1 //! THIR datatypes and definitions. See the [rustc dev guide] for more info.
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.
9 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/thir.html
11 use rustc_ast::{InlineAsmOptions, InlineAsmTemplatePiece};
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::{
21 BinOp, BorrowKind, FakeReadCause, Field, Mutability, UnOp, UserTypeProjection,
23 use rustc_middle::ty::adjustment::PointerCast;
24 use rustc_middle::ty::subst::SubstsRef;
25 use rustc_middle::ty::{self, AdtDef, Const, Ty, UpvarSubsts, UserType};
26 use rustc_middle::ty::{
27 CanonicalUserType, CanonicalUserTypeAnnotation, CanonicalUserTypeAnnotations,
29 use rustc_span::{Span, Symbol, DUMMY_SP};
30 use rustc_target::abi::VariantIdx;
31 use rustc_target::asm::InlineAsmRegOrRegClass;
37 /// An index to an [`Arm`] stored in [`Thir::arms`]
45 /// An index to an [`Expr`] stored in [`Thir::exprs`]
54 /// An index to a [`Stmt`] stored in [`Thir::stmts`]
60 macro_rules! thir_with_elements {
61 ($($name:ident: $id:ty => $value:ty,)*) => {
62 /// A container for a THIR body.
64 /// This can be indexed directly by any THIR index (e.g. [`ExprId`]).
65 #[derive(Debug, HashStable)]
66 pub struct Thir<'tcx> {
68 pub $name: IndexVec<$id, $value>,
72 impl<'tcx> Thir<'tcx> {
73 pub fn new() -> Thir<'tcx> {
76 $name: IndexVec::new(),
83 impl<'tcx> Index<$id> for Thir<'tcx> {
85 fn index(&self, index: $id) -> &Self::Output {
94 arms: ArmId => Arm<'tcx>,
95 exprs: ExprId => Expr<'tcx>,
96 stmts: StmtId => Stmt<'tcx>,
99 #[derive(Copy, Clone, Debug, HashStable)]
102 Explicit(hir::HirId),
105 #[derive(Debug, HashStable)]
107 /// Whether the block itself has a label. Used by `label: {}`
108 /// and `try` blocks.
110 /// This does *not* include labels on loops, e.g. `'label: loop {}`.
111 pub targeted_by_break: bool,
112 pub region_scope: region::Scope,
113 pub opt_destruction_scope: Option<region::Scope>,
114 /// The span of the block, including the opening braces,
115 /// the label, and the `unsafe` keyword, if present.
117 /// The statements in the blocK.
118 pub stmts: Box<[StmtId]>,
119 /// The trailing expression of the block, if any.
120 pub expr: Option<ExprId>,
121 pub safety_mode: BlockSafety,
124 #[derive(Debug, HashStable)]
125 pub struct Adt<'tcx> {
126 /// The ADT we're constructing.
127 pub adt_def: &'tcx AdtDef,
128 /// The variant of the ADT.
129 pub variant_index: VariantIdx,
130 pub substs: SubstsRef<'tcx>,
132 /// Optional user-given substs: for something like `let x =
133 /// Bar::<T> { ... }`.
134 pub user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
136 pub fields: Box<[FieldExpr]>,
137 /// The base, e.g. `Foo {x: 1, .. base}`.
138 pub base: Option<FruInfo<'tcx>>,
141 #[derive(Copy, Clone, Debug, HashStable)]
142 pub enum BlockSafety {
144 /// A compiler-generated unsafe block
146 /// An `unsafe` block. The `HirId` is the ID of the block.
147 ExplicitUnsafe(hir::HirId),
150 #[derive(Debug, HashStable)]
151 pub struct Stmt<'tcx> {
152 pub kind: StmtKind<'tcx>,
153 pub opt_destruction_scope: Option<region::Scope>,
156 #[derive(Debug, HashStable)]
157 pub enum StmtKind<'tcx> {
158 /// An expression with a trailing semicolon.
160 /// The scope for this statement; may be used as lifetime of temporaries.
161 scope: region::Scope,
163 /// The expression being evaluated in this statement.
169 /// The scope for variables bound in this `let`; it covers this and
170 /// all the remaining statements in the block.
171 remainder_scope: region::Scope,
173 /// The scope for the initialization itself; might be used as
174 /// lifetime of temporaries.
175 init_scope: region::Scope,
177 /// `let <PAT> = ...`
179 /// If a type annotation is included, it is added as an ascription pattern.
182 /// `let pat: ty = <INIT>`
183 initializer: Option<ExprId>,
185 /// The lint level for this `let` statement.
186 lint_level: LintLevel,
190 // `Expr` is used a lot. Make sure it doesn't unintentionally get bigger.
191 #[cfg(all(target_arch = "x86_64", target_pointer_width = "64"))]
192 rustc_data_structures::static_assert_size!(Expr<'_>, 104);
194 /// A THIR expression.
195 #[derive(Debug, HashStable)]
196 pub struct Expr<'tcx> {
197 /// The type of this expression
200 /// The lifetime of this expression if it should be spilled into a
201 /// temporary; should be `None` only if in a constant context
202 pub temp_lifetime: Option<region::Scope>,
204 /// span of the expression in the source
207 /// kind of expression
208 pub kind: ExprKind<'tcx>,
211 #[derive(Debug, HashStable)]
212 pub enum ExprKind<'tcx> {
213 /// `Scope`s are used to explicitely mark destruction scopes,
214 /// and to track the `HirId` of the expressions within the scope.
216 region_scope: region::Scope,
217 lint_level: LintLevel,
220 /// A `box <value>` expression.
224 /// An `if` expression.
228 else_opt: Option<ExprId>,
230 /// A function call. Method calls and overloaded operators are converted to plain function calls.
232 /// The type of the function. This is often a [`FnDef`] or a [`FnPtr`].
234 /// [`FnDef`]: ty::TyKind::FnDef
235 /// [`FnPtr`]: ty::TyKind::FnPtr
237 /// The function itself.
239 /// The arguments passed to the function.
241 /// Note: in some cases (like calling a closure), the function call `f(...args)` gets
242 /// rewritten as a call to a function trait method (e.g. `FnOnce::call_once(f, (...args))`).
244 /// Whether this is from an overloaded operator rather than a
245 /// function call from HIR. `true` for overloaded function call.
247 /// The span of the function, without the dot and receiver
248 /// (e.g. `foo(a, b)` in `x.foo(a, b)`).
251 /// A *non-overloaded* dereference.
255 /// A *non-overloaded* binary operation.
261 /// A logical operation. This is distinct from `BinaryOp` because
262 /// the operands need to be lazily evaluated.
268 /// A *non-overloaded* unary operation. Note that here the deref (`*`)
269 /// operator is represented by `ExprKind::Deref`.
274 /// A cast: `<source> as <type>`. The type we cast to is the type of
275 /// the parent expression.
281 }, // Use a lexpr to get a vexpr.
282 /// A coercion from `!` to any type.
286 /// A pointer cast. More information can be found in [`PointerCast`].
291 /// A `loop` expression.
299 /// A `match` expression.
308 /// An assignment: `lhs = rhs`.
313 /// A *non-overloaded* operation assignment, e.g. `lhs += rhs`.
319 /// Access to a struct or tuple field.
322 /// This can be a named (`.foo`) or unnamed (`.0`) field.
325 /// A *non-overloaded* indexing operation.
330 /// A local variable.
334 /// Used to represent upvars mentioned in a closure/generator
336 /// DefId of the closure/generator
337 closure_def_id: DefId,
339 /// HirId of the root variable
340 var_hir_id: hir::HirId,
342 /// A borrow, e.g. `&arg`.
344 borrow_kind: BorrowKind,
347 /// A `&raw [const|mut] $place_expr` raw borrow resulting in type `*[const|mut] T`.
349 mutability: hir::Mutability,
352 /// A `break` expression.
354 label: region::Scope,
355 value: Option<ExprId>,
357 /// A `continue` expression.
359 label: region::Scope,
361 /// A `return` expression.
363 value: Option<ExprId>,
365 /// An inline `const` block, e.g. `const {}`.
367 value: &'tcx Const<'tcx>,
369 /// An array literal constructed from one repeated element, e.g. `[1; 5]`.
372 count: &'tcx Const<'tcx>,
374 /// An array, e.g. `[a, b, c, d]`.
376 fields: Box<[ExprId]>,
378 /// A tuple, e.g. `(a, b, c, d)`.
380 fields: Box<[ExprId]>,
382 /// An ADT constructor, e.g. `Foo {x: 1, y: 2}`.
384 /// A type ascription on a place.
385 PlaceTypeAscription {
387 /// Type that the user gave to this expression
388 user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
390 /// A type ascription on a value, e.g. `42: i32`.
391 ValueTypeAscription {
393 /// Type that the user gave to this expression
394 user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
396 /// A closure definition.
399 substs: UpvarSubsts<'tcx>,
400 upvars: Box<[ExprId]>,
401 movability: Option<hir::Movability>,
402 fake_reads: Vec<(ExprId, FakeReadCause, hir::HirId)>,
406 literal: &'tcx Const<'tcx>,
407 user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
408 /// The `DefId` of the `const` item this literal
409 /// was produced from, if this is not a user-written
411 const_id: Option<DefId>,
413 /// A literal containing the address of a `static`.
415 /// This is only distinguished from `Literal` so that we can register some
416 /// info for diagnostics.
418 literal: &'tcx Const<'tcx>,
421 /// Inline assembly, i.e. `asm!()`.
423 template: &'tcx [InlineAsmTemplatePiece],
424 operands: Box<[InlineAsmOperand<'tcx>]>,
425 options: InlineAsmOptions,
426 line_spans: &'tcx [Span],
428 /// An expression taking a reference to a thread local.
429 ThreadLocalRef(DefId),
430 /// Inline LLVM assembly, i.e. `llvm_asm!()`.
432 asm: &'tcx hir::LlvmInlineAsmInner,
433 outputs: Box<[ExprId]>,
434 inputs: Box<[ExprId]>,
436 /// A `yield` expression.
442 /// Represents the association of a field identifier and an expression.
444 /// This is used in struct constructors.
445 #[derive(Debug, HashStable)]
446 pub struct FieldExpr {
451 #[derive(Debug, HashStable)]
452 pub struct FruInfo<'tcx> {
454 pub field_types: Box<[Ty<'tcx>]>,
458 #[derive(Debug, HashStable)]
459 pub struct Arm<'tcx> {
460 pub pattern: Pat<'tcx>,
461 pub guard: Option<Guard<'tcx>>,
463 pub lint_level: LintLevel,
464 pub scope: region::Scope,
469 #[derive(Debug, HashStable)]
470 pub enum Guard<'tcx> {
472 IfLet(Pat<'tcx>, ExprId),
475 #[derive(Copy, Clone, Debug, HashStable)]
477 /// The `&&` operator.
479 /// The `||` operator.
483 #[derive(Debug, HashStable)]
484 pub enum InlineAsmOperand<'tcx> {
486 reg: InlineAsmRegOrRegClass,
490 reg: InlineAsmRegOrRegClass,
492 expr: Option<ExprId>,
495 reg: InlineAsmRegOrRegClass,
500 reg: InlineAsmRegOrRegClass,
503 out_expr: Option<ExprId>,
506 value: &'tcx Const<'tcx>,
517 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
518 pub enum BindingMode {
523 #[derive(Clone, Debug, PartialEq, HashStable)]
524 pub struct FieldPat<'tcx> {
526 pub pattern: Pat<'tcx>,
529 #[derive(Clone, Debug, PartialEq, HashStable)]
530 pub struct Pat<'tcx> {
533 pub kind: Box<PatKind<'tcx>>,
536 impl<'tcx> Pat<'tcx> {
537 pub fn wildcard_from_ty(ty: Ty<'tcx>) -> Self {
538 Pat { ty, span: DUMMY_SP, kind: Box::new(PatKind::Wild) }
542 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
543 pub struct PatTyProj<'tcx> {
544 pub user_ty: CanonicalUserType<'tcx>,
547 impl<'tcx> PatTyProj<'tcx> {
548 pub fn from_user_type(user_annotation: CanonicalUserType<'tcx>) -> Self {
549 Self { user_ty: user_annotation }
554 annotations: &mut CanonicalUserTypeAnnotations<'tcx>,
555 inferred_ty: Ty<'tcx>,
557 ) -> UserTypeProjection {
559 base: annotations.push(CanonicalUserTypeAnnotation {
561 user_ty: self.user_ty,
569 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
570 pub struct Ascription<'tcx> {
571 pub user_ty: PatTyProj<'tcx>,
572 /// Variance to use when relating the type `user_ty` to the **type of the value being
573 /// matched**. Typically, this is `Variance::Covariant`, since the value being matched must
574 /// have a type that is some subtype of the ascribed type.
576 /// Note that this variance does not apply for any bindings within subpatterns. The type
577 /// assigned to those bindings must be exactly equal to the `user_ty` given here.
579 /// The only place where this field is not `Covariant` is when matching constants, where
580 /// we currently use `Contravariant` -- this is because the constant type just needs to
581 /// be "comparable" to the type of the input value. So, for example:
584 /// match x { "foo" => .. }
587 /// requires that `&'static str <: T_x`, where `T_x` is the type of `x`. Really, we should
588 /// probably be checking for a `PartialEq` impl instead, but this preserves the behavior
589 /// of the old type-check for now. See #57280 for details.
590 pub variance: ty::Variance,
591 pub user_ty_span: Span,
594 #[derive(Clone, Debug, PartialEq, HashStable)]
595 pub enum PatKind<'tcx> {
596 /// A wildward pattern: `_`.
600 ascription: Ascription<'tcx>,
601 subpattern: Pat<'tcx>,
604 /// `x`, `ref x`, `x @ P`, etc.
606 mutability: Mutability,
611 subpattern: Option<Pat<'tcx>>,
612 /// Is this the leftmost occurrence of the binding, i.e., is `var` the
613 /// `HirId` of this pattern?
617 /// `Foo(...)` or `Foo{...}` or `Foo`, where `Foo` is a variant name from an ADT with
618 /// multiple variants.
620 adt_def: &'tcx AdtDef,
621 substs: SubstsRef<'tcx>,
622 variant_index: VariantIdx,
623 subpatterns: Vec<FieldPat<'tcx>>,
626 /// `(...)`, `Foo(...)`, `Foo{...}`, or `Foo`, where `Foo` is a variant name from an ADT with
627 /// a single variant.
629 subpatterns: Vec<FieldPat<'tcx>>,
632 /// `box P`, `&P`, `&mut P`, etc.
634 subpattern: Pat<'tcx>,
637 /// One of the following:
638 /// * `&str`, which will be handled as a string pattern and thus exhaustiveness
639 /// checking will detect if you use the same string twice in different patterns.
640 /// * integer, bool, char or float, which will be handled by exhaustivenes to cover exactly
641 /// its own value, similar to `&str`, but these values are much simpler.
642 /// * Opaque constants, that must not be matched structurally. So anything that does not derive
643 /// `PartialEq` and `Eq`.
645 value: &'tcx ty::Const<'tcx>,
648 Range(PatRange<'tcx>),
650 /// Matches against a slice, checking the length and extracting elements.
651 /// irrefutable when there is a slice pattern and both `prefix` and `suffix` are empty.
652 /// e.g., `&[ref xs @ ..]`.
654 prefix: Vec<Pat<'tcx>>,
655 slice: Option<Pat<'tcx>>,
656 suffix: Vec<Pat<'tcx>>,
659 /// Fixed match against an array; irrefutable.
661 prefix: Vec<Pat<'tcx>>,
662 slice: Option<Pat<'tcx>>,
663 suffix: Vec<Pat<'tcx>>,
666 /// An or-pattern, e.g. `p | q`.
667 /// Invariant: `pats.len() >= 2`.
669 pats: Vec<Pat<'tcx>>,
673 #[derive(Copy, Clone, Debug, PartialEq, HashStable)]
674 pub struct PatRange<'tcx> {
675 pub lo: &'tcx ty::Const<'tcx>,
676 pub hi: &'tcx ty::Const<'tcx>,
680 impl<'tcx> fmt::Display for Pat<'tcx> {
681 fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
682 // Printing lists is a chore.
683 let mut first = true;
684 let mut start_or_continue = |s| {
692 let mut start_or_comma = || start_or_continue(", ");
695 PatKind::Wild => write!(f, "_"),
696 PatKind::AscribeUserType { ref subpattern, .. } => write!(f, "{}: _", subpattern),
697 PatKind::Binding { mutability, name, mode, ref subpattern, .. } => {
698 let is_mut = match mode {
699 BindingMode::ByValue => mutability == Mutability::Mut,
700 BindingMode::ByRef(bk) => {
702 matches!(bk, BorrowKind::Mut { .. })
708 write!(f, "{}", name)?;
709 if let Some(ref subpattern) = *subpattern {
710 write!(f, " @ {}", subpattern)?;
714 PatKind::Variant { ref subpatterns, .. } | PatKind::Leaf { ref subpatterns } => {
715 let variant = match *self.kind {
716 PatKind::Variant { adt_def, variant_index, .. } => {
717 Some(&adt_def.variants[variant_index])
719 _ => self.ty.ty_adt_def().and_then(|adt| {
720 if !adt.is_enum() { Some(adt.non_enum_variant()) } else { None }
724 if let Some(variant) = variant {
725 write!(f, "{}", variant.ident)?;
727 // Only for Adt we can have `S {...}`,
728 // which we handle separately here.
729 if variant.ctor_kind == CtorKind::Fictive {
733 for p in subpatterns {
734 if let PatKind::Wild = *p.pattern.kind {
737 let name = variant.fields[p.field.index()].ident;
738 write!(f, "{}{}: {}", start_or_comma(), name, p.pattern)?;
742 if printed < variant.fields.len() {
743 write!(f, "{}..", start_or_comma())?;
746 return write!(f, " }}");
750 let num_fields = variant.map_or(subpatterns.len(), |v| v.fields.len());
751 if num_fields != 0 || variant.is_none() {
753 for i in 0..num_fields {
754 write!(f, "{}", start_or_comma())?;
756 // Common case: the field is where we expect it.
757 if let Some(p) = subpatterns.get(i) {
758 if p.field.index() == i {
759 write!(f, "{}", p.pattern)?;
764 // Otherwise, we have to go looking for it.
765 if let Some(p) = subpatterns.iter().find(|p| p.field.index() == i) {
766 write!(f, "{}", p.pattern)?;
776 PatKind::Deref { ref subpattern } => {
777 match self.ty.kind() {
778 ty::Adt(def, _) if def.is_box() => write!(f, "box ")?,
779 ty::Ref(_, _, mutbl) => {
780 write!(f, "&{}", mutbl.prefix_str())?;
782 _ => bug!("{} is a bad Deref pattern type", self.ty),
784 write!(f, "{}", subpattern)
786 PatKind::Constant { value } => write!(f, "{}", value),
787 PatKind::Range(PatRange { lo, hi, end }) => {
788 write!(f, "{}", lo)?;
789 write!(f, "{}", end)?;
792 PatKind::Slice { ref prefix, ref slice, ref suffix }
793 | PatKind::Array { ref prefix, ref slice, ref suffix } => {
796 write!(f, "{}{}", start_or_comma(), p)?;
798 if let Some(ref slice) = *slice {
799 write!(f, "{}", start_or_comma())?;
802 _ => write!(f, "{}", slice)?,
807 write!(f, "{}{}", start_or_comma(), p)?;
811 PatKind::Or { ref pats } => {
813 write!(f, "{}{}", start_or_continue(" | "), pat)?;