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

   1 use rustc::hir;
   2 use rustc::lint::*;
   3 use rustc::middle::const_val::ConstVal;
   4 use rustc::ty::{self, Ty};
   5 use rustc::hir::def::Def;
   6 use rustc::ty::subst::Substs;
   7 use rustc_const_eval::ConstContext;
   8 use std::borrow::Cow;
   9 use std::fmt;
  10 use std::iter;
  11 use syntax::ast;
  12 use syntax::codemap::{Span, BytePos};
  13 use utils::{get_arg_name, get_trait_def_id, implements_trait, in_external_macro, in_macro, is_copy, is_self, is_self_ty,
  14             iter_input_pats, last_path_segment, match_def_path, match_path, match_qpath, match_trait_method,
  15             match_type, method_chain_args, match_var, return_ty, remove_blocks, same_tys, single_segment_path, snippet,
  16             span_lint, span_lint_and_sugg, span_lint_and_then, span_note_and_lint, walk_ptrs_ty, walk_ptrs_ty_depth};
  17 use utils::paths;
  18 use utils::sugg;
  19 use utils::const_to_u64;
  20
  21 #[derive(Clone)]
  22 pub struct Pass;
  23
  24 /// **What it does:** Checks for `.unwrap()` calls on `Option`s.
  25 ///
  26 /// **Why is this bad?** Usually it is better to handle the `None` case, or to
  27 /// at least call `.expect(_)` with a more helpful message. Still, for a lot of
  28 /// quick-and-dirty code, `unwrap` is a good choice, which is why this lint is
  29 /// `Allow` by default.
  30 ///
  31 /// **Known problems:** None.
  32 ///
  33 /// **Example:**
  34 /// ```rust
  35 /// x.unwrap()
  36 /// ```
  37 declare_lint! {
  38     pub OPTION_UNWRAP_USED,
  39     Allow,
  40     "using `Option.unwrap()`, which should at least get a better message using `expect()`"
  41 }
  42
  43 /// **What it does:** Checks for `.unwrap()` calls on `Result`s.
  44 ///
  45 /// **Why is this bad?** `result.unwrap()` will let the thread panic on `Err`
  46 /// values. Normally, you want to implement more sophisticated error handling,
  47 /// and propagate errors upwards with `try!`.
  48 ///
  49 /// Even if you want to panic on errors, not all `Error`s implement good
  50 /// messages on display.  Therefore it may be beneficial to look at the places
  51 /// where they may get displayed. Activate this lint to do just that.
  52 ///
  53 /// **Known problems:** None.
  54 ///
  55 /// **Example:**
  56 /// ```rust
  57 /// x.unwrap()
  58 /// ```
  59 declare_lint! {
  60     pub RESULT_UNWRAP_USED,
  61     Allow,
  62     "using `Result.unwrap()`, which might be better handled"
  63 }
  64
  65 /// **What it does:** Checks for methods that should live in a trait
  66 /// implementation of a `std` trait (see [llogiq's blog
  67 /// post](http://llogiq.github.io/2015/07/30/traits.html) for further
  68 /// information) instead of an inherent implementation.
  69 ///
  70 /// **Why is this bad?** Implementing the traits improve ergonomics for users of
  71 /// the code, often with very little cost. Also people seeing a `mul(...)`
  72 /// method
  73 /// may expect `*` to work equally, so you should have good reason to disappoint
  74 /// them.
  75 ///
  76 /// **Known problems:** None.
  77 ///
  78 /// **Example:**
  79 /// ```rust
  80 /// struct X;
  81 /// impl X {
  82 ///    fn add(&self, other: &X) -> X { .. }
  83 /// }
  84 /// ```
  85 declare_lint! {
  86     pub SHOULD_IMPLEMENT_TRAIT,
  87     Warn,
  88     "defining a method that should be implementing a std trait"
  89 }
  90
  91 /// **What it does:** Checks for methods with certain name prefixes and which
  92 /// doesn't match how self is taken. The actual rules are:
  93 ///
  94 /// |Prefix |`self` taken          |
  95 /// |-------|----------------------|
  96 /// |`as_`  |`&self` or `&mut self`|
  97 /// |`from_`| none                 |
  98 /// |`into_`|`self`                |
  99 /// |`is_`  |`&self` or none       |
 100 /// |`to_`  |`&self`               |
 101 ///
 102 /// **Why is this bad?** Consistency breeds readability. If you follow the
 103 /// conventions, your users won't be surprised that they, e.g., need to supply a
 104 /// mutable reference to a `as_..` function.
 105 ///
 106 /// **Known problems:** None.
 107 ///
 108 /// **Example:**
 109 /// ```rust
 110 /// impl X {
 111 ///     fn as_str(self) -> &str { .. }
 112 /// }
 113 /// ```
 114 declare_lint! {
 115     pub WRONG_SELF_CONVENTION,
 116     Warn,
 117     "defining a method named with an established prefix (like \"into_\") that takes \
 118      `self` with the wrong convention"
 119 }
 120
 121 /// **What it does:** This is the same as
 122 /// [`wrong_self_convention`](#wrong_self_convention), but for public items.
 123 ///
 124 /// **Why is this bad?** See [`wrong_self_convention`](#wrong_self_convention).
 125 ///
 126 /// **Known problems:** Actually *renaming* the function may break clients if
 127 /// the function is part of the public interface. In that case, be mindful of
 128 /// the stability guarantees you've given your users.
 129 ///
 130 /// **Example:**
 131 /// ```rust
 132 /// impl X {
 133 ///     pub fn as_str(self) -> &str { .. }
 134 /// }
 135 /// ```
 136 declare_lint! {
 137     pub WRONG_PUB_SELF_CONVENTION,
 138     Allow,
 139     "defining a public method named with an established prefix (like \"into_\") that takes \
 140      `self` with the wrong convention"
 141 }
 142
 143 /// **What it does:** Checks for usage of `ok().expect(..)`.
 144 ///
 145 /// **Why is this bad?** Because you usually call `expect()` on the `Result`
 146 /// directly to get a better error message.
 147 ///
 148 /// **Known problems:** None.
 149 ///
 150 /// **Example:**
 151 /// ```rust
 152 /// x.ok().expect("why did I do this again?")
 153 /// ```
 154 declare_lint! {
 155     pub OK_EXPECT,
 156     Warn,
 157     "using `ok().expect()`, which gives worse error messages than \
 158      calling `expect` directly on the Result"
 159 }
 160
 161 /// **What it does:** Checks for usage of `_.map(_).unwrap_or(_)`.
 162 ///
 163 /// **Why is this bad?** Readability, this can be written more concisely as
 164 /// `_.map_or(_, _)`.
 165 ///
 166 /// **Known problems:** None.
 167 ///
 168 /// **Example:**
 169 /// ```rust
 170 /// x.map(|a| a + 1).unwrap_or(0)
 171 /// ```
 172 declare_lint! {
 173     pub OPTION_MAP_UNWRAP_OR,
 174     Allow,
 175     "using `Option.map(f).unwrap_or(a)`, which is more succinctly expressed as \
 176      `map_or(a, f)`"
 177 }
 178
 179 /// **What it does:** Checks for usage of `_.map(_).unwrap_or_else(_)`.
 180 ///
 181 /// **Why is this bad?** Readability, this can be written more concisely as
 182 /// `_.map_or_else(_, _)`.
 183 ///
 184 /// **Known problems:** None.
 185 ///
 186 /// **Example:**
 187 /// ```rust
 188 /// x.map(|a| a + 1).unwrap_or_else(some_function)
 189 /// ```
 190 declare_lint! {
 191     pub OPTION_MAP_UNWRAP_OR_ELSE,
 192     Allow,
 193     "using `Option.map(f).unwrap_or_else(g)`, which is more succinctly expressed as \
 194      `map_or_else(g, f)`"
 195 }
 196
 197 /// **What it does:** Checks for usage of `result.map(_).unwrap_or_else(_)`.
 198 ///
 199 /// **Why is this bad?** Readability, this can be written more concisely as
 200 /// `result.ok().map_or_else(_, _)`.
 201 ///
 202 /// **Known problems:** None.
 203 ///
 204 /// **Example:**
 205 /// ```rust
 206 /// x.map(|a| a + 1).unwrap_or_else(some_function)
 207 /// ```
 208 declare_lint! {
 209     pub RESULT_MAP_UNWRAP_OR_ELSE,
 210     Allow,
 211     "using `Result.map(f).unwrap_or_else(g)`, which is more succinctly expressed as \
 212      `.ok().map_or_else(g, f)`"
 213 }
 214
 215 /// **What it does:** Checks for usage of `_.map_or(None, _)`.
 216 ///
 217 /// **Why is this bad?** Readability, this can be written more concisely as
 218 /// `_.and_then(_)`.
 219 ///
 220 /// **Known problems:** None.
 221 ///
 222 /// **Example:**
 223 /// ```rust
 224 /// opt.map_or(None, |a| a + 1)
 225 /// ```
 226 declare_lint! {
 227     pub OPTION_MAP_OR_NONE,
 228     Warn,
 229     "using `Option.map_or(None, f)`, which is more succinctly expressed as \
 230      `and_then(f)`"
 231 }
 232
 233 /// **What it does:** Checks for usage of `_.filter(_).next()`.
 234 ///
 235 /// **Why is this bad?** Readability, this can be written more concisely as
 236 /// `_.find(_)`.
 237 ///
 238 /// **Known problems:** None.
 239 ///
 240 /// **Example:**
 241 /// ```rust
 242 /// iter.filter(|x| x == 0).next()
 243 /// ```
 244 declare_lint! {
 245     pub FILTER_NEXT,
 246     Warn,
 247     "using `filter(p).next()`, which is more succinctly expressed as `.find(p)`"
 248 }
 249
 250 /// **What it does:** Checks for usage of `_.filter(_).map(_)`,
 251 /// `_.filter(_).flat_map(_)`, `_.filter_map(_).flat_map(_)` and similar.
 252 ///
 253 /// **Why is this bad?** Readability, this can be written more concisely as a
 254 /// single method call.
 255 ///
 256 /// **Known problems:** Often requires a condition + Option/Iterator creation
 257 /// inside the closure.
 258 ///
 259 /// **Example:**
 260 /// ```rust
 261 /// iter.filter(|x| x == 0).map(|x| x * 2)
 262 /// ```
 263 declare_lint! {
 264     pub FILTER_MAP,
 265     Allow,
 266     "using combinations of `filter`, `map`, `filter_map` and `flat_map` which can \
 267      usually be written as a single method call"
 268 }
 269
 270 /// **What it does:** Checks for an iterator search (such as `find()`,
 271 /// `position()`, or `rposition()`) followed by a call to `is_some()`.
 272 ///
 273 /// **Why is this bad?** Readability, this can be written more concisely as
 274 /// `_.any(_)`.
 275 ///
 276 /// **Known problems:** None.
 277 ///
 278 /// **Example:**
 279 /// ```rust
 280 /// iter.find(|x| x == 0).is_some()
 281 /// ```
 282 declare_lint! {
 283     pub SEARCH_IS_SOME,
 284     Warn,
 285     "using an iterator search followed by `is_some()`, which is more succinctly \
 286      expressed as a call to `any()`"
 287 }
 288
 289 /// **What it does:** Checks for usage of `.chars().next()` on a `str` to check
 290 /// if it starts with a given char.
 291 ///
 292 /// **Why is this bad?** Readability, this can be written more concisely as
 293 /// `_.starts_with(_)`.
 294 ///
 295 /// **Known problems:** None.
 296 ///
 297 /// **Example:**
 298 /// ```rust
 299 /// name.chars().next() == Some('_')
 300 /// ```
 301 declare_lint! {
 302     pub CHARS_NEXT_CMP,
 303     Warn,
 304     "using `.chars().next()` to check if a string starts with a char"
 305 }
 306
 307 /// **What it does:** Checks for calls to `.or(foo(..))`, `.unwrap_or(foo(..))`,
 308 /// etc., and suggests to use `or_else`, `unwrap_or_else`, etc., or
 309 /// `unwrap_or_default` instead.
 310 ///
 311 /// **Why is this bad?** The function will always be called and potentially
 312 /// allocate an object acting as the default.
 313 ///
 314 /// **Known problems:** If the function has side-effects, not calling it will
 315 /// change the semantic of the program, but you shouldn't rely on that anyway.
 316 ///
 317 /// **Example:**
 318 /// ```rust
 319 /// foo.unwrap_or(String::new())
 320 /// ```
 321 /// this can instead be written:
 322 /// ```rust
 323 /// foo.unwrap_or_else(String::new)
 324 /// ```
 325 /// or
 326 /// ```rust
 327 /// foo.unwrap_or_default()
 328 /// ```
 329 declare_lint! {
 330     pub OR_FUN_CALL,
 331     Warn,
 332     "using any `*or` method with a function call, which suggests `*or_else`"
 333 }
 334
 335 /// **What it does:** Checks for usage of `.clone()` on a `Copy` type.
 336 ///
 337 /// **Why is this bad?** The only reason `Copy` types implement `Clone` is for
 338 /// generics, not for using the `clone` method on a concrete type.
 339 ///
 340 /// **Known problems:** None.
 341 ///
 342 /// **Example:**
 343 /// ```rust
 344 /// 42u64.clone()
 345 /// ```
 346 declare_lint! {
 347     pub CLONE_ON_COPY,
 348     Warn,
 349     "using `clone` on a `Copy` type"
 350 }
 351
 352 /// **What it does:** Checks for usage of `.clone()` on a ref-counted pointer,
 353 /// (Rc, Arc, rc::Weak, or sync::Weak), and suggests calling Clone on
 354 /// the corresponding trait instead.
 355 ///
 356 /// **Why is this bad?**: Calling '.clone()' on an Rc, Arc, or Weak
 357 /// can obscure the fact that only the pointer is being cloned, not the underlying
 358 /// data.
 359 ///
 360 /// **Example:**
 361 /// ```rust
 362 /// x.clone()
 363 /// ```
 364 declare_restriction_lint! {
 365     pub CLONE_ON_REF_PTR,
 366     "using 'clone' on a ref-counted pointer"
 367 }
 368
 369 /// **What it does:** Checks for usage of `.clone()` on an `&&T`.
 370 ///
 371 /// **Why is this bad?** Cloning an `&&T` copies the inner `&T`, instead of
 372 /// cloning the underlying `T`.
 373 ///
 374 /// **Known problems:** None.
 375 ///
 376 /// **Example:**
 377 /// ```rust
 378 /// fn main() {
 379 ///    let x = vec![1];
 380 ///    let y = &&x;
 381 ///    let z = y.clone();
 382 ///    println!("{:p} {:p}",*y, z); // prints out the same pointer
 383 /// }
 384 /// ```
 385 declare_lint! {
 386     pub CLONE_DOUBLE_REF,
 387     Warn,
 388     "using `clone` on `&&T`"
 389 }
 390
 391 /// **What it does:** Checks for `new` not returning `Self`.
 392 ///
 393 /// **Why is this bad?** As a convention, `new` methods are used to make a new
 394 /// instance of a type.
 395 ///
 396 /// **Known problems:** None.
 397 ///
 398 /// **Example:**
 399 /// ```rust
 400 /// impl Foo {
 401 ///     fn new(..) -> NotAFoo {
 402 ///     }
 403 /// }
 404 /// ```
 405 declare_lint! {
 406     pub NEW_RET_NO_SELF,
 407     Warn,
 408     "not returning `Self` in a `new` method"
 409 }
 410
 411 /// **What it does:** Checks for string methods that receive a single-character
 412 /// `str` as an argument, e.g. `_.split("x")`.
 413 ///
 414 /// **Why is this bad?** Performing these methods using a `char` is faster than
 415 /// using a `str`.
 416 ///
 417 /// **Known problems:** Does not catch multi-byte unicode characters.
 418 ///
 419 /// **Example:**
 420 /// `_.split("x")` could be `_.split('x')
 421 declare_lint! {
 422     pub SINGLE_CHAR_PATTERN,
 423     Warn,
 424     "using a single-character str where a char could be used, e.g. \
 425      `_.split(\"x\")`"
 426 }
 427
 428 /// **What it does:** Checks for getting the inner pointer of a temporary
 429 /// `CString`.
 430 ///
 431 /// **Why is this bad?** The inner pointer of a `CString` is only valid as long
 432 /// as the `CString` is alive.
 433 ///
 434 /// **Known problems:** None.
 435 ///
 436 /// **Example:**
 437 /// ```rust,ignore
 438 /// let c_str = CString::new("foo").unwrap().as_ptr();
 439 /// unsafe {
 440 /// call_some_ffi_func(c_str);
 441 /// }
 442 /// ```
 443 /// Here `c_str` point to a freed address. The correct use would be:
 444 /// ```rust,ignore
 445 /// let c_str = CString::new("foo").unwrap();
 446 /// unsafe {
 447 ///     call_some_ffi_func(c_str.as_ptr());
 448 /// }
 449 /// ```
 450 declare_lint! {
 451     pub TEMPORARY_CSTRING_AS_PTR,
 452     Warn,
 453     "getting the inner pointer of a temporary `CString`"
 454 }
 455
 456 /// **What it does:** Checks for use of `.iter().nth()` (and the related
 457 /// `.iter_mut().nth()`) on standard library types with O(1) element access.
 458 ///
 459 /// **Why is this bad?** `.get()` and `.get_mut()` are more efficient and more
 460 /// readable.
 461 ///
 462 /// **Known problems:** None.
 463 ///
 464 /// **Example:**
 465 /// ```rust
 466 /// let some_vec = vec![0, 1, 2, 3];
 467 /// let bad_vec = some_vec.iter().nth(3);
 468 /// let bad_slice = &some_vec[..].iter().nth(3);
 469 /// ```
 470 /// The correct use would be:
 471 /// ```rust
 472 /// let some_vec = vec![0, 1, 2, 3];
 473 /// let bad_vec = some_vec.get(3);
 474 /// let bad_slice = &some_vec[..].get(3);
 475 /// ```
 476 declare_lint! {
 477     pub ITER_NTH,
 478     Warn,
 479     "using `.iter().nth()` on a standard library type with O(1) element access"
 480 }
 481
 482 /// **What it does:** Checks for use of `.skip(x).next()` on iterators.
 483 ///
 484 /// **Why is this bad?** `.nth(x)` is cleaner
 485 ///
 486 /// **Known problems:** None.
 487 ///
 488 /// **Example:**
 489 /// ```rust
 490 /// let some_vec = vec![0, 1, 2, 3];
 491 /// let bad_vec = some_vec.iter().skip(3).next();
 492 /// let bad_slice = &some_vec[..].iter().skip(3).next();
 493 /// ```
 494 /// The correct use would be:
 495 /// ```rust
 496 /// let some_vec = vec![0, 1, 2, 3];
 497 /// let bad_vec = some_vec.iter().nth(3);
 498 /// let bad_slice = &some_vec[..].iter().nth(3);
 499 /// ```
 500 declare_lint! {
 501     pub ITER_SKIP_NEXT,
 502     Warn,
 503     "using `.skip(x).next()` on an iterator"
 504 }
 505
 506 /// **What it does:** Checks for use of `.get().unwrap()` (or
 507 /// `.get_mut().unwrap`) on a standard library type which implements `Index`
 508 ///
 509 /// **Why is this bad?** Using the Index trait (`[]`) is more clear and more
 510 /// concise.
 511 ///
 512 /// **Known problems:** None.
 513 ///
 514 /// **Example:**
 515 /// ```rust
 516 /// let some_vec = vec![0, 1, 2, 3];
 517 /// let last = some_vec.get(3).unwrap();
 518 /// *some_vec.get_mut(0).unwrap() = 1;
 519 /// ```
 520 /// The correct use would be:
 521 /// ```rust
 522 /// let some_vec = vec![0, 1, 2, 3];
 523 /// let last = some_vec[3];
 524 /// some_vec[0] = 1;
 525 /// ```
 526 declare_lint! {
 527     pub GET_UNWRAP,
 528     Warn,
 529     "using `.get().unwrap()` or `.get_mut().unwrap()` when using `[]` would work instead"
 530 }
 531
 532 /// **What it does:** Checks for the use of `.extend(s.chars())` where s is a
 533 /// `&str` or `String`.
 534 ///
 535 /// **Why is this bad?** `.push_str(s)` is clearer
 536 ///
 537 /// **Known problems:** None.
 538 ///
 539 /// **Example:**
 540 /// ```rust
 541 /// let abc = "abc";
 542 /// let def = String::from("def");
 543 /// let mut s = String::new();
 544 /// s.extend(abc.chars());
 545 /// s.extend(def.chars());
 546 /// ```
 547 /// The correct use would be:
 548 /// ```rust
 549 /// let abc = "abc";
 550 /// let def = String::from("def");
 551 /// let mut s = String::new();
 552 /// s.push_str(abc);
 553 /// s.push_str(&def));
 554 /// ```
 555 declare_lint! {
 556     pub STRING_EXTEND_CHARS,
 557     Warn,
 558     "using `x.extend(s.chars())` where s is a `&str` or `String`"
 559 }
 560
 561 /// **What it does:** Checks for the use of `.cloned().collect()` on slice to
 562 /// create a `Vec`.
 563 ///
 564 /// **Why is this bad?** `.to_vec()` is clearer
 565 ///
 566 /// **Known problems:** None.
 567 ///
 568 /// **Example:**
 569 /// ```rust
 570 /// let s = [1,2,3,4,5];
 571 /// let s2 : Vec<isize> = s[..].iter().cloned().collect();
 572 /// ```
 573 /// The better use would be:
 574 /// ```rust
 575 /// let s = [1,2,3,4,5];
 576 /// let s2 : Vec<isize> = s.to_vec();
 577 /// ```
 578 declare_lint! {
 579     pub ITER_CLONED_COLLECT,
 580     Warn,
 581     "using `.cloned().collect()` on slice to create a `Vec`"
 582 }
 583
 584 /// **What it does:** Checks for usage of `.chars().last()` or
 585 /// `.chars().next_back()` on a `str` to check if it ends with a given char.
 586 ///
 587 /// **Why is this bad?** Readability, this can be written more concisely as
 588 /// `_.ends_with(_)`.
 589 ///
 590 /// **Known problems:** None.
 591 ///
 592 /// **Example:**
 593 /// ```rust
 594 /// name.chars().last() == Some('_') || name.chars().next_back() == Some('-')
 595 /// ```
 596 declare_lint! {
 597     pub CHARS_LAST_CMP,
 598     Warn,
 599     "using `.chars().last()` or `.chars().next_back()` to check if a string ends with a char"
 600 }
 601
 602 /// **What it does:** Checks for usage of `.as_ref()` or `.as_mut()` where the
 603 /// types before and after the call are the same.
 604 ///
 605 /// **Why is this bad?** The call is unnecessary.
 606 ///
 607 /// **Known problems:** None.
 608 ///
 609 /// **Example:**
 610 /// ```rust
 611 /// let x: &[i32] = &[1,2,3,4,5];
 612 /// do_stuff(x.as_ref());
 613 /// ```
 614 /// The correct use would be:
 615 /// ```rust
 616 /// let x: &[i32] = &[1,2,3,4,5];
 617 /// do_stuff(x);
 618 /// ```
 619 declare_lint! {
 620     pub USELESS_ASREF,
 621     Warn,
 622     "using `as_ref` where the types before and after the call are the same"
 623 }
 624
 625
 626 /// **What it does:** Checks for using `fold` when a more succinct alternative exists.
 627 /// Specifically, this checks for `fold`s which could be replaced by `any`, `all`,
 628 /// `sum` or `product`.
 629 ///
 630 /// **Why is this bad?** Readability.
 631 ///
 632 /// **Known problems:** None.
 633 ///
 634 /// **Example:**
 635 /// ```rust
 636 /// let _ = (0..3).fold(false, |acc, x| acc || x > 2);
 637 /// ```
 638 /// This could be written as:
 639 /// ```rust
 640 /// let _ = (0..3).any(|x| x > 2);
 641 /// ```
 642 declare_lint! {
 643     pub UNNECESSARY_FOLD,
 644     Warn,
 645     "using `fold` when a more succinct alternative exists"
 646 }
 647
 648 impl LintPass for Pass {
 649     fn get_lints(&self) -> LintArray {
 650         lint_array!(
 651             OPTION_UNWRAP_USED,
 652             RESULT_UNWRAP_USED,
 653             SHOULD_IMPLEMENT_TRAIT,
 654             WRONG_SELF_CONVENTION,
 655             WRONG_PUB_SELF_CONVENTION,
 656             OK_EXPECT,
 657             OPTION_MAP_UNWRAP_OR,
 658             OPTION_MAP_UNWRAP_OR_ELSE,
 659             RESULT_MAP_UNWRAP_OR_ELSE,
 660             OPTION_MAP_OR_NONE,
 661             OR_FUN_CALL,
 662             CHARS_NEXT_CMP,
 663             CHARS_LAST_CMP,
 664             CLONE_ON_COPY,
 665             CLONE_ON_REF_PTR,
 666             CLONE_DOUBLE_REF,
 667             NEW_RET_NO_SELF,
 668             SINGLE_CHAR_PATTERN,
 669             SEARCH_IS_SOME,
 670             TEMPORARY_CSTRING_AS_PTR,
 671             FILTER_NEXT,
 672             FILTER_MAP,
 673             ITER_NTH,
 674             ITER_SKIP_NEXT,
 675             GET_UNWRAP,
 676             STRING_EXTEND_CHARS,
 677             ITER_CLONED_COLLECT,
 678             USELESS_ASREF,
 679             UNNECESSARY_FOLD
 680         )
 681     }
 682 }
 683
 684 impl<'a, 'tcx> LateLintPass<'a, 'tcx> for Pass {
 685     #[allow(unused_attributes)]
 686     // ^ required because `cyclomatic_complexity` attribute shows up as unused
 687     #[cyclomatic_complexity = "30"]
 688     fn check_expr(&mut self, cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr) {
 689         if in_macro(expr.span) {
 690             return;
 691         }
 692
 693         match expr.node {
 694             hir::ExprMethodCall(ref method_call, _, ref args) => {
 695                 // Chain calls
 696                 // GET_UNWRAP needs to be checked before general `UNWRAP` lints
 697                 if let Some(arglists) = method_chain_args(expr, &["get", "unwrap"]) {
 698                     lint_get_unwrap(cx, expr, arglists[0], false);
 699                 } else if let Some(arglists) = method_chain_args(expr, &["get_mut", "unwrap"]) {
 700                     lint_get_unwrap(cx, expr, arglists[0], true);
 701                 } else if let Some(arglists) = method_chain_args(expr, &["unwrap"]) {
 702                     lint_unwrap(cx, expr, arglists[0]);
 703                 } else if let Some(arglists) = method_chain_args(expr, &["ok", "expect"]) {
 704                     lint_ok_expect(cx, expr, arglists[0]);
 705                 } else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or"]) {
 706                     lint_map_unwrap_or(cx, expr, arglists[0], arglists[1]);
 707                 } else if let Some(arglists) = method_chain_args(expr, &["map", "unwrap_or_else"]) {
 708                     lint_map_unwrap_or_else(cx, expr, arglists[0], arglists[1]);
 709                 } else if let Some(arglists) = method_chain_args(expr, &["map_or"]) {
 710                     lint_map_or_none(cx, expr, arglists[0]);
 711                 } else if let Some(arglists) = method_chain_args(expr, &["filter", "next"]) {
 712                     lint_filter_next(cx, expr, arglists[0]);
 713                 } else if let Some(arglists) = method_chain_args(expr, &["filter", "map"]) {
 714                     lint_filter_map(cx, expr, arglists[0], arglists[1]);
 715                 } else if let Some(arglists) = method_chain_args(expr, &["filter_map", "map"]) {
 716                     lint_filter_map_map(cx, expr, arglists[0], arglists[1]);
 717                 } else if let Some(arglists) = method_chain_args(expr, &["filter", "flat_map"]) {
 718                     lint_filter_flat_map(cx, expr, arglists[0], arglists[1]);
 719                 } else if let Some(arglists) = method_chain_args(expr, &["filter_map", "flat_map"]) {
 720                     lint_filter_map_flat_map(cx, expr, arglists[0], arglists[1]);
 721                 } else if let Some(arglists) = method_chain_args(expr, &["find", "is_some"]) {
 722                     lint_search_is_some(cx, expr, "find", arglists[0], arglists[1]);
 723                 } else if let Some(arglists) = method_chain_args(expr, &["position", "is_some"]) {
 724                     lint_search_is_some(cx, expr, "position", arglists[0], arglists[1]);
 725                 } else if let Some(arglists) = method_chain_args(expr, &["rposition", "is_some"]) {
 726                     lint_search_is_some(cx, expr, "rposition", arglists[0], arglists[1]);
 727                 } else if let Some(arglists) = method_chain_args(expr, &["extend"]) {
 728                     lint_extend(cx, expr, arglists[0]);
 729                 } else if let Some(arglists) = method_chain_args(expr, &["unwrap", "as_ptr"]) {
 730                     lint_cstring_as_ptr(cx, expr, &arglists[0][0], &arglists[1][0]);
 731                 } else if let Some(arglists) = method_chain_args(expr, &["iter", "nth"]) {
 732                     lint_iter_nth(cx, expr, arglists[0], false);
 733                 } else if let Some(arglists) = method_chain_args(expr, &["iter_mut", "nth"]) {
 734                     lint_iter_nth(cx, expr, arglists[0], true);
 735                 } else if method_chain_args(expr, &["skip", "next"]).is_some() {
 736                     lint_iter_skip_next(cx, expr);
 737                 } else if let Some(arglists) = method_chain_args(expr, &["cloned", "collect"]) {
 738                     lint_iter_cloned_collect(cx, expr, arglists[0]);
 739                 } else if let Some(arglists) = method_chain_args(expr, &["as_ref"]) {
 740                     lint_asref(cx, expr, "as_ref", arglists[0]);
 741                 } else if let Some(arglists) = method_chain_args(expr, &["as_mut"]) {
 742                     lint_asref(cx, expr, "as_mut", arglists[0]);
 743                 } else if let Some(arglists) = method_chain_args(expr, &["fold"]) {
 744                     lint_unnecessary_fold(cx, expr, arglists[0]);
 745                 }
 746
 747                 lint_or_fun_call(cx, expr, &method_call.name.as_str(), args);
 748
 749                 let self_ty = cx.tables.expr_ty_adjusted(&args[0]);
 750                 if args.len() == 1 && method_call.name == "clone" {
 751                     lint_clone_on_copy(cx, expr, &args[0], self_ty);
 752                     lint_clone_on_ref_ptr(cx, expr, &args[0]);
 753                 }
 754
 755                 match self_ty.sty {
 756                     ty::TyRef(_, ty) if ty.ty.sty == ty::TyStr => for &(method, pos) in &PATTERN_METHODS {
 757                         if method_call.name == method && args.len() > pos {
 758                             lint_single_char_pattern(cx, expr, &args[pos]);
 759                         }
 760                     },
 761                     _ => (),
 762                 }
 763             },
 764             hir::ExprBinary(op, ref lhs, ref rhs) if op.node == hir::BiEq || op.node == hir::BiNe => {
 765                 let mut info = BinaryExprInfo {
 766                     expr: expr,
 767                     chain: lhs,
 768                     other: rhs,
 769                     eq: op.node == hir::BiEq,
 770                 };
 771                 lint_binary_expr_with_method_call(cx, &mut info);
 772             },
 773             _ => (),
 774         }
 775     }
 776
 777     fn check_impl_item(&mut self, cx: &LateContext<'a, 'tcx>, implitem: &'tcx hir::ImplItem) {
 778         if in_external_macro(cx, implitem.span) {
 779             return;
 780         }
 781         let name = implitem.name;
 782         let parent = cx.tcx.hir.get_parent(implitem.id);
 783         let item = cx.tcx.hir.expect_item(parent);
 784         if_chain! {
 785             if let hir::ImplItemKind::Method(ref sig, id) = implitem.node;
 786             if let Some(first_arg_ty) = sig.decl.inputs.get(0);
 787             if let Some(first_arg) = iter_input_pats(&sig.decl, cx.tcx.hir.body(id)).next();
 788             if let hir::ItemImpl(_, _, _, _, None, ref self_ty, _) = item.node;
 789             then {
 790                 if cx.access_levels.is_exported(implitem.id) {
 791                 // check missing trait implementations
 792                     for &(method_name, n_args, self_kind, out_type, trait_name) in &TRAIT_METHODS {
 793                         if name == method_name &&
 794                         sig.decl.inputs.len() == n_args &&
 795                         out_type.matches(&sig.decl.output) &&
 796                         self_kind.matches(first_arg_ty, first_arg, self_ty, false, &implitem.generics) {
 797                             span_lint(cx, SHOULD_IMPLEMENT_TRAIT, implitem.span, &format!(
 798                                 "defining a method called `{}` on this type; consider implementing \
 799                                 the `{}` trait or choosing a less ambiguous name", name, trait_name));
 800                         }
 801                     }
 802                 }
 803
 804                 // check conventions w.r.t. conversion method names and predicates
 805                 let def_id = cx.tcx.hir.local_def_id(item.id);
 806                 let ty = cx.tcx.type_of(def_id);
 807                 let is_copy = is_copy(cx, ty);
 808                 for &(ref conv, self_kinds) in &CONVENTIONS {
 809                     if_chain! {
 810                         if conv.check(&name.as_str());
 811                         if !self_kinds
 812                             .iter()
 813                             .any(|k| k.matches(first_arg_ty, first_arg, self_ty, is_copy, &implitem.generics));
 814                         then {
 815                             let lint = if item.vis == hir::Visibility::Public {
 816                                 WRONG_PUB_SELF_CONVENTION
 817                             } else {
 818                                 WRONG_SELF_CONVENTION
 819                             };
 820                             span_lint(cx,
 821                                       lint,
 822                                       first_arg.pat.span,
 823                                       &format!("methods called `{}` usually take {}; consider choosing a less \
 824                                                 ambiguous name",
 825                                                conv,
 826                                                &self_kinds.iter()
 827                                                           .map(|k| k.description())
 828                                                           .collect::<Vec<_>>()
 829                                                           .join(" or ")));
 830                         }
 831                     }
 832                 }
 833
 834                 let ret_ty = return_ty(cx, implitem.id);
 835                 if name == "new" &&
 836                    !ret_ty.walk().any(|t| same_tys(cx, t, ty)) {
 837                     span_lint(cx,
 838                               NEW_RET_NO_SELF,
 839                               implitem.span,
 840                               "methods called `new` usually return `Self`");
 841                 }
 842             }
 843         }
 844     }
 845 }
 846
 847 /// Checks for the `OR_FUN_CALL` lint.
 848 fn lint_or_fun_call(cx: &LateContext, expr: &hir::Expr, name: &str, args: &[hir::Expr]) {
 849     /// Check for `unwrap_or(T::new())` or `unwrap_or(T::default())`.
 850     fn check_unwrap_or_default(
 851         cx: &LateContext,
 852         name: &str,
 853         fun: &hir::Expr,
 854         self_expr: &hir::Expr,
 855         arg: &hir::Expr,
 856         or_has_args: bool,
 857         span: Span,
 858     ) -> bool {
 859         if or_has_args {
 860             return false;
 861         }
 862
 863         if name == "unwrap_or" {
 864             if let hir::ExprPath(ref qpath) = fun.node {
 865                 let path = &*last_path_segment(qpath).name.as_str();
 866
 867                 if ["default", "new"].contains(&path) {
 868                     let arg_ty = cx.tables.expr_ty(arg);
 869                     let default_trait_id = if let Some(default_trait_id) = get_trait_def_id(cx, &paths::DEFAULT_TRAIT) {
 870                         default_trait_id
 871                     } else {
 872                         return false;
 873                     };
 874
 875                     if implements_trait(cx, arg_ty, default_trait_id, &[]) {
 876                         span_lint_and_sugg(
 877                             cx,
 878                             OR_FUN_CALL,
 879                             span,
 880                             &format!("use of `{}` followed by a call to `{}`", name, path),
 881                             "try this",
 882                             format!("{}.unwrap_or_default()", snippet(cx, self_expr.span, "_")),
 883                         );
 884                         return true;
 885                     }
 886                 }
 887             }
 888         }
 889
 890         false
 891     }
 892
 893     /// Check for `*or(foo())`.
 894     fn check_general_case(
 895         cx: &LateContext,
 896         name: &str,
 897         fun_span: Span,
 898         self_expr: &hir::Expr,
 899         arg: &hir::Expr,
 900         or_has_args: bool,
 901         span: Span,
 902     ) {
 903         // (path, fn_has_argument, methods, suffix)
 904         let know_types: &[(&[_], _, &[_], _)] = &[
 905             (&paths::BTREEMAP_ENTRY, false, &["or_insert"], "with"),
 906             (&paths::HASHMAP_ENTRY, false, &["or_insert"], "with"),
 907             (&paths::OPTION, false, &["map_or", "ok_or", "or", "unwrap_or"], "else"),
 908             (&paths::RESULT, true, &["or", "unwrap_or"], "else"),
 909         ];
 910
 911         // early check if the name is one we care about
 912         if know_types.iter().all(|k| !k.2.contains(&name)) {
 913             return;
 914         }
 915
 916         // don't lint for constant values
 917         let owner_def = cx.tcx.hir.get_parent_did(arg.id);
 918         let promotable = cx.tcx.rvalue_promotable_map(owner_def).contains(&arg.hir_id.local_id);
 919         if promotable {
 920             return;
 921         }
 922
 923         let self_ty = cx.tables.expr_ty(self_expr);
 924
 925         let (fn_has_arguments, poss, suffix) = if let Some(&(_, fn_has_arguments, poss, suffix)) =
 926             know_types.iter().find(|&&i| match_type(cx, self_ty, i.0))
 927         {
 928             (fn_has_arguments, poss, suffix)
 929         } else {
 930             return;
 931         };
 932
 933         if !poss.contains(&name) {
 934             return;
 935         }
 936
 937         let sugg: Cow<_> = match (fn_has_arguments, !or_has_args) {
 938             (true, _) => format!("|_| {}", snippet(cx, arg.span, "..")).into(),
 939             (false, false) => format!("|| {}", snippet(cx, arg.span, "..")).into(),
 940             (false, true) => snippet(cx, fun_span, ".."),
 941         };
 942
 943         span_lint_and_sugg(
 944             cx,
 945             OR_FUN_CALL,
 946             span,
 947             &format!("use of `{}` followed by a function call", name),
 948             "try this",
 949             format!("{}.{}_{}({})", snippet(cx, self_expr.span, "_"), name, suffix, sugg),
 950         );
 951     }
 952
 953     if args.len() == 2 {
 954         match args[1].node {
 955             hir::ExprCall(ref fun, ref or_args) => {
 956                 let or_has_args = !or_args.is_empty();
 957                 if !check_unwrap_or_default(cx, name, fun, &args[0], &args[1], or_has_args, expr.span) {
 958                     check_general_case(cx, name, fun.span, &args[0], &args[1], or_has_args, expr.span);
 959                 }
 960             },
 961             hir::ExprMethodCall(_, span, ref or_args) => {
 962                 check_general_case(cx, name, span, &args[0], &args[1], !or_args.is_empty(), expr.span)
 963             },
 964             _ => {},
 965         }
 966     }
 967 }
 968
 969 /// Checks for the `CLONE_ON_COPY` lint.
 970 fn lint_clone_on_copy(cx: &LateContext, expr: &hir::Expr, arg: &hir::Expr, arg_ty: Ty) {
 971     let ty = cx.tables.expr_ty(expr);
 972     if let ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) = arg_ty.sty {
 973         if let ty::TyRef(_, ty::TypeAndMut { ty: innermost, .. }) = inner.sty {
 974             span_lint_and_then(
 975                 cx,
 976                 CLONE_DOUBLE_REF,
 977                 expr.span,
 978                 "using `clone` on a double-reference; \
 979                  this will copy the reference instead of cloning the inner type",
 980                 |db| if let Some(snip) = sugg::Sugg::hir_opt(cx, arg) {
 981                     let mut ty = innermost;
 982                     let mut n = 0;
 983                     while let ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) = ty.sty {
 984                         ty = inner;
 985                         n += 1;
 986                     }
 987                     let refs: String = iter::repeat('&').take(n + 1).collect();
 988                     let derefs: String = iter::repeat('*').take(n).collect();
 989                     let explicit = format!("{}{}::clone({})", refs, ty, snip);
 990                     db.span_suggestion(expr.span, "try dereferencing it", format!("{}({}{}).clone()", refs, derefs, snip.deref()));
 991                     db.span_suggestion(expr.span, "or try being explicit about what type to clone", explicit);
 992                 },
 993             );
 994             return; // don't report clone_on_copy
 995         }
 996     }
 997
 998     if is_copy(cx, ty) {
 999         let snip;
1000         if let Some(snippet) = sugg::Sugg::hir_opt(cx, arg) {
1001             if let ty::TyRef(..) = cx.tables.expr_ty(arg).sty {
1002                 let parent = cx.tcx.hir.get_parent_node(expr.id);
1003                 match cx.tcx.hir.get(parent) {
1004                     hir::map::NodeExpr(parent) => match parent.node {
1005                         // &*x is a nop, &x.clone() is not
1006                         hir::ExprAddrOf(..) |
1007                         // (*x).func() is useless, x.clone().func() can work in case func borrows mutably
1008                         hir::ExprMethodCall(..) => return,
1009                         _ => {},
1010                     }
1011                     hir::map::NodeStmt(stmt) => {
1012                         if let hir::StmtDecl(ref decl, _) = stmt.node {
1013                             if let hir::DeclLocal(ref loc) = decl.node {
1014                                 if let hir::PatKind::Ref(..) = loc.pat.node {
1015                                     // let ref y = *x borrows x, let ref y = x.clone() does not
1016                                     return;
1017                                 }
1018                             }
1019                         }
1020                     },
1021                     _ => {},
1022                 }
1023                 snip = Some(("try dereferencing it", format!("{}", snippet.deref())));
1024             } else {
1025                 snip = Some(("try removing the `clone` call", format!("{}", snippet)));
1026             }
1027         } else {
1028             snip = None;
1029         }
1030         span_lint_and_then(cx, CLONE_ON_COPY, expr.span, "using `clone` on a `Copy` type", |db| {
1031             if let Some((text, snip)) = snip {
1032                 db.span_suggestion(expr.span, text, snip);
1033             }
1034         });
1035     }
1036 }
1037
1038 fn lint_clone_on_ref_ptr(cx: &LateContext, expr: &hir::Expr, arg: &hir::Expr) {
1039     let (obj_ty, _) = walk_ptrs_ty_depth(cx.tables.expr_ty(arg));
1040
1041     if let ty::TyAdt(_, subst) = obj_ty.sty {
1042         let caller_type = if match_type(cx, obj_ty, &paths::RC) {
1043             "Rc"
1044         } else if match_type(cx, obj_ty, &paths::ARC) {
1045             "Arc"
1046         } else if match_type(cx, obj_ty, &paths::WEAK_RC) || match_type(cx, obj_ty, &paths::WEAK_ARC) {
1047             "Weak"
1048         } else {
1049             return;
1050         };
1051
1052         span_lint_and_sugg(
1053             cx,
1054             CLONE_ON_REF_PTR,
1055             expr.span,
1056             "using '.clone()' on a ref-counted pointer",
1057             "try this",
1058             format!("{}::<{}>::clone(&{})", caller_type, subst.type_at(0), snippet(cx, arg.span, "_")),
1059         );
1060     }
1061 }
1062
1063
1064 fn lint_string_extend(cx: &LateContext, expr: &hir::Expr, args: &[hir::Expr]) {
1065     let arg = &args[1];
1066     if let Some(arglists) = method_chain_args(arg, &["chars"]) {
1067         let target = &arglists[0][0];
1068         let (self_ty, _) = walk_ptrs_ty_depth(cx.tables.expr_ty(target));
1069         let ref_str = if self_ty.sty == ty::TyStr {
1070             ""
1071         } else if match_type(cx, self_ty, &paths::STRING) {
1072             "&"
1073         } else {
1074             return;
1075         };
1076
1077         span_lint_and_sugg(
1078             cx,
1079             STRING_EXTEND_CHARS,
1080             expr.span,
1081             "calling `.extend(_.chars())`",
1082             "try this",
1083             format!(
1084                 "{}.push_str({}{})",
1085                 snippet(cx, args[0].span, "_"),
1086                 ref_str,
1087                 snippet(cx, target.span, "_")
1088             ),
1089         );
1090     }
1091 }
1092
1093 fn lint_extend(cx: &LateContext, expr: &hir::Expr, args: &[hir::Expr]) {
1094     let (obj_ty, _) = walk_ptrs_ty_depth(cx.tables.expr_ty(&args[0]));
1095     if match_type(cx, obj_ty, &paths::STRING) {
1096         lint_string_extend(cx, expr, args);
1097     }
1098 }
1099
1100 fn lint_cstring_as_ptr(cx: &LateContext, expr: &hir::Expr, new: &hir::Expr, unwrap: &hir::Expr) {
1101     if_chain! {
1102         if let hir::ExprCall(ref fun, ref args) = new.node;
1103         if args.len() == 1;
1104         if let hir::ExprPath(ref path) = fun.node;
1105         if let Def::Method(did) = cx.tables.qpath_def(path, fun.hir_id);
1106         if match_def_path(cx.tcx, did, &paths::CSTRING_NEW);
1107         then {
1108             span_lint_and_then(
1109                 cx,
1110                 TEMPORARY_CSTRING_AS_PTR,
1111                 expr.span,
1112                 "you are getting the inner pointer of a temporary `CString`",
1113                 |db| {
1114                     db.note("that pointer will be invalid outside this expression");
1115                     db.span_help(unwrap.span, "assign the `CString` to a variable to extend its lifetime");
1116                 });
1117         }
1118     }
1119 }
1120
1121 fn lint_iter_cloned_collect(cx: &LateContext, expr: &hir::Expr, iter_args: &[hir::Expr]) {
1122     if match_type(cx, cx.tables.expr_ty(expr), &paths::VEC)
1123         && derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some()
1124     {
1125         span_lint(
1126             cx,
1127             ITER_CLONED_COLLECT,
1128             expr.span,
1129             "called `cloned().collect()` on a slice to create a `Vec`. Calling `to_vec()` is both faster and \
1130              more readable",
1131         );
1132     }
1133 }
1134
1135 fn lint_unnecessary_fold(cx: &LateContext, expr: &hir::Expr, fold_args: &[hir::Expr]) {
1136     // Check that this is a call to Iterator::fold rather than just some function called fold
1137     if !match_trait_method(cx, expr, &paths::ITERATOR) {
1138         return;
1139     }
1140
1141     assert!(fold_args.len() == 3,
1142         "Expected fold_args to have three entries - the receiver, the initial value and the closure");
1143
1144     fn check_fold_with_op(
1145         cx: &LateContext,
1146         fold_args: &[hir::Expr],
1147         op: hir::BinOp_,
1148         replacement_method_name: &str,
1149         replacement_has_args: bool) {
1150
1151         if_chain! {
1152             // Extract the body of the closure passed to fold
1153             if let hir::ExprClosure(_, _, body_id, _, _) = fold_args[2].node;
1154             let closure_body = cx.tcx.hir.body(body_id);
1155             let closure_expr = remove_blocks(&closure_body.value);
1156
1157             // Check if the closure body is of the form `acc <op> some_expr(x)`
1158             if let hir::ExprBinary(ref bin_op, ref left_expr, ref right_expr) = closure_expr.node;
1159             if bin_op.node == op;
1160
1161             // Extract the names of the two arguments to the closure
1162             if let Some(first_arg_ident) = get_arg_name(&closure_body.arguments[0].pat);
1163             if let Some(second_arg_ident) = get_arg_name(&closure_body.arguments[1].pat);
1164
1165             if match_var(&*left_expr, first_arg_ident);
1166             if replacement_has_args || match_var(&*right_expr, second_arg_ident);
1167
1168             then {
1169                 // Span containing `.fold(...)`
1170                 let next_point = cx.sess().codemap().next_point(fold_args[0].span);
1171                 let fold_span = next_point.with_hi(fold_args[2].span.hi() + BytePos(1));
1172
1173                 let sugg = if replacement_has_args {
1174                     format!(
1175                         ".{replacement}(|{s}| {r})",
1176                         replacement = replacement_method_name,
1177                         s = second_arg_ident,
1178                         r = snippet(cx, right_expr.span, "EXPR"),
1179                     )
1180                 } else {
1181                     format!(
1182                         ".{replacement}()",
1183                         replacement = replacement_method_name,
1184                     )
1185                 };
1186
1187                 span_lint_and_sugg(
1188                     cx,
1189                     UNNECESSARY_FOLD,
1190                     fold_span,
1191                     // TODO #2371 don't suggest e.g. .any(|x| f(x)) if we can suggest .any(f)
1192                     "this `.fold` can be written more succinctly using another method",
1193                     "try",
1194                     sugg,
1195                 );
1196             }
1197         }
1198     }
1199
1200     // Check if the first argument to .fold is a suitable literal
1201     match fold_args[1].node {
1202         hir::ExprLit(ref lit) => {
1203             match lit.node {
1204                 ast::LitKind::Bool(false) => check_fold_with_op(
1205                     cx, fold_args, hir::BinOp_::BiOr, "any", true
1206                 ),
1207                 ast::LitKind::Bool(true) => check_fold_with_op(
1208                     cx, fold_args, hir::BinOp_::BiAnd, "all", true
1209                 ),
1210                 ast::LitKind::Int(0, _) => check_fold_with_op(
1211                     cx, fold_args, hir::BinOp_::BiAdd, "sum", false
1212                 ),
1213                 ast::LitKind::Int(1, _) => check_fold_with_op(
1214                     cx, fold_args, hir::BinOp_::BiMul, "product", false
1215                 ),
1216                 _ => return
1217             }
1218         }
1219         _ => return
1220     };
1221 }
1222
1223 fn lint_iter_nth(cx: &LateContext, expr: &hir::Expr, iter_args: &[hir::Expr], is_mut: bool) {
1224     let mut_str = if is_mut { "_mut" } else { "" };
1225     let caller_type = if derefs_to_slice(cx, &iter_args[0], cx.tables.expr_ty(&iter_args[0])).is_some() {
1226         "slice"
1227     } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC) {
1228         "Vec"
1229     } else if match_type(cx, cx.tables.expr_ty(&iter_args[0]), &paths::VEC_DEQUE) {
1230         "VecDeque"
1231     } else {
1232         return; // caller is not a type that we want to lint
1233     };
1234
1235     span_lint(
1236         cx,
1237         ITER_NTH,
1238         expr.span,
1239         &format!(
1240             "called `.iter{0}().nth()` on a {1}. Calling `.get{0}()` is both faster and more readable",
1241             mut_str,
1242             caller_type
1243         ),
1244     );
1245 }
1246
1247 fn lint_get_unwrap(cx: &LateContext, expr: &hir::Expr, get_args: &[hir::Expr], is_mut: bool) {
1248     // Note: we don't want to lint `get_mut().unwrap` for HashMap or BTreeMap,
1249     // because they do not implement `IndexMut`
1250     let expr_ty = cx.tables.expr_ty(&get_args[0]);
1251     let caller_type = if derefs_to_slice(cx, &get_args[0], expr_ty).is_some() {
1252         "slice"
1253     } else if match_type(cx, expr_ty, &paths::VEC) {
1254         "Vec"
1255     } else if match_type(cx, expr_ty, &paths::VEC_DEQUE) {
1256         "VecDeque"
1257     } else if !is_mut && match_type(cx, expr_ty, &paths::HASHMAP) {
1258         "HashMap"
1259     } else if !is_mut && match_type(cx, expr_ty, &paths::BTREEMAP) {
1260         "BTreeMap"
1261     } else {
1262         return; // caller is not a type that we want to lint
1263     };
1264
1265     let mut_str = if is_mut { "_mut" } else { "" };
1266     let borrow_str = if is_mut { "&mut " } else { "&" };
1267     span_lint_and_sugg(
1268         cx,
1269         GET_UNWRAP,
1270         expr.span,
1271         &format!(
1272             "called `.get{0}().unwrap()` on a {1}. Using `[]` is more clear and more concise",
1273             mut_str,
1274             caller_type
1275         ),
1276         "try this",
1277         format!(
1278             "{}{}[{}]",
1279             borrow_str,
1280             snippet(cx, get_args[0].span, "_"),
1281             snippet(cx, get_args[1].span, "_")
1282         ),
1283     );
1284 }
1285
1286 fn lint_iter_skip_next(cx: &LateContext, expr: &hir::Expr) {
1287     // lint if caller of skip is an Iterator
1288     if match_trait_method(cx, expr, &paths::ITERATOR) {
1289         span_lint(
1290             cx,
1291             ITER_SKIP_NEXT,
1292             expr.span,
1293             "called `skip(x).next()` on an iterator. This is more succinctly expressed by calling `nth(x)`",
1294         );
1295     }
1296 }
1297
1298 fn derefs_to_slice(cx: &LateContext, expr: &hir::Expr, ty: Ty) -> Option<sugg::Sugg<'static>> {
1299     fn may_slice(cx: &LateContext, ty: Ty) -> bool {
1300         match ty.sty {
1301             ty::TySlice(_) => true,
1302             ty::TyAdt(def, _) if def.is_box() => may_slice(cx, ty.boxed_ty()),
1303             ty::TyAdt(..) => match_type(cx, ty, &paths::VEC),
1304             ty::TyArray(_, size) => const_to_u64(size) < 32,
1305             ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) => may_slice(cx, inner),
1306             _ => false,
1307         }
1308     }
1309
1310     if let hir::ExprMethodCall(ref path, _, ref args) = expr.node {
1311         if path.name == "iter" && may_slice(cx, cx.tables.expr_ty(&args[0])) {
1312             sugg::Sugg::hir_opt(cx, &args[0]).map(|sugg| sugg.addr())
1313         } else {
1314             None
1315         }
1316     } else {
1317         match ty.sty {
1318             ty::TySlice(_) => sugg::Sugg::hir_opt(cx, expr),
1319             ty::TyAdt(def, _) if def.is_box() && may_slice(cx, ty.boxed_ty()) => sugg::Sugg::hir_opt(cx, expr),
1320             ty::TyRef(_, ty::TypeAndMut { ty: inner, .. }) => if may_slice(cx, inner) {
1321                 sugg::Sugg::hir_opt(cx, expr)
1322             } else {
1323                 None
1324             },
1325             _ => None,
1326         }
1327     }
1328 }
1329
1330 /// lint use of `unwrap()` for `Option`s and `Result`s
1331 fn lint_unwrap(cx: &LateContext, expr: &hir::Expr, unwrap_args: &[hir::Expr]) {
1332     let (obj_ty, _) = walk_ptrs_ty_depth(cx.tables.expr_ty(&unwrap_args[0]));
1333
1334     let mess = if match_type(cx, obj_ty, &paths::OPTION) {
1335         Some((OPTION_UNWRAP_USED, "an Option", "None"))
1336     } else if match_type(cx, obj_ty, &paths::RESULT) {
1337         Some((RESULT_UNWRAP_USED, "a Result", "Err"))
1338     } else {
1339         None
1340     };
1341
1342     if let Some((lint, kind, none_value)) = mess {
1343         span_lint(
1344             cx,
1345             lint,
1346             expr.span,
1347             &format!(
1348                 "used unwrap() on {} value. If you don't want to handle the {} case gracefully, consider \
1349                  using expect() to provide a better panic \
1350                  message",
1351                 kind,
1352                 none_value
1353             ),
1354         );
1355     }
1356 }
1357
1358 /// lint use of `ok().expect()` for `Result`s
1359 fn lint_ok_expect(cx: &LateContext, expr: &hir::Expr, ok_args: &[hir::Expr]) {
1360     // lint if the caller of `ok()` is a `Result`
1361     if match_type(cx, cx.tables.expr_ty(&ok_args[0]), &paths::RESULT) {
1362         let result_type = cx.tables.expr_ty(&ok_args[0]);
1363         if let Some(error_type) = get_error_type(cx, result_type) {
1364             if has_debug_impl(error_type, cx) {
1365                 span_lint(
1366                     cx,
1367                     OK_EXPECT,
1368                     expr.span,
1369                     "called `ok().expect()` on a Result value. You can call `expect` directly on the `Result`",
1370                 );
1371             }
1372         }
1373     }
1374 }
1375
1376 /// lint use of `map().unwrap_or()` for `Option`s
1377 fn lint_map_unwrap_or(cx: &LateContext, expr: &hir::Expr, map_args: &[hir::Expr], unwrap_args: &[hir::Expr]) {
1378     // lint if the caller of `map()` is an `Option`
1379     if match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION) {
1380         // get snippets for args to map() and unwrap_or()
1381         let map_snippet = snippet(cx, map_args[1].span, "..");
1382         let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
1383         // lint message
1384         // comparing the snippet from source to raw text ("None") below is safe
1385         // because we already have checked the type.
1386         let arg = if unwrap_snippet == "None" {
1387             "None"
1388         } else {
1389             "a"
1390         };
1391         let suggest = if unwrap_snippet == "None" {
1392             "and_then(f)"
1393         } else {
1394             "map_or(a, f)"
1395         };
1396         let msg = &format!(
1397             "called `map(f).unwrap_or({})` on an Option value. \
1398              This can be done more directly by calling `{}` instead",
1399             arg,
1400             suggest
1401         );
1402         // lint, with note if neither arg is > 1 line and both map() and
1403         // unwrap_or() have the same span
1404         let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
1405         let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
1406         if same_span && !multiline {
1407             let suggest = if unwrap_snippet == "None" {
1408                 format!("and_then({})", map_snippet)
1409             } else {
1410                 format!("map_or({}, {})", unwrap_snippet, map_snippet)
1411             };
1412             let note = format!(
1413                 "replace `map({}).unwrap_or({})` with `{}`",
1414                 map_snippet,
1415                 unwrap_snippet,
1416                 suggest
1417             );
1418             span_note_and_lint(cx, OPTION_MAP_UNWRAP_OR, expr.span, msg, expr.span, &note);
1419         } else if same_span && multiline {
1420             span_lint(cx, OPTION_MAP_UNWRAP_OR, expr.span, msg);
1421         };
1422     }
1423 }
1424
1425 /// lint use of `map().unwrap_or_else()` for `Option`s and `Result`s
1426 fn lint_map_unwrap_or_else<'a, 'tcx>(
1427     cx: &LateContext<'a, 'tcx>,
1428     expr: &'tcx hir::Expr,
1429     map_args: &'tcx [hir::Expr],
1430     unwrap_args: &'tcx [hir::Expr],
1431 ) {
1432     // lint if the caller of `map()` is an `Option`
1433     let is_option = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::OPTION);
1434     let is_result = match_type(cx, cx.tables.expr_ty(&map_args[0]), &paths::RESULT);
1435     if is_option || is_result {
1436         // lint message
1437         let msg = if is_option {
1438             "called `map(f).unwrap_or_else(g)` on an Option value. This can be done more directly by calling \
1439              `map_or_else(g, f)` instead"
1440         } else {
1441             "called `map(f).unwrap_or_else(g)` on a Result value. This can be done more directly by calling \
1442              `ok().map_or_else(g, f)` instead"
1443         };
1444         // get snippets for args to map() and unwrap_or_else()
1445         let map_snippet = snippet(cx, map_args[1].span, "..");
1446         let unwrap_snippet = snippet(cx, unwrap_args[1].span, "..");
1447         // lint, with note if neither arg is > 1 line and both map() and
1448         // unwrap_or_else() have the same span
1449         let multiline = map_snippet.lines().count() > 1 || unwrap_snippet.lines().count() > 1;
1450         let same_span = map_args[1].span.ctxt() == unwrap_args[1].span.ctxt();
1451         if same_span && !multiline {
1452             span_note_and_lint(
1453                 cx,
1454                 if is_option {
1455                     OPTION_MAP_UNWRAP_OR_ELSE
1456                 } else {
1457                     RESULT_MAP_UNWRAP_OR_ELSE
1458                 },
1459                 expr.span,
1460                 msg,
1461                 expr.span,
1462                 &format!(
1463                     "replace `map({0}).unwrap_or_else({1})` with `{2}map_or_else({1}, {0})`",
1464                     map_snippet,
1465                     unwrap_snippet,
1466                     if is_result { "ok()." } else { "" }
1467                 ),
1468             );
1469         } else if same_span && multiline {
1470             span_lint(
1471                 cx,
1472                 if is_option {
1473                     OPTION_MAP_UNWRAP_OR_ELSE
1474                 } else {
1475                     RESULT_MAP_UNWRAP_OR_ELSE
1476                 },
1477                 expr.span,
1478                 msg,
1479             );
1480         };
1481     }
1482 }
1483
1484 /// lint use of `_.map_or(None, _)` for `Option`s
1485 fn lint_map_or_none<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, map_or_args: &'tcx [hir::Expr]) {
1486     if match_type(cx, cx.tables.expr_ty(&map_or_args[0]), &paths::OPTION) {
1487         // check if the first non-self argument to map_or() is None
1488         let map_or_arg_is_none = if let hir::Expr_::ExprPath(ref qpath) = map_or_args[1].node {
1489             match_qpath(qpath, &paths::OPTION_NONE)
1490         } else {
1491             false
1492         };
1493
1494         if map_or_arg_is_none {
1495             // lint message
1496             let msg = "called `map_or(None, f)` on an Option value. This can be done more directly by calling \
1497                        `and_then(f)` instead";
1498             let map_or_self_snippet = snippet(cx, map_or_args[0].span, "..");
1499             let map_or_func_snippet = snippet(cx, map_or_args[2].span, "..");
1500             let hint = format!("{0}.and_then({1})", map_or_self_snippet, map_or_func_snippet);
1501             span_lint_and_then(cx, OPTION_MAP_OR_NONE, expr.span, msg, |db| {
1502                 db.span_suggestion(expr.span, "try using and_then instead", hint);
1503             });
1504         }
1505     }
1506 }
1507
1508 /// lint use of `filter().next()` for `Iterators`
1509 fn lint_filter_next<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, filter_args: &'tcx [hir::Expr]) {
1510     // lint if caller of `.filter().next()` is an Iterator
1511     if match_trait_method(cx, expr, &paths::ITERATOR) {
1512         let msg = "called `filter(p).next()` on an `Iterator`. This is more succinctly expressed by calling \
1513                    `.find(p)` instead.";
1514         let filter_snippet = snippet(cx, filter_args[1].span, "..");
1515         if filter_snippet.lines().count() <= 1 {
1516             // add note if not multi-line
1517             span_note_and_lint(
1518                 cx,
1519                 FILTER_NEXT,
1520                 expr.span,
1521                 msg,
1522                 expr.span,
1523                 &format!("replace `filter({0}).next()` with `find({0})`", filter_snippet),
1524             );
1525         } else {
1526             span_lint(cx, FILTER_NEXT, expr.span, msg);
1527         }
1528     }
1529 }
1530
1531 /// lint use of `filter().map()` for `Iterators`
1532 fn lint_filter_map<'a, 'tcx>(
1533     cx: &LateContext<'a, 'tcx>,
1534     expr: &'tcx hir::Expr,
1535     _filter_args: &'tcx [hir::Expr],
1536     _map_args: &'tcx [hir::Expr],
1537 ) {
1538     // lint if caller of `.filter().map()` is an Iterator
1539     if match_trait_method(cx, expr, &paths::ITERATOR) {
1540         let msg = "called `filter(p).map(q)` on an `Iterator`. \
1541                    This is more succinctly expressed by calling `.filter_map(..)` instead.";
1542         span_lint(cx, FILTER_MAP, expr.span, msg);
1543     }
1544 }
1545
1546 /// lint use of `filter().map()` for `Iterators`
1547 fn lint_filter_map_map<'a, 'tcx>(
1548     cx: &LateContext<'a, 'tcx>,
1549     expr: &'tcx hir::Expr,
1550     _filter_args: &'tcx [hir::Expr],
1551     _map_args: &'tcx [hir::Expr],
1552 ) {
1553     // lint if caller of `.filter().map()` is an Iterator
1554     if match_trait_method(cx, expr, &paths::ITERATOR) {
1555         let msg = "called `filter_map(p).map(q)` on an `Iterator`. \
1556                    This is more succinctly expressed by only calling `.filter_map(..)` instead.";
1557         span_lint(cx, FILTER_MAP, expr.span, msg);
1558     }
1559 }
1560
1561 /// lint use of `filter().flat_map()` for `Iterators`
1562 fn lint_filter_flat_map<'a, 'tcx>(
1563     cx: &LateContext<'a, 'tcx>,
1564     expr: &'tcx hir::Expr,
1565     _filter_args: &'tcx [hir::Expr],
1566     _map_args: &'tcx [hir::Expr],
1567 ) {
1568     // lint if caller of `.filter().flat_map()` is an Iterator
1569     if match_trait_method(cx, expr, &paths::ITERATOR) {
1570         let msg = "called `filter(p).flat_map(q)` on an `Iterator`. \
1571                    This is more succinctly expressed by calling `.flat_map(..)` \
1572                    and filtering by returning an empty Iterator.";
1573         span_lint(cx, FILTER_MAP, expr.span, msg);
1574     }
1575 }
1576
1577 /// lint use of `filter_map().flat_map()` for `Iterators`
1578 fn lint_filter_map_flat_map<'a, 'tcx>(
1579     cx: &LateContext<'a, 'tcx>,
1580     expr: &'tcx hir::Expr,
1581     _filter_args: &'tcx [hir::Expr],
1582     _map_args: &'tcx [hir::Expr],
1583 ) {
1584     // lint if caller of `.filter_map().flat_map()` is an Iterator
1585     if match_trait_method(cx, expr, &paths::ITERATOR) {
1586         let msg = "called `filter_map(p).flat_map(q)` on an `Iterator`. \
1587                    This is more succinctly expressed by calling `.flat_map(..)` \
1588                    and filtering by returning an empty Iterator.";
1589         span_lint(cx, FILTER_MAP, expr.span, msg);
1590     }
1591 }
1592
1593 /// lint searching an Iterator followed by `is_some()`
1594 fn lint_search_is_some<'a, 'tcx>(
1595     cx: &LateContext<'a, 'tcx>,
1596     expr: &'tcx hir::Expr,
1597     search_method: &str,
1598     search_args: &'tcx [hir::Expr],
1599     is_some_args: &'tcx [hir::Expr],
1600 ) {
1601     // lint if caller of search is an Iterator
1602     if match_trait_method(cx, &is_some_args[0], &paths::ITERATOR) {
1603         let msg = format!(
1604             "called `is_some()` after searching an `Iterator` with {}. This is more succinctly \
1605              expressed by calling `any()`.",
1606             search_method
1607         );
1608         let search_snippet = snippet(cx, search_args[1].span, "..");
1609         if search_snippet.lines().count() <= 1 {
1610             // add note if not multi-line
1611             span_note_and_lint(
1612                 cx,
1613                 SEARCH_IS_SOME,
1614                 expr.span,
1615                 &msg,
1616                 expr.span,
1617                 &format!("replace `{0}({1}).is_some()` with `any({1})`", search_method, search_snippet),
1618             );
1619         } else {
1620             span_lint(cx, SEARCH_IS_SOME, expr.span, &msg);
1621         }
1622     }
1623 }
1624
1625 /// Used for `lint_binary_expr_with_method_call`.
1626 #[derive(Copy, Clone)]
1627 struct BinaryExprInfo<'a> {
1628     expr: &'a hir::Expr,
1629     chain: &'a hir::Expr,
1630     other: &'a hir::Expr,
1631     eq: bool,
1632 }
1633
1634 /// Checks for the `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints.
1635 fn lint_binary_expr_with_method_call<'a, 'tcx: 'a>(cx: &LateContext<'a, 'tcx>, info: &mut BinaryExprInfo) {
1636     macro_rules! lint_with_both_lhs_and_rhs {
1637         ($func:ident, $cx:expr, $info:ident) => {
1638             if !$func($cx, $info) {
1639                 ::std::mem::swap(&mut $info.chain, &mut $info.other);
1640                 if $func($cx, $info) {
1641                     return;
1642                 }
1643             }
1644         }
1645     }
1646
1647     lint_with_both_lhs_and_rhs!(lint_chars_next_cmp, cx, info);
1648     lint_with_both_lhs_and_rhs!(lint_chars_last_cmp, cx, info);
1649     lint_with_both_lhs_and_rhs!(lint_chars_next_cmp_with_unwrap, cx, info);
1650     lint_with_both_lhs_and_rhs!(lint_chars_last_cmp_with_unwrap, cx, info);
1651 }
1652
1653 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_NEXT_CMP` lints.
1654 fn lint_chars_cmp<'a, 'tcx>(
1655     cx: &LateContext<'a, 'tcx>,
1656     info: &BinaryExprInfo,
1657     chain_methods: &[&str],
1658     lint: &'static Lint,
1659     suggest: &str,
1660 ) -> bool {
1661     if_chain! {
1662         if let Some(args) = method_chain_args(info.chain, chain_methods);
1663         if let hir::ExprCall(ref fun, ref arg_char) = info.other.node;
1664         if arg_char.len() == 1;
1665         if let hir::ExprPath(ref qpath) = fun.node;
1666         if let Some(segment) = single_segment_path(qpath);
1667         if segment.name == "Some";
1668         then {
1669             let self_ty = walk_ptrs_ty(cx.tables.expr_ty_adjusted(&args[0][0]));
1670
1671             if self_ty.sty != ty::TyStr {
1672                 return false;
1673             }
1674
1675             span_lint_and_sugg(cx,
1676                                lint,
1677                                info.expr.span,
1678                                &format!("you should use the `{}` method", suggest),
1679                                "like this",
1680                                format!("{}{}.{}({})",
1681                                        if info.eq { "" } else { "!" },
1682                                        snippet(cx, args[0][0].span, "_"),
1683                                        suggest,
1684                                        snippet(cx, arg_char[0].span, "_")));
1685
1686             return true;
1687         }
1688     }
1689
1690     false
1691 }
1692
1693 /// Checks for the `CHARS_NEXT_CMP` lint.
1694 fn lint_chars_next_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo) -> bool {
1695     lint_chars_cmp(cx, info, &["chars", "next"], CHARS_NEXT_CMP, "starts_with")
1696 }
1697
1698 /// Checks for the `CHARS_LAST_CMP` lint.
1699 fn lint_chars_last_cmp<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo) -> bool {
1700     if lint_chars_cmp(cx, info, &["chars", "last"], CHARS_NEXT_CMP, "ends_with") {
1701         true
1702     } else {
1703         lint_chars_cmp(cx, info, &["chars", "next_back"], CHARS_NEXT_CMP, "ends_with")
1704     }
1705 }
1706
1707 /// Wrapper fn for `CHARS_NEXT_CMP` and `CHARS_LAST_CMP` lints with `unwrap()`.
1708 fn lint_chars_cmp_with_unwrap<'a, 'tcx>(
1709     cx: &LateContext<'a, 'tcx>,
1710     info: &BinaryExprInfo,
1711     chain_methods: &[&str],
1712     lint: &'static Lint,
1713     suggest: &str,
1714 ) -> bool {
1715     if_chain! {
1716         if let Some(args) = method_chain_args(info.chain, chain_methods);
1717         if let hir::ExprLit(ref lit) = info.other.node;
1718         if let ast::LitKind::Char(c) = lit.node;
1719         then {
1720             span_lint_and_sugg(
1721                 cx,
1722                 lint,
1723                 info.expr.span,
1724                 &format!("you should use the `{}` method", suggest),
1725                 "like this",
1726                 format!("{}{}.{}('{}')",
1727                         if info.eq { "" } else { "!" },
1728                         snippet(cx, args[0][0].span, "_"),
1729                         suggest,
1730                         c)
1731             );
1732
1733             return true;
1734         }
1735     }
1736
1737     false
1738 }
1739
1740 /// Checks for the `CHARS_NEXT_CMP` lint with `unwrap()`.
1741 fn lint_chars_next_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo) -> bool {
1742     lint_chars_cmp_with_unwrap(cx, info, &["chars", "next", "unwrap"], CHARS_NEXT_CMP, "starts_with")
1743 }
1744
1745 /// Checks for the `CHARS_LAST_CMP` lint with `unwrap()`.
1746 fn lint_chars_last_cmp_with_unwrap<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, info: &BinaryExprInfo) -> bool {
1747     if lint_chars_cmp_with_unwrap(cx, info, &["chars", "last", "unwrap"], CHARS_LAST_CMP, "ends_with") {
1748         true
1749     } else {
1750         lint_chars_cmp_with_unwrap(cx, info, &["chars", "next_back", "unwrap"], CHARS_LAST_CMP, "ends_with")
1751     }
1752 }
1753
1754 /// lint for length-1 `str`s for methods in `PATTERN_METHODS`
1755 fn lint_single_char_pattern<'a, 'tcx>(cx: &LateContext<'a, 'tcx>, expr: &'tcx hir::Expr, arg: &'tcx hir::Expr) {
1756     let parent_item = cx.tcx.hir.get_parent(arg.id);
1757     let parent_def_id = cx.tcx.hir.local_def_id(parent_item);
1758     let substs = Substs::identity_for_item(cx.tcx, parent_def_id);
1759     if let Ok(&ty::Const {
1760         val: ConstVal::Str(r),
1761         ..
1762     }) = ConstContext::new(cx.tcx, cx.param_env.and(substs), cx.tables).eval(arg)
1763     {
1764         if r.len() == 1 {
1765             let hint = snippet(cx, expr.span, "..").replace(&format!("\"{}\"", r), &format!("'{}'", r));
1766             span_lint_and_then(
1767                 cx,
1768                 SINGLE_CHAR_PATTERN,
1769                 arg.span,
1770                 "single-character string constant used as pattern",
1771                 |db| {
1772                     db.span_suggestion(expr.span, "try using a char instead", hint);
1773                 },
1774             );
1775         }
1776     }
1777 }
1778
1779 /// Checks for the `USELESS_ASREF` lint.
1780 fn lint_asref(cx: &LateContext, expr: &hir::Expr, call_name: &str, as_ref_args: &[hir::Expr]) {
1781     // when we get here, we've already checked that the call name is "as_ref" or "as_mut"
1782     // check if the call is to the actual `AsRef` or `AsMut` trait
1783     if match_trait_method(cx, expr, &paths::ASREF_TRAIT) || match_trait_method(cx, expr, &paths::ASMUT_TRAIT) {
1784         // check if the type after `as_ref` or `as_mut` is the same as before
1785         let recvr = &as_ref_args[0];
1786         let rcv_ty = cx.tables.expr_ty(recvr);
1787         let res_ty = cx.tables.expr_ty(expr);
1788         let (base_res_ty, res_depth) = walk_ptrs_ty_depth(res_ty);
1789         let (base_rcv_ty, rcv_depth) = walk_ptrs_ty_depth(rcv_ty);
1790         if base_rcv_ty == base_res_ty && rcv_depth >= res_depth {
1791             span_lint_and_sugg(
1792                 cx,
1793                 USELESS_ASREF,
1794                 expr.span,
1795                 &format!("this call to `{}` does nothing", call_name),
1796                 "try this",
1797                 snippet(cx, recvr.span, "_").into_owned(),
1798             );
1799         }
1800     }
1801 }
1802
1803 /// Given a `Result<T, E>` type, return its error type (`E`).
1804 fn get_error_type<'a>(cx: &LateContext, ty: Ty<'a>) -> Option<Ty<'a>> {
1805     if let ty::TyAdt(_, substs) = ty.sty {
1806         if match_type(cx, ty, &paths::RESULT) {
1807             substs.types().nth(1)
1808         } else {
1809             None
1810         }
1811     } else {
1812         None
1813     }
1814 }
1815
1816 /// This checks whether a given type is known to implement Debug.
1817 fn has_debug_impl<'a, 'b>(ty: Ty<'a>, cx: &LateContext<'b, 'a>) -> bool {
1818     match cx.tcx.lang_items().debug_trait() {
1819         Some(debug) => implements_trait(cx, ty, debug, &[]),
1820         None => false,
1821     }
1822 }
1823
1824 enum Convention {
1825     Eq(&'static str),
1826     StartsWith(&'static str),
1827 }
1828
1829 #[cfg_attr(rustfmt, rustfmt_skip)]
1830 const CONVENTIONS: [(Convention, &[SelfKind]); 6] = [
1831     (Convention::Eq("new"), &[SelfKind::No]),
1832     (Convention::StartsWith("as_"), &[SelfKind::Ref, SelfKind::RefMut]),
1833     (Convention::StartsWith("from_"), &[SelfKind::No]),
1834     (Convention::StartsWith("into_"), &[SelfKind::Value]),
1835     (Convention::StartsWith("is_"), &[SelfKind::Ref, SelfKind::No]),
1836     (Convention::StartsWith("to_"), &[SelfKind::Ref]),
1837 ];
1838
1839 #[cfg_attr(rustfmt, rustfmt_skip)]
1840 const TRAIT_METHODS: [(&str, usize, SelfKind, OutType, &str); 30] = [
1841     ("add", 2, SelfKind::Value, OutType::Any, "std::ops::Add"),
1842     ("as_mut", 1, SelfKind::RefMut, OutType::Ref, "std::convert::AsMut"),
1843     ("as_ref", 1, SelfKind::Ref, OutType::Ref, "std::convert::AsRef"),
1844     ("bitand", 2, SelfKind::Value, OutType::Any, "std::ops::BitAnd"),
1845     ("bitor", 2, SelfKind::Value, OutType::Any, "std::ops::BitOr"),
1846     ("bitxor", 2, SelfKind::Value, OutType::Any, "std::ops::BitXor"),
1847     ("borrow", 1, SelfKind::Ref, OutType::Ref, "std::borrow::Borrow"),
1848     ("borrow_mut", 1, SelfKind::RefMut, OutType::Ref, "std::borrow::BorrowMut"),
1849     ("clone", 1, SelfKind::Ref, OutType::Any, "std::clone::Clone"),
1850     ("cmp", 2, SelfKind::Ref, OutType::Any, "std::cmp::Ord"),
1851     ("default", 0, SelfKind::No, OutType::Any, "std::default::Default"),
1852     ("deref", 1, SelfKind::Ref, OutType::Ref, "std::ops::Deref"),
1853     ("deref_mut", 1, SelfKind::RefMut, OutType::Ref, "std::ops::DerefMut"),
1854     ("div", 2, SelfKind::Value, OutType::Any, "std::ops::Div"),
1855     ("drop", 1, SelfKind::RefMut, OutType::Unit, "std::ops::Drop"),
1856     ("eq", 2, SelfKind::Ref, OutType::Bool, "std::cmp::PartialEq"),
1857     ("from_iter", 1, SelfKind::No, OutType::Any, "std::iter::FromIterator"),
1858     ("from_str", 1, SelfKind::No, OutType::Any, "std::str::FromStr"),
1859     ("hash", 2, SelfKind::Ref, OutType::Unit, "std::hash::Hash"),
1860     ("index", 2, SelfKind::Ref, OutType::Ref, "std::ops::Index"),
1861     ("index_mut", 2, SelfKind::RefMut, OutType::Ref, "std::ops::IndexMut"),
1862     ("into_iter", 1, SelfKind::Value, OutType::Any, "std::iter::IntoIterator"),
1863     ("mul", 2, SelfKind::Value, OutType::Any, "std::ops::Mul"),
1864     ("neg", 1, SelfKind::Value, OutType::Any, "std::ops::Neg"),
1865     ("next", 1, SelfKind::RefMut, OutType::Any, "std::iter::Iterator"),
1866     ("not", 1, SelfKind::Value, OutType::Any, "std::ops::Not"),
1867     ("rem", 2, SelfKind::Value, OutType::Any, "std::ops::Rem"),
1868     ("shl", 2, SelfKind::Value, OutType::Any, "std::ops::Shl"),
1869     ("shr", 2, SelfKind::Value, OutType::Any, "std::ops::Shr"),
1870     ("sub", 2, SelfKind::Value, OutType::Any, "std::ops::Sub"),
1871 ];
1872
1873 #[cfg_attr(rustfmt, rustfmt_skip)]
1874 const PATTERN_METHODS: [(&str, usize); 17] = [
1875     ("contains", 1),
1876     ("starts_with", 1),
1877     ("ends_with", 1),
1878     ("find", 1),
1879     ("rfind", 1),
1880     ("split", 1),
1881     ("rsplit", 1),
1882     ("split_terminator", 1),
1883     ("rsplit_terminator", 1),
1884     ("splitn", 2),
1885     ("rsplitn", 2),
1886     ("matches", 1),
1887     ("rmatches", 1),
1888     ("match_indices", 1),
1889     ("rmatch_indices", 1),
1890     ("trim_left_matches", 1),
1891     ("trim_right_matches", 1),
1892 ];
1893
1894
1895 #[derive(Clone, Copy, PartialEq, Debug)]
1896 enum SelfKind {
1897     Value,
1898     Ref,
1899     RefMut,
1900     No,
1901 }
1902
1903 impl SelfKind {
1904     fn matches(
1905         self,
1906         ty: &hir::Ty,
1907         arg: &hir::Arg,
1908         self_ty: &hir::Ty,
1909         allow_value_for_ref: bool,
1910         generics: &hir::Generics,
1911     ) -> bool {
1912         // Self types in the HIR are desugared to explicit self types. So it will
1913         // always be `self:
1914         // SomeType`,
1915         // where SomeType can be `Self` or an explicit impl self type (e.g. `Foo` if
1916         // the impl is on `Foo`)
1917         // Thus, we only need to test equality against the impl self type or if it is
1918         // an explicit
1919         // `Self`. Furthermore, the only possible types for `self: ` are `&Self`,
1920         // `Self`, `&mut Self`,
1921         // and `Box<Self>`, including the equivalent types with `Foo`.
1922
1923         let is_actually_self = |ty| is_self_ty(ty) || ty == self_ty;
1924         if is_self(arg) {
1925             match self {
1926                 SelfKind::Value => is_actually_self(ty),
1927                 SelfKind::Ref | SelfKind::RefMut => {
1928                     if allow_value_for_ref && is_actually_self(ty) {
1929                         return true;
1930                     }
1931                     match ty.node {
1932                         hir::TyRptr(_, ref mt_ty) => {
1933                             let mutability_match = if self == SelfKind::Ref {
1934                                 mt_ty.mutbl == hir::MutImmutable
1935                             } else {
1936                                 mt_ty.mutbl == hir::MutMutable
1937                             };
1938                             is_actually_self(&mt_ty.ty) && mutability_match
1939                         },
1940                         _ => false,
1941                     }
1942                 },
1943                 _ => false,
1944             }
1945         } else {
1946             match self {
1947                 SelfKind::Value => false,
1948                 SelfKind::Ref => is_as_ref_or_mut_trait(ty, self_ty, generics, &paths::ASREF_TRAIT),
1949                 SelfKind::RefMut => is_as_ref_or_mut_trait(ty, self_ty, generics, &paths::ASMUT_TRAIT),
1950                 SelfKind::No => true,
1951             }
1952         }
1953     }
1954
1955     fn description(&self) -> &'static str {
1956         match *self {
1957             SelfKind::Value => "self by value",
1958             SelfKind::Ref => "self by reference",
1959             SelfKind::RefMut => "self by mutable reference",
1960             SelfKind::No => "no self",
1961         }
1962     }
1963 }
1964
1965 fn is_as_ref_or_mut_trait(ty: &hir::Ty, self_ty: &hir::Ty, generics: &hir::Generics, name: &[&str]) -> bool {
1966     single_segment_ty(ty).map_or(false, |seg| {
1967         generics.ty_params().any(|param| {
1968             param.name == seg.name && param.bounds.iter().any(|bound| {
1969                 if let hir::TyParamBound::TraitTyParamBound(ref ptr, ..) = *bound {
1970                     let path = &ptr.trait_ref.path;
1971                     match_path(path, name) && path.segments.last().map_or(false, |s| {
1972                         if let Some(ref params) = s.parameters {
1973                             if params.parenthesized {
1974                                 false
1975                             } else {
1976                                 params.types.len() == 1
1977                                     && (is_self_ty(&params.types[0]) || is_ty(&*params.types[0], self_ty))
1978                             }
1979                         } else {
1980                             false
1981                         }
1982                     })
1983                 } else {
1984                     false
1985                 }
1986             })
1987         })
1988     })
1989 }
1990
1991 fn is_ty(ty: &hir::Ty, self_ty: &hir::Ty) -> bool {
1992     match (&ty.node, &self_ty.node) {
1993         (
1994             &hir::TyPath(hir::QPath::Resolved(_, ref ty_path)),
1995             &hir::TyPath(hir::QPath::Resolved(_, ref self_ty_path)),
1996         ) => ty_path
1997             .segments
1998             .iter()
1999             .map(|seg| seg.name)
2000             .eq(self_ty_path.segments.iter().map(|seg| seg.name)),
2001         _ => false,
2002     }
2003 }
2004
2005 fn single_segment_ty(ty: &hir::Ty) -> Option<&hir::PathSegment> {
2006     if let hir::TyPath(ref path) = ty.node {
2007         single_segment_path(path)
2008     } else {
2009         None
2010     }
2011 }
2012
2013 impl Convention {
2014     fn check(&self, other: &str) -> bool {
2015         match *self {
2016             Convention::Eq(this) => this == other,
2017             Convention::StartsWith(this) => other.starts_with(this) && this != other,
2018         }
2019     }
2020 }
2021
2022 impl fmt::Display for Convention {
2023     fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
2024         match *self {
2025             Convention::Eq(this) => this.fmt(f),
2026             Convention::StartsWith(this) => this.fmt(f).and_then(|_| '*'.fmt(f)),
2027         }
2028     }
2029 }
2030
2031 #[derive(Clone, Copy)]
2032 enum OutType {
2033     Unit,
2034     Bool,
2035     Any,
2036     Ref,
2037 }
2038
2039 impl OutType {
2040     fn matches(&self, ty: &hir::FunctionRetTy) -> bool {
2041         match (self, ty) {
2042             (&OutType::Unit, &hir::DefaultReturn(_)) => true,
2043             (&OutType::Unit, &hir::Return(ref ty)) if ty.node == hir::TyTup(vec![].into()) => true,
2044             (&OutType::Bool, &hir::Return(ref ty)) if is_bool(ty) => true,
2045             (&OutType::Any, &hir::Return(ref ty)) if ty.node != hir::TyTup(vec![].into()) => true,
2046             (&OutType::Ref, &hir::Return(ref ty)) => matches!(ty.node, hir::TyRptr(_, _)),
2047             _ => false,
2048         }
2049     }
2050 }
2051
2052 fn is_bool(ty: &hir::Ty) -> bool {
2053     if let hir::TyPath(ref p) = ty.node {
2054         match_qpath(p, &["bool"])
2055     } else {
2056         false
2057     }
2058 }