1 mod bind_instead_of_map;
2 mod bytes_nth;
3 mod chars_cmp;
4 mod chars_cmp_with_unwrap;
5 mod chars_last_cmp;
6 mod chars_last_cmp_with_unwrap;
7 mod chars_next_cmp;
8 mod chars_next_cmp_with_unwrap;
9 mod clone_on_copy;
10 mod clone_on_ref_ptr;
11 mod cloned_instead_of_copied;
12 mod expect_fun_call;
13 mod expect_used;
14 mod extend_with_drain;
15 mod filetype_is_file;
16 mod filter_map;
17 mod filter_map_identity;
18 mod filter_map_next;
19 mod filter_next;
20 mod flat_map_identity;
21 mod flat_map_option;
22 mod from_iter_instead_of_collect;
23 mod get_unwrap;
24 mod implicit_clone;
25 mod inefficient_to_string;
26 mod inspect_for_each;
27 mod into_iter_on_ref;
28 mod iter_cloned_collect;
29 mod iter_count;
30 mod iter_next_slice;
31 mod iter_nth;
32 mod iter_nth_zero;
33 mod iter_skip_next;
34 mod iterator_step_by_zero;
35 mod manual_saturating_arithmetic;
36 mod manual_split_once;
37 mod manual_str_repeat;
38 mod map_collect_result_unit;
39 mod map_flatten;
40 mod map_identity;
41 mod map_unwrap_or;
42 mod ok_expect;
43 mod option_as_ref_deref;
44 mod option_map_or_none;
45 mod option_map_unwrap_or;
46 mod or_fun_call;
47 mod search_is_some;
48 mod single_char_add_str;
49 mod single_char_insert_string;
50 mod single_char_pattern;
51 mod single_char_push_string;
52 mod skip_while_next;
53 mod string_extend_chars;
54 mod suspicious_map;
55 mod suspicious_splitn;
56 mod uninit_assumed_init;
57 mod unnecessary_filter_map;
58 mod unnecessary_fold;
59 mod unnecessary_lazy_eval;
60 mod unwrap_or_else_default;
61 mod unwrap_used;
62 mod useless_asref;
63 mod utils;
64 mod wrong_self_convention;
65 mod zst_offset;
66
67 use bind_instead_of_map::BindInsteadOfMap;
68 use clippy_utils::consts::{constant, Constant};
69 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
70 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
71 use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
72 use if_chain::if_chain;
73 use rustc_hir as hir;
74 use rustc_hir::def::Res;
75 use rustc_hir::{Expr, ExprKind, PrimTy, QPath, TraitItem, TraitItemKind};
76 use rustc_lint::{LateContext, LateLintPass, LintContext};
77 use rustc_middle::lint::in_external_macro;
78 use rustc_middle::ty::{self, TraitRef, Ty, TyS};
79 use rustc_semver::RustcVersion;
80 use rustc_session::{declare_tool_lint, impl_lint_pass};
81 use rustc_span::symbol::SymbolStr;
82 use rustc_span::{sym, Span};
83 use rustc_typeck::hir_ty_to_ty;
84
85 declare_clippy_lint! {
86 /// ### What it does
87 /// Checks for usages of `cloned()` on an `Iterator` or `Option` where
88 /// `copied()` could be used instead.
89 ///
90 /// ### Why is this bad?
91 /// `copied()` is better because it guarantees that the type being cloned
92 /// implements `Copy`.
93 ///
94 /// ### Example
95 /// ```rust
96 /// [1, 2, 3].iter().cloned();
97 /// ```
98 /// Use instead:
99 /// ```rust
100 /// [1, 2, 3].iter().copied();
101 /// ```
102 pub CLONED_INSTEAD_OF_COPIED,
103 pedantic,
104 "used `cloned` where `copied` could be used instead"
105 }
106
107 declare_clippy_lint! {
108 /// ### What it does
109 /// Checks for usages of `Iterator::flat_map()` where `filter_map()` could be
110 /// used instead.
111 ///
112 /// ### Why is this bad?
113 /// When applicable, `filter_map()` is more clear since it shows that
114 /// `Option` is used to produce 0 or 1 items.
115 ///
116 /// ### Example
117 /// ```rust
118 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().flat_map(|x| x.parse().ok()).collect();
119 /// ```
120 /// Use instead:
121 /// ```rust
122 /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().filter_map(|x| x.parse().ok()).collect();
123 /// ```
124 pub FLAT_MAP_OPTION,
125 pedantic,
126 "used `flat_map` where `filter_map` could be used instead"
127 }
128
129 declare_clippy_lint! {
130 /// ### What it does
131 /// Checks for `.unwrap()` calls on `Option`s and on `Result`s.
132 ///
133 /// ### Why is this bad?
134 /// It is better to handle the `None` or `Err` case,
135 /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
136 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
137 /// `Allow` by default.
138 ///
139 /// `result.unwrap()` will let the thread panic on `Err` values.
140 /// Normally, you want to implement more sophisticated error handling,
141 /// and propagate errors upwards with `?` operator.
142 ///
143 /// Even if you want to panic on errors, not all `Error`s implement good
144 /// messages on display. Therefore, it may be beneficial to look at the places
145 /// where they may get displayed. Activate this lint to do just that.
146 ///
147 /// ### Examples
148 /// ```rust
149 /// # let opt = Some(1);
150 ///
151 /// // Bad
152 /// opt.unwrap();
153 ///
154 /// // Good
155 /// opt.expect("more helpful message");
156 /// ```
157 ///
158 /// // or
159 ///
160 /// ```rust
161 /// # let res: Result<usize, ()> = Ok(1);
162 ///
163 /// // Bad
164 /// res.unwrap();
165 ///
166 /// // Good
167 /// res.expect("more helpful message");
168 /// ```
169 pub UNWRAP_USED,
170 restriction,
171 "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
172 }
173
174 declare_clippy_lint! {
175 /// ### What it does
176 /// Checks for `.expect()` calls on `Option`s and `Result`s.
177 ///
178 /// ### Why is this bad?
179 /// Usually it is better to handle the `None` or `Err` case.
180 /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
181 /// this lint is `Allow` by default.
182 ///
183 /// `result.expect()` will let the thread panic on `Err`
184 /// values. Normally, you want to implement more sophisticated error handling,
185 /// and propagate errors upwards with `?` operator.
186 ///
187 /// ### Examples
188 /// ```rust,ignore
189 /// # let opt = Some(1);
190 ///
191 /// // Bad
192 /// opt.expect("one");
193 ///
194 /// // Good
195 /// let opt = Some(1);
196 /// opt?;
197 /// ```
198 ///
199 /// // or
200 ///
201 /// ```rust
202 /// # let res: Result<usize, ()> = Ok(1);
203 ///
204 /// // Bad
205 /// res.expect("one");
206 ///
207 /// // Good
208 /// res?;
209 /// # Ok::<(), ()>(())
210 /// ```
211 pub EXPECT_USED,
212 restriction,
213 "using `.expect()` on `Result` or `Option`, which might be better handled"
214 }
215
216 declare_clippy_lint! {
217 /// ### What it does
218 /// Checks for methods that should live in a trait
219 /// implementation of a `std` trait (see [llogiq's blog
220 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
221 /// information) instead of an inherent implementation.
222 ///
223 /// ### Why is this bad?
224 /// Implementing the traits improve ergonomics for users of
225 /// the code, often with very little cost. Also people seeing a `mul(...)`
226 /// method
227 /// may expect `*` to work equally, so you should have good reason to disappoint
228 /// them.
229 ///
230 /// ### Example
231 /// ```rust
232 /// struct X;
233 /// impl X {
234 /// fn add(&self, other: &X) -> X {
235 /// // ..
236 /// # X
237 /// }
238 /// }
239 /// ```
240 pub SHOULD_IMPLEMENT_TRAIT,
241 style,
242 "defining a method that should be implementing a std trait"
243 }
244
245 declare_clippy_lint! {
246 /// ### What it does
247 /// Checks for methods with certain name prefixes and which
248 /// doesn't match how self is taken. The actual rules are:
249 ///
250 /// |Prefix |Postfix |`self` taken | `self` type |
251 /// |-------|------------|-----------------------|--------------|
252 /// |`as_` | none |`&self` or `&mut self` | any |
253 /// |`from_`| none | none | any |
254 /// |`into_`| none |`self` | any |
255 /// |`is_` | none |`&self` or none | any |
256 /// |`to_` | `_mut` |`&mut self` | any |
257 /// |`to_` | not `_mut` |`self` | `Copy` |
258 /// |`to_` | not `_mut` |`&self` | not `Copy` |
259 ///
260 /// Note: Clippy doesn't trigger methods with `to_` prefix in:
261 /// - Traits definition.
262 /// Clippy can not tell if a type that implements a trait is `Copy` or not.
263 /// - Traits implementation, when `&self` is taken.
264 /// The method signature is controlled by the trait and often `&self` is required for all types that implement the trait
265 /// (see e.g. the `std::string::ToString` trait).
266 ///
267 /// Clippy allows `Pin<&Self>` and `Pin<&mut Self>` if `&self` and `&mut self` is required.
268 ///
269 /// Please find more info here:
270 /// https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
271 ///
272 /// ### Why is this bad?
273 /// Consistency breeds readability. If you follow the
274 /// conventions, your users won't be surprised that they, e.g., need to supply a
275 /// mutable reference to a `as_..` function.
276 ///
277 /// ### Example
278 /// ```rust
279 /// # struct X;
280 /// impl X {
281 /// fn as_str(self) -> &'static str {
282 /// // ..
283 /// # ""
284 /// }
285 /// }
286 /// ```
287 pub WRONG_SELF_CONVENTION,
288 style,
289 "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
290 }
291
292 declare_clippy_lint! {
293 /// ### What it does
294 /// Checks for usage of `ok().expect(..)`.
295 ///
296 /// ### Why is this bad?
297 /// Because you usually call `expect()` on the `Result`
298 /// directly to get a better error message.
299 ///
300 /// ### Known problems
301 /// The error type needs to implement `Debug`
302 ///
303 /// ### Example
304 /// ```rust
305 /// # let x = Ok::<_, ()>(());
306 ///
307 /// // Bad
308 /// x.ok().expect("why did I do this again?");
309 ///
310 /// // Good
311 /// x.expect("why did I do this again?");
312 /// ```
313 pub OK_EXPECT,
314 style,
315 "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
316 }
317
318 declare_clippy_lint! {
319 /// ### What it does
320 /// Checks for usages of `_.unwrap_or_else(Default::default)` on `Option` and
321 /// `Result` values.
322 ///
323 /// ### Why is this bad?
324 /// Readability, these can be written as `_.unwrap_or_default`, which is
325 /// simpler and more concise.
326 ///
327 /// ### Examples
328 /// ```rust
329 /// # let x = Some(1);
330 ///
331 /// // Bad
332 /// x.unwrap_or_else(Default::default);
333 /// x.unwrap_or_else(u32::default);
334 ///
335 /// // Good
336 /// x.unwrap_or_default();
337 /// ```
338 pub UNWRAP_OR_ELSE_DEFAULT,
339 style,
340 "using `.unwrap_or_else(Default::default)`, which is more succinctly expressed as `.unwrap_or_default()`"
341 }
342
343 declare_clippy_lint! {
344 /// ### What it does
345 /// Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
346 /// `result.map(_).unwrap_or_else(_)`.
347 ///
348 /// ### Why is this bad?
349 /// Readability, these can be written more concisely (resp.) as
350 /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
351 ///
352 /// ### Known problems
353 /// The order of the arguments is not in execution order
354 ///
355 /// ### Examples
356 /// ```rust
357 /// # let x = Some(1);
358 ///
359 /// // Bad
360 /// x.map(|a| a + 1).unwrap_or(0);
361 ///
362 /// // Good
363 /// x.map_or(0, |a| a + 1);
364 /// ```
365 ///
366 /// // or
367 ///
368 /// ```rust
369 /// # let x: Result<usize, ()> = Ok(1);
370 /// # fn some_function(foo: ()) -> usize { 1 }
371 ///
372 /// // Bad
373 /// x.map(|a| a + 1).unwrap_or_else(some_function);
374 ///
375 /// // Good
376 /// x.map_or_else(some_function, |a| a + 1);
377 /// ```
378 pub MAP_UNWRAP_OR,
379 pedantic,
380 "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)`"
381 }
382
383 declare_clippy_lint! {
384 /// ### What it does
385 /// Checks for usage of `_.map_or(None, _)`.
386 ///
387 /// ### Why is this bad?
388 /// Readability, this can be written more concisely as
389 /// `_.and_then(_)`.
390 ///
391 /// ### Known problems
392 /// The order of the arguments is not in execution order.
393 ///
394 /// ### Example
395 /// ```rust
396 /// # let opt = Some(1);
397 ///
398 /// // Bad
399 /// opt.map_or(None, |a| Some(a + 1));
400 ///
401 /// // Good
402 /// opt.and_then(|a| Some(a + 1));
403 /// ```
404 pub OPTION_MAP_OR_NONE,
405 style,
406 "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
407 }
408
409 declare_clippy_lint! {
410 /// ### What it does
411 /// Checks for usage of `_.map_or(None, Some)`.
412 ///
413 /// ### Why is this bad?
414 /// Readability, this can be written more concisely as
415 /// `_.ok()`.
416 ///
417 /// ### Example
418 /// Bad:
419 /// ```rust
420 /// # let r: Result<u32, &str> = Ok(1);
421 /// assert_eq!(Some(1), r.map_or(None, Some));
422 /// ```
423 ///
424 /// Good:
425 /// ```rust
426 /// # let r: Result<u32, &str> = Ok(1);
427 /// assert_eq!(Some(1), r.ok());
428 /// ```
429 pub RESULT_MAP_OR_INTO_OPTION,
430 style,
431 "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
432 }
433
434 declare_clippy_lint! {
435 /// ### What it does
436 /// Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
437 /// `_.or_else(|x| Err(y))`.
438 ///
439 /// ### Why is this bad?
440 /// Readability, this can be written more concisely as
441 /// `_.map(|x| y)` or `_.map_err(|x| y)`.
442 ///
443 /// ### Example
444 /// ```rust
445 /// # fn opt() -> Option<&'static str> { Some("42") }
446 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
447 /// let _ = opt().and_then(|s| Some(s.len()));
448 /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
449 /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
450 /// ```
451 ///
452 /// The correct use would be:
453 ///
454 /// ```rust
455 /// # fn opt() -> Option<&'static str> { Some("42") }
456 /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
457 /// let _ = opt().map(|s| s.len());
458 /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
459 /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
460 /// ```
461 pub BIND_INSTEAD_OF_MAP,
462 complexity,
463 "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
464 }
465
466 declare_clippy_lint! {
467 /// ### What it does
468 /// Checks for usage of `_.filter(_).next()`.
469 ///
470 /// ### Why is this bad?
471 /// Readability, this can be written more concisely as
472 /// `_.find(_)`.
473 ///
474 /// ### Example
475 /// ```rust
476 /// # let vec = vec![1];
477 /// vec.iter().filter(|x| **x == 0).next();
478 /// ```
479 /// Could be written as
480 /// ```rust
481 /// # let vec = vec![1];
482 /// vec.iter().find(|x| **x == 0);
483 /// ```
484 pub FILTER_NEXT,
485 complexity,
486 "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
487 }
488
489 declare_clippy_lint! {
490 /// ### What it does
491 /// Checks for usage of `_.skip_while(condition).next()`.
492 ///
493 /// ### Why is this bad?
494 /// Readability, this can be written more concisely as
495 /// `_.find(!condition)`.
496 ///
497 /// ### Example
498 /// ```rust
499 /// # let vec = vec![1];
500 /// vec.iter().skip_while(|x| **x == 0).next();
501 /// ```
502 /// Could be written as
503 /// ```rust
504 /// # let vec = vec![1];
505 /// vec.iter().find(|x| **x != 0);
506 /// ```
507 pub SKIP_WHILE_NEXT,
508 complexity,
509 "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
510 }
511
512 declare_clippy_lint! {
513 /// ### What it does
514 /// Checks for usage of `_.map(_).flatten(_)` on `Iterator` and `Option`
515 ///
516 /// ### Why is this bad?
517 /// Readability, this can be written more concisely as
518 /// `_.flat_map(_)`
519 ///
520 /// ### Example
521 /// ```rust
522 /// let vec = vec![vec![1]];
523 ///
524 /// // Bad
525 /// vec.iter().map(|x| x.iter()).flatten();
526 ///
527 /// // Good
528 /// vec.iter().flat_map(|x| x.iter());
529 /// ```
530 pub MAP_FLATTEN,
531 pedantic,
532 "using combinations of `flatten` and `map` which can usually be written as a single method call"
533 }
534
535 declare_clippy_lint! {
536 /// ### What it does
537 /// Checks for usage of `_.filter(_).map(_)` that can be written more simply
538 /// as `filter_map(_)`.
539 ///
540 /// ### Why is this bad?
541 /// Redundant code in the `filter` and `map` operations is poor style and
542 /// less performant.
543 ///
544 /// ### Example
545 /// Bad:
546 /// ```rust
547 /// (0_i32..10)
548 /// .filter(|n| n.checked_add(1).is_some())
549 /// .map(|n| n.checked_add(1).unwrap());
550 /// ```
551 ///
552 /// Good:
553 /// ```rust
554 /// (0_i32..10).filter_map(|n| n.checked_add(1));
555 /// ```
556 pub MANUAL_FILTER_MAP,
557 complexity,
558 "using `_.filter(_).map(_)` in a way that can be written more simply as `filter_map(_)`"
559 }
560
561 declare_clippy_lint! {
562 /// ### What it does
563 /// Checks for usage of `_.find(_).map(_)` that can be written more simply
564 /// as `find_map(_)`.
565 ///
566 /// ### Why is this bad?
567 /// Redundant code in the `find` and `map` operations is poor style and
568 /// less performant.
569 ///
570 /// ### Example
571 /// Bad:
572 /// ```rust
573 /// (0_i32..10)
574 /// .find(|n| n.checked_add(1).is_some())
575 /// .map(|n| n.checked_add(1).unwrap());
576 /// ```
577 ///
578 /// Good:
579 /// ```rust
580 /// (0_i32..10).find_map(|n| n.checked_add(1));
581 /// ```
582 pub MANUAL_FIND_MAP,
583 complexity,
584 "using `_.find(_).map(_)` in a way that can be written more simply as `find_map(_)`"
585 }
586
587 declare_clippy_lint! {
588 /// ### What it does
589 /// Checks for usage of `_.filter_map(_).next()`.
590 ///
591 /// ### Why is this bad?
592 /// Readability, this can be written more concisely as
593 /// `_.find_map(_)`.
594 ///
595 /// ### Example
596 /// ```rust
597 /// (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
598 /// ```
599 /// Can be written as
600 ///
601 /// ```rust
602 /// (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
603 /// ```
604 pub FILTER_MAP_NEXT,
605 pedantic,
606 "using combination of `filter_map` and `next` which can usually be written as a single method call"
607 }
608
609 declare_clippy_lint! {
610 /// ### What it does
611 /// Checks for usage of `flat_map(|x| x)`.
612 ///
613 /// ### Why is this bad?
614 /// Readability, this can be written more concisely by using `flatten`.
615 ///
616 /// ### Example
617 /// ```rust
618 /// # let iter = vec![vec![0]].into_iter();
619 /// iter.flat_map(|x| x);
620 /// ```
621 /// Can be written as
622 /// ```rust
623 /// # let iter = vec![vec![0]].into_iter();
624 /// iter.flatten();
625 /// ```
626 pub FLAT_MAP_IDENTITY,
627 complexity,
628 "call to `flat_map` where `flatten` is sufficient"
629 }
630
631 declare_clippy_lint! {
632 /// ### What it does
633 /// Checks for an iterator or string search (such as `find()`,
634 /// `position()`, or `rposition()`) followed by a call to `is_some()` or `is_none()`.
635 ///
636 /// ### Why is this bad?
637 /// Readability, this can be written more concisely as:
638 /// * `_.any(_)`, or `_.contains(_)` for `is_some()`,
639 /// * `!_.any(_)`, or `!_.contains(_)` for `is_none()`.
640 ///
641 /// ### Example
642 /// ```rust
643 /// let vec = vec![1];
644 /// vec.iter().find(|x| **x == 0).is_some();
645 ///
646 /// let _ = "hello world".find("world").is_none();
647 /// ```
648 /// Could be written as
649 /// ```rust
650 /// let vec = vec![1];
651 /// vec.iter().any(|x| *x == 0);
652 ///
653 /// let _ = !"hello world".contains("world");
654 /// ```
655 pub SEARCH_IS_SOME,
656 complexity,
657 "using an iterator or string search followed by `is_some()` or `is_none()`, which is more succinctly expressed as a call to `any()` or `contains()` (with negation in case of `is_none()`)"
658 }
659
660 declare_clippy_lint! {
661 /// ### What it does
662 /// Checks for usage of `.chars().next()` on a `str` to check
663 /// if it starts with a given char.
664 ///
665 /// ### Why is this bad?
666 /// Readability, this can be written more concisely as
667 /// `_.starts_with(_)`.
668 ///
669 /// ### Example
670 /// ```rust
671 /// let name = "foo";
672 /// if name.chars().next() == Some('_') {};
673 /// ```
674 /// Could be written as
675 /// ```rust
676 /// let name = "foo";
677 /// if name.starts_with('_') {};
678 /// ```
679 pub CHARS_NEXT_CMP,
680 style,
681 "using `.chars().next()` to check if a string starts with a char"
682 }
683
684 declare_clippy_lint! {
685 /// ### What it does
686 /// Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
687 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
688 /// `unwrap_or_default` instead.
689 ///
690 /// ### Why is this bad?
691 /// The function will always be called and potentially
692 /// allocate an object acting as the default.
693 ///
694 /// ### Known problems
695 /// If the function has side-effects, not calling it will
696 /// change the semantic of the program, but you shouldn't rely on that anyway.
697 ///
698 /// ### Example
699 /// ```rust
700 /// # let foo = Some(String::new());
701 /// foo.unwrap_or(String::new());
702 /// ```
703 /// this can instead be written:
704 /// ```rust
705 /// # let foo = Some(String::new());
706 /// foo.unwrap_or_else(String::new);
707 /// ```
708 /// or
709 /// ```rust
710 /// # let foo = Some(String::new());
711 /// foo.unwrap_or_default();
712 /// ```
713 pub OR_FUN_CALL,
714 perf,
715 "using any `*or` method with a function call, which suggests `*or_else`"
716 }
717
718 declare_clippy_lint! {
719 /// ### What it does
720 /// Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
721 /// etc., and suggests to use `unwrap_or_else` instead
722 ///
723 /// ### Why is this bad?
724 /// The function will always be called.
725 ///
726 /// ### Known problems
727 /// If the function has side-effects, not calling it will
728 /// change the semantics of the program, but you shouldn't rely on that anyway.
729 ///
730 /// ### Example
731 /// ```rust
732 /// # let foo = Some(String::new());
733 /// # let err_code = "418";
734 /// # let err_msg = "I'm a teapot";
735 /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
736 /// ```
737 /// or
738 /// ```rust
739 /// # let foo = Some(String::new());
740 /// # let err_code = "418";
741 /// # let err_msg = "I'm a teapot";
742 /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
743 /// ```
744 /// this can instead be written:
745 /// ```rust
746 /// # let foo = Some(String::new());
747 /// # let err_code = "418";
748 /// # let err_msg = "I'm a teapot";
749 /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
750 /// ```
751 pub EXPECT_FUN_CALL,
752 perf,
753 "using any `expect` method with a function call"
754 }
755
756 declare_clippy_lint! {
757 /// ### What it does
758 /// Checks for usage of `.clone()` on a `Copy` type.
759 ///
760 /// ### Why is this bad?
761 /// The only reason `Copy` types implement `Clone` is for
762 /// generics, not for using the `clone` method on a concrete type.
763 ///
764 /// ### Example
765 /// ```rust
766 /// 42u64.clone();
767 /// ```
768 pub CLONE_ON_COPY,
769 complexity,
770 "using `clone` on a `Copy` type"
771 }
772
773 declare_clippy_lint! {
774 /// ### What it does
775 /// Checks for usage of `.clone()` on a ref-counted pointer,
776 /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
777 /// function syntax instead (e.g., `Rc::clone(foo)`).
778 ///
779 /// ### Why is this bad?
780 /// Calling '.clone()' on an Rc, Arc, or Weak
781 /// can obscure the fact that only the pointer is being cloned, not the underlying
782 /// data.
783 ///
784 /// ### Example
785 /// ```rust
786 /// # use std::rc::Rc;
787 /// let x = Rc::new(1);
788 ///
789 /// // Bad
790 /// x.clone();
791 ///
792 /// // Good
793 /// Rc::clone(&x);
794 /// ```
795 pub CLONE_ON_REF_PTR,
796 restriction,
797 "using 'clone' on a ref-counted pointer"
798 }
799
800 declare_clippy_lint! {
801 /// ### What it does
802 /// Checks for usage of `.clone()` on an `&&T`.
803 ///
804 /// ### Why is this bad?
805 /// Cloning an `&&T` copies the inner `&T`, instead of
806 /// cloning the underlying `T`.
807 ///
808 /// ### Example
809 /// ```rust
810 /// fn main() {
811 /// let x = vec![1];
812 /// let y = &&x;
813 /// let z = y.clone();
814 /// println!("{:p} {:p}", *y, z); // prints out the same pointer
815 /// }
816 /// ```
817 pub CLONE_DOUBLE_REF,
818 correctness,
819 "using `clone` on `&&T`"
820 }
821
822 declare_clippy_lint! {
823 /// ### What it does
824 /// Checks for usage of `.to_string()` on an `&&T` where
825 /// `T` implements `ToString` directly (like `&&str` or `&&String`).
826 ///
827 /// ### Why is this bad?
828 /// This bypasses the specialized implementation of
829 /// `ToString` and instead goes through the more expensive string formatting
830 /// facilities.
831 ///
832 /// ### Example
833 /// ```rust
834 /// // Generic implementation for `T: Display` is used (slow)
835 /// ["foo", "bar"].iter().map(|s| s.to_string());
836 ///
837 /// // OK, the specialized impl is used
838 /// ["foo", "bar"].iter().map(|&s| s.to_string());
839 /// ```
840 pub INEFFICIENT_TO_STRING,
841 pedantic,
842 "using `to_string` on `&&T` where `T: ToString`"
843 }
844
845 declare_clippy_lint! {
846 /// ### What it does
847 /// Checks for `new` not returning a type that contains `Self`.
848 ///
849 /// ### Why is this bad?
850 /// As a convention, `new` methods are used to make a new
851 /// instance of a type.
852 ///
853 /// ### Example
854 /// In an impl block:
855 /// ```rust
856 /// # struct Foo;
857 /// # struct NotAFoo;
858 /// impl Foo {
859 /// fn new() -> NotAFoo {
860 /// # NotAFoo
861 /// }
862 /// }
863 /// ```
864 ///
865 /// ```rust
866 /// # struct Foo;
867 /// struct Bar(Foo);
868 /// impl Foo {
869 /// // Bad. The type name must contain `Self`
870 /// fn new() -> Bar {
871 /// # Bar(Foo)
872 /// }
873 /// }
874 /// ```
875 ///
876 /// ```rust
877 /// # struct Foo;
878 /// # struct FooError;
879 /// impl Foo {
880 /// // Good. Return type contains `Self`
881 /// fn new() -> Result<Foo, FooError> {
882 /// # Ok(Foo)
883 /// }
884 /// }
885 /// ```
886 ///
887 /// Or in a trait definition:
888 /// ```rust
889 /// pub trait Trait {
890 /// // Bad. The type name must contain `Self`
891 /// fn new();
892 /// }
893 /// ```
894 ///
895 /// ```rust
896 /// pub trait Trait {
897 /// // Good. Return type contains `Self`
898 /// fn new() -> Self;
899 /// }
900 /// ```
901 pub NEW_RET_NO_SELF,
902 style,
903 "not returning type containing `Self` in a `new` method"
904 }
905
906 declare_clippy_lint! {
907 /// ### What it does
908 /// Checks for string methods that receive a single-character
909 /// `str` as an argument, e.g., `_.split("x")`.
910 ///
911 /// ### Why is this bad?
912 /// Performing these methods using a `char` is faster than
913 /// using a `str`.
914 ///
915 /// ### Known problems
916 /// Does not catch multi-byte unicode characters.
917 ///
918 /// ### Example
919 /// ```rust,ignore
920 /// // Bad
921 /// _.split("x");
922 ///
923 /// // Good
924 /// _.split('x');
925 pub SINGLE_CHAR_PATTERN,
926 perf,
927 "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
928 }
929
930 declare_clippy_lint! {
931 /// ### What it does
932 /// Checks for calling `.step_by(0)` on iterators which panics.
933 ///
934 /// ### Why is this bad?
935 /// This very much looks like an oversight. Use `panic!()` instead if you
936 /// actually intend to panic.
937 ///
938 /// ### Example
939 /// ```rust,should_panic
940 /// for x in (0..100).step_by(0) {
941 /// //..
942 /// }
943 /// ```
944 pub ITERATOR_STEP_BY_ZERO,
945 correctness,
946 "using `Iterator::step_by(0)`, which will panic at runtime"
947 }
948
949 declare_clippy_lint! {
950 /// ### What it does
951 /// Checks for indirect collection of populated `Option`
952 ///
953 /// ### Why is this bad?
954 /// `Option` is like a collection of 0-1 things, so `flatten`
955 /// automatically does this without suspicious-looking `unwrap` calls.
956 ///
957 /// ### Example
958 /// ```rust
959 /// let _ = std::iter::empty::<Option<i32>>().filter(Option::is_some).map(Option::unwrap);
960 /// ```
961 /// Use instead:
962 /// ```rust
963 /// let _ = std::iter::empty::<Option<i32>>().flatten();
964 /// ```
965 pub OPTION_FILTER_MAP,
966 complexity,
967 "filtering `Option` for `Some` then force-unwrapping, which can be one type-safe operation"
968 }
969
970 declare_clippy_lint! {
971 /// ### What it does
972 /// Checks for the use of `iter.nth(0)`.
973 ///
974 /// ### Why is this bad?
975 /// `iter.next()` is equivalent to
976 /// `iter.nth(0)`, as they both consume the next element,
977 /// but is more readable.
978 ///
979 /// ### Example
980 /// ```rust
981 /// # use std::collections::HashSet;
982 /// // Bad
983 /// # let mut s = HashSet::new();
984 /// # s.insert(1);
985 /// let x = s.iter().nth(0);
986 ///
987 /// // Good
988 /// # let mut s = HashSet::new();
989 /// # s.insert(1);
990 /// let x = s.iter().next();
991 /// ```
992 pub ITER_NTH_ZERO,
993 style,
994 "replace `iter.nth(0)` with `iter.next()`"
995 }
996
997 declare_clippy_lint! {
998 /// ### What it does
999 /// Checks for use of `.iter().nth()` (and the related
1000 /// `.iter_mut().nth()`) on standard library types with *O*(1) element access.
1001 ///
1002 /// ### Why is this bad?
1003 /// `.get()` and `.get_mut()` are more efficient and more
1004 /// readable.
1005 ///
1006 /// ### Example
1007 /// ```rust
1008 /// let some_vec = vec![0, 1, 2, 3];
1009 /// let bad_vec = some_vec.iter().nth(3);
1010 /// let bad_slice = &some_vec[..].iter().nth(3);
1011 /// ```
1012 /// The correct use would be:
1013 /// ```rust
1014 /// let some_vec = vec![0, 1, 2, 3];
1015 /// let bad_vec = some_vec.get(3);
1016 /// let bad_slice = &some_vec[..].get(3);
1017 /// ```
1018 pub ITER_NTH,
1019 perf,
1020 "using `.iter().nth()` on a standard library type with O(1) element access"
1021 }
1022
1023 declare_clippy_lint! {
1024 /// ### What it does
1025 /// Checks for use of `.skip(x).next()` on iterators.
1026 ///
1027 /// ### Why is this bad?
1028 /// `.nth(x)` is cleaner
1029 ///
1030 /// ### Example
1031 /// ```rust
1032 /// let some_vec = vec![0, 1, 2, 3];
1033 /// let bad_vec = some_vec.iter().skip(3).next();
1034 /// let bad_slice = &some_vec[..].iter().skip(3).next();
1035 /// ```
1036 /// The correct use would be:
1037 /// ```rust
1038 /// let some_vec = vec![0, 1, 2, 3];
1039 /// let bad_vec = some_vec.iter().nth(3);
1040 /// let bad_slice = &some_vec[..].iter().nth(3);
1041 /// ```
1042 pub ITER_SKIP_NEXT,
1043 style,
1044 "using `.skip(x).next()` on an iterator"
1045 }
1046
1047 declare_clippy_lint! {
1048 /// ### What it does
1049 /// Checks for use of `.get().unwrap()` (or
1050 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
1051 ///
1052 /// ### Why is this bad?
1053 /// Using the Index trait (`[]`) is more clear and more
1054 /// concise.
1055 ///
1056 /// ### Known problems
1057 /// Not a replacement for error handling: Using either
1058 /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
1059 /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
1060 /// temporary placeholder for dealing with the `Option` type, then this does
1061 /// not mitigate the need for error handling. If there is a chance that `.get()`
1062 /// will be `None` in your program, then it is advisable that the `None` case
1063 /// is handled in a future refactor instead of using `.unwrap()` or the Index
1064 /// trait.
1065 ///
1066 /// ### Example
1067 /// ```rust
1068 /// let mut some_vec = vec![0, 1, 2, 3];
1069 /// let last = some_vec.get(3).unwrap();
1070 /// *some_vec.get_mut(0).unwrap() = 1;
1071 /// ```
1072 /// The correct use would be:
1073 /// ```rust
1074 /// let mut some_vec = vec![0, 1, 2, 3];
1075 /// let last = some_vec[3];
1076 /// some_vec[0] = 1;
1077 /// ```
1078 pub GET_UNWRAP,
1079 restriction,
1080 "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
1081 }
1082
1083 declare_clippy_lint! {
1084 /// ### What it does
1085 /// Checks for occurrences where one vector gets extended instead of append
1086 ///
1087 /// ### Why is this bad?
1088 /// Using `append` instead of `extend` is more concise and faster
1089 ///
1090 /// ### Example
1091 /// ```rust
1092 /// let mut a = vec![1, 2, 3];
1093 /// let mut b = vec![4, 5, 6];
1094 ///
1095 /// // Bad
1096 /// a.extend(b.drain(..));
1097 ///
1098 /// // Good
1099 /// a.append(&mut b);
1100 /// ```
1101 pub EXTEND_WITH_DRAIN,
1102 perf,
1103 "using vec.append(&mut vec) to move the full range of a vecor to another"
1104 }
1105
1106 declare_clippy_lint! {
1107 /// ### What it does
1108 /// Checks for the use of `.extend(s.chars())` where s is a
1109 /// `&str` or `String`.
1110 ///
1111 /// ### Why is this bad?
1112 /// `.push_str(s)` is clearer
1113 ///
1114 /// ### Example
1115 /// ```rust
1116 /// let abc = "abc";
1117 /// let def = String::from("def");
1118 /// let mut s = String::new();
1119 /// s.extend(abc.chars());
1120 /// s.extend(def.chars());
1121 /// ```
1122 /// The correct use would be:
1123 /// ```rust
1124 /// let abc = "abc";
1125 /// let def = String::from("def");
1126 /// let mut s = String::new();
1127 /// s.push_str(abc);
1128 /// s.push_str(&def);
1129 /// ```
1130 pub STRING_EXTEND_CHARS,
1131 style,
1132 "using `x.extend(s.chars())` where s is a `&str` or `String`"
1133 }
1134
1135 declare_clippy_lint! {
1136 /// ### What it does
1137 /// Checks for the use of `.cloned().collect()` on slice to
1138 /// create a `Vec`.
1139 ///
1140 /// ### Why is this bad?
1141 /// `.to_vec()` is clearer
1142 ///
1143 /// ### Example
1144 /// ```rust
1145 /// let s = [1, 2, 3, 4, 5];
1146 /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1147 /// ```
1148 /// The better use would be:
1149 /// ```rust
1150 /// let s = [1, 2, 3, 4, 5];
1151 /// let s2: Vec<isize> = s.to_vec();
1152 /// ```
1153 pub ITER_CLONED_COLLECT,
1154 style,
1155 "using `.cloned().collect()` on slice to create a `Vec`"
1156 }
1157
1158 declare_clippy_lint! {
1159 /// ### What it does
1160 /// Checks for usage of `_.chars().last()` or
1161 /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1162 ///
1163 /// ### Why is this bad?
1164 /// Readability, this can be written more concisely as
1165 /// `_.ends_with(_)`.
1166 ///
1167 /// ### Example
1168 /// ```rust
1169 /// # let name = "_";
1170 ///
1171 /// // Bad
1172 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1173 ///
1174 /// // Good
1175 /// name.ends_with('_') || name.ends_with('-');
1176 /// ```
1177 pub CHARS_LAST_CMP,
1178 style,
1179 "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1180 }
1181
1182 declare_clippy_lint! {
1183 /// ### What it does
1184 /// Checks for usage of `.as_ref()` or `.as_mut()` where the
1185 /// types before and after the call are the same.
1186 ///
1187 /// ### Why is this bad?
1188 /// The call is unnecessary.
1189 ///
1190 /// ### Example
1191 /// ```rust
1192 /// # fn do_stuff(x: &[i32]) {}
1193 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1194 /// do_stuff(x.as_ref());
1195 /// ```
1196 /// The correct use would be:
1197 /// ```rust
1198 /// # fn do_stuff(x: &[i32]) {}
1199 /// let x: &[i32] = &[1, 2, 3, 4, 5];
1200 /// do_stuff(x);
1201 /// ```
1202 pub USELESS_ASREF,
1203 complexity,
1204 "using `as_ref` where the types before and after the call are the same"
1205 }
1206
1207 declare_clippy_lint! {
1208 /// ### What it does
1209 /// Checks for using `fold` when a more succinct alternative exists.
1210 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1211 /// `sum` or `product`.
1212 ///
1213 /// ### Why is this bad?
1214 /// Readability.
1215 ///
1216 /// ### Example
1217 /// ```rust
1218 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1219 /// ```
1220 /// This could be written as:
1221 /// ```rust
1222 /// let _ = (0..3).any(|x| x > 2);
1223 /// ```
1224 pub UNNECESSARY_FOLD,
1225 style,
1226 "using `fold` when a more succinct alternative exists"
1227 }
1228
1229 declare_clippy_lint! {
1230 /// ### What it does
1231 /// Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1232 /// More specifically it checks if the closure provided is only performing one of the
1233 /// filter or map operations and suggests the appropriate option.
1234 ///
1235 /// ### Why is this bad?
1236 /// Complexity. The intent is also clearer if only a single
1237 /// operation is being performed.
1238 ///
1239 /// ### Example
1240 /// ```rust
1241 /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1242 ///
1243 /// // As there is no transformation of the argument this could be written as:
1244 /// let _ = (0..3).filter(|&x| x > 2);
1245 /// ```
1246 ///
1247 /// ```rust
1248 /// let _ = (0..4).filter_map(|x| Some(x + 1));
1249 ///
1250 /// // As there is no conditional check on the argument this could be written as:
1251 /// let _ = (0..4).map(|x| x + 1);
1252 /// ```
1253 pub UNNECESSARY_FILTER_MAP,
1254 complexity,
1255 "using `filter_map` when a more succinct alternative exists"
1256 }
1257
1258 declare_clippy_lint! {
1259 /// ### What it does
1260 /// Checks for `into_iter` calls on references which should be replaced by `iter`
1261 /// or `iter_mut`.
1262 ///
1263 /// ### Why is this bad?
1264 /// Readability. Calling `into_iter` on a reference will not move out its
1265 /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1266 /// `iter_mut` directly.
1267 ///
1268 /// ### Example
1269 /// ```rust
1270 /// // Bad
1271 /// let _ = (&vec![3, 4, 5]).into_iter();
1272 ///
1273 /// // Good
1274 /// let _ = (&vec![3, 4, 5]).iter();
1275 /// ```
1276 pub INTO_ITER_ON_REF,
1277 style,
1278 "using `.into_iter()` on a reference"
1279 }
1280
1281 declare_clippy_lint! {
1282 /// ### What it does
1283 /// Checks for calls to `map` followed by a `count`.
1284 ///
1285 /// ### Why is this bad?
1286 /// It looks suspicious. Maybe `map` was confused with `filter`.
1287 /// If the `map` call is intentional, this should be rewritten
1288 /// using `inspect`. Or, if you intend to drive the iterator to
1289 /// completion, you can just use `for_each` instead.
1290 ///
1291 /// ### Example
1292 /// ```rust
1293 /// let _ = (0..3).map(|x| x + 2).count();
1294 /// ```
1295 pub SUSPICIOUS_MAP,
1296 suspicious,
1297 "suspicious usage of map"
1298 }
1299
1300 declare_clippy_lint! {
1301 /// ### What it does
1302 /// Checks for `MaybeUninit::uninit().assume_init()`.
1303 ///
1304 /// ### Why is this bad?
1305 /// For most types, this is undefined behavior.
1306 ///
1307 /// ### Known problems
1308 /// For now, we accept empty tuples and tuples / arrays
1309 /// of `MaybeUninit`. There may be other types that allow uninitialized
1310 /// data, but those are not yet rigorously defined.
1311 ///
1312 /// ### Example
1313 /// ```rust
1314 /// // Beware the UB
1315 /// use std::mem::MaybeUninit;
1316 ///
1317 /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1318 /// ```
1319 ///
1320 /// Note that the following is OK:
1321 ///
1322 /// ```rust
1323 /// use std::mem::MaybeUninit;
1324 ///
1325 /// let _: [MaybeUninit<bool>; 5] = unsafe {
1326 /// MaybeUninit::uninit().assume_init()
1327 /// };
1328 /// ```
1329 pub UNINIT_ASSUMED_INIT,
1330 correctness,
1331 "`MaybeUninit::uninit().assume_init()`"
1332 }
1333
1334 declare_clippy_lint! {
1335 /// ### What it does
1336 /// Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1337 ///
1338 /// ### Why is this bad?
1339 /// These can be written simply with `saturating_add/sub` methods.
1340 ///
1341 /// ### Example
1342 /// ```rust
1343 /// # let y: u32 = 0;
1344 /// # let x: u32 = 100;
1345 /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1346 /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1347 /// ```
1348 ///
1349 /// can be written using dedicated methods for saturating addition/subtraction as:
1350 ///
1351 /// ```rust
1352 /// # let y: u32 = 0;
1353 /// # let x: u32 = 100;
1354 /// let add = x.saturating_add(y);
1355 /// let sub = x.saturating_sub(y);
1356 /// ```
1357 pub MANUAL_SATURATING_ARITHMETIC,
1358 style,
1359 "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1360 }
1361
1362 declare_clippy_lint! {
1363 /// ### What it does
1364 /// Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1365 /// zero-sized types
1366 ///
1367 /// ### Why is this bad?
1368 /// This is a no-op, and likely unintended
1369 ///
1370 /// ### Example
1371 /// ```rust
1372 /// unsafe { (&() as *const ()).offset(1) };
1373 /// ```
1374 pub ZST_OFFSET,
1375 correctness,
1376 "Check for offset calculations on raw pointers to zero-sized types"
1377 }
1378
1379 declare_clippy_lint! {
1380 /// ### What it does
1381 /// Checks for `FileType::is_file()`.
1382 ///
1383 /// ### Why is this bad?
1384 /// When people testing a file type with `FileType::is_file`
1385 /// they are testing whether a path is something they can get bytes from. But
1386 /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1387 /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1388 ///
1389 /// ### Example
1390 /// ```rust
1391 /// # || {
1392 /// let metadata = std::fs::metadata("foo.txt")?;
1393 /// let filetype = metadata.file_type();
1394 ///
1395 /// if filetype.is_file() {
1396 /// // read file
1397 /// }
1398 /// # Ok::<_, std::io::Error>(())
1399 /// # };
1400 /// ```
1401 ///
1402 /// should be written as:
1403 ///
1404 /// ```rust
1405 /// # || {
1406 /// let metadata = std::fs::metadata("foo.txt")?;
1407 /// let filetype = metadata.file_type();
1408 ///
1409 /// if !filetype.is_dir() {
1410 /// // read file
1411 /// }
1412 /// # Ok::<_, std::io::Error>(())
1413 /// # };
1414 /// ```
1415 pub FILETYPE_IS_FILE,
1416 restriction,
1417 "`FileType::is_file` is not recommended to test for readable file type"
1418 }
1419
1420 declare_clippy_lint! {
1421 /// ### What it does
1422 /// Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1423 ///
1424 /// ### Why is this bad?
1425 /// Readability, this can be written more concisely as
1426 /// `_.as_deref()`.
1427 ///
1428 /// ### Example
1429 /// ```rust
1430 /// # let opt = Some("".to_string());
1431 /// opt.as_ref().map(String::as_str)
1432 /// # ;
1433 /// ```
1434 /// Can be written as
1435 /// ```rust
1436 /// # let opt = Some("".to_string());
1437 /// opt.as_deref()
1438 /// # ;
1439 /// ```
1440 pub OPTION_AS_REF_DEREF,
1441 complexity,
1442 "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1443 }
1444
1445 declare_clippy_lint! {
1446 /// ### What it does
1447 /// Checks for usage of `iter().next()` on a Slice or an Array
1448 ///
1449 /// ### Why is this bad?
1450 /// These can be shortened into `.get()`
1451 ///
1452 /// ### Example
1453 /// ```rust
1454 /// # let a = [1, 2, 3];
1455 /// # let b = vec![1, 2, 3];
1456 /// a[2..].iter().next();
1457 /// b.iter().next();
1458 /// ```
1459 /// should be written as:
1460 /// ```rust
1461 /// # let a = [1, 2, 3];
1462 /// # let b = vec![1, 2, 3];
1463 /// a.get(2);
1464 /// b.get(0);
1465 /// ```
1466 pub ITER_NEXT_SLICE,
1467 style,
1468 "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1469 }
1470
1471 declare_clippy_lint! {
1472 /// ### What it does
1473 /// Warns when using `push_str`/`insert_str` with a single-character string literal
1474 /// where `push`/`insert` with a `char` would work fine.
1475 ///
1476 /// ### Why is this bad?
1477 /// It's less clear that we are pushing a single character.
1478 ///
1479 /// ### Example
1480 /// ```rust
1481 /// let mut string = String::new();
1482 /// string.insert_str(0, "R");
1483 /// string.push_str("R");
1484 /// ```
1485 /// Could be written as
1486 /// ```rust
1487 /// let mut string = String::new();
1488 /// string.insert(0, 'R');
1489 /// string.push('R');
1490 /// ```
1491 pub SINGLE_CHAR_ADD_STR,
1492 style,
1493 "`push_str()` or `insert_str()` used with a single-character string literal as parameter"
1494 }
1495
1496 declare_clippy_lint! {
1497 /// ### What it does
1498 /// As the counterpart to `or_fun_call`, this lint looks for unnecessary
1499 /// lazily evaluated closures on `Option` and `Result`.
1500 ///
1501 /// This lint suggests changing the following functions, when eager evaluation results in
1502 /// simpler code:
1503 /// - `unwrap_or_else` to `unwrap_or`
1504 /// - `and_then` to `and`
1505 /// - `or_else` to `or`
1506 /// - `get_or_insert_with` to `get_or_insert`
1507 /// - `ok_or_else` to `ok_or`
1508 ///
1509 /// ### Why is this bad?
1510 /// Using eager evaluation is shorter and simpler in some cases.
1511 ///
1512 /// ### Known problems
1513 /// It is possible, but not recommended for `Deref` and `Index` to have
1514 /// side effects. Eagerly evaluating them can change the semantics of the program.
1515 ///
1516 /// ### Example
1517 /// ```rust
1518 /// // example code where clippy issues a warning
1519 /// let opt: Option<u32> = None;
1520 ///
1521 /// opt.unwrap_or_else(|| 42);
1522 /// ```
1523 /// Use instead:
1524 /// ```rust
1525 /// let opt: Option<u32> = None;
1526 ///
1527 /// opt.unwrap_or(42);
1528 /// ```
1529 pub UNNECESSARY_LAZY_EVALUATIONS,
1530 style,
1531 "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1532 }
1533
1534 declare_clippy_lint! {
1535 /// ### What it does
1536 /// Checks for usage of `_.map(_).collect::<Result<(), _>()`.
1537 ///
1538 /// ### Why is this bad?
1539 /// Using `try_for_each` instead is more readable and idiomatic.
1540 ///
1541 /// ### Example
1542 /// ```rust
1543 /// (0..3).map(|t| Err(t)).collect::<Result<(), _>>();
1544 /// ```
1545 /// Use instead:
1546 /// ```rust
1547 /// (0..3).try_for_each(|t| Err(t));
1548 /// ```
1549 pub MAP_COLLECT_RESULT_UNIT,
1550 style,
1551 "using `.map(_).collect::<Result<(),_>()`, which can be replaced with `try_for_each`"
1552 }
1553
1554 declare_clippy_lint! {
1555 /// ### What it does
1556 /// Checks for `from_iter()` function calls on types that implement the `FromIterator`
1557 /// trait.
1558 ///
1559 /// ### Why is this bad?
1560 /// It is recommended style to use collect. See
1561 /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
1562 ///
1563 /// ### Example
1564 /// ```rust
1565 /// use std::iter::FromIterator;
1566 ///
1567 /// let five_fives = std::iter::repeat(5).take(5);
1568 ///
1569 /// let v = Vec::from_iter(five_fives);
1570 ///
1571 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1572 /// ```
1573 /// Use instead:
1574 /// ```rust
1575 /// let five_fives = std::iter::repeat(5).take(5);
1576 ///
1577 /// let v: Vec<i32> = five_fives.collect();
1578 ///
1579 /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1580 /// ```
1581 pub FROM_ITER_INSTEAD_OF_COLLECT,
1582 pedantic,
1583 "use `.collect()` instead of `::from_iter()`"
1584 }
1585
1586 declare_clippy_lint! {
1587 /// ### What it does
1588 /// Checks for usage of `inspect().for_each()`.
1589 ///
1590 /// ### Why is this bad?
1591 /// It is the same as performing the computation
1592 /// inside `inspect` at the beginning of the closure in `for_each`.
1593 ///
1594 /// ### Example
1595 /// ```rust
1596 /// [1,2,3,4,5].iter()
1597 /// .inspect(|&x| println!("inspect the number: {}", x))
1598 /// .for_each(|&x| {
1599 /// assert!(x >= 0);
1600 /// });
1601 /// ```
1602 /// Can be written as
1603 /// ```rust
1604 /// [1,2,3,4,5].iter()
1605 /// .for_each(|&x| {
1606 /// println!("inspect the number: {}", x);
1607 /// assert!(x >= 0);
1608 /// });
1609 /// ```
1610 pub INSPECT_FOR_EACH,
1611 complexity,
1612 "using `.inspect().for_each()`, which can be replaced with `.for_each()`"
1613 }
1614
1615 declare_clippy_lint! {
1616 /// ### What it does
1617 /// Checks for usage of `filter_map(|x| x)`.
1618 ///
1619 /// ### Why is this bad?
1620 /// Readability, this can be written more concisely by using `flatten`.
1621 ///
1622 /// ### Example
1623 /// ```rust
1624 /// # let iter = vec![Some(1)].into_iter();
1625 /// iter.filter_map(|x| x);
1626 /// ```
1627 /// Use instead:
1628 /// ```rust
1629 /// # let iter = vec![Some(1)].into_iter();
1630 /// iter.flatten();
1631 /// ```
1632 pub FILTER_MAP_IDENTITY,
1633 complexity,
1634 "call to `filter_map` where `flatten` is sufficient"
1635 }
1636
1637 declare_clippy_lint! {
1638 /// ### What it does
1639 /// Checks for instances of `map(f)` where `f` is the identity function.
1640 ///
1641 /// ### Why is this bad?
1642 /// It can be written more concisely without the call to `map`.
1643 ///
1644 /// ### Example
1645 /// ```rust
1646 /// let x = [1, 2, 3];
1647 /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
1648 /// ```
1649 /// Use instead:
1650 /// ```rust
1651 /// let x = [1, 2, 3];
1652 /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
1653 /// ```
1654 pub MAP_IDENTITY,
1655 complexity,
1656 "using iterator.map(|x| x)"
1657 }
1658
1659 declare_clippy_lint! {
1660 /// ### What it does
1661 /// Checks for the use of `.bytes().nth()`.
1662 ///
1663 /// ### Why is this bad?
1664 /// `.as_bytes().get()` is more efficient and more
1665 /// readable.
1666 ///
1667 /// ### Example
1668 /// ```rust
1669 /// // Bad
1670 /// let _ = "Hello".bytes().nth(3);
1671 ///
1672 /// // Good
1673 /// let _ = "Hello".as_bytes().get(3);
1674 /// ```
1675 pub BYTES_NTH,
1676 style,
1677 "replace `.bytes().nth()` with `.as_bytes().get()`"
1678 }
1679
1680 declare_clippy_lint! {
1681 /// ### What it does
1682 /// Checks for the usage of `_.to_owned()`, `vec.to_vec()`, or similar when calling `_.clone()` would be clearer.
1683 ///
1684 /// ### Why is this bad?
1685 /// These methods do the same thing as `_.clone()` but may be confusing as
1686 /// to why we are calling `to_vec` on something that is already a `Vec` or calling `to_owned` on something that is already owned.
1687 ///
1688 /// ### Example
1689 /// ```rust
1690 /// let a = vec![1, 2, 3];
1691 /// let b = a.to_vec();
1692 /// let c = a.to_owned();
1693 /// ```
1694 /// Use instead:
1695 /// ```rust
1696 /// let a = vec![1, 2, 3];
1697 /// let b = a.clone();
1698 /// let c = a.clone();
1699 /// ```
1700 pub IMPLICIT_CLONE,
1701 pedantic,
1702 "implicitly cloning a value by invoking a function on its dereferenced type"
1703 }
1704
1705 declare_clippy_lint! {
1706 /// ### What it does
1707 /// Checks for the use of `.iter().count()`.
1708 ///
1709 /// ### Why is this bad?
1710 /// `.len()` is more efficient and more
1711 /// readable.
1712 ///
1713 /// ### Example
1714 /// ```rust
1715 /// // Bad
1716 /// let some_vec = vec![0, 1, 2, 3];
1717 /// let _ = some_vec.iter().count();
1718 /// let _ = &some_vec[..].iter().count();
1719 ///
1720 /// // Good
1721 /// let some_vec = vec![0, 1, 2, 3];
1722 /// let _ = some_vec.len();
1723 /// let _ = &some_vec[..].len();
1724 /// ```
1725 pub ITER_COUNT,
1726 complexity,
1727 "replace `.iter().count()` with `.len()`"
1728 }
1729
1730 declare_clippy_lint! {
1731 /// ### What it does
1732 /// Checks for calls to [`splitn`]
1733 /// (https://doc.rust-lang.org/std/primitive.str.html#method.splitn) and
1734 /// related functions with either zero or one splits.
1735 ///
1736 /// ### Why is this bad?
1737 /// These calls don't actually split the value and are
1738 /// likely to be intended as a different number.
1739 ///
1740 /// ### Example
1741 /// ```rust
1742 /// // Bad
1743 /// let s = "";
1744 /// for x in s.splitn(1, ":") {
1745 /// // use x
1746 /// }
1747 ///
1748 /// // Good
1749 /// let s = "";
1750 /// for x in s.splitn(2, ":") {
1751 /// // use x
1752 /// }
1753 /// ```
1754 pub SUSPICIOUS_SPLITN,
1755 correctness,
1756 "checks for `.splitn(0, ..)` and `.splitn(1, ..)`"
1757 }
1758
1759 declare_clippy_lint! {
1760 /// ### What it does
1761 /// Checks for manual implementations of `str::repeat`
1762 ///
1763 /// ### Why is this bad?
1764 /// These are both harder to read, as well as less performant.
1765 ///
1766 /// ### Example
1767 /// ```rust
1768 /// // Bad
1769 /// let x: String = std::iter::repeat('x').take(10).collect();
1770 ///
1771 /// // Good
1772 /// let x: String = "x".repeat(10);
1773 /// ```
1774 pub MANUAL_STR_REPEAT,
1775 perf,
1776 "manual implementation of `str::repeat`"
1777 }
1778
1779 declare_clippy_lint! {
1780 /// ### What it does
1781 /// Checks for usages of `str::splitn(2, _)`
1782 ///
1783 /// ### Why is this bad?
1784 /// `split_once` is both clearer in intent and slightly more efficient.
1785 ///
1786 /// ### Example
1787 /// ```rust,ignore
1788 /// // Bad
1789 /// let (key, value) = _.splitn(2, '=').next_tuple()?;
1790 /// let value = _.splitn(2, '=').nth(1)?;
1791 ///
1792 /// // Good
1793 /// let (key, value) = _.split_once('=')?;
1794 /// let value = _.split_once('=')?.1;
1795 /// ```
1796 pub MANUAL_SPLIT_ONCE,
1797 complexity,
1798 "replace `.splitn(2, pat)` with `.split_once(pat)`"
1799 }
1800
1801 pub struct Methods {
1802 avoid_breaking_exported_api: bool,
1803 msrv: Option<RustcVersion>,
1804 }
1805
1806 impl Methods {
1807 #[must_use]
new(avoid_breaking_exported_api: bool, msrv: Option<RustcVersion>) -> Self1808 pub fn new(avoid_breaking_exported_api: bool, msrv: Option<RustcVersion>) -> Self {
1809 Self {
1810 avoid_breaking_exported_api,
1811 msrv,
1812 }
1813 }
1814 }
1815
1816 impl_lint_pass!(Methods => [
1817 UNWRAP_USED,
1818 EXPECT_USED,
1819 SHOULD_IMPLEMENT_TRAIT,
1820 WRONG_SELF_CONVENTION,
1821 OK_EXPECT,
1822 UNWRAP_OR_ELSE_DEFAULT,
1823 MAP_UNWRAP_OR,
1824 RESULT_MAP_OR_INTO_OPTION,
1825 OPTION_MAP_OR_NONE,
1826 BIND_INSTEAD_OF_MAP,
1827 OR_FUN_CALL,
1828 EXPECT_FUN_CALL,
1829 CHARS_NEXT_CMP,
1830 CHARS_LAST_CMP,
1831 CLONE_ON_COPY,
1832 CLONE_ON_REF_PTR,
1833 CLONE_DOUBLE_REF,
1834 CLONED_INSTEAD_OF_COPIED,
1835 FLAT_MAP_OPTION,
1836 INEFFICIENT_TO_STRING,
1837 NEW_RET_NO_SELF,
1838 SINGLE_CHAR_PATTERN,
1839 SINGLE_CHAR_ADD_STR,
1840 SEARCH_IS_SOME,
1841 FILTER_NEXT,
1842 SKIP_WHILE_NEXT,
1843 FILTER_MAP_IDENTITY,
1844 MAP_IDENTITY,
1845 MANUAL_FILTER_MAP,
1846 MANUAL_FIND_MAP,
1847 OPTION_FILTER_MAP,
1848 FILTER_MAP_NEXT,
1849 FLAT_MAP_IDENTITY,
1850 MAP_FLATTEN,
1851 ITERATOR_STEP_BY_ZERO,
1852 ITER_NEXT_SLICE,
1853 ITER_COUNT,
1854 ITER_NTH,
1855 ITER_NTH_ZERO,
1856 BYTES_NTH,
1857 ITER_SKIP_NEXT,
1858 GET_UNWRAP,
1859 STRING_EXTEND_CHARS,
1860 ITER_CLONED_COLLECT,
1861 USELESS_ASREF,
1862 UNNECESSARY_FOLD,
1863 UNNECESSARY_FILTER_MAP,
1864 INTO_ITER_ON_REF,
1865 SUSPICIOUS_MAP,
1866 UNINIT_ASSUMED_INIT,
1867 MANUAL_SATURATING_ARITHMETIC,
1868 ZST_OFFSET,
1869 FILETYPE_IS_FILE,
1870 OPTION_AS_REF_DEREF,
1871 UNNECESSARY_LAZY_EVALUATIONS,
1872 MAP_COLLECT_RESULT_UNIT,
1873 FROM_ITER_INSTEAD_OF_COLLECT,
1874 INSPECT_FOR_EACH,
1875 IMPLICIT_CLONE,
1876 SUSPICIOUS_SPLITN,
1877 MANUAL_STR_REPEAT,
1878 EXTEND_WITH_DRAIN,
1879 MANUAL_SPLIT_ONCE
1880 ]);
1881
1882 /// Extracts a method call name, args, and `Span` of the method name.
method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(SymbolStr, &'tcx [hir::Expr<'tcx>], Span)>1883 fn method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(SymbolStr, &'tcx [hir::Expr<'tcx>], Span)> {
1884 if let ExprKind::MethodCall(path, span, args, _) = recv.kind {
1885 if !args.iter().any(|e| e.span.from_expansion()) {
1886 return Some((path.ident.name.as_str(), args, span));
1887 }
1888 }
1889 None
1890 }
1891
1892 /// Same as `method_call` but the `SymbolStr` is dereferenced into a temporary `&str`
1893 macro_rules! method_call {
1894 ($expr:expr) => {
1895 method_call($expr)
1896 .as_ref()
1897 .map(|&(ref name, args, span)| (&**name, args, span))
1898 };
1899 }
1900
1901 impl<'tcx> LateLintPass<'tcx> for Methods {
check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>)1902 fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1903 if in_macro(expr.span) {
1904 return;
1905 }
1906
1907 check_methods(cx, expr, self.msrv.as_ref());
1908
1909 match expr.kind {
1910 hir::ExprKind::Call(func, args) => {
1911 from_iter_instead_of_collect::check(cx, expr, args, func);
1912 },
1913 hir::ExprKind::MethodCall(method_call, ref method_span, args, _) => {
1914 or_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1915 expect_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1916 clone_on_copy::check(cx, expr, method_call.ident.name, args);
1917 clone_on_ref_ptr::check(cx, expr, method_call.ident.name, args);
1918 inefficient_to_string::check(cx, expr, method_call.ident.name, args);
1919 single_char_add_str::check(cx, expr, args);
1920 into_iter_on_ref::check(cx, expr, *method_span, method_call.ident.name, args);
1921 single_char_pattern::check(cx, expr, method_call.ident.name, args);
1922 },
1923 hir::ExprKind::Binary(op, lhs, rhs) if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne => {
1924 let mut info = BinaryExprInfo {
1925 expr,
1926 chain: lhs,
1927 other: rhs,
1928 eq: op.node == hir::BinOpKind::Eq,
1929 };
1930 lint_binary_expr_with_method_call(cx, &mut info);
1931 },
1932 _ => (),
1933 }
1934 }
1935
1936 #[allow(clippy::too_many_lines)]
check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>)1937 fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1938 if in_external_macro(cx.sess(), impl_item.span) {
1939 return;
1940 }
1941 let name = impl_item.ident.name.as_str();
1942 let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
1943 let item = cx.tcx.hir().expect_item(parent);
1944 let self_ty = cx.tcx.type_of(item.def_id);
1945
1946 let implements_trait = matches!(item.kind, hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }));
1947 if_chain! {
1948 if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1949 if let Some(first_arg) = iter_input_pats(sig.decl, cx.tcx.hir().body(id)).next();
1950
1951 let method_sig = cx.tcx.fn_sig(impl_item.def_id);
1952 let method_sig = cx.tcx.erase_late_bound_regions(method_sig);
1953
1954 let first_arg_ty = &method_sig.inputs().iter().next();
1955
1956 // check conventions w.r.t. conversion method names and predicates
1957 if let Some(first_arg_ty) = first_arg_ty;
1958
1959 then {
1960 // if this impl block implements a trait, lint in trait definition instead
1961 if !implements_trait && cx.access_levels.is_exported(impl_item.def_id) {
1962 // check missing trait implementations
1963 for method_config in &TRAIT_METHODS {
1964 if name == method_config.method_name &&
1965 sig.decl.inputs.len() == method_config.param_count &&
1966 method_config.output_type.matches(&sig.decl.output) &&
1967 method_config.self_kind.matches(cx, self_ty, first_arg_ty) &&
1968 fn_header_equals(method_config.fn_header, sig.header) &&
1969 method_config.lifetime_param_cond(impl_item)
1970 {
1971 span_lint_and_help(
1972 cx,
1973 SHOULD_IMPLEMENT_TRAIT,
1974 impl_item.span,
1975 &format!(
1976 "method `{}` can be confused for the standard trait method `{}::{}`",
1977 method_config.method_name,
1978 method_config.trait_name,
1979 method_config.method_name
1980 ),
1981 None,
1982 &format!(
1983 "consider implementing the trait `{}` or choosing a less ambiguous method name",
1984 method_config.trait_name
1985 )
1986 );
1987 }
1988 }
1989 }
1990
1991 if sig.decl.implicit_self.has_implicit_self()
1992 && !(self.avoid_breaking_exported_api
1993 && cx.access_levels.is_exported(impl_item.def_id))
1994 {
1995 wrong_self_convention::check(
1996 cx,
1997 &name,
1998 self_ty,
1999 first_arg_ty,
2000 first_arg.pat.span,
2001 implements_trait,
2002 false
2003 );
2004 }
2005 }
2006 }
2007
2008 // if this impl block implements a trait, lint in trait definition instead
2009 if implements_trait {
2010 return;
2011 }
2012
2013 if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
2014 let ret_ty = return_ty(cx, impl_item.hir_id());
2015
2016 // walk the return type and check for Self (this does not check associated types)
2017 if let Some(self_adt) = self_ty.ty_adt_def() {
2018 if contains_adt_constructor(cx.tcx, ret_ty, self_adt) {
2019 return;
2020 }
2021 } else if contains_ty(cx.tcx, ret_ty, self_ty) {
2022 return;
2023 }
2024
2025 // if return type is impl trait, check the associated types
2026 if let ty::Opaque(def_id, _) = *ret_ty.kind() {
2027 // one of the associated types must be Self
2028 for &(predicate, _span) in cx.tcx.explicit_item_bounds(def_id) {
2029 if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
2030 // walk the associated type and check for Self
2031 if let Some(self_adt) = self_ty.ty_adt_def() {
2032 if contains_adt_constructor(cx.tcx, projection_predicate.ty, self_adt) {
2033 return;
2034 }
2035 } else if contains_ty(cx.tcx, projection_predicate.ty, self_ty) {
2036 return;
2037 }
2038 }
2039 }
2040 }
2041
2042 if name == "new" && !TyS::same_type(ret_ty, self_ty) {
2043 span_lint(
2044 cx,
2045 NEW_RET_NO_SELF,
2046 impl_item.span,
2047 "methods called `new` usually return `Self`",
2048 );
2049 }
2050 }
2051 }
2052
check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>)2053 fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
2054 if in_external_macro(cx.tcx.sess, item.span) {
2055 return;
2056 }
2057
2058 if_chain! {
2059 if let TraitItemKind::Fn(ref sig, _) = item.kind;
2060 if sig.decl.implicit_self.has_implicit_self();
2061 if let Some(first_arg_ty) = sig.decl.inputs.iter().next();
2062
2063 then {
2064 let first_arg_span = first_arg_ty.span;
2065 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
2066 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty().skip_binder();
2067 wrong_self_convention::check(
2068 cx,
2069 &item.ident.name.as_str(),
2070 self_ty,
2071 first_arg_ty,
2072 first_arg_span,
2073 false,
2074 true
2075 );
2076 }
2077 }
2078
2079 if_chain! {
2080 if item.ident.name == sym::new;
2081 if let TraitItemKind::Fn(_, _) = item.kind;
2082 let ret_ty = return_ty(cx, item.hir_id());
2083 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty().skip_binder();
2084 if !contains_ty(cx.tcx, ret_ty, self_ty);
2085
2086 then {
2087 span_lint(
2088 cx,
2089 NEW_RET_NO_SELF,
2090 item.span,
2091 "methods called `new` usually return `Self`",
2092 );
2093 }
2094 }
2095 }
2096
2097 extract_msrv_attr!(LateContext);
2098 }
2099
2100 #[allow(clippy::too_many_lines)]
check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>)2101 fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>) {
2102 if let Some((name, [recv, args @ ..], span)) = method_call!(expr) {
2103 match (name, args) {
2104 ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
2105 zst_offset::check(cx, expr, recv);
2106 },
2107 ("and_then", [arg]) => {
2108 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::check(cx, expr, recv, arg);
2109 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::check(cx, expr, recv, arg);
2110 if !biom_option_linted && !biom_result_linted {
2111 unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
2112 }
2113 },
2114 ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
2115 ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
2116 ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
2117 ("cloned", []) => cloned_instead_of_copied::check(cx, expr, recv, span, msrv),
2118 ("collect", []) => match method_call!(recv) {
2119 Some(("cloned", [recv2], _)) => iter_cloned_collect::check(cx, expr, recv2),
2120 Some(("map", [m_recv, m_arg], _)) => {
2121 map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
2122 },
2123 Some(("take", [take_self_arg, take_arg], _)) => {
2124 if meets_msrv(msrv, &msrvs::STR_REPEAT) {
2125 manual_str_repeat::check(cx, expr, recv, take_self_arg, take_arg);
2126 }
2127 },
2128 _ => {},
2129 },
2130 ("count", []) => match method_call!(recv) {
2131 Some((name @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
2132 iter_count::check(cx, expr, recv2, name);
2133 },
2134 Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
2135 _ => {},
2136 },
2137 ("expect", [_]) => match method_call!(recv) {
2138 Some(("ok", [recv], _)) => ok_expect::check(cx, expr, recv),
2139 _ => expect_used::check(cx, expr, recv),
2140 },
2141 ("extend", [arg]) => {
2142 string_extend_chars::check(cx, expr, recv, arg);
2143 extend_with_drain::check(cx, expr, recv, arg);
2144 },
2145 ("filter_map", [arg]) => {
2146 unnecessary_filter_map::check(cx, expr, arg);
2147 filter_map_identity::check(cx, expr, arg, span);
2148 },
2149 ("flat_map", [arg]) => {
2150 flat_map_identity::check(cx, expr, arg, span);
2151 flat_map_option::check(cx, expr, arg, span);
2152 },
2153 ("flatten", []) => {
2154 if let Some(("map", [recv, map_arg], _)) = method_call!(recv) {
2155 map_flatten::check(cx, expr, recv, map_arg);
2156 }
2157 },
2158 ("fold", [init, acc]) => unnecessary_fold::check(cx, expr, init, acc, span),
2159 ("for_each", [_]) => {
2160 if let Some(("inspect", [_, _], span2)) = method_call!(recv) {
2161 inspect_for_each::check(cx, expr, span2);
2162 }
2163 },
2164 ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
2165 ("is_file", []) => filetype_is_file::check(cx, expr, recv),
2166 ("is_none", []) => check_is_some_is_none(cx, expr, recv, false),
2167 ("is_some", []) => check_is_some_is_none(cx, expr, recv, true),
2168 ("map", [m_arg]) => {
2169 if let Some((name, [recv2, args @ ..], span2)) = method_call!(recv) {
2170 match (name, args) {
2171 ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, msrv),
2172 ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, msrv),
2173 ("filter", [f_arg]) => {
2174 filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, false);
2175 },
2176 ("find", [f_arg]) => filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, true),
2177 _ => {},
2178 }
2179 }
2180 map_identity::check(cx, expr, recv, m_arg, span);
2181 },
2182 ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
2183 ("next", []) => {
2184 if let Some((name, [recv, args @ ..], _)) = method_call!(recv) {
2185 match (name, args) {
2186 ("filter", [arg]) => filter_next::check(cx, expr, recv, arg),
2187 ("filter_map", [arg]) => filter_map_next::check(cx, expr, recv, arg, msrv),
2188 ("iter", []) => iter_next_slice::check(cx, expr, recv),
2189 ("skip", [arg]) => iter_skip_next::check(cx, expr, recv, arg),
2190 ("skip_while", [_]) => skip_while_next::check(cx, expr),
2191 _ => {},
2192 }
2193 }
2194 },
2195 ("nth", [n_arg]) => match method_call!(recv) {
2196 Some(("bytes", [recv2], _)) => bytes_nth::check(cx, expr, recv2, n_arg),
2197 Some(("iter", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
2198 Some(("iter_mut", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
2199 _ => iter_nth_zero::check(cx, expr, recv, n_arg),
2200 },
2201 ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
2202 ("or_else", [arg]) => {
2203 if !bind_instead_of_map::ResultOrElseErrInfo::check(cx, expr, recv, arg) {
2204 unnecessary_lazy_eval::check(cx, expr, recv, arg, "or");
2205 }
2206 },
2207 ("splitn" | "rsplitn", [count_arg, pat_arg]) => {
2208 if let Some((Constant::Int(count), _)) = constant(cx, cx.typeck_results(), count_arg) {
2209 suspicious_splitn::check(cx, name, expr, recv, count);
2210 if count == 2 && meets_msrv(msrv, &msrvs::STR_SPLIT_ONCE) {
2211 manual_split_once::check(cx, name, expr, recv, pat_arg);
2212 }
2213 }
2214 },
2215 ("splitn_mut" | "rsplitn_mut", [count_arg, _]) => {
2216 if let Some((Constant::Int(count), _)) = constant(cx, cx.typeck_results(), count_arg) {
2217 suspicious_splitn::check(cx, name, expr, recv, count);
2218 }
2219 },
2220 ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
2221 ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
2222 implicit_clone::check(cx, name, expr, recv, span);
2223 },
2224 ("unwrap", []) => match method_call!(recv) {
2225 Some(("get", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, false),
2226 Some(("get_mut", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, true),
2227 _ => unwrap_used::check(cx, expr, recv),
2228 },
2229 ("unwrap_or", [u_arg]) => match method_call!(recv) {
2230 Some((arith @ ("checked_add" | "checked_sub" | "checked_mul"), [lhs, rhs], _)) => {
2231 manual_saturating_arithmetic::check(cx, expr, lhs, rhs, u_arg, &arith["checked_".len()..]);
2232 },
2233 Some(("map", [m_recv, m_arg], span)) => {
2234 option_map_unwrap_or::check(cx, expr, m_recv, m_arg, recv, u_arg, span);
2235 },
2236 _ => {},
2237 },
2238 ("unwrap_or_else", [u_arg]) => match method_call!(recv) {
2239 Some(("map", [recv, map_arg], _)) if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, msrv) => {},
2240 _ => {
2241 unwrap_or_else_default::check(cx, expr, recv, u_arg);
2242 unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or");
2243 },
2244 },
2245 _ => {},
2246 }
2247 }
2248 }
2249
check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool)2250 fn check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool) {
2251 if let Some((name @ ("find" | "position" | "rposition"), [f_recv, arg], span)) = method_call!(recv) {
2252 search_is_some::check(cx, expr, name, is_some, f_recv, arg, recv, span);
2253 }
2254 }
2255
2256 /// Used for `lint_binary_expr_with_method_call`.
2257 #[derive(Copy, Clone)]
2258 struct BinaryExprInfo<'a> {
2259 expr: &'a hir::Expr<'a>,
2260 chain: &'a hir::Expr<'a>,
2261 other: &'a hir::Expr<'a>,
2262 eq: bool,
2263 }
2264
2265 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>)2266 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
2267 macro_rules! lint_with_both_lhs_and_rhs {
2268 ($func:expr, $cx:expr, $info:ident) => {
2269 if !$func($cx, $info) {
2270 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2271 if $func($cx, $info) {
2272 return;
2273 }
2274 }
2275 };
2276 }
2277
2278 lint_with_both_lhs_and_rhs!(chars_next_cmp::check, cx, info);
2279 lint_with_both_lhs_and_rhs!(chars_last_cmp::check, cx, info);
2280 lint_with_both_lhs_and_rhs!(chars_next_cmp_with_unwrap::check, cx, info);
2281 lint_with_both_lhs_and_rhs!(chars_last_cmp_with_unwrap::check, cx, info);
2282 }
2283
2284 const FN_HEADER: hir::FnHeader = hir::FnHeader {
2285 unsafety: hir::Unsafety::Normal,
2286 constness: hir::Constness::NotConst,
2287 asyncness: hir::IsAsync::NotAsync,
2288 abi: rustc_target::spec::abi::Abi::Rust,
2289 };
2290
2291 struct ShouldImplTraitCase {
2292 trait_name: &'static str,
2293 method_name: &'static str,
2294 param_count: usize,
2295 fn_header: hir::FnHeader,
2296 // implicit self kind expected (none, self, &self, ...)
2297 self_kind: SelfKind,
2298 // checks against the output type
2299 output_type: OutType,
2300 // certain methods with explicit lifetimes can't implement the equivalent trait method
2301 lint_explicit_lifetime: bool,
2302 }
2303 impl ShouldImplTraitCase {
new( trait_name: &'static str, method_name: &'static str, param_count: usize, fn_header: hir::FnHeader, self_kind: SelfKind, output_type: OutType, lint_explicit_lifetime: bool, ) -> ShouldImplTraitCase2304 const fn new(
2305 trait_name: &'static str,
2306 method_name: &'static str,
2307 param_count: usize,
2308 fn_header: hir::FnHeader,
2309 self_kind: SelfKind,
2310 output_type: OutType,
2311 lint_explicit_lifetime: bool,
2312 ) -> ShouldImplTraitCase {
2313 ShouldImplTraitCase {
2314 trait_name,
2315 method_name,
2316 param_count,
2317 fn_header,
2318 self_kind,
2319 output_type,
2320 lint_explicit_lifetime,
2321 }
2322 }
2323
lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool2324 fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
2325 self.lint_explicit_lifetime
2326 || !impl_item.generics.params.iter().any(|p| {
2327 matches!(
2328 p.kind,
2329 hir::GenericParamKind::Lifetime {
2330 kind: hir::LifetimeParamKind::Explicit
2331 }
2332 )
2333 })
2334 }
2335 }
2336
2337 #[rustfmt::skip]
2338 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
2339 ShouldImplTraitCase::new("std::ops::Add", "add", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2340 ShouldImplTraitCase::new("std::convert::AsMut", "as_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2341 ShouldImplTraitCase::new("std::convert::AsRef", "as_ref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2342 ShouldImplTraitCase::new("std::ops::BitAnd", "bitand", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2343 ShouldImplTraitCase::new("std::ops::BitOr", "bitor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2344 ShouldImplTraitCase::new("std::ops::BitXor", "bitxor", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2345 ShouldImplTraitCase::new("std::borrow::Borrow", "borrow", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2346 ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2347 ShouldImplTraitCase::new("std::clone::Clone", "clone", 1, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2348 ShouldImplTraitCase::new("std::cmp::Ord", "cmp", 2, FN_HEADER, SelfKind::Ref, OutType::Any, true),
2349 // FIXME: default doesn't work
2350 ShouldImplTraitCase::new("std::default::Default", "default", 0, FN_HEADER, SelfKind::No, OutType::Any, true),
2351 ShouldImplTraitCase::new("std::ops::Deref", "deref", 1, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2352 ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut", 1, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2353 ShouldImplTraitCase::new("std::ops::Div", "div", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2354 ShouldImplTraitCase::new("std::ops::Drop", "drop", 1, FN_HEADER, SelfKind::RefMut, OutType::Unit, true),
2355 ShouldImplTraitCase::new("std::cmp::PartialEq", "eq", 2, FN_HEADER, SelfKind::Ref, OutType::Bool, true),
2356 ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2357 ShouldImplTraitCase::new("std::str::FromStr", "from_str", 1, FN_HEADER, SelfKind::No, OutType::Any, true),
2358 ShouldImplTraitCase::new("std::hash::Hash", "hash", 2, FN_HEADER, SelfKind::Ref, OutType::Unit, true),
2359 ShouldImplTraitCase::new("std::ops::Index", "index", 2, FN_HEADER, SelfKind::Ref, OutType::Ref, true),
2360 ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut", 2, FN_HEADER, SelfKind::RefMut, OutType::Ref, true),
2361 ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2362 ShouldImplTraitCase::new("std::ops::Mul", "mul", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2363 ShouldImplTraitCase::new("std::ops::Neg", "neg", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2364 ShouldImplTraitCase::new("std::iter::Iterator", "next", 1, FN_HEADER, SelfKind::RefMut, OutType::Any, false),
2365 ShouldImplTraitCase::new("std::ops::Not", "not", 1, FN_HEADER, SelfKind::Value, OutType::Any, true),
2366 ShouldImplTraitCase::new("std::ops::Rem", "rem", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2367 ShouldImplTraitCase::new("std::ops::Shl", "shl", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2368 ShouldImplTraitCase::new("std::ops::Shr", "shr", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2369 ShouldImplTraitCase::new("std::ops::Sub", "sub", 2, FN_HEADER, SelfKind::Value, OutType::Any, true),
2370 ];
2371
2372 #[derive(Clone, Copy, PartialEq, Debug)]
2373 enum SelfKind {
2374 Value,
2375 Ref,
2376 RefMut,
2377 No,
2378 }
2379
2380 impl SelfKind {
matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool2381 fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2382 fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2383 if ty == parent_ty {
2384 true
2385 } else if ty.is_box() {
2386 ty.boxed_ty() == parent_ty
2387 } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
2388 if let ty::Adt(_, substs) = ty.kind() {
2389 substs.types().next().map_or(false, |t| t == parent_ty)
2390 } else {
2391 false
2392 }
2393 } else {
2394 false
2395 }
2396 }
2397
2398 fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2399 if let ty::Ref(_, t, m) = *ty.kind() {
2400 return m == mutability && t == parent_ty;
2401 }
2402
2403 let trait_path = match mutability {
2404 hir::Mutability::Not => &paths::ASREF_TRAIT,
2405 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
2406 };
2407
2408 let trait_def_id = match get_trait_def_id(cx, trait_path) {
2409 Some(did) => did,
2410 None => return false,
2411 };
2412 implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2413 }
2414
2415 match self {
2416 Self::Value => matches_value(cx, parent_ty, ty),
2417 Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
2418 Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
2419 Self::No => ty != parent_ty,
2420 }
2421 }
2422
2423 #[must_use]
description(self) -> &'static str2424 fn description(self) -> &'static str {
2425 match self {
2426 Self::Value => "`self` by value",
2427 Self::Ref => "`self` by reference",
2428 Self::RefMut => "`self` by mutable reference",
2429 Self::No => "no `self`",
2430 }
2431 }
2432 }
2433
2434 #[derive(Clone, Copy)]
2435 enum OutType {
2436 Unit,
2437 Bool,
2438 Any,
2439 Ref,
2440 }
2441
2442 impl OutType {
matches(self, ty: &hir::FnRetTy<'_>) -> bool2443 fn matches(self, ty: &hir::FnRetTy<'_>) -> bool {
2444 let is_unit = |ty: &hir::Ty<'_>| matches!(ty.kind, hir::TyKind::Tup(&[]));
2445 match (self, ty) {
2446 (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
2447 (Self::Unit, &hir::FnRetTy::Return(ty)) if is_unit(ty) => true,
2448 (Self::Bool, &hir::FnRetTy::Return(ty)) if is_bool(ty) => true,
2449 (Self::Any, &hir::FnRetTy::Return(ty)) if !is_unit(ty) => true,
2450 (Self::Ref, &hir::FnRetTy::Return(ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
2451 _ => false,
2452 }
2453 }
2454 }
2455
is_bool(ty: &hir::Ty<'_>) -> bool2456 fn is_bool(ty: &hir::Ty<'_>) -> bool {
2457 if let hir::TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
2458 matches!(path.res, Res::PrimTy(PrimTy::Bool))
2459 } else {
2460 false
2461 }
2462 }
2463
fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool2464 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
2465 expected.constness == actual.constness
2466 && expected.unsafety == actual.unsafety
2467 && expected.asyncness == actual.asyncness
2468 }
2469