clippy_lints/src/types.rs

   1 #![allow(rustc::default_hash_types)]
   2
   3 use std::borrow::Cow;
   4 use std::cmp::Ordering;
   5 use std::collections::BTreeMap;
   6
   7 use if_chain::if_chain;
   8 use rustc_ast::{FloatTy, IntTy, LitFloatType, LitIntType, LitKind, UintTy};
   9 use rustc_errors::{Applicability, DiagnosticBuilder};
  10 use rustc_hir as hir;
  11 use rustc_hir::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, InferTy, Ty, TyCtxt, TyS, TypeAndMut, TypeckResults};
  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, qpath_res, 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,
  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 { 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) = qpath_res(cx, 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 = qpath_res(cx, 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 = qpath_res(cx, 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 = qpath_res(cx, 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) = qpath_res(cx, 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!(&arg.kind, ExprKind::Match(.., MatchSource::TryDesugar))
 959                         } else {
 960                             false
 961                         }
 962                     })
 963                     .collect::<Vec<_>>();
 964                 if !args_to_recover.is_empty() {
 965                     lint_unit_args(cx, expr, &args_to_recover);
 966                 }
 967             },
 968             _ => (),
 969         }
 970     }
 971 }
 972
 973 fn fmt_stmts_and_call(
 974     cx: &LateContext<'_>,
 975     call_expr: &Expr<'_>,
 976     call_snippet: &str,
 977     args_snippets: &[impl AsRef<str>],
 978     non_empty_block_args_snippets: &[impl AsRef<str>],
 979 ) -> String {
 980     let call_expr_indent = indent_of(cx, call_expr.span).unwrap_or(0);
 981     let call_snippet_with_replacements = args_snippets
 982         .iter()
 983         .fold(call_snippet.to_owned(), |acc, arg| acc.replacen(arg.as_ref(), "()", 1));
 984
 985     let mut stmts_and_call = non_empty_block_args_snippets
 986         .iter()
 987         .map(|it| it.as_ref().to_owned())
 988         .collect::<Vec<_>>();
 989     stmts_and_call.push(call_snippet_with_replacements);
 990     stmts_and_call = stmts_and_call
 991         .into_iter()
 992         .map(|v| reindent_multiline(v.into(), true, Some(call_expr_indent)).into_owned())
 993         .collect();
 994
 995     let mut stmts_and_call_snippet = stmts_and_call.join(&format!("{}{}", ";\n", " ".repeat(call_expr_indent)));
 996     // expr is not in a block statement or result expression position, wrap in a block
 997     let parent_node = cx.tcx.hir().find(cx.tcx.hir().get_parent_node(call_expr.hir_id));
 998     if !matches!(parent_node, Some(Node::Block(_))) && !matches!(parent_node, Some(Node::Stmt(_))) {
 999         let block_indent = call_expr_indent + 4;
1000         stmts_and_call_snippet =
1001             reindent_multiline(stmts_and_call_snippet.into(), true, Some(block_indent)).into_owned();
1002         stmts_and_call_snippet = format!(
1003             "{{\n{}{}\n{}}}",
1004             " ".repeat(block_indent),
1005             &stmts_and_call_snippet,
1006             " ".repeat(call_expr_indent)
1007         );
1008     }
1009     stmts_and_call_snippet
1010 }
1011
1012 fn lint_unit_args(cx: &LateContext<'_>, expr: &Expr<'_>, args_to_recover: &[&Expr<'_>]) {
1013     let mut applicability = Applicability::MachineApplicable;
1014     let (singular, plural) = if args_to_recover.len() > 1 {
1015         ("", "s")
1016     } else {
1017         ("a ", "")
1018     };
1019     span_lint_and_then(
1020         cx,
1021         UNIT_ARG,
1022         expr.span,
1023         &format!("passing {}unit value{} to a function", singular, plural),
1024         |db| {
1025             let mut or = "";
1026             args_to_recover
1027                 .iter()
1028                 .filter_map(|arg| {
1029                     if_chain! {
1030                         if let ExprKind::Block(block, _) = arg.kind;
1031                         if block.expr.is_none();
1032                         if let Some(last_stmt) = block.stmts.iter().last();
1033                         if let StmtKind::Semi(last_expr) = last_stmt.kind;
1034                         if let Some(snip) = snippet_opt(cx, last_expr.span);
1035                         then {
1036                             Some((
1037                                 last_stmt.span,
1038                                 snip,
1039                             ))
1040                         }
1041                         else {
1042                             None
1043                         }
1044                     }
1045                 })
1046                 .for_each(|(span, sugg)| {
1047                     db.span_suggestion(
1048                         span,
1049                         "remove the semicolon from the last statement in the block",
1050                         sugg,
1051                         Applicability::MaybeIncorrect,
1052                     );
1053                     or = "or ";
1054                     applicability = Applicability::MaybeIncorrect;
1055                 });
1056
1057             let arg_snippets: Vec<String> = args_to_recover
1058                 .iter()
1059                 .filter_map(|arg| snippet_opt(cx, arg.span))
1060                 .collect();
1061             let arg_snippets_without_empty_blocks: Vec<String> = args_to_recover
1062                 .iter()
1063                 .filter(|arg| !is_empty_block(arg))
1064                 .filter_map(|arg| snippet_opt(cx, arg.span))
1065                 .collect();
1066
1067             if let Some(call_snippet) = snippet_opt(cx, expr.span) {
1068                 let sugg = fmt_stmts_and_call(
1069                     cx,
1070                     expr,
1071                     &call_snippet,
1072                     &arg_snippets,
1073                     &arg_snippets_without_empty_blocks,
1074                 );
1075
1076                 if arg_snippets_without_empty_blocks.is_empty() {
1077                     db.multipart_suggestion(
1078                         &format!("use {}unit literal{} instead", singular, plural),
1079                         args_to_recover
1080                             .iter()
1081                             .map(|arg| (arg.span, "()".to_string()))
1082                             .collect::<Vec<_>>(),
1083                         applicability,
1084                     );
1085                 } else {
1086                     let plural = arg_snippets_without_empty_blocks.len() > 1;
1087                     let empty_or_s = if plural { "s" } else { "" };
1088                     let it_or_them = if plural { "them" } else { "it" };
1089                     db.span_suggestion(
1090                         expr.span,
1091                         &format!(
1092                             "{}move the expression{} in front of the call and replace {} with the unit literal `()`",
1093                             or, empty_or_s, it_or_them
1094                         ),
1095                         sugg,
1096                         applicability,
1097                     );
1098                 }
1099             }
1100         },
1101     );
1102 }
1103
1104 fn is_empty_block(expr: &Expr<'_>) -> bool {
1105     matches!(
1106         expr.kind,
1107         ExprKind::Block(
1108             Block {
1109                 stmts: &[],
1110                 expr: None,
1111                 ..
1112             },
1113             _,
1114         )
1115     )
1116 }
1117
1118 fn is_questionmark_desugar_marked_call(expr: &Expr<'_>) -> bool {
1119     use rustc_span::hygiene::DesugaringKind;
1120     if let ExprKind::Call(ref callee, _) = expr.kind {
1121         callee.span.is_desugaring(DesugaringKind::QuestionMark)
1122     } else {
1123         false
1124     }
1125 }
1126
1127 fn is_unit(ty: Ty<'_>) -> bool {
1128     matches!(ty.kind(), ty::Tuple(slice) if slice.is_empty())
1129 }
1130
1131 fn is_unit_literal(expr: &Expr<'_>) -> bool {
1132     matches!(expr.kind, ExprKind::Tup(ref slice) if slice.is_empty())
1133 }
1134
1135 declare_clippy_lint! {
1136     /// **What it does:** Checks for casts from any numerical to a float type where
1137     /// the receiving type cannot store all values from the original type without
1138     /// rounding errors. This possible rounding is to be expected, so this lint is
1139     /// `Allow` by default.
1140     ///
1141     /// Basically, this warns on casting any integer with 32 or more bits to `f32`
1142     /// or any 64-bit integer to `f64`.
1143     ///
1144     /// **Why is this bad?** It's not bad at all. But in some applications it can be
1145     /// helpful to know where precision loss can take place. This lint can help find
1146     /// those places in the code.
1147     ///
1148     /// **Known problems:** None.
1149     ///
1150     /// **Example:**
1151     /// ```rust
1152     /// let x = u64::MAX;
1153     /// x as f64;
1154     /// ```
1155     pub CAST_PRECISION_LOSS,
1156     pedantic,
1157     "casts that cause loss of precision, e.g., `x as f32` where `x: u64`"
1158 }
1159
1160 declare_clippy_lint! {
1161     /// **What it does:** Checks for casts from a signed to an unsigned numerical
1162     /// type. In this case, negative values wrap around to large positive values,
1163     /// which can be quite surprising in practice. However, as the cast works as
1164     /// defined, this lint is `Allow` by default.
1165     ///
1166     /// **Why is this bad?** Possibly surprising results. You can activate this lint
1167     /// as a one-time check to see where numerical wrapping can arise.
1168     ///
1169     /// **Known problems:** None.
1170     ///
1171     /// **Example:**
1172     /// ```rust
1173     /// let y: i8 = -1;
1174     /// y as u128; // will return 18446744073709551615
1175     /// ```
1176     pub CAST_SIGN_LOSS,
1177     pedantic,
1178     "casts from signed types to unsigned types, e.g., `x as u32` where `x: i32`"
1179 }
1180
1181 declare_clippy_lint! {
1182     /// **What it does:** Checks for casts between numerical types that may
1183     /// truncate large values. This is expected behavior, so the cast is `Allow` by
1184     /// default.
1185     ///
1186     /// **Why is this bad?** In some problem domains, it is good practice to avoid
1187     /// truncation. This lint can be activated to help assess where additional
1188     /// checks could be beneficial.
1189     ///
1190     /// **Known problems:** None.
1191     ///
1192     /// **Example:**
1193     /// ```rust
1194     /// fn as_u8(x: u64) -> u8 {
1195     ///     x as u8
1196     /// }
1197     /// ```
1198     pub CAST_POSSIBLE_TRUNCATION,
1199     pedantic,
1200     "casts that may cause truncation of the value, e.g., `x as u8` where `x: u32`, or `x as i32` where `x: f32`"
1201 }
1202
1203 declare_clippy_lint! {
1204     /// **What it does:** Checks for casts from an unsigned type to a signed type of
1205     /// the same size. Performing such a cast is a 'no-op' for the compiler,
1206     /// i.e., nothing is changed at the bit level, and the binary representation of
1207     /// the value is reinterpreted. This can cause wrapping if the value is too big
1208     /// for the target signed type. However, the cast works as defined, so this lint
1209     /// is `Allow` by default.
1210     ///
1211     /// **Why is this bad?** While such a cast is not bad in itself, the results can
1212     /// be surprising when this is not the intended behavior, as demonstrated by the
1213     /// example below.
1214     ///
1215     /// **Known problems:** None.
1216     ///
1217     /// **Example:**
1218     /// ```rust
1219     /// u32::MAX as i32; // will yield a value of `-1`
1220     /// ```
1221     pub CAST_POSSIBLE_WRAP,
1222     pedantic,
1223     "casts that may cause wrapping around the value, e.g., `x as i32` where `x: u32` and `x > i32::MAX`"
1224 }
1225
1226 declare_clippy_lint! {
1227     /// **What it does:** Checks for casts between numerical types that may
1228     /// be replaced by safe conversion functions.
1229     ///
1230     /// **Why is this bad?** Rust's `as` keyword will perform many kinds of
1231     /// conversions, including silently lossy conversions. Conversion functions such
1232     /// as `i32::from` will only perform lossless conversions. Using the conversion
1233     /// functions prevents conversions from turning into silent lossy conversions if
1234     /// the types of the input expressions ever change, and make it easier for
1235     /// people reading the code to know that the conversion is lossless.
1236     ///
1237     /// **Known problems:** None.
1238     ///
1239     /// **Example:**
1240     /// ```rust
1241     /// fn as_u64(x: u8) -> u64 {
1242     ///     x as u64
1243     /// }
1244     /// ```
1245     ///
1246     /// Using `::from` would look like this:
1247     ///
1248     /// ```rust
1249     /// fn as_u64(x: u8) -> u64 {
1250     ///     u64::from(x)
1251     /// }
1252     /// ```
1253     pub CAST_LOSSLESS,
1254     pedantic,
1255     "casts using `as` that are known to be lossless, e.g., `x as u64` where `x: u8`"
1256 }
1257
1258 declare_clippy_lint! {
1259     /// **What it does:** Checks for casts to the same type, casts of int literals to integer types
1260     /// and casts of float literals to float types.
1261     ///
1262     /// **Why is this bad?** It's just unnecessary.
1263     ///
1264     /// **Known problems:** None.
1265     ///
1266     /// **Example:**
1267     /// ```rust
1268     /// let _ = 2i32 as i32;
1269     /// let _ = 0.5 as f32;
1270     /// ```
1271     ///
1272     /// Better:
1273     ///
1274     /// ```rust
1275     /// let _ = 2_i32;
1276     /// let _ = 0.5_f32;
1277     /// ```
1278     pub UNNECESSARY_CAST,
1279     complexity,
1280     "cast to the same type, e.g., `x as i32` where `x: i32`"
1281 }
1282
1283 declare_clippy_lint! {
1284     /// **What it does:** Checks for casts, using `as` or `pointer::cast`,
1285     /// from a less-strictly-aligned pointer to a more-strictly-aligned pointer
1286     ///
1287     /// **Why is this bad?** Dereferencing the resulting pointer may be undefined
1288     /// behavior.
1289     ///
1290     /// **Known problems:** Using `std::ptr::read_unaligned` and `std::ptr::write_unaligned` or similar
1291     /// on the resulting pointer is fine. Is over-zealous: Casts with manual alignment checks or casts like
1292     /// u64-> u8 -> u16 can be fine. Miri is able to do a more in-depth analysis.
1293     ///
1294     /// **Example:**
1295     /// ```rust
1296     /// let _ = (&1u8 as *const u8) as *const u16;
1297     /// let _ = (&mut 1u8 as *mut u8) as *mut u16;
1298     ///
1299     /// (&1u8 as *const u8).cast::<u16>();
1300     /// (&mut 1u8 as *mut u8).cast::<u16>();
1301     /// ```
1302     pub CAST_PTR_ALIGNMENT,
1303     pedantic,
1304     "cast from a pointer to a more-strictly-aligned pointer"
1305 }
1306
1307 declare_clippy_lint! {
1308     /// **What it does:** Checks for casts of function pointers to something other than usize
1309     ///
1310     /// **Why is this bad?**
1311     /// Casting a function pointer to anything other than usize/isize is not portable across
1312     /// architectures, because you end up losing bits if the target type is too small or end up with a
1313     /// bunch of extra bits that waste space and add more instructions to the final binary than
1314     /// strictly necessary for the problem
1315     ///
1316     /// Casting to isize also doesn't make sense since there are no signed addresses.
1317     ///
1318     /// **Example**
1319     ///
1320     /// ```rust
1321     /// // Bad
1322     /// fn fun() -> i32 { 1 }
1323     /// let a = fun as i64;
1324     ///
1325     /// // Good
1326     /// fn fun2() -> i32 { 1 }
1327     /// let a = fun2 as usize;
1328     /// ```
1329     pub FN_TO_NUMERIC_CAST,
1330     style,
1331     "casting a function pointer to a numeric type other than usize"
1332 }
1333
1334 declare_clippy_lint! {
1335     /// **What it does:** Checks for casts of a function pointer to a numeric type not wide enough to
1336     /// store address.
1337     ///
1338     /// **Why is this bad?**
1339     /// Such a cast discards some bits of the function's address. If this is intended, it would be more
1340     /// clearly expressed by casting to usize first, then casting the usize to the intended type (with
1341     /// a comment) to perform the truncation.
1342     ///
1343     /// **Example**
1344     ///
1345     /// ```rust
1346     /// // Bad
1347     /// fn fn1() -> i16 {
1348     ///     1
1349     /// };
1350     /// let _ = fn1 as i32;
1351     ///
1352     /// // Better: Cast to usize first, then comment with the reason for the truncation
1353     /// fn fn2() -> i16 {
1354     ///     1
1355     /// };
1356     /// let fn_ptr = fn2 as usize;
1357     /// let fn_ptr_truncated = fn_ptr as i32;
1358     /// ```
1359     pub FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1360     style,
1361     "casting a function pointer to a numeric type not wide enough to store the address"
1362 }
1363
1364 /// Returns the size in bits of an integral type.
1365 /// Will return 0 if the type is not an int or uint variant
1366 fn int_ty_to_nbits(typ: Ty<'_>, tcx: TyCtxt<'_>) -> u64 {
1367     match typ.kind() {
1368         ty::Int(i) => match i {
1369             IntTy::Isize => tcx.data_layout.pointer_size.bits(),
1370             IntTy::I8 => 8,
1371             IntTy::I16 => 16,
1372             IntTy::I32 => 32,
1373             IntTy::I64 => 64,
1374             IntTy::I128 => 128,
1375         },
1376         ty::Uint(i) => match i {
1377             UintTy::Usize => tcx.data_layout.pointer_size.bits(),
1378             UintTy::U8 => 8,
1379             UintTy::U16 => 16,
1380             UintTy::U32 => 32,
1381             UintTy::U64 => 64,
1382             UintTy::U128 => 128,
1383         },
1384         _ => 0,
1385     }
1386 }
1387
1388 fn is_isize_or_usize(typ: Ty<'_>) -> bool {
1389     matches!(typ.kind(), ty::Int(IntTy::Isize) | ty::Uint(UintTy::Usize))
1390 }
1391
1392 fn span_precision_loss_lint(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to_f64: bool) {
1393     let mantissa_nbits = if cast_to_f64 { 52 } else { 23 };
1394     let arch_dependent = is_isize_or_usize(cast_from) && cast_to_f64;
1395     let arch_dependent_str = "on targets with 64-bit wide pointers ";
1396     let from_nbits_str = if arch_dependent {
1397         "64".to_owned()
1398     } else if is_isize_or_usize(cast_from) {
1399         "32 or 64".to_owned()
1400     } else {
1401         int_ty_to_nbits(cast_from, cx.tcx).to_string()
1402     };
1403     span_lint(
1404         cx,
1405         CAST_PRECISION_LOSS,
1406         expr.span,
1407         &format!(
1408             "casting `{0}` to `{1}` causes a loss of precision {2}(`{0}` is {3} bits wide, \
1409              but `{1}`'s mantissa is only {4} bits wide)",
1410             cast_from,
1411             if cast_to_f64 { "f64" } else { "f32" },
1412             if arch_dependent { arch_dependent_str } else { "" },
1413             from_nbits_str,
1414             mantissa_nbits
1415         ),
1416     );
1417 }
1418
1419 fn should_strip_parens(op: &Expr<'_>, snip: &str) -> bool {
1420     if let ExprKind::Binary(_, _, _) = op.kind {
1421         if snip.starts_with('(') && snip.ends_with(')') {
1422             return true;
1423         }
1424     }
1425     false
1426 }
1427
1428 fn span_lossless_lint(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1429     // Do not suggest using From in consts/statics until it is valid to do so (see #2267).
1430     if in_constant(cx, expr.hir_id) {
1431         return;
1432     }
1433     // The suggestion is to use a function call, so if the original expression
1434     // has parens on the outside, they are no longer needed.
1435     let mut applicability = Applicability::MachineApplicable;
1436     let opt = snippet_opt(cx, op.span);
1437     let sugg = opt.as_ref().map_or_else(
1438         || {
1439             applicability = Applicability::HasPlaceholders;
1440             ".."
1441         },
1442         |snip| {
1443             if should_strip_parens(op, snip) {
1444                 &snip[1..snip.len() - 1]
1445             } else {
1446                 snip.as_str()
1447             }
1448         },
1449     );
1450
1451     span_lint_and_sugg(
1452         cx,
1453         CAST_LOSSLESS,
1454         expr.span,
1455         &format!(
1456             "casting `{}` to `{}` may become silently lossy if you later change the type",
1457             cast_from, cast_to
1458         ),
1459         "try",
1460         format!("{}::from({})", cast_to, sugg),
1461         applicability,
1462     );
1463 }
1464
1465 enum ArchSuffix {
1466     _32,
1467     _64,
1468     None,
1469 }
1470
1471 fn check_loss_of_sign(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1472     if !cast_from.is_signed() || cast_to.is_signed() {
1473         return;
1474     }
1475
1476     // don't lint for positive constants
1477     let const_val = constant(cx, &cx.typeck_results(), op);
1478     if_chain! {
1479         if let Some((Constant::Int(n), _)) = const_val;
1480         if let ty::Int(ity) = *cast_from.kind();
1481         if sext(cx.tcx, n, ity) >= 0;
1482         then {
1483             return
1484         }
1485     }
1486
1487     // don't lint for the result of methods that always return non-negative values
1488     if let ExprKind::MethodCall(ref path, _, _, _) = op.kind {
1489         let mut method_name = path.ident.name.as_str();
1490         let allowed_methods = ["abs", "checked_abs", "rem_euclid", "checked_rem_euclid"];
1491
1492         if_chain! {
1493             if method_name == "unwrap";
1494             if let Some(arglist) = method_chain_args(op, &["unwrap"]);
1495             if let ExprKind::MethodCall(ref inner_path, _, _, _) = &arglist[0][0].kind;
1496             then {
1497                 method_name = inner_path.ident.name.as_str();
1498             }
1499         }
1500
1501         if allowed_methods.iter().any(|&name| method_name == name) {
1502             return;
1503         }
1504     }
1505
1506     span_lint(
1507         cx,
1508         CAST_SIGN_LOSS,
1509         expr.span,
1510         &format!(
1511             "casting `{}` to `{}` may lose the sign of the value",
1512             cast_from, cast_to
1513         ),
1514     );
1515 }
1516
1517 fn check_truncation_and_wrapping(cx: &LateContext<'_>, expr: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1518     let arch_64_suffix = " on targets with 64-bit wide pointers";
1519     let arch_32_suffix = " on targets with 32-bit wide pointers";
1520     let cast_unsigned_to_signed = !cast_from.is_signed() && cast_to.is_signed();
1521     let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1522     let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1523     let (span_truncation, suffix_truncation, span_wrap, suffix_wrap) =
1524         match (is_isize_or_usize(cast_from), is_isize_or_usize(cast_to)) {
1525             (true, true) | (false, false) => (
1526                 to_nbits < from_nbits,
1527                 ArchSuffix::None,
1528                 to_nbits == from_nbits && cast_unsigned_to_signed,
1529                 ArchSuffix::None,
1530             ),
1531             (true, false) => (
1532                 to_nbits <= 32,
1533                 if to_nbits == 32 {
1534                     ArchSuffix::_64
1535                 } else {
1536                     ArchSuffix::None
1537                 },
1538                 to_nbits <= 32 && cast_unsigned_to_signed,
1539                 ArchSuffix::_32,
1540             ),
1541             (false, true) => (
1542                 from_nbits == 64,
1543                 ArchSuffix::_32,
1544                 cast_unsigned_to_signed,
1545                 if from_nbits == 64 {
1546                     ArchSuffix::_64
1547                 } else {
1548                     ArchSuffix::_32
1549                 },
1550             ),
1551         };
1552     if span_truncation {
1553         span_lint(
1554             cx,
1555             CAST_POSSIBLE_TRUNCATION,
1556             expr.span,
1557             &format!(
1558                 "casting `{}` to `{}` may truncate the value{}",
1559                 cast_from,
1560                 cast_to,
1561                 match suffix_truncation {
1562                     ArchSuffix::_32 => arch_32_suffix,
1563                     ArchSuffix::_64 => arch_64_suffix,
1564                     ArchSuffix::None => "",
1565                 }
1566             ),
1567         );
1568     }
1569     if span_wrap {
1570         span_lint(
1571             cx,
1572             CAST_POSSIBLE_WRAP,
1573             expr.span,
1574             &format!(
1575                 "casting `{}` to `{}` may wrap around the value{}",
1576                 cast_from,
1577                 cast_to,
1578                 match suffix_wrap {
1579                     ArchSuffix::_32 => arch_32_suffix,
1580                     ArchSuffix::_64 => arch_64_suffix,
1581                     ArchSuffix::None => "",
1582                 }
1583             ),
1584         );
1585     }
1586 }
1587
1588 fn check_lossless(cx: &LateContext<'_>, expr: &Expr<'_>, op: &Expr<'_>, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1589     let cast_signed_to_unsigned = cast_from.is_signed() && !cast_to.is_signed();
1590     let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1591     let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1592     if !is_isize_or_usize(cast_from) && !is_isize_or_usize(cast_to) && from_nbits < to_nbits && !cast_signed_to_unsigned
1593     {
1594         span_lossless_lint(cx, expr, op, cast_from, cast_to);
1595     }
1596 }
1597
1598 declare_lint_pass!(Casts => [
1599     CAST_PRECISION_LOSS,
1600     CAST_SIGN_LOSS,
1601     CAST_POSSIBLE_TRUNCATION,
1602     CAST_POSSIBLE_WRAP,
1603     CAST_LOSSLESS,
1604     UNNECESSARY_CAST,
1605     CAST_PTR_ALIGNMENT,
1606     FN_TO_NUMERIC_CAST,
1607     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1608 ]);
1609
1610 // Check if the given type is either `core::ffi::c_void` or
1611 // one of the platform specific `libc::<platform>::c_void` of libc.
1612 fn is_c_void(cx: &LateContext<'_>, ty: Ty<'_>) -> bool {
1613     if let ty::Adt(adt, _) = ty.kind() {
1614         let names = cx.get_def_path(adt.did);
1615
1616         if names.is_empty() {
1617             return false;
1618         }
1619         if names[0] == sym::libc || names[0] == sym::core && *names.last().unwrap() == sym!(c_void) {
1620             return true;
1621         }
1622     }
1623     false
1624 }
1625
1626 /// Returns the mantissa bits wide of a fp type.
1627 /// Will return 0 if the type is not a fp
1628 fn fp_ty_mantissa_nbits(typ: Ty<'_>) -> u32 {
1629     match typ.kind() {
1630         ty::Float(FloatTy::F32) => 23,
1631         ty::Float(FloatTy::F64) | ty::Infer(InferTy::FloatVar(_)) => 52,
1632         _ => 0,
1633     }
1634 }
1635
1636 impl<'tcx> LateLintPass<'tcx> for Casts {
1637     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
1638         if expr.span.from_expansion() {
1639             return;
1640         }
1641         if let ExprKind::Cast(ref ex, cast_to) = expr.kind {
1642             if is_hir_ty_cfg_dependant(cx, cast_to) {
1643                 return;
1644             }
1645             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(ex), cx.typeck_results().expr_ty(expr));
1646             lint_fn_to_numeric_cast(cx, expr, ex, cast_from, cast_to);
1647             if let Some(lit) = get_numeric_literal(ex) {
1648                 let literal_str = snippet_opt(cx, ex.span).unwrap_or_default();
1649
1650                 if_chain! {
1651                     if let LitKind::Int(n, _) = lit.node;
1652                     if let Some(src) = snippet_opt(cx, lit.span);
1653                     if cast_to.is_floating_point();
1654                     if let Some(num_lit) = NumericLiteral::from_lit_kind(&src, &lit.node);
1655                     let from_nbits = 128 - n.leading_zeros();
1656                     let to_nbits = fp_ty_mantissa_nbits(cast_to);
1657                     if from_nbits != 0 && to_nbits != 0 && from_nbits <= to_nbits && num_lit.is_decimal();
1658                     then {
1659                         let literal_str = if is_unary_neg(ex) { format!("-{}", num_lit.integer) } else { num_lit.integer.into() };
1660                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1661                         return;
1662                     }
1663                 }
1664
1665                 match lit.node {
1666                     LitKind::Int(_, LitIntType::Unsuffixed) if cast_to.is_integral() => {
1667                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1668                     },
1669                     LitKind::Float(_, LitFloatType::Unsuffixed) if cast_to.is_floating_point() => {
1670                         show_unnecessary_cast(cx, expr, &literal_str, cast_from, cast_to);
1671                     },
1672                     LitKind::Int(_, LitIntType::Unsuffixed) | LitKind::Float(_, LitFloatType::Unsuffixed) => {},
1673                     _ => {
1674                         if cast_from.kind() == cast_to.kind() && !in_external_macro(cx.sess(), expr.span) {
1675                             span_lint(
1676                                 cx,
1677                                 UNNECESSARY_CAST,
1678                                 expr.span,
1679                                 &format!(
1680                                     "casting to the same type is unnecessary (`{}` -> `{}`)",
1681                                     cast_from, cast_to
1682                                 ),
1683                             );
1684                         }
1685                     },
1686                 }
1687             }
1688             if cast_from.is_numeric() && cast_to.is_numeric() && !in_external_macro(cx.sess(), expr.span) {
1689                 lint_numeric_casts(cx, expr, ex, cast_from, cast_to);
1690             }
1691
1692             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1693         } else if let ExprKind::MethodCall(method_path, _, args, _) = expr.kind {
1694             if method_path.ident.name != sym!(cast) {
1695                 return;
1696             }
1697             if_chain! {
1698                 if let Some(generic_args) = method_path.args;
1699                 if let [GenericArg::Type(cast_to)] = generic_args.args;
1700                 // There probably is no obvious reason to do this, just to be consistent with `as` cases.
1701                 if is_hir_ty_cfg_dependant(cx, cast_to);
1702                 then {
1703                     return;
1704                 }
1705             }
1706             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(&args[0]), cx.typeck_results().expr_ty(expr));
1707             lint_cast_ptr_alignment(cx, expr, cast_from, cast_to);
1708         }
1709     }
1710 }
1711
1712 fn is_unary_neg(expr: &Expr<'_>) -> bool {
1713     matches!(expr.kind, ExprKind::Unary(UnOp::UnNeg, _))
1714 }
1715
1716 fn get_numeric_literal<'e>(expr: &'e Expr<'e>) -> Option<&'e Lit> {
1717     match expr.kind {
1718         ExprKind::Lit(ref lit) => Some(lit),
1719         ExprKind::Unary(UnOp::UnNeg, e) => {
1720             if let ExprKind::Lit(ref lit) = e.kind {
1721                 Some(lit)
1722             } else {
1723                 None
1724             }
1725         },
1726         _ => None,
1727     }
1728 }
1729
1730 fn show_unnecessary_cast(cx: &LateContext<'_>, expr: &Expr<'_>, literal_str: &str, cast_from: Ty<'_>, cast_to: Ty<'_>) {
1731     let literal_kind_name = if cast_from.is_integral() { "integer" } else { "float" };
1732     span_lint_and_sugg(
1733         cx,
1734         UNNECESSARY_CAST,
1735         expr.span,
1736         &format!("casting {} literal to `{}` is unnecessary", literal_kind_name, cast_to),
1737         "try",
1738         format!("{}_{}", literal_str.trim_end_matches('.'), cast_to),
1739         Applicability::MachineApplicable,
1740     );
1741 }
1742
1743 fn lint_numeric_casts<'tcx>(
1744     cx: &LateContext<'tcx>,
1745     expr: &Expr<'tcx>,
1746     cast_expr: &Expr<'_>,
1747     cast_from: Ty<'tcx>,
1748     cast_to: Ty<'tcx>,
1749 ) {
1750     match (cast_from.is_integral(), cast_to.is_integral()) {
1751         (true, false) => {
1752             let from_nbits = int_ty_to_nbits(cast_from, cx.tcx);
1753             let to_nbits = if let ty::Float(FloatTy::F32) = cast_to.kind() {
1754                 32
1755             } else {
1756                 64
1757             };
1758             if is_isize_or_usize(cast_from) || from_nbits >= to_nbits {
1759                 span_precision_loss_lint(cx, expr, cast_from, to_nbits == 64);
1760             }
1761             if from_nbits < to_nbits {
1762                 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1763             }
1764         },
1765         (false, true) => {
1766             span_lint(
1767                 cx,
1768                 CAST_POSSIBLE_TRUNCATION,
1769                 expr.span,
1770                 &format!("casting `{}` to `{}` may truncate the value", cast_from, cast_to),
1771             );
1772             if !cast_to.is_signed() {
1773                 span_lint(
1774                     cx,
1775                     CAST_SIGN_LOSS,
1776                     expr.span,
1777                     &format!(
1778                         "casting `{}` to `{}` may lose the sign of the value",
1779                         cast_from, cast_to
1780                     ),
1781                 );
1782             }
1783         },
1784         (true, true) => {
1785             check_loss_of_sign(cx, expr, cast_expr, cast_from, cast_to);
1786             check_truncation_and_wrapping(cx, expr, cast_from, cast_to);
1787             check_lossless(cx, expr, cast_expr, cast_from, cast_to);
1788         },
1789         (false, false) => {
1790             if let (&ty::Float(FloatTy::F64), &ty::Float(FloatTy::F32)) = (&cast_from.kind(), &cast_to.kind()) {
1791                 span_lint(
1792                     cx,
1793                     CAST_POSSIBLE_TRUNCATION,
1794                     expr.span,
1795                     "casting `f64` to `f32` may truncate the value",
1796                 );
1797             }
1798             if let (&ty::Float(FloatTy::F32), &ty::Float(FloatTy::F64)) = (&cast_from.kind(), &cast_to.kind()) {
1799                 span_lossless_lint(cx, expr, cast_expr, cast_from, cast_to);
1800             }
1801         },
1802     }
1803 }
1804
1805 fn lint_cast_ptr_alignment<'tcx>(cx: &LateContext<'tcx>, expr: &Expr<'_>, cast_from: Ty<'tcx>, cast_to: Ty<'tcx>) {
1806     if_chain! {
1807         if let ty::RawPtr(from_ptr_ty) = &cast_from.kind();
1808         if let ty::RawPtr(to_ptr_ty) = &cast_to.kind();
1809         if let Ok(from_layout) = cx.layout_of(from_ptr_ty.ty);
1810         if let Ok(to_layout) = cx.layout_of(to_ptr_ty.ty);
1811         if from_layout.align.abi < to_layout.align.abi;
1812         // with c_void, we inherently need to trust the user
1813         if !is_c_void(cx, from_ptr_ty.ty);
1814         // when casting from a ZST, we don't know enough to properly lint
1815         if !from_layout.is_zst();
1816         then {
1817             span_lint(
1818                 cx,
1819                 CAST_PTR_ALIGNMENT,
1820                 expr.span,
1821                 &format!(
1822                     "casting from `{}` to a more-strictly-aligned pointer (`{}`) ({} < {} bytes)",
1823                     cast_from,
1824                     cast_to,
1825                     from_layout.align.abi.bytes(),
1826                     to_layout.align.abi.bytes(),
1827                 ),
1828             );
1829         }
1830     }
1831 }
1832
1833 fn lint_fn_to_numeric_cast(
1834     cx: &LateContext<'_>,
1835     expr: &Expr<'_>,
1836     cast_expr: &Expr<'_>,
1837     cast_from: Ty<'_>,
1838     cast_to: Ty<'_>,
1839 ) {
1840     // We only want to check casts to `ty::Uint` or `ty::Int`
1841     match cast_to.kind() {
1842         ty::Uint(_) | ty::Int(..) => { /* continue on */ },
1843         _ => return,
1844     }
1845     match cast_from.kind() {
1846         ty::FnDef(..) | ty::FnPtr(_) => {
1847             let mut applicability = Applicability::MaybeIncorrect;
1848             let from_snippet = snippet_with_applicability(cx, cast_expr.span, "x", &mut applicability);
1849
1850             let to_nbits = int_ty_to_nbits(cast_to, cx.tcx);
1851             if to_nbits < cx.tcx.data_layout.pointer_size.bits() {
1852                 span_lint_and_sugg(
1853                     cx,
1854                     FN_TO_NUMERIC_CAST_WITH_TRUNCATION,
1855                     expr.span,
1856                     &format!(
1857                         "casting function pointer `{}` to `{}`, which truncates the value",
1858                         from_snippet, cast_to
1859                     ),
1860                     "try",
1861                     format!("{} as usize", from_snippet),
1862                     applicability,
1863                 );
1864             } else if *cast_to.kind() != ty::Uint(UintTy::Usize) {
1865                 span_lint_and_sugg(
1866                     cx,
1867                     FN_TO_NUMERIC_CAST,
1868                     expr.span,
1869                     &format!("casting function pointer `{}` to `{}`", from_snippet, cast_to),
1870                     "try",
1871                     format!("{} as usize", from_snippet),
1872                     applicability,
1873                 );
1874             }
1875         },
1876         _ => {},
1877     }
1878 }
1879
1880 declare_clippy_lint! {
1881     /// **What it does:** Checks for types used in structs, parameters and `let`
1882     /// declarations above a certain complexity threshold.
1883     ///
1884     /// **Why is this bad?** Too complex types make the code less readable. Consider
1885     /// using a `type` definition to simplify them.
1886     ///
1887     /// **Known problems:** None.
1888     ///
1889     /// **Example:**
1890     /// ```rust
1891     /// # use std::rc::Rc;
1892     /// struct Foo {
1893     ///     inner: Rc<Vec<Vec<Box<(u32, u32, u32, u32)>>>>,
1894     /// }
1895     /// ```
1896     pub TYPE_COMPLEXITY,
1897     complexity,
1898     "usage of very complex types that might be better factored into `type` definitions"
1899 }
1900
1901 pub struct TypeComplexity {
1902     threshold: u64,
1903 }
1904
1905 impl TypeComplexity {
1906     #[must_use]
1907     pub fn new(threshold: u64) -> Self {
1908         Self { threshold }
1909     }
1910 }
1911
1912 impl_lint_pass!(TypeComplexity => [TYPE_COMPLEXITY]);
1913
1914 impl<'tcx> LateLintPass<'tcx> for TypeComplexity {
1915     fn check_fn(
1916         &mut self,
1917         cx: &LateContext<'tcx>,
1918         _: FnKind<'tcx>,
1919         decl: &'tcx FnDecl<'_>,
1920         _: &'tcx Body<'_>,
1921         _: Span,
1922         _: HirId,
1923     ) {
1924         self.check_fndecl(cx, decl);
1925     }
1926
1927     fn check_struct_field(&mut self, cx: &LateContext<'tcx>, field: &'tcx hir::StructField<'_>) {
1928         // enum variants are also struct fields now
1929         self.check_type(cx, &field.ty);
1930     }
1931
1932     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
1933         match item.kind {
1934             ItemKind::Static(ref ty, _, _) | ItemKind::Const(ref ty, _) => self.check_type(cx, ty),
1935             // functions, enums, structs, impls and traits are covered
1936             _ => (),
1937         }
1938     }
1939
1940     fn check_trait_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx TraitItem<'_>) {
1941         match item.kind {
1942             TraitItemKind::Const(ref ty, _) | TraitItemKind::Type(_, Some(ref ty)) => self.check_type(cx, ty),
1943             TraitItemKind::Fn(FnSig { ref decl, .. }, TraitFn::Required(_)) => self.check_fndecl(cx, decl),
1944             // methods with default impl are covered by check_fn
1945             _ => (),
1946         }
1947     }
1948
1949     fn check_impl_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx ImplItem<'_>) {
1950         match item.kind {
1951             ImplItemKind::Const(ref ty, _) | ImplItemKind::TyAlias(ref ty) => self.check_type(cx, ty),
1952             // methods are covered by check_fn
1953             _ => (),
1954         }
1955     }
1956
1957     fn check_local(&mut self, cx: &LateContext<'tcx>, local: &'tcx Local<'_>) {
1958         if let Some(ref ty) = local.ty {
1959             self.check_type(cx, ty);
1960         }
1961     }
1962 }
1963
1964 impl<'tcx> TypeComplexity {
1965     fn check_fndecl(&self, cx: &LateContext<'tcx>, decl: &'tcx FnDecl<'_>) {
1966         for arg in decl.inputs {
1967             self.check_type(cx, arg);
1968         }
1969         if let FnRetTy::Return(ref ty) = decl.output {
1970             self.check_type(cx, ty);
1971         }
1972     }
1973
1974     fn check_type(&self, cx: &LateContext<'_>, ty: &hir::Ty<'_>) {
1975         if ty.span.from_expansion() {
1976             return;
1977         }
1978         let score = {
1979             let mut visitor = TypeComplexityVisitor { score: 0, nest: 1 };
1980             visitor.visit_ty(ty);
1981             visitor.score
1982         };
1983
1984         if score > self.threshold {
1985             span_lint(
1986                 cx,
1987                 TYPE_COMPLEXITY,
1988                 ty.span,
1989                 "very complex type used. Consider factoring parts into `type` definitions",
1990             );
1991         }
1992     }
1993 }
1994
1995 /// Walks a type and assigns a complexity score to it.
1996 struct TypeComplexityVisitor {
1997     /// total complexity score of the type
1998     score: u64,
1999     /// current nesting level
2000     nest: u64,
2001 }
2002
2003 impl<'tcx> Visitor<'tcx> for TypeComplexityVisitor {
2004     type Map = Map<'tcx>;
2005
2006     fn visit_ty(&mut self, ty: &'tcx hir::Ty<'_>) {
2007         let (add_score, sub_nest) = match ty.kind {
2008             // _, &x and *x have only small overhead; don't mess with nesting level
2009             TyKind::Infer | TyKind::Ptr(..) | TyKind::Rptr(..) => (1, 0),
2010
2011             // the "normal" components of a type: named types, arrays/tuples
2012             TyKind::Path(..) | TyKind::Slice(..) | TyKind::Tup(..) | TyKind::Array(..) => (10 * self.nest, 1),
2013
2014             // function types bring a lot of overhead
2015             TyKind::BareFn(ref bare) if bare.abi == Abi::Rust => (50 * self.nest, 1),
2016
2017             TyKind::TraitObject(ref param_bounds, _) => {
2018                 let has_lifetime_parameters = param_bounds.iter().any(|bound| {
2019                     bound
2020                         .bound_generic_params
2021                         .iter()
2022                         .any(|gen| matches!(gen.kind, GenericParamKind::Lifetime { .. }))
2023                 });
2024                 if has_lifetime_parameters {
2025                     // complex trait bounds like A<'a, 'b>
2026                     (50 * self.nest, 1)
2027                 } else {
2028                     // simple trait bounds like A + B
2029                     (20 * self.nest, 0)
2030                 }
2031             },
2032
2033             _ => (0, 0),
2034         };
2035         self.score += add_score;
2036         self.nest += sub_nest;
2037         walk_ty(self, ty);
2038         self.nest -= sub_nest;
2039     }
2040     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2041         NestedVisitorMap::None
2042     }
2043 }
2044
2045 declare_clippy_lint! {
2046     /// **What it does:** Checks for expressions where a character literal is cast
2047     /// to `u8` and suggests using a byte literal instead.
2048     ///
2049     /// **Why is this bad?** In general, casting values to smaller types is
2050     /// error-prone and should be avoided where possible. In the particular case of
2051     /// converting a character literal to u8, it is easy to avoid by just using a
2052     /// byte literal instead. As an added bonus, `b'a'` is even slightly shorter
2053     /// than `'a' as u8`.
2054     ///
2055     /// **Known problems:** None.
2056     ///
2057     /// **Example:**
2058     /// ```rust,ignore
2059     /// 'x' as u8
2060     /// ```
2061     ///
2062     /// A better version, using the byte literal:
2063     ///
2064     /// ```rust,ignore
2065     /// b'x'
2066     /// ```
2067     pub CHAR_LIT_AS_U8,
2068     complexity,
2069     "casting a character literal to `u8` truncates"
2070 }
2071
2072 declare_lint_pass!(CharLitAsU8 => [CHAR_LIT_AS_U8]);
2073
2074 impl<'tcx> LateLintPass<'tcx> for CharLitAsU8 {
2075     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2076         if_chain! {
2077             if !expr.span.from_expansion();
2078             if let ExprKind::Cast(e, _) = &expr.kind;
2079             if let ExprKind::Lit(l) = &e.kind;
2080             if let LitKind::Char(c) = l.node;
2081             if ty::Uint(UintTy::U8) == *cx.typeck_results().expr_ty(expr).kind();
2082             then {
2083                 let mut applicability = Applicability::MachineApplicable;
2084                 let snippet = snippet_with_applicability(cx, e.span, "'x'", &mut applicability);
2085
2086                 span_lint_and_then(
2087                     cx,
2088                     CHAR_LIT_AS_U8,
2089                     expr.span,
2090                     "casting a character literal to `u8` truncates",
2091                     |diag| {
2092                         diag.note("`char` is four bytes wide, but `u8` is a single byte");
2093
2094                         if c.is_ascii() {
2095                             diag.span_suggestion(
2096                                 expr.span,
2097                                 "use a byte literal instead",
2098                                 format!("b{}", snippet),
2099                                 applicability,
2100                             );
2101                         }
2102                 });
2103             }
2104         }
2105     }
2106 }
2107
2108 declare_clippy_lint! {
2109     /// **What it does:** Checks for comparisons where one side of the relation is
2110     /// either the minimum or maximum value for its type and warns if it involves a
2111     /// case that is always true or always false. Only integer and boolean types are
2112     /// checked.
2113     ///
2114     /// **Why is this bad?** An expression like `min <= x` may misleadingly imply
2115     /// that it is possible for `x` to be less than the minimum. Expressions like
2116     /// `max < x` are probably mistakes.
2117     ///
2118     /// **Known problems:** For `usize` the size of the current compile target will
2119     /// be assumed (e.g., 64 bits on 64 bit systems). This means code that uses such
2120     /// a comparison to detect target pointer width will trigger this lint. One can
2121     /// use `mem::sizeof` and compare its value or conditional compilation
2122     /// attributes
2123     /// like `#[cfg(target_pointer_width = "64")] ..` instead.
2124     ///
2125     /// **Example:**
2126     ///
2127     /// ```rust
2128     /// let vec: Vec<isize> = Vec::new();
2129     /// if vec.len() <= 0 {}
2130     /// if 100 > i32::MAX {}
2131     /// ```
2132     pub ABSURD_EXTREME_COMPARISONS,
2133     correctness,
2134     "a comparison with a maximum or minimum value that is always true or false"
2135 }
2136
2137 declare_lint_pass!(AbsurdExtremeComparisons => [ABSURD_EXTREME_COMPARISONS]);
2138
2139 enum ExtremeType {
2140     Minimum,
2141     Maximum,
2142 }
2143
2144 struct ExtremeExpr<'a> {
2145     which: ExtremeType,
2146     expr: &'a Expr<'a>,
2147 }
2148
2149 enum AbsurdComparisonResult {
2150     AlwaysFalse,
2151     AlwaysTrue,
2152     InequalityImpossible,
2153 }
2154
2155 fn is_cast_between_fixed_and_target<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'tcx>) -> bool {
2156     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2157         let precast_ty = cx.typeck_results().expr_ty(cast_exp);
2158         let cast_ty = cx.typeck_results().expr_ty(expr);
2159
2160         return is_isize_or_usize(precast_ty) != is_isize_or_usize(cast_ty);
2161     }
2162
2163     false
2164 }
2165
2166 fn detect_absurd_comparison<'tcx>(
2167     cx: &LateContext<'tcx>,
2168     op: BinOpKind,
2169     lhs: &'tcx Expr<'_>,
2170     rhs: &'tcx Expr<'_>,
2171 ) -> Option<(ExtremeExpr<'tcx>, AbsurdComparisonResult)> {
2172     use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2173     use crate::types::ExtremeType::{Maximum, Minimum};
2174     use crate::utils::comparisons::{normalize_comparison, Rel};
2175
2176     // absurd comparison only makes sense on primitive types
2177     // primitive types don't implement comparison operators with each other
2178     if cx.typeck_results().expr_ty(lhs) != cx.typeck_results().expr_ty(rhs) {
2179         return None;
2180     }
2181
2182     // comparisons between fix sized types and target sized types are considered unanalyzable
2183     if is_cast_between_fixed_and_target(cx, lhs) || is_cast_between_fixed_and_target(cx, rhs) {
2184         return None;
2185     }
2186
2187     let (rel, normalized_lhs, normalized_rhs) = normalize_comparison(op, lhs, rhs)?;
2188
2189     let lx = detect_extreme_expr(cx, normalized_lhs);
2190     let rx = detect_extreme_expr(cx, normalized_rhs);
2191
2192     Some(match rel {
2193         Rel::Lt => {
2194             match (lx, rx) {
2195                 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, AlwaysFalse), // max < x
2196                 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, AlwaysFalse), // x < min
2197                 _ => return None,
2198             }
2199         },
2200         Rel::Le => {
2201             match (lx, rx) {
2202                 (Some(l @ ExtremeExpr { which: Minimum, .. }), _) => (l, AlwaysTrue), // min <= x
2203                 (Some(l @ ExtremeExpr { which: Maximum, .. }), _) => (l, InequalityImpossible), // max <= x
2204                 (_, Some(r @ ExtremeExpr { which: Minimum, .. })) => (r, InequalityImpossible), // x <= min
2205                 (_, Some(r @ ExtremeExpr { which: Maximum, .. })) => (r, AlwaysTrue), // x <= max
2206                 _ => return None,
2207             }
2208         },
2209         Rel::Ne | Rel::Eq => return None,
2210     })
2211 }
2212
2213 fn detect_extreme_expr<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<ExtremeExpr<'tcx>> {
2214     use crate::types::ExtremeType::{Maximum, Minimum};
2215
2216     let ty = cx.typeck_results().expr_ty(expr);
2217
2218     let cv = constant(cx, cx.typeck_results(), expr)?.0;
2219
2220     let which = match (ty.kind(), cv) {
2221         (&ty::Bool, Constant::Bool(false)) | (&ty::Uint(_), Constant::Int(0)) => Minimum,
2222         (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MIN >> (128 - int_bits(cx.tcx, ity)), ity) => {
2223             Minimum
2224         },
2225
2226         (&ty::Bool, Constant::Bool(true)) => Maximum,
2227         (&ty::Int(ity), Constant::Int(i)) if i == unsext(cx.tcx, i128::MAX >> (128 - int_bits(cx.tcx, ity)), ity) => {
2228             Maximum
2229         },
2230         (&ty::Uint(uty), Constant::Int(i)) if clip(cx.tcx, u128::MAX, uty) == i => Maximum,
2231
2232         _ => return None,
2233     };
2234     Some(ExtremeExpr { which, expr })
2235 }
2236
2237 impl<'tcx> LateLintPass<'tcx> for AbsurdExtremeComparisons {
2238     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2239         use crate::types::AbsurdComparisonResult::{AlwaysFalse, AlwaysTrue, InequalityImpossible};
2240         use crate::types::ExtremeType::{Maximum, Minimum};
2241
2242         if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2243             if let Some((culprit, result)) = detect_absurd_comparison(cx, cmp.node, lhs, rhs) {
2244                 if !expr.span.from_expansion() {
2245                     let msg = "this comparison involving the minimum or maximum element for this \
2246                                type contains a case that is always true or always false";
2247
2248                     let conclusion = match result {
2249                         AlwaysFalse => "this comparison is always false".to_owned(),
2250                         AlwaysTrue => "this comparison is always true".to_owned(),
2251                         InequalityImpossible => format!(
2252                             "the case where the two sides are not equal never occurs, consider using `{} == {}` \
2253                              instead",
2254                             snippet(cx, lhs.span, "lhs"),
2255                             snippet(cx, rhs.span, "rhs")
2256                         ),
2257                     };
2258
2259                     let help = format!(
2260                         "because `{}` is the {} value for this type, {}",
2261                         snippet(cx, culprit.expr.span, "x"),
2262                         match culprit.which {
2263                             Minimum => "minimum",
2264                             Maximum => "maximum",
2265                         },
2266                         conclusion
2267                     );
2268
2269                     span_lint_and_help(cx, ABSURD_EXTREME_COMPARISONS, expr.span, msg, None, &help);
2270                 }
2271             }
2272         }
2273     }
2274 }
2275
2276 declare_clippy_lint! {
2277     /// **What it does:** Checks for comparisons where the relation is always either
2278     /// true or false, but where one side has been upcast so that the comparison is
2279     /// necessary. Only integer types are checked.
2280     ///
2281     /// **Why is this bad?** An expression like `let x : u8 = ...; (x as u32) > 300`
2282     /// will mistakenly imply that it is possible for `x` to be outside the range of
2283     /// `u8`.
2284     ///
2285     /// **Known problems:**
2286     /// https://github.com/rust-lang/rust-clippy/issues/886
2287     ///
2288     /// **Example:**
2289     /// ```rust
2290     /// let x: u8 = 1;
2291     /// (x as u32) > 300;
2292     /// ```
2293     pub INVALID_UPCAST_COMPARISONS,
2294     pedantic,
2295     "a comparison involving an upcast which is always true or false"
2296 }
2297
2298 declare_lint_pass!(InvalidUpcastComparisons => [INVALID_UPCAST_COMPARISONS]);
2299
2300 #[derive(Copy, Clone, Debug, Eq)]
2301 enum FullInt {
2302     S(i128),
2303     U(u128),
2304 }
2305
2306 impl FullInt {
2307     #[allow(clippy::cast_sign_loss)]
2308     #[must_use]
2309     fn cmp_s_u(s: i128, u: u128) -> Ordering {
2310         if s < 0 {
2311             Ordering::Less
2312         } else if u > (i128::MAX as u128) {
2313             Ordering::Greater
2314         } else {
2315             (s as u128).cmp(&u)
2316         }
2317     }
2318 }
2319
2320 impl PartialEq for FullInt {
2321     #[must_use]
2322     fn eq(&self, other: &Self) -> bool {
2323         self.partial_cmp(other).expect("`partial_cmp` only returns `Some(_)`") == Ordering::Equal
2324     }
2325 }
2326
2327 impl PartialOrd for FullInt {
2328     #[must_use]
2329     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
2330         Some(match (self, other) {
2331             (&Self::S(s), &Self::S(o)) => s.cmp(&o),
2332             (&Self::U(s), &Self::U(o)) => s.cmp(&o),
2333             (&Self::S(s), &Self::U(o)) => Self::cmp_s_u(s, o),
2334             (&Self::U(s), &Self::S(o)) => Self::cmp_s_u(o, s).reverse(),
2335         })
2336     }
2337 }
2338
2339 impl Ord for FullInt {
2340     #[must_use]
2341     fn cmp(&self, other: &Self) -> Ordering {
2342         self.partial_cmp(other)
2343             .expect("`partial_cmp` for FullInt can never return `None`")
2344     }
2345 }
2346
2347 fn numeric_cast_precast_bounds<'a>(cx: &LateContext<'_>, expr: &'a Expr<'_>) -> Option<(FullInt, FullInt)> {
2348     if let ExprKind::Cast(ref cast_exp, _) = expr.kind {
2349         let pre_cast_ty = cx.typeck_results().expr_ty(cast_exp);
2350         let cast_ty = cx.typeck_results().expr_ty(expr);
2351         // if it's a cast from i32 to u32 wrapping will invalidate all these checks
2352         if cx.layout_of(pre_cast_ty).ok().map(|l| l.size) == cx.layout_of(cast_ty).ok().map(|l| l.size) {
2353             return None;
2354         }
2355         match pre_cast_ty.kind() {
2356             ty::Int(int_ty) => Some(match int_ty {
2357                 IntTy::I8 => (FullInt::S(i128::from(i8::MIN)), FullInt::S(i128::from(i8::MAX))),
2358                 IntTy::I16 => (FullInt::S(i128::from(i16::MIN)), FullInt::S(i128::from(i16::MAX))),
2359                 IntTy::I32 => (FullInt::S(i128::from(i32::MIN)), FullInt::S(i128::from(i32::MAX))),
2360                 IntTy::I64 => (FullInt::S(i128::from(i64::MIN)), FullInt::S(i128::from(i64::MAX))),
2361                 IntTy::I128 => (FullInt::S(i128::MIN), FullInt::S(i128::MAX)),
2362                 IntTy::Isize => (FullInt::S(isize::MIN as i128), FullInt::S(isize::MAX as i128)),
2363             }),
2364             ty::Uint(uint_ty) => Some(match uint_ty {
2365                 UintTy::U8 => (FullInt::U(u128::from(u8::MIN)), FullInt::U(u128::from(u8::MAX))),
2366                 UintTy::U16 => (FullInt::U(u128::from(u16::MIN)), FullInt::U(u128::from(u16::MAX))),
2367                 UintTy::U32 => (FullInt::U(u128::from(u32::MIN)), FullInt::U(u128::from(u32::MAX))),
2368                 UintTy::U64 => (FullInt::U(u128::from(u64::MIN)), FullInt::U(u128::from(u64::MAX))),
2369                 UintTy::U128 => (FullInt::U(u128::MIN), FullInt::U(u128::MAX)),
2370                 UintTy::Usize => (FullInt::U(usize::MIN as u128), FullInt::U(usize::MAX as u128)),
2371             }),
2372             _ => None,
2373         }
2374     } else {
2375         None
2376     }
2377 }
2378
2379 fn node_as_const_fullint<'tcx>(cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) -> Option<FullInt> {
2380     let val = constant(cx, cx.typeck_results(), expr)?.0;
2381     if let Constant::Int(const_int) = val {
2382         match *cx.typeck_results().expr_ty(expr).kind() {
2383             ty::Int(ity) => Some(FullInt::S(sext(cx.tcx, const_int, ity))),
2384             ty::Uint(_) => Some(FullInt::U(const_int)),
2385             _ => None,
2386         }
2387     } else {
2388         None
2389     }
2390 }
2391
2392 fn err_upcast_comparison(cx: &LateContext<'_>, span: Span, expr: &Expr<'_>, always: bool) {
2393     if let ExprKind::Cast(ref cast_val, _) = expr.kind {
2394         span_lint(
2395             cx,
2396             INVALID_UPCAST_COMPARISONS,
2397             span,
2398             &format!(
2399                 "because of the numeric bounds on `{}` prior to casting, this expression is always {}",
2400                 snippet(cx, cast_val.span, "the expression"),
2401                 if always { "true" } else { "false" },
2402             ),
2403         );
2404     }
2405 }
2406
2407 fn upcast_comparison_bounds_err<'tcx>(
2408     cx: &LateContext<'tcx>,
2409     span: Span,
2410     rel: comparisons::Rel,
2411     lhs_bounds: Option<(FullInt, FullInt)>,
2412     lhs: &'tcx Expr<'_>,
2413     rhs: &'tcx Expr<'_>,
2414     invert: bool,
2415 ) {
2416     use crate::utils::comparisons::Rel;
2417
2418     if let Some((lb, ub)) = lhs_bounds {
2419         if let Some(norm_rhs_val) = node_as_const_fullint(cx, rhs) {
2420             if rel == Rel::Eq || rel == Rel::Ne {
2421                 if norm_rhs_val < lb || norm_rhs_val > ub {
2422                     err_upcast_comparison(cx, span, lhs, rel == Rel::Ne);
2423                 }
2424             } else if match rel {
2425                 Rel::Lt => {
2426                     if invert {
2427                         norm_rhs_val < lb
2428                     } else {
2429                         ub < norm_rhs_val
2430                     }
2431                 },
2432                 Rel::Le => {
2433                     if invert {
2434                         norm_rhs_val <= lb
2435                     } else {
2436                         ub <= norm_rhs_val
2437                     }
2438                 },
2439                 Rel::Eq | Rel::Ne => unreachable!(),
2440             } {
2441                 err_upcast_comparison(cx, span, lhs, true)
2442             } else if match rel {
2443                 Rel::Lt => {
2444                     if invert {
2445                         norm_rhs_val >= ub
2446                     } else {
2447                         lb >= norm_rhs_val
2448                     }
2449                 },
2450                 Rel::Le => {
2451                     if invert {
2452                         norm_rhs_val > ub
2453                     } else {
2454                         lb > norm_rhs_val
2455                     }
2456                 },
2457                 Rel::Eq | Rel::Ne => unreachable!(),
2458             } {
2459                 err_upcast_comparison(cx, span, lhs, false)
2460             }
2461         }
2462     }
2463 }
2464
2465 impl<'tcx> LateLintPass<'tcx> for InvalidUpcastComparisons {
2466     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2467         if let ExprKind::Binary(ref cmp, ref lhs, ref rhs) = expr.kind {
2468             let normalized = comparisons::normalize_comparison(cmp.node, lhs, rhs);
2469             let (rel, normalized_lhs, normalized_rhs) = if let Some(val) = normalized {
2470                 val
2471             } else {
2472                 return;
2473             };
2474
2475             let lhs_bounds = numeric_cast_precast_bounds(cx, normalized_lhs);
2476             let rhs_bounds = numeric_cast_precast_bounds(cx, normalized_rhs);
2477
2478             upcast_comparison_bounds_err(cx, expr.span, rel, lhs_bounds, normalized_lhs, normalized_rhs, false);
2479             upcast_comparison_bounds_err(cx, expr.span, rel, rhs_bounds, normalized_rhs, normalized_lhs, true);
2480         }
2481     }
2482 }
2483
2484 declare_clippy_lint! {
2485     /// **What it does:** Checks for public `impl` or `fn` missing generalization
2486     /// over different hashers and implicitly defaulting to the default hashing
2487     /// algorithm (`SipHash`).
2488     ///
2489     /// **Why is this bad?** `HashMap` or `HashSet` with custom hashers cannot be
2490     /// used with them.
2491     ///
2492     /// **Known problems:** Suggestions for replacing constructors can contain
2493     /// false-positives. Also applying suggestions can require modification of other
2494     /// pieces of code, possibly including external crates.
2495     ///
2496     /// **Example:**
2497     /// ```rust
2498     /// # use std::collections::HashMap;
2499     /// # use std::hash::{Hash, BuildHasher};
2500     /// # trait Serialize {};
2501     /// impl<K: Hash + Eq, V> Serialize for HashMap<K, V> { }
2502     ///
2503     /// pub fn foo(map: &mut HashMap<i32, i32>) { }
2504     /// ```
2505     /// could be rewritten as
2506     /// ```rust
2507     /// # use std::collections::HashMap;
2508     /// # use std::hash::{Hash, BuildHasher};
2509     /// # trait Serialize {};
2510     /// impl<K: Hash + Eq, V, S: BuildHasher> Serialize for HashMap<K, V, S> { }
2511     ///
2512     /// pub fn foo<S: BuildHasher>(map: &mut HashMap<i32, i32, S>) { }
2513     /// ```
2514     pub IMPLICIT_HASHER,
2515     pedantic,
2516     "missing generalization over different hashers"
2517 }
2518
2519 declare_lint_pass!(ImplicitHasher => [IMPLICIT_HASHER]);
2520
2521 impl<'tcx> LateLintPass<'tcx> for ImplicitHasher {
2522     #[allow(clippy::cast_possible_truncation, clippy::too_many_lines)]
2523     fn check_item(&mut self, cx: &LateContext<'tcx>, item: &'tcx Item<'_>) {
2524         use rustc_span::BytePos;
2525
2526         fn suggestion<'tcx>(
2527             cx: &LateContext<'tcx>,
2528             diag: &mut DiagnosticBuilder<'_>,
2529             generics_span: Span,
2530             generics_suggestion_span: Span,
2531             target: &ImplicitHasherType<'_>,
2532             vis: ImplicitHasherConstructorVisitor<'_, '_, '_>,
2533         ) {
2534             let generics_snip = snippet(cx, generics_span, "");
2535             // trim `<` `>`
2536             let generics_snip = if generics_snip.is_empty() {
2537                 ""
2538             } else {
2539                 &generics_snip[1..generics_snip.len() - 1]
2540             };
2541
2542             multispan_sugg(
2543                 diag,
2544                 "consider adding a type parameter",
2545                 vec![
2546                     (
2547                         generics_suggestion_span,
2548                         format!(
2549                             "<{}{}S: ::std::hash::BuildHasher{}>",
2550                             generics_snip,
2551                             if generics_snip.is_empty() { "" } else { ", " },
2552                             if vis.suggestions.is_empty() {
2553                                 ""
2554                             } else {
2555                                 // request users to add `Default` bound so that generic constructors can be used
2556                                 " + Default"
2557                             },
2558                         ),
2559                     ),
2560                     (
2561                         target.span(),
2562                         format!("{}<{}, S>", target.type_name(), target.type_arguments(),),
2563                     ),
2564                 ],
2565             );
2566
2567             if !vis.suggestions.is_empty() {
2568                 multispan_sugg(diag, "...and use generic constructor", vis.suggestions);
2569             }
2570         }
2571
2572         if !cx.access_levels.is_exported(item.hir_id) {
2573             return;
2574         }
2575
2576         match item.kind {
2577             ItemKind::Impl {
2578                 ref generics,
2579                 self_ty: ref ty,
2580                 ref items,
2581                 ..
2582             } => {
2583                 let mut vis = ImplicitHasherTypeVisitor::new(cx);
2584                 vis.visit_ty(ty);
2585
2586                 for target in &vis.found {
2587                     if differing_macro_contexts(item.span, target.span()) {
2588                         return;
2589                     }
2590
2591                     let generics_suggestion_span = generics.span.substitute_dummy({
2592                         let pos = snippet_opt(cx, item.span.until(target.span()))
2593                             .and_then(|snip| Some(item.span.lo() + BytePos(snip.find("impl")? as u32 + 4)));
2594                         if let Some(pos) = pos {
2595                             Span::new(pos, pos, item.span.data().ctxt)
2596                         } else {
2597                             return;
2598                         }
2599                     });
2600
2601                     let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2602                     for item in items.iter().map(|item| cx.tcx.hir().impl_item(item.id)) {
2603                         ctr_vis.visit_impl_item(item);
2604                     }
2605
2606                     span_lint_and_then(
2607                         cx,
2608                         IMPLICIT_HASHER,
2609                         target.span(),
2610                         &format!(
2611                             "impl for `{}` should be generalized over different hashers",
2612                             target.type_name()
2613                         ),
2614                         move |diag| {
2615                             suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2616                         },
2617                     );
2618                 }
2619             },
2620             ItemKind::Fn(ref sig, ref generics, body_id) => {
2621                 let body = cx.tcx.hir().body(body_id);
2622
2623                 for ty in sig.decl.inputs {
2624                     let mut vis = ImplicitHasherTypeVisitor::new(cx);
2625                     vis.visit_ty(ty);
2626
2627                     for target in &vis.found {
2628                         if in_external_macro(cx.sess(), generics.span) {
2629                             continue;
2630                         }
2631                         let generics_suggestion_span = generics.span.substitute_dummy({
2632                             let pos = snippet_opt(cx, item.span.until(body.params[0].pat.span))
2633                                 .and_then(|snip| {
2634                                     let i = snip.find("fn")?;
2635                                     Some(item.span.lo() + BytePos((i + (&snip[i..]).find('(')?) as u32))
2636                                 })
2637                                 .expect("failed to create span for type parameters");
2638                             Span::new(pos, pos, item.span.data().ctxt)
2639                         });
2640
2641                         let mut ctr_vis = ImplicitHasherConstructorVisitor::new(cx, target);
2642                         ctr_vis.visit_body(body);
2643
2644                         span_lint_and_then(
2645                             cx,
2646                             IMPLICIT_HASHER,
2647                             target.span(),
2648                             &format!(
2649                                 "parameter of type `{}` should be generalized over different hashers",
2650                                 target.type_name()
2651                             ),
2652                             move |diag| {
2653                                 suggestion(cx, diag, generics.span, generics_suggestion_span, target, ctr_vis);
2654                             },
2655                         );
2656                     }
2657                 }
2658             },
2659             _ => {},
2660         }
2661     }
2662 }
2663
2664 enum ImplicitHasherType<'tcx> {
2665     HashMap(Span, Ty<'tcx>, Cow<'static, str>, Cow<'static, str>),
2666     HashSet(Span, Ty<'tcx>, Cow<'static, str>),
2667 }
2668
2669 impl<'tcx> ImplicitHasherType<'tcx> {
2670     /// Checks that `ty` is a target type without a `BuildHasher`.
2671     fn new(cx: &LateContext<'tcx>, hir_ty: &hir::Ty<'_>) -> Option<Self> {
2672         if let TyKind::Path(QPath::Resolved(None, ref path)) = hir_ty.kind {
2673             let params: Vec<_> = path
2674                 .segments
2675                 .last()
2676                 .as_ref()?
2677                 .args
2678                 .as_ref()?
2679                 .args
2680                 .iter()
2681                 .filter_map(|arg| match arg {
2682                     GenericArg::Type(ty) => Some(ty),
2683                     _ => None,
2684                 })
2685                 .collect();
2686             let params_len = params.len();
2687
2688             let ty = hir_ty_to_ty(cx.tcx, hir_ty);
2689
2690             if is_type_diagnostic_item(cx, ty, sym!(hashmap_type)) && params_len == 2 {
2691                 Some(ImplicitHasherType::HashMap(
2692                     hir_ty.span,
2693                     ty,
2694                     snippet(cx, params[0].span, "K"),
2695                     snippet(cx, params[1].span, "V"),
2696                 ))
2697             } else if is_type_diagnostic_item(cx, ty, sym!(hashset_type)) && params_len == 1 {
2698                 Some(ImplicitHasherType::HashSet(
2699                     hir_ty.span,
2700                     ty,
2701                     snippet(cx, params[0].span, "T"),
2702                 ))
2703             } else {
2704                 None
2705             }
2706         } else {
2707             None
2708         }
2709     }
2710
2711     fn type_name(&self) -> &'static str {
2712         match *self {
2713             ImplicitHasherType::HashMap(..) => "HashMap",
2714             ImplicitHasherType::HashSet(..) => "HashSet",
2715         }
2716     }
2717
2718     fn type_arguments(&self) -> String {
2719         match *self {
2720             ImplicitHasherType::HashMap(.., ref k, ref v) => format!("{}, {}", k, v),
2721             ImplicitHasherType::HashSet(.., ref t) => format!("{}", t),
2722         }
2723     }
2724
2725     fn ty(&self) -> Ty<'tcx> {
2726         match *self {
2727             ImplicitHasherType::HashMap(_, ty, ..) | ImplicitHasherType::HashSet(_, ty, ..) => ty,
2728         }
2729     }
2730
2731     fn span(&self) -> Span {
2732         match *self {
2733             ImplicitHasherType::HashMap(span, ..) | ImplicitHasherType::HashSet(span, ..) => span,
2734         }
2735     }
2736 }
2737
2738 struct ImplicitHasherTypeVisitor<'a, 'tcx> {
2739     cx: &'a LateContext<'tcx>,
2740     found: Vec<ImplicitHasherType<'tcx>>,
2741 }
2742
2743 impl<'a, 'tcx> ImplicitHasherTypeVisitor<'a, 'tcx> {
2744     fn new(cx: &'a LateContext<'tcx>) -> Self {
2745         Self { cx, found: vec![] }
2746     }
2747 }
2748
2749 impl<'a, 'tcx> Visitor<'tcx> for ImplicitHasherTypeVisitor<'a, 'tcx> {
2750     type Map = Map<'tcx>;
2751
2752     fn visit_ty(&mut self, t: &'tcx hir::Ty<'_>) {
2753         if let Some(target) = ImplicitHasherType::new(self.cx, t) {
2754             self.found.push(target);
2755         }
2756
2757         walk_ty(self, t);
2758     }
2759
2760     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2761         NestedVisitorMap::None
2762     }
2763 }
2764
2765 /// Looks for default-hasher-dependent constructors like `HashMap::new`.
2766 struct ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2767     cx: &'a LateContext<'tcx>,
2768     maybe_typeck_results: Option<&'tcx TypeckResults<'tcx>>,
2769     target: &'b ImplicitHasherType<'tcx>,
2770     suggestions: BTreeMap<Span, String>,
2771 }
2772
2773 impl<'a, 'b, 'tcx> ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2774     fn new(cx: &'a LateContext<'tcx>, target: &'b ImplicitHasherType<'tcx>) -> Self {
2775         Self {
2776             cx,
2777             maybe_typeck_results: cx.maybe_typeck_results(),
2778             target,
2779             suggestions: BTreeMap::new(),
2780         }
2781     }
2782 }
2783
2784 impl<'a, 'b, 'tcx> Visitor<'tcx> for ImplicitHasherConstructorVisitor<'a, 'b, 'tcx> {
2785     type Map = Map<'tcx>;
2786
2787     fn visit_body(&mut self, body: &'tcx Body<'_>) {
2788         let old_maybe_typeck_results = self.maybe_typeck_results.replace(self.cx.tcx.typeck_body(body.id()));
2789         walk_body(self, body);
2790         self.maybe_typeck_results = old_maybe_typeck_results;
2791     }
2792
2793     fn visit_expr(&mut self, e: &'tcx Expr<'_>) {
2794         if_chain! {
2795             if let ExprKind::Call(ref fun, ref args) = e.kind;
2796             if let ExprKind::Path(QPath::TypeRelative(ref ty, ref method)) = fun.kind;
2797             if let TyKind::Path(QPath::Resolved(None, ty_path)) = ty.kind;
2798             then {
2799                 if !TyS::same_type(self.target.ty(), self.maybe_typeck_results.unwrap().expr_ty(e)) {
2800                     return;
2801                 }
2802
2803                 if match_path(ty_path, &paths::HASHMAP) {
2804                     if method.ident.name == sym::new {
2805                         self.suggestions
2806                             .insert(e.span, "HashMap::default()".to_string());
2807                     } else if method.ident.name == sym!(with_capacity) {
2808                         self.suggestions.insert(
2809                             e.span,
2810                             format!(
2811                                 "HashMap::with_capacity_and_hasher({}, Default::default())",
2812                                 snippet(self.cx, args[0].span, "capacity"),
2813                             ),
2814                         );
2815                     }
2816                 } else if match_path(ty_path, &paths::HASHSET) {
2817                     if method.ident.name == sym::new {
2818                         self.suggestions
2819                             .insert(e.span, "HashSet::default()".to_string());
2820                     } else if method.ident.name == sym!(with_capacity) {
2821                         self.suggestions.insert(
2822                             e.span,
2823                             format!(
2824                                 "HashSet::with_capacity_and_hasher({}, Default::default())",
2825                                 snippet(self.cx, args[0].span, "capacity"),
2826                             ),
2827                         );
2828                     }
2829                 }
2830             }
2831         }
2832
2833         walk_expr(self, e);
2834     }
2835
2836     fn nested_visit_map(&mut self) -> NestedVisitorMap<Self::Map> {
2837         NestedVisitorMap::OnlyBodies(self.cx.tcx.hir())
2838     }
2839 }
2840
2841 declare_clippy_lint! {
2842     /// **What it does:** Checks for casts of `&T` to `&mut T` anywhere in the code.
2843     ///
2844     /// **Why is this bad?** It’s basically guaranteed to be undefined behaviour.
2845     /// `UnsafeCell` is the only way to obtain aliasable data that is considered
2846     /// mutable.
2847     ///
2848     /// **Known problems:** None.
2849     ///
2850     /// **Example:**
2851     /// ```rust,ignore
2852     /// fn x(r: &i32) {
2853     ///     unsafe {
2854     ///         *(r as *const _ as *mut _) += 1;
2855     ///     }
2856     /// }
2857     /// ```
2858     ///
2859     /// Instead consider using interior mutability types.
2860     ///
2861     /// ```rust
2862     /// use std::cell::UnsafeCell;
2863     ///
2864     /// fn x(r: &UnsafeCell<i32>) {
2865     ///     unsafe {
2866     ///         *r.get() += 1;
2867     ///     }
2868     /// }
2869     /// ```
2870     pub CAST_REF_TO_MUT,
2871     correctness,
2872     "a cast of reference to a mutable pointer"
2873 }
2874
2875 declare_lint_pass!(RefToMut => [CAST_REF_TO_MUT]);
2876
2877 impl<'tcx> LateLintPass<'tcx> for RefToMut {
2878     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2879         if_chain! {
2880             if let ExprKind::Unary(UnOp::UnDeref, e) = &expr.kind;
2881             if let ExprKind::Cast(e, t) = &e.kind;
2882             if let TyKind::Ptr(MutTy { mutbl: Mutability::Mut, .. }) = t.kind;
2883             if let ExprKind::Cast(e, t) = &e.kind;
2884             if let TyKind::Ptr(MutTy { mutbl: Mutability::Not, .. }) = t.kind;
2885             if let ty::Ref(..) = cx.typeck_results().node_type(e.hir_id).kind();
2886             then {
2887                 span_lint(
2888                     cx,
2889                     CAST_REF_TO_MUT,
2890                     expr.span,
2891                     "casting `&T` to `&mut T` may cause undefined behavior, consider instead using an `UnsafeCell`",
2892                 );
2893             }
2894         }
2895     }
2896 }
2897
2898 const PTR_AS_PTR_MSRV: RustcVersion = RustcVersion::new(1, 38, 0);
2899
2900 declare_clippy_lint! {
2901     /// **What it does:**
2902     /// Checks for `as` casts between raw pointers without changing its mutability,
2903     /// namely `*const T` to `*const U` and `*mut T` to `*mut U`.
2904     ///
2905     /// **Why is this bad?**
2906     /// Though `as` casts between raw pointers is not terrible, `pointer::cast` is safer because
2907     /// it cannot accidentally change the pointer's mutability nor cast the pointer to other types like `usize`.
2908     ///
2909     /// **Known problems:** None.
2910     ///
2911     /// **Example:**
2912     ///
2913     /// ```rust
2914     /// let ptr: *const u32 = &42_u32;
2915     /// let mut_ptr: *mut u32 = &mut 42_u32;
2916     /// let _ = ptr as *const i32;
2917     /// let _ = mut_ptr as *mut i32;
2918     /// ```
2919     /// Use instead:
2920     /// ```rust
2921     /// let ptr: *const u32 = &42_u32;
2922     /// let mut_ptr: *mut u32 = &mut 42_u32;
2923     /// let _ = ptr.cast::<i32>();
2924     /// let _ = mut_ptr.cast::<i32>();
2925     /// ```
2926     pub PTR_AS_PTR,
2927     pedantic,
2928     "casting using `as` from and to raw pointers that doesn't change its mutability, where `pointer::cast` could take the place of `as`"
2929 }
2930
2931 pub struct PtrAsPtr {
2932     msrv: Option<RustcVersion>,
2933 }
2934
2935 impl PtrAsPtr {
2936     #[must_use]
2937     pub fn new(msrv: Option<RustcVersion>) -> Self {
2938         Self { msrv }
2939     }
2940 }
2941
2942 impl_lint_pass!(PtrAsPtr => [PTR_AS_PTR]);
2943
2944 impl<'tcx> LateLintPass<'tcx> for PtrAsPtr {
2945     fn check_expr(&mut self, cx: &LateContext<'tcx>, expr: &'tcx Expr<'_>) {
2946         if !meets_msrv(self.msrv.as_ref(), &PTR_AS_PTR_MSRV) {
2947             return;
2948         }
2949
2950         if expr.span.from_expansion() {
2951             return;
2952         }
2953
2954         if_chain! {
2955             if let ExprKind::Cast(cast_expr, cast_to_hir_ty) = expr.kind;
2956             let (cast_from, cast_to) = (cx.typeck_results().expr_ty(cast_expr), cx.typeck_results().expr_ty(expr));
2957             if let ty::RawPtr(TypeAndMut { mutbl: from_mutbl, .. }) = cast_from.kind();
2958             if let ty::RawPtr(TypeAndMut { ty: to_pointee_ty, mutbl: to_mutbl }) = cast_to.kind();
2959             if matches!((from_mutbl, to_mutbl),
2960                 (Mutability::Not, Mutability::Not) | (Mutability::Mut, Mutability::Mut));
2961             // The `U` in `pointer::cast` have to be `Sized`
2962             // as explained here: https://github.com/rust-lang/rust/issues/60602.
2963             if to_pointee_ty.is_sized(cx.tcx.at(expr.span), cx.param_env);
2964             then {
2965                 let mut applicability = Applicability::MachineApplicable;
2966                 let cast_expr_sugg = Sugg::hir_with_applicability(cx, cast_expr, "_", &mut applicability);
2967                 let turbofish = match &cast_to_hir_ty.kind {
2968                         TyKind::Infer => Cow::Borrowed(""),
2969                         TyKind::Ptr(mut_ty) if matches!(mut_ty.ty.kind, TyKind::Infer) => Cow::Borrowed(""),
2970                         _ => Cow::Owned(format!("::<{}>", to_pointee_ty)),
2971                     };
2972                 span_lint_and_sugg(
2973                     cx,
2974                     PTR_AS_PTR,
2975                     expr.span,
2976                     "`as` casting between raw pointers without changing its mutability",
2977                     "try `pointer::cast`, a safer alternative",
2978                     format!("{}.cast{}()", cast_expr_sugg.maybe_par(), turbofish),
2979                     applicability,
2980                 );
2981             }
2982         }
2983     }
2984
2985     extract_msrv_attr!(LateContext);
2986 }