx>,
2943 expr: &'tcx hir::Expr<'_>,
2944 _filter_args: &'tcx [hir::Expr<'_>],
2945 _map_args: &'tcx [hir::Expr<'_>],
2947 // lint if caller of `.filter().map()` is an Iterator
2948 if match_trait_method(cx, expr, &paths::ITERATOR) {
2949 let msg = "called `filter_map(p).map(q)` on an `Iterator`";
2950 let hint = "this is more succinctly expressed by only calling `.filter_map(..)` instead";
2951 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2955 /// lint use of `filter().flat_map()` for `Iterators`
2956 fn lint_filter_flat_map<'tcx>(
2957 cx: &LateContext<'tcx>,
2958 expr: &'tcx hir::Expr<'_>,
2959 _filter_args: &'tcx [hir::Expr<'_>],
2960 _map_args: &'tcx [hir::Expr<'_>],
2962 // lint if caller of `.filter().flat_map()` is an Iterator
2963 if match_trait_method(cx, expr, &paths::ITERATOR) {
2964 let msg = "called `filter(p).flat_map(q)` on an `Iterator`";
2965 let hint = "this is more succinctly expressed by calling `.flat_map(..)` \
2966 and filtering by returning `iter::empty()`";
2967 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2971 /// lint use of `filter_map().flat_map()` for `Iterators`
2972 fn lint_filter_map_flat_map<'tcx>(
2973 cx: &LateContext<'tcx>,
2974 expr: &'tcx hir::Expr<'_>,
2975 _filter_args: &'tcx [hir::Expr<'_>],
2976 _map_args: &'tcx [hir::Expr<'_>],
2978 // lint if caller of `.filter_map().flat_map()` is an Iterator
2979 if match_trait_method(cx, expr, &paths::ITERATOR) {
2980 let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`";
2981 let hint = "this is more succinctly expressed by calling `.flat_map(..)` \
2982 and filtering by returning `iter::empty()`";
2983 span_lint_and_help(cx, FILTER_MAP, expr.span, msg, None, hint);
2987 /// lint use of `flat_map` for `Iterators` where `flatten` would be sufficient
2988 fn lint_flat_map_identity<'tcx>(
2989 cx: &LateContext<'tcx>,
2990 expr: &'tcx hir::Expr<'_>,
2991 flat_map_args: &'tcx [hir::Expr<'_>],
2992 flat_map_span: Span,
2994 if match_trait_method(cx, expr, &paths::ITERATOR) {
2995 let arg_node = &flat_map_args[1].kind;
2997 let apply_lint = |message: &str| {
3001 flat_map_span.with_hi(expr.span.hi()),
3004 "flatten()".to_string(),
3005 Applicability::MachineApplicable,
3010 if let hir::ExprKind::Closure(_, _, body_id, _, _) = arg_node;
3011 let body = cx.tcx.hir().body(*body_id);
3013 if let hir::PatKind::Binding(_, _, binding_ident, _) = body.params[0].pat.kind;
3014 if let hir::ExprKind::Path(hir::QPath::Resolved(_, ref path)) = body.value.kind;
3016 if path.segments.len() == 1;
3017 if path.segments[0].ident.as_str() == binding_ident.as_str();
3020 apply_lint("called `flat_map(|x| x)` on an `Iterator`");
3025 if let hir::ExprKind::Path(ref qpath) = arg_node;
3027 if match_qpath(qpath, &paths::STD_CONVERT_IDENTITY);
3030 apply_lint("called `flat_map(std::convert::identity)` on an `Iterator`");
3036 /// lint searching an Iterator followed by `is_some()`
3037 fn lint_search_is_some<'tcx>(
3038 cx: &LateContext<'tcx>,
3039 expr: &'tcx hir::Expr<'_>,
3040 search_method: &str,
3041 search_args: &'tcx [hir::Expr<'_>],
3042 is_some_args: &'tcx [hir::Expr<'_>],
3045 // lint if caller of search is an Iterator
3046 if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
3048 "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
3049 expressed by calling `any()`.",
3052 let search_snippet = snippet(cx, search_args[1].span, "..");
3053 if search_snippet.lines().count() <= 1 {
3054 // suggest `any(|x| ..)` instead of `any(|&x| ..)` for `find(|&x| ..).is_some()`
3055 // suggest `any(|..| *..)` instead of `any(|..| **..)` for `find(|..| **..).is_some()`
3056 let any_search_snippet = if_chain! {
3057 if search_method == "find";
3058 if let hir::ExprKind::Closure(_, _, body_id, ..) = search_args[1].kind;
3059 let closure_body = cx.tcx.hir().body(body_id);
3060 if let Some(closure_arg) = closure_body.params.get(0);
3062 if let hir::PatKind::Ref(..) = closure_arg.pat.kind {
3063 Some(search_snippet.replacen('&', "", 1))
3064 } else if let Some(name) = get_arg_name(&closure_arg.pat) {
3065 Some(search_snippet.replace(&format!("*{}", name), &name.as_str()))
3073 // add note if not multi-line
3077 method_span.with_hi(expr.span.hi()),
3082 any_search_snippet.as_ref().map_or(&*search_snippet, String::as_str)
3084 Applicability::MachineApplicable,
3087 span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
3092 /// Used for `lint_binary_expr_with_method_call`.
3093 #[derive(Copy, Clone)]
3094 struct BinaryExprInfo<'a> {
3095 expr: &'a hir::Expr<'a>,
3096 chain: &'a hir::Expr<'a>,
3097 other: &'a hir::Expr<'a>,
3101 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
3102 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
3103 macro_rules! lint_with_both_lhs_and_rhs {
3104 ($func:ident, $cx:expr, $info:ident) => {
3105 if !$func($cx, $info) {
3106 ::std::mem::swap(&mut $info.chain, &mut $info.other);
3107 if $func($cx, $info) {
3114 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
3115 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
3116 lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
3117 lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
3120 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
3122 cx: &LateContext<'_>,
3123 info: &BinaryExprInfo<'_>,
3124 chain_methods: &[&str],
3125 lint: &'static Lint,
3129 if let Some(args) = method_chain_args(info.chain, chain_methods);
3130 if let hir::ExprKind::Call(ref fun, ref arg_char) = info.other.kind;
3131 if arg_char.len() == 1;
3132 if let hir::ExprKind::Path(ref qpath) = fun.kind;
3133 if let Some(segment) = single_segment_path(qpath);
3134 if segment.ident.name == sym!(Some);
3136 let mut applicability = Applicability::MachineApplicable;
3137 let self_ty = cx.typeck_results().expr_ty_adjusted(&args[0][0]).peel_refs();
3139 if *self_ty.kind() != ty::Str {
3147 &format!("you should use the `{}` method", suggest),
3149 format!("{}{}.{}({})",
3150 if info.eq { "" } else { "!" },
3151 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
3153 snippet_with_applicability(cx, arg_char[0].span, "_", &mut applicability)),
3164 /// Checks for the `CHARS_NEXT_CMP` lint.
3165 fn lint_chars_next_cmp<'tcx>(cx: &LateContext<'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3166 lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
3169 /// Checks for the `CHARS_LAST_CMP` lint.
3170 fn lint_chars_last_cmp<'tcx>(cx: &LateContext<'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3171 if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_LAST_CMP, "ends_with") {
3174 lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_LAST_CMP, "ends_with")
3178 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
3179 fn lint_chars_cmp_with_unwrap<'tcx>(
3180 cx: &LateContext<'tcx>,
3181 info: &BinaryExprInfo<'_>,
3182 chain_methods: &[&str],
3183 lint: &'static Lint,
3187 if let Some(args) = method_chain_args(info.chain, chain_methods);
3188 if let hir::ExprKind::Lit(ref lit) = info.other.kind;
3189 if let ast::LitKind::Char(c) = lit.node;
3191 let mut applicability = Applicability::MachineApplicable;
3196 &format!("you should use the `{}` method", suggest),
3198 format!("{}{}.{}('{}')",
3199 if info.eq { "" } else { "!" },
3200 snippet_with_applicability(cx, args[0][0].span, "_", &mut applicability),
3213 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
3214 fn lint_chars_next_cmp_with_unwrap<'tcx>(cx: &LateContext<'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3215 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
3218 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
3219 fn lint_chars_last_cmp_with_unwrap<'tcx>(cx: &LateContext<'tcx>, info: &BinaryExprInfo<'_>) -> bool {
3220 if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
3223 lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
3227 fn get_hint_if_single_char_arg(
3228 cx: &LateContext<'_>,
3229 arg: &hir::Expr<'_>,
3230 applicability: &mut Applicability,
3231 ) -> Option<String> {
3233 if let hir::ExprKind::Lit(lit) = &arg.kind;
3234 if let ast::LitKind::Str(r, style) = lit.node;
3235 let string = r.as_str();
3236 if string.len() == 1;
3238 let snip = snippet_with_applicability(cx, arg.span, &string, applicability);
3239 let ch = if let ast::StrStyle::Raw(nhash) = style {
3240 let nhash = nhash as usize;
3241 // for raw string: r##"a"##
3242 &snip[(nhash + 2)..(snip.len() - 1 - nhash)]
3244 // for regular string: "a"
3245 &snip[1..(snip.len() - 1)]
3247 let hint = format!("'{}'", if ch == "'" { "\\'" } else { ch });
3255 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
3256 fn lint_single_char_pattern(cx: &LateContext<'_>, _expr: &hir::Expr<'_>, arg: &hir::Expr<'_>) {
3257 let mut applicability = Applicability::MachineApplicable;
3258 if let Some(hint) = get_hint_if_single_char_arg(cx, arg, &mut applicability) {
3261 SINGLE_CHAR_PATTERN,
3263 "single-character string constant used as pattern",
3264 "try using a `char` instead",
3271 /// lint for length-1 `str`s as argument for `push_str`
3272 fn lint_single_char_push_string(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
3273 let mut applicability = Applicability::MachineApplicable;
3274 if let Some(extension_string) = get_hint_if_single_char_arg(cx, &args[1], &mut applicability) {
3275 let base_string_snippet = snippet_with_applicability(cx, args[0].span, "_", &mut applicability);
3276 let sugg = format!("{}.push({})", base_string_snippet, extension_string);
3279 SINGLE_CHAR_PUSH_STR,
3281 "calling `push_str()` using a single-character string literal",
3282 "consider using `push` with a character literal",
3289 /// Checks for the `USELESS_ASREF` lint.
3290 fn lint_asref(cx: &LateContext<'_>, expr: &hir::Expr<'_>, call_name: &str, as_ref_args: &[hir::Expr<'_>]) {
3291 // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
3292 // check if the call is to the actual `AsRef` or `AsMut` trait
3293 if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
3294 // check if the type after `as_ref` or `as_mut` is the same as before
3295 let recvr = &as_ref_args[0];
3296 let rcv_ty = cx.typeck_results().expr_ty(recvr);
3297 let res_ty = cx.typeck_results().expr_ty(expr);
3298 let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
3299 let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
3300 if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
3301 // allow the `as_ref` or `as_mut` if it is followed by another method call
3303 if let Some(parent) = get_parent_expr(cx, expr);
3304 if let hir::ExprKind::MethodCall(_, ref span, _, _) = parent.kind;
3305 if span != &expr.span;
3311 let mut applicability = Applicability::MachineApplicable;
3316 &format!("this call to `{}` does nothing", call_name),
3318 snippet_with_applicability(cx, recvr.span, "_", &mut applicability).to_string(),
3325 fn ty_has_iter_method(cx: &LateContext<'_>, self_ref_ty: Ty<'_>) -> Option<(&'static str, &'static str)> {
3326 has_iter_method(cx, self_ref_ty).map(|ty_name| {
3327 let mutbl = match self_ref_ty.kind() {
3328 ty::Ref(_, _, mutbl) => mutbl,
3329 _ => unreachable!(),
3331 let method_name = match mutbl {
3332 hir::Mutability::Not => "iter",
3333 hir::Mutability::Mut => "iter_mut",
3335 (ty_name, method_name)
3339 fn lint_into_iter(cx: &LateContext<'_>, expr: &hir::Expr<'_>, self_ref_ty: Ty<'_>, method_span: Span) {
3340 if !match_trait_method(cx, expr, &paths::INTO_ITERATOR) {
3343 if let Some((kind, method_name)) = ty_has_iter_method(cx, self_ref_ty) {
3349 "this `.into_iter()` call is equivalent to `.{}()` and will not consume the `{}`",
3353 method_name.to_string(),
3354 Applicability::MachineApplicable,
3359 /// lint for `MaybeUninit::uninit().assume_init()` (we already have the latter)
3360 fn lint_maybe_uninit(cx: &LateContext<'_>, expr: &hir::Expr<'_>, outer: &hir::Expr<'_>) {
3362 if let hir::ExprKind::Call(ref callee, ref args) = expr.kind;
3364 if let hir::ExprKind::Path(ref path) = callee.kind;
3365 if match_qpath(path, &paths::MEM_MAYBEUNINIT_UNINIT);
3366 if !is_maybe_uninit_ty_valid(cx, cx.typeck_results().expr_ty_adjusted(outer));
3370 UNINIT_ASSUMED_INIT,
3372 "this call for this type may be undefined behavior"
3378 fn is_maybe_uninit_ty_valid(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
3380 ty::Array(ref component, _) => is_maybe_uninit_ty_valid(cx, component),
3381 ty::Tuple(ref types) => types.types().all(|ty| is_maybe_uninit_ty_valid(cx, ty)),
3382 ty::Adt(ref adt, _) => match_def_path(cx, adt.did, &paths::MEM_MAYBEUNINIT),
3387 fn lint_suspicious_map(cx: &LateContext<'_>, expr: &hir::Expr<'_>) {
3392 "this call to `map()` won't have an effect on the call to `count()`",
3394 "make sure you did not confuse `map` with `filter` or `for_each`",
3398 /// lint use of `_.as_ref().map(Deref::deref)` for `Option`s
3399 fn lint_option_as_ref_deref<'tcx>(
3400 cx: &LateContext<'tcx>,
3401 expr: &hir::Expr<'_>,
3402 as_ref_args: &[hir::Expr<'_>],
3403 map_args: &[hir::Expr<'_>],
3406 let same_mutability = |m| (is_mut && m == &hir::Mutability::Mut) || (!is_mut && m == &hir::Mutability::Not);
3408 let option_ty = cx.typeck_results().expr_ty(&as_ref_args[0]);
3409 if !is_type_diagnostic_item(cx, option_ty, sym!(option_type)) {
3413 let deref_aliases: [&[&str]; 9] = [
3414 &paths::DEREF_TRAIT_METHOD,
3415 &paths::DEREF_MUT_TRAIT_METHOD,
3416 &paths::CSTRING_AS_C_STR,
3417 &paths::OS_STRING_AS_OS_STR,
3418 &paths::PATH_BUF_AS_PATH,
3419 &paths::STRING_AS_STR,
3420 &paths::STRING_AS_MUT_STR,
3421 &paths::VEC_AS_SLICE,
3422 &paths::VEC_AS_MUT_SLICE,
3425 let is_deref = match map_args[1].kind {
3426 hir::ExprKind::Path(ref expr_qpath) => cx
3427 .qpath_res(expr_qpath, map_args[1].hir_id)
3429 .map_or(false, |fun_def_id| {
3430 deref_aliases.iter().any(|path| match_def_path(cx, fun_def_id, path))
3432 hir::ExprKind::Closure(_, _, body_id, _, _) => {
3433 let closure_body = cx.tcx.hir().body(body_id);
3434 let closure_expr = remove_blocks(&closure_body.value);
3436 match &closure_expr.kind {
3437 hir::ExprKind::MethodCall(_, _, args, _) => {
3440 if let hir::ExprKind::Path(qpath) = &args[0].kind;
3441 if let hir::def::Res::Local(local_id) = cx.qpath_res(qpath, args[0].hir_id);
3442 if closure_body.params[0].pat.hir_id == local_id;
3445 .expr_adjustments(&args[0])
3448 .collect::<Box<[_]>>();
3449 if let [ty::adjustment::Adjust::Deref(None), ty::adjustment::Adjust::Borrow(_)] = *adj;
3451 let method_did = cx.typeck_results().type_dependent_def_id(closure_expr.hir_id).unwrap();
3452 deref_aliases.iter().any(|path| match_def_path(cx, method_did, path))
3458 hir::ExprKind::AddrOf(hir::BorrowKind::Ref, m, ref inner) if same_mutability(m) => {
3460 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner1) = inner.kind;
3461 if let hir::ExprKind::Unary(hir::UnOp::UnDeref, ref inner2) = inner1.kind;
3462 if let hir::ExprKind::Path(ref qpath) = inner2.kind;
3463 if let hir::def::Res::Local(local_id) = cx.qpath_res(qpath, inner2.hir_id);
3465 closure_body.params[0].pat.hir_id == local_id
3478 let current_method = if is_mut {
3479 format!(".as_mut().map({})", snippet(cx, map_args[1].span, ".."))
3481 format!(".as_ref().map({})", snippet(cx, map_args[1].span, ".."))
3483 let method_hint = if is_mut { "as_deref_mut" } else { "as_deref" };
3484 let hint = format!("{}.{}()", snippet(cx, as_ref_args[0].span, ".."), method_hint);
3485 let suggestion = format!("try using {} instead", method_hint);
3488 "called `{0}` on an Option value. This can be done more directly \
3489 by calling `{1}` instead",
3490 current_method, hint
3494 OPTION_AS_REF_DEREF,
3499 Applicability::MachineApplicable,
3504 /// Given a `Result<T, E>` type, return its error type (`E`).
3505 fn get_error_type<'a>(cx: &LateContext<'_>, ty: Ty<'a>) -> Option<Ty<'a>> {
3507 ty::Adt(_, substs) if is_type_diagnostic_item(cx, ty, sym!(result_type)) => substs.types().nth(1),
3512 /// This checks whether a given type is known to implement Debug.
3513 fn has_debug_impl<'tcx>(ty: Ty<'tcx>, cx: &LateContext<'tcx>) -> bool {
3515 .get_diagnostic_item(sym::debug_trait)
3516 .map_or(false, |debug| implements_trait(cx, ty, debug, &[]))
3521 StartsWith(&'static str),
3525 const CONVENTIONS: [(Convention, &[SelfKind]); 7] = [
3526 (Convention::Eq("new"), &[SelfKind::No]),
3527 (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
3528 (Convention::StartsWith("from_"), &[SelfKind::No]),
3529 (Convention::StartsWith("into_"), &[SelfKind::Value]),
3530 (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
3531 (Convention::Eq("to_mut"), &[SelfKind::RefMut]),
3532 (Convention::StartsWith("to_"), &[SelfKind::Ref]),
3535 const FN_HEADER: hir::FnHeader = hir::FnHeader {
3536 unsafety: hir::Unsafety::Normal,
3537 constness: hir::Constness::NotConst,
3538 asyncness: hir::IsAsync::NotAsync,
3539 abi: rustc_target::spec::abi::Abi::Rust,
3542 struct ShouldImplTraitCase {
3543 trait_name: &'static str,
3544 method_name: &'static str,
3546 fn_header: hir::FnHeader,
3547 // implicit self kind expected (none, self, &self, ...)
3548 self_kind: SelfKind,
3549 // checks against the output type
3550 output_type: OutType,
3551 // certain methods with explicit lifetimes can't implement the equivalent trait method
3552 lint_explicit_lifetime: bool,
3554 impl ShouldImplTraitCase {
3556 trait_name: &'static str,
3557 method_name: &'static str,
3559 fn_header: hir::FnHeader,
3560 self_kind: SelfKind,
3561 output_type: OutType,
3562 lint_explicit_lifetime: bool,
3563 ) -> ShouldImplTraitCase {
3564 ShouldImplTraitCase {
3571 lint_explicit_lifetime,
3575 fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
3576 self.lint_explicit_lifetime
3577 || !impl_item.generics.params.iter().any(|p| {
3580 hir::GenericParamKind::Lifetime {
3581 kind: hir::LifetimeParamKind::Explicit
3589 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
3590 ShouldImplTraitCase::new("std::ops::Add", "add", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3591 ShouldImplTraitCase::new("std::convert::AsMut", "as_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
3592 ShouldImplTraitCase::new("std::convert::AsRef", "as_ref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
3593 ShouldImplTraitCase::new("std::ops::BitAnd", "bitand", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3594 ShouldImplTraitCase::new("std::ops::BitOr", "bitor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3595 ShouldImplTraitCase::new("std::ops::BitXor", "bitxor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3596 ShouldImplTraitCase::new("std::borrow::Borrow", "borrow", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
3597 ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
3598 ShouldImplTraitCase::new("std::clone::Clone", "clone", 1, FN_HEADER, SelfKind::Ref, OutType::Any, true),
3599 ShouldImplTraitCase::new("std::cmp::Ord", "cmp", 2, FN_HEADER, SelfKind::Ref, OutType::Any, true),
3600 // FIXME: default doesn't work
3601 ShouldImplTraitCase::new("std::default::Default", "default", 0, FN_HEADER, SelfKind::No, OutType::Any, true),
3602 ShouldImplTraitCase::new("std::ops::Deref", "deref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
3603 ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
3604 ShouldImplTraitCase::new("std::ops::Div", "div", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3605 ShouldImplTraitCase::new("std::ops::Drop", "drop", 1, FN_HEADER, SelfKind::RefMut, OutType::Unit, true),
3606 ShouldImplTraitCase::new("std::cmp::PartialEq", "eq", 2, FN_HEADER, SelfKind::Ref, OutType::Bool, true),
3607 ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
3608 ShouldImplTraitCase::new("std::str::FromStr", "from_str", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
3609 ShouldImplTraitCase::new("std::hash::Hash", "hash", 2, FN_HEADER, SelfKind::Ref, OutType::Unit, true),
3610 ShouldImplTraitCase::new("std::ops::Index", "index", 2, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
3611 ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut", 2, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
3612 ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
3613 ShouldImplTraitCase::new("std::ops::Mul", "mul", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3614 ShouldImplTraitCase::new("std::ops::Neg", "neg", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
3615 ShouldImplTraitCase::new("std::iter::Iterator", "next", 1, FN_HEADER, SelfKind::RefMut, OutType::Any, false),
3616 ShouldImplTraitCase::new("std::ops::Not", "not", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
3617 ShouldImplTraitCase::new("std::ops::Rem", "rem", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3618 ShouldImplTraitCase::new("std::ops::Shl", "shl", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3619 ShouldImplTraitCase::new("std::ops::Shr", "shr", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3620 ShouldImplTraitCase::new("std::ops::Sub", "sub", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
3624 const PATTERN_METHODS: [(&str, usize); 17] = [
3632 ("split_terminator", 1),
3633 ("rsplit_terminator", 1),
3638 ("match_indices", 1),
3639 ("rmatch_indices", 1),
3640 ("trim_start_matches", 1),
3641 ("trim_end_matches", 1),
3644 #[derive(Clone, Copy, PartialEq, Debug)]
3653 fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
3654 fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
3655 if ty == parent_ty {
3657 } else if ty.is_box() {
3658 ty.boxed_ty() == parent_ty
3659 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
3660 if let ty::Adt(_, substs) = ty.kind() {
3661 substs.types().next().map_or(false, |t| t == parent_ty)
3670 fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
3671 if let ty::Ref(_, t, m) = *ty.kind() {
3672 return m == mutability && t == parent_ty;
3675 let trait_path = match mutability {
3676 hir::Mutability::Not => &paths::ASREF_TRAIT,
3677 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
3680 let trait_def_id = match get_trait_def_id(cx, trait_path) {
3682 None => return false,
3684 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
3688 Self::Value => matches_value(cx, parent_ty, ty),
3689 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
3690 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
3691 Self::No => ty != parent_ty,
3696 fn description(self) -> &'static str {
3698 Self::Value => "self by value",
3699 Self::Ref => "self by reference",
3700 Self::RefMut => "self by mutable reference",
3701 Self::No => "no self",
3708 fn check(&self, other: &str) -> bool {
3710 Self::Eq(this) => this == other,
3711 Self::StartsWith(this) => other.starts_with(this) && this != other,
3716 impl fmt::Display for Convention {
3717 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> Result<(), fmt::Error> {
3719 Self::Eq(this) => this.fmt(f),
3720 Self::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
3725 #[derive(Clone, Copy)]
3734 fn matches(self, cx: &LateContext<'_>, ty: &hir::FnRetTy<'_>) -> bool {
3735 let is_unit = |ty: &hir::Ty<'_>| SpanlessEq::new(cx).eq_ty_kind(&ty.kind, &hir::TyKind::Tup(&[]));
3737 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
3738 (Self::Unit, &hir::FnRetTy::Return(ref ty)) if is_unit(ty) => true,
3739 (Self::Bool, &hir::FnRetTy::Return(ref ty)) if is_bool(ty) => true,
3740 (Self::Any, &hir::FnRetTy::Return(ref ty)) if !is_unit(ty) => true,
3741 (Self::Ref, &hir::FnRetTy::Return(ref ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
3747 fn is_bool(ty: &hir::Ty<'_>) -> bool {
3748 if let hir::TyKind::Path(ref p) = ty.kind {
3749 match_qpath(p, &["bool"])
3755 // Returns `true` if `expr` contains a return expression
3756 fn contains_return(expr: &hir::Expr<'_>) -> bool {
3757 struct RetCallFinder {
3761 impl<'tcx> intravisit::Visitor<'tcx> for RetCallFinder {
3762 type Map = Map<'tcx>;
3764 fn visit_expr(&mut self, expr: &'tcx hir::Expr<'_>) {
3768 if let hir::ExprKind::Ret(..) = &expr.kind {
3771 intravisit::walk_expr(self, expr);
3775 fn nested_visit_map(&mut self) -> intravisit::NestedVisitorMap<Self::Map> {
3776 intravisit::NestedVisitorMap::None
3780 let mut visitor = RetCallFinder { found: false };
3781 visitor.visit_expr(expr);
3785 fn check_pointer_offset(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
3788 if let ty::RawPtr(ty::TypeAndMut { ref ty, .. }) = cx.typeck_results().expr_ty(&args[0]).kind();
3789 if let Ok(layout) = cx.tcx.layout_of(cx.param_env.and(ty));
3792 span_lint(cx, ZST_OFFSET, expr.span, "offset calculation on zero-sized value");
3797 fn lint_filetype_is_file(cx: &LateContext<'_>, expr: &hir::Expr<'_>, args: &[hir::Expr<'_>]) {
3798 let ty = cx.typeck_results().expr_ty(&args[0]);
3800 if !match_type(cx, ty, &paths::FILE_TYPE) {
3806 let lint_unary: &str;
3807 let help_unary: &str;
3809 if let Some(parent) = get_parent_expr(cx, expr);
3810 if let hir::ExprKind::Unary(op, _) = parent.kind;
3811 if op == hir::UnOp::UnNot;
3824 let lint_msg = format!("`{}FileType::is_file()` only {} regular files", lint_unary, verb);
3825 let help_msg = format!("use `{}FileType::is_dir()` instead", help_unary);
3826 span_lint_and_help(cx, FILETYPE_IS_FILE, span, &lint_msg, None, &help_msg);
3829 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
3830 expected.constness == actual.constness
3831 && expected.unsafety == actual.unsafety
3832 && expected.asyncness == actual.asyncness