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::{LitFloatType, LitIntType, LitKind};
   9 use rustc_errors::{Applicability, DiagnosticBuilder};
  10 use rustc_hir as hir;
  11 use rustc_hir::intravisit::{walk_body, walk_expr, walk_ty, FnKind, NestedVisitorMap, Visitor};
  12 use rustc_hir::{
  13     BinOpKind, Block, Body, Expr, ExprKind, FnDecl, FnRetTy, FnSig, GenericArg, GenericBounds, GenericParamKind, HirId,
  14     ImplItem, ImplItemKind, Item, ItemKind, Lifetime, Lit, Local, MatchSource, MutTy, Mutability, Node, QPath, Stmt,
  15     StmtKind, SyntheticTyParamKind, TraitFn, TraitItem, TraitItemKind, TyKind, UnOp,
  16 };
  17 use rustc_lint::{LateContext, LateLintPass, LintContext};
  18 use rustc_middle::hir::map::Map;
  19 use rustc_middle::lint::in_external_macro;
  20 use rustc_middle::ty::TypeFoldable;
  21 use rustc_middle::ty::{self, FloatTy, InferTy, IntTy, Ty, TyCtxt, TyS, TypeAndMut, TypeckResults, UintTy};
  22 use rustc_semver::RustcVersion;
  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::sugg::Sugg;
  34 use crate::utils::{
  35     clip, comparisons, differing_macro_contexts, higher, in_constant, indent_of, int_bits, is_hir_ty_cfg_dependant,
  36     is_type_diagnostic_item, last_path_segment, match_def_path, match_path, meets_msrv, method_chain_args,
  37     multispan_sugg, numeric_literal::NumericLiteral, reindent_multiline, sext, snippet, snippet_opt,
  38     snippet_with_applicability, snippet_with_macro_callsite, span_lint, span_lint_and_help, span_lint_and_sugg,
  39     span_lint_and_then, unsext,
  40 };
  41
  42 declare_clippy_lint! {
  43     /// **What it does:** Checks for use of `Box<Vec<_>>` anywhere in the code.
  44     /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
  45     ///
  46     /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
  47     /// the heap. So if you `Box` it, you just add another level of indirection
  48     /// without any benefit whatsoever.
  49     ///
  50     /// **Known problems:** None.
  51     ///
  52     /// **Example:**
  53     /// ```rust,ignore
  54     /// struct X {
  55     ///     values: Box<Vec<Foo>>,
  56     /// }
  57     /// ```
  58     ///
  59     /// Better:
  60     ///
  61     /// ```rust,ignore
  62     /// struct X {
  63     ///     values: Vec<Foo>,
  64     /// }
  65     /// ```
  66     pub BOX_VEC,
  67     perf,
  68     "usage of `Box<Vec<T>>`, vector elements are already on the heap"
  69 }
  70
  71 declare_clippy_lint! {
  72     /// **What it does:** Checks for use of `Vec<Box<T>>` where T: Sized anywhere in the code.
  73     /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
  74     ///
  75     /// **Why is this bad?** `Vec` already keeps its contents in a separate area on
  76     /// the heap. So if you `Box` its contents, you just add another level of indirection.
  77     ///
  78     /// **Known problems:** Vec<Box<T: Sized>> makes sense if T is a large type (see [#3530](https://github.com/rust-lang/rust-clippy/issues/3530),
  79     /// 1st comment).
  80     ///
  81     /// **Example:**
  82     /// ```rust
  83     /// struct X {
  84     ///     values: Vec<Box<i32>>,
  85     /// }
  86     /// ```
  87     ///
  88     /// Better:
  89     ///
  90     /// ```rust
  91     /// struct X {
  92     ///     values: Vec<i32>,
  93     /// }
  94     /// ```
  95     pub VEC_BOX,
  96     complexity,
  97     "usage of `Vec<Box<T>>` where T: Sized, vector elements are already on the heap"
  98 }
  99
 100 declare_clippy_lint! {
 101     /// **What it does:** Checks for use of `Option<Option<_>>` in function signatures and type
 102     /// definitions
 103     ///
 104     /// **Why is this bad?** `Option<_>` represents an optional value. `Option<Option<_>>`
 105     /// represents an optional optional value which is logically the same thing as an optional
 106     /// value but has an unneeded extra level of wrapping.
 107     ///
 108     /// If you have a case where `Some(Some(_))`, `Some(None)` and `None` are distinct cases,
 109     /// consider a custom `enum` instead, with clear names for each case.
 110     ///
 111     /// **Known problems:** None.
 112     ///
 113     /// **Example**
 114     /// ```rust
 115     /// fn get_data() -> Option<Option<u32>> {
 116     ///     None
 117     /// }
 118     /// ```
 119     ///
 120     /// Better:
 121     ///
 122     /// ```rust
 123     /// pub enum Contents {
 124     ///     Data(Vec<u8>), // Was Some(Some(Vec<u8>))
 125     ///     NotYetFetched, // Was Some(None)
 126     ///     None,          // Was None
 127     /// }
 128     ///
 129     /// fn get_data() -> Contents {
 130     ///     Contents::None
 131     /// }
 132     /// ```
 133     pub OPTION_OPTION,
 134     pedantic,
 135     "usage of `Option<Option<T>>`"
 136 }
 137
 138 declare_clippy_lint! {
 139     /// **What it does:** Checks for usage of any `LinkedList`, suggesting to use a
 140     /// `Vec` or a `VecDeque` (formerly called `RingBuf`).
 141     ///
 142     /// **Why is this bad?** Gankro says:
 143     ///
 144     /// > The TL;DR of `LinkedList` is that it's built on a massive amount of
 145     /// pointers and indirection.
 146     /// > It wastes memory, it has terrible cache locality, and is all-around slow.
 147     /// `RingBuf`, while
 148     /// > "only" amortized for push/pop, should be faster in the general case for
 149     /// almost every possible
 150     /// > workload, and isn't even amortized at all if you can predict the capacity
 151     /// you need.
 152     /// >
 153     /// > `LinkedList`s are only really good if you're doing a lot of merging or
 154     /// splitting of lists.
 155     /// > This is because they can just mangle some pointers instead of actually
 156     /// copying the data. Even
 157     /// > if you're doing a lot of insertion in the middle of the list, `RingBuf`
 158     /// can still be better
 159     /// > because of how expensive it is to seek to the middle of a `LinkedList`.
 160     ///
 161     /// **Known problems:** False positives – the instances where using a
 162     /// `LinkedList` makes sense are few and far between, but they can still happen.
 163     ///
 164     /// **Example:**
 165     /// ```rust
 166     /// # use std::collections::LinkedList;
 167     /// let x: LinkedList<usize> = LinkedList::new();
 168     /// ```
 169     pub LINKEDLIST,
 170     pedantic,
 171     "usage of LinkedList, usually a vector is faster, or a more specialized data structure like a `VecDeque`"
 172 }
 173
 174 declare_clippy_lint! {
 175     /// **What it does:** Checks for use of `&Box<T>` anywhere in the code.
 176     /// Check the [Box documentation](https://doc.rust-lang.org/std/boxed/index.html) for more information.
 177     ///
 178     /// **Why is this bad?** Any `&Box<T>` can also be a `&T`, which is more
 179     /// general.
 180     ///
 181     /// **Known problems:** None.
 182     ///
 183     /// **Example:**
 184     /// ```rust,ignore
 185     /// fn foo(bar: &Box<T>) { ... }
 186     /// ```
 187     ///
 188     /// Better:
 189     ///
 190     /// ```rust,ignore
 191     /// fn foo(bar: &T) { ... }
 192     /// ```
 193     pub BORROWED_BOX,
 194     complexity,
 195     "a borrow of a boxed type"
 196 }
 197
 198 declare_clippy_lint! {
 199     /// **What it does:** Checks for use of redundant allocations anywhere in the code.
 200     ///
 201     /// **Why is this bad?** Expressions such as `Rc<&T>`, `Rc<Rc<T>>`, `Rc<Box<T>>`, `Box<&T>`
 202     /// add an unnecessary level of indirection.
 203     ///
 204     /// **Known problems:** None.
 205     ///
 206     /// **Example:**
 207     /// ```rust
 208     /// # use std::rc::Rc;
 209     /// fn foo(bar: Rc<&usize>) {}
 210     /// ```
 211     ///
 212     /// Better:
 213     ///
 214     /// ```rust
 215     /// fn foo(bar: &usize) {}
 216     /// ```
 217     pub REDUNDANT_ALLOCATION,
 218     perf,
 219     "redundant allocation"
 220 }
 221
 222 declare_clippy_lint! {
 223     /// **What it does:** Checks for `Rc<T>` and `Arc<T>` when `T` is a mutable buffer type such as `String` or `Vec`.
 224     ///
 225     /// **Why is this bad?** Expressions such as `Rc<String>` usually have no advantage over `Rc<str>`, since
 226     /// it is larger and involves an extra level of indirection, and doesn't implement `Borrow<str>`.
 227     ///
 228     /// While mutating a buffer type would still be possible with `Rc::get_mut()`, it only
 229     /// works if there are no additional references yet, which usually defeats the purpose of
 230     /// enclosing it in a shared ownership type. Instead, additionally wrapping the inner
 231     /// type with an interior mutable container (such as `RefCell` or `Mutex`) would normally
 232     /// be used.
 233     ///
 234     /// **Known problems:** This pattern can be desirable to avoid the overhead of a `RefCell` or `Mutex` for
 235     /// cases where mutation only happens before there are any additional references.
 236     ///
 237     /// **Example:**
 238     /// ```rust,ignore
 239     /// # use std::rc::Rc;
 240     /// fn foo(interned: Rc<String>) { ... }
 241     /// ```
 242     ///
 243     /// Better:
 244     ///
 245     /// ```rust,ignore
 246     /// fn foo(interned: Rc<str>) { ... }
 247     /// ```
 248     pub RC_BUFFER,
 249     restriction,
 250     "shared ownership of a buffer type"
 251 }
 252
 253 pub struct Types {
 254     vec_box_size_threshold: u64,
 255 }
 256
 257 impl_lint_pass!(Types => [BOX_VEC, VEC_BOX, OPTION_OPTION, LINKEDLIST, BORROWED_BOX, REDUNDANT_ALLOCATION, RC_BUFFER]);
 258
 259 impl<'tcx> LateLintPass<'tcx> for Types {
 260     fn check_fn(&mut self, cx: &LateContext<'_>, _: FnKind<'_>, decl: &FnDecl<'_>, _: &Body<'_>, _: Span, id: HirId) {
 261         // Skip trait implementations; see issue #605.
 262         if let Some(hir::Node::Item(item)) = cx.tcx.hir().find(cx.tcx.hir().get_parent_item(id)) {
 263             if let ItemKind::Impl(hir::Impl { of_trait: Some(_), .. }) = item.kind {
 264                 return;
 265             }
 266         }
 267
 268         self.check_fn_decl(cx, decl);
 269     }
 270
 271     fn check_struct_field(&mut self, cx: &LateContext<'_>, field: &hir::StructField<'_>) {
 272         self.check_ty(cx, &field.ty, false);
 273     }
 274
 275     fn check_trait_item(&mut self, cx: &LateContext<'_>, item: &TraitItem<'_>) {
 276         match item.kind {
 277             TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_ty(cx, ty, false),
 278             TraitItemKind::Fn(ref sig, _) => self.check_fn_decl(cx, &sig.decl),
 279             _ => (),
 280         }
 281     }
 282
 283     fn check_local(&mut self, cx: &LateContext<'_>, local: &Local<'_>) {
 284         if let Some(ref ty) = local.ty {
 285             self.check_ty(cx, ty, true);
 286         }
 287     }
 288 }
 289
 290 /// Checks if `qpath` has last segment with type parameter matching `path`
 291 fn match_type_parameter(cx: &LateContext<'_>, qpath: &QPath<'_>, path: &[&str]) -> Option<Span> {
 292     let last = last_path_segment(qpath);
 293     if_chain! {
 294         if let Some(ref params) = last.args;
 295         if !params.parenthesized;
 296         if let Some(ty) = params.args.iter().find_map(|arg| match arg {
 297             GenericArg::Type(ty) => Some(ty),
 298             _ => None,
 299         });
 300         if let TyKind::Path(ref qpath) = ty.kind;
 301         if let Some(did) = cx.qpath_res(qpath, ty.hir_id).opt_def_id();
 302         if match_def_path(cx, did, path);
 303         then {
 304             return Some(ty.span);
 305         }
 306     }
 307     None
 308 }
 309
 310 fn match_buffer_type(cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<&'static str> {
 311     if match_type_parameter(cx, qpath, &paths::STRING).is_some() {
 312         return Some("str");
 313     }
 314     if match_type_parameter(cx, qpath, &paths::OS_STRING).is_some() {
 315         return Some("std::ffi::OsStr");
 316     }
 317     if match_type_parameter(cx, qpath, &paths::PATH_BUF).is_some() {
 318         return Some("std::path::Path");
 319     }
 320     None
 321 }
 322
 323 fn match_borrows_parameter(_cx: &LateContext<'_>, qpath: &QPath<'_>) -> Option<Span> {
 324     let last = last_path_segment(qpath);
 325     if_chain! {
 326         if let Some(ref params) = last.args;
 327         if !params.parenthesized;
 328         if let Some(ty) = params.args.iter().find_map(|arg| match arg {
 329             GenericArg::Type(ty) => Some(ty),
 330             _ => None,
 331         });
 332         if let TyKind::Rptr(..) = ty.kind;
 333         then {
 334             return Some(ty.span);
 335         }
 336     }
 337     None
 338 }
 339
 340 impl Types {
 341     pub fn new(vec_box_size_threshold: u64) -> Self {
 342         Self { vec_box_size_threshold }
 343     }
 344
 345     fn check_fn_decl(&mut self, cx: &LateContext<'_>, decl: &FnDecl<'_>) {
 346         for input in decl.inputs {
 347             self.check_ty(cx, input, false);
 348         }
 349
 350         if let FnRetTy::Return(ref ty) = decl.output {
 351             self.check_ty(cx, ty, false);
 352         }
 353     }
 354
 355     /// Recursively check for `TypePass` lints in the given type. Stop at the first
 356     /// lint found.
 357     ///
 358     /// The parameter `is_local` distinguishes the context of the type; types from
 359     /// local bindings should only be checked for the `BORROWED_BOX` lint.
 360     #[allow(clippy::too_many_lines)]
 361     fn check_ty(&mut self, cx: &LateContext<'_>, hir_ty: &hir::Ty<'_>, is_local: bool) {
 362         if hir_ty.span.from_expansion() {
 363             return;
 364         }
 365         match hir_ty.kind {
 366             TyKind::Path(ref qpath) if !is_local => {
 367                 let hir_id = hir_ty.hir_id;
 368                 let res = cx.qpath_res(qpath, hir_id);
 369                 if let Some(def_id) = res.opt_def_id() {
 370                     if Some(def_id) == cx.tcx.lang_items().owned_box() {
 371                         if let Some(span) = match_borrows_parameter(cx, qpath) {
 372                             let mut applicability = Applicability::MachineApplicable;
 373                             span_lint_and_sugg(
 374                                 cx,
 375                                 REDUNDANT_ALLOCATION,
 376                                 hir_ty.span,
 377                                 "usage of `Box<&T>`",
 378                                 "try",
 379                                 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
 380                                 applicability,
 381                             );
 382                             return; // don't recurse into the type
 383                         }
 384                         if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
 385                             span_lint_and_help(
 386                                 cx,
 387                                 BOX_VEC,
 388                                 hir_ty.span,
 389                                 "you seem to be trying to use `Box<Vec<T>>`. Consider using just `Vec<T>`",
 390                                 None,
 391                                 "`Vec<T>` is already on the heap, `Box<Vec<T>>` makes an extra allocation.",
 392                             );
 393                             return; // don't recurse into the type
 394                         }
 395                     } else if cx.tcx.is_diagnostic_item(sym::Rc, def_id) {
 396                         if let Some(span) = match_type_parameter(cx, qpath, &paths::RC) {
 397                             let mut applicability = Applicability::MachineApplicable;
 398                             span_lint_and_sugg(
 399                                 cx,
 400                                 REDUNDANT_ALLOCATION,
 401                                 hir_ty.span,
 402                                 "usage of `Rc<Rc<T>>`",
 403                                 "try",
 404                                 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
 405                                 applicability,
 406                             );
 407                             return; // don't recurse into the type
 408                         }
 409                         if match_type_parameter(cx, qpath, &paths::BOX).is_some() {
 410                             let box_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
 411                                 GenericArg::Type(ty) => match &ty.kind {
 412                                     TyKind::Path(qpath) => qpath,
 413                                     _ => return,
 414                                 },
 415                                 _ => return,
 416                             };
 417                             let inner_span = match &last_path_segment(&box_ty).args.unwrap().args[0] {
 418                                 GenericArg::Type(ty) => ty.span,
 419                                 _ => return,
 420                             };
 421                             let mut applicability = Applicability::MachineApplicable;
 422                             span_lint_and_sugg(
 423                                 cx,
 424                                 REDUNDANT_ALLOCATION,
 425                                 hir_ty.span,
 426                                 "usage of `Rc<Box<T>>`",
 427                                 "try",
 428                                 format!(
 429                                     "Rc<{}>",
 430                                     snippet_with_applicability(cx, inner_span, "..", &mut applicability)
 431                                 ),
 432                                 applicability,
 433                             );
 434                             return; // don't recurse into the type
 435                         }
 436                         if let Some(alternate) = match_buffer_type(cx, qpath) {
 437                             span_lint_and_sugg(
 438                                 cx,
 439                                 RC_BUFFER,
 440                                 hir_ty.span,
 441                                 "usage of `Rc<T>` when T is a buffer type",
 442                                 "try",
 443                                 format!("Rc<{}>", alternate),
 444                                 Applicability::MachineApplicable,
 445                             );
 446                             return; // don't recurse into the type
 447                         }
 448                         if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
 449                             let vec_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
 450                                 GenericArg::Type(ty) => match &ty.kind {
 451                                     TyKind::Path(qpath) => qpath,
 452                                     _ => return,
 453                                 },
 454                                 _ => return,
 455                             };
 456                             let inner_span = match &last_path_segment(&vec_ty).args.unwrap().args[0] {
 457                                 GenericArg::Type(ty) => ty.span,
 458                                 _ => return,
 459                             };
 460                             let mut applicability = Applicability::MachineApplicable;
 461                             span_lint_and_sugg(
 462                                 cx,
 463                                 RC_BUFFER,
 464                                 hir_ty.span,
 465                                 "usage of `Rc<T>` when T is a buffer type",
 466                                 "try",
 467                                 format!(
 468                                     "Rc<[{}]>",
 469                                     snippet_with_applicability(cx, inner_span, "..", &mut applicability)
 470                                 ),
 471                                 Applicability::MachineApplicable,
 472                             );
 473                             return; // don't recurse into the type
 474                         }
 475                         if let Some(span) = match_borrows_parameter(cx, qpath) {
 476                             let mut applicability = Applicability::MachineApplicable;
 477                             span_lint_and_sugg(
 478                                 cx,
 479                                 REDUNDANT_ALLOCATION,
 480                                 hir_ty.span,
 481                                 "usage of `Rc<&T>`",
 482                                 "try",
 483                                 snippet_with_applicability(cx, span, "..", &mut applicability).to_string(),
 484                                 applicability,
 485                             );
 486                             return; // don't recurse into the type
 487                         }
 488                     } else if cx.tcx.is_diagnostic_item(sym::Arc, def_id) {
 489                         if let Some(alternate) = match_buffer_type(cx, qpath) {
 490                             span_lint_and_sugg(
 491                                 cx,
 492                                 RC_BUFFER,
 493                                 hir_ty.span,
 494                                 "usage of `Arc<T>` when T is a buffer type",
 495                                 "try",
 496                                 format!("Arc<{}>", alternate),
 497                                 Applicability::MachineApplicable,
 498                             );
 499                             return; // don't recurse into the type
 500                         }
 501                         if match_type_parameter(cx, qpath, &paths::VEC).is_some() {
 502                             let vec_ty = match &last_path_segment(qpath).args.unwrap().args[0] {
 503                                 GenericArg::Type(ty) => match &ty.kind {
 504                                     TyKind::Path(qpath) => qpath,
 505                                     _ => return,
 506                                 },
 507                                 _ => return,
 508                             };
 509                             let inner_span = match &last_path_segment(&vec_ty).args.unwrap().args[0] {
 510                                 GenericArg::Type(ty) => ty.span,
 511                                 _ => return,
 512                             };
 513                             let mut applicability = Applicability::MachineApplicable;
 514                             span_lint_and_sugg(
 515                                 cx,
 516                                 RC_BUFFER,
 517                                 hir_ty.span,
 518                                 "usage of `Arc<T>` when T is a buffer type",
 519                                 "try",
 520                                 format!(
 521                                     "Arc<[{}]>",
 522                                     snippet_with_applicability(cx, inner_span, "..", &mut applicability)
 523                                 ),
 524                                 Applicability::MachineApplicable,
 525                             );
 526                             return; // don't recurse into the type
 527                         }
 528                     } else if cx.tcx.is_diagnostic_item(sym::vec_type, def_id) {
 529                         if_chain! {
 530                             // Get the _ part of Vec<_>
 531                             if let Some(ref last) = last_path_segment(qpath).args;
 532                             if let Some(ty) = last.args.iter().find_map(|arg| match arg {
 533                                 GenericArg::Type(ty) => Some(ty),
 534                                 _ => None,
 535                             });
 536                             // ty is now _ at this point
 537                             if let TyKind::Path(ref ty_qpath) = ty.kind;
 538                             let res = cx.qpath_res(ty_qpath, ty.hir_id);
 539                             if let Some(def_id) = res.opt_def_id();
 540                             if Some(def_id) == cx.tcx.lang_items().owned_box();
 541                             // At this point, we know ty is Box<T>, now get T
 542                             if let Some(ref last) = last_path_segment(ty_qpath).args;
 543                             if let Some(boxed_ty) = last.args.iter().find_map(|arg| match arg {
 544                                 GenericArg::Type(ty) => Some(ty),
 545                                 _ => None,
 546                             });
 547                             let ty_ty = hir_ty_to_ty(cx.tcx, boxed_ty);
 548                             if !ty_ty.has_escaping_bound_vars();
 549                             if ty_ty.is_sized(cx.tcx.at(ty.span), cx.param_env);
 550                             if let Ok(ty_ty_size) = cx.layout_of(ty_ty).map(|l| l.size.bytes());
 551                             if ty_ty_size <= self.vec_box_size_threshold;
 552                             then {
 553                                 span_lint_and_sugg(
 554                                     cx,
 555                                     VEC_BOX,
 556                                     hir_ty.span,
 557                                     "`Vec<T>` is already on the heap, the boxing is unnecessary.",
 558                                     "try",
 559                                     format!("Vec<{}>", snippet(cx, boxed_ty.span, "..")),
 560                                     Applicability::MachineApplicable,
 561                                 );
 562                                 return; // don't recurse into the type
 563                             }
 564                         }
 565                     } else if cx.tcx.is_diagnostic_item(sym::option_type, def_id) {
 566                         if match_type_parameter(cx, qpath, &paths::OPTION).is_some() {
 567                             span_lint(
 568                                 cx,
 569                                 OPTION_OPTION,
 570                                 hir_ty.span,
 571                                 "consider using `Option<T>` instead of `Option<Option<T>>` or a custom \
 572                                  enum if you need to distinguish all 3 cases",
 573                             );
 574                             return; // don't recurse into the type
 575                         }
 576                     } else if match_def_path(cx, def_id, &paths::LINKED_LIST) {
 577                         span_lint_and_help(
 578                             cx,
 579                             LINKEDLIST,
 580                             hir_ty.span,
 581                             "I see you're using a LinkedList! Perhaps you meant some other data structure?",
 582                             None,
 583                             "a `VecDeque` might work",
 584                         );
 585                         return; // don't recurse into the type
 586                     }
 587                 }
 588                 match *qpath {
 589                     QPath::Resolved(Some(ref ty), ref p) => {
 590                         self.check_ty(cx, ty, is_local);
 591                         for ty in p.segments.iter().flat_map(|seg| {
 592                             seg.args
 593                                 .as_ref()
 594                                 .map_or_else(|| [].iter(), |params| params.args.iter())
 595                                 .filter_map(|arg| match arg {
 596                                     GenericArg::Type(ty) => Some(ty),
 597                                     _ => None,
 598                                 })
 599                         }) {
 600                             self.check_ty(cx, ty, is_local);
 601                         }
 602                     },
 603                     QPath::Resolved(None, ref p) => {
 604                         for ty in p.segments.iter().flat_map(|seg| {
 605                             seg.args
 606                                 .as_ref()
 607                                 .map_or_else(|| [].iter(), |params| params.args.iter())
 608                                 .filter_map(|arg| match arg {
 609                                     GenericArg::Type(ty) => Some(ty),
 610                                     _ => None,
 611                                 })
 612                         }) {
 613                             self.check_ty(cx, ty, is_local);
 614                         }
 615                     },
 616                     QPath::TypeRelative(ref ty, ref seg) => {
 617                         self.check_ty(cx, ty, is_local);
 618                         if let Some(ref params) = seg.args {
 619                             for ty in params.args.iter().filter_map(|arg| match arg {
 620                                 GenericArg::Type(ty) => Some(ty),
 621                                 _ => None,
 622                             }) {
 623                                 self.check_ty(cx, ty, is_local);
 624                             }
 625                         }
 626                     },
 627                     QPath::LangItem(..) => {},
 628                 }
 629             },
 630             TyKind::Rptr(ref lt, ref mut_ty) => self.check_ty_rptr(cx, hir_ty, is_local, lt, mut_ty),
 631             // recurse
 632             TyKind::Slice(ref ty) | TyKind::Array(ref ty, _) | TyKind::Ptr(MutTy { ref ty, .. }) => {
 633                 self.check_ty(cx, ty, is_local)
 634             },
 635             TyKind::Tup(tys) => {
 636                 for ty in tys {
 637                     self.check_ty(cx, ty, is_local);
 638                 }
 639             },
 640             _ => {},
 641         }
 642     }
 643
 644     fn check_ty_rptr(
 645         &mut self,
 646         cx: &LateContext<'_>,
 647         hir_ty: &hir::Ty<'_>,
 648         is_local: bool,
 649         lt: &Lifetime,
 650         mut_ty: &MutTy<'_>,
 651     ) {
 652         match mut_ty.ty.kind {
 653             TyKind::Path(ref qpath) => {
 654                 let hir_id = mut_ty.ty.hir_id;
 655                 let def = cx.qpath_res(qpath, hir_id);
 656                 if_chain! {
 657                     if let Some(def_id) = def.opt_def_id();
 658                     if Some(def_id) == cx.tcx.lang_items().owned_box();
 659                     if let QPath::Resolved(None, ref path) = *qpath;
 660                     if let [ref bx] = *path.segments;
 661                     if let Some(ref params) = bx.args;
 662                     if !params.parenthesized;
 663                     if let Some(inner) = params.args.iter().find_map(|arg| match arg {
 664                         GenericArg::Type(ty) => Some(ty),
 665                         _ => None,
 666                     });
 667                     then {
 668                         if is_any_trait(inner) {
 669                             // Ignore `Box<Any>` types; see issue #1884 for details.
 670                             return;
 671                         }
 672
 673                         let ltopt = if lt.is_elided() {
 674                             String::new()
 675                         } else {
 676                             format!("{} ", lt.name.ident().as_str())
 677                         };
 678
 679                         if mut_ty.mutbl == Mutability::Mut {
 680                             // Ignore `&mut Box<T>` types; see issue #2907 for
 681                             // details.
 682                             return;
 683                         }
 684
 685                         // When trait objects or opaque types have lifetime or auto-trait bounds,
 686                         // we need to add parentheses to avoid a syntax error due to its ambiguity.
 687                         // Originally reported as the issue #3128.
 688                         let inner_snippet = snippet(cx, inner.span, "..");
 689                         let suggestion = match &inner.kind {
 690                             TyKind::TraitObject(bounds, lt_bound) if bounds.len() > 1 || !lt_bound.is_elided() => {
 691                                 format!("&{}({})", ltopt, &inner_snippet)
 692                             },
 693                             TyKind::Path(qpath)
 694                                 if get_bounds_if_impl_trait(cx, qpath, inner.hir_id)
 695                                     .map_or(false, |bounds| bounds.len() > 1) =>
 696                             {
 697                                 format!("&{}({})", ltopt, &inner_snippet)
 698                             },
 699                             _ => format!("&{}{}", ltopt, &inner_snippet),
 700                         };
 701                         span_lint_and_sugg(
 702                             cx,
 703                             BORROWED_BOX,
 704                             hir_ty.span,
 705                             "you seem to be trying to use `&Box<T>`. Consider using just `&T`",
 706                             "try",
 707                             suggestion,
 708                             // To make this `MachineApplicable`, at least one needs to check if it isn't a trait item
 709                             // because the trait impls of it will break otherwise;
 710                             // and there may be other cases that result in invalid code.
 711                             // For example, type coercion doesn't work nicely.
 712                             Applicability::Unspecified,
 713                         );
 714                         return; // don't recurse into the type
 715                     }
 716                 };
 717                 self.check_ty(cx, &mut_ty.ty, is_local);
 718             },
 719             _ => self.check_ty(cx, &mut_ty.ty, is_local),
 720         }
 721     }
 722 }
 723
 724 // Returns true if given type is `Any` trait.
 725 fn is_any_trait(t: &hir::Ty<'_>) -> bool {
 726     if_chain! {
 727         if let TyKind::TraitObject(ref traits, _) = t.kind;
 728         if !traits.is_empty();
 729         // Only Send/Sync can be used as additional traits, so it is enough to
 730         // check only the first trait.
 731         if match_path(&traits[0].trait_ref.path, &paths::ANY_TRAIT);
 732         then {
 733             return true;
 734         }
 735     }
 736
 737     false
 738 }
 739
 740 fn get_bounds_if_impl_trait<'tcx>(cx: &LateContext<'tcx>, qpath: &QPath<'_>, id: HirId) -> Option<GenericBounds<'tcx>> {
 741     if_chain! {
 742         if let Some(did) = cx.qpath_res(qpath, id).opt_def_id();
 743         if let Some(Node::GenericParam(generic_param)) = cx.tcx.hir().get_if_local(did);
 744         if let GenericParamKind::Type { synthetic, .. } = generic_param.kind;
 745         if synthetic == Some(SyntheticTyParamKind::ImplTrait);
 746         then {
 747             Some(generic_param.bounds)
 748         } else {
 749             None
 750         }
 751     }
 752 }
 753
 754 declare_clippy_lint! {
 755     /// **What it does:** Checks for binding a unit value.
 756     ///
 757     /// **Why is this bad?** A unit value cannot usefully be used anywhere. So
 758     /// binding one is kind of pointless.
 759     ///
 760     /// **Known problems:** None.
 761     ///
 762     /// **Example:**
 763     /// ```rust
 764     /// let x = {
 765     ///     1;
 766     /// };
 767     /// ```
 768     pub LET_UNIT_VALUE,
 769     pedantic,
 770     "creating a `let` binding to a value of unit type, which usually can't be used afterwards"
 771 }
 772
 773 declare_lint_pass!(LetUnitValue => [LET_UNIT_VALUE]);
 774
 775 impl<'tcx> LateLintPass<'tcx> for LetUnitValue {
 776     fn check_stmt(&mut self, cx: &LateContext<'tcx>, stmt: &'tcx Stmt<'_>) {
 777         if let StmtKind::Local(ref local) = stmt.kind {
 778             if is_unit(cx.typeck_results().pat_ty(&local.pat)) {
 779                 if in_external_macro(cx.sess(), stmt.span) || local.pat.span.from_expansion() {
 780                     return;
 781                 }
 782                 if higher::is_from_for_desugar(local) {
 783                     return;
 784                 }
 785                 span_lint_and_then(
 786                     cx,
 787                     LET_UNIT_VALUE,
 788                     stmt.span,
 789                     "this let-binding has unit value",
 790                     |diag| {
 791                         if let Some(expr) = &local.init {
 792                             let snip = snippet_with_macro_callsite(cx, expr.span, "()");
 793                             diag.span_suggestion(
 794                                 stmt.span,
 795                                 "omit the `let` binding",
 796                                 format!("{};", snip),
 797                                 Applicability::MachineApplicable, // snippet
 798                             );
 799                         }
 800                     },
 801                 );
 802             }
 803         }
 804     }
 805 }
 806
 807 declare_clippy_lint! {
 808     /// **What it does:** Checks for comparisons to unit. This includes all binary
 809     /// comparisons (like `==` and `<`) and asserts.
 810     ///
 811     /// **Why is this bad?** Unit is always equal to itself, and thus is just a
 812     /// clumsily written constant. Mostly this happens when someone accidentally
 813     /// adds semicolons at the end of the operands.
 814     ///
 815     /// **Known problems:** None.
 816     ///
 817     /// **Example:**
 818     /// ```rust
 819     /// # fn foo() {};
 820     /// # fn bar() {};
 821     /// # fn baz() {};
 822     /// if {
 823     ///     foo();
 824     /// } == {
 825     ///     bar();
 826     /// } {
 827     ///     baz();
 828     /// }
 829     /// ```
 830     /// is equal to
 831     /// ```rust
 832     /// # fn foo() {};
 833     /// # fn bar() {};
 834     /// # fn baz() {};
 835     /// {
 836     ///     foo();
 837     ///     bar();
 838     ///     baz();
 839     /// }
 840     /// ```
 841     ///
 842     /// For asserts:
 843     /// ```rust
 844     /// # fn foo() {};
 845     /// # fn bar() {};
 846     /// assert_eq!({ foo(); }, { bar(); });
 847     /// ```
 848     /// will always succeed
 849     pub UNIT_CMP,
 850     correctness,
 851     "comparing unit values"
 852 }
 853
 854 declare_lint_pass!(UnitCmp => [UNIT_CMP]);
 855
 856 impl<'tcx> LateLintPass<'tcx> for UnitCmp {
 857     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) {
 858         if expr.span.from_expansion() {
 859             if let Some(callee) = expr.span.source_callee() {
 860                 if let ExpnKind::Macro(MacroKind::Bang, symbol) = callee.kind {
 861                     if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
 862                         let op = cmp.node;
 863                         if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
 864                             let result = match &*symbol.as_str() {
 865                                 "assert_eq" | "debug_assert_eq" => "succeed",
 866                                 "assert_ne" | "debug_assert_ne" => "fail",
 867                                 _ => return,
 868                             };
 869                             span_lint(
 870                                 cx,
 871                                 UNIT_CMP,
 872                                 expr.span,
 873                                 &format!(
 874                                     "`{}` of unit values detected. This will always {}",
 875                                     symbol.as_str(),
 876                                     result
 877                                 ),
 878                             );
 879                         }
 880                     }
 881                 }
 882             }
 883             return;
 884         }
 885         if let ExprKind::Binary(ref cmp, ref left, _) = expr.kind {
 886             let op = cmp.node;
 887             if op.is_comparison() && is_unit(cx.typeck_results().expr_ty(left)) {
 888                 let result = match op {
 889                     BinOpKind::Eq | BinOpKind::Le | BinOpKind::Ge => "true",
 890                     _ => "false",
 891                 };
 892                 span_lint(
 893                     cx,
 894                     UNIT_CMP,
 895                     expr.span,
 896                     &format!(
 897                         "{}-comparison of unit values detected. This will always be {}",
 898                         op.as_str(),
 899                         result
 900                     ),
 901                 );
 902             }
 903         }
 904     }
 905 }
 906
 907 declare_clippy_lint! {
 908     /// **What it does:** Checks for passing a unit value as an argument to a function without using a
 909     /// unit literal (`()`).
 910     ///
 911     /// **Why is this bad?** This is likely the result of an accidental semicolon.
 912     ///
 913     /// **Known problems:** None.
 914     ///
 915     /// **Example:**
 916     /// ```rust,ignore
 917     /// foo({
 918     ///     let a = bar();
 919     ///     baz(a);
 920     /// })
 921     /// ```
 922     pub UNIT_ARG,
 923     complexity,
 924     "passing unit to a function"
 925 }
 926
 927 declare_lint_pass!(UnitArg => [UNIT_ARG]);
 928
 929 impl<'tcx> LateLintPass<'tcx> for UnitArg {
 930     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
 931         if expr.span.from_expansion() {
 932             return;
 933         }
 934
 935         // apparently stuff in the desugaring of `?` can trigger this
 936         // so check for that here
 937         // only the calls to `Try::from_error` is marked as desugared,
 938         // so we need to check both the current Expr and its parent.
 939         if is_questionmark_desugar_marked_call(expr) {
 940             return;
 941         }
 942         if_chain! {
 943             let map = &cx.tcx.hir();
 944             let opt_parent_node = map.find(map.get_parent_node(expr.hir_id));
 945             if let Some(hir::Node::Expr(parent_expr)) = opt_parent_node;
 946             if is_questionmark_desugar_marked_call(parent_expr);
 947             then {
 948                 return;
 949             }
 950         }
 951
 952         match expr.kind {
 953             ExprKind::Call(_, args) | ExprKind::MethodCall(_, _, args, _) => {
 954                 let args_to_recover = args
 955                     .iter()
 956                     .filter(|arg| {
 957                         if is_unit(cx.typeck_results().expr_ty(arg)) && !is_unit_literal(arg) {
 958                             !matches!(
 959                                 &arg.kind,
 960                                 ExprKind::Match(.., MatchSource::TryDesugar) | ExprKind::Path(..)
 961                             )
 962                         } else {
 963                             false
 964                         }
 965                     })
 966                     .collect::<Vec<_>>();
 967                 if !args_to_recover.is_empty() {
 968                     lint_unit_args(cx, expr, &args_to_recover);
 969                 }
 970             },
 971             _ => (),
 972         }
 973     }
 974 }
 975
 976 fn fmt_stmts_and_call(
 977     cx: &LateContext<'_>,
 978     call_expr: &Expr<'_>,
 979     call_snippet: &str,
 980     args_snippets: &[impl AsRef<str>],
 981     non_empty_block_args_snippets: &[impl AsRef<str>],
 982 ) -> String {
 983     let call_expr_indent = indent_of(cx, call_expr.span).unwrap_or(0);
 984     let call_snippet_with_replacements = args_snippets
 985         .iter()
 986         .fold(call_snippet.to_owned(), |acc, arg| acc.replacen(arg.as_ref(), "()", 1));
 987
 988     let mut stmts_and_call = non_empty_block_args_snippets
 989         .iter()
 990         .map(|it| it.as_ref().to_owned())
 991         .collect::<Vec<_>>();
 992     stmts_and_call.push(call_snippet_with_replacements);
 993     stmts_and_call = stmts_and_call
 994         .into_iter()
 995         .map(|v| reindent_multiline(v.into(), true, Some(call_expr_indent)).into_owned())
 996         .collect();
 997
 998     let mut stmts_and_call_snippet = stmts_and_call.join(&format!("{}{}", ";\n", " ".repeat(call_expr_indent)));
 999     // expr is not in a block statement or result expression position, wrap in a block
1000     let parent_node = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(call_expr.hir_id));
1001     if !matches!(parent_node, Some(Node::Block(_))) && !matches!(parent_node, Some(Node::Stmt(_))) {
1002         let block_indent = call_expr_indent + 4;
1003         stmts_and_call_snippet =
1004             reindent_multiline(stmts_and_call_snippet.into(), true, Some(block_indent)).into_owned();
1005         stmts_and_call_snippet = format!(
1006             "{{\n{}{}\n{}}}",
1007             " ".repeat(block_indent),
1008             &stmts_and_call_snippet,
1009             " ".repeat(call_expr_indent)
1010         );
1011     }
1012     stmts_and_call_snippet
1013 }
1014
1015 fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Expr<'_>]) {
1016     let mut applicability = Applicability::MachineApplicable;
1017     let (singular, plural) = if args_to_recover.len() > 1 {
1018         ("", "s")
1019     } else {
1020         ("a ", "")
1021     };
1022     span_lint_and_then(
1023         cx,
1024         UNIT_ARG,
1025         expr.span,
1026         &format!("passing {}unit value{} to a function", singular, plural),
1027         |db| {
1028             let mut or = "";
1029             args_to_recover
1030                 .iter()
1031                 .filter_map(|arg| {
1032                     if_chain! {
1033                         if let ExprKind::Block(block, _) = arg.kind;
1034                         if block.expr.is_none();
1035                         if let Some(last_stmt) = block.stmts.iter().last();
1036                         if let StmtKind::Semi(last_expr) = last_stmt.kind;
1037                         if let Some(snip) = snippet_opt(cx, last_expr.span);
1038                         then {
1039                             Some((
1040                                 last_stmt.span,
1041                                 snip,
1042                             ))
1043                         }
1044                         else {
1045                             None
1046                         }
1047                     }
1048                 })
1049                 .for_each(|(span, sugg)| {
1050                     db.span_suggestion(
1051                         span,
1052                         "remove the semicolon from the last statement in the block",
1053                         sugg,
1054                         Applicability::MaybeIncorrect,
1055                     );
1056                     or = "or ";
1057                     applicability = Applicability::MaybeIncorrect;
1058                 });
1059
1060             let arg_snippets: Vec<String> = args_to_recover
1061                 .iter()
1062                 .filter_map(|arg| snippet_opt(cx, arg.span))
1063                 .collect();
1064             let arg_snippets_without_empty_blocks: Vec<String> = args_to_recover
1065                 .iter()
1066                 .filter(|arg| !is_empty_block(arg))
1067                 .filter_map(|arg| snippet_opt(cx, arg.span))
1068                 .collect();
1069
1070             if let Some(call_snippet) = snippet_opt(cx, expr.span) {
1071                 let sugg = fmt_stmts_and_call(
1072                     cx,
1073                     expr,
1074                     &call_snippet,
1075                     &arg_snippets,
1076                     &arg_snippets_without_empty_blocks,
1077                 );
1078
1079                 if arg_snippets_without_empty_blocks.is_empty() {
1080                     db.multipart_suggestion(
1081                         &format!("use {}unit literal{} instead", singular, plural),
1082                         args_to_recover
1083                             .iter()
1084                             .map(|arg| (arg.span, "()".to_string()))
1085                             .collect::<Vec<_>>(),
1086                         applicability,
1087                     );
1088                 } else {
1089                     let plural = arg_snippets_without_empty_blocks.len() > 1;
1090                     let empty_or_s = if plural { "s" } else { "" };
1091                     let it_or_them = if plural { "them" } else { "it" };
1092                     db.span_suggestion(
1093                         expr.span,
1094                         &format!(
1095                             "{}move the expression{} in front of the call and replace {} with the unit literal `()`",
1096                             or, empty_or_s, it_or_them
1097                         ),
1098                         sugg,
1099                         applicability,
1100                     );
1101                 }
1102             }
1103         },
1104     );
1105 }
1106
1107 fn is_empty_block(expr: &Expr<'_>) -> bool {
1108     matches!(
1109         expr.kind,
1110         ExprKind::Block(
1111             Block {
1112                 stmts: &[],
1113                 expr: None,
1114                 ..
1115             },
1116             _,
1117         )
1118     )
1119 }
1120
1121 fn is_questionmark_desugar_marked_call(expr: &Expr<'_>) -> bool {
1122     use rustc_span::hygiene::DesugaringKind;
1123     if let ExprKind::Call(ref callee, _) = expr.kind {
1124         callee.span.is_desugaring(DesugaringKind::QuestionMark)
1125     } else {
1126         false
1127     }
1128 }
1129
1130 fn is_unit(ty: Ty<'_>) -> bool {
1131     matches!(ty.kind(), ty::Tuple(slice) if slice.is_empty())
1132 }
1133
1134 fn is_unit_literal(expr: &Expr<'_>) -> bool {
1135     matches!(expr.kind, ExprKind::Tup(ref slice) if slice.is_empty())
1136 }
1137
1138 declare_clippy_lint! {
1139     /// **What it does:** Checks for casts from any numerical to a float type where
1140     /// the receiving type cannot store all values from the original type without
1141     /// rounding errors. This possible rounding is to be expected, so this lint is
1142     /// `Allow` by default.
1143     ///
1144     /// Basically, this warns on casting any integer with 32 or more bits to `f32`
1145     /// or any 64-bit integer to `f64`.
1146     ///
1147     /// **Why is this bad?** It's not bad at all. But in some applications it can be
1148     /// helpful to know where precision loss can take place. This lint can help find
1149     /// those places in the code.
1150     ///
1151     /// **Known problems:** None.
1152     ///
1153     /// **Example:**
1154     /// ```rust
1155     /// let x = u64::MAX;
1156     /// x as f64;
1157     /// ```
1158     pub CAST_PRECISION_LOSS,
1159     pedantic,
1160     "casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
1161 }
1162
1163 declare_clippy_lint! {
1164     /// **What it does:** Checks for casts from a signed to an unsigned numerical
1165     /// type. In this case, negative values wrap around to large positive values,
1166     /// which can be quite surprising in practice. However, as the cast works as
1167     /// defined, this lint is `Allow` by default.
1168     ///
1169     /// **Why is this bad?** Possibly surprising results. You can activate this lint
1170     /// as a one-time check to see where numerical wrapping can arise.
1171     ///
1172     /// **Known problems:** None.
1173     ///
1174     /// **Example:**
1175     /// ```rust
1176     /// let y: i8 = -1;
1177     /// y as u128; // will return 18446744073709551615
1178     /// ```
1179     pub CAST_SIGN_LOSS,
1180     pedantic,
1181     "casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
1182 }
1183
1184 declare_clippy_lint! {
1185     /// **What it does:** Checks for casts between numerical types that may
1186     /// truncate large values. This is expected behavior, so the cast is `Allow` by
1187     /// default.
1188     ///
1189     /// **Why is this bad?** In some problem domains, it is good practice to avoid
1190     /// truncation. This lint can be activated to help assess where additional
1191     /// checks could be beneficial.
1192     ///
1193     /// **Known problems:** None.
1194     ///
1195     /// **Example:**
1196     /// ```rust
1197     /// fn as_u8(x: u64) -> u8 {
1198     ///     x as u8
1199     /// }
1200     /// ```
1201     pub CAST_POSSIBLE_TRUNCATION,
1202     pedantic,
1203     "casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
1204 }
1205
1206 declare_clippy_lint! {
1207     /// **What it does:** Checks for casts from an unsigned type to a signed type of
1208     /// the same size. Performing such a cast is a 'no-op' for the compiler,
1209     /// i.e., nothing is changed at the bit level, and the binary representation of
1210     /// the value is reinterpreted. This can cause wrapping if the value is too big
1211     /// for the target signed type. However, the cast works as defined, so this lint
1212     /// is `Allow` by default.
1213     ///
1214     /// **Why is this bad?** While such a cast is not bad in itself, the results can
1215     /// be surprising when this is not the intended behavior, as demonstrated by the
1216     /// example below.
1217     ///
1218     /// **Known problems:** None.
1219     ///
1220     /// **Example:**
1221     /// ```rust
1222     /// u32::MAX as i32; // will yield a value of `-1`
1223     /// ```
1224     pub CAST_POSSIBLE_WRAP,
1225     pedantic,
1226     "casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
1227 }
1228
1229 declare_clippy_lint! {
1230     /// **What it does:** Checks for casts between numerical types that may
1231     /// be replaced by safe conversion functions.
1232     ///
1233     /// **Why is this bad?** Rust's `as` keyword will perform many kinds of
1234     /// conversions, including silently lossy conversions. Conversion functions such
1235     /// as `i32::from` will only perform lossless conversions. Using the conversion
1236     /// functions prevents conversions from turning into silent lossy conversions if
1237     /// the types of the input expressions ever change, and make it easier for
1238     /// people reading the code to know that the conversion is lossless.
1239     ///
1240     /// **Known problems:** None.
1241     ///
1242     /// **Example:**
1243     /// ```rust
1244     /// fn as_u64(x: u8) -> u64 {
1245     ///     x as u64
1246     /// }
1247     /// ```
1248     ///
1249     /// Using `::from` would look like this:
1250     ///
1251     /// ```rust
1252     /// fn as_u64(x: u8) -> u64 {
1253     ///     u64::from(x)
1254     /// }
1255     /// ```
1256     pub CAST_LOSSLESS,
1257     pedantic,
1258     "casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
1259 }
1260
1261 declare_clippy_lint! {
1262     /// **What it does:** Checks for casts to the same type, casts of int literals to integer types
1263     /// and casts of float literals to float types.
1264     ///
1265     /// **Why is this bad?** It's just unnecessary.
1266     ///
1267     /// **Known problems:** None.
1268     ///
1269     /// **Example:**
1270     /// ```rust
1271     /// let _ = 2i32 as i32;
1272     /// let _ = 0.5 as f32;
1273     /// ```
1274     ///
1275     /// Better:
1276     ///
1277     /// ```rust
1278     /// let _ = 2_i32;
1279     /// let _ = 0.5_f32;
1280     /// ```
1281     pub UNNECESSARY_CAST,
1282     complexity,
1283     "cast to the same type, e.g., `x as i32` where `x: i32`"
1284 }
1285
1286 declare_clippy_lint! {
1287     /// **What it does:** Checks for casts, using `as` or `pointer::cast`,
1288     /// from a less-strictly-aligned pointer to a more-strictly-aligned pointer
1289     ///
1290     /// **Why is this bad?** Dereferencing the resulting pointer may be undefined
1291     /// behavior.
1292     ///
1293     /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
1294     /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
1295     /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
1296     ///
1297     /// **Example:**
1298     /// ```rust
1299     /// let _ = (&1u8 as *const u8) as *const u16;
1300     /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
1301     ///
1302     /// (&1u8 as *const u8).cast::<u16>();
1303     /// (&mut 1u8 as *mut u8).cast::<u16>();
1304     /// ```
1305     pub CAST_PTR_ALIGNMENT,
1306     pedantic,
1307     "cast from a pointer to a more-strictly-aligned pointer"
1308 }
1309
1310 declare_clippy_lint! {
1311     /// **What it does:** Checks for casts of function pointers to something other than usize
1312     ///
1313     /// **Why is this bad?**
1314     /// Casting a function pointer to anything other than usize/isize is not portable across
1315     /// architectures, because you end up losing bits if the target type is too small or end up with a
1316     /// bunch of extra bits that waste space and add more instructions to the final binary than
1317     /// strictly necessary for the problem
1318     ///
1319     /// Casting to isize also doesn't make sense since there are no signed addresses.
1320     ///
1321     /// **Example**
1322     ///
1323     /// ```rust
1324     /// // Bad
1325     /// fn fun() -> i32 { 1 }
1326     /// let a = fun as i64;
1327     ///
1328     /// // Good
1329     /// fn fun2() -> i32 { 1 }
1330     /// let a = fun2 as usize;
1331     /// ```
1332     pub FN_TO_NUMERIC_CAST,
1333     style,
1334     "casting a function pointer to a numeric type other than usize"
1335 }
1336
1337 declare_clippy_lint! {
1338     /// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
1339     /// store address.
1340     ///
1341     /// **Why is this bad?**
1342     /// Such a cast discards some bits of the function's address. If this is intended, it would be more
1343     /// clearly expressed by casting to usize first, then casting the usize to the intended type (with
1344     /// a comment) to perform the truncation.
1345     ///
1346     /// **Example**
1347     ///
1348     /// ```rust
1349     /// // Bad
1350     /// fn fn1() -> i16 {
1351     ///     1
1352     /// };
1353     /// let _ = fn1 as i32;
1354     ///
1355     /// // Better: Cast to usize first, then comment with the reason for the truncation
1356     /// fn fn2() -> i16 {
1357     ///     1
1358     /// };
1359     /// let fn_ptr = fn2 as usize;
1360     /// let fn_ptr_truncated = fn_ptr as i32;
1361     /// ```
1362     pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1363     style,
1364     "casting a function pointer to a numeric type not wide enough to store the address"
1365 }
1366
1367 /// Returns the size in bits of an integral type.
1368 /// Will return 0 if the type is not an int or uint variant
1369 fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
1370     match typ.kind() {
1371         ty::Int(i) => match i {
1372             IntTy::Isize => tcx.data_layout.pointer_size.bits(),
1373             IntTy::I8 => 8,
1374             IntTy::I16 => 16,
1375             IntTy::I32 => 32,
1376             IntTy::I64 => 64,
1377             IntTy::I128 => 128,
1378         },
1379         ty::Uint(i) => match i {
1380             UintTy::Usize => tcx.data_layout.pointer_size.bits(),
1381             UintTy::U8 => 8,
1382             UintTy::U16 => 16,
1383             UintTy::U32 => 32,
1384             UintTy::U64 => 64,
1385             UintTy::U128 => 128,
1386         },
1387         _ => 0,
1388     }
1389 }
1390
1391 fn is_isize_or_usize(typ: Ty<'_>) -> bool {
1392     matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
1393 }
1394
1395 fn span_precision_loss_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to_f64: bool) {
1396     let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
1397     let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
1398     let arch_dependent_str = "on targets with 64-bit wide pointers ";
1399     let from_nbits_str = if arch_dependent {
1400         "64".to_owned()
1401     } else if is_isize_or_usize(cast_from) {
1402         "32 or 64".to_owned()
1403     } else {
1404         int_ty_to_nbits(cast_from, cx.tcx).to_string()
1405     };
1406     span_lint(
1407         cx,
1408         CAST_PRECISION_LOSS,
1409         expr.span,
1410         &format!(
1411             "casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
1412              but `{1}`'s mantissa is only {4} bits wide)",
1413             cast_from,
1414             if cast_to_f64 { "f64" } else { "f32" },
1415             if arch_dependent { arch_dependent_str } else { "" },
1416             from_nbits_str,
1417             mantissa_nbits
1418         ),
1419     );
1420 }
1421
1422 fn should_strip_parens(op: &Expr<'_>, snip: &str) -> bool {
1423     if let ExprKind::Binary(_, _, _) = op.kind {
1424         if snip.starts_with('(') && snip.ends_with(')') {
1425             return true;
1426         }
1427     }
1428     false
1429 }
1430
1431 fn span_lossless_lint(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1432     // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
1433     if in_constant(cx, expr.hir_id) {
1434         return;
1435     }
1436     // The suggestion is to use a function call, so if the original expression
1437     // has parens on the outside, they are no longer needed.
1438     let mut applicability = Applicability::MachineApplicable;
1439     let opt = snippet_opt(cx, op.span);
1440     let sugg = opt.as_ref().map_or_else(
1441         || {
1442             applicability = Applicability::HasPlaceholders;
1443             ".."
1444         },
1445         |snip| {
1446             if should_strip_parens(op, snip) {
1447                 &snip[1..snip.len() - 1]
1448             } else {
1449                 snip.as_str()
1450             }
1451         },
1452     );
1453
1454     span_lint_and_sugg(
1455         cx,
1456         CAST_LOSSLESS,
1457         expr.span,
1458         &format!(
1459             "casting `{}` to `{}` may become silently lossy if you later change the type",
1460             cast_from, cast_to
1461         ),
1462         "try",
1463         format!("{}::from({})", cast_to, sugg),
1464         applicability,
1465     );
1466 }
1467
1468 enum ArchSuffix {
1469     _32,
1470     _64,
1471     None,
1472 }
1473
1474 fn check_loss_of_sign(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1475     if !cast_from.is_signed() || cast_to.is_signed() {
1476         return;
1477     }
1478
1479     // don't lint for positive constants
1480     let const_val = constant(cx, &cx.typeck_results(), op);
1481     if_chain! {
1482         if let Some((Constant::Int(n), _)) = const_val;
1483         if let ty::Int(ity) = *cast_from.kind();
1484         if sext(cx.tcx, n, ity) >= 0;
1485         then {
1486             return
1487         }
1488     }
1489
1490     // don't lint for the result of methods that always return non-negative values
1491     if let ExprKind::MethodCall(ref path, _, _, _) = op.kind {
1492         let mut method_name = path.ident.name.as_str();
1493         let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
1494
1495         if_chain! {
1496             if method_name == "unwrap";
1497             if let Some(arglist) = method_chain_args(op, &["unwrap"]);
1498             if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
1499             then {
1500                 method_name = inner_path.ident.name.as_str();
1501             }
1502         }
1503
1504         if allowed_methods.iter().any(|&name| method_name == name) {
1505             return;
1506         }
1507     }
1508
1509     span_lint(
1510         cx,
1511         CAST_SIGN_LOSS,
1512         expr.span,
1513         &format!(
1514             "casting `{}` to `{}` may lose the sign of the value",
1515             cast_from, cast_to
1516         ),
1517     );
1518 }
1519
1520 fn check_truncation_and_wrapping(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1521     let arch_64_suffix = " on targets with 64-bit wide pointers";
1522     let arch_32_suffix = " on targets with 32-bit wide pointers";
1523     let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
1524     let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1525     let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1526     let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) =
1527         match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
1528             (true, true) | (false, false) => (
1529                 to_nbits < from_nbits,
1530                 ArchSuffix::None,
1531                 to_nbits == from_nbits && cast_unsigned_to_signed,
1532                 ArchSuffix::None,
1533             ),
1534             (true, false) => (
1535                 to_nbits <= 32,
1536                 if to_nbits == 32 {
1537                     ArchSuffix::_64
1538                 } else {
1539                     ArchSuffix::None
1540                 },
1541                 to_nbits <= 32 && cast_unsigned_to_signed,
1542                 ArchSuffix::_32,
1543             ),
1544             (false, true) => (
1545                 from_nbits == 64,
1546                 ArchSuffix::_32,
1547                 cast_unsigned_to_signed,
1548                 if from_nbits == 64 {
1549                     ArchSuffix::_64
1550                 } else {
1551                     ArchSuffix::_32
1552                 },
1553             ),
1554         };
1555     if span_truncation {
1556         span_lint(
1557             cx,
1558             CAST_POSSIBLE_TRUNCATION,
1559             expr.span,
1560             &format!(
1561                 "casting `{}` to `{}` may truncate the value{}",
1562                 cast_from,
1563                 cast_to,
1564                 match suffix_truncation {
1565                     ArchSuffix::_32 => arch_32_suffix,
1566                     ArchSuffix::_64 => arch_64_suffix,
1567                     ArchSuffix::None => "",
1568                 }
1569             ),
1570         );
1571     }
1572     if span_wrap {
1573         span_lint(
1574             cx,
1575             CAST_POSSIBLE_WRAP,
1576             expr.span,
1577             &format!(
1578                 "casting `{}` to `{}` may wrap around the value{}",
1579                 cast_from,
1580                 cast_to,
1581                 match suffix_wrap {
1582                     ArchSuffix::_32 => arch_32_suffix,
1583                     ArchSuffix::_64 => arch_64_suffix,
1584                     ArchSuffix::None => "",
1585                 }
1586             ),
1587         );
1588     }
1589 }
1590
1591 fn check_lossless(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1592     let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
1593     let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1594     let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1595     if !is_isize_or_usize(cast_from) && !is_isize_or_usize(cast_to) && from_nbits < to_nbits && !cast_signed_to_unsigned
1596     {
1597         span_lossless_lint(cx, expr, op, cast_from, cast_to);
1598     }
1599 }
1600
1601 declare_lint_pass!(Casts => [
1602     CAST_PRECISION_LOSS,
1603     CAST_SIGN_LOSS,
1604     CAST_POSSIBLE_TRUNCATION,
1605     CAST_POSSIBLE_WRAP,
1606     CAST_LOSSLESS,
1607     UNNECESSARY_CAST,
1608     CAST_PTR_ALIGNMENT,
1609     FN_TO_NUMERIC_CAST,
1610     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1611 ]);
1612
1613 // Check if the given type is either `core::ffi::c_void` or
1614 // one of the platform specific `libc::<platform>::c_void` of libc.
1615 fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
1616     if let ty::Adt(adt, _) = ty.kind() {
1617         let names = cx.get_def_path(adt.did);
1618
1619         if names.is_empty() {
1620             return false;
1621         }
1622         if names[0] == sym::libc || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
1623             return true;
1624         }
1625     }
1626     false
1627 }
1628
1629 /// Returns the mantissa bits wide of a fp type.
1630 /// Will return 0 if the type is not a fp
1631 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
1632     match typ.kind() {
1633         ty::Float(FloatTy::F32) => 23,
1634         ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
1635         _ => 0,
1636     }
1637 }
1638
1639 impl<'tcx> LateLintPass<'tcx> for Casts {
1640     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1641         if expr.span.from_expansion() {
1642             return;
1643         }
1644         if let ExprKind::Cast(ref ex, cast_to) = expr.kind {
1645             if is_hir_ty_cfg_dependant(cx, cast_to) {
1646                 return;
1647             }
1648             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
1649             lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
1650             if let Some(lit) = get_numeric_literal(ex) {
1651                 let literal_str = snippet_opt(cx, ex.span).unwrap_or_default();
1652
1653                 if_chain! {
1654                     if let LitKind::Int(n, _) = lit.node;
1655                     if let Some(src) = snippet_opt(cx, lit.span);
1656                     if cast_to.is_floating_point();
1657                     if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
1658                     let from_nbits = 128 - n.leading_zeros();
1659                     let to_nbits = fp_ty_mantissa_nbits(cast_to);
1660                     if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
1661                     then {
1662                         let literal_str = if is_unary_neg(ex) { format!("-{}", num_lit.integer) } else { num_lit.integer.into() };
1663                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1664                         return;
1665                     }
1666                 }
1667
1668                 match lit.node {
1669                     LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
1670                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1671                     },
1672                     LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
1673                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1674                     },
1675                     LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
1676                     _ => {
1677                         if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
1678                             span_lint(
1679                                 cx,
1680                                 UNNECESSARY_CAST,
1681                                 expr.span,
1682                                 &format!(
1683                                     "casting to the same type is unnecessary (`{}` -> `{}`)",
1684                                     cast_from, cast_to
1685                                 ),
1686                             );
1687                         }
1688                     },
1689                 }
1690             }
1691             if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
1692                 lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
1693             }
1694
1695             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1696         } else if let ExprKind::MethodCall(method_path, _, args, _) = expr.kind {
1697             if_chain! {
1698             if method_path.ident.name == sym!(cast);
1699             if let Some(generic_args) = method_path.args;
1700             if let [GenericArg::Type(cast_to)] = generic_args.args;
1701             // There probably is no obvious reason to do this, just to be consistent with `as` cases.
1702             if !is_hir_ty_cfg_dependant(cx, cast_to);
1703             then {
1704                 let (cast_from, cast_to) =
1705                     (cx.typeck_results().expr_ty(&args[0]), cx.typeck_results().expr_ty(expr));
1706                 lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1707             }
1708             }
1709         }
1710     }
1711 }
1712
1713 fn is_unary_neg(expr: &Expr<'_>) -> bool {
1714     matches!(expr.kind, ExprKind::Unary(UnOp::Neg, _))
1715 }
1716
1717 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
1718     match expr.kind {
1719         ExprKind::Lit(ref lit) => Some(lit),
1720         ExprKind::Unary(UnOp::Neg, e) => {
1721             if let ExprKind::Lit(ref lit) = e.kind {
1722                 Some(lit)
1723             } else {
1724                 None
1725             }
1726         },
1727         _ => None,
1728     }
1729 }
1730
1731 fn show_unnecessary_cast(cx: &LateContext<'_>, expr: &Expr<'_>, literal_str: &str, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1732     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
1733     span_lint_and_sugg(
1734         cx,
1735         UNNECESSARY_CAST,
1736         expr.span,
1737         &format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
1738         "try",
1739         format!("{}_{}", literal_str.trim_end_matches('.'), cast_to),
1740         Applicability::MachineApplicable,
1741     );
1742 }
1743
1744 fn lint_numeric_casts<'tcx>(
1745     cx: &LateContext<'tcx>,
1746     expr: &Expr<'tcx>,
1747     cast_expr: &Expr<'_>,
1748     cast_from: Ty<'tcx>,
1749     cast_to: Ty<'tcx>,
1750 ) {
1751     match (cast_from.is_integral(), cast_to.is_integral()) {
1752         (true, false) => {
1753             let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1754             let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
1755                 32
1756             } else {
1757                 64
1758             };
1759             if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
1760                 span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
1761             }
1762             if from_nbits < to_nbits {
1763                 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1764             }
1765         },
1766         (false, true) => {
1767             span_lint(
1768                 cx,
1769                 CAST_POSSIBLE_TRUNCATION,
1770                 expr.span,
1771                 &format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to),
1772             );
1773             if !cast_to.is_signed() {
1774                 span_lint(
1775                     cx,
1776                     CAST_SIGN_LOSS,
1777                     expr.span,
1778                     &format!(
1779                         "casting `{}` to `{}` may lose the sign of the value",
1780                         cast_from, cast_to
1781                     ),
1782                 );
1783             }
1784         },
1785         (true, true) => {
1786             check_loss_of_sign(cx, expr, cast_expr, cast_from, cast_to);
1787             check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
1788             check_lossless(cx, expr, cast_expr, cast_from, cast_to);
1789         },
1790         (false, false) => {
1791             if let (&ty::Float(FloatTy::F64), &ty::Float(FloatTy::F32)) = (&cast_from.kind(), &cast_to.kind()) {
1792                 span_lint(
1793                     cx,
1794                     CAST_POSSIBLE_TRUNCATION,
1795                     expr.span,
1796                     "casting `f64` to `f32` may truncate the value",
1797                 );
1798             }
1799             if let (&ty::Float(FloatTy::F32), &ty::Float(FloatTy::F64)) = (&cast_from.kind(), &cast_to.kind()) {
1800                 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1801             }
1802         },
1803     }
1804 }
1805
1806 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
1807     if_chain! {
1808         if let ty::RawPtr(from_ptr_ty) = &cast_from.kind();
1809         if let ty::RawPtr(to_ptr_ty) = &cast_to.kind();
1810         if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
1811         if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
1812         if from_layout.align.abi < to_layout.align.abi;
1813         // with c_void, we inherently need to trust the user
1814         if !is_c_void(cx, from_ptr_ty.ty);
1815         // when casting from a ZST, we don't know enough to properly lint
1816         if !from_layout.is_zst();
1817         then {
1818             span_lint(
1819                 cx,
1820                 CAST_PTR_ALIGNMENT,
1821                 expr.span,
1822                 &format!(
1823                     "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
1824                     cast_from,
1825                     cast_to,
1826                     from_layout.align.abi.bytes(),
1827                     to_layout.align.abi.bytes(),
1828                 ),
1829             );
1830         }
1831     }
1832 }
1833
1834 fn lint_fn_to_numeric_cast(
1835     cx: &LateContext<'_>,
1836     expr: &Expr<'_>,
1837     cast_expr: &Expr<'_>,
1838     cast_from: Ty<'_>,
1839     cast_to: Ty<'_>,
1840 ) {
1841     // We only want to check casts to `ty::Uint` or `ty::Int`
1842     match cast_to.kind() {
1843         ty::Uint(_) | ty::Int(..) => { /* continue on */ },
1844         _ => return,
1845     }
1846     match cast_from.kind() {
1847         ty::FnDef(..) | ty::FnPtr(_) => {
1848             let mut applicability = Applicability::MaybeIncorrect;
1849             let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
1850
1851             let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1852             if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
1853                 span_lint_and_sugg(
1854                     cx,
1855                     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1856                     expr.span,
1857                     &format!(
1858                         "casting function pointer `{}` to `{}`, which truncates the value",
1859                         from_snippet, cast_to
1860                     ),
1861                     "try",
1862                     format!("{} as usize", from_snippet),
1863                     applicability,
1864                 );
1865             } else if *cast_to.kind() != ty::Uint(UintTy::Usize) {
1866                 span_lint_and_sugg(
1867                     cx,
1868                     FN_TO_NUMERIC_CAST,
1869                     expr.span,
1870                     &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
1871                     "try",
1872                     format!("{} as usize", from_snippet),
1873                     applicability,
1874                 );
1875             }
1876         },
1877         _ => {},
1878     }
1879 }
1880
1881 declare_clippy_lint! {
1882     /// **What it does:** Checks for types used in structs, parameters and `let`
1883     /// declarations above a certain complexity threshold.
1884     ///
1885     /// **Why is this bad?** Too complex types make the code less readable. Consider
1886     /// using a `type` definition to simplify them.
1887     ///
1888     /// **Known problems:** None.
1889     ///
1890     /// **Example:**
1891     /// ```rust
1892     /// # use std::rc::Rc;
1893     /// struct Foo {
1894     ///     inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
1895     /// }
1896     /// ```
1897     pub TYPE_COMPLEXITY,
1898     complexity,
1899     "usage of very complex types that might be better factored into `type` definitions"
1900 }
1901
1902 pub struct TypeComplexity {
1903     threshold: u64,
1904 }
1905
1906 impl TypeComplexity {
1907     #[must_use]
1908     pub fn new(threshold: u64) -> Self {
1909         Self { threshold }
1910     }
1911 }
1912
1913 impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
1914
1915 impl<'tcx> LateLintPass<'tcx> for TypeComplexity {
1916     fn check_fn(
1917         &mut self,
1918         cx: &LateContext<'tcx>,
1919         _: FnKind<'tcx>,
1920         decl: &'tcx FnDecl<'_>,
1921         _: &'tcx Body<'_>,
1922         _: Span,
1923         _: HirId,
1924     ) {
1925         self.check_fndecl(cx, decl);
1926     }
1927
1928     fn check_struct_field(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::StructField<'_>) {
1929         // enum variants are also struct fields now
1930         self.check_type(cx, &field.ty);
1931     }
1932
1933     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
1934         match item.kind {
1935             ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
1936             // functions, enums, structs, impls and traits are covered
1937             _ => (),
1938         }
1939     }
1940
1941     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1942         match item.kind {
1943             TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
1944             TraitItemKind::Fn(FnSig { ref decl, .. }, TraitFn::Required(_)) => self.check_fndecl(cx, decl),
1945             // methods with default impl are covered by check_fn
1946             _ => (),
1947         }
1948     }
1949
1950     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
1951         match item.kind {
1952             ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
1953             // methods are covered by check_fn
1954             _ => (),
1955         }
1956     }
1957
1958     fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
1959         if let Some(ref ty) = local.ty {
1960             self.check_type(cx, ty);
1961         }
1962     }
1963 }
1964
1965 impl<'tcx> TypeComplexity {
1966     fn check_fndecl(&self, cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>) {
1967         for arg in decl.inputs {
1968             self.check_type(cx, arg);
1969         }
1970         if let FnRetTy::Return(ref ty) = decl.output {
1971             self.check_type(cx, ty);
1972         }
1973     }
1974
1975     fn check_type(&self, cx: &LateContext<'_>, ty: &hir::Ty<'_>) {
1976         if ty.span.from_expansion() {
1977             return;
1978         }
1979         let score = {
1980             let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
1981             visitor.visit_ty(ty);
1982             visitor.score
1983         };
1984
1985         if score > self.threshold {
1986             span_lint(
1987                 cx,
1988                 TYPE_COMPLEXITY,
1989                 ty.span,
1990                 "very complex type used. Consider factoring parts into `type` definitions",
1991             );
1992         }
1993     }
1994 }
1995
1996 /// Walks a type and assigns a complexity score to it.
1997 struct TypeComplexityVisitor {
1998     /// total complexity score of the type
1999     score: u64,
2000     /// current nesting level
2001     nest: u64,
2002 }
2003
2004 impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
2005     type Map = Map<'tcx>;
2006
2007     fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
2008         let (add_score, sub_nest) = match ty.kind {
2009             // _, &x and *x have only small overhead; don't mess with nesting level
2010             TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
2011
2012             // the "normal" components of a type: named types, arrays/tuples
2013             TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
2014
2015             // function types bring a lot of overhead
2016             TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
2017
2018             TyKind::TraitObject(ref param_bounds, _) => {
2019                 let has_lifetime_parameters = param_bounds.iter().any(|bound| {
2020                     bound
2021                         .bound_generic_params
2022                         .iter()
2023                         .any(|gen| matches!(gen.kind, GenericParamKind::Lifetime { .. }))
2024                 });
2025                 if has_lifetime_parameters {
2026                     // complex trait bounds like A<'a, 'b>
2027                     (50 * self.nest, 1)
2028                 } else {
2029                     // simple trait bounds like A + B
2030                     (20 * self.nest, 0)
2031                 }
2032             },
2033
2034             _ => (0, 0),
2035         };
2036         self.score += add_score;
2037         self.nest += sub_nest;
2038         walk_ty(self, ty);
2039         self.nest -= sub_nest;
2040     }
2041     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2042         NestedVisitorMap::None
2043     }
2044 }
2045
2046 declare_clippy_lint! {
2047     /// **What it does:** Checks for expressions where a character literal is cast
2048     /// to `u8` and suggests using a byte literal instead.
2049     ///
2050     /// **Why is this bad?** In general, casting values to smaller types is
2051     /// error-prone and should be avoided where possible. In the particular case of
2052     /// converting a character literal to u8, it is easy to avoid by just using a
2053     /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
2054     /// than `'a' as u8`.
2055     ///
2056     /// **Known problems:** None.
2057     ///
2058     /// **Example:**
2059     /// ```rust,ignore
2060     /// 'x' as u8
2061     /// ```
2062     ///
2063     /// A better version, using the byte literal:
2064     ///
2065     /// ```rust,ignore
2066     /// b'x'
2067     /// ```
2068     pub CHAR_LIT_AS_U8,
2069     complexity,
2070     "casting a character literal to `u8` truncates"
2071 }
2072
2073 declare_lint_pass!(CharLitAsU8 => [CHAR_LIT_AS_U8]);
2074
2075 impl<'tcx> LateLintPass<'tcx> for CharLitAsU8 {
2076     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2077         if_chain! {
2078             if !expr.span.from_expansion();
2079             if let ExprKind::Cast(e, _) = &expr.kind;
2080             if let ExprKind::Lit(l) = &e.kind;
2081             if let LitKind::Char(c) = l.node;
2082             if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
2083             then {
2084                 let mut applicability = Applicability::MachineApplicable;
2085                 let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
2086
2087                 span_lint_and_then(
2088                     cx,
2089                     CHAR_LIT_AS_U8,
2090                     expr.span,
2091                     "casting a character literal to `u8` truncates",
2092                     |diag| {
2093                         diag.note("`char` is four bytes wide, but `u8` is a single byte");
2094
2095                         if c.is_ascii() {
2096                             diag.span_suggestion(
2097                                 expr.span,
2098                                 "use a byte literal instead",
2099                                 format!("b{}", snippet),
2100                                 applicability,
2101                             );
2102                         }
2103                 });
2104             }
2105         }
2106     }
2107 }
2108
2109 declare_clippy_lint! {
2110     /// **What it does:** Checks for comparisons where one side of the relation is
2111     /// either the minimum or maximum value for its type and warns if it involves a
2112     /// case that is always true or always false. Only integer and boolean types are
2113     /// checked.
2114     ///
2115     /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
2116     /// that it is possible for `x` to be less than the minimum. Expressions like
2117     /// `max < x` are probably mistakes.
2118     ///
2119     /// **Known problems:** For `usize` the size of the current compile target will
2120     /// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
2121     /// a comparison to detect target pointer width will trigger this lint. One can
2122     /// use `mem::sizeof` and compare its value or conditional compilation
2123     /// attributes
2124     /// like `#[cfg(target_pointer_width = "64")] ..` instead.
2125     ///
2126     /// **Example:**
2127     ///
2128     /// ```rust
2129     /// let vec: Vec<isize> = Vec::new();
2130     /// if vec.len() <= 0 {}
2131     /// if 100 > i32::MAX {}
2132     /// ```
2133     pub ABSURD_EXTREME_COMPARISONS,
2134     correctness,
2135     "a comparison with a maximum or minimum value that is always true or false"
2136 }
2137
2138 declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
2139
2140 enum ExtremeType {
2141     Minimum,
2142     Maximum,
2143 }
2144
2145 struct ExtremeExpr<'a> {
2146     which: ExtremeType,
2147     expr: &'a Expr<'a>,
2148 }
2149
2150 enum AbsurdComparisonResult {
2151     AlwaysFalse,
2152     AlwaysTrue,
2153     InequalityImpossible,
2154 }
2155
2156 fn is_cast_between_fixed_and_target<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
2157     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2158         let precast_ty = cx.typeck_results().expr_ty(cast_exp);
2159         let cast_ty = cx.typeck_results().expr_ty(expr);
2160
2161         return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
2162     }
2163
2164     false
2165 }
2166
2167 fn detect_absurd_comparison<'tcx>(
2168     cx: &LateContext<'tcx>,
2169     op: BinOpKind,
2170     lhs: &'tcx Expr<'_>,
2171     rhs: &'tcx Expr<'_>,
2172 ) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
2173     use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2174     use crate::types::ExtremeType::{Maximum, Minimum};
2175     use crate::utils::comparisons::{normalize_comparison, Rel};
2176
2177     // absurd comparison only makes sense on primitive types
2178     // primitive types don't implement comparison operators with each other
2179     if cx.typeck_results().expr_ty(lhs) != cx.typeck_results().expr_ty(rhs) {
2180         return None;
2181     }
2182
2183     // comparisons between fix sized types and target sized types are considered unanalyzable
2184     if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
2185         return None;
2186     }
2187
2188     let (rel, normalized_lhs, normalized_rhs) = normalize_comparison(op, lhs, rhs)?;
2189
2190     let lx = detect_extreme_expr(cx, normalized_lhs);
2191     let rx = detect_extreme_expr(cx, normalized_rhs);
2192
2193     Some(match rel {
2194         Rel::Lt => {
2195             match (lx, rx) {
2196                 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
2197                 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
2198                 _ => return None,
2199             }
2200         },
2201         Rel::Le => {
2202             match (lx, rx) {
2203                 (Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
2204                 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
2205                 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
2206                 (_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
2207                 _ => return None,
2208             }
2209         },
2210         Rel::Ne | Rel::Eq => return None,
2211     })
2212 }
2213
2214 fn detect_extreme_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<ExtremeExpr<'tcx>> {
2215     use crate::types::ExtremeType::{Maximum, Minimum};
2216
2217     let ty = cx.typeck_results().expr_ty(expr);
2218
2219     let cv = constant(cx, cx.typeck_results(), expr)?.0;
2220
2221     let which = match (ty.kind(), cv) {
2222         (&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
2223         (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
2224             Minimum
2225         },
2226
2227         (&ty::Bool, Constant::Bool(true)) => Maximum,
2228         (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
2229             Maximum
2230         },
2231         (&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::MAX, uty) == i => Maximum,
2232
2233         _ => return None,
2234     };
2235     Some(ExtremeExpr { which, expr })
2236 }
2237
2238 impl<'tcx> LateLintPass<'tcx> for AbsurdExtremeComparisons {
2239     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2240         use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2241         use crate::types::ExtremeType::{Maximum, Minimum};
2242
2243         if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2244             if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
2245                 if !expr.span.from_expansion() {
2246                     let msg = "this comparison involving the minimum or maximum element for this \
2247                                type contains a case that is always true or always false";
2248
2249                     let conclusion = match result {
2250                         AlwaysFalse => "this comparison is always false".to_owned(),
2251                         AlwaysTrue => "this comparison is always true".to_owned(),
2252                         InequalityImpossible => format!(
2253                             "the case where the two sides are not equal never occurs, consider using `{} == {}` \
2254                              instead",
2255                             snippet(cx, lhs.span, "lhs"),
2256                             snippet(cx, rhs.span, "rhs")
2257                         ),
2258                     };
2259
2260                     let help = format!(
2261                         "because `{}` is the {} value for this type, {}",
2262                         snippet(cx, culprit.expr.span, "x"),
2263                         match culprit.which {
2264                             Minimum => "minimum",
2265                             Maximum => "maximum",
2266                         },
2267                         conclusion
2268                     );
2269
2270                     span_lint_and_help(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, None, &help);
2271                 }
2272             }
2273         }
2274     }
2275 }
2276
2277 declare_clippy_lint! {
2278     /// **What it does:** Checks for comparisons where the relation is always either
2279     /// true or false, but where one side has been upcast so that the comparison is
2280     /// necessary. Only integer types are checked.
2281     ///
2282     /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
2283     /// will mistakenly imply that it is possible for `x` to be outside the range of
2284     /// `u8`.
2285     ///
2286     /// **Known problems:**
2287     /// https://github.com/rust-lang/rust-clippy/issues/886
2288     ///
2289     /// **Example:**
2290     /// ```rust
2291     /// let x: u8 = 1;
2292     /// (x as u32) > 300;
2293     /// ```
2294     pub INVALID_UPCAST_COMPARISONS,
2295     pedantic,
2296     "a comparison involving an upcast which is always true or false"
2297 }
2298
2299 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
2300
2301 #[derive(Copy, Clone, Debug, Eq)]
2302 enum FullInt {
2303     S(i128),
2304     U(u128),
2305 }
2306
2307 impl FullInt {
2308     #[allow(clippy::cast_sign_loss)]
2309     #[must_use]
2310     fn cmp_s_u(s: i128, u: u128) -> Ordering {
2311         if s < 0 {
2312             Ordering::Less
2313         } else if u > (i128::MAX as u128) {
2314             Ordering::Greater
2315         } else {
2316             (s as u128).cmp(&u)
2317         }
2318     }
2319 }
2320
2321 impl PartialEq for FullInt {
2322     #[must_use]
2323     fn eq(&self, other: &Self) -> bool {
2324         self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
2325     }
2326 }
2327
2328 impl PartialOrd for FullInt {
2329     #[must_use]
2330     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2331         Some(match (self, other) {
2332             (&Self::S(s), &Self::S(o)) => s.cmp(&o),
2333             (&Self::U(s), &Self::U(o)) => s.cmp(&o),
2334             (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
2335             (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
2336         })
2337     }
2338 }
2339
2340 impl Ord for FullInt {
2341     #[must_use]
2342     fn cmp(&self, other: &Self) -> Ordering {
2343         self.partial_cmp(other)
2344             .expect("`partial_cmp` for FullInt can never return `None`")
2345     }
2346 }
2347
2348 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
2349     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2350         let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
2351         let cast_ty = cx.typeck_results().expr_ty(expr);
2352         // if it's a cast from i32 to u32 wrapping will invalidate all these checks
2353         if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
2354             return None;
2355         }
2356         match pre_cast_ty.kind() {
2357             ty::Int(int_ty) => Some(match int_ty {
2358                 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
2359                 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
2360                 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
2361                 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
2362                 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
2363                 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
2364             }),
2365             ty::Uint(uint_ty) => Some(match uint_ty {
2366                 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
2367                 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
2368                 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
2369                 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
2370                 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
2371                 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
2372             }),
2373             _ => None,
2374         }
2375     } else {
2376         None
2377     }
2378 }
2379
2380 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
2381     let val = constant(cx, cx.typeck_results(), expr)?.0;
2382     if let Constant::Int(const_int) = val {
2383         match *cx.typeck_results().expr_ty(expr).kind() {
2384             ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
2385             ty::Uint(_) => Some(FullInt::U(const_int)),
2386             _ => None,
2387         }
2388     } else {
2389         None
2390     }
2391 }
2392
2393 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
2394     if let ExprKind::Cast(ref cast_val, _) = expr.kind {
2395         span_lint(
2396             cx,
2397             INVALID_UPCAST_COMPARISONS,
2398             span,
2399             &format!(
2400                 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
2401                 snippet(cx, cast_val.span, "the expression"),
2402                 if always { "true" } else { "false" },
2403             ),
2404         );
2405     }
2406 }
2407
2408 fn upcast_comparison_bounds_err<'tcx>(
2409     cx: &LateContext<'tcx>,
2410     span: Span,
2411     rel: comparisons::Rel,
2412     lhs_bounds: Option<(FullInt, FullInt)>,
2413     lhs: &'tcx Expr<'_>,
2414     rhs: &'tcx Expr<'_>,
2415     invert: bool,
2416 ) {
2417     use crate::utils::comparisons::Rel;
2418
2419     if let Some((lb, ub)) = lhs_bounds {
2420         if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
2421             if rel == Rel::Eq || rel == Rel::Ne {
2422                 if norm_rhs_val < lb || norm_rhs_val > ub {
2423                     err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
2424                 }
2425             } else if match rel {
2426                 Rel::Lt => {
2427                     if invert {
2428                         norm_rhs_val < lb
2429                     } else {
2430                         ub < norm_rhs_val
2431                     }
2432                 },
2433                 Rel::Le => {
2434                     if invert {
2435                         norm_rhs_val <= lb
2436                     } else {
2437                         ub <= norm_rhs_val
2438                     }
2439                 },
2440                 Rel::Eq | Rel::Ne => unreachable!(),
2441             } {
2442                 err_upcast_comparison(cx, span, lhs, true)
2443             } else if match rel {
2444                 Rel::Lt => {
2445                     if invert {
2446                         norm_rhs_val >= ub
2447                     } else {
2448                         lb >= norm_rhs_val
2449                     }
2450                 },
2451                 Rel::Le => {
2452                     if invert {
2453                         norm_rhs_val > ub
2454                     } else {
2455                         lb > norm_rhs_val
2456                     }
2457                 },
2458                 Rel::Eq | Rel::Ne => unreachable!(),
2459             } {
2460                 err_upcast_comparison(cx, span, lhs, false)
2461             }
2462         }
2463     }
2464 }
2465
2466 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
2467     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2468         if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2469             let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
2470             let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
2471                 val
2472             } else {
2473                 return;
2474             };
2475
2476             let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
2477             let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
2478
2479             upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
2480             upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
2481         }
2482     }
2483 }
2484
2485 declare_clippy_lint! {
2486     /// **What it does:** Checks for public `impl` or `fn` missing generalization
2487     /// over different hashers and implicitly defaulting to the default hashing
2488     /// algorithm (`SipHash`).
2489     ///
2490     /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
2491     /// used with them.
2492     ///
2493     /// **Known problems:** Suggestions for replacing constructors can contain
2494     /// false-positives. Also applying suggestions can require modification of other
2495     /// pieces of code, possibly including external crates.
2496     ///
2497     /// **Example:**
2498     /// ```rust
2499     /// # use std::collections::HashMap;
2500     /// # use std::hash::{Hash, BuildHasher};
2501     /// # trait Serialize {};
2502     /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
2503     ///
2504     /// pub fn foo(map: &mut HashMap<i32, i32>) { }
2505     /// ```
2506     /// could be rewritten as
2507     /// ```rust
2508     /// # use std::collections::HashMap;
2509     /// # use std::hash::{Hash, BuildHasher};
2510     /// # trait Serialize {};
2511     /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
2512     ///
2513     /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
2514     /// ```
2515     pub IMPLICIT_HASHER,
2516     pedantic,
2517     "missing generalization over different hashers"
2518 }
2519
2520 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
2521
2522 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
2523     #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
2524     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
2525         use rustc_span::BytePos;
2526
2527         fn suggestion<'tcx>(
2528             cx: &LateContext<'tcx>,
2529             diag: &mut DiagnosticBuilder<'_>,
2530             generics_span: Span,
2531             generics_suggestion_span: Span,
2532             target: &ImplicitHasherType<'_>,
2533             vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
2534         ) {
2535             let generics_snip = snippet(cx, generics_span, "");
2536             // trim `<` `>`
2537             let generics_snip = if generics_snip.is_empty() {
2538                 ""
2539             } else {
2540                 &generics_snip[1..generics_snip.len() - 1]
2541             };
2542
2543             multispan_sugg(
2544                 diag,
2545                 "consider adding a type parameter",
2546                 vec![
2547                     (
2548                         generics_suggestion_span,
2549                         format!(
2550                             "<{}{}S: ::std::hash::BuildHasher{}>",
2551                             generics_snip,
2552                             if generics_snip.is_empty() { "" } else { ", " },
2553                             if vis.suggestions.is_empty() {
2554                                 ""
2555                             } else {
2556                                 // request users to add `Default` bound so that generic constructors can be used
2557                                 " + Default"
2558                             },
2559                         ),
2560                     ),
2561                     (
2562                         target.span(),
2563                         format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
2564                     ),
2565                 ],
2566             );
2567
2568             if !vis.suggestions.is_empty() {
2569                 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
2570             }
2571         }
2572
2573         if !cx.access_levels.is_exported(item.hir_id()) {
2574             return;
2575         }
2576
2577         match item.kind {
2578             ItemKind::Impl(ref impl_) => {
2579                 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2580                 vis.visit_ty(impl_.self_ty);
2581
2582                 for target in &vis.found {
2583                     if differing_macro_contexts(item.span, target.span()) {
2584                         return;
2585                     }
2586
2587                     let generics_suggestion_span = impl_.generics.span.substitute_dummy({
2588                         let pos = snippet_opt(cx, item.span.until(target.span()))
2589                             .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
2590                         if let Some(pos) = pos {
2591                             Span::new(pos, pos, item.span.data().ctxt)
2592                         } else {
2593                             return;
2594                         }
2595                     });
2596
2597                     let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2598                     for item in impl_.items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
2599                         ctr_vis.visit_impl_item(item);
2600                     }
2601
2602                     span_lint_and_then(
2603                         cx,
2604                         IMPLICIT_HASHER,
2605                         target.span(),
2606                         &format!(
2607                             "impl for `{}` should be generalized over different hashers",
2608                             target.type_name()
2609                         ),
2610                         move |diag| {
2611                             suggestion(cx, diag, impl_.generics.span, generics_suggestion_span, target, ctr_vis);
2612                         },
2613                     );
2614                 }
2615             },
2616             ItemKind::Fn(ref sig, ref generics, body_id) => {
2617                 let body = cx.tcx.hir().body(body_id);
2618
2619                 for ty in sig.decl.inputs {
2620                     let mut vis = ImplicitHasherTypeVisitor::new(cx);
2621                     vis.visit_ty(ty);
2622
2623                     for target in &vis.found {
2624                         if in_external_macro(cx.sess(), generics.span) {
2625                             continue;
2626                         }
2627                         let generics_suggestion_span = generics.span.substitute_dummy({
2628                             let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
2629                                 .and_then(|snip| {
2630                                     let i = snip.find("fn")?;
2631                                     Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
2632                                 })
2633                                 .expect("failed to create span for type parameters");
2634                             Span::new(pos, pos, item.span.data().ctxt)
2635                         });
2636
2637                         let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2638                         ctr_vis.visit_body(body);
2639
2640                         span_lint_and_then(
2641                             cx,
2642                             IMPLICIT_HASHER,
2643                             target.span(),
2644                             &format!(
2645                                 "parameter of type `{}` should be generalized over different hashers",
2646                                 target.type_name()
2647                             ),
2648                             move |diag| {
2649                                 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2650                             },
2651                         );
2652                     }
2653                 }
2654             },
2655             _ => {},
2656         }
2657     }
2658 }
2659
2660 enum ImplicitHasherType<'tcx> {
2661     HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
2662     HashSet(Span, Ty<'tcx>, Cow<'static, str>),
2663 }
2664
2665 impl<'tcx> ImplicitHasherType<'tcx> {
2666     /// Checks that `ty` is a target type without a `BuildHasher`.
2667     fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
2668         if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
2669             let params: Vec<_> = path
2670                 .segments
2671                 .last()
2672                 .as_ref()?
2673                 .args
2674                 .as_ref()?
2675                 .args
2676                 .iter()
2677                 .filter_map(|arg| match arg {
2678                     GenericArg::Type(ty) => Some(ty),
2679                     _ => None,
2680                 })
2681                 .collect();
2682             let params_len = params.len();
2683
2684             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
2685
2686             if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) && params_len == 2 {
2687                 Some(ImplicitHasherType::HashMap(
2688                     hir_ty.span,
2689                     ty,
2690                     snippet(cx, params[0].span, "K"),
2691                     snippet(cx, params[1].span, "V"),
2692                 ))
2693             } else if is_type_diagnostic_item(cx, ty, sym!(hashset_type)) && params_len == 1 {
2694                 Some(ImplicitHasherType::HashSet(
2695                     hir_ty.span,
2696                     ty,
2697                     snippet(cx, params[0].span, "T"),
2698                 ))
2699             } else {
2700                 None
2701             }
2702         } else {
2703             None
2704         }
2705     }
2706
2707     fn type_name(&self) -> &'static str {
2708         match *self {
2709             ImplicitHasherType::HashMap(..) => "HashMap",
2710             ImplicitHasherType::HashSet(..) => "HashSet",
2711         }
2712     }
2713
2714     fn type_arguments(&self) -> String {
2715         match *self {
2716             ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
2717             ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
2718         }
2719     }
2720
2721     fn ty(&self) -> Ty<'tcx> {
2722         match *self {
2723             ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
2724         }
2725     }
2726
2727     fn span(&self) -> Span {
2728         match *self {
2729             ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
2730         }
2731     }
2732 }
2733
2734 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
2735     cx: &'a LateContext<'tcx>,
2736     found: Vec<ImplicitHasherType<'tcx>>,
2737 }
2738
2739 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
2740     fn new(cx: &'a LateContext<'tcx>) -> Self {
2741         Self { cx, found: vec![] }
2742     }
2743 }
2744
2745 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
2746     type Map = Map<'tcx>;
2747
2748     fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
2749         if let Some(target) = ImplicitHasherType::new(self.cx, t) {
2750             self.found.push(target);
2751         }
2752
2753         walk_ty(self, t);
2754     }
2755
2756     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2757         NestedVisitorMap::None
2758     }
2759 }
2760
2761 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
2762 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2763     cx: &'a LateContext<'tcx>,
2764     maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
2765     target: &'b ImplicitHasherType<'tcx>,
2766     suggestions: BTreeMap<Span, String>,
2767 }
2768
2769 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2770     fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
2771         Self {
2772             cx,
2773             maybe_typeck_results: cx.maybe_typeck_results(),
2774             target,
2775             suggestions: BTreeMap::new(),
2776         }
2777     }
2778 }
2779
2780 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2781     type Map = Map<'tcx>;
2782
2783     fn visit_body(&mut self, body: &'tcx Body<'_>) {
2784         let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
2785         walk_body(self, body);
2786         self.maybe_typeck_results = old_maybe_typeck_results;
2787     }
2788
2789     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
2790         if_chain! {
2791             if let ExprKind::Call(ref fun, ref args) = e.kind;
2792             if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
2793             if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
2794             then {
2795                 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
2796                     return;
2797                 }
2798
2799                 if match_path(ty_path, &paths::HASHMAP) {
2800                     if method.ident.name == sym::new {
2801                         self.suggestions
2802                             .insert(e.span, "HashMap::default()".to_string());
2803                     } else if method.ident.name == sym!(with_capacity) {
2804                         self.suggestions.insert(
2805                             e.span,
2806                             format!(
2807                                 "HashMap::with_capacity_and_hasher({}, Default::default())",
2808                                 snippet(self.cx, args[0].span, "capacity"),
2809                             ),
2810                         );
2811                     }
2812                 } else if match_path(ty_path, &paths::HASHSET) {
2813                     if method.ident.name == sym::new {
2814                         self.suggestions
2815                             .insert(e.span, "HashSet::default()".to_string());
2816                     } else if method.ident.name == sym!(with_capacity) {
2817                         self.suggestions.insert(
2818                             e.span,
2819                             format!(
2820                                 "HashSet::with_capacity_and_hasher({}, Default::default())",
2821                                 snippet(self.cx, args[0].span, "capacity"),
2822                             ),
2823                         );
2824                     }
2825                 }
2826             }
2827         }
2828
2829         walk_expr(self, e);
2830     }
2831
2832     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2833         NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2834     }
2835 }
2836
2837 declare_clippy_lint! {
2838     /// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
2839     ///
2840     /// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
2841     /// `UnsafeCell` is the only way to obtain aliasable data that is considered
2842     /// mutable.
2843     ///
2844     /// **Known problems:** None.
2845     ///
2846     /// **Example:**
2847     /// ```rust,ignore
2848     /// fn x(r: &i32) {
2849     ///     unsafe {
2850     ///         *(r as *const _ as *mut _) += 1;
2851     ///     }
2852     /// }
2853     /// ```
2854     ///
2855     /// Instead consider using interior mutability types.
2856     ///
2857     /// ```rust
2858     /// use std::cell::UnsafeCell;
2859     ///
2860     /// fn x(r: &UnsafeCell<i32>) {
2861     ///     unsafe {
2862     ///         *r.get() += 1;
2863     ///     }
2864     /// }
2865     /// ```
2866     pub CAST_REF_TO_MUT,
2867     correctness,
2868     "a cast of reference to a mutable pointer"
2869 }
2870
2871 declare_lint_pass!(RefToMut => [CAST_REF_TO_MUT]);
2872
2873 impl<'tcx> LateLintPass<'tcx> for RefToMut {
2874     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2875         if_chain! {
2876             if let ExprKind::Unary(UnOp::Deref, e) = &expr.kind;
2877             if let ExprKind::Cast(e, t) = &e.kind;
2878             if let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind;
2879             if let ExprKind::Cast(e, t) = &e.kind;
2880             if let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind;
2881             if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind();
2882             then {
2883                 span_lint(
2884                     cx,
2885                     CAST_REF_TO_MUT,
2886                     expr.span,
2887                     "casting `&T` to `&mut T` may cause undefined behavior, consider instead using an `UnsafeCell`",
2888                 );
2889             }
2890         }
2891     }
2892 }
2893
2894 const PTR_AS_PTR_MSRV: RustcVersion = RustcVersion::new(1, 38, 0);
2895
2896 declare_clippy_lint! {
2897     /// **What it does:**
2898     /// Checks for `as` casts between raw pointers without changing its mutability,
2899     /// namely `*const T` to `*const U` and `*mut T` to `*mut U`.
2900     ///
2901     /// **Why is this bad?**
2902     /// Though `as` casts between raw pointers is not terrible, `pointer::cast` is safer because
2903     /// it cannot accidentally change the pointer's mutability nor cast the pointer to other types like `usize`.
2904     ///
2905     /// **Known problems:** None.
2906     ///
2907     /// **Example:**
2908     ///
2909     /// ```rust
2910     /// let ptr: *const u32 = &42_u32;
2911     /// let mut_ptr: *mut u32 = &mut 42_u32;
2912     /// let _ = ptr as *const i32;
2913     /// let _ = mut_ptr as *mut i32;
2914     /// ```
2915     /// Use instead:
2916     /// ```rust
2917     /// let ptr: *const u32 = &42_u32;
2918     /// let mut_ptr: *mut u32 = &mut 42_u32;
2919     /// let _ = ptr.cast::<i32>();
2920     /// let _ = mut_ptr.cast::<i32>();
2921     /// ```
2922     pub PTR_AS_PTR,
2923     pedantic,
2924     "casting using `as` from and to raw pointers that doesn't change its mutability, where `pointer::cast` could take the place of `as`"
2925 }
2926
2927 pub struct PtrAsPtr {
2928     msrv: Option<RustcVersion>,
2929 }
2930
2931 impl PtrAsPtr {
2932     #[must_use]
2933     pub fn new(msrv: Option<RustcVersion>) -> Self {
2934         Self { msrv }
2935     }
2936 }
2937
2938 impl_lint_pass!(PtrAsPtr => [PTR_AS_PTR]);
2939
2940 impl<'tcx> LateLintPass<'tcx> for PtrAsPtr {
2941     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2942         if !meets_msrv(self.msrv.as_ref(), &PTR_AS_PTR_MSRV) {
2943             return;
2944         }
2945
2946         if expr.span.from_expansion() {
2947             return;
2948         }
2949
2950         if_chain! {
2951             if let ExprKind::Cast(cast_expr, cast_to_hir_ty) = expr.kind;
2952             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(cast_expr), cx.typeck_results().expr_ty(expr));
2953             if let ty::RawPtr(TypeAndMut { mutbl: from_mutbl, .. }) = cast_from.kind();
2954             if let ty::RawPtr(TypeAndMut { ty: to_pointee_ty, mutbl: to_mutbl }) = cast_to.kind();
2955             if matches!((from_mutbl, to_mutbl),
2956                 (Mutability::Not, Mutability::Not) | (Mutability::Mut, Mutability::Mut));
2957             // The `U` in `pointer::cast` have to be `Sized`
2958             // as explained here: https://github.com/rust-lang/rust/issues/60602.
2959             if to_pointee_ty.is_sized(cx.tcx.at(expr.span), cx.param_env);
2960             then {
2961                 let mut applicability = Applicability::MachineApplicable;
2962                 let cast_expr_sugg = Sugg::hir_with_applicability(cx, cast_expr, "_", &mut applicability);
2963                 let turbofish = match &cast_to_hir_ty.kind {
2964                         TyKind::Infer => Cow::Borrowed(""),
2965                         TyKind::Ptr(mut_ty) if matches!(mut_ty.ty.kind, TyKind::Infer) => Cow::Borrowed(""),
2966                         _ => Cow::Owned(format!("::<{}>", to_pointee_ty)),
2967                     };
2968                 span_lint_and_sugg(
2969                     cx,
2970                     PTR_AS_PTR,
2971                     expr.span,
2972                     "`as` casting between raw pointers without changing its mutability",
2973                     "try `pointer::cast`, a safer alternative",
2974                     format!("{}.cast{}()", cast_expr_sugg.maybe_par(), turbofish),
2975                     applicability,
2976                 );
2977             }
2978         }
2979     }
2980
2981     extract_msrv_attr!(LateContext);
2982 }