src/tools/clippy/clippy_lints/src/types.rs

   1 #![allow(rustc::default_hash_types)]
   2
   3 use std::borrow::Cow;
   4 use std::cmp::Ordering;
   5 use std::collections::BTreeMap;
   6
   7 use if_chain::if_chain;
   8 use rustc_ast::{FloatTy, IntTy, LitFloatType, LitIntType, LitKind, UintTy};
   9 use rustc_errors::{Applicability, DiagnosticBuilder};
  10 use rustc_hir as hir;
  11 use rustc_hir::def::Res;
  12 use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
  13 use rustc_hir::{
  14     BinOpKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericBounds, GenericParamKind, HirId,
  15     ImplItem, ImplItemKind, Item, ItemKind, Lifetime, Lit, Local, MatchSource, MutTy, Mutability, Node, QPath, Stmt,
  16     StmtKind, SyntheticTyParamKind, TraitFn, TraitItem, TraitItemKind, TyKind, UnOp,
  17 };
  18 use rustc_lint::{LateContext, LateLintPass, LintContext};
  19 use rustc_middle::hir::map::Map;
  20 use rustc_middle::lint::in_external_macro;
  21 use rustc_middle::ty::TypeFoldable;
  22 use rustc_middle::ty::{self, InferTy, Ty, TyCtxt, TyS, TypeckResults};
  23 use rustc_session::{declare_lint_pass, declare_tool_lint, impl_lint_pass};
  24 use rustc_span::hygiene::{ExpnKind, MacroKind};
  25 use rustc_span::source_map::Span;
  26 use rustc_span::symbol::sym;
  27 use rustc_target::abi::LayoutOf;
  28 use rustc_target::spec::abi::Abi;
  29 use rustc_typeck::hir_ty_to_ty;
  30
  31 use crate::consts::{constant, Constant};
  32 use crate::utils::paths;
  33 use crate::utils::{
  34     clip, comparisons, differing_macro_contexts, higher, in_constant, indent_of, int_bits, is_type_diagnostic_item,
  35     last_path_segment, match_def_path, match_path, method_chain_args, multispan_sugg, numeric_literal::NumericLiteral,
  36     qpath_res, reindent_multiline, sext, snippet, snippet_opt, snippet_with_applicability, snippet_with_macro_callsite,
  37     span_lint, span_lint_and_help, span_lint_and_sugg, span_lint_and_then, unsext,
  38 };
  39
  40 declare_clippy_lint! {
  41     /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
  42     /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
  43     ///
  44     /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
  45     /// the heap. So if you `Box` it, you just add another level of indirection
  46     /// without any benefit whatsoever.
  47     ///
  48     /// **Known problems:** None.
  49     ///
  50     /// **Example:**
  51     /// ```rust,ignore
  52     /// struct X {
  53     ///     values: Box<Vec<Foo>>,
  54     /// }
  55     /// ```
  56     ///
  57     /// Better:
  58     ///
  59     /// ```rust,ignore
  60     /// struct X {
  61     ///     values: Vec<Foo>,
  62     /// }
  63     /// ```
  64     pub BOX_VEC,
  65     perf,
  66     "usage of `Box<Vec<T>>`, vector elements are already on the heap"
  67 }
  68
  69 declare_clippy_lint! {
  70     /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
  71     /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
  72     ///
  73     /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
  74     /// the heap. So if you `Box` its contents, you just add another level of indirection.
  75     ///
  76     /// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see #3530,
  77     /// 1st comment).
  78     ///
  79     /// **Example:**
  80     /// ```rust
  81     /// struct X {
  82     ///     values: Vec<Box<i32>>,
  83     /// }
  84     /// ```
  85     ///
  86     /// Better:
  87     ///
  88     /// ```rust
  89     /// struct X {
  90     ///     values: Vec<i32>,
  91     /// }
  92     /// ```
  93     pub VEC_BOX,
  94     complexity,
  95     "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
  96 }
  97
  98 declare_clippy_lint! {
  99     /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
 100     /// definitions
 101     ///
 102     /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
 103     /// represents an optional optional value which is logically the same thing as an optional
 104     /// value but has an unneeded extra level of wrapping.
 105     ///
 106     /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
 107     /// consider a custom `enum` instead, with clear names for each case.
 108     ///
 109     /// **Known problems:** None.
 110     ///
 111     /// **Example**
 112     /// ```rust
 113     /// fn get_data() -> Option<Option<u32>> {
 114     ///     None
 115     /// }
 116     /// ```
 117     ///
 118     /// Better:
 119     ///
 120     /// ```rust
 121     /// pub enum Contents {
 122     ///     Data(Vec<u8>), // Was Some(Some(Vec<u8>))
 123     ///     NotYetFetched, // Was Some(None)
 124     ///     None,          // Was None
 125     /// }
 126     ///
 127     /// fn get_data() -> Contents {
 128     ///     Contents::None
 129     /// }
 130     /// ```
 131     pub OPTION_OPTION,
 132     pedantic,
 133     "usage of `Option<Option<T>>`"
 134 }
 135
 136 declare_clippy_lint! {
 137     /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
 138     /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
 139     ///
 140     /// **Why is this bad?** Gankro says:
 141     ///
 142     /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
 143     /// pointers and indirection.
 144     /// > It wastes memory, it has terrible cache locality, and is all-around slow.
 145     /// `RingBuf`, while
 146     /// > "only" amortized for push/pop, should be faster in the general case for
 147     /// almost every possible
 148     /// > workload, and isn't even amortized at all if you can predict the capacity
 149     /// you need.
 150     /// >
 151     /// > `LinkedList`s are only really good if you're doing a lot of merging or
 152     /// splitting of lists.
 153     /// > This is because they can just mangle some pointers instead of actually
 154     /// copying the data. Even
 155     /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
 156     /// can still be better
 157     /// > because of how expensive it is to seek to the middle of a `LinkedList`.
 158     ///
 159     /// **Known problems:** False positives – the instances where using a
 160     /// `LinkedList` makes sense are few and far between, but they can still happen.
 161     ///
 162     /// **Example:**
 163     /// ```rust
 164     /// # use std::collections::LinkedList;
 165     /// let x: LinkedList<usize> = LinkedList::new();
 166     /// ```
 167     pub LINKEDLIST,
 168     pedantic,
 169     "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
 170 }
 171
 172 declare_clippy_lint! {
 173     /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
 174     /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
 175     ///
 176     /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
 177     /// general.
 178     ///
 179     /// **Known problems:** None.
 180     ///
 181     /// **Example:**
 182     /// ```rust,ignore
 183     /// fn foo(bar: &Box<T>) { ... }
 184     /// ```
 185     ///
 186     /// Better:
 187     ///
 188     /// ```rust,ignore
 189     /// fn foo(bar: &T) { ... }
 190     /// ```
 191     pub BORROWED_BOX,
 192     complexity,
 193     "a borrow of a boxed type"
 194 }
 195
 196 declare_clippy_lint! {
 197     /// **What it does:** Checks for use of redundant allocations anywhere in the code.
 198     ///
 199     /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
 200     /// add an unnecessary level of indirection.
 201     ///
 202     /// **Known problems:** None.
 203     ///
 204     /// **Example:**
 205     /// ```rust
 206     /// # use std::rc::Rc;
 207     /// fn foo(bar: Rc<&usize>) {}
 208     /// ```
 209     ///
 210     /// Better:
 211     ///
 212     /// ```rust
 213     /// fn foo(bar: &usize) {}
 214     /// ```
 215     pub REDUNDANT_ALLOCATION,
 216     perf,
 217     "redundant allocation"
 218 }
 219
 220 declare_clippy_lint! {
 221     /// **What it does:** Checks for `Rc<T>` and `Arc<T>` when `T` is a mutable buffer type such as `String` or `Vec`.
 222     ///
 223     /// **Why is this bad?** Expressions such as `Rc<String>` usually have no advantage over `Rc<str>`, since
 224     /// it is larger and involves an extra level of indirection, and doesn't implement `Borrow<str>`.
 225     ///
 226     /// While mutating a buffer type would still be possible with `Rc::get_mut()`, it only
 227     /// works if there are no additional references yet, which usually defeats the purpose of
 228     /// enclosing it in a shared ownership type. Instead, additionally wrapping the inner
 229     /// type with an interior mutable container (such as `RefCell` or `Mutex`) would normally
 230     /// be used.
 231     ///
 232     /// **Known problems:** This pattern can be desirable to avoid the overhead of a `RefCell` or `Mutex` for
 233     /// cases where mutation only happens before there are any additional references.
 234     ///
 235     /// **Example:**
 236     /// ```rust,ignore
 237     /// # use std::rc::Rc;
 238     /// fn foo(interned: Rc<String>) { ... }
 239     /// ```
 240     ///
 241     /// Better:
 242     ///
 243     /// ```rust,ignore
 244     /// fn foo(interned: Rc<str>) { ... }
 245     /// ```
 246     pub RC_BUFFER,
 247     restriction,
 248     "shared ownership of a buffer type"
 249 }
 250
 251 pub struct Types {
 252     vec_box_size_threshold: u64,
 253 }
 254
 255 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION, RC_BUFFER]);
 256
 257 impl<'tcx> LateLintPass<'tcx> for Types {
 258     fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
 259         // Skip trait implementations; see issue #605.
 260         if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id)) {
 261             if let ItemKind::Impl { of_trait: Some(_), .. } = item.kind {
 262                 return;
 263             }
 264         }
 265
 266         self.check_fn_decl(cx, decl);
 267     }
 268
 269     fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
 270         self.check_ty(cx, &field.ty, false);
 271     }
 272
 273     fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
 274         match item.kind {
 275             TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_ty(cx, ty, false),
 276             TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, &sig.decl),
 277             _ => (),
 278         }
 279     }
 280
 281     fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
 282         if let Some(ref ty) = local.ty {
 283             self.check_ty(cx, ty, true);
 284         }
 285     }
 286 }
 287
 288 /// Checks if `qpath` has last segment with type parameter matching `path`
 289 fn match_type_parameter(cx: &LateContext<'_>, qpath: &QPath<'_>, path: &[&str]) -> Option<Span> {
 290     let last = last_path_segment(qpath);
 291     if_chain! {
 292         if let Some(ref params) = last.args;
 293         if !params.parenthesized;
 294         if let Some(ty) = params.args.iter().find_map(|arg| match arg {
 295             GenericArg::Type(ty) => Some(ty),
 296             _ => None,
 297         });
 298         if let TyKind::Path(ref qpath) = ty.kind;
 299         if let Some(did) = qpath_res(cx, qpath, ty.hir_id).opt_def_id();
 300         if match_def_path(cx, did, path);
 301         then {
 302             return Some(ty.span);
 303         }
 304     }
 305     None
 306 }
 307
 308 fn match_buffer_type(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<&'static str> {
 309     if match_type_parameter(cx, qpath, &paths::STRING).is_some() {
 310         return Some("str");
 311     }
 312     if match_type_parameter(cx, qpath, &paths::OS_STRING).is_some() {
 313         return Some("std::ffi::OsStr");
 314     }
 315     if match_type_parameter(cx, qpath, &paths::PATH_BUF).is_some() {
 316         return Some("std::path::Path");
 317     }
 318     None
 319 }
 320
 321 fn match_borrows_parameter(_cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Span> {
 322     let last = last_path_segment(qpath);
 323     if_chain! {
 324         if let Some(ref params) = last.args;
 325         if !params.parenthesized;
 326         if let Some(ty) = params.args.iter().find_map(|arg| match arg {
 327             GenericArg::Type(ty) => Some(ty),
 328             _ => None,
 329         });
 330         if let TyKind::Rptr(..) = ty.kind;
 331         then {
 332             return Some(ty.span);
 333         }
 334     }
 335     None
 336 }
 337
 338 impl Types {
 339     pub fn new(vec_box_size_threshold: u64) -> Self {
 340         Self { vec_box_size_threshold }
 341     }
 342
 343     fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>) {
 344         for input in decl.inputs {
 345             self.check_ty(cx, input, false);
 346         }
 347
 348         if let FnRetTy::Return(ref ty) = decl.output {
 349             self.check_ty(cx, ty, false);
 350         }
 351     }
 352
 353     /// Recursively check for `TypePass` lints in the given type. Stop at the first
 354     /// lint found.
 355     ///
 356     /// The parameter `is_local` distinguishes the context of the type; types from
 357     /// local bindings should only be checked for the `BORROWED_BOX` lint.
 358     #[allow(clippy::too_many_lines)]
 359     fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, is_local: bool) {
 360         if hir_ty.span.from_expansion() {
 361             return;
 362         }
 363         match hir_ty.kind {
 364             TyKind::Path(ref qpath) if !is_local => {
 365                 let hir_id = hir_ty.hir_id;
 366                 let res = qpath_res(cx, qpath, hir_id);
 367                 if let Some(def_id) = res.opt_def_id() {
 368                     if Some(def_id) == cx.tcx.lang_items().owned_box() {
 369                         if let Some(span) = match_borrows_parameter(cx, qpath) {
 370                             let mut applicability = Applicability::MachineApplicable;
 371                             span_lint_and_sugg(
 372                                 cx,
 373                                 REDUNDANT_ALLOCATION,
 374                                 hir_ty.span,
 375                                 "usage of `Box<&T>`",
 376                                 "try",
 377                                 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
 378                                 applicability,
 379                             );
 380                             return; // don't recurse into the type
 381                         }
 382                         if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
 383                             span_lint_and_help(
 384                                 cx,
 385                                 BOX_VEC,
 386                                 hir_ty.span,
 387                                 "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
 388                                 None,
 389                                 "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation.",
 390                             );
 391                             return; // don't recurse into the type
 392                         }
 393                     } else if cx.tcx.is_diagnostic_item(sym::Rc, def_id) {
 394                         if let Some(span) = match_type_parameter(cx, qpath, &paths::RC) {
 395                             let mut applicability = Applicability::MachineApplicable;
 396                             span_lint_and_sugg(
 397                                 cx,
 398                                 REDUNDANT_ALLOCATION,
 399                                 hir_ty.span,
 400                                 "usage of `Rc<Rc<T>>`",
 401                                 "try",
 402                                 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
 403                                 applicability,
 404                             );
 405                             return; // don't recurse into the type
 406                         }
 407                         if match_type_parameter(cx, qpath, &paths::BOX).is_some() {
 408                             let box_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
 409                                 GenericArg::Type(ty) => match &ty.kind {
 410                                     TyKind::Path(qpath) => qpath,
 411                                     _ => return,
 412                                 },
 413                                 _ => return,
 414                             };
 415                             let inner_span = match &last_path_segment(&box_ty).args.unwrap().args[0] {
 416                                 GenericArg::Type(ty) => ty.span,
 417                                 _ => return,
 418                             };
 419                             let mut applicability = Applicability::MachineApplicable;
 420                             span_lint_and_sugg(
 421                                 cx,
 422                                 REDUNDANT_ALLOCATION,
 423                                 hir_ty.span,
 424                                 "usage of `Rc<Box<T>>`",
 425                                 "try",
 426                                 format!(
 427                                     "Rc<{}>",
 428                                     snippet_with_applicability(cx, inner_span, "..", &mut applicability)
 429                                 ),
 430                                 applicability,
 431                             );
 432                             return; // don't recurse into the type
 433                         }
 434                         if let Some(alternate) = match_buffer_type(cx, qpath) {
 435                             span_lint_and_sugg(
 436                                 cx,
 437                                 RC_BUFFER,
 438                                 hir_ty.span,
 439                                 "usage of `Rc<T>` when T is a buffer type",
 440                                 "try",
 441                                 format!("Rc<{}>", alternate),
 442                                 Applicability::MachineApplicable,
 443                             );
 444                             return; // don't recurse into the type
 445                         }
 446                         if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
 447                             let vec_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
 448                                 GenericArg::Type(ty) => match &ty.kind {
 449                                     TyKind::Path(qpath) => qpath,
 450                                     _ => return,
 451                                 },
 452                                 _ => return,
 453                             };
 454                             let inner_span = match &last_path_segment(&vec_ty).args.unwrap().args[0] {
 455                                 GenericArg::Type(ty) => ty.span,
 456                                 _ => return,
 457                             };
 458                             let mut applicability = Applicability::MachineApplicable;
 459                             span_lint_and_sugg(
 460                                 cx,
 461                                 RC_BUFFER,
 462                                 hir_ty.span,
 463                                 "usage of `Rc<T>` when T is a buffer type",
 464                                 "try",
 465                                 format!(
 466                                     "Rc<[{}]>",
 467                                     snippet_with_applicability(cx, inner_span, "..", &mut applicability)
 468                                 ),
 469                                 Applicability::MachineApplicable,
 470                             );
 471                             return; // don't recurse into the type
 472                         }
 473                         if let Some(span) = match_borrows_parameter(cx, qpath) {
 474                             let mut applicability = Applicability::MachineApplicable;
 475                             span_lint_and_sugg(
 476                                 cx,
 477                                 REDUNDANT_ALLOCATION,
 478                                 hir_ty.span,
 479                                 "usage of `Rc<&T>`",
 480                                 "try",
 481                                 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
 482                                 applicability,
 483                             );
 484                             return; // don't recurse into the type
 485                         }
 486                     } else if cx.tcx.is_diagnostic_item(sym::Arc, def_id) {
 487                         if let Some(alternate) = match_buffer_type(cx, qpath) {
 488                             span_lint_and_sugg(
 489                                 cx,
 490                                 RC_BUFFER,
 491                                 hir_ty.span,
 492                                 "usage of `Arc<T>` when T is a buffer type",
 493                                 "try",
 494                                 format!("Arc<{}>", alternate),
 495                                 Applicability::MachineApplicable,
 496                             );
 497                             return; // don't recurse into the type
 498                         }
 499                         if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
 500                             let vec_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
 501                                 GenericArg::Type(ty) => match &ty.kind {
 502                                     TyKind::Path(qpath) => qpath,
 503                                     _ => return,
 504                                 },
 505                                 _ => return,
 506                             };
 507                             let inner_span = match &last_path_segment(&vec_ty).args.unwrap().args[0] {
 508                                 GenericArg::Type(ty) => ty.span,
 509                                 _ => return,
 510                             };
 511                             let mut applicability = Applicability::MachineApplicable;
 512                             span_lint_and_sugg(
 513                                 cx,
 514                                 RC_BUFFER,
 515                                 hir_ty.span,
 516                                 "usage of `Arc<T>` when T is a buffer type",
 517                                 "try",
 518                                 format!(
 519                                     "Arc<[{}]>",
 520                                     snippet_with_applicability(cx, inner_span, "..", &mut applicability)
 521                                 ),
 522                                 Applicability::MachineApplicable,
 523                             );
 524                             return; // don't recurse into the type
 525                         }
 526                     } else if cx.tcx.is_diagnostic_item(sym::vec_type, def_id) {
 527                         if_chain! {
 528                             // Get the _ part of Vec<_>
 529                             if let Some(ref last) = last_path_segment(qpath).args;
 530                             if let Some(ty) = last.args.iter().find_map(|arg| match arg {
 531                                 GenericArg::Type(ty) => Some(ty),
 532                                 _ => None,
 533                             });
 534                             // ty is now _ at this point
 535                             if let TyKind::Path(ref ty_qpath) = ty.kind;
 536                             let res = qpath_res(cx, ty_qpath, ty.hir_id);
 537                             if let Some(def_id) = res.opt_def_id();
 538                             if Some(def_id) == cx.tcx.lang_items().owned_box();
 539                             // At this point, we know ty is Box<T>, now get T
 540                             if let Some(ref last) = last_path_segment(ty_qpath).args;
 541                             if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
 542                                 GenericArg::Type(ty) => Some(ty),
 543                                 _ => None,
 544                             });
 545                             let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
 546                             if !ty_ty.has_escaping_bound_vars();
 547                             if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env);
 548                             if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
 549                             if ty_ty_size <= self.vec_box_size_threshold;
 550                             then {
 551                                 span_lint_and_sugg(
 552                                     cx,
 553                                     VEC_BOX,
 554                                     hir_ty.span,
 555                                     "`Vec<T>` is already on the heap, the boxing is unnecessary.",
 556                                     "try",
 557                                     format!("Vec<{}>", snippet(cx, boxed_ty.span, "..")),
 558                                     Applicability::MachineApplicable,
 559                                 );
 560                                 return; // don't recurse into the type
 561                             }
 562                         }
 563                     } else if cx.tcx.is_diagnostic_item(sym::option_type, def_id) {
 564                         if match_type_parameter(cx, qpath, &paths::OPTION).is_some() {
 565                             span_lint(
 566                                 cx,
 567                                 OPTION_OPTION,
 568                                 hir_ty.span,
 569                                 "consider using `Option<T>` instead of `Option<Option<T>>` or a custom \
 570                                  enum if you need to distinguish all 3 cases",
 571                             );
 572                             return; // don't recurse into the type
 573                         }
 574                     } else if match_def_path(cx, def_id, &paths::LINKED_LIST) {
 575                         span_lint_and_help(
 576                             cx,
 577                             LINKEDLIST,
 578                             hir_ty.span,
 579                             "I see you're using a LinkedList! Perhaps you meant some other data structure?",
 580                             None,
 581                             "a `VecDeque` might work",
 582                         );
 583                         return; // don't recurse into the type
 584                     }
 585                 }
 586                 match *qpath {
 587                     QPath::Resolved(Some(ref ty), ref p) => {
 588                         self.check_ty(cx, ty, is_local);
 589                         for ty in p.segments.iter().flat_map(|seg| {
 590                             seg.args
 591                                 .as_ref()
 592                                 .map_or_else(|| [].iter(), |params| params.args.iter())
 593                                 .filter_map(|arg| match arg {
 594                                     GenericArg::Type(ty) => Some(ty),
 595                                     _ => None,
 596                                 })
 597                         }) {
 598                             self.check_ty(cx, ty, is_local);
 599                         }
 600                     },
 601                     QPath::Resolved(None, ref p) => {
 602                         for ty in p.segments.iter().flat_map(|seg| {
 603                             seg.args
 604                                 .as_ref()
 605                                 .map_or_else(|| [].iter(), |params| params.args.iter())
 606                                 .filter_map(|arg| match arg {
 607                                     GenericArg::Type(ty) => Some(ty),
 608                                     _ => None,
 609                                 })
 610                         }) {
 611                             self.check_ty(cx, ty, is_local);
 612                         }
 613                     },
 614                     QPath::TypeRelative(ref ty, ref seg) => {
 615                         self.check_ty(cx, ty, is_local);
 616                         if let Some(ref params) = seg.args {
 617                             for ty in params.args.iter().filter_map(|arg| match arg {
 618                                 GenericArg::Type(ty) => Some(ty),
 619                                 _ => None,
 620                             }) {
 621                                 self.check_ty(cx, ty, is_local);
 622                             }
 623                         }
 624                     },
 625                     QPath::LangItem(..) => {},
 626                 }
 627             },
 628             TyKind::Rptr(ref lt, ref mut_ty) => self.check_ty_rptr(cx, hir_ty, is_local, lt, mut_ty),
 629             // recurse
 630             TyKind::Slice(ref ty) | TyKind::Array(ref ty, _) | TyKind::Ptr(MutTy { ref ty, .. }) => {
 631                 self.check_ty(cx, ty, is_local)
 632             },
 633             TyKind::Tup(tys) => {
 634                 for ty in tys {
 635                     self.check_ty(cx, ty, is_local);
 636                 }
 637             },
 638             _ => {},
 639         }
 640     }
 641
 642     fn check_ty_rptr(
 643         &mut self,
 644         cx: &LateContext<'_>,
 645         hir_ty: &hir::Ty<'_>,
 646         is_local: bool,
 647         lt: &Lifetime,
 648         mut_ty: &MutTy<'_>,
 649     ) {
 650         match mut_ty.ty.kind {
 651             TyKind::Path(ref qpath) => {
 652                 let hir_id = mut_ty.ty.hir_id;
 653                 let def = qpath_res(cx, qpath, hir_id);
 654                 if_chain! {
 655                     if let Some(def_id) = def.opt_def_id();
 656                     if Some(def_id) == cx.tcx.lang_items().owned_box();
 657                     if let QPath::Resolved(None, ref path) = *qpath;
 658                     if let [ref bx] = *path.segments;
 659                     if let Some(ref params) = bx.args;
 660                     if !params.parenthesized;
 661                     if let Some(inner) = params.args.iter().find_map(|arg| match arg {
 662                         GenericArg::Type(ty) => Some(ty),
 663                         _ => None,
 664                     });
 665                     then {
 666                         if is_any_trait(inner) {
 667                             // Ignore `Box<Any>` types; see issue #1884 for details.
 668                             return;
 669                         }
 670
 671                         let ltopt = if lt.is_elided() {
 672                             String::new()
 673                         } else {
 674                             format!("{} ", lt.name.ident().as_str())
 675                         };
 676
 677                         if mut_ty.mutbl == Mutability::Mut {
 678                             // Ignore `&mut Box<T>` types; see issue #2907 for
 679                             // details.
 680                             return;
 681                         }
 682
 683                         // When trait objects or opaque types have lifetime or auto-trait bounds,
 684                         // we need to add parentheses to avoid a syntax error due to its ambiguity.
 685                         // Originally reported as the issue #3128.
 686                         let inner_snippet = snippet(cx, inner.span, "..");
 687                         let suggestion = match &inner.kind {
 688                             TyKind::TraitObject(bounds, lt_bound) if bounds.len() > 1 || !lt_bound.is_elided() => {
 689                                 format!("&{}({})", ltopt, &inner_snippet)
 690                             },
 691                             TyKind::Path(qpath)
 692                                 if get_bounds_if_impl_trait(cx, qpath, inner.hir_id)
 693                                     .map_or(false, |bounds| bounds.len() > 1) =>
 694                             {
 695                                 format!("&{}({})", ltopt, &inner_snippet)
 696                             },
 697                             _ => format!("&{}{}", ltopt, &inner_snippet),
 698                         };
 699                         span_lint_and_sugg(
 700                             cx,
 701                             BORROWED_BOX,
 702                             hir_ty.span,
 703                             "you seem to be trying to use `&Box<T>`. Consider using just `&T`",
 704                             "try",
 705                             suggestion,
 706                             // To make this `MachineApplicable`, at least one needs to check if it isn't a trait item
 707                             // because the trait impls of it will break otherwise;
 708                             // and there may be other cases that result in invalid code.
 709                             // For example, type coercion doesn't work nicely.
 710                             Applicability::Unspecified,
 711                         );
 712                         return; // don't recurse into the type
 713                     }
 714                 };
 715                 self.check_ty(cx, &mut_ty.ty, is_local);
 716             },
 717             _ => self.check_ty(cx, &mut_ty.ty, is_local),
 718         }
 719     }
 720 }
 721
 722 // Returns true if given type is `Any` trait.
 723 fn is_any_trait(t: &hir::Ty<'_>) -> bool {
 724     if_chain! {
 725         if let TyKind::TraitObject(ref traits, _) = t.kind;
 726         if !traits.is_empty();
 727         // Only Send/Sync can be used as additional traits, so it is enough to
 728         // check only the first trait.
 729         if match_path(&traits[0].trait_ref.path, &paths::ANY_TRAIT);
 730         then {
 731             return true;
 732         }
 733     }
 734
 735     false
 736 }
 737
 738 fn get_bounds_if_impl_trait<'tcx>(cx: &LateContext<'tcx>, qpath: &QPath<'_>, id: HirId) -> Option<GenericBounds<'tcx>> {
 739     if_chain! {
 740         if let Some(did) = qpath_res(cx, qpath, id).opt_def_id();
 741         if let Some(Node::GenericParam(generic_param)) = cx.tcx.hir().get_if_local(did);
 742         if let GenericParamKind::Type { synthetic, .. } = generic_param.kind;
 743         if synthetic == Some(SyntheticTyParamKind::ImplTrait);
 744         then {
 745             Some(generic_param.bounds)
 746         } else {
 747             None
 748         }
 749     }
 750 }
 751
 752 declare_clippy_lint! {
 753     /// **What it does:** Checks for binding a unit value.
 754     ///
 755     /// **Why is this bad?** A unit value cannot usefully be used anywhere. So
 756     /// binding one is kind of pointless.
 757     ///
 758     /// **Known problems:** None.
 759     ///
 760     /// **Example:**
 761     /// ```rust
 762     /// let x = {
 763     ///     1;
 764     /// };
 765     /// ```
 766     pub LET_UNIT_VALUE,
 767     pedantic,
 768     "creating a `let` binding to a value of unit type, which usually can't be used afterwards"
 769 }
 770
 771 declare_lint_pass!(LetUnitValue => [LET_UNIT_VALUE]);
 772
 773 impl<'tcx> LateLintPass<'tcx> for LetUnitValue {
 774     fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
 775         if let StmtKind::Local(ref local) = stmt.kind {
 776             if is_unit(cx.typeck_results().pat_ty(&local.pat)) {
 777                 if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
 778                     return;
 779                 }
 780                 if higher::is_from_for_desugar(local) {
 781                     return;
 782                 }
 783                 span_lint_and_then(
 784                     cx,
 785                     LET_UNIT_VALUE,
 786                     stmt.span,
 787                     "this let-binding has unit value",
 788                     |diag| {
 789                         if let Some(expr) = &local.init {
 790                             let snip = snippet_with_macro_callsite(cx, expr.span, "()");
 791                             diag.span_suggestion(
 792                                 stmt.span,
 793                                 "omit the `let` binding",
 794                                 format!("{};", snip),
 795                                 Applicability::MachineApplicable, // snippet
 796                             );
 797                         }
 798                     },
 799                 );
 800             }
 801         }
 802     }
 803 }
 804
 805 declare_clippy_lint! {
 806     /// **What it does:** Checks for comparisons to unit. This includes all binary
 807     /// comparisons (like `==` and `<`) and asserts.
 808     ///
 809     /// **Why is this bad?** Unit is always equal to itself, and thus is just a
 810     /// clumsily written constant. Mostly this happens when someone accidentally
 811     /// adds semicolons at the end of the operands.
 812     ///
 813     /// **Known problems:** None.
 814     ///
 815     /// **Example:**
 816     /// ```rust
 817     /// # fn foo() {};
 818     /// # fn bar() {};
 819     /// # fn baz() {};
 820     /// if {
 821     ///     foo();
 822     /// } == {
 823     ///     bar();
 824     /// } {
 825     ///     baz();
 826     /// }
 827     /// ```
 828     /// is equal to
 829     /// ```rust
 830     /// # fn foo() {};
 831     /// # fn bar() {};
 832     /// # fn baz() {};
 833     /// {
 834     ///     foo();
 835     ///     bar();
 836     ///     baz();
 837     /// }
 838     /// ```
 839     ///
 840     /// For asserts:
 841     /// ```rust
 842     /// # fn foo() {};
 843     /// # fn bar() {};
 844     /// assert_eq!({ foo(); }, { bar(); });
 845     /// ```
 846     /// will always succeed
 847     pub UNIT_CMP,
 848     correctness,
 849     "comparing unit values"
 850 }
 851
 852 declare_lint_pass!(UnitCmp => [UNIT_CMP]);
 853
 854 impl<'tcx> LateLintPass<'tcx> for UnitCmp {
 855     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
 856         if expr.span.from_expansion() {
 857             if let Some(callee) = expr.span.source_callee() {
 858                 if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind {
 859                     if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
 860                         let op = cmp.node;
 861                         if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
 862                             let result = match &*symbol.as_str() {
 863                                 "assert_eq" | "debug_assert_eq" => "succeed",
 864                                 "assert_ne" | "debug_assert_ne" => "fail",
 865                                 _ => return,
 866                             };
 867                             span_lint(
 868                                 cx,
 869                                 UNIT_CMP,
 870                                 expr.span,
 871                                 &format!(
 872                                     "`{}` of unit values detected. This will always {}",
 873                                     symbol.as_str(),
 874                                     result
 875                                 ),
 876                             );
 877                         }
 878                     }
 879                 }
 880             }
 881             return;
 882         }
 883         if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
 884             let op = cmp.node;
 885             if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
 886                 let result = match op {
 887                     BinOpKind::Eq | BinOpKind::Le | BinOpKind::Ge => "true",
 888                     _ => "false",
 889                 };
 890                 span_lint(
 891                     cx,
 892                     UNIT_CMP,
 893                     expr.span,
 894                     &format!(
 895                         "{}-comparison of unit values detected. This will always be {}",
 896                         op.as_str(),
 897                         result
 898                     ),
 899                 );
 900             }
 901         }
 902     }
 903 }
 904
 905 declare_clippy_lint! {
 906     /// **What it does:** Checks for passing a unit value as an argument to a function without using a
 907     /// unit literal (`()`).
 908     ///
 909     /// **Why is this bad?** This is likely the result of an accidental semicolon.
 910     ///
 911     /// **Known problems:** None.
 912     ///
 913     /// **Example:**
 914     /// ```rust,ignore
 915     /// foo({
 916     ///     let a = bar();
 917     ///     baz(a);
 918     /// })
 919     /// ```
 920     pub UNIT_ARG,
 921     complexity,
 922     "passing unit to a function"
 923 }
 924
 925 declare_lint_pass!(UnitArg => [UNIT_ARG]);
 926
 927 impl<'tcx> LateLintPass<'tcx> for UnitArg {
 928     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 929         if expr.span.from_expansion() {
 930             return;
 931         }
 932
 933         // apparently stuff in the desugaring of `?` can trigger this
 934         // so check for that here
 935         // only the calls to `Try::from_error` is marked as desugared,
 936         // so we need to check both the current Expr and its parent.
 937         if is_questionmark_desugar_marked_call(expr) {
 938             return;
 939         }
 940         if_chain! {
 941             let map = &cx.tcx.hir();
 942             let opt_parent_node = map.find(map.get_parent_node(expr.hir_id));
 943             if let Some(hir::Node::Expr(parent_expr)) = opt_parent_node;
 944             if is_questionmark_desugar_marked_call(parent_expr);
 945             then {
 946                 return;
 947             }
 948         }
 949
 950         match expr.kind {
 951             ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
 952                 let args_to_recover = args
 953                     .iter()
 954                     .filter(|arg| {
 955                         if is_unit(cx.typeck_results().expr_ty(arg)) && !is_unit_literal(arg) {
 956                             !matches!(&arg.kind, ExprKind::Match(.., MatchSource::TryDesugar))
 957                         } else {
 958                             false
 959                         }
 960                     })
 961                     .collect::<Vec<_>>();
 962                 if !args_to_recover.is_empty() {
 963                     lint_unit_args(cx, expr, &args_to_recover);
 964                 }
 965             },
 966             _ => (),
 967         }
 968     }
 969 }
 970
 971 fn fmt_stmts_and_call(
 972     cx: &LateContext<'_>,
 973     call_expr: &Expr<'_>,
 974     call_snippet: &str,
 975     args_snippets: &[impl AsRef<str>],
 976     non_empty_block_args_snippets: &[impl AsRef<str>],
 977 ) -> String {
 978     let call_expr_indent = indent_of(cx, call_expr.span).unwrap_or(0);
 979     let call_snippet_with_replacements = args_snippets
 980         .iter()
 981         .fold(call_snippet.to_owned(), |acc, arg| acc.replacen(arg.as_ref(), "()", 1));
 982
 983     let mut stmts_and_call = non_empty_block_args_snippets
 984         .iter()
 985         .map(|it| it.as_ref().to_owned())
 986         .collect::<Vec<_>>();
 987     stmts_and_call.push(call_snippet_with_replacements);
 988     stmts_and_call = stmts_and_call
 989         .into_iter()
 990         .map(|v| reindent_multiline(v.into(), true, Some(call_expr_indent)).into_owned())
 991         .collect();
 992
 993     let mut stmts_and_call_snippet = stmts_and_call.join(&format!("{}{}", ";\n", " ".repeat(call_expr_indent)));
 994     // expr is not in a block statement or result expression position, wrap in a block
 995     let parent_node = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(call_expr.hir_id));
 996     if !matches!(parent_node, Some(Node::Block(_))) && !matches!(parent_node, Some(Node::Stmt(_))) {
 997         let block_indent = call_expr_indent + 4;
 998         stmts_and_call_snippet =
 999             reindent_multiline(stmts_and_call_snippet.into(), true, Some(block_indent)).into_owned();
1000         stmts_and_call_snippet = format!(
1001             "{{\n{}{}\n{}}}",
1002             " ".repeat(block_indent),
1003             &stmts_and_call_snippet,
1004             " ".repeat(call_expr_indent)
1005         );
1006     }
1007     stmts_and_call_snippet
1008 }
1009
1010 fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Expr<'_>]) {
1011     let mut applicability = Applicability::MachineApplicable;
1012     let (singular, plural) = if args_to_recover.len() > 1 {
1013         ("", "s")
1014     } else {
1015         ("a ", "")
1016     };
1017     span_lint_and_then(
1018         cx,
1019         UNIT_ARG,
1020         expr.span,
1021         &format!("passing {}unit value{} to a function", singular, plural),
1022         |db| {
1023             let mut or = "";
1024             args_to_recover
1025                 .iter()
1026                 .filter_map(|arg| {
1027                     if_chain! {
1028                         if let ExprKind::Block(block, _) = arg.kind;
1029                         if block.expr.is_none();
1030                         if let Some(last_stmt) = block.stmts.iter().last();
1031                         if let StmtKind::Semi(last_expr) = last_stmt.kind;
1032                         if let Some(snip) = snippet_opt(cx, last_expr.span);
1033                         then {
1034                             Some((
1035                                 last_stmt.span,
1036                                 snip,
1037                             ))
1038                         }
1039                         else {
1040                             None
1041                         }
1042                     }
1043                 })
1044                 .for_each(|(span, sugg)| {
1045                     db.span_suggestion(
1046                         span,
1047                         "remove the semicolon from the last statement in the block",
1048                         sugg,
1049                         Applicability::MaybeIncorrect,
1050                     );
1051                     or = "or ";
1052                     applicability = Applicability::MaybeIncorrect;
1053                 });
1054
1055             let arg_snippets: Vec<String> = args_to_recover
1056                 .iter()
1057                 .filter_map(|arg| snippet_opt(cx, arg.span))
1058                 .collect();
1059             let arg_snippets_without_empty_blocks: Vec<String> = args_to_recover
1060                 .iter()
1061                 .filter(|arg| !is_empty_block(arg))
1062                 .filter_map(|arg| snippet_opt(cx, arg.span))
1063                 .collect();
1064
1065             if let Some(call_snippet) = snippet_opt(cx, expr.span) {
1066                 let sugg = fmt_stmts_and_call(
1067                     cx,
1068                     expr,
1069                     &call_snippet,
1070                     &arg_snippets,
1071                     &arg_snippets_without_empty_blocks,
1072                 );
1073
1074                 if arg_snippets_without_empty_blocks.is_empty() {
1075                     db.multipart_suggestion(
1076                         &format!("use {}unit literal{} instead", singular, plural),
1077                         args_to_recover
1078                             .iter()
1079                             .map(|arg| (arg.span, "()".to_string()))
1080                             .collect::<Vec<_>>(),
1081                         applicability,
1082                     );
1083                 } else {
1084                     let plural = arg_snippets_without_empty_blocks.len() > 1;
1085                     let empty_or_s = if plural { "s" } else { "" };
1086                     let it_or_them = if plural { "them" } else { "it" };
1087                     db.span_suggestion(
1088                         expr.span,
1089                         &format!(
1090                             "{}move the expression{} in front of the call and replace {} with the unit literal `()`",
1091                             or, empty_or_s, it_or_them
1092                         ),
1093                         sugg,
1094                         applicability,
1095                     );
1096                 }
1097             }
1098         },
1099     );
1100 }
1101
1102 fn is_empty_block(expr: &Expr<'_>) -> bool {
1103     matches!(
1104         expr.kind,
1105         ExprKind::Block(
1106             Block {
1107                 stmts: &[], expr: None, ..
1108             },
1109             _,
1110         )
1111     )
1112 }
1113
1114 fn is_questionmark_desugar_marked_call(expr: &Expr<'_>) -> bool {
1115     use rustc_span::hygiene::DesugaringKind;
1116     if let ExprKind::Call(ref callee, _) = expr.kind {
1117         callee.span.is_desugaring(DesugaringKind::QuestionMark)
1118     } else {
1119         false
1120     }
1121 }
1122
1123 fn is_unit(ty: Ty<'_>) -> bool {
1124     matches!(ty.kind(), ty::Tuple(slice) if slice.is_empty())
1125 }
1126
1127 fn is_unit_literal(expr: &Expr<'_>) -> bool {
1128     matches!(expr.kind, ExprKind::Tup(ref slice) if slice.is_empty())
1129 }
1130
1131 declare_clippy_lint! {
1132     /// **What it does:** Checks for casts from any numerical to a float type where
1133     /// the receiving type cannot store all values from the original type without
1134     /// rounding errors. This possible rounding is to be expected, so this lint is
1135     /// `Allow` by default.
1136     ///
1137     /// Basically, this warns on casting any integer with 32 or more bits to `f32`
1138     /// or any 64-bit integer to `f64`.
1139     ///
1140     /// **Why is this bad?** It's not bad at all. But in some applications it can be
1141     /// helpful to know where precision loss can take place. This lint can help find
1142     /// those places in the code.
1143     ///
1144     /// **Known problems:** None.
1145     ///
1146     /// **Example:**
1147     /// ```rust
1148     /// let x = u64::MAX;
1149     /// x as f64;
1150     /// ```
1151     pub CAST_PRECISION_LOSS,
1152     pedantic,
1153     "casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
1154 }
1155
1156 declare_clippy_lint! {
1157     /// **What it does:** Checks for casts from a signed to an unsigned numerical
1158     /// type. In this case, negative values wrap around to large positive values,
1159     /// which can be quite surprising in practice. However, as the cast works as
1160     /// defined, this lint is `Allow` by default.
1161     ///
1162     /// **Why is this bad?** Possibly surprising results. You can activate this lint
1163     /// as a one-time check to see where numerical wrapping can arise.
1164     ///
1165     /// **Known problems:** None.
1166     ///
1167     /// **Example:**
1168     /// ```rust
1169     /// let y: i8 = -1;
1170     /// y as u128; // will return 18446744073709551615
1171     /// ```
1172     pub CAST_SIGN_LOSS,
1173     pedantic,
1174     "casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
1175 }
1176
1177 declare_clippy_lint! {
1178     /// **What it does:** Checks for casts between numerical types that may
1179     /// truncate large values. This is expected behavior, so the cast is `Allow` by
1180     /// default.
1181     ///
1182     /// **Why is this bad?** In some problem domains, it is good practice to avoid
1183     /// truncation. This lint can be activated to help assess where additional
1184     /// checks could be beneficial.
1185     ///
1186     /// **Known problems:** None.
1187     ///
1188     /// **Example:**
1189     /// ```rust
1190     /// fn as_u8(x: u64) -> u8 {
1191     ///     x as u8
1192     /// }
1193     /// ```
1194     pub CAST_POSSIBLE_TRUNCATION,
1195     pedantic,
1196     "casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
1197 }
1198
1199 declare_clippy_lint! {
1200     /// **What it does:** Checks for casts from an unsigned type to a signed type of
1201     /// the same size. Performing such a cast is a 'no-op' for the compiler,
1202     /// i.e., nothing is changed at the bit level, and the binary representation of
1203     /// the value is reinterpreted. This can cause wrapping if the value is too big
1204     /// for the target signed type. However, the cast works as defined, so this lint
1205     /// is `Allow` by default.
1206     ///
1207     /// **Why is this bad?** While such a cast is not bad in itself, the results can
1208     /// be surprising when this is not the intended behavior, as demonstrated by the
1209     /// example below.
1210     ///
1211     /// **Known problems:** None.
1212     ///
1213     /// **Example:**
1214     /// ```rust
1215     /// u32::MAX as i32; // will yield a value of `-1`
1216     /// ```
1217     pub CAST_POSSIBLE_WRAP,
1218     pedantic,
1219     "casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
1220 }
1221
1222 declare_clippy_lint! {
1223     /// **What it does:** Checks for casts between numerical types that may
1224     /// be replaced by safe conversion functions.
1225     ///
1226     /// **Why is this bad?** Rust's `as` keyword will perform many kinds of
1227     /// conversions, including silently lossy conversions. Conversion functions such
1228     /// as `i32::from` will only perform lossless conversions. Using the conversion
1229     /// functions prevents conversions from turning into silent lossy conversions if
1230     /// the types of the input expressions ever change, and make it easier for
1231     /// people reading the code to know that the conversion is lossless.
1232     ///
1233     /// **Known problems:** None.
1234     ///
1235     /// **Example:**
1236     /// ```rust
1237     /// fn as_u64(x: u8) -> u64 {
1238     ///     x as u64
1239     /// }
1240     /// ```
1241     ///
1242     /// Using `::from` would look like this:
1243     ///
1244     /// ```rust
1245     /// fn as_u64(x: u8) -> u64 {
1246     ///     u64::from(x)
1247     /// }
1248     /// ```
1249     pub CAST_LOSSLESS,
1250     pedantic,
1251     "casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
1252 }
1253
1254 declare_clippy_lint! {
1255     /// **What it does:** Checks for casts to the same type, casts of int literals to integer types
1256     /// and casts of float literals to float types.
1257     ///
1258     /// **Why is this bad?** It's just unnecessary.
1259     ///
1260     /// **Known problems:** None.
1261     ///
1262     /// **Example:**
1263     /// ```rust
1264     /// let _ = 2i32 as i32;
1265     /// let _ = 0.5 as f32;
1266     /// ```
1267     ///
1268     /// Better:
1269     ///
1270     /// ```rust
1271     /// let _ = 2_i32;
1272     /// let _ = 0.5_f32;
1273     /// ```
1274     pub UNNECESSARY_CAST,
1275     complexity,
1276     "cast to the same type, e.g., `x as i32` where `x: i32`"
1277 }
1278
1279 declare_clippy_lint! {
1280     /// **What it does:** Checks for casts from a less-strictly-aligned pointer to a
1281     /// more-strictly-aligned pointer
1282     ///
1283     /// **Why is this bad?** Dereferencing the resulting pointer may be undefined
1284     /// behavior.
1285     ///
1286     /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
1287     /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
1288     /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
1289     ///
1290     /// **Example:**
1291     /// ```rust
1292     /// let _ = (&1u8 as *const u8) as *const u16;
1293     /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
1294     /// ```
1295     pub CAST_PTR_ALIGNMENT,
1296     pedantic,
1297     "cast from a pointer to a more-strictly-aligned pointer"
1298 }
1299
1300 declare_clippy_lint! {
1301     /// **What it does:** Checks for casts of function pointers to something other than usize
1302     ///
1303     /// **Why is this bad?**
1304     /// Casting a function pointer to anything other than usize/isize is not portable across
1305     /// architectures, because you end up losing bits if the target type is too small or end up with a
1306     /// bunch of extra bits that waste space and add more instructions to the final binary than
1307     /// strictly necessary for the problem
1308     ///
1309     /// Casting to isize also doesn't make sense since there are no signed addresses.
1310     ///
1311     /// **Example**
1312     ///
1313     /// ```rust
1314     /// // Bad
1315     /// fn fun() -> i32 { 1 }
1316     /// let a = fun as i64;
1317     ///
1318     /// // Good
1319     /// fn fun2() -> i32 { 1 }
1320     /// let a = fun2 as usize;
1321     /// ```
1322     pub FN_TO_NUMERIC_CAST,
1323     style,
1324     "casting a function pointer to a numeric type other than usize"
1325 }
1326
1327 declare_clippy_lint! {
1328     /// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
1329     /// store address.
1330     ///
1331     /// **Why is this bad?**
1332     /// Such a cast discards some bits of the function's address. If this is intended, it would be more
1333     /// clearly expressed by casting to usize first, then casting the usize to the intended type (with
1334     /// a comment) to perform the truncation.
1335     ///
1336     /// **Example**
1337     ///
1338     /// ```rust
1339     /// // Bad
1340     /// fn fn1() -> i16 {
1341     ///     1
1342     /// };
1343     /// let _ = fn1 as i32;
1344     ///
1345     /// // Better: Cast to usize first, then comment with the reason for the truncation
1346     /// fn fn2() -> i16 {
1347     ///     1
1348     /// };
1349     /// let fn_ptr = fn2 as usize;
1350     /// let fn_ptr_truncated = fn_ptr as i32;
1351     /// ```
1352     pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1353     style,
1354     "casting a function pointer to a numeric type not wide enough to store the address"
1355 }
1356
1357 /// Returns the size in bits of an integral type.
1358 /// Will return 0 if the type is not an int or uint variant
1359 fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
1360     match typ.kind() {
1361         ty::Int(i) => match i {
1362             IntTy::Isize => tcx.data_layout.pointer_size.bits(),
1363             IntTy::I8 => 8,
1364             IntTy::I16 => 16,
1365             IntTy::I32 => 32,
1366             IntTy::I64 => 64,
1367             IntTy::I128 => 128,
1368         },
1369         ty::Uint(i) => match i {
1370             UintTy::Usize => tcx.data_layout.pointer_size.bits(),
1371             UintTy::U8 => 8,
1372             UintTy::U16 => 16,
1373             UintTy::U32 => 32,
1374             UintTy::U64 => 64,
1375             UintTy::U128 => 128,
1376         },
1377         _ => 0,
1378     }
1379 }
1380
1381 fn is_isize_or_usize(typ: Ty<'_>) -> bool {
1382     matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
1383 }
1384
1385 fn span_precision_loss_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to_f64: bool) {
1386     let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
1387     let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
1388     let arch_dependent_str = "on targets with 64-bit wide pointers ";
1389     let from_nbits_str = if arch_dependent {
1390         "64".to_owned()
1391     } else if is_isize_or_usize(cast_from) {
1392         "32 or 64".to_owned()
1393     } else {
1394         int_ty_to_nbits(cast_from, cx.tcx).to_string()
1395     };
1396     span_lint(
1397         cx,
1398         CAST_PRECISION_LOSS,
1399         expr.span,
1400         &format!(
1401             "casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
1402              but `{1}`'s mantissa is only {4} bits wide)",
1403             cast_from,
1404             if cast_to_f64 { "f64" } else { "f32" },
1405             if arch_dependent { arch_dependent_str } else { "" },
1406             from_nbits_str,
1407             mantissa_nbits
1408         ),
1409     );
1410 }
1411
1412 fn should_strip_parens(op: &Expr<'_>, snip: &str) -> bool {
1413     if let ExprKind::Binary(_, _, _) = op.kind {
1414         if snip.starts_with('(') && snip.ends_with(')') {
1415             return true;
1416         }
1417     }
1418     false
1419 }
1420
1421 fn span_lossless_lint(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1422     // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
1423     if in_constant(cx, expr.hir_id) {
1424         return;
1425     }
1426     // The suggestion is to use a function call, so if the original expression
1427     // has parens on the outside, they are no longer needed.
1428     let mut applicability = Applicability::MachineApplicable;
1429     let opt = snippet_opt(cx, op.span);
1430     let sugg = opt.as_ref().map_or_else(
1431         || {
1432             applicability = Applicability::HasPlaceholders;
1433             ".."
1434         },
1435         |snip| {
1436             if should_strip_parens(op, snip) {
1437                 &snip[1..snip.len() - 1]
1438             } else {
1439                 snip.as_str()
1440             }
1441         },
1442     );
1443
1444     span_lint_and_sugg(
1445         cx,
1446         CAST_LOSSLESS,
1447         expr.span,
1448         &format!(
1449             "casting `{}` to `{}` may become silently lossy if you later change the type",
1450             cast_from, cast_to
1451         ),
1452         "try",
1453         format!("{}::from({})", cast_to, sugg),
1454         applicability,
1455     );
1456 }
1457
1458 enum ArchSuffix {
1459     _32,
1460     _64,
1461     None,
1462 }
1463
1464 fn check_loss_of_sign(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1465     if !cast_from.is_signed() || cast_to.is_signed() {
1466         return;
1467     }
1468
1469     // don't lint for positive constants
1470     let const_val = constant(cx, &cx.typeck_results(), op);
1471     if_chain! {
1472         if let Some((Constant::Int(n), _)) = const_val;
1473         if let ty::Int(ity) = *cast_from.kind();
1474         if sext(cx.tcx, n, ity) >= 0;
1475         then {
1476             return
1477         }
1478     }
1479
1480     // don't lint for the result of methods that always return non-negative values
1481     if let ExprKind::MethodCall(ref path, _, _, _) = op.kind {
1482         let mut method_name = path.ident.name.as_str();
1483         let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
1484
1485         if_chain! {
1486             if method_name == "unwrap";
1487             if let Some(arglist) = method_chain_args(op, &["unwrap"]);
1488             if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
1489             then {
1490                 method_name = inner_path.ident.name.as_str();
1491             }
1492         }
1493
1494         if allowed_methods.iter().any(|&name| method_name == name) {
1495             return;
1496         }
1497     }
1498
1499     span_lint(
1500         cx,
1501         CAST_SIGN_LOSS,
1502         expr.span,
1503         &format!(
1504             "casting `{}` to `{}` may lose the sign of the value",
1505             cast_from, cast_to
1506         ),
1507     );
1508 }
1509
1510 fn check_truncation_and_wrapping(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1511     let arch_64_suffix = " on targets with 64-bit wide pointers";
1512     let arch_32_suffix = " on targets with 32-bit wide pointers";
1513     let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
1514     let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1515     let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1516     let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) =
1517         match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
1518             (true, true) | (false, false) => (
1519                 to_nbits < from_nbits,
1520                 ArchSuffix::None,
1521                 to_nbits == from_nbits && cast_unsigned_to_signed,
1522                 ArchSuffix::None,
1523             ),
1524             (true, false) => (
1525                 to_nbits <= 32,
1526                 if to_nbits == 32 {
1527                     ArchSuffix::_64
1528                 } else {
1529                     ArchSuffix::None
1530                 },
1531                 to_nbits <= 32 && cast_unsigned_to_signed,
1532                 ArchSuffix::_32,
1533             ),
1534             (false, true) => (
1535                 from_nbits == 64,
1536                 ArchSuffix::_32,
1537                 cast_unsigned_to_signed,
1538                 if from_nbits == 64 {
1539                     ArchSuffix::_64
1540                 } else {
1541                     ArchSuffix::_32
1542                 },
1543             ),
1544         };
1545     if span_truncation {
1546         span_lint(
1547             cx,
1548             CAST_POSSIBLE_TRUNCATION,
1549             expr.span,
1550             &format!(
1551                 "casting `{}` to `{}` may truncate the value{}",
1552                 cast_from,
1553                 cast_to,
1554                 match suffix_truncation {
1555                     ArchSuffix::_32 => arch_32_suffix,
1556                     ArchSuffix::_64 => arch_64_suffix,
1557                     ArchSuffix::None => "",
1558                 }
1559             ),
1560         );
1561     }
1562     if span_wrap {
1563         span_lint(
1564             cx,
1565             CAST_POSSIBLE_WRAP,
1566             expr.span,
1567             &format!(
1568                 "casting `{}` to `{}` may wrap around the value{}",
1569                 cast_from,
1570                 cast_to,
1571                 match suffix_wrap {
1572                     ArchSuffix::_32 => arch_32_suffix,
1573                     ArchSuffix::_64 => arch_64_suffix,
1574                     ArchSuffix::None => "",
1575                 }
1576             ),
1577         );
1578     }
1579 }
1580
1581 fn check_lossless(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1582     let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
1583     let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1584     let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1585     if !is_isize_or_usize(cast_from) && !is_isize_or_usize(cast_to) && from_nbits < to_nbits && !cast_signed_to_unsigned
1586     {
1587         span_lossless_lint(cx, expr, op, cast_from, cast_to);
1588     }
1589 }
1590
1591 declare_lint_pass!(Casts => [
1592     CAST_PRECISION_LOSS,
1593     CAST_SIGN_LOSS,
1594     CAST_POSSIBLE_TRUNCATION,
1595     CAST_POSSIBLE_WRAP,
1596     CAST_LOSSLESS,
1597     UNNECESSARY_CAST,
1598     CAST_PTR_ALIGNMENT,
1599     FN_TO_NUMERIC_CAST,
1600     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1601 ]);
1602
1603 // Check if the given type is either `core::ffi::c_void` or
1604 // one of the platform specific `libc::<platform>::c_void` of libc.
1605 fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
1606     if let ty::Adt(adt, _) = ty.kind() {
1607         let names = cx.get_def_path(adt.did);
1608
1609         if names.is_empty() {
1610             return false;
1611         }
1612         if names[0] == sym::libc || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
1613             return true;
1614         }
1615     }
1616     false
1617 }
1618
1619 /// Returns the mantissa bits wide of a fp type.
1620 /// Will return 0 if the type is not a fp
1621 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
1622     match typ.kind() {
1623         ty::Float(FloatTy::F32) => 23,
1624         ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
1625         _ => 0,
1626     }
1627 }
1628
1629 impl<'tcx> LateLintPass<'tcx> for Casts {
1630     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1631         if expr.span.from_expansion() {
1632             return;
1633         }
1634         if let ExprKind::Cast(ref ex, cast_to) = expr.kind {
1635             if let TyKind::Path(QPath::Resolved(_, path)) = cast_to.kind {
1636                 if let Res::Def(_, def_id) = path.res {
1637                     if cx.tcx.has_attr(def_id, sym::cfg) || cx.tcx.has_attr(def_id, sym::cfg_attr) {
1638                         return;
1639                     }
1640                 }
1641             }
1642             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
1643             lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
1644             if let Some(lit) = get_numeric_literal(ex) {
1645                 let literal_str = snippet_opt(cx, ex.span).unwrap_or_default();
1646
1647                 if_chain! {
1648                     if let LitKind::Int(n, _) = lit.node;
1649                     if let Some(src) = snippet_opt(cx, lit.span);
1650                     if cast_to.is_floating_point();
1651                     if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
1652                     let from_nbits = 128 - n.leading_zeros();
1653                     let to_nbits = fp_ty_mantissa_nbits(cast_to);
1654                     if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
1655                     then {
1656                         let literal_str = if is_unary_neg(ex) { format!("-{}", num_lit.integer) } else { num_lit.integer.into() };
1657                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1658                         return;
1659                     }
1660                 }
1661
1662                 match lit.node {
1663                     LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
1664                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1665                     },
1666                     LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
1667                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1668                     },
1669                     LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
1670                     _ => {
1671                         if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
1672                             span_lint(
1673                                 cx,
1674                                 UNNECESSARY_CAST,
1675                                 expr.span,
1676                                 &format!(
1677                                     "casting to the same type is unnecessary (`{}` -> `{}`)",
1678                                     cast_from, cast_to
1679                                 ),
1680                             );
1681                         }
1682                     },
1683                 }
1684             }
1685             if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
1686                 lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
1687             }
1688
1689             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1690         }
1691     }
1692 }
1693
1694 fn is_unary_neg(expr: &Expr<'_>) -> bool {
1695     matches!(expr.kind, ExprKind::Unary(UnOp::UnNeg, _))
1696 }
1697
1698 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
1699     match expr.kind {
1700         ExprKind::Lit(ref lit) => Some(lit),
1701         ExprKind::Unary(UnOp::UnNeg, e) => {
1702             if let ExprKind::Lit(ref lit) = e.kind {
1703                 Some(lit)
1704             } else {
1705                 None
1706             }
1707         },
1708         _ => None,
1709     }
1710 }
1711
1712 fn show_unnecessary_cast(cx: &LateContext<'_>, expr: &Expr<'_>, literal_str: &str, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1713     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
1714     span_lint_and_sugg(
1715         cx,
1716         UNNECESSARY_CAST,
1717         expr.span,
1718         &format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
1719         "try",
1720         format!("{}_{}", literal_str.trim_end_matches('.'), cast_to),
1721         Applicability::MachineApplicable,
1722     );
1723 }
1724
1725 fn lint_numeric_casts<'tcx>(
1726     cx: &LateContext<'tcx>,
1727     expr: &Expr<'tcx>,
1728     cast_expr: &Expr<'_>,
1729     cast_from: Ty<'tcx>,
1730     cast_to: Ty<'tcx>,
1731 ) {
1732     match (cast_from.is_integral(), cast_to.is_integral()) {
1733         (true, false) => {
1734             let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1735             let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
1736                 32
1737             } else {
1738                 64
1739             };
1740             if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
1741                 span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
1742             }
1743             if from_nbits < to_nbits {
1744                 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1745             }
1746         },
1747         (false, true) => {
1748             span_lint(
1749                 cx,
1750                 CAST_POSSIBLE_TRUNCATION,
1751                 expr.span,
1752                 &format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to),
1753             );
1754             if !cast_to.is_signed() {
1755                 span_lint(
1756                     cx,
1757                     CAST_SIGN_LOSS,
1758                     expr.span,
1759                     &format!(
1760                         "casting `{}` to `{}` may lose the sign of the value",
1761                         cast_from, cast_to
1762                     ),
1763                 );
1764             }
1765         },
1766         (true, true) => {
1767             check_loss_of_sign(cx, expr, cast_expr, cast_from, cast_to);
1768             check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
1769             check_lossless(cx, expr, cast_expr, cast_from, cast_to);
1770         },
1771         (false, false) => {
1772             if let (&ty::Float(FloatTy::F64), &ty::Float(FloatTy::F32)) = (&cast_from.kind(), &cast_to.kind()) {
1773                 span_lint(
1774                     cx,
1775                     CAST_POSSIBLE_TRUNCATION,
1776                     expr.span,
1777                     "casting `f64` to `f32` may truncate the value",
1778                 );
1779             }
1780             if let (&ty::Float(FloatTy::F32), &ty::Float(FloatTy::F64)) = (&cast_from.kind(), &cast_to.kind()) {
1781                 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1782             }
1783         },
1784     }
1785 }
1786
1787 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
1788     if_chain! {
1789         if let ty::RawPtr(from_ptr_ty) = &cast_from.kind();
1790         if let ty::RawPtr(to_ptr_ty) = &cast_to.kind();
1791         if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
1792         if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
1793         if from_layout.align.abi < to_layout.align.abi;
1794         // with c_void, we inherently need to trust the user
1795         if !is_c_void(cx, from_ptr_ty.ty);
1796         // when casting from a ZST, we don't know enough to properly lint
1797         if !from_layout.is_zst();
1798         then {
1799             span_lint(
1800                 cx,
1801                 CAST_PTR_ALIGNMENT,
1802                 expr.span,
1803                 &format!(
1804                     "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
1805                     cast_from,
1806                     cast_to,
1807                     from_layout.align.abi.bytes(),
1808                     to_layout.align.abi.bytes(),
1809                 ),
1810             );
1811         }
1812     }
1813 }
1814
1815 fn lint_fn_to_numeric_cast(
1816     cx: &LateContext<'_>,
1817     expr: &Expr<'_>,
1818     cast_expr: &Expr<'_>,
1819     cast_from: Ty<'_>,
1820     cast_to: Ty<'_>,
1821 ) {
1822     // We only want to check casts to `ty::Uint` or `ty::Int`
1823     match cast_to.kind() {
1824         ty::Uint(_) | ty::Int(..) => { /* continue on */ },
1825         _ => return,
1826     }
1827     match cast_from.kind() {
1828         ty::FnDef(..) | ty::FnPtr(_) => {
1829             let mut applicability = Applicability::MaybeIncorrect;
1830             let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
1831
1832             let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1833             if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
1834                 span_lint_and_sugg(
1835                     cx,
1836                     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1837                     expr.span,
1838                     &format!(
1839                         "casting function pointer `{}` to `{}`, which truncates the value",
1840                         from_snippet, cast_to
1841                     ),
1842                     "try",
1843                     format!("{} as usize", from_snippet),
1844                     applicability,
1845                 );
1846             } else if *cast_to.kind() != ty::Uint(UintTy::Usize) {
1847                 span_lint_and_sugg(
1848                     cx,
1849                     FN_TO_NUMERIC_CAST,
1850                     expr.span,
1851                     &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
1852                     "try",
1853                     format!("{} as usize", from_snippet),
1854                     applicability,
1855                 );
1856             }
1857         },
1858         _ => {},
1859     }
1860 }
1861
1862 declare_clippy_lint! {
1863     /// **What it does:** Checks for types used in structs, parameters and `let`
1864     /// declarations above a certain complexity threshold.
1865     ///
1866     /// **Why is this bad?** Too complex types make the code less readable. Consider
1867     /// using a `type` definition to simplify them.
1868     ///
1869     /// **Known problems:** None.
1870     ///
1871     /// **Example:**
1872     /// ```rust
1873     /// # use std::rc::Rc;
1874     /// struct Foo {
1875     ///     inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
1876     /// }
1877     /// ```
1878     pub TYPE_COMPLEXITY,
1879     complexity,
1880     "usage of very complex types that might be better factored into `type` definitions"
1881 }
1882
1883 pub struct TypeComplexity {
1884     threshold: u64,
1885 }
1886
1887 impl TypeComplexity {
1888     #[must_use]
1889     pub fn new(threshold: u64) -> Self {
1890         Self { threshold }
1891     }
1892 }
1893
1894 impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
1895
1896 impl<'tcx> LateLintPass<'tcx> for TypeComplexity {
1897     fn check_fn(
1898         &mut self,
1899         cx: &LateContext<'tcx>,
1900         _: FnKind<'tcx>,
1901         decl: &'tcx FnDecl<'_>,
1902         _: &'tcx Body<'_>,
1903         _: Span,
1904         _: HirId,
1905     ) {
1906         self.check_fndecl(cx, decl);
1907     }
1908
1909     fn check_struct_field(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::StructField<'_>) {
1910         // enum variants are also struct fields now
1911         self.check_type(cx, &field.ty);
1912     }
1913
1914     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
1915         match item.kind {
1916             ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
1917             // functions, enums, structs, impls and traits are covered
1918             _ => (),
1919         }
1920     }
1921
1922     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1923         match item.kind {
1924             TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
1925             TraitItemKind::Fn(FnSig { ref decl, .. }, TraitFn::Required(_)) => self.check_fndecl(cx, decl),
1926             // methods with default impl are covered by check_fn
1927             _ => (),
1928         }
1929     }
1930
1931     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
1932         match item.kind {
1933             ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
1934             // methods are covered by check_fn
1935             _ => (),
1936         }
1937     }
1938
1939     fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
1940         if let Some(ref ty) = local.ty {
1941             self.check_type(cx, ty);
1942         }
1943     }
1944 }
1945
1946 impl<'tcx> TypeComplexity {
1947     fn check_fndecl(&self, cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>) {
1948         for arg in decl.inputs {
1949             self.check_type(cx, arg);
1950         }
1951         if let FnRetTy::Return(ref ty) = decl.output {
1952             self.check_type(cx, ty);
1953         }
1954     }
1955
1956     fn check_type(&self, cx: &LateContext<'_>, ty: &hir::Ty<'_>) {
1957         if ty.span.from_expansion() {
1958             return;
1959         }
1960         let score = {
1961             let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
1962             visitor.visit_ty(ty);
1963             visitor.score
1964         };
1965
1966         if score > self.threshold {
1967             span_lint(
1968                 cx,
1969                 TYPE_COMPLEXITY,
1970                 ty.span,
1971                 "very complex type used. Consider factoring parts into `type` definitions",
1972             );
1973         }
1974     }
1975 }
1976
1977 /// Walks a type and assigns a complexity score to it.
1978 struct TypeComplexityVisitor {
1979     /// total complexity score of the type
1980     score: u64,
1981     /// current nesting level
1982     nest: u64,
1983 }
1984
1985 impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
1986     type Map = Map<'tcx>;
1987
1988     fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
1989         let (add_score, sub_nest) = match ty.kind {
1990             // _, &x and *x have only small overhead; don't mess with nesting level
1991             TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
1992
1993             // the "normal" components of a type: named types, arrays/tuples
1994             TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
1995
1996             // function types bring a lot of overhead
1997             TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
1998
1999             TyKind::TraitObject(ref param_bounds, _) => {
2000                 let has_lifetime_parameters = param_bounds.iter().any(|bound| {
2001                     bound
2002                         .bound_generic_params
2003                         .iter()
2004                         .any(|gen| matches!(gen.kind, GenericParamKind::Lifetime { .. }))
2005                 });
2006                 if has_lifetime_parameters {
2007                     // complex trait bounds like A<'a, 'b>
2008                     (50 * self.nest, 1)
2009                 } else {
2010                     // simple trait bounds like A + B
2011                     (20 * self.nest, 0)
2012                 }
2013             },
2014
2015             _ => (0, 0),
2016         };
2017         self.score += add_score;
2018         self.nest += sub_nest;
2019         walk_ty(self, ty);
2020         self.nest -= sub_nest;
2021     }
2022     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2023         NestedVisitorMap::None
2024     }
2025 }
2026
2027 declare_clippy_lint! {
2028     /// **What it does:** Checks for expressions where a character literal is cast
2029     /// to `u8` and suggests using a byte literal instead.
2030     ///
2031     /// **Why is this bad?** In general, casting values to smaller types is
2032     /// error-prone and should be avoided where possible. In the particular case of
2033     /// converting a character literal to u8, it is easy to avoid by just using a
2034     /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
2035     /// than `'a' as u8`.
2036     ///
2037     /// **Known problems:** None.
2038     ///
2039     /// **Example:**
2040     /// ```rust,ignore
2041     /// 'x' as u8
2042     /// ```
2043     ///
2044     /// A better version, using the byte literal:
2045     ///
2046     /// ```rust,ignore
2047     /// b'x'
2048     /// ```
2049     pub CHAR_LIT_AS_U8,
2050     complexity,
2051     "casting a character literal to `u8` truncates"
2052 }
2053
2054 declare_lint_pass!(CharLitAsU8 => [CHAR_LIT_AS_U8]);
2055
2056 impl<'tcx> LateLintPass<'tcx> for CharLitAsU8 {
2057     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2058         if_chain! {
2059             if !expr.span.from_expansion();
2060             if let ExprKind::Cast(e, _) = &expr.kind;
2061             if let ExprKind::Lit(l) = &e.kind;
2062             if let LitKind::Char(c) = l.node;
2063             if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
2064             then {
2065                 let mut applicability = Applicability::MachineApplicable;
2066                 let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
2067
2068                 span_lint_and_then(
2069                     cx,
2070                     CHAR_LIT_AS_U8,
2071                     expr.span,
2072                     "casting a character literal to `u8` truncates",
2073                     |diag| {
2074                         diag.note("`char` is four bytes wide, but `u8` is a single byte");
2075
2076                         if c.is_ascii() {
2077                             diag.span_suggestion(
2078                                 expr.span,
2079                                 "use a byte literal instead",
2080                                 format!("b{}", snippet),
2081                                 applicability,
2082                             );
2083                         }
2084                 });
2085             }
2086         }
2087     }
2088 }
2089
2090 declare_clippy_lint! {
2091     /// **What it does:** Checks for comparisons where one side of the relation is
2092     /// either the minimum or maximum value for its type and warns if it involves a
2093     /// case that is always true or always false. Only integer and boolean types are
2094     /// checked.
2095     ///
2096     /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
2097     /// that it is possible for `x` to be less than the minimum. Expressions like
2098     /// `max < x` are probably mistakes.
2099     ///
2100     /// **Known problems:** For `usize` the size of the current compile target will
2101     /// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
2102     /// a comparison to detect target pointer width will trigger this lint. One can
2103     /// use `mem::sizeof` and compare its value or conditional compilation
2104     /// attributes
2105     /// like `#[cfg(target_pointer_width = "64")] ..` instead.
2106     ///
2107     /// **Example:**
2108     ///
2109     /// ```rust
2110     /// let vec: Vec<isize> = Vec::new();
2111     /// if vec.len() <= 0 {}
2112     /// if 100 > i32::MAX {}
2113     /// ```
2114     pub ABSURD_EXTREME_COMPARISONS,
2115     correctness,
2116     "a comparison with a maximum or minimum value that is always true or false"
2117 }
2118
2119 declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
2120
2121 enum ExtremeType {
2122     Minimum,
2123     Maximum,
2124 }
2125
2126 struct ExtremeExpr<'a> {
2127     which: ExtremeType,
2128     expr: &'a Expr<'a>,
2129 }
2130
2131 enum AbsurdComparisonResult {
2132     AlwaysFalse,
2133     AlwaysTrue,
2134     InequalityImpossible,
2135 }
2136
2137 fn is_cast_between_fixed_and_target<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
2138     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2139         let precast_ty = cx.typeck_results().expr_ty(cast_exp);
2140         let cast_ty = cx.typeck_results().expr_ty(expr);
2141
2142         return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
2143     }
2144
2145     false
2146 }
2147
2148 fn detect_absurd_comparison<'tcx>(
2149     cx: &LateContext<'tcx>,
2150     op: BinOpKind,
2151     lhs: &'tcx Expr<'_>,
2152     rhs: &'tcx Expr<'_>,
2153 ) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
2154     use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2155     use crate::types::ExtremeType::{Maximum, Minimum};
2156     use crate::utils::comparisons::{normalize_comparison, Rel};
2157
2158     // absurd comparison only makes sense on primitive types
2159     // primitive types don't implement comparison operators with each other
2160     if cx.typeck_results().expr_ty(lhs) != cx.typeck_results().expr_ty(rhs) {
2161         return None;
2162     }
2163
2164     // comparisons between fix sized types and target sized types are considered unanalyzable
2165     if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
2166         return None;
2167     }
2168
2169     let (rel, normalized_lhs, normalized_rhs) = normalize_comparison(op, lhs, rhs)?;
2170
2171     let lx = detect_extreme_expr(cx, normalized_lhs);
2172     let rx = detect_extreme_expr(cx, normalized_rhs);
2173
2174     Some(match rel {
2175         Rel::Lt => {
2176             match (lx, rx) {
2177                 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
2178                 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
2179                 _ => return None,
2180             }
2181         },
2182         Rel::Le => {
2183             match (lx, rx) {
2184                 (Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
2185                 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
2186                 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
2187                 (_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
2188                 _ => return None,
2189             }
2190         },
2191         Rel::Ne | Rel::Eq => return None,
2192     })
2193 }
2194
2195 fn detect_extreme_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<ExtremeExpr<'tcx>> {
2196     use crate::types::ExtremeType::{Maximum, Minimum};
2197
2198     let ty = cx.typeck_results().expr_ty(expr);
2199
2200     let cv = constant(cx, cx.typeck_results(), expr)?.0;
2201
2202     let which = match (ty.kind(), cv) {
2203         (&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
2204         (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
2205             Minimum
2206         },
2207
2208         (&ty::Bool, Constant::Bool(true)) => Maximum,
2209         (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
2210             Maximum
2211         },
2212         (&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::MAX, uty) == i => Maximum,
2213
2214         _ => return None,
2215     };
2216     Some(ExtremeExpr { which, expr })
2217 }
2218
2219 impl<'tcx> LateLintPass<'tcx> for AbsurdExtremeComparisons {
2220     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2221         use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2222         use crate::types::ExtremeType::{Maximum, Minimum};
2223
2224         if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2225             if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
2226                 if !expr.span.from_expansion() {
2227                     let msg = "this comparison involving the minimum or maximum element for this \
2228                                type contains a case that is always true or always false";
2229
2230                     let conclusion = match result {
2231                         AlwaysFalse => "this comparison is always false".to_owned(),
2232                         AlwaysTrue => "this comparison is always true".to_owned(),
2233                         InequalityImpossible => format!(
2234                             "the case where the two sides are not equal never occurs, consider using `{} == {}` \
2235                              instead",
2236                             snippet(cx, lhs.span, "lhs"),
2237                             snippet(cx, rhs.span, "rhs")
2238                         ),
2239                     };
2240
2241                     let help = format!(
2242                         "because `{}` is the {} value for this type, {}",
2243                         snippet(cx, culprit.expr.span, "x"),
2244                         match culprit.which {
2245                             Minimum => "minimum",
2246                             Maximum => "maximum",
2247                         },
2248                         conclusion
2249                     );
2250
2251                     span_lint_and_help(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, None, &help);
2252                 }
2253             }
2254         }
2255     }
2256 }
2257
2258 declare_clippy_lint! {
2259     /// **What it does:** Checks for comparisons where the relation is always either
2260     /// true or false, but where one side has been upcast so that the comparison is
2261     /// necessary. Only integer types are checked.
2262     ///
2263     /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
2264     /// will mistakenly imply that it is possible for `x` to be outside the range of
2265     /// `u8`.
2266     ///
2267     /// **Known problems:**
2268     /// https://github.com/rust-lang/rust-clippy/issues/886
2269     ///
2270     /// **Example:**
2271     /// ```rust
2272     /// let x: u8 = 1;
2273     /// (x as u32) > 300;
2274     /// ```
2275     pub INVALID_UPCAST_COMPARISONS,
2276     pedantic,
2277     "a comparison involving an upcast which is always true or false"
2278 }
2279
2280 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
2281
2282 #[derive(Copy, Clone, Debug, Eq)]
2283 enum FullInt {
2284     S(i128),
2285     U(u128),
2286 }
2287
2288 impl FullInt {
2289     #[allow(clippy::cast_sign_loss)]
2290     #[must_use]
2291     fn cmp_s_u(s: i128, u: u128) -> Ordering {
2292         if s < 0 {
2293             Ordering::Less
2294         } else if u > (i128::MAX as u128) {
2295             Ordering::Greater
2296         } else {
2297             (s as u128).cmp(&u)
2298         }
2299     }
2300 }
2301
2302 impl PartialEq for FullInt {
2303     #[must_use]
2304     fn eq(&self, other: &Self) -> bool {
2305         self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
2306     }
2307 }
2308
2309 impl PartialOrd for FullInt {
2310     #[must_use]
2311     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2312         Some(match (self, other) {
2313             (&Self::S(s), &Self::S(o)) => s.cmp(&o),
2314             (&Self::U(s), &Self::U(o)) => s.cmp(&o),
2315             (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
2316             (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
2317         })
2318     }
2319 }
2320
2321 impl Ord for FullInt {
2322     #[must_use]
2323     fn cmp(&self, other: &Self) -> Ordering {
2324         self.partial_cmp(other)
2325             .expect("`partial_cmp` for FullInt can never return `None`")
2326     }
2327 }
2328
2329 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
2330     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2331         let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
2332         let cast_ty = cx.typeck_results().expr_ty(expr);
2333         // if it's a cast from i32 to u32 wrapping will invalidate all these checks
2334         if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
2335             return None;
2336         }
2337         match pre_cast_ty.kind() {
2338             ty::Int(int_ty) => Some(match int_ty {
2339                 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
2340                 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
2341                 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
2342                 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
2343                 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
2344                 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
2345             }),
2346             ty::Uint(uint_ty) => Some(match uint_ty {
2347                 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
2348                 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
2349                 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
2350                 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
2351                 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
2352                 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
2353             }),
2354             _ => None,
2355         }
2356     } else {
2357         None
2358     }
2359 }
2360
2361 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
2362     let val = constant(cx, cx.typeck_results(), expr)?.0;
2363     if let Constant::Int(const_int) = val {
2364         match *cx.typeck_results().expr_ty(expr).kind() {
2365             ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
2366             ty::Uint(_) => Some(FullInt::U(const_int)),
2367             _ => None,
2368         }
2369     } else {
2370         None
2371     }
2372 }
2373
2374 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
2375     if let ExprKind::Cast(ref cast_val, _) = expr.kind {
2376         span_lint(
2377             cx,
2378             INVALID_UPCAST_COMPARISONS,
2379             span,
2380             &format!(
2381                 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
2382                 snippet(cx, cast_val.span, "the expression"),
2383                 if always { "true" } else { "false" },
2384             ),
2385         );
2386     }
2387 }
2388
2389 fn upcast_comparison_bounds_err<'tcx>(
2390     cx: &LateContext<'tcx>,
2391     span: Span,
2392     rel: comparisons::Rel,
2393     lhs_bounds: Option<(FullInt, FullInt)>,
2394     lhs: &'tcx Expr<'_>,
2395     rhs: &'tcx Expr<'_>,
2396     invert: bool,
2397 ) {
2398     use crate::utils::comparisons::Rel;
2399
2400     if let Some((lb, ub)) = lhs_bounds {
2401         if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
2402             if rel == Rel::Eq || rel == Rel::Ne {
2403                 if norm_rhs_val < lb || norm_rhs_val > ub {
2404                     err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
2405                 }
2406             } else if match rel {
2407                 Rel::Lt => {
2408                     if invert {
2409                         norm_rhs_val < lb
2410                     } else {
2411                         ub < norm_rhs_val
2412                     }
2413                 },
2414                 Rel::Le => {
2415                     if invert {
2416                         norm_rhs_val <= lb
2417                     } else {
2418                         ub <= norm_rhs_val
2419                     }
2420                 },
2421                 Rel::Eq | Rel::Ne => unreachable!(),
2422             } {
2423                 err_upcast_comparison(cx, span, lhs, true)
2424             } else if match rel {
2425                 Rel::Lt => {
2426                     if invert {
2427                         norm_rhs_val >= ub
2428                     } else {
2429                         lb >= norm_rhs_val
2430                     }
2431                 },
2432                 Rel::Le => {
2433                     if invert {
2434                         norm_rhs_val > ub
2435                     } else {
2436                         lb > norm_rhs_val
2437                     }
2438                 },
2439                 Rel::Eq | Rel::Ne => unreachable!(),
2440             } {
2441                 err_upcast_comparison(cx, span, lhs, false)
2442             }
2443         }
2444     }
2445 }
2446
2447 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
2448     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2449         if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2450             let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
2451             let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
2452                 val
2453             } else {
2454                 return;
2455             };
2456
2457             let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
2458             let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
2459
2460             upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
2461             upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
2462         }
2463     }
2464 }
2465
2466 declare_clippy_lint! {
2467     /// **What it does:** Checks for public `impl` or `fn` missing generalization
2468     /// over different hashers and implicitly defaulting to the default hashing
2469     /// algorithm (`SipHash`).
2470     ///
2471     /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
2472     /// used with them.
2473     ///
2474     /// **Known problems:** Suggestions for replacing constructors can contain
2475     /// false-positives. Also applying suggestions can require modification of other
2476     /// pieces of code, possibly including external crates.
2477     ///
2478     /// **Example:**
2479     /// ```rust
2480     /// # use std::collections::HashMap;
2481     /// # use std::hash::{Hash, BuildHasher};
2482     /// # trait Serialize {};
2483     /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
2484     ///
2485     /// pub fn foo(map: &mut HashMap<i32, i32>) { }
2486     /// ```
2487     /// could be rewritten as
2488     /// ```rust
2489     /// # use std::collections::HashMap;
2490     /// # use std::hash::{Hash, BuildHasher};
2491     /// # trait Serialize {};
2492     /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
2493     ///
2494     /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
2495     /// ```
2496     pub IMPLICIT_HASHER,
2497     pedantic,
2498     "missing generalization over different hashers"
2499 }
2500
2501 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
2502
2503 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
2504     #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
2505     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
2506         use rustc_span::BytePos;
2507
2508         fn suggestion<'tcx>(
2509             cx: &LateContext<'tcx>,
2510             diag: &mut DiagnosticBuilder<'_>,
2511             generics_span: Span,
2512             generics_suggestion_span: Span,
2513             target: &ImplicitHasherType<'_>,
2514             vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
2515         ) {
2516             let generics_snip = snippet(cx, generics_span, "");
2517             // trim `<` `>`
2518             let generics_snip = if generics_snip.is_empty() {
2519                 ""
2520             } else {
2521                 &generics_snip[1..generics_snip.len() - 1]
2522             };
2523
2524             multispan_sugg(
2525                 diag,
2526                 "consider adding a type parameter",
2527                 vec![
2528                     (
2529                         generics_suggestion_span,
2530                         format!(
2531                             "<{}{}S: ::std::hash::BuildHasher{}>",
2532                             generics_snip,
2533                             if generics_snip.is_empty() { "" } else { ", " },
2534                             if vis.suggestions.is_empty() {
2535                                 ""
2536                             } else {
2537                                 // request users to add `Default` bound so that generic constructors can be used
2538                                 " + Default"
2539                             },
2540                         ),
2541                     ),
2542                     (
2543                         target.span(),
2544                         format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
2545                     ),
2546                 ],
2547             );
2548
2549             if !vis.suggestions.is_empty() {
2550                 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
2551             }
2552         }
2553
2554         if !cx.access_levels.is_exported(item.hir_id) {
2555             return;
2556         }
2557
2558         match item.kind {
2559             ItemKind::Impl {
2560                 ref generics,
2561                 self_ty: ref ty,
2562                 ref items,
2563                 ..
2564             } => {
2565                 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2566                 vis.visit_ty(ty);
2567
2568                 for target in &vis.found {
2569                     if differing_macro_contexts(item.span, target.span()) {
2570                         return;
2571                     }
2572
2573                     let generics_suggestion_span = generics.span.substitute_dummy({
2574                         let pos = snippet_opt(cx, item.span.until(target.span()))
2575                             .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
2576                         if let Some(pos) = pos {
2577                             Span::new(pos, pos, item.span.data().ctxt)
2578                         } else {
2579                             return;
2580                         }
2581                     });
2582
2583                     let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2584                     for item in items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
2585                         ctr_vis.visit_impl_item(item);
2586                     }
2587
2588                     span_lint_and_then(
2589                         cx,
2590                         IMPLICIT_HASHER,
2591                         target.span(),
2592                         &format!(
2593                             "impl for `{}` should be generalized over different hashers",
2594                             target.type_name()
2595                         ),
2596                         move |diag| {
2597                             suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2598                         },
2599                     );
2600                 }
2601             },
2602             ItemKind::Fn(ref sig, ref generics, body_id) => {
2603                 let body = cx.tcx.hir().body(body_id);
2604
2605                 for ty in sig.decl.inputs {
2606                     let mut vis = ImplicitHasherTypeVisitor::new(cx);
2607                     vis.visit_ty(ty);
2608
2609                     for target in &vis.found {
2610                         if in_external_macro(cx.sess(), generics.span) {
2611                             continue;
2612                         }
2613                         let generics_suggestion_span = generics.span.substitute_dummy({
2614                             let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
2615                                 .and_then(|snip| {
2616                                     let i = snip.find("fn")?;
2617                                     Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
2618                                 })
2619                                 .expect("failed to create span for type parameters");
2620                             Span::new(pos, pos, item.span.data().ctxt)
2621                         });
2622
2623                         let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2624                         ctr_vis.visit_body(body);
2625
2626                         span_lint_and_then(
2627                             cx,
2628                             IMPLICIT_HASHER,
2629                             target.span(),
2630                             &format!(
2631                                 "parameter of type `{}` should be generalized over different hashers",
2632                                 target.type_name()
2633                             ),
2634                             move |diag| {
2635                                 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2636                             },
2637                         );
2638                     }
2639                 }
2640             },
2641             _ => {},
2642         }
2643     }
2644 }
2645
2646 enum ImplicitHasherType<'tcx> {
2647     HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
2648     HashSet(Span, Ty<'tcx>, Cow<'static, str>),
2649 }
2650
2651 impl<'tcx> ImplicitHasherType<'tcx> {
2652     /// Checks that `ty` is a target type without a `BuildHasher`.
2653     fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
2654         if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
2655             let params: Vec<_> = path
2656                 .segments
2657                 .last()
2658                 .as_ref()?
2659                 .args
2660                 .as_ref()?
2661                 .args
2662                 .iter()
2663                 .filter_map(|arg| match arg {
2664                     GenericArg::Type(ty) => Some(ty),
2665                     _ => None,
2666                 })
2667                 .collect();
2668             let params_len = params.len();
2669
2670             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
2671
2672             if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) && params_len == 2 {
2673                 Some(ImplicitHasherType::HashMap(
2674                     hir_ty.span,
2675                     ty,
2676                     snippet(cx, params[0].span, "K"),
2677                     snippet(cx, params[1].span, "V"),
2678                 ))
2679             } else if is_type_diagnostic_item(cx, ty, sym!(hashset_type)) && params_len == 1 {
2680                 Some(ImplicitHasherType::HashSet(
2681                     hir_ty.span,
2682                     ty,
2683                     snippet(cx, params[0].span, "T"),
2684                 ))
2685             } else {
2686                 None
2687             }
2688         } else {
2689             None
2690         }
2691     }
2692
2693     fn type_name(&self) -> &'static str {
2694         match *self {
2695             ImplicitHasherType::HashMap(..) => "HashMap",
2696             ImplicitHasherType::HashSet(..) => "HashSet",
2697         }
2698     }
2699
2700     fn type_arguments(&self) -> String {
2701         match *self {
2702             ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
2703             ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
2704         }
2705     }
2706
2707     fn ty(&self) -> Ty<'tcx> {
2708         match *self {
2709             ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
2710         }
2711     }
2712
2713     fn span(&self) -> Span {
2714         match *self {
2715             ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
2716         }
2717     }
2718 }
2719
2720 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
2721     cx: &'a LateContext<'tcx>,
2722     found: Vec<ImplicitHasherType<'tcx>>,
2723 }
2724
2725 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
2726     fn new(cx: &'a LateContext<'tcx>) -> Self {
2727         Self { cx, found: vec![] }
2728     }
2729 }
2730
2731 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
2732     type Map = Map<'tcx>;
2733
2734     fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
2735         if let Some(target) = ImplicitHasherType::new(self.cx, t) {
2736             self.found.push(target);
2737         }
2738
2739         walk_ty(self, t);
2740     }
2741
2742     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2743         NestedVisitorMap::None
2744     }
2745 }
2746
2747 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
2748 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2749     cx: &'a LateContext<'tcx>,
2750     maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
2751     target: &'b ImplicitHasherType<'tcx>,
2752     suggestions: BTreeMap<Span, String>,
2753 }
2754
2755 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2756     fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
2757         Self {
2758             cx,
2759             maybe_typeck_results: cx.maybe_typeck_results(),
2760             target,
2761             suggestions: BTreeMap::new(),
2762         }
2763     }
2764 }
2765
2766 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2767     type Map = Map<'tcx>;
2768
2769     fn visit_body(&mut self, body: &'tcx Body<'_>) {
2770         let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
2771         walk_body(self, body);
2772         self.maybe_typeck_results = old_maybe_typeck_results;
2773     }
2774
2775     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
2776         if_chain! {
2777             if let ExprKind::Call(ref fun, ref args) = e.kind;
2778             if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
2779             if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
2780             then {
2781                 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
2782                     return;
2783                 }
2784
2785                 if match_path(ty_path, &paths::HASHMAP) {
2786                     if method.ident.name == sym::new {
2787                         self.suggestions
2788                             .insert(e.span, "HashMap::default()".to_string());
2789                     } else if method.ident.name == sym!(with_capacity) {
2790                         self.suggestions.insert(
2791                             e.span,
2792                             format!(
2793                                 "HashMap::with_capacity_and_hasher({}, Default::default())",
2794                                 snippet(self.cx, args[0].span, "capacity"),
2795                             ),
2796                         );
2797                     }
2798                 } else if match_path(ty_path, &paths::HASHSET) {
2799                     if method.ident.name == sym::new {
2800                         self.suggestions
2801                             .insert(e.span, "HashSet::default()".to_string());
2802                     } else if method.ident.name == sym!(with_capacity) {
2803                         self.suggestions.insert(
2804                             e.span,
2805                             format!(
2806                                 "HashSet::with_capacity_and_hasher({}, Default::default())",
2807                                 snippet(self.cx, args[0].span, "capacity"),
2808                             ),
2809                         );
2810                     }
2811                 }
2812             }
2813         }
2814
2815         walk_expr(self, e);
2816     }
2817
2818     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2819         NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2820     }
2821 }
2822
2823 declare_clippy_lint! {
2824     /// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
2825     ///
2826     /// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
2827     /// `UnsafeCell` is the only way to obtain aliasable data that is considered
2828     /// mutable.
2829     ///
2830     /// **Known problems:** None.
2831     ///
2832     /// **Example:**
2833     /// ```rust,ignore
2834     /// fn x(r: &i32) {
2835     ///     unsafe {
2836     ///         *(r as *const _ as *mut _) += 1;
2837     ///     }
2838     /// }
2839     /// ```
2840     ///
2841     /// Instead consider using interior mutability types.
2842     ///
2843     /// ```rust
2844     /// use std::cell::UnsafeCell;
2845     ///
2846     /// fn x(r: &UnsafeCell<i32>) {
2847     ///     unsafe {
2848     ///         *r.get() += 1;
2849     ///     }
2850     /// }
2851     /// ```
2852     pub CAST_REF_TO_MUT,
2853     correctness,
2854     "a cast of reference to a mutable pointer"
2855 }
2856
2857 declare_lint_pass!(RefToMut => [CAST_REF_TO_MUT]);
2858
2859 impl<'tcx> LateLintPass<'tcx> for RefToMut {
2860     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2861         if_chain! {
2862             if let ExprKind::Unary(UnOp::UnDeref, e) = &expr.kind;
2863             if let ExprKind::Cast(e, t) = &e.kind;
2864             if let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind;
2865             if let ExprKind::Cast(e, t) = &e.kind;
2866             if let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind;
2867             if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind();
2868             then {
2869                 span_lint(
2870                     cx,
2871                     CAST_REF_TO_MUT,
2872                     expr.span,
2873                     "casting `&T` to `&mut T` may cause undefined behavior, consider instead using an `UnsafeCell`",
2874                 );
2875             }
2876         }
2877     }
2878 }