compiler/rustc_middle/src/thir.rs

   1 //! THIR datatypes and definitions. See the [rustc dev guide] for more info.
   2 //!
   3 //! If you compare the THIR [`ExprKind`] to [`hir::ExprKind`], you will see it is
   4 //! a good bit simpler. In fact, a number of the more straight-forward
   5 //! MIR simplifications are already done in the lowering to THIR. For
   6 //! example, method calls and overloaded operators are absent: they are
   7 //! expected to be converted into [`ExprKind::Call`] instances.
   8 //!
   9 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/thir.html
  10
  11 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
  12 use rustc_hir as hir;
  13 use rustc_hir::def::CtorKind;
  14 use rustc_hir::def_id::DefId;
  15 use rustc_hir::RangeEnd;
  16 use rustc_index::newtype_index;
  17 use rustc_index::vec::IndexVec;
  18 use rustc_middle::infer::canonical::Canonical;
  19 use rustc_middle::middle::region;
  20 use rustc_middle::mir::interpret::AllocId;
  21 use rustc_middle::mir::{
  22     BinOp, BorrowKind, FakeReadCause, Field, Mutability, UnOp, UserTypeProjection,
  23 };
  24 use rustc_middle::ty::adjustment::PointerCast;
  25 use rustc_middle::ty::subst::SubstsRef;
  26 use rustc_middle::ty::{self, AdtDef, Const, Ty, UpvarSubsts, UserType};
  27 use rustc_middle::ty::{
  28     CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
  29 };
  30 use rustc_span::{Span, Symbol, DUMMY_SP};
  31 use rustc_target::abi::VariantIdx;
  32 use rustc_target::asm::InlineAsmRegOrRegClass;
  33
  34 use std::fmt;
  35 use std::ops::Index;
  36
  37 pub mod abstract_const;
  38 pub mod visit;
  39
  40 newtype_index! {
  41     /// An index to an [`Arm`] stored in [`Thir::arms`]
  42     #[derive(HashStable)]
  43     pub struct ArmId {
  44         DEBUG_FORMAT = "a{}"
  45     }
  46 }
  47
  48 newtype_index! {
  49     /// An index to an [`Expr`] stored in [`Thir::exprs`]
  50     #[derive(HashStable)]
  51     pub struct ExprId {
  52         DEBUG_FORMAT = "e{}"
  53     }
  54 }
  55
  56 newtype_index! {
  57     #[derive(HashStable)]
  58     /// An index to a [`Stmt`] stored in [`Thir::stmts`]
  59     pub struct StmtId {
  60         DEBUG_FORMAT = "s{}"
  61     }
  62 }
  63
  64 macro_rules! thir_with_elements {
  65     ($($name:ident: $id:ty => $value:ty,)*) => {
  66         /// A container for a THIR body.
  67         ///
  68         /// This can be indexed directly by any THIR index (e.g. [`ExprId`]).
  69         #[derive(Debug, HashStable)]
  70         pub struct Thir<'tcx> {
  71             $(
  72                 pub $name: IndexVec<$id, $value>,
  73             )*
  74         }
  75
  76         impl<'tcx> Thir<'tcx> {
  77             pub fn new() -> Thir<'tcx> {
  78                 Thir {
  79                     $(
  80                         $name: IndexVec::new(),
  81                     )*
  82                 }
  83             }
  84         }
  85
  86         $(
  87             impl<'tcx> Index<$id> for Thir<'tcx> {
  88                 type Output = $value;
  89                 fn index(&self, index: $id) -> &Self::Output {
  90                     &self.$name[index]
  91                 }
  92             }
  93         )*
  94     }
  95 }
  96
  97 thir_with_elements! {
  98     arms: ArmId => Arm<'tcx>,
  99     exprs: ExprId => Expr<'tcx>,
 100     stmts: StmtId => Stmt<'tcx>,
 101 }
 102
 103 #[derive(Copy, Clone, Debug, HashStable)]
 104 pub enum LintLevel {
 105     Inherited,
 106     Explicit(hir::HirId),
 107 }
 108
 109 #[derive(Debug, HashStable)]
 110 pub struct Block {
 111     /// Whether the block itself has a label. Used by `label: {}`
 112     /// and `try` blocks.
 113     ///
 114     /// This does *not* include labels on loops, e.g. `'label: loop {}`.
 115     pub targeted_by_break: bool,
 116     pub region_scope: region::Scope,
 117     pub opt_destruction_scope: Option<region::Scope>,
 118     /// The span of the block, including the opening braces,
 119     /// the label, and the `unsafe` keyword, if present.
 120     pub span: Span,
 121     /// The statements in the blocK.
 122     pub stmts: Box<[StmtId]>,
 123     /// The trailing expression of the block, if any.
 124     pub expr: Option<ExprId>,
 125     pub safety_mode: BlockSafety,
 126 }
 127
 128 #[derive(Debug, HashStable)]
 129 pub struct Adt<'tcx> {
 130     /// The ADT we're constructing.
 131     pub adt_def: AdtDef<'tcx>,
 132     /// The variant of the ADT.
 133     pub variant_index: VariantIdx,
 134     pub substs: SubstsRef<'tcx>,
 135
 136     /// Optional user-given substs: for something like `let x =
 137     /// Bar::<T> { ... }`.
 138     pub user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 139
 140     pub fields: Box<[FieldExpr]>,
 141     /// The base, e.g. `Foo {x: 1, .. base}`.
 142     pub base: Option<FruInfo<'tcx>>,
 143 }
 144
 145 #[derive(Copy, Clone, Debug, HashStable)]
 146 pub enum BlockSafety {
 147     Safe,
 148     /// A compiler-generated unsafe block
 149     BuiltinUnsafe,
 150     /// An `unsafe` block. The `HirId` is the ID of the block.
 151     ExplicitUnsafe(hir::HirId),
 152 }
 153
 154 #[derive(Debug, HashStable)]
 155 pub struct Stmt<'tcx> {
 156     pub kind: StmtKind<'tcx>,
 157     pub opt_destruction_scope: Option<region::Scope>,
 158 }
 159
 160 #[derive(Debug, HashStable)]
 161 pub enum StmtKind<'tcx> {
 162     /// An expression with a trailing semicolon.
 163     Expr {
 164         /// The scope for this statement; may be used as lifetime of temporaries.
 165         scope: region::Scope,
 166
 167         /// The expression being evaluated in this statement.
 168         expr: ExprId,
 169     },
 170
 171     /// A `let` binding.
 172     Let {
 173         /// The scope for variables bound in this `let`; it covers this and
 174         /// all the remaining statements in the block.
 175         remainder_scope: region::Scope,
 176
 177         /// The scope for the initialization itself; might be used as
 178         /// lifetime of temporaries.
 179         init_scope: region::Scope,
 180
 181         /// `let <PAT> = ...`
 182         ///
 183         /// If a type annotation is included, it is added as an ascription pattern.
 184         pattern: Pat<'tcx>,
 185
 186         /// `let pat: ty = <INIT>`
 187         initializer: Option<ExprId>,
 188
 189         /// The lint level for this `let` statement.
 190         lint_level: LintLevel,
 191     },
 192 }
 193
 194 // `Expr` is used a lot. Make sure it doesn't unintentionally get bigger.
 195 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
 196 rustc_data_structures::static_assert_size!(Expr<'_>, 104);
 197
 198 /// A THIR expression.
 199 #[derive(Debug, HashStable)]
 200 pub struct Expr<'tcx> {
 201     /// The type of this expression
 202     pub ty: Ty<'tcx>,
 203
 204     /// The lifetime of this expression if it should be spilled into a
 205     /// temporary; should be `None` only if in a constant context
 206     pub temp_lifetime: Option<region::Scope>,
 207
 208     /// span of the expression in the source
 209     pub span: Span,
 210
 211     /// kind of expression
 212     pub kind: ExprKind<'tcx>,
 213 }
 214
 215 #[derive(Debug, HashStable)]
 216 pub enum ExprKind<'tcx> {
 217     /// `Scope`s are used to explicitly mark destruction scopes,
 218     /// and to track the `HirId` of the expressions within the scope.
 219     Scope {
 220         region_scope: region::Scope,
 221         lint_level: LintLevel,
 222         value: ExprId,
 223     },
 224     /// A `box <value>` expression.
 225     Box {
 226         value: ExprId,
 227     },
 228     /// An `if` expression.
 229     If {
 230         if_then_scope: region::Scope,
 231         cond: ExprId,
 232         then: ExprId,
 233         else_opt: Option<ExprId>,
 234     },
 235     /// A function call. Method calls and overloaded operators are converted to plain function calls.
 236     Call {
 237         /// The type of the function. This is often a [`FnDef`] or a [`FnPtr`].
 238         ///
 239         /// [`FnDef`]: ty::TyKind::FnDef
 240         /// [`FnPtr`]: ty::TyKind::FnPtr
 241         ty: Ty<'tcx>,
 242         /// The function itself.
 243         fun: ExprId,
 244         /// The arguments passed to the function.
 245         ///
 246         /// Note: in some cases (like calling a closure), the function call `f(...args)` gets
 247         /// rewritten as a call to a function trait method (e.g. `FnOnce::call_once(f, (...args))`).
 248         args: Box<[ExprId]>,
 249         /// Whether this is from an overloaded operator rather than a
 250         /// function call from HIR. `true` for overloaded function call.
 251         from_hir_call: bool,
 252         /// The span of the function, without the dot and receiver
 253         /// (e.g. `foo(a, b)` in `x.foo(a, b)`).
 254         fn_span: Span,
 255     },
 256     /// A *non-overloaded* dereference.
 257     Deref {
 258         arg: ExprId,
 259     },
 260     /// A *non-overloaded* binary operation.
 261     Binary {
 262         op: BinOp,
 263         lhs: ExprId,
 264         rhs: ExprId,
 265     },
 266     /// A logical operation. This is distinct from `BinaryOp` because
 267     /// the operands need to be lazily evaluated.
 268     LogicalOp {
 269         op: LogicalOp,
 270         lhs: ExprId,
 271         rhs: ExprId,
 272     },
 273     /// A *non-overloaded* unary operation. Note that here the deref (`*`)
 274     /// operator is represented by `ExprKind::Deref`.
 275     Unary {
 276         op: UnOp,
 277         arg: ExprId,
 278     },
 279     /// A cast: `<source> as <type>`. The type we cast to is the type of
 280     /// the parent expression.
 281     Cast {
 282         source: ExprId,
 283     },
 284     Use {
 285         source: ExprId,
 286     }, // Use a lexpr to get a vexpr.
 287     /// A coercion from `!` to any type.
 288     NeverToAny {
 289         source: ExprId,
 290     },
 291     /// A pointer cast. More information can be found in [`PointerCast`].
 292     Pointer {
 293         cast: PointerCast,
 294         source: ExprId,
 295     },
 296     /// A `loop` expression.
 297     Loop {
 298         body: ExprId,
 299     },
 300     Let {
 301         expr: ExprId,
 302         pat: Pat<'tcx>,
 303     },
 304     /// A `match` expression.
 305     Match {
 306         scrutinee: ExprId,
 307         arms: Box<[ArmId]>,
 308     },
 309     /// A block.
 310     Block {
 311         body: Block,
 312     },
 313     /// An assignment: `lhs = rhs`.
 314     Assign {
 315         lhs: ExprId,
 316         rhs: ExprId,
 317     },
 318     /// A *non-overloaded* operation assignment, e.g. `lhs += rhs`.
 319     AssignOp {
 320         op: BinOp,
 321         lhs: ExprId,
 322         rhs: ExprId,
 323     },
 324     /// Access to a struct or tuple field.
 325     Field {
 326         lhs: ExprId,
 327         /// This can be a named (`.foo`) or unnamed (`.0`) field.
 328         name: Field,
 329     },
 330     /// A *non-overloaded* indexing operation.
 331     Index {
 332         lhs: ExprId,
 333         index: ExprId,
 334     },
 335     /// A local variable.
 336     VarRef {
 337         id: hir::HirId,
 338     },
 339     /// Used to represent upvars mentioned in a closure/generator
 340     UpvarRef {
 341         /// DefId of the closure/generator
 342         closure_def_id: DefId,
 343
 344         /// HirId of the root variable
 345         var_hir_id: hir::HirId,
 346     },
 347     /// A borrow, e.g. `&arg`.
 348     Borrow {
 349         borrow_kind: BorrowKind,
 350         arg: ExprId,
 351     },
 352     /// A `&raw [const|mut] $place_expr` raw borrow resulting in type `*[const|mut] T`.
 353     AddressOf {
 354         mutability: hir::Mutability,
 355         arg: ExprId,
 356     },
 357     /// A `break` expression.
 358     Break {
 359         label: region::Scope,
 360         value: Option<ExprId>,
 361     },
 362     /// A `continue` expression.
 363     Continue {
 364         label: region::Scope,
 365     },
 366     /// A `return` expression.
 367     Return {
 368         value: Option<ExprId>,
 369     },
 370     /// An inline `const` block, e.g. `const {}`.
 371     ConstBlock {
 372         did: DefId,
 373         substs: SubstsRef<'tcx>,
 374     },
 375     /// An array literal constructed from one repeated element, e.g. `[1; 5]`.
 376     Repeat {
 377         value: ExprId,
 378         count: Const<'tcx>,
 379     },
 380     /// An array, e.g. `[a, b, c, d]`.
 381     Array {
 382         fields: Box<[ExprId]>,
 383     },
 384     /// A tuple, e.g. `(a, b, c, d)`.
 385     Tuple {
 386         fields: Box<[ExprId]>,
 387     },
 388     /// An ADT constructor, e.g. `Foo {x: 1, y: 2}`.
 389     Adt(Box<Adt<'tcx>>),
 390     /// A type ascription on a place.
 391     PlaceTypeAscription {
 392         source: ExprId,
 393         /// Type that the user gave to this expression
 394         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 395     },
 396     /// A type ascription on a value, e.g. `42: i32`.
 397     ValueTypeAscription {
 398         source: ExprId,
 399         /// Type that the user gave to this expression
 400         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 401     },
 402     /// A closure definition.
 403     Closure {
 404         closure_id: DefId,
 405         substs: UpvarSubsts<'tcx>,
 406         upvars: Box<[ExprId]>,
 407         movability: Option<hir::Movability>,
 408         fake_reads: Vec<(ExprId, FakeReadCause, hir::HirId)>,
 409     },
 410     /// A literal.
 411     Literal {
 412         lit: &'tcx hir::Lit,
 413         neg: bool,
 414     },
 415     /// For literals that don't correspond to anything in the HIR
 416     NonHirLiteral {
 417         lit: ty::ScalarInt,
 418         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 419     },
 420     /// Associated constants and named constants
 421     NamedConst {
 422         def_id: DefId,
 423         substs: SubstsRef<'tcx>,
 424         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
 425     },
 426     ConstParam {
 427         param: ty::ParamConst,
 428         def_id: DefId,
 429     },
 430     // FIXME improve docs for `StaticRef` by distinguishing it from `NamedConst`
 431     /// A literal containing the address of a `static`.
 432     ///
 433     /// This is only distinguished from `Literal` so that we can register some
 434     /// info for diagnostics.
 435     StaticRef {
 436         alloc_id: AllocId,
 437         ty: Ty<'tcx>,
 438         def_id: DefId,
 439     },
 440     /// Inline assembly, i.e. `asm!()`.
 441     InlineAsm {
 442         template: &'tcx [InlineAsmTemplatePiece],
 443         operands: Box<[InlineAsmOperand<'tcx>]>,
 444         options: InlineAsmOptions,
 445         line_spans: &'tcx [Span],
 446     },
 447     /// An expression taking a reference to a thread local.
 448     ThreadLocalRef(DefId),
 449     /// A `yield` expression.
 450     Yield {
 451         value: ExprId,
 452     },
 453 }
 454
 455 impl<'tcx> ExprKind<'tcx> {
 456     pub fn zero_sized_literal(user_ty: Option<Canonical<'tcx, UserType<'tcx>>>) -> Self {
 457         ExprKind::NonHirLiteral { lit: ty::ScalarInt::ZST, user_ty }
 458     }
 459 }
 460
 461 /// Represents the association of a field identifier and an expression.
 462 ///
 463 /// This is used in struct constructors.
 464 #[derive(Debug, HashStable)]
 465 pub struct FieldExpr {
 466     pub name: Field,
 467     pub expr: ExprId,
 468 }
 469
 470 #[derive(Debug, HashStable)]
 471 pub struct FruInfo<'tcx> {
 472     pub base: ExprId,
 473     pub field_types: Box<[Ty<'tcx>]>,
 474 }
 475
 476 /// A `match` arm.
 477 #[derive(Debug, HashStable)]
 478 pub struct Arm<'tcx> {
 479     pub pattern: Pat<'tcx>,
 480     pub guard: Option<Guard<'tcx>>,
 481     pub body: ExprId,
 482     pub lint_level: LintLevel,
 483     pub scope: region::Scope,
 484     pub span: Span,
 485 }
 486
 487 /// A `match` guard.
 488 #[derive(Debug, HashStable)]
 489 pub enum Guard<'tcx> {
 490     If(ExprId),
 491     IfLet(Pat<'tcx>, ExprId),
 492 }
 493
 494 #[derive(Copy, Clone, Debug, HashStable)]
 495 pub enum LogicalOp {
 496     /// The `&&` operator.
 497     And,
 498     /// The `||` operator.
 499     Or,
 500 }
 501
 502 #[derive(Debug, HashStable)]
 503 pub enum InlineAsmOperand<'tcx> {
 504     In {
 505         reg: InlineAsmRegOrRegClass,
 506         expr: ExprId,
 507     },
 508     Out {
 509         reg: InlineAsmRegOrRegClass,
 510         late: bool,
 511         expr: Option<ExprId>,
 512     },
 513     InOut {
 514         reg: InlineAsmRegOrRegClass,
 515         late: bool,
 516         expr: ExprId,
 517     },
 518     SplitInOut {
 519         reg: InlineAsmRegOrRegClass,
 520         late: bool,
 521         in_expr: ExprId,
 522         out_expr: Option<ExprId>,
 523     },
 524     Const {
 525         value: Const<'tcx>,
 526         span: Span,
 527     },
 528     SymFn {
 529         expr: ExprId,
 530     },
 531     SymStatic {
 532         def_id: DefId,
 533     },
 534 }
 535
 536 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
 537 pub enum BindingMode {
 538     ByValue,
 539     ByRef(BorrowKind),
 540 }
 541
 542 #[derive(Clone, Debug, PartialEq, HashStable)]
 543 pub struct FieldPat<'tcx> {
 544     pub field: Field,
 545     pub pattern: Pat<'tcx>,
 546 }
 547
 548 #[derive(Clone, Debug, PartialEq, HashStable)]
 549 pub struct Pat<'tcx> {
 550     pub ty: Ty<'tcx>,
 551     pub span: Span,
 552     pub kind: Box<PatKind<'tcx>>,
 553 }
 554
 555 impl<'tcx> Pat<'tcx> {
 556     pub fn wildcard_from_ty(ty: Ty<'tcx>) -> Self {
 557         Pat { ty, span: DUMMY_SP, kind: Box::new(PatKind::Wild) }
 558     }
 559 }
 560
 561 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
 562 pub struct PatTyProj<'tcx> {
 563     pub user_ty: CanonicalUserType<'tcx>,
 564 }
 565
 566 impl<'tcx> PatTyProj<'tcx> {
 567     pub fn from_user_type(user_annotation: CanonicalUserType<'tcx>) -> Self {
 568         Self { user_ty: user_annotation }
 569     }
 570
 571     pub fn user_ty(
 572         self,
 573         annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
 574         inferred_ty: Ty<'tcx>,
 575         span: Span,
 576     ) -> UserTypeProjection {
 577         UserTypeProjection {
 578             base: annotations.push(CanonicalUserTypeAnnotation {
 579                 span,
 580                 user_ty: self.user_ty,
 581                 inferred_ty,
 582             }),
 583             projs: Vec::new(),
 584         }
 585     }
 586 }
 587
 588 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
 589 pub struct Ascription<'tcx> {
 590     pub user_ty: PatTyProj<'tcx>,
 591     /// Variance to use when relating the type `user_ty` to the **type of the value being
 592     /// matched**. Typically, this is `Variance::Covariant`, since the value being matched must
 593     /// have a type that is some subtype of the ascribed type.
 594     ///
 595     /// Note that this variance does not apply for any bindings within subpatterns. The type
 596     /// assigned to those bindings must be exactly equal to the `user_ty` given here.
 597     ///
 598     /// The only place where this field is not `Covariant` is when matching constants, where
 599     /// we currently use `Contravariant` -- this is because the constant type just needs to
 600     /// be "comparable" to the type of the input value. So, for example:
 601     ///
 602     /// ```text
 603     /// match x { "foo" => .. }
 604     /// ```
 605     ///
 606     /// requires that `&'static str <: T_x`, where `T_x` is the type of `x`. Really, we should
 607     /// probably be checking for a `PartialEq` impl instead, but this preserves the behavior
 608     /// of the old type-check for now. See #57280 for details.
 609     pub variance: ty::Variance,
 610     pub user_ty_span: Span,
 611 }
 612
 613 #[derive(Clone, Debug, PartialEq, HashStable)]
 614 pub enum PatKind<'tcx> {
 615     /// A wildward pattern: `_`.
 616     Wild,
 617
 618     AscribeUserType {
 619         ascription: Ascription<'tcx>,
 620         subpattern: Pat<'tcx>,
 621     },
 622
 623     /// `x`, `ref x`, `x @ P`, etc.
 624     Binding {
 625         mutability: Mutability,
 626         name: Symbol,
 627         mode: BindingMode,
 628         var: hir::HirId,
 629         ty: Ty<'tcx>,
 630         subpattern: Option<Pat<'tcx>>,
 631         /// Is this the leftmost occurrence of the binding, i.e., is `var` the
 632         /// `HirId` of this pattern?
 633         is_primary: bool,
 634     },
 635
 636     /// `Foo(...)` or `Foo{...}` or `Foo`, where `Foo` is a variant name from an ADT with
 637     /// multiple variants.
 638     Variant {
 639         adt_def: AdtDef<'tcx>,
 640         substs: SubstsRef<'tcx>,
 641         variant_index: VariantIdx,
 642         subpatterns: Vec<FieldPat<'tcx>>,
 643     },
 644
 645     /// `(...)`, `Foo(...)`, `Foo{...}`, or `Foo`, where `Foo` is a variant name from an ADT with
 646     /// a single variant.
 647     Leaf {
 648         subpatterns: Vec<FieldPat<'tcx>>,
 649     },
 650
 651     /// `box P`, `&P`, `&mut P`, etc.
 652     Deref {
 653         subpattern: Pat<'tcx>,
 654     },
 655
 656     /// One of the following:
 657     /// * `&str`, which will be handled as a string pattern and thus exhaustiveness
 658     ///   checking will detect if you use the same string twice in different patterns.
 659     /// * integer, bool, char or float, which will be handled by exhaustiveness to cover exactly
 660     ///   its own value, similar to `&str`, but these values are much simpler.
 661     /// * Opaque constants, that must not be matched structurally. So anything that does not derive
 662     ///   `PartialEq` and `Eq`.
 663     Constant {
 664         value: ty::Const<'tcx>,
 665     },
 666
 667     Range(PatRange<'tcx>),
 668
 669     /// Matches against a slice, checking the length and extracting elements.
 670     /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
 671     /// e.g., `&[ref xs @ ..]`.
 672     Slice {
 673         prefix: Vec<Pat<'tcx>>,
 674         slice: Option<Pat<'tcx>>,
 675         suffix: Vec<Pat<'tcx>>,
 676     },
 677
 678     /// Fixed match against an array; irrefutable.
 679     Array {
 680         prefix: Vec<Pat<'tcx>>,
 681         slice: Option<Pat<'tcx>>,
 682         suffix: Vec<Pat<'tcx>>,
 683     },
 684
 685     /// An or-pattern, e.g. `p | q`.
 686     /// Invariant: `pats.len() >= 2`.
 687     Or {
 688         pats: Vec<Pat<'tcx>>,
 689     },
 690 }
 691
 692 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
 693 pub struct PatRange<'tcx> {
 694     pub lo: ty::Const<'tcx>,
 695     pub hi: ty::Const<'tcx>,
 696     pub end: RangeEnd,
 697 }
 698
 699 impl<'tcx> fmt::Display for Pat<'tcx> {
 700     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
 701         // Printing lists is a chore.
 702         let mut first = true;
 703         let mut start_or_continue = |s| {
 704             if first {
 705                 first = false;
 706                 ""
 707             } else {
 708                 s
 709             }
 710         };
 711         let mut start_or_comma = || start_or_continue(", ");
 712
 713         match *self.kind {
 714             PatKind::Wild => write!(f, "_"),
 715             PatKind::AscribeUserType { ref subpattern, .. } => write!(f, "{}: _", subpattern),
 716             PatKind::Binding { mutability, name, mode, ref subpattern, .. } => {
 717                 let is_mut = match mode {
 718                     BindingMode::ByValue => mutability == Mutability::Mut,
 719                     BindingMode::ByRef(bk) => {
 720                         write!(f, "ref ")?;
 721                         matches!(bk, BorrowKind::Mut { .. })
 722                     }
 723                 };
 724                 if is_mut {
 725                     write!(f, "mut ")?;
 726                 }
 727                 write!(f, "{}", name)?;
 728                 if let Some(ref subpattern) = *subpattern {
 729                     write!(f, " @ {}", subpattern)?;
 730                 }
 731                 Ok(())
 732             }
 733             PatKind::Variant { ref subpatterns, .. } | PatKind::Leaf { ref subpatterns } => {
 734                 let variant = match *self.kind {
 735                     PatKind::Variant { adt_def, variant_index, .. } => {
 736                         Some(adt_def.variant(variant_index))
 737                     }
 738                     _ => self.ty.ty_adt_def().and_then(|adt| {
 739                         if !adt.is_enum() { Some(adt.non_enum_variant()) } else { None }
 740                     }),
 741                 };
 742
 743                 if let Some(variant) = variant {
 744                     write!(f, "{}", variant.name)?;
 745
 746                     // Only for Adt we can have `S {...}`,
 747                     // which we handle separately here.
 748                     if variant.ctor_kind == CtorKind::Fictive {
 749                         write!(f, " {{ ")?;
 750
 751                         let mut printed = 0;
 752                         for p in subpatterns {
 753                             if let PatKind::Wild = *p.pattern.kind {
 754                                 continue;
 755                             }
 756                             let name = variant.fields[p.field.index()].name;
 757                             write!(f, "{}{}: {}", start_or_comma(), name, p.pattern)?;
 758                             printed += 1;
 759                         }
 760
 761                         if printed < variant.fields.len() {
 762                             write!(f, "{}..", start_or_comma())?;
 763                         }
 764
 765                         return write!(f, " }}");
 766                     }
 767                 }
 768
 769                 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
 770                 if num_fields != 0 || variant.is_none() {
 771                     write!(f, "(")?;
 772                     for i in 0..num_fields {
 773                         write!(f, "{}", start_or_comma())?;
 774
 775                         // Common case: the field is where we expect it.
 776                         if let Some(p) = subpatterns.get(i) {
 777                             if p.field.index() == i {
 778                                 write!(f, "{}", p.pattern)?;
 779                                 continue;
 780                             }
 781                         }
 782
 783                         // Otherwise, we have to go looking for it.
 784                         if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
 785                             write!(f, "{}", p.pattern)?;
 786                         } else {
 787                             write!(f, "_")?;
 788                         }
 789                     }
 790                     write!(f, ")")?;
 791                 }
 792
 793                 Ok(())
 794             }
 795             PatKind::Deref { ref subpattern } => {
 796                 match self.ty.kind() {
 797                     ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
 798                     ty::Ref(_, _, mutbl) => {
 799                         write!(f, "&{}", mutbl.prefix_str())?;
 800                     }
 801                     _ => bug!("{} is a bad Deref pattern type", self.ty),
 802                 }
 803                 write!(f, "{}", subpattern)
 804             }
 805             PatKind::Constant { value } => write!(f, "{}", value),
 806             PatKind::Range(PatRange { lo, hi, end }) => {
 807                 write!(f, "{}", lo)?;
 808                 write!(f, "{}", end)?;
 809                 write!(f, "{}", hi)
 810             }
 811             PatKind::Slice { ref prefix, ref slice, ref suffix }
 812             | PatKind::Array { ref prefix, ref slice, ref suffix } => {
 813                 write!(f, "[")?;
 814                 for p in prefix {
 815                     write!(f, "{}{}", start_or_comma(), p)?;
 816                 }
 817                 if let Some(ref slice) = *slice {
 818                     write!(f, "{}", start_or_comma())?;
 819                     match *slice.kind {
 820                         PatKind::Wild => {}
 821                         _ => write!(f, "{}", slice)?,
 822                     }
 823                     write!(f, "..")?;
 824                 }
 825                 for p in suffix {
 826                     write!(f, "{}{}", start_or_comma(), p)?;
 827                 }
 828                 write!(f, "]")
 829             }
 830             PatKind::Or { ref pats } => {
 831                 for pat in pats {
 832                     write!(f, "{}{}", start_or_continue(" | "), pat)?;
 833                 }
 834                 Ok(())
 835             }
 836         }
 837     }
 838 }