src/tools/clippy/clippy_lints/src/methods/mod.rs

   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_str_repeat;
  37 mod map_collect_result_unit;
  38 mod map_flatten;
  39 mod map_identity;
  40 mod map_unwrap_or;
  41 mod ok_expect;
  42 mod option_as_ref_deref;
  43 mod option_map_or_none;
  44 mod option_map_unwrap_or;
  45 mod or_fun_call;
  46 mod search_is_some;
  47 mod single_char_add_str;
  48 mod single_char_insert_string;
  49 mod single_char_pattern;
  50 mod single_char_push_string;
  51 mod skip_while_next;
  52 mod string_extend_chars;
  53 mod suspicious_map;
  54 mod suspicious_splitn;
  55 mod uninit_assumed_init;
  56 mod unnecessary_filter_map;
  57 mod unnecessary_fold;
  58 mod unnecessary_lazy_eval;
  59 mod unwrap_used;
  60 mod useless_asref;
  61 mod utils;
  62 mod wrong_self_convention;
  63 mod zst_offset;
  64
  65 use bind_instead_of_map::BindInsteadOfMap;
  66 use clippy_utils::diagnostics::{span_lint, span_lint_and_help};
  67 use clippy_utils::ty::{contains_adt_constructor, contains_ty, implements_trait, is_copy, is_type_diagnostic_item};
  68 use clippy_utils::{contains_return, get_trait_def_id, in_macro, iter_input_pats, meets_msrv, msrvs, paths, return_ty};
  69 use if_chain::if_chain;
  70 use rustc_hir as hir;
  71 use rustc_hir::def::Res;
  72 use rustc_hir::{Expr, ExprKind, PrimTy, QPath, TraitItem, TraitItemKind};
  73 use rustc_lint::{LateContext, LateLintPass, LintContext};
  74 use rustc_middle::lint::in_external_macro;
  75 use rustc_middle::ty::{self, TraitRef, Ty, TyS};
  76 use rustc_semver::RustcVersion;
  77 use rustc_session::{declare_tool_lint, impl_lint_pass};
  78 use rustc_span::symbol::SymbolStr;
  79 use rustc_span::{sym, Span};
  80 use rustc_typeck::hir_ty_to_ty;
  81
  82 declare_clippy_lint! {
  83     /// **What it does:** Checks for usages of `cloned()` on an `Iterator` or `Option` where
  84     /// `copied()` could be used instead.
  85     ///
  86     /// **Why is this bad?** `copied()` is better because it guarantees that the type being cloned
  87     /// implements `Copy`.
  88     ///
  89     /// **Known problems:** None.
  90     ///
  91     /// **Example:**
  92     ///
  93     /// ```rust
  94     /// [1, 2, 3].iter().cloned();
  95     /// ```
  96     /// Use instead:
  97     /// ```rust
  98     /// [1, 2, 3].iter().copied();
  99     /// ```
 100     pub CLONED_INSTEAD_OF_COPIED,
 101     pedantic,
 102     "used `cloned` where `copied` could be used instead"
 103 }
 104
 105 declare_clippy_lint! {
 106     /// **What it does:** Checks for usages of `Iterator::flat_map()` where `filter_map()` could be
 107     /// used instead.
 108     ///
 109     /// **Why is this bad?** When applicable, `filter_map()` is more clear since it shows that
 110     /// `Option` is used to produce 0 or 1 items.
 111     ///
 112     /// **Known problems:** None.
 113     ///
 114     /// **Example:**
 115     ///
 116     /// ```rust
 117     /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().flat_map(|x| x.parse().ok()).collect();
 118     /// ```
 119     /// Use instead:
 120     /// ```rust
 121     /// let nums: Vec<i32> = ["1", "2", "whee!"].iter().filter_map(|x| x.parse().ok()).collect();
 122     /// ```
 123     pub FLAT_MAP_OPTION,
 124     pedantic,
 125     "used `flat_map` where `filter_map` could be used instead"
 126 }
 127
 128 declare_clippy_lint! {
 129     /// **What it does:** Checks for `.unwrap()` calls on `Option`s and on `Result`s.
 130     ///
 131     /// **Why is this bad?** It is better to handle the `None` or `Err` case,
 132     /// or at least call `.expect(_)` with a more helpful message. Still, for a lot of
 133     /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
 134     /// `Allow` by default.
 135     ///
 136     /// `result.unwrap()` will let the thread panic on `Err` values.
 137     /// Normally, you want to implement more sophisticated error handling,
 138     /// and propagate errors upwards with `?` operator.
 139     ///
 140     /// Even if you want to panic on errors, not all `Error`s implement good
 141     /// messages on display. Therefore, it may be beneficial to look at the places
 142     /// where they may get displayed. Activate this lint to do just that.
 143     ///
 144     /// **Known problems:** None.
 145     ///
 146     /// **Examples:**
 147     /// ```rust
 148     /// # let opt = Some(1);
 149     ///
 150     /// // Bad
 151     /// opt.unwrap();
 152     ///
 153     /// // Good
 154     /// opt.expect("more helpful message");
 155     /// ```
 156     ///
 157     /// // or
 158     ///
 159     /// ```rust
 160     /// # let res: Result<usize, ()> = Ok(1);
 161     ///
 162     /// // Bad
 163     /// res.unwrap();
 164     ///
 165     /// // Good
 166     /// res.expect("more helpful message");
 167     /// ```
 168     pub UNWRAP_USED,
 169     restriction,
 170     "using `.unwrap()` on `Result` or `Option`, which should at least get a better message using `expect()`"
 171 }
 172
 173 declare_clippy_lint! {
 174     /// **What it does:** Checks for `.expect()` calls on `Option`s and `Result`s.
 175     ///
 176     /// **Why is this bad?** Usually it is better to handle the `None` or `Err` case.
 177     /// Still, for a lot of quick-and-dirty code, `expect` is a good choice, which is why
 178     /// this lint is `Allow` by default.
 179     ///
 180     /// `result.expect()` will let the thread panic on `Err`
 181     /// values. Normally, you want to implement more sophisticated error handling,
 182     /// and propagate errors upwards with `?` operator.
 183     ///
 184     /// **Known problems:** None.
 185     ///
 186     /// **Examples:**
 187     /// ```rust,ignore
 188     /// # let opt = Some(1);
 189     ///
 190     /// // Bad
 191     /// opt.expect("one");
 192     ///
 193     /// // Good
 194     /// let opt = Some(1);
 195     /// opt?;
 196     /// ```
 197     ///
 198     /// // or
 199     ///
 200     /// ```rust
 201     /// # let res: Result<usize, ()> = Ok(1);
 202     ///
 203     /// // Bad
 204     /// res.expect("one");
 205     ///
 206     /// // Good
 207     /// res?;
 208     /// # Ok::<(), ()>(())
 209     /// ```
 210     pub EXPECT_USED,
 211     restriction,
 212     "using `.expect()` on `Result` or `Option`, which might be better handled"
 213 }
 214
 215 declare_clippy_lint! {
 216     /// **What it does:** Checks for methods that should live in a trait
 217     /// implementation of a `std` trait (see [llogiq's blog
 218     /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
 219     /// information) instead of an inherent implementation.
 220     ///
 221     /// **Why is this bad?** Implementing the traits improve ergonomics for users of
 222     /// the code, often with very little cost. Also people seeing a `mul(...)`
 223     /// method
 224     /// may expect `*` to work equally, so you should have good reason to disappoint
 225     /// them.
 226     ///
 227     /// **Known problems:** None.
 228     ///
 229     /// **Example:**
 230     /// ```rust
 231     /// struct X;
 232     /// impl X {
 233     ///     fn add(&self, other: &X) -> X {
 234     ///         // ..
 235     /// # X
 236     ///     }
 237     /// }
 238     /// ```
 239     pub SHOULD_IMPLEMENT_TRAIT,
 240     style,
 241     "defining a method that should be implementing a std trait"
 242 }
 243
 244 declare_clippy_lint! {
 245     /// **What it does:** Checks for methods with certain name prefixes and which
 246     /// doesn't match how self is taken. The actual rules are:
 247     ///
 248     /// |Prefix |Postfix     |`self` taken           | `self` type  |
 249     /// |-------|------------|-----------------------|--------------|
 250     /// |`as_`  | none       |`&self` or `&mut self` | any          |
 251     /// |`from_`| none       | none                  | any          |
 252     /// |`into_`| none       |`self`                 | any          |
 253     /// |`is_`  | none       |`&self` or none        | any          |
 254     /// |`to_`  | `_mut`     |`&mut self`            | any          |
 255     /// |`to_`  | not `_mut` |`self`                 | `Copy`       |
 256     /// |`to_`  | not `_mut` |`&self`                | not `Copy`   |
 257     ///
 258     /// Note: Clippy doesn't trigger methods with `to_` prefix in:
 259     /// - Traits definition.
 260     /// Clippy can not tell if a type that implements a trait is `Copy` or not.
 261     /// - Traits implementation, when `&self` is taken.
 262     /// The method signature is controlled by the trait and often `&self` is required for all types that implement the trait
 263     /// (see e.g. the `std::string::ToString` trait).
 264     ///
 265     /// Please find more info here:
 266     /// https://rust-lang.github.io/api-guidelines/naming.html#ad-hoc-conversions-follow-as_-to_-into_-conventions-c-conv
 267     ///
 268     /// **Why is this bad?** Consistency breeds readability. If you follow the
 269     /// conventions, your users won't be surprised that they, e.g., need to supply a
 270     /// mutable reference to a `as_..` function.
 271     ///
 272     /// **Known problems:** None.
 273     ///
 274     /// **Example:**
 275     /// ```rust
 276     /// # struct X;
 277     /// impl X {
 278     ///     fn as_str(self) -> &'static str {
 279     ///         // ..
 280     /// # ""
 281     ///     }
 282     /// }
 283     /// ```
 284     pub WRONG_SELF_CONVENTION,
 285     style,
 286     "defining a method named with an established prefix (like \"into_\") that takes `self` with the wrong convention"
 287 }
 288
 289 declare_clippy_lint! {
 290     /// **What it does:** Checks for usage of `ok().expect(..)`.
 291     ///
 292     /// **Why is this bad?** Because you usually call `expect()` on the `Result`
 293     /// directly to get a better error message.
 294     ///
 295     /// **Known problems:** The error type needs to implement `Debug`
 296     ///
 297     /// **Example:**
 298     /// ```rust
 299     /// # let x = Ok::<_, ()>(());
 300     ///
 301     /// // Bad
 302     /// x.ok().expect("why did I do this again?");
 303     ///
 304     /// // Good
 305     /// x.expect("why did I do this again?");
 306     /// ```
 307     pub OK_EXPECT,
 308     style,
 309     "using `ok().expect()`, which gives worse error messages than calling `expect` directly on the Result"
 310 }
 311
 312 declare_clippy_lint! {
 313     /// **What it does:** Checks for usage of `option.map(_).unwrap_or(_)` or `option.map(_).unwrap_or_else(_)` or
 314     /// `result.map(_).unwrap_or_else(_)`.
 315     ///
 316     /// **Why is this bad?** Readability, these can be written more concisely (resp.) as
 317     /// `option.map_or(_, _)`, `option.map_or_else(_, _)` and `result.map_or_else(_, _)`.
 318     ///
 319     /// **Known problems:** The order of the arguments is not in execution order
 320     ///
 321     /// **Examples:**
 322     /// ```rust
 323     /// # let x = Some(1);
 324     ///
 325     /// // Bad
 326     /// x.map(|a| a + 1).unwrap_or(0);
 327     ///
 328     /// // Good
 329     /// x.map_or(0, |a| a + 1);
 330     /// ```
 331     ///
 332     /// // or
 333     ///
 334     /// ```rust
 335     /// # let x: Result<usize, ()> = Ok(1);
 336     /// # fn some_function(foo: ()) -> usize { 1 }
 337     ///
 338     /// // Bad
 339     /// x.map(|a| a + 1).unwrap_or_else(some_function);
 340     ///
 341     /// // Good
 342     /// x.map_or_else(some_function, |a| a + 1);
 343     /// ```
 344     pub MAP_UNWRAP_OR,
 345     pedantic,
 346     "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)`"
 347 }
 348
 349 declare_clippy_lint! {
 350     /// **What it does:** Checks for usage of `_.map_or(None, _)`.
 351     ///
 352     /// **Why is this bad?** Readability, this can be written more concisely as
 353     /// `_.and_then(_)`.
 354     ///
 355     /// **Known problems:** The order of the arguments is not in execution order.
 356     ///
 357     /// **Example:**
 358     /// ```rust
 359     /// # let opt = Some(1);
 360     ///
 361     /// // Bad
 362     /// opt.map_or(None, |a| Some(a + 1));
 363     ///
 364     /// // Good
 365     /// opt.and_then(|a| Some(a + 1));
 366     /// ```
 367     pub OPTION_MAP_OR_NONE,
 368     style,
 369     "using `Option.map_or(None, f)`, which is more succinctly expressed as `and_then(f)`"
 370 }
 371
 372 declare_clippy_lint! {
 373     /// **What it does:** Checks for usage of `_.map_or(None, Some)`.
 374     ///
 375     /// **Why is this bad?** Readability, this can be written more concisely as
 376     /// `_.ok()`.
 377     ///
 378     /// **Known problems:** None.
 379     ///
 380     /// **Example:**
 381     ///
 382     /// Bad:
 383     /// ```rust
 384     /// # let r: Result<u32, &str> = Ok(1);
 385     /// assert_eq!(Some(1), r.map_or(None, Some));
 386     /// ```
 387     ///
 388     /// Good:
 389     /// ```rust
 390     /// # let r: Result<u32, &str> = Ok(1);
 391     /// assert_eq!(Some(1), r.ok());
 392     /// ```
 393     pub RESULT_MAP_OR_INTO_OPTION,
 394     style,
 395     "using `Result.map_or(None, Some)`, which is more succinctly expressed as `ok()`"
 396 }
 397
 398 declare_clippy_lint! {
 399     /// **What it does:** Checks for usage of `_.and_then(|x| Some(y))`, `_.and_then(|x| Ok(y))` or
 400     /// `_.or_else(|x| Err(y))`.
 401     ///
 402     /// **Why is this bad?** Readability, this can be written more concisely as
 403     /// `_.map(|x| y)` or `_.map_err(|x| y)`.
 404     ///
 405     /// **Known problems:** None
 406     ///
 407     /// **Example:**
 408     ///
 409     /// ```rust
 410     /// # fn opt() -> Option<&'static str> { Some("42") }
 411     /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
 412     /// let _ = opt().and_then(|s| Some(s.len()));
 413     /// let _ = res().and_then(|s| if s.len() == 42 { Ok(10) } else { Ok(20) });
 414     /// let _ = res().or_else(|s| if s.len() == 42 { Err(10) } else { Err(20) });
 415     /// ```
 416     ///
 417     /// The correct use would be:
 418     ///
 419     /// ```rust
 420     /// # fn opt() -> Option<&'static str> { Some("42") }
 421     /// # fn res() -> Result<&'static str, &'static str> { Ok("42") }
 422     /// let _ = opt().map(|s| s.len());
 423     /// let _ = res().map(|s| if s.len() == 42 { 10 } else { 20 });
 424     /// let _ = res().map_err(|s| if s.len() == 42 { 10 } else { 20 });
 425     /// ```
 426     pub BIND_INSTEAD_OF_MAP,
 427     complexity,
 428     "using `Option.and_then(|x| Some(y))`, which is more succinctly expressed as `map(|x| y)`"
 429 }
 430
 431 declare_clippy_lint! {
 432     /// **What it does:** Checks for usage of `_.filter(_).next()`.
 433     ///
 434     /// **Why is this bad?** Readability, this can be written more concisely as
 435     /// `_.find(_)`.
 436     ///
 437     /// **Known problems:** None.
 438     ///
 439     /// **Example:**
 440     /// ```rust
 441     /// # let vec = vec![1];
 442     /// vec.iter().filter(|x| **x == 0).next();
 443     /// ```
 444     /// Could be written as
 445     /// ```rust
 446     /// # let vec = vec![1];
 447     /// vec.iter().find(|x| **x == 0);
 448     /// ```
 449     pub FILTER_NEXT,
 450     complexity,
 451     "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
 452 }
 453
 454 declare_clippy_lint! {
 455     /// **What it does:** Checks for usage of `_.skip_while(condition).next()`.
 456     ///
 457     /// **Why is this bad?** Readability, this can be written more concisely as
 458     /// `_.find(!condition)`.
 459     ///
 460     /// **Known problems:** None.
 461     ///
 462     /// **Example:**
 463     /// ```rust
 464     /// # let vec = vec![1];
 465     /// vec.iter().skip_while(|x| **x == 0).next();
 466     /// ```
 467     /// Could be written as
 468     /// ```rust
 469     /// # let vec = vec![1];
 470     /// vec.iter().find(|x| **x != 0);
 471     /// ```
 472     pub SKIP_WHILE_NEXT,
 473     complexity,
 474     "using `skip_while(p).next()`, which is more succinctly expressed as `.find(!p)`"
 475 }
 476
 477 declare_clippy_lint! {
 478     /// **What it does:** Checks for usage of `_.map(_).flatten(_)` on `Iterator` and `Option`
 479     ///
 480     /// **Why is this bad?** Readability, this can be written more concisely as
 481     /// `_.flat_map(_)`
 482     ///
 483     /// **Known problems:**
 484     ///
 485     /// **Example:**
 486     /// ```rust
 487     /// let vec = vec![vec![1]];
 488     ///
 489     /// // Bad
 490     /// vec.iter().map(|x| x.iter()).flatten();
 491     ///
 492     /// // Good
 493     /// vec.iter().flat_map(|x| x.iter());
 494     /// ```
 495     pub MAP_FLATTEN,
 496     pedantic,
 497     "using combinations of `flatten` and `map` which can usually be written as a single method call"
 498 }
 499
 500 declare_clippy_lint! {
 501     /// **What it does:** Checks for usage of `_.filter(_).map(_)` that can be written more simply
 502     /// as `filter_map(_)`.
 503     ///
 504     /// **Why is this bad?** Redundant code in the `filter` and `map` operations is poor style and
 505     /// less performant.
 506     ///
 507     /// **Known problems:** None.
 508     ///
 509      /// **Example:**
 510     /// Bad:
 511     /// ```rust
 512     /// (0_i32..10)
 513     ///     .filter(|n| n.checked_add(1).is_some())
 514     ///     .map(|n| n.checked_add(1).unwrap());
 515     /// ```
 516     ///
 517     /// Good:
 518     /// ```rust
 519     /// (0_i32..10).filter_map(|n| n.checked_add(1));
 520     /// ```
 521     pub MANUAL_FILTER_MAP,
 522     complexity,
 523     "using `_.filter(_).map(_)` in a way that can be written more simply as `filter_map(_)`"
 524 }
 525
 526 declare_clippy_lint! {
 527     /// **What it does:** Checks for usage of `_.find(_).map(_)` that can be written more simply
 528     /// as `find_map(_)`.
 529     ///
 530     /// **Why is this bad?** Redundant code in the `find` and `map` operations is poor style and
 531     /// less performant.
 532     ///
 533     /// **Known problems:** None.
 534     ///
 535      /// **Example:**
 536     /// Bad:
 537     /// ```rust
 538     /// (0_i32..10)
 539     ///     .find(|n| n.checked_add(1).is_some())
 540     ///     .map(|n| n.checked_add(1).unwrap());
 541     /// ```
 542     ///
 543     /// Good:
 544     /// ```rust
 545     /// (0_i32..10).find_map(|n| n.checked_add(1));
 546     /// ```
 547     pub MANUAL_FIND_MAP,
 548     complexity,
 549     "using `_.find(_).map(_)` in a way that can be written more simply as `find_map(_)`"
 550 }
 551
 552 declare_clippy_lint! {
 553     /// **What it does:** Checks for usage of `_.filter_map(_).next()`.
 554     ///
 555     /// **Why is this bad?** Readability, this can be written more concisely as
 556     /// `_.find_map(_)`.
 557     ///
 558     /// **Known problems:** None
 559     ///
 560     /// **Example:**
 561     /// ```rust
 562     ///  (0..3).filter_map(|x| if x == 2 { Some(x) } else { None }).next();
 563     /// ```
 564     /// Can be written as
 565     ///
 566     /// ```rust
 567     ///  (0..3).find_map(|x| if x == 2 { Some(x) } else { None });
 568     /// ```
 569     pub FILTER_MAP_NEXT,
 570     pedantic,
 571     "using combination of `filter_map` and `next` which can usually be written as a single method call"
 572 }
 573
 574 declare_clippy_lint! {
 575     /// **What it does:** Checks for usage of `flat_map(|x| x)`.
 576     ///
 577     /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
 578     ///
 579     /// **Known problems:** None
 580     ///
 581     /// **Example:**
 582     /// ```rust
 583     /// # let iter = vec![vec![0]].into_iter();
 584     /// iter.flat_map(|x| x);
 585     /// ```
 586     /// Can be written as
 587     /// ```rust
 588     /// # let iter = vec![vec![0]].into_iter();
 589     /// iter.flatten();
 590     /// ```
 591     pub FLAT_MAP_IDENTITY,
 592     complexity,
 593     "call to `flat_map` where `flatten` is sufficient"
 594 }
 595
 596 declare_clippy_lint! {
 597     /// **What it does:** Checks for an iterator or string search (such as `find()`,
 598     /// `position()`, or `rposition()`) followed by a call to `is_some()` or `is_none()`.
 599     ///
 600     /// **Why is this bad?** Readability, this can be written more concisely as:
 601     /// * `_.any(_)`, or `_.contains(_)` for `is_some()`,
 602     /// * `!_.any(_)`, or `!_.contains(_)` for `is_none()`.
 603     ///
 604     /// **Known problems:** None.
 605     ///
 606     /// **Example:**
 607     /// ```rust
 608     /// let vec = vec![1];
 609     /// vec.iter().find(|x| **x == 0).is_some();
 610     ///
 611     /// let _ = "hello world".find("world").is_none();
 612     /// ```
 613     /// Could be written as
 614     /// ```rust
 615     /// let vec = vec![1];
 616     /// vec.iter().any(|x| *x == 0);
 617     ///
 618     /// let _ = !"hello world".contains("world");
 619     /// ```
 620     pub SEARCH_IS_SOME,
 621     complexity,
 622     "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()`)"
 623 }
 624
 625 declare_clippy_lint! {
 626     /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
 627     /// if it starts with a given char.
 628     ///
 629     /// **Why is this bad?** Readability, this can be written more concisely as
 630     /// `_.starts_with(_)`.
 631     ///
 632     /// **Known problems:** None.
 633     ///
 634     /// **Example:**
 635     /// ```rust
 636     /// let name = "foo";
 637     /// if name.chars().next() == Some('_') {};
 638     /// ```
 639     /// Could be written as
 640     /// ```rust
 641     /// let name = "foo";
 642     /// if name.starts_with('_') {};
 643     /// ```
 644     pub CHARS_NEXT_CMP,
 645     style,
 646     "using `.chars().next()` to check if a string starts with a char"
 647 }
 648
 649 declare_clippy_lint! {
 650     /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
 651     /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
 652     /// `unwrap_or_default` instead.
 653     ///
 654     /// **Why is this bad?** The function will always be called and potentially
 655     /// allocate an object acting as the default.
 656     ///
 657     /// **Known problems:** If the function has side-effects, not calling it will
 658     /// change the semantic of the program, but you shouldn't rely on that anyway.
 659     ///
 660     /// **Example:**
 661     /// ```rust
 662     /// # let foo = Some(String::new());
 663     /// foo.unwrap_or(String::new());
 664     /// ```
 665     /// this can instead be written:
 666     /// ```rust
 667     /// # let foo = Some(String::new());
 668     /// foo.unwrap_or_else(String::new);
 669     /// ```
 670     /// or
 671     /// ```rust
 672     /// # let foo = Some(String::new());
 673     /// foo.unwrap_or_default();
 674     /// ```
 675     pub OR_FUN_CALL,
 676     perf,
 677     "using any `*or` method with a function call, which suggests `*or_else`"
 678 }
 679
 680 declare_clippy_lint! {
 681     /// **What it does:** Checks for calls to `.expect(&format!(...))`, `.expect(foo(..))`,
 682     /// etc., and suggests to use `unwrap_or_else` instead
 683     ///
 684     /// **Why is this bad?** The function will always be called.
 685     ///
 686     /// **Known problems:** If the function has side-effects, not calling it will
 687     /// change the semantics of the program, but you shouldn't rely on that anyway.
 688     ///
 689     /// **Example:**
 690     /// ```rust
 691     /// # let foo = Some(String::new());
 692     /// # let err_code = "418";
 693     /// # let err_msg = "I'm a teapot";
 694     /// foo.expect(&format!("Err {}: {}", err_code, err_msg));
 695     /// ```
 696     /// or
 697     /// ```rust
 698     /// # let foo = Some(String::new());
 699     /// # let err_code = "418";
 700     /// # let err_msg = "I'm a teapot";
 701     /// foo.expect(format!("Err {}: {}", err_code, err_msg).as_str());
 702     /// ```
 703     /// this can instead be written:
 704     /// ```rust
 705     /// # let foo = Some(String::new());
 706     /// # let err_code = "418";
 707     /// # let err_msg = "I'm a teapot";
 708     /// foo.unwrap_or_else(|| panic!("Err {}: {}", err_code, err_msg));
 709     /// ```
 710     pub EXPECT_FUN_CALL,
 711     perf,
 712     "using any `expect` method with a function call"
 713 }
 714
 715 declare_clippy_lint! {
 716     /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
 717     ///
 718     /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
 719     /// generics, not for using the `clone` method on a concrete type.
 720     ///
 721     /// **Known problems:** None.
 722     ///
 723     /// **Example:**
 724     /// ```rust
 725     /// 42u64.clone();
 726     /// ```
 727     pub CLONE_ON_COPY,
 728     complexity,
 729     "using `clone` on a `Copy` type"
 730 }
 731
 732 declare_clippy_lint! {
 733     /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
 734     /// (`Rc`, `Arc`, `rc::Weak`, or `sync::Weak`), and suggests calling Clone via unified
 735     /// function syntax instead (e.g., `Rc::clone(foo)`).
 736     ///
 737     /// **Why is this bad?** Calling '.clone()' on an Rc, Arc, or Weak
 738     /// can obscure the fact that only the pointer is being cloned, not the underlying
 739     /// data.
 740     ///
 741     /// **Example:**
 742     /// ```rust
 743     /// # use std::rc::Rc;
 744     /// let x = Rc::new(1);
 745     ///
 746     /// // Bad
 747     /// x.clone();
 748     ///
 749     /// // Good
 750     /// Rc::clone(&x);
 751     /// ```
 752     pub CLONE_ON_REF_PTR,
 753     restriction,
 754     "using 'clone' on a ref-counted pointer"
 755 }
 756
 757 declare_clippy_lint! {
 758     /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
 759     ///
 760     /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
 761     /// cloning the underlying `T`.
 762     ///
 763     /// **Known problems:** None.
 764     ///
 765     /// **Example:**
 766     /// ```rust
 767     /// fn main() {
 768     ///     let x = vec![1];
 769     ///     let y = &&x;
 770     ///     let z = y.clone();
 771     ///     println!("{:p} {:p}", *y, z); // prints out the same pointer
 772     /// }
 773     /// ```
 774     pub CLONE_DOUBLE_REF,
 775     correctness,
 776     "using `clone` on `&&T`"
 777 }
 778
 779 declare_clippy_lint! {
 780     /// **What it does:** Checks for usage of `.to_string()` on an `&&T` where
 781     /// `T` implements `ToString` directly (like `&&str` or `&&String`).
 782     ///
 783     /// **Why is this bad?** This bypasses the specialized implementation of
 784     /// `ToString` and instead goes through the more expensive string formatting
 785     /// facilities.
 786     ///
 787     /// **Known problems:** None.
 788     ///
 789     /// **Example:**
 790     /// ```rust
 791     /// // Generic implementation for `T: Display` is used (slow)
 792     /// ["foo", "bar"].iter().map(|s| s.to_string());
 793     ///
 794     /// // OK, the specialized impl is used
 795     /// ["foo", "bar"].iter().map(|&s| s.to_string());
 796     /// ```
 797     pub INEFFICIENT_TO_STRING,
 798     pedantic,
 799     "using `to_string` on `&&T` where `T: ToString`"
 800 }
 801
 802 declare_clippy_lint! {
 803     /// **What it does:** Checks for `new` not returning a type that contains `Self`.
 804     ///
 805     /// **Why is this bad?** As a convention, `new` methods are used to make a new
 806     /// instance of a type.
 807     ///
 808     /// **Known problems:** None.
 809     ///
 810     /// **Example:**
 811     /// In an impl block:
 812     /// ```rust
 813     /// # struct Foo;
 814     /// # struct NotAFoo;
 815     /// impl Foo {
 816     ///     fn new() -> NotAFoo {
 817     /// # NotAFoo
 818     ///     }
 819     /// }
 820     /// ```
 821     ///
 822     /// ```rust
 823     /// # struct Foo;
 824     /// struct Bar(Foo);
 825     /// impl Foo {
 826     ///     // Bad. The type name must contain `Self`
 827     ///     fn new() -> Bar {
 828     /// # Bar(Foo)
 829     ///     }
 830     /// }
 831     /// ```
 832     ///
 833     /// ```rust
 834     /// # struct Foo;
 835     /// # struct FooError;
 836     /// impl Foo {
 837     ///     // Good. Return type contains `Self`
 838     ///     fn new() -> Result<Foo, FooError> {
 839     /// # Ok(Foo)
 840     ///     }
 841     /// }
 842     /// ```
 843     ///
 844     /// Or in a trait definition:
 845     /// ```rust
 846     /// pub trait Trait {
 847     ///     // Bad. The type name must contain `Self`
 848     ///     fn new();
 849     /// }
 850     /// ```
 851     ///
 852     /// ```rust
 853     /// pub trait Trait {
 854     ///     // Good. Return type contains `Self`
 855     ///     fn new() -> Self;
 856     /// }
 857     /// ```
 858     pub NEW_RET_NO_SELF,
 859     style,
 860     "not returning type containing `Self` in a `new` method"
 861 }
 862
 863 declare_clippy_lint! {
 864     /// **What it does:** Checks for string methods that receive a single-character
 865     /// `str` as an argument, e.g., `_.split("x")`.
 866     ///
 867     /// **Why is this bad?** Performing these methods using a `char` is faster than
 868     /// using a `str`.
 869     ///
 870     /// **Known problems:** Does not catch multi-byte unicode characters.
 871     ///
 872     /// **Example:**
 873     /// ```rust,ignore
 874     /// // Bad
 875     /// _.split("x");
 876     ///
 877     /// // Good
 878     /// _.split('x');
 879     pub SINGLE_CHAR_PATTERN,
 880     perf,
 881     "using a single-character str where a char could be used, e.g., `_.split(\"x\")`"
 882 }
 883
 884 declare_clippy_lint! {
 885     /// **What it does:** Checks for calling `.step_by(0)` on iterators which panics.
 886     ///
 887     /// **Why is this bad?** This very much looks like an oversight. Use `panic!()` instead if you
 888     /// actually intend to panic.
 889     ///
 890     /// **Known problems:** None.
 891     ///
 892     /// **Example:**
 893     /// ```rust,should_panic
 894     /// for x in (0..100).step_by(0) {
 895     ///     //..
 896     /// }
 897     /// ```
 898     pub ITERATOR_STEP_BY_ZERO,
 899     correctness,
 900     "using `Iterator::step_by(0)`, which will panic at runtime"
 901 }
 902
 903 declare_clippy_lint! {
 904     /// **What it does:** Checks for indirect collection of populated `Option`
 905     ///
 906     /// **Why is this bad?** `Option` is like a collection of 0-1 things, so `flatten`
 907     /// automatically does this without suspicious-looking `unwrap` calls.
 908     ///
 909     /// **Known problems:** None.
 910     ///
 911     /// **Example:**
 912     ///
 913     /// ```rust
 914     /// let _ = std::iter::empty::<Option<i32>>().filter(Option::is_some).map(Option::unwrap);
 915     /// ```
 916     /// Use instead:
 917     /// ```rust
 918     /// let _ = std::iter::empty::<Option<i32>>().flatten();
 919     /// ```
 920     pub OPTION_FILTER_MAP,
 921     complexity,
 922     "filtering `Option` for `Some` then force-unwrapping, which can be one type-safe operation"
 923 }
 924
 925 declare_clippy_lint! {
 926     /// **What it does:** Checks for the use of `iter.nth(0)`.
 927     ///
 928     /// **Why is this bad?** `iter.next()` is equivalent to
 929     /// `iter.nth(0)`, as they both consume the next element,
 930     ///  but is more readable.
 931     ///
 932     /// **Known problems:** None.
 933     ///
 934     /// **Example:**
 935     ///
 936     /// ```rust
 937     /// # use std::collections::HashSet;
 938     /// // Bad
 939     /// # let mut s = HashSet::new();
 940     /// # s.insert(1);
 941     /// let x = s.iter().nth(0);
 942     ///
 943     /// // Good
 944     /// # let mut s = HashSet::new();
 945     /// # s.insert(1);
 946     /// let x = s.iter().next();
 947     /// ```
 948     pub ITER_NTH_ZERO,
 949     style,
 950     "replace `iter.nth(0)` with `iter.next()`"
 951 }
 952
 953 declare_clippy_lint! {
 954     /// **What it does:** Checks for use of `.iter().nth()` (and the related
 955     /// `.iter_mut().nth()`) on standard library types with O(1) element access.
 956     ///
 957     /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
 958     /// readable.
 959     ///
 960     /// **Known problems:** None.
 961     ///
 962     /// **Example:**
 963     /// ```rust
 964     /// let some_vec = vec![0, 1, 2, 3];
 965     /// let bad_vec = some_vec.iter().nth(3);
 966     /// let bad_slice = &some_vec[..].iter().nth(3);
 967     /// ```
 968     /// The correct use would be:
 969     /// ```rust
 970     /// let some_vec = vec![0, 1, 2, 3];
 971     /// let bad_vec = some_vec.get(3);
 972     /// let bad_slice = &some_vec[..].get(3);
 973     /// ```
 974     pub ITER_NTH,
 975     perf,
 976     "using `.iter().nth()` on a standard library type with O(1) element access"
 977 }
 978
 979 declare_clippy_lint! {
 980     /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
 981     ///
 982     /// **Why is this bad?** `.nth(x)` is cleaner
 983     ///
 984     /// **Known problems:** None.
 985     ///
 986     /// **Example:**
 987     /// ```rust
 988     /// let some_vec = vec![0, 1, 2, 3];
 989     /// let bad_vec = some_vec.iter().skip(3).next();
 990     /// let bad_slice = &some_vec[..].iter().skip(3).next();
 991     /// ```
 992     /// The correct use would be:
 993     /// ```rust
 994     /// let some_vec = vec![0, 1, 2, 3];
 995     /// let bad_vec = some_vec.iter().nth(3);
 996     /// let bad_slice = &some_vec[..].iter().nth(3);
 997     /// ```
 998     pub ITER_SKIP_NEXT,
 999     style,
1000     "using `.skip(x).next()` on an iterator"
1001 }
1002
1003 declare_clippy_lint! {
1004     /// **What it does:** Checks for use of `.get().unwrap()` (or
1005     /// `.get_mut().unwrap`) on a standard library type which implements `Index`
1006     ///
1007     /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
1008     /// concise.
1009     ///
1010     /// **Known problems:** Not a replacement for error handling: Using either
1011     /// `.unwrap()` or the Index trait (`[]`) carries the risk of causing a `panic`
1012     /// if the value being accessed is `None`. If the use of `.get().unwrap()` is a
1013     /// temporary placeholder for dealing with the `Option` type, then this does
1014     /// not mitigate the need for error handling. If there is a chance that `.get()`
1015     /// will be `None` in your program, then it is advisable that the `None` case
1016     /// is handled in a future refactor instead of using `.unwrap()` or the Index
1017     /// trait.
1018     ///
1019     /// **Example:**
1020     /// ```rust
1021     /// let mut some_vec = vec![0, 1, 2, 3];
1022     /// let last = some_vec.get(3).unwrap();
1023     /// *some_vec.get_mut(0).unwrap() = 1;
1024     /// ```
1025     /// The correct use would be:
1026     /// ```rust
1027     /// let mut some_vec = vec![0, 1, 2, 3];
1028     /// let last = some_vec[3];
1029     /// some_vec[0] = 1;
1030     /// ```
1031     pub GET_UNWRAP,
1032     restriction,
1033     "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
1034 }
1035
1036 declare_clippy_lint! {
1037     /// **What it does:** Checks for occurrences where one vector gets extended instead of append
1038     ///
1039     /// **Why is this bad?** Using `append` instead of `extend` is more concise and faster
1040     ///
1041     /// **Known problems:** None.
1042     ///
1043     /// **Example:**
1044     ///
1045     /// ```rust
1046     /// let mut a = vec![1, 2, 3];
1047     /// let mut b = vec![4, 5, 6];
1048     ///
1049     /// // Bad
1050     /// a.extend(b.drain(..));
1051     ///
1052     /// // Good
1053     /// a.append(&mut b);
1054     /// ```
1055     pub EXTEND_WITH_DRAIN,
1056     perf,
1057     "using vec.append(&mut vec) to move the full range of a vecor to another"
1058 }
1059
1060 declare_clippy_lint! {
1061     /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
1062     /// `&str` or `String`.
1063     ///
1064     /// **Why is this bad?** `.push_str(s)` is clearer
1065     ///
1066     /// **Known problems:** None.
1067     ///
1068     /// **Example:**
1069     /// ```rust
1070     /// let abc = "abc";
1071     /// let def = String::from("def");
1072     /// let mut s = String::new();
1073     /// s.extend(abc.chars());
1074     /// s.extend(def.chars());
1075     /// ```
1076     /// The correct use would be:
1077     /// ```rust
1078     /// let abc = "abc";
1079     /// let def = String::from("def");
1080     /// let mut s = String::new();
1081     /// s.push_str(abc);
1082     /// s.push_str(&def);
1083     /// ```
1084     pub STRING_EXTEND_CHARS,
1085     style,
1086     "using `x.extend(s.chars())` where s is a `&str` or `String`"
1087 }
1088
1089 declare_clippy_lint! {
1090     /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
1091     /// create a `Vec`.
1092     ///
1093     /// **Why is this bad?** `.to_vec()` is clearer
1094     ///
1095     /// **Known problems:** None.
1096     ///
1097     /// **Example:**
1098     /// ```rust
1099     /// let s = [1, 2, 3, 4, 5];
1100     /// let s2: Vec<isize> = s[..].iter().cloned().collect();
1101     /// ```
1102     /// The better use would be:
1103     /// ```rust
1104     /// let s = [1, 2, 3, 4, 5];
1105     /// let s2: Vec<isize> = s.to_vec();
1106     /// ```
1107     pub ITER_CLONED_COLLECT,
1108     style,
1109     "using `.cloned().collect()` on slice to create a `Vec`"
1110 }
1111
1112 declare_clippy_lint! {
1113     /// **What it does:** Checks for usage of `_.chars().last()` or
1114     /// `_.chars().next_back()` on a `str` to check if it ends with a given char.
1115     ///
1116     /// **Why is this bad?** Readability, this can be written more concisely as
1117     /// `_.ends_with(_)`.
1118     ///
1119     /// **Known problems:** None.
1120     ///
1121     /// **Example:**
1122     /// ```rust
1123     /// # let name = "_";
1124     ///
1125     /// // Bad
1126     /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-');
1127     ///
1128     /// // Good
1129     /// name.ends_with('_') || name.ends_with('-');
1130     /// ```
1131     pub CHARS_LAST_CMP,
1132     style,
1133     "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
1134 }
1135
1136 declare_clippy_lint! {
1137     /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
1138     /// types before and after the call are the same.
1139     ///
1140     /// **Why is this bad?** The call is unnecessary.
1141     ///
1142     /// **Known problems:** None.
1143     ///
1144     /// **Example:**
1145     /// ```rust
1146     /// # fn do_stuff(x: &[i32]) {}
1147     /// let x: &[i32] = &[1, 2, 3, 4, 5];
1148     /// do_stuff(x.as_ref());
1149     /// ```
1150     /// The correct use would be:
1151     /// ```rust
1152     /// # fn do_stuff(x: &[i32]) {}
1153     /// let x: &[i32] = &[1, 2, 3, 4, 5];
1154     /// do_stuff(x);
1155     /// ```
1156     pub USELESS_ASREF,
1157     complexity,
1158     "using `as_ref` where the types before and after the call are the same"
1159 }
1160
1161 declare_clippy_lint! {
1162     /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
1163     /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
1164     /// `sum` or `product`.
1165     ///
1166     /// **Why is this bad?** Readability.
1167     ///
1168     /// **Known problems:** None.
1169     ///
1170     /// **Example:**
1171     /// ```rust
1172     /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
1173     /// ```
1174     /// This could be written as:
1175     /// ```rust
1176     /// let _ = (0..3).any(|x| x > 2);
1177     /// ```
1178     pub UNNECESSARY_FOLD,
1179     style,
1180     "using `fold` when a more succinct alternative exists"
1181 }
1182
1183 declare_clippy_lint! {
1184     /// **What it does:** Checks for `filter_map` calls which could be replaced by `filter` or `map`.
1185     /// More specifically it checks if the closure provided is only performing one of the
1186     /// filter or map operations and suggests the appropriate option.
1187     ///
1188     /// **Why is this bad?** Complexity. The intent is also clearer if only a single
1189     /// operation is being performed.
1190     ///
1191     /// **Known problems:** None
1192     ///
1193     /// **Example:**
1194     /// ```rust
1195     /// let _ = (0..3).filter_map(|x| if x > 2 { Some(x) } else { None });
1196     ///
1197     /// // As there is no transformation of the argument this could be written as:
1198     /// let _ = (0..3).filter(|&x| x > 2);
1199     /// ```
1200     ///
1201     /// ```rust
1202     /// let _ = (0..4).filter_map(|x| Some(x + 1));
1203     ///
1204     /// // As there is no conditional check on the argument this could be written as:
1205     /// let _ = (0..4).map(|x| x + 1);
1206     /// ```
1207     pub UNNECESSARY_FILTER_MAP,
1208     complexity,
1209     "using `filter_map` when a more succinct alternative exists"
1210 }
1211
1212 declare_clippy_lint! {
1213     /// **What it does:** Checks for `into_iter` calls on references which should be replaced by `iter`
1214     /// or `iter_mut`.
1215     ///
1216     /// **Why is this bad?** Readability. Calling `into_iter` on a reference will not move out its
1217     /// content into the resulting iterator, which is confusing. It is better just call `iter` or
1218     /// `iter_mut` directly.
1219     ///
1220     /// **Known problems:** None
1221     ///
1222     /// **Example:**
1223     ///
1224     /// ```rust
1225     /// // Bad
1226     /// let _ = (&vec![3, 4, 5]).into_iter();
1227     ///
1228     /// // Good
1229     /// let _ = (&vec![3, 4, 5]).iter();
1230     /// ```
1231     pub INTO_ITER_ON_REF,
1232     style,
1233     "using `.into_iter()` on a reference"
1234 }
1235
1236 declare_clippy_lint! {
1237     /// **What it does:** Checks for calls to `map` followed by a `count`.
1238     ///
1239     /// **Why is this bad?** It looks suspicious. Maybe `map` was confused with `filter`.
1240     /// If the `map` call is intentional, this should be rewritten. Or, if you intend to
1241     /// drive the iterator to completion, you can just use `for_each` instead.
1242     ///
1243     /// **Known problems:** None
1244     ///
1245     /// **Example:**
1246     ///
1247     /// ```rust
1248     /// let _ = (0..3).map(|x| x + 2).count();
1249     /// ```
1250     pub SUSPICIOUS_MAP,
1251     suspicious,
1252     "suspicious usage of map"
1253 }
1254
1255 declare_clippy_lint! {
1256     /// **What it does:** Checks for `MaybeUninit::uninit().assume_init()`.
1257     ///
1258     /// **Why is this bad?** For most types, this is undefined behavior.
1259     ///
1260     /// **Known problems:** For now, we accept empty tuples and tuples / arrays
1261     /// of `MaybeUninit`. There may be other types that allow uninitialized
1262     /// data, but those are not yet rigorously defined.
1263     ///
1264     /// **Example:**
1265     ///
1266     /// ```rust
1267     /// // Beware the UB
1268     /// use std::mem::MaybeUninit;
1269     ///
1270     /// let _: usize = unsafe { MaybeUninit::uninit().assume_init() };
1271     /// ```
1272     ///
1273     /// Note that the following is OK:
1274     ///
1275     /// ```rust
1276     /// use std::mem::MaybeUninit;
1277     ///
1278     /// let _: [MaybeUninit<bool>; 5] = unsafe {
1279     ///     MaybeUninit::uninit().assume_init()
1280     /// };
1281     /// ```
1282     pub UNINIT_ASSUMED_INIT,
1283     correctness,
1284     "`MaybeUninit::uninit().assume_init()`"
1285 }
1286
1287 declare_clippy_lint! {
1288     /// **What it does:** Checks for `.checked_add/sub(x).unwrap_or(MAX/MIN)`.
1289     ///
1290     /// **Why is this bad?** These can be written simply with `saturating_add/sub` methods.
1291     ///
1292     /// **Example:**
1293     ///
1294     /// ```rust
1295     /// # let y: u32 = 0;
1296     /// # let x: u32 = 100;
1297     /// let add = x.checked_add(y).unwrap_or(u32::MAX);
1298     /// let sub = x.checked_sub(y).unwrap_or(u32::MIN);
1299     /// ```
1300     ///
1301     /// can be written using dedicated methods for saturating addition/subtraction as:
1302     ///
1303     /// ```rust
1304     /// # let y: u32 = 0;
1305     /// # let x: u32 = 100;
1306     /// let add = x.saturating_add(y);
1307     /// let sub = x.saturating_sub(y);
1308     /// ```
1309     pub MANUAL_SATURATING_ARITHMETIC,
1310     style,
1311     "`.chcked_add/sub(x).unwrap_or(MAX/MIN)`"
1312 }
1313
1314 declare_clippy_lint! {
1315     /// **What it does:** Checks for `offset(_)`, `wrapping_`{`add`, `sub`}, etc. on raw pointers to
1316     /// zero-sized types
1317     ///
1318     /// **Why is this bad?** This is a no-op, and likely unintended
1319     ///
1320     /// **Known problems:** None
1321     ///
1322     /// **Example:**
1323     /// ```rust
1324     /// unsafe { (&() as *const ()).offset(1) };
1325     /// ```
1326     pub ZST_OFFSET,
1327     correctness,
1328     "Check for offset calculations on raw pointers to zero-sized types"
1329 }
1330
1331 declare_clippy_lint! {
1332     /// **What it does:** Checks for `FileType::is_file()`.
1333     ///
1334     /// **Why is this bad?** When people testing a file type with `FileType::is_file`
1335     /// they are testing whether a path is something they can get bytes from. But
1336     /// `is_file` doesn't cover special file types in unix-like systems, and doesn't cover
1337     /// symlink in windows. Using `!FileType::is_dir()` is a better way to that intention.
1338     ///
1339     /// **Example:**
1340     ///
1341     /// ```rust
1342     /// # || {
1343     /// let metadata = std::fs::metadata("foo.txt")?;
1344     /// let filetype = metadata.file_type();
1345     ///
1346     /// if filetype.is_file() {
1347     ///     // read file
1348     /// }
1349     /// # Ok::<_, std::io::Error>(())
1350     /// # };
1351     /// ```
1352     ///
1353     /// should be written as:
1354     ///
1355     /// ```rust
1356     /// # || {
1357     /// let metadata = std::fs::metadata("foo.txt")?;
1358     /// let filetype = metadata.file_type();
1359     ///
1360     /// if !filetype.is_dir() {
1361     ///     // read file
1362     /// }
1363     /// # Ok::<_, std::io::Error>(())
1364     /// # };
1365     /// ```
1366     pub FILETYPE_IS_FILE,
1367     restriction,
1368     "`FileType::is_file` is not recommended to test for readable file type"
1369 }
1370
1371 declare_clippy_lint! {
1372     /// **What it does:** Checks for usage of `_.as_ref().map(Deref::deref)` or it's aliases (such as String::as_str).
1373     ///
1374     /// **Why is this bad?** Readability, this can be written more concisely as
1375     /// `_.as_deref()`.
1376     ///
1377     /// **Known problems:** None.
1378     ///
1379     /// **Example:**
1380     /// ```rust
1381     /// # let opt = Some("".to_string());
1382     /// opt.as_ref().map(String::as_str)
1383     /// # ;
1384     /// ```
1385     /// Can be written as
1386     /// ```rust
1387     /// # let opt = Some("".to_string());
1388     /// opt.as_deref()
1389     /// # ;
1390     /// ```
1391     pub OPTION_AS_REF_DEREF,
1392     complexity,
1393     "using `as_ref().map(Deref::deref)`, which is more succinctly expressed as `as_deref()`"
1394 }
1395
1396 declare_clippy_lint! {
1397     /// **What it does:** Checks for usage of `iter().next()` on a Slice or an Array
1398     ///
1399     /// **Why is this bad?** These can be shortened into `.get()`
1400     ///
1401     /// **Known problems:** None.
1402     ///
1403     /// **Example:**
1404     /// ```rust
1405     /// # let a = [1, 2, 3];
1406     /// # let b = vec![1, 2, 3];
1407     /// a[2..].iter().next();
1408     /// b.iter().next();
1409     /// ```
1410     /// should be written as:
1411     /// ```rust
1412     /// # let a = [1, 2, 3];
1413     /// # let b = vec![1, 2, 3];
1414     /// a.get(2);
1415     /// b.get(0);
1416     /// ```
1417     pub ITER_NEXT_SLICE,
1418     style,
1419     "using `.iter().next()` on a sliced array, which can be shortened to just `.get()`"
1420 }
1421
1422 declare_clippy_lint! {
1423     /// **What it does:** Warns when using `push_str`/`insert_str` with a single-character string literal
1424     /// where `push`/`insert` with a `char` would work fine.
1425     ///
1426     /// **Why is this bad?** It's less clear that we are pushing a single character.
1427     ///
1428     /// **Known problems:** None
1429     ///
1430     /// **Example:**
1431     /// ```rust
1432     /// let mut string = String::new();
1433     /// string.insert_str(0, "R");
1434     /// string.push_str("R");
1435     /// ```
1436     /// Could be written as
1437     /// ```rust
1438     /// let mut string = String::new();
1439     /// string.insert(0, 'R');
1440     /// string.push('R');
1441     /// ```
1442     pub SINGLE_CHAR_ADD_STR,
1443     style,
1444     "`push_str()` or `insert_str()` used with a single-character string literal as parameter"
1445 }
1446
1447 declare_clippy_lint! {
1448     /// **What it does:** As the counterpart to `or_fun_call`, this lint looks for unnecessary
1449     /// lazily evaluated closures on `Option` and `Result`.
1450     ///
1451     /// This lint suggests changing the following functions, when eager evaluation results in
1452     /// simpler code:
1453     ///  - `unwrap_or_else` to `unwrap_or`
1454     ///  - `and_then` to `and`
1455     ///  - `or_else` to `or`
1456     ///  - `get_or_insert_with` to `get_or_insert`
1457     ///  - `ok_or_else` to `ok_or`
1458     ///
1459     /// **Why is this bad?** Using eager evaluation is shorter and simpler in some cases.
1460     ///
1461     /// **Known problems:** It is possible, but not recommended for `Deref` and `Index` to have
1462     /// side effects. Eagerly evaluating them can change the semantics of the program.
1463     ///
1464     /// **Example:**
1465     ///
1466     /// ```rust
1467     /// // example code where clippy issues a warning
1468     /// let opt: Option<u32> = None;
1469     ///
1470     /// opt.unwrap_or_else(|| 42);
1471     /// ```
1472     /// Use instead:
1473     /// ```rust
1474     /// let opt: Option<u32> = None;
1475     ///
1476     /// opt.unwrap_or(42);
1477     /// ```
1478     pub UNNECESSARY_LAZY_EVALUATIONS,
1479     style,
1480     "using unnecessary lazy evaluation, which can be replaced with simpler eager evaluation"
1481 }
1482
1483 declare_clippy_lint! {
1484     /// **What it does:** Checks for usage of `_.map(_).collect::<Result<(), _>()`.
1485     ///
1486     /// **Why is this bad?** Using `try_for_each` instead is more readable and idiomatic.
1487     ///
1488     /// **Known problems:** None
1489     ///
1490     /// **Example:**
1491     ///
1492     /// ```rust
1493     /// (0..3).map(|t| Err(t)).collect::<Result<(), _>>();
1494     /// ```
1495     /// Use instead:
1496     /// ```rust
1497     /// (0..3).try_for_each(|t| Err(t));
1498     /// ```
1499     pub MAP_COLLECT_RESULT_UNIT,
1500     style,
1501     "using `.map(_).collect::<Result<(),_>()`, which can be replaced with `try_for_each`"
1502 }
1503
1504 declare_clippy_lint! {
1505     /// **What it does:** Checks for `from_iter()` function calls on types that implement the `FromIterator`
1506     /// trait.
1507     ///
1508     /// **Why is this bad?** It is recommended style to use collect. See
1509     /// [FromIterator documentation](https://doc.rust-lang.org/std/iter/trait.FromIterator.html)
1510     ///
1511     /// **Known problems:** None.
1512     ///
1513     /// **Example:**
1514     ///
1515     /// ```rust
1516     /// use std::iter::FromIterator;
1517     ///
1518     /// let five_fives = std::iter::repeat(5).take(5);
1519     ///
1520     /// let v = Vec::from_iter(five_fives);
1521     ///
1522     /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1523     /// ```
1524     /// Use instead:
1525     /// ```rust
1526     /// let five_fives = std::iter::repeat(5).take(5);
1527     ///
1528     /// let v: Vec<i32> = five_fives.collect();
1529     ///
1530     /// assert_eq!(v, vec![5, 5, 5, 5, 5]);
1531     /// ```
1532     pub FROM_ITER_INSTEAD_OF_COLLECT,
1533     pedantic,
1534     "use `.collect()` instead of `::from_iter()`"
1535 }
1536
1537 declare_clippy_lint! {
1538     /// **What it does:** Checks for usage of `inspect().for_each()`.
1539     ///
1540     /// **Why is this bad?** It is the same as performing the computation
1541     /// inside `inspect` at the beginning of the closure in `for_each`.
1542     ///
1543     /// **Known problems:** None.
1544     ///
1545     /// **Example:**
1546     ///
1547     /// ```rust
1548     /// [1,2,3,4,5].iter()
1549     /// .inspect(|&x| println!("inspect the number: {}", x))
1550     /// .for_each(|&x| {
1551     ///     assert!(x >= 0);
1552     /// });
1553     /// ```
1554     /// Can be written as
1555     /// ```rust
1556     /// [1,2,3,4,5].iter()
1557     /// .for_each(|&x| {
1558     ///     println!("inspect the number: {}", x);
1559     ///     assert!(x >= 0);
1560     /// });
1561     /// ```
1562     pub INSPECT_FOR_EACH,
1563     complexity,
1564     "using `.inspect().for_each()`, which can be replaced with `.for_each()`"
1565 }
1566
1567 declare_clippy_lint! {
1568     /// **What it does:** Checks for usage of `filter_map(|x| x)`.
1569     ///
1570     /// **Why is this bad?** Readability, this can be written more concisely by using `flatten`.
1571     ///
1572     /// **Known problems:** None.
1573     ///
1574     /// **Example:**
1575     ///
1576     /// ```rust
1577     /// # let iter = vec![Some(1)].into_iter();
1578     /// iter.filter_map(|x| x);
1579     /// ```
1580     /// Use instead:
1581     /// ```rust
1582     /// # let iter = vec![Some(1)].into_iter();
1583     /// iter.flatten();
1584     /// ```
1585     pub FILTER_MAP_IDENTITY,
1586     complexity,
1587     "call to `filter_map` where `flatten` is sufficient"
1588 }
1589
1590 declare_clippy_lint! {
1591     /// **What it does:** Checks for instances of `map(f)` where `f` is the identity function.
1592     ///
1593     /// **Why is this bad?** It can be written more concisely without the call to `map`.
1594     ///
1595     /// **Known problems:** None.
1596     ///
1597     /// **Example:**
1598     ///
1599     /// ```rust
1600     /// let x = [1, 2, 3];
1601     /// let y: Vec<_> = x.iter().map(|x| x).map(|x| 2*x).collect();
1602     /// ```
1603     /// Use instead:
1604     /// ```rust
1605     /// let x = [1, 2, 3];
1606     /// let y: Vec<_> = x.iter().map(|x| 2*x).collect();
1607     /// ```
1608     pub MAP_IDENTITY,
1609     complexity,
1610     "using iterator.map(|x| x)"
1611 }
1612
1613 declare_clippy_lint! {
1614     /// **What it does:** Checks for the use of `.bytes().nth()`.
1615     ///
1616     /// **Why is this bad?** `.as_bytes().get()` is more efficient and more
1617     /// readable.
1618     ///
1619     /// **Known problems:** None.
1620     ///
1621     /// **Example:**
1622     ///
1623     /// ```rust
1624     /// // Bad
1625     /// let _ = "Hello".bytes().nth(3);
1626     ///
1627     /// // Good
1628     /// let _ = "Hello".as_bytes().get(3);
1629     /// ```
1630     pub BYTES_NTH,
1631     style,
1632     "replace `.bytes().nth()` with `.as_bytes().get()`"
1633 }
1634
1635 declare_clippy_lint! {
1636     /// **What it does:** Checks for the usage of `_.to_owned()`, `vec.to_vec()`, or similar when calling `_.clone()` would be clearer.
1637     ///
1638     /// **Why is this bad?** These methods do the same thing as `_.clone()` but may be confusing as
1639     /// to why we are calling `to_vec` on something that is already a `Vec` or calling `to_owned` on something that is already owned.
1640     ///
1641     /// **Known problems:** None.
1642     ///
1643     /// **Example:**
1644     ///
1645     /// ```rust
1646     /// let a = vec![1, 2, 3];
1647     /// let b = a.to_vec();
1648     /// let c = a.to_owned();
1649     /// ```
1650     /// Use instead:
1651     /// ```rust
1652     /// let a = vec![1, 2, 3];
1653     /// let b = a.clone();
1654     /// let c = a.clone();
1655     /// ```
1656     pub IMPLICIT_CLONE,
1657     pedantic,
1658     "implicitly cloning a value by invoking a function on its dereferenced type"
1659 }
1660
1661 declare_clippy_lint! {
1662     /// **What it does:** Checks for the use of `.iter().count()`.
1663     ///
1664     /// **Why is this bad?** `.len()` is more efficient and more
1665     /// readable.
1666     ///
1667     /// **Known problems:** None.
1668     ///
1669     /// **Example:**
1670     ///
1671     /// ```rust
1672     /// // Bad
1673     /// let some_vec = vec![0, 1, 2, 3];
1674     /// let _ = some_vec.iter().count();
1675     /// let _ = &some_vec[..].iter().count();
1676     ///
1677     /// // Good
1678     /// let some_vec = vec![0, 1, 2, 3];
1679     /// let _ = some_vec.len();
1680     /// let _ = &some_vec[..].len();
1681     /// ```
1682     pub ITER_COUNT,
1683     complexity,
1684     "replace `.iter().count()` with `.len()`"
1685 }
1686
1687 declare_clippy_lint! {
1688     /// **What it does:** Checks for calls to [`splitn`]
1689     /// (https://doc.rust-lang.org/std/primitive.str.html#method.splitn) and
1690     /// related functions with either zero or one splits.
1691     ///
1692     /// **Why is this bad?** These calls don't actually split the value and are
1693     /// likely to be intended as a different number.
1694     ///
1695     /// **Known problems:** None.
1696     ///
1697     /// **Example:**
1698     ///
1699     /// ```rust
1700     /// // Bad
1701     /// let s = "";
1702     /// for x in s.splitn(1, ":") {
1703     ///     // use x
1704     /// }
1705     ///
1706     /// // Good
1707     /// let s = "";
1708     /// for x in s.splitn(2, ":") {
1709     ///     // use x
1710     /// }
1711     /// ```
1712     pub SUSPICIOUS_SPLITN,
1713     correctness,
1714     "checks for `.splitn(0, ..)` and `.splitn(1, ..)`"
1715 }
1716
1717 declare_clippy_lint! {
1718     /// **What it does:** Checks for manual implementations of `str::repeat`
1719     ///
1720     /// **Why is this bad?** These are both harder to read, as well as less performant.
1721     ///
1722     /// **Known problems:** None.
1723     ///
1724     /// **Example:**
1725     ///
1726     /// ```rust
1727     /// // Bad
1728     /// let x: String = std::iter::repeat('x').take(10).collect();
1729     ///
1730     /// // Good
1731     /// let x: String = "x".repeat(10);
1732     /// ```
1733     pub MANUAL_STR_REPEAT,
1734     perf,
1735     "manual implementation of `str::repeat`"
1736 }
1737
1738 pub struct Methods {
1739     avoid_breaking_exported_api: bool,
1740     msrv: Option<RustcVersion>,
1741 }
1742
1743 impl Methods {
1744     #[must_use]
1745     pub fn new(avoid_breaking_exported_api: bool, msrv: Option<RustcVersion>) -> Self {
1746         Self {
1747             avoid_breaking_exported_api,
1748             msrv,
1749         }
1750     }
1751 }
1752
1753 impl_lint_pass!(Methods => [
1754     UNWRAP_USED,
1755     EXPECT_USED,
1756     SHOULD_IMPLEMENT_TRAIT,
1757     WRONG_SELF_CONVENTION,
1758     OK_EXPECT,
1759     MAP_UNWRAP_OR,
1760     RESULT_MAP_OR_INTO_OPTION,
1761     OPTION_MAP_OR_NONE,
1762     BIND_INSTEAD_OF_MAP,
1763     OR_FUN_CALL,
1764     EXPECT_FUN_CALL,
1765     CHARS_NEXT_CMP,
1766     CHARS_LAST_CMP,
1767     CLONE_ON_COPY,
1768     CLONE_ON_REF_PTR,
1769     CLONE_DOUBLE_REF,
1770     CLONED_INSTEAD_OF_COPIED,
1771     FLAT_MAP_OPTION,
1772     INEFFICIENT_TO_STRING,
1773     NEW_RET_NO_SELF,
1774     SINGLE_CHAR_PATTERN,
1775     SINGLE_CHAR_ADD_STR,
1776     SEARCH_IS_SOME,
1777     FILTER_NEXT,
1778     SKIP_WHILE_NEXT,
1779     FILTER_MAP_IDENTITY,
1780     MAP_IDENTITY,
1781     MANUAL_FILTER_MAP,
1782     MANUAL_FIND_MAP,
1783     OPTION_FILTER_MAP,
1784     FILTER_MAP_NEXT,
1785     FLAT_MAP_IDENTITY,
1786     MAP_FLATTEN,
1787     ITERATOR_STEP_BY_ZERO,
1788     ITER_NEXT_SLICE,
1789     ITER_COUNT,
1790     ITER_NTH,
1791     ITER_NTH_ZERO,
1792     BYTES_NTH,
1793     ITER_SKIP_NEXT,
1794     GET_UNWRAP,
1795     STRING_EXTEND_CHARS,
1796     ITER_CLONED_COLLECT,
1797     USELESS_ASREF,
1798     UNNECESSARY_FOLD,
1799     UNNECESSARY_FILTER_MAP,
1800     INTO_ITER_ON_REF,
1801     SUSPICIOUS_MAP,
1802     UNINIT_ASSUMED_INIT,
1803     MANUAL_SATURATING_ARITHMETIC,
1804     ZST_OFFSET,
1805     FILETYPE_IS_FILE,
1806     OPTION_AS_REF_DEREF,
1807     UNNECESSARY_LAZY_EVALUATIONS,
1808     MAP_COLLECT_RESULT_UNIT,
1809     FROM_ITER_INSTEAD_OF_COLLECT,
1810     INSPECT_FOR_EACH,
1811     IMPLICIT_CLONE,
1812     SUSPICIOUS_SPLITN,
1813     MANUAL_STR_REPEAT,
1814     EXTEND_WITH_DRAIN
1815 ]);
1816
1817 /// Extracts a method call name, args, and `Span` of the method name.
1818 fn method_call<'tcx>(recv: &'tcx hir::Expr<'tcx>) -> Option<(SymbolStr, &'tcx [hir::Expr<'tcx>], Span)> {
1819     if let ExprKind::MethodCall(path, span, args, _) = recv.kind {
1820         if !args.iter().any(|e| e.span.from_expansion()) {
1821             return Some((path.ident.name.as_str(), args, span));
1822         }
1823     }
1824     None
1825 }
1826
1827 /// Same as `method_call` but the `SymbolStr` is dereferenced into a temporary `&str`
1828 macro_rules! method_call {
1829     ($expr:expr) => {
1830         method_call($expr)
1831             .as_ref()
1832             .map(|&(ref name, args, span)| (&**name, args, span))
1833     };
1834 }
1835
1836 impl<'tcx> LateLintPass<'tcx> for Methods {
1837     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx hir::Expr<'_>) {
1838         if in_macro(expr.span) {
1839             return;
1840         }
1841
1842         check_methods(cx, expr, self.msrv.as_ref());
1843
1844         match expr.kind {
1845             hir::ExprKind::Call(func, args) => {
1846                 from_iter_instead_of_collect::check(cx, expr, args, func);
1847             },
1848             hir::ExprKind::MethodCall(method_call, ref method_span, args, _) => {
1849                 or_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1850                 expect_fun_call::check(cx, expr, *method_span, &method_call.ident.as_str(), args);
1851                 clone_on_copy::check(cx, expr, method_call.ident.name, args);
1852                 clone_on_ref_ptr::check(cx, expr, method_call.ident.name, args);
1853                 inefficient_to_string::check(cx, expr, method_call.ident.name, args);
1854                 single_char_add_str::check(cx, expr, args);
1855                 into_iter_on_ref::check(cx, expr, *method_span, method_call.ident.name, args);
1856                 single_char_pattern::check(cx, expr, method_call.ident.name, args);
1857             },
1858             hir::ExprKind::Binary(op, lhs, rhs) if op.node == hir::BinOpKind::Eq || op.node == hir::BinOpKind::Ne => {
1859                 let mut info = BinaryExprInfo {
1860                     expr,
1861                     chain: lhs,
1862                     other: rhs,
1863                     eq: op.node == hir::BinOpKind::Eq,
1864                 };
1865                 lint_binary_expr_with_method_call(cx, &mut info);
1866             },
1867             _ => (),
1868         }
1869     }
1870
1871     #[allow(clippy::too_many_lines)]
1872     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, impl_item: &'tcx hir::ImplItem<'_>) {
1873         if in_external_macro(cx.sess(), impl_item.span) {
1874             return;
1875         }
1876         let name = impl_item.ident.name.as_str();
1877         let parent = cx.tcx.hir().get_parent_item(impl_item.hir_id());
1878         let item = cx.tcx.hir().expect_item(parent);
1879         let self_ty = cx.tcx.type_of(item.def_id);
1880
1881         let implements_trait = matches!(item.kind, hir::ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }));
1882         if_chain! {
1883             if let hir::ImplItemKind::Fn(ref sig, id) = impl_item.kind;
1884             if let Some(first_arg) = iter_input_pats(sig.decl, cx.tcx.hir().body(id)).next();
1885
1886             let method_sig = cx.tcx.fn_sig(impl_item.def_id);
1887             let method_sig = cx.tcx.erase_late_bound_regions(method_sig);
1888
1889             let first_arg_ty = &method_sig.inputs().iter().next();
1890
1891             // check conventions w.r.t. conversion method names and predicates
1892             if let Some(first_arg_ty) = first_arg_ty;
1893
1894             then {
1895                 // if this impl block implements a trait, lint in trait definition instead
1896                 if !implements_trait && cx.access_levels.is_exported(impl_item.hir_id()) {
1897                     // check missing trait implementations
1898                     for method_config in &TRAIT_METHODS {
1899                         if name == method_config.method_name &&
1900                             sig.decl.inputs.len() == method_config.param_count &&
1901                             method_config.output_type.matches(&sig.decl.output) &&
1902                             method_config.self_kind.matches(cx, self_ty, first_arg_ty) &&
1903                             fn_header_equals(method_config.fn_header, sig.header) &&
1904                             method_config.lifetime_param_cond(impl_item)
1905                         {
1906                             span_lint_and_help(
1907                                 cx,
1908                                 SHOULD_IMPLEMENT_TRAIT,
1909                                 impl_item.span,
1910                                 &format!(
1911                                     "method `{}` can be confused for the standard trait method `{}::{}`",
1912                                     method_config.method_name,
1913                                     method_config.trait_name,
1914                                     method_config.method_name
1915                                 ),
1916                                 None,
1917                                 &format!(
1918                                     "consider implementing the trait `{}` or choosing a less ambiguous method name",
1919                                     method_config.trait_name
1920                                 )
1921                             );
1922                         }
1923                     }
1924                 }
1925
1926                 if sig.decl.implicit_self.has_implicit_self()
1927                     && !(self.avoid_breaking_exported_api
1928                         && cx.access_levels.is_exported(impl_item.hir_id()))
1929                 {
1930                     wrong_self_convention::check(
1931                         cx,
1932                         &name,
1933                         self_ty,
1934                         first_arg_ty,
1935                         first_arg.pat.span,
1936                         implements_trait,
1937                         false
1938                     );
1939                 }
1940             }
1941         }
1942
1943         // if this impl block implements a trait, lint in trait definition instead
1944         if implements_trait {
1945             return;
1946         }
1947
1948         if let hir::ImplItemKind::Fn(_, _) = impl_item.kind {
1949             let ret_ty = return_ty(cx, impl_item.hir_id());
1950
1951             // walk the return type and check for Self (this does not check associated types)
1952             if let Some(self_adt) = self_ty.ty_adt_def() {
1953                 if contains_adt_constructor(ret_ty, self_adt) {
1954                     return;
1955                 }
1956             } else if contains_ty(ret_ty, self_ty) {
1957                 return;
1958             }
1959
1960             // if return type is impl trait, check the associated types
1961             if let ty::Opaque(def_id, _) = *ret_ty.kind() {
1962                 // one of the associated types must be Self
1963                 for &(predicate, _span) in cx.tcx.explicit_item_bounds(def_id) {
1964                     if let ty::PredicateKind::Projection(projection_predicate) = predicate.kind().skip_binder() {
1965                         // walk the associated type and check for Self
1966                         if let Some(self_adt) = self_ty.ty_adt_def() {
1967                             if contains_adt_constructor(projection_predicate.ty, self_adt) {
1968                                 return;
1969                             }
1970                         } else if contains_ty(projection_predicate.ty, self_ty) {
1971                             return;
1972                         }
1973                     }
1974                 }
1975             }
1976
1977             if name == "new" && !TyS::same_type(ret_ty, self_ty) {
1978                 span_lint(
1979                     cx,
1980                     NEW_RET_NO_SELF,
1981                     impl_item.span,
1982                     "methods called `new` usually return `Self`",
1983                 );
1984             }
1985         }
1986     }
1987
1988     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1989         if in_external_macro(cx.tcx.sess, item.span) {
1990             return;
1991         }
1992
1993         if_chain! {
1994             if let TraitItemKind::Fn(ref sig, _) = item.kind;
1995             if sig.decl.implicit_self.has_implicit_self();
1996             if let Some(first_arg_ty) = sig.decl.inputs.iter().next();
1997
1998             then {
1999                 let first_arg_span = first_arg_ty.span;
2000                 let first_arg_ty = hir_ty_to_ty(cx.tcx, first_arg_ty);
2001                 let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
2002                 wrong_self_convention::check(
2003                     cx,
2004                     &item.ident.name.as_str(),
2005                     self_ty,
2006                     first_arg_ty,
2007                     first_arg_span,
2008                     false,
2009                     true
2010                 );
2011             }
2012         }
2013
2014         if_chain! {
2015             if item.ident.name == sym::new;
2016             if let TraitItemKind::Fn(_, _) = item.kind;
2017             let ret_ty = return_ty(cx, item.hir_id());
2018             let self_ty = TraitRef::identity(cx.tcx, item.def_id.to_def_id()).self_ty();
2019             if !contains_ty(ret_ty, self_ty);
2020
2021             then {
2022                 span_lint(
2023                     cx,
2024                     NEW_RET_NO_SELF,
2025                     item.span,
2026                     "methods called `new` usually return `Self`",
2027                 );
2028             }
2029         }
2030     }
2031
2032     extract_msrv_attr!(LateContext);
2033 }
2034
2035 #[allow(clippy::too_many_lines)]
2036 fn check_methods<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>, msrv: Option<&RustcVersion>) {
2037     if let Some((name, [recv, args @ ..], span)) = method_call!(expr) {
2038         match (name, args) {
2039             ("add" | "offset" | "sub" | "wrapping_offset" | "wrapping_add" | "wrapping_sub", [_arg]) => {
2040                 zst_offset::check(cx, expr, recv);
2041             },
2042             ("and_then", [arg]) => {
2043                 let biom_option_linted = bind_instead_of_map::OptionAndThenSome::check(cx, expr, recv, arg);
2044                 let biom_result_linted = bind_instead_of_map::ResultAndThenOk::check(cx, expr, recv, arg);
2045                 if !biom_option_linted && !biom_result_linted {
2046                     unnecessary_lazy_eval::check(cx, expr, recv, arg, "and");
2047                 }
2048             },
2049             ("as_mut", []) => useless_asref::check(cx, expr, "as_mut", recv),
2050             ("as_ref", []) => useless_asref::check(cx, expr, "as_ref", recv),
2051             ("assume_init", []) => uninit_assumed_init::check(cx, expr, recv),
2052             ("cloned", []) => cloned_instead_of_copied::check(cx, expr, recv, span, msrv),
2053             ("collect", []) => match method_call!(recv) {
2054                 Some(("cloned", [recv2], _)) => iter_cloned_collect::check(cx, expr, recv2),
2055                 Some(("map", [m_recv, m_arg], _)) => {
2056                     map_collect_result_unit::check(cx, expr, m_recv, m_arg, recv);
2057                 },
2058                 Some(("take", [take_self_arg, take_arg], _)) => {
2059                     if meets_msrv(msrv, &msrvs::STR_REPEAT) {
2060                         manual_str_repeat::check(cx, expr, recv, take_self_arg, take_arg);
2061                     }
2062                 },
2063                 _ => {},
2064             },
2065             ("count", []) => match method_call!(recv) {
2066                 Some((name @ ("into_iter" | "iter" | "iter_mut"), [recv2], _)) => {
2067                     iter_count::check(cx, expr, recv2, name);
2068                 },
2069                 Some(("map", [_, arg], _)) => suspicious_map::check(cx, expr, recv, arg),
2070                 _ => {},
2071             },
2072             ("expect", [_]) => match method_call!(recv) {
2073                 Some(("ok", [recv], _)) => ok_expect::check(cx, expr, recv),
2074                 _ => expect_used::check(cx, expr, recv),
2075             },
2076             ("extend", [arg]) => {
2077                 string_extend_chars::check(cx, expr, recv, arg);
2078                 extend_with_drain::check(cx, expr, recv, arg);
2079             },
2080             ("filter_map", [arg]) => {
2081                 unnecessary_filter_map::check(cx, expr, arg);
2082                 filter_map_identity::check(cx, expr, arg, span);
2083             },
2084             ("flat_map", [arg]) => {
2085                 flat_map_identity::check(cx, expr, arg, span);
2086                 flat_map_option::check(cx, expr, arg, span);
2087             },
2088             ("flatten", []) => {
2089                 if let Some(("map", [recv, map_arg], _)) = method_call!(recv) {
2090                     map_flatten::check(cx, expr, recv, map_arg);
2091                 }
2092             },
2093             ("fold", [init, acc]) => unnecessary_fold::check(cx, expr, init, acc, span),
2094             ("for_each", [_]) => {
2095                 if let Some(("inspect", [_, _], span2)) = method_call!(recv) {
2096                     inspect_for_each::check(cx, expr, span2);
2097                 }
2098             },
2099             ("get_or_insert_with", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "get_or_insert"),
2100             ("is_file", []) => filetype_is_file::check(cx, expr, recv),
2101             ("is_none", []) => check_is_some_is_none(cx, expr, recv, false),
2102             ("is_some", []) => check_is_some_is_none(cx, expr, recv, true),
2103             ("map", [m_arg]) => {
2104                 if let Some((name, [recv2, args @ ..], span2)) = method_call!(recv) {
2105                     match (name, args) {
2106                         ("as_mut", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, true, msrv),
2107                         ("as_ref", []) => option_as_ref_deref::check(cx, expr, recv2, m_arg, false, msrv),
2108                         ("filter", [f_arg]) => {
2109                             filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, false);
2110                         },
2111                         ("find", [f_arg]) => filter_map::check(cx, expr, recv2, f_arg, span2, recv, m_arg, span, true),
2112                         _ => {},
2113                     }
2114                 }
2115                 map_identity::check(cx, expr, recv, m_arg, span);
2116             },
2117             ("map_or", [def, map]) => option_map_or_none::check(cx, expr, recv, def, map),
2118             ("next", []) => {
2119                 if let Some((name, [recv, args @ ..], _)) = method_call!(recv) {
2120                     match (name, args) {
2121                         ("filter", [arg]) => filter_next::check(cx, expr, recv, arg),
2122                         ("filter_map", [arg]) => filter_map_next::check(cx, expr, recv, arg, msrv),
2123                         ("iter", []) => iter_next_slice::check(cx, expr, recv),
2124                         ("skip", [arg]) => iter_skip_next::check(cx, expr, recv, arg),
2125                         ("skip_while", [_]) => skip_while_next::check(cx, expr),
2126                         _ => {},
2127                     }
2128                 }
2129             },
2130             ("nth", [n_arg]) => match method_call!(recv) {
2131                 Some(("bytes", [recv2], _)) => bytes_nth::check(cx, expr, recv2, n_arg),
2132                 Some(("iter", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, false),
2133                 Some(("iter_mut", [recv2], _)) => iter_nth::check(cx, expr, recv2, recv, n_arg, true),
2134                 _ => iter_nth_zero::check(cx, expr, recv, n_arg),
2135             },
2136             ("ok_or_else", [arg]) => unnecessary_lazy_eval::check(cx, expr, recv, arg, "ok_or"),
2137             ("or_else", [arg]) => {
2138                 if !bind_instead_of_map::ResultOrElseErrInfo::check(cx, expr, recv, arg) {
2139                     unnecessary_lazy_eval::check(cx, expr, recv, arg, "or");
2140                 }
2141             },
2142             ("splitn" | "splitn_mut" | "rsplitn" | "rsplitn_mut", [count_arg, _]) => {
2143                 suspicious_splitn::check(cx, name, expr, recv, count_arg);
2144             },
2145             ("step_by", [arg]) => iterator_step_by_zero::check(cx, expr, arg),
2146             ("to_os_string" | "to_owned" | "to_path_buf" | "to_vec", []) => {
2147                 implicit_clone::check(cx, name, expr, recv, span);
2148             },
2149             ("unwrap", []) => match method_call!(recv) {
2150                 Some(("get", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, false),
2151                 Some(("get_mut", [recv, get_arg], _)) => get_unwrap::check(cx, expr, recv, get_arg, true),
2152                 _ => unwrap_used::check(cx, expr, recv),
2153             },
2154             ("unwrap_or", [u_arg]) => match method_call!(recv) {
2155                 Some((arith @ ("checked_add" | "checked_sub" | "checked_mul"), [lhs, rhs], _)) => {
2156                     manual_saturating_arithmetic::check(cx, expr, lhs, rhs, u_arg, &arith["checked_".len()..]);
2157                 },
2158                 Some(("map", [m_recv, m_arg], span)) => {
2159                     option_map_unwrap_or::check(cx, expr, m_recv, m_arg, recv, u_arg, span);
2160                 },
2161                 _ => {},
2162             },
2163             ("unwrap_or_else", [u_arg]) => match method_call!(recv) {
2164                 Some(("map", [recv, map_arg], _)) if map_unwrap_or::check(cx, expr, recv, map_arg, u_arg, msrv) => {},
2165                 _ => unnecessary_lazy_eval::check(cx, expr, recv, u_arg, "unwrap_or"),
2166             },
2167             _ => {},
2168         }
2169     }
2170 }
2171
2172 fn check_is_some_is_none(cx: &LateContext<'_>, expr: &Expr<'_>, recv: &Expr<'_>, is_some: bool) {
2173     if let Some((name @ ("find" | "position" | "rposition"), [f_recv, arg], span)) = method_call!(recv) {
2174         search_is_some::check(cx, expr, name, is_some, f_recv, arg, recv, span);
2175     }
2176 }
2177
2178 /// Used for `lint_binary_expr_with_method_call`.
2179 #[derive(Copy, Clone)]
2180 struct BinaryExprInfo<'a> {
2181     expr: &'a hir::Expr<'a>,
2182     chain: &'a hir::Expr<'a>,
2183     other: &'a hir::Expr<'a>,
2184     eq: bool,
2185 }
2186
2187 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
2188 fn lint_binary_expr_with_method_call(cx: &LateContext<'_>, info: &mut BinaryExprInfo<'_>) {
2189     macro_rules! lint_with_both_lhs_and_rhs {
2190         ($func:expr, $cx:expr, $info:ident) => {
2191             if !$func($cx, $info) {
2192                 ::std::mem::swap(&mut $info.chain, &mut $info.other);
2193                 if $func($cx, $info) {
2194                     return;
2195                 }
2196             }
2197         };
2198     }
2199
2200     lint_with_both_lhs_and_rhs!(chars_next_cmp::check, cx, info);
2201     lint_with_both_lhs_and_rhs!(chars_last_cmp::check, cx, info);
2202     lint_with_both_lhs_and_rhs!(chars_next_cmp_with_unwrap::check, cx, info);
2203     lint_with_both_lhs_and_rhs!(chars_last_cmp_with_unwrap::check, cx, info);
2204 }
2205
2206 const FN_HEADER: hir::FnHeader = hir::FnHeader {
2207     unsafety: hir::Unsafety::Normal,
2208     constness: hir::Constness::NotConst,
2209     asyncness: hir::IsAsync::NotAsync,
2210     abi: rustc_target::spec::abi::Abi::Rust,
2211 };
2212
2213 struct ShouldImplTraitCase {
2214     trait_name: &'static str,
2215     method_name: &'static str,
2216     param_count: usize,
2217     fn_header: hir::FnHeader,
2218     // implicit self kind expected (none, self, &self, ...)
2219     self_kind: SelfKind,
2220     // checks against the output type
2221     output_type: OutType,
2222     // certain methods with explicit lifetimes can't implement the equivalent trait method
2223     lint_explicit_lifetime: bool,
2224 }
2225 impl ShouldImplTraitCase {
2226     const fn new(
2227         trait_name: &'static str,
2228         method_name: &'static str,
2229         param_count: usize,
2230         fn_header: hir::FnHeader,
2231         self_kind: SelfKind,
2232         output_type: OutType,
2233         lint_explicit_lifetime: bool,
2234     ) -> ShouldImplTraitCase {
2235         ShouldImplTraitCase {
2236             trait_name,
2237             method_name,
2238             param_count,
2239             fn_header,
2240             self_kind,
2241             output_type,
2242             lint_explicit_lifetime,
2243         }
2244     }
2245
2246     fn lifetime_param_cond(&self, impl_item: &hir::ImplItem<'_>) -> bool {
2247         self.lint_explicit_lifetime
2248             || !impl_item.generics.params.iter().any(|p| {
2249                 matches!(
2250                     p.kind,
2251                     hir::GenericParamKind::Lifetime {
2252                         kind: hir::LifetimeParamKind::Explicit
2253                     }
2254                 )
2255             })
2256     }
2257 }
2258
2259 #[rustfmt::skip]
2260 const TRAIT_METHODS: [ShouldImplTraitCase; 30] = [
2261     ShouldImplTraitCase::new("std::ops::Add", "add",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2262     ShouldImplTraitCase::new("std::convert::AsMut", "as_mut",  1,  FN_HEADER,  SelfKind::RefMut,  OutType::Ref, true),
2263     ShouldImplTraitCase::new("std::convert::AsRef", "as_ref",  1,  FN_HEADER,  SelfKind::Ref,  OutType::Ref, true),
2264     ShouldImplTraitCase::new("std::ops::BitAnd", "bitand",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2265     ShouldImplTraitCase::new("std::ops::BitOr", "bitor",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2266     ShouldImplTraitCase::new("std::ops::BitXor", "bitxor",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2267     ShouldImplTraitCase::new("std::borrow::Borrow", "borrow",  1,  FN_HEADER,  SelfKind::Ref,  OutType::Ref, true),
2268     ShouldImplTraitCase::new("std::borrow::BorrowMut", "borrow_mut",  1,  FN_HEADER,  SelfKind::RefMut,  OutType::Ref, true),
2269     ShouldImplTraitCase::new("std::clone::Clone", "clone",  1,  FN_HEADER,  SelfKind::Ref,  OutType::Any, true),
2270     ShouldImplTraitCase::new("std::cmp::Ord", "cmp",  2,  FN_HEADER,  SelfKind::Ref,  OutType::Any, true),
2271     // FIXME: default doesn't work
2272     ShouldImplTraitCase::new("std::default::Default", "default",  0,  FN_HEADER,  SelfKind::No,  OutType::Any, true),
2273     ShouldImplTraitCase::new("std::ops::Deref", "deref",  1,  FN_HEADER,  SelfKind::Ref,  OutType::Ref, true),
2274     ShouldImplTraitCase::new("std::ops::DerefMut", "deref_mut",  1,  FN_HEADER,  SelfKind::RefMut,  OutType::Ref, true),
2275     ShouldImplTraitCase::new("std::ops::Div", "div",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2276     ShouldImplTraitCase::new("std::ops::Drop", "drop",  1,  FN_HEADER,  SelfKind::RefMut,  OutType::Unit, true),
2277     ShouldImplTraitCase::new("std::cmp::PartialEq", "eq",  2,  FN_HEADER,  SelfKind::Ref,  OutType::Bool, true),
2278     ShouldImplTraitCase::new("std::iter::FromIterator", "from_iter",  1,  FN_HEADER,  SelfKind::No,  OutType::Any, true),
2279     ShouldImplTraitCase::new("std::str::FromStr", "from_str",  1,  FN_HEADER,  SelfKind::No,  OutType::Any, true),
2280     ShouldImplTraitCase::new("std::hash::Hash", "hash",  2,  FN_HEADER,  SelfKind::Ref,  OutType::Unit, true),
2281     ShouldImplTraitCase::new("std::ops::Index", "index",  2,  FN_HEADER,  SelfKind::Ref,  OutType::Ref, true),
2282     ShouldImplTraitCase::new("std::ops::IndexMut", "index_mut",  2,  FN_HEADER,  SelfKind::RefMut,  OutType::Ref, true),
2283     ShouldImplTraitCase::new("std::iter::IntoIterator", "into_iter",  1,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2284     ShouldImplTraitCase::new("std::ops::Mul", "mul",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2285     ShouldImplTraitCase::new("std::ops::Neg", "neg",  1,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2286     ShouldImplTraitCase::new("std::iter::Iterator", "next",  1,  FN_HEADER,  SelfKind::RefMut,  OutType::Any, false),
2287     ShouldImplTraitCase::new("std::ops::Not", "not",  1,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2288     ShouldImplTraitCase::new("std::ops::Rem", "rem",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2289     ShouldImplTraitCase::new("std::ops::Shl", "shl",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2290     ShouldImplTraitCase::new("std::ops::Shr", "shr",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2291     ShouldImplTraitCase::new("std::ops::Sub", "sub",  2,  FN_HEADER,  SelfKind::Value,  OutType::Any, true),
2292 ];
2293
2294 #[derive(Clone, Copy, PartialEq, Debug)]
2295 enum SelfKind {
2296     Value,
2297     Ref,
2298     RefMut,
2299     No,
2300 }
2301
2302 impl SelfKind {
2303     fn matches<'a>(self, cx: &LateContext<'a>, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2304         fn matches_value<'a>(cx: &LateContext<'a>, parent_ty: Ty<'_>, ty: Ty<'_>) -> bool {
2305             if ty == parent_ty {
2306                 true
2307             } else if ty.is_box() {
2308                 ty.boxed_ty() == parent_ty
2309             } else if is_type_diagnostic_item(cx, ty, sym::Rc) || is_type_diagnostic_item(cx, ty, sym::Arc) {
2310                 if let ty::Adt(_, substs) = ty.kind() {
2311                     substs.types().next().map_or(false, |t| t == parent_ty)
2312                 } else {
2313                     false
2314                 }
2315             } else {
2316                 false
2317             }
2318         }
2319
2320         fn matches_ref<'a>(cx: &LateContext<'a>, mutability: hir::Mutability, parent_ty: Ty<'a>, ty: Ty<'a>) -> bool {
2321             if let ty::Ref(_, t, m) = *ty.kind() {
2322                 return m == mutability && t == parent_ty;
2323             }
2324
2325             let trait_path = match mutability {
2326                 hir::Mutability::Not => &paths::ASREF_TRAIT,
2327                 hir::Mutability::Mut => &paths::ASMUT_TRAIT,
2328             };
2329
2330             let trait_def_id = match get_trait_def_id(cx, trait_path) {
2331                 Some(did) => did,
2332                 None => return false,
2333             };
2334             implements_trait(cx, ty, trait_def_id, &[parent_ty.into()])
2335         }
2336
2337         match self {
2338             Self::Value => matches_value(cx, parent_ty, ty),
2339             Self::Ref => matches_ref(cx, hir::Mutability::Not, parent_ty, ty) || ty == parent_ty && is_copy(cx, ty),
2340             Self::RefMut => matches_ref(cx, hir::Mutability::Mut, parent_ty, ty),
2341             Self::No => ty != parent_ty,
2342         }
2343     }
2344
2345     #[must_use]
2346     fn description(self) -> &'static str {
2347         match self {
2348             Self::Value => "`self` by value",
2349             Self::Ref => "`self` by reference",
2350             Self::RefMut => "`self` by mutable reference",
2351             Self::No => "no `self`",
2352         }
2353     }
2354 }
2355
2356 #[derive(Clone, Copy)]
2357 enum OutType {
2358     Unit,
2359     Bool,
2360     Any,
2361     Ref,
2362 }
2363
2364 impl OutType {
2365     fn matches(self, ty: &hir::FnRetTy<'_>) -> bool {
2366         let is_unit = |ty: &hir::Ty<'_>| matches!(ty.kind, hir::TyKind::Tup(&[]));
2367         match (self, ty) {
2368             (Self::Unit, &hir::FnRetTy::DefaultReturn(_)) => true,
2369             (Self::Unit, &hir::FnRetTy::Return(ty)) if is_unit(ty) => true,
2370             (Self::Bool, &hir::FnRetTy::Return(ty)) if is_bool(ty) => true,
2371             (Self::Any, &hir::FnRetTy::Return(ty)) if !is_unit(ty) => true,
2372             (Self::Ref, &hir::FnRetTy::Return(ty)) => matches!(ty.kind, hir::TyKind::Rptr(_, _)),
2373             _ => false,
2374         }
2375     }
2376 }
2377
2378 fn is_bool(ty: &hir::Ty<'_>) -> bool {
2379     if let hir::TyKind::Path(QPath::Resolved(_, path)) = ty.kind {
2380         matches!(path.res, Res::PrimTy(PrimTy::Bool))
2381     } else {
2382         false
2383     }
2384 }
2385
2386 fn fn_header_equals(expected: hir::FnHeader, actual: hir::FnHeader) -> bool {
2387     expected.constness == actual.constness
2388         && expected.unsafety == actual.unsafety
2389         && expected.asyncness == actual.asyncness
2390 }