src/librustc_mir/hair/mod.rs - third_party/rust - Git at Google

 //! The MIR is built from some high-level abstract IR
 //! (HAIR). This section defines the HAIR along with a trait for
 //! accessing it. The intention is to allow MIR construction to be
 //! unit-tested and separated from the Rust source and compiler data
 //! structures.

 use rustc::mir::{BinOp, BorrowKind, Field, UnOp};
 use rustc::hir::def_id::DefId;
 use rustc::infer::canonical::Canonical;
 use rustc::middle::region;
 use rustc::ty::subst::SubstsRef;
 use rustc::ty::{AdtDef, UpvarSubsts, Ty, Const, UserType};
 use rustc::ty::adjustment::{PointerCast};
 use rustc::ty::layout::VariantIdx;
 use rustc::hir;
 use syntax_pos::Span;
 use self::cx::Cx;

 pub mod cx;
 mod constant;

 pub mod pattern;
 pub use self::pattern::{BindingMode, Pattern, PatternKind, PatternRange, FieldPattern};
 pub(crate) use self::pattern::PatternTypeProjection;

 mod util;

 #[derive(Copy, Clone, Debug)]
 pub enum LintLevel {
     Inherited,
     Explicit(hir::HirId)
 }

 #[derive(Clone, Debug)]
 pub struct Block<'tcx> {
     pub targeted_by_break: bool,
     pub region_scope: region::Scope,
     pub opt_destruction_scope: Option<region::Scope>,
     pub span: Span,
     pub stmts: Vec<StmtRef<'tcx>>,
     pub expr: Option<ExprRef<'tcx>>,
     pub safety_mode: BlockSafety,
 }

 #[derive(Copy, Clone, Debug)]
 pub enum BlockSafety {
     Safe,
     ExplicitUnsafe(hir::HirId),
     PushUnsafe,
     PopUnsafe
 }

 #[derive(Clone, Debug)]
 pub enum StmtRef<'tcx> {
     Mirror(Box<Stmt<'tcx>>),
 }

 #[derive(Clone, Debug)]
 pub struct Stmt<'tcx> {
     pub kind: StmtKind<'tcx>,
     pub opt_destruction_scope: Option<region::Scope>,
 }

 #[derive(Clone, Debug)]
 pub enum StmtKind<'tcx> {
     Expr {
         /// scope for this statement; may be used as lifetime of temporaries
         scope: region::Scope,

         /// expression being evaluated in this statement
         expr: ExprRef<'tcx>,
     },

     Let {
         /// scope for variables bound in this let; covers this and
         /// remaining statements in block
         remainder_scope: region::Scope,

         /// scope for the initialization itself; might be used as
         /// lifetime of temporaries
         init_scope: region::Scope,

         /// `let <PAT> = ...`
         ///
         /// if a type is included, it is added as an ascription pattern
         pattern: Pattern<'tcx>,

         /// let pat: ty = <INIT> ...
         initializer: Option<ExprRef<'tcx>>,

         /// the lint level for this let-statement
         lint_level: LintLevel,
     },
 }

 /// The Hair trait implementor lowers their expressions (`&'tcx H::Expr`)
 /// into instances of this `Expr` enum. This lowering can be done
 /// basically as lazily or as eagerly as desired: every recursive
 /// reference to an expression in this enum is an `ExprRef<'tcx>`, which
 /// may in turn be another instance of this enum (boxed), or else an
 /// unlowered `&'tcx H::Expr`. Note that instances of `Expr` are very
 /// short-lived. They are created by `Hair::to_expr`, analyzed and
 /// converted into MIR, and then discarded.
 ///
 /// If you compare `Expr` to the full compiler AST, you will see it is
 /// a good bit simpler. In fact, a number of the more straight-forward
 /// MIR simplifications are already done in the impl of `Hair`. For
 /// example, method calls and overloaded operators are absent: they are
 /// expected to be converted into `Expr::Call` instances.
 #[derive(Clone, Debug)]
 pub struct Expr<'tcx> {
     /// type of this expression
     pub ty: Ty<'tcx>,

     /// lifetime of this expression if it should be spilled into a
     /// temporary; should be None only if in a constant context
     pub temp_lifetime: Option<region::Scope>,

     /// span of the expression in the source
     pub span: Span,

     /// kind of expression
     pub kind: ExprKind<'tcx>,
 }

 #[derive(Clone, Debug)]
 pub enum ExprKind<'tcx> {
     Scope {
         region_scope: region::Scope,
         lint_level: LintLevel,
         value: ExprRef<'tcx>,
     },
     Box {
         value: ExprRef<'tcx>,
     },
     Call {
         ty: Ty<'tcx>,
         fun: ExprRef<'tcx>,
         args: Vec<ExprRef<'tcx>>,
         // Whether this is from a call in HIR, rather than from an overloaded
         // operator. True for overloaded function call.
         from_hir_call: bool,
     },
     Deref {
         arg: ExprRef<'tcx>,
     }, // NOT overloaded!
     Binary {
         op: BinOp,
         lhs: ExprRef<'tcx>,
         rhs: ExprRef<'tcx>,
     }, // NOT overloaded!
     LogicalOp {
         op: LogicalOp,
         lhs: ExprRef<'tcx>,
         rhs: ExprRef<'tcx>,
     }, // NOT overloaded!
        // LogicalOp is distinct from BinaryOp because of lazy evaluation of the operands.
     Unary {
         op: UnOp,
         arg: ExprRef<'tcx>,
     }, // NOT overloaded!
     Cast {
         source: ExprRef<'tcx>,
     },
     Use {
         source: ExprRef<'tcx>,
     }, // Use a lexpr to get a vexpr.
     NeverToAny {
         source: ExprRef<'tcx>,
     },
     Pointer {
         cast: PointerCast,
         source: ExprRef<'tcx>,
     },
     Loop {
         body: ExprRef<'tcx>,
     },
     Match {
         scrutinee: ExprRef<'tcx>,
         arms: Vec<Arm<'tcx>>,
     },
     Block {
         body: &'tcx hir::Block,
     },
     Assign {
         lhs: ExprRef<'tcx>,
         rhs: ExprRef<'tcx>,
     },
     AssignOp {
         op: BinOp,
         lhs: ExprRef<'tcx>,
         rhs: ExprRef<'tcx>,
     },
     Field {
         lhs: ExprRef<'tcx>,
         name: Field,
     },
     Index {
         lhs: ExprRef<'tcx>,
         index: ExprRef<'tcx>,
     },
     VarRef {
         id: hir::HirId,
     },
     /// first argument, used for self in a closure
     SelfRef,
     StaticRef {
         id: DefId,
     },
     Borrow {
         borrow_kind: BorrowKind,
         arg: ExprRef<'tcx>,
     },
     Break {
         label: region::Scope,
         value: Option<ExprRef<'tcx>>,
     },
     Continue {
         label: region::Scope,
     },
     Return {
         value: Option<ExprRef<'tcx>>,
     },
     Repeat {
         value: ExprRef<'tcx>,
         count: u64,
     },
     Array {
         fields: Vec<ExprRef<'tcx>>,
     },
     Tuple {
         fields: Vec<ExprRef<'tcx>>,
     },
     Adt {
         adt_def: &'tcx AdtDef,
         variant_index: VariantIdx,
         substs: SubstsRef<'tcx>,

         /// Optional user-given substs: for something like `let x =
         /// Bar::<T> { ... }`.
         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,

         fields: Vec<FieldExprRef<'tcx>>,
         base: Option<FruInfo<'tcx>>
     },
     PlaceTypeAscription {
         source: ExprRef<'tcx>,
         /// Type that the user gave to this expression
         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
     },
     ValueTypeAscription {
         source: ExprRef<'tcx>,
         /// Type that the user gave to this expression
         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
     },
     Closure {
         closure_id: DefId,
         substs: UpvarSubsts<'tcx>,
         upvars: Vec<ExprRef<'tcx>>,
         movability: Option<hir::GeneratorMovability>,
     },
     Literal {
         literal: &'tcx Const<'tcx>,
         user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
     },
     InlineAsm {
         asm: &'tcx hir::InlineAsm,
         outputs: Vec<ExprRef<'tcx>>,
         inputs: Vec<ExprRef<'tcx>>
     },
     Yield {
         value: ExprRef<'tcx>,
     },
 }

 #[derive(Clone, Debug)]
 pub enum ExprRef<'tcx> {
     Hair(&'tcx hir::Expr),
     Mirror(Box<Expr<'tcx>>),
 }

 #[derive(Clone, Debug)]
 pub struct FieldExprRef<'tcx> {
     pub name: Field,
     pub expr: ExprRef<'tcx>,
 }

 #[derive(Clone, Debug)]
 pub struct FruInfo<'tcx> {
     pub base: ExprRef<'tcx>,
     pub field_types: Vec<Ty<'tcx>>
 }

 #[derive(Clone, Debug)]
 pub struct Arm<'tcx> {
     pub patterns: Vec<Pattern<'tcx>>,
     pub guard: Option<Guard<'tcx>>,
     pub body: ExprRef<'tcx>,
     pub lint_level: LintLevel,
     pub scope: region::Scope,
     pub span: Span,
 }

 #[derive(Clone, Debug)]
 pub enum Guard<'tcx> {
     If(ExprRef<'tcx>),
 }

 #[derive(Copy, Clone, Debug)]
 pub enum LogicalOp {
     And,
     Or,
 }

 impl<'tcx> ExprRef<'tcx> {
     pub fn span(&self) -> Span {
         match self {
             ExprRef::Hair(expr) => expr.span,
             ExprRef::Mirror(expr) => expr.span,
         }
     }
 }

 ///////////////////////////////////////////////////////////////////////////
 // The Mirror trait

 /// "Mirroring" is the process of converting from a HIR type into one
 /// of the HAIR types defined in this file. This is basically a "on
 /// the fly" desugaring step that hides a lot of the messiness in the
 /// tcx. For example, the mirror of a `&'tcx hir::Expr` is an
 /// `Expr<'tcx>`.
 ///
 /// Mirroring is gradual: when you mirror an outer expression like `e1
 /// + e2`, the references to the inner expressions `e1` and `e2` are
 /// `ExprRef<'tcx>` instances, and they may or may not be eagerly
 /// mirrored. This allows a single AST node from the compiler to
 /// expand into one or more Hair nodes, which lets the Hair nodes be
 /// simpler.
 pub trait Mirror<'tcx> {
     type Output;

     fn make_mirror(self, cx: &mut Cx<'_, 'tcx>) -> Self::Output;
 }

 impl<'tcx> Mirror<'tcx> for Expr<'tcx> {
     type Output = Expr<'tcx>;

     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Expr<'tcx> {
         self
     }
 }

 impl<'tcx> Mirror<'tcx> for ExprRef<'tcx> {
     type Output = Expr<'tcx>;

     fn make_mirror(self, hir: &mut Cx<'a, 'tcx>) -> Expr<'tcx> {
         match self {
             ExprRef::Hair(h) => h.make_mirror(hir),
             ExprRef::Mirror(m) => *m,
         }
     }
 }

 impl<'tcx> Mirror<'tcx> for Stmt<'tcx> {
     type Output = Stmt<'tcx>;

     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Stmt<'tcx> {
         self
     }
 }

 impl<'tcx> Mirror<'tcx> for StmtRef<'tcx> {
     type Output = Stmt<'tcx>;

     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Stmt<'tcx> {
         match self {
             StmtRef::Mirror(m) => *m,
         }
     }
 }

 impl<'tcx> Mirror<'tcx> for Block<'tcx> {
     type Output = Block<'tcx>;

     fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Block<'tcx> {
         self
     }
 }
	//! The MIR is built from some high-level abstract IR
	//! (HAIR). This section defines the HAIR along with a trait for
	//! accessing it. The intention is to allow MIR construction to be
	//! unit-tested and separated from the Rust source and compiler data
	//! structures.

	use rustc::mir::{BinOp, BorrowKind, Field, UnOp};
	use rustc::hir::def_id::DefId;
	use rustc::infer::canonical::Canonical;
	use rustc::middle::region;
	use rustc::ty::subst::SubstsRef;
	use rustc::ty::{AdtDef, UpvarSubsts, Ty, Const, UserType};
	use rustc::ty::adjustment::{PointerCast};
	use rustc::ty::layout::VariantIdx;
	use rustc::hir;
	use syntax_pos::Span;
	use self::cx::Cx;

	pub mod cx;
	mod constant;

	pub mod pattern;
	pub use self::pattern::{BindingMode, Pattern, PatternKind, PatternRange, FieldPattern};
	pub(crate) use self::pattern::PatternTypeProjection;

	mod util;

	#[derive(Copy, Clone, Debug)]
	pub enum LintLevel {
	Inherited,
	Explicit(hir::HirId)
	}

	#[derive(Clone, Debug)]
	pub struct Block<'tcx> {
	pub targeted_by_break: bool,
	pub region_scope: region::Scope,
	pub opt_destruction_scope: Option<region::Scope>,
	pub span: Span,
	pub stmts: Vec<StmtRef<'tcx>>,
	pub expr: Option<ExprRef<'tcx>>,
	pub safety_mode: BlockSafety,
	}

	#[derive(Copy, Clone, Debug)]
	pub enum BlockSafety {
	Safe,
	ExplicitUnsafe(hir::HirId),
	PushUnsafe,
	PopUnsafe
	}

	#[derive(Clone, Debug)]
	pub enum StmtRef<'tcx> {
	Mirror(Box<Stmt<'tcx>>),
	}

	#[derive(Clone, Debug)]
	pub struct Stmt<'tcx> {
	pub kind: StmtKind<'tcx>,
	pub opt_destruction_scope: Option<region::Scope>,
	}

	#[derive(Clone, Debug)]
	pub enum StmtKind<'tcx> {
	Expr {
	/// scope for this statement; may be used as lifetime of temporaries
	scope: region::Scope,

	/// expression being evaluated in this statement
	expr: ExprRef<'tcx>,
	},

	Let {
	/// scope for variables bound in this let; covers this and
	/// remaining statements in block
	remainder_scope: region::Scope,

	/// scope for the initialization itself; might be used as
	/// lifetime of temporaries
	init_scope: region::Scope,

	/// `let <PAT> = ...`
	///
	/// if a type is included, it is added as an ascription pattern
	pattern: Pattern<'tcx>,

	/// let pat: ty = <INIT> ...
	initializer: Option<ExprRef<'tcx>>,

	/// the lint level for this let-statement
	lint_level: LintLevel,
	},
	}

	/// The Hair trait implementor lowers their expressions (`&'tcx H::Expr`)
	/// into instances of this `Expr` enum. This lowering can be done
	/// basically as lazily or as eagerly as desired: every recursive
	/// reference to an expression in this enum is an `ExprRef<'tcx>`, which
	/// may in turn be another instance of this enum (boxed), or else an
	/// unlowered `&'tcx H::Expr`. Note that instances of `Expr` are very
	/// short-lived. They are created by `Hair::to_expr`, analyzed and
	/// converted into MIR, and then discarded.
	///
	/// If you compare `Expr` to the full compiler AST, you will see it is
	/// a good bit simpler. In fact, a number of the more straight-forward
	/// MIR simplifications are already done in the impl of `Hair`. For
	/// example, method calls and overloaded operators are absent: they are
	/// expected to be converted into `Expr::Call` instances.
	#[derive(Clone, Debug)]
	pub struct Expr<'tcx> {
	/// type of this expression
	pub ty: Ty<'tcx>,

	/// lifetime of this expression if it should be spilled into a
	/// temporary; should be None only if in a constant context
	pub temp_lifetime: Option<region::Scope>,

	/// span of the expression in the source
	pub span: Span,

	/// kind of expression
	pub kind: ExprKind<'tcx>,
	}

	#[derive(Clone, Debug)]
	pub enum ExprKind<'tcx> {
	Scope {
	region_scope: region::Scope,
	lint_level: LintLevel,
	value: ExprRef<'tcx>,
	},
	Box {
	value: ExprRef<'tcx>,
	},
	Call {
	ty: Ty<'tcx>,
	fun: ExprRef<'tcx>,
	args: Vec<ExprRef<'tcx>>,
	// Whether this is from a call in HIR, rather than from an overloaded
	// operator. True for overloaded function call.
	from_hir_call: bool,
	},
	Deref {
	arg: ExprRef<'tcx>,
	}, // NOT overloaded!
	Binary {
	op: BinOp,
	lhs: ExprRef<'tcx>,
	rhs: ExprRef<'tcx>,
	}, // NOT overloaded!
	LogicalOp {
	op: LogicalOp,
	lhs: ExprRef<'tcx>,
	rhs: ExprRef<'tcx>,
	}, // NOT overloaded!
	// LogicalOp is distinct from BinaryOp because of lazy evaluation of the operands.
	Unary {
	op: UnOp,
	arg: ExprRef<'tcx>,
	}, // NOT overloaded!
	Cast {
	source: ExprRef<'tcx>,
	},
	Use {
	source: ExprRef<'tcx>,
	}, // Use a lexpr to get a vexpr.
	NeverToAny {
	source: ExprRef<'tcx>,
	},
	Pointer {
	cast: PointerCast,
	source: ExprRef<'tcx>,
	},
	Loop {
	body: ExprRef<'tcx>,
	},
	Match {
	scrutinee: ExprRef<'tcx>,
	arms: Vec<Arm<'tcx>>,
	},
	Block {
	body: &'tcx hir::Block,
	},
	Assign {
	lhs: ExprRef<'tcx>,
	rhs: ExprRef<'tcx>,
	},
	AssignOp {
	op: BinOp,
	lhs: ExprRef<'tcx>,
	rhs: ExprRef<'tcx>,
	},
	Field {
	lhs: ExprRef<'tcx>,
	name: Field,
	},
	Index {
	lhs: ExprRef<'tcx>,
	index: ExprRef<'tcx>,
	},
	VarRef {
	id: hir::HirId,
	},
	/// first argument, used for self in a closure
	SelfRef,
	StaticRef {
	id: DefId,
	},
	Borrow {
	borrow_kind: BorrowKind,
	arg: ExprRef<'tcx>,
	},
	Break {
	label: region::Scope,
	value: Option<ExprRef<'tcx>>,
	},
	Continue {
	label: region::Scope,
	},
	Return {
	value: Option<ExprRef<'tcx>>,
	},
	Repeat {
	value: ExprRef<'tcx>,
	count: u64,
	},
	Array {
	fields: Vec<ExprRef<'tcx>>,
	},
	Tuple {
	fields: Vec<ExprRef<'tcx>>,
	},
	Adt {
	adt_def: &'tcx AdtDef,
	variant_index: VariantIdx,
	substs: SubstsRef<'tcx>,

	/// Optional user-given substs: for something like `let x =
	/// Bar::<T> { ... }`.
	user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,

	fields: Vec<FieldExprRef<'tcx>>,
	base: Option<FruInfo<'tcx>>
	},
	PlaceTypeAscription {
	source: ExprRef<'tcx>,
	/// Type that the user gave to this expression
	user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
	},
	ValueTypeAscription {
	source: ExprRef<'tcx>,
	/// Type that the user gave to this expression
	user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
	},
	Closure {
	closure_id: DefId,
	substs: UpvarSubsts<'tcx>,
	upvars: Vec<ExprRef<'tcx>>,
	movability: Option<hir::GeneratorMovability>,
	},
	Literal {
	literal: &'tcx Const<'tcx>,
	user_ty: Option<Canonical<'tcx, UserType<'tcx>>>,
	},
	InlineAsm {
	asm: &'tcx hir::InlineAsm,
	outputs: Vec<ExprRef<'tcx>>,
	inputs: Vec<ExprRef<'tcx>>
	},
	Yield {
	value: ExprRef<'tcx>,
	},
	}

	#[derive(Clone, Debug)]
	pub enum ExprRef<'tcx> {
	Hair(&'tcx hir::Expr),
	Mirror(Box<Expr<'tcx>>),
	}

	#[derive(Clone, Debug)]
	pub struct FieldExprRef<'tcx> {
	pub name: Field,
	pub expr: ExprRef<'tcx>,
	}

	#[derive(Clone, Debug)]
	pub struct FruInfo<'tcx> {
	pub base: ExprRef<'tcx>,
	pub field_types: Vec<Ty<'tcx>>
	}

	#[derive(Clone, Debug)]
	pub struct Arm<'tcx> {
	pub patterns: Vec<Pattern<'tcx>>,
	pub guard: Option<Guard<'tcx>>,
	pub body: ExprRef<'tcx>,
	pub lint_level: LintLevel,
	pub scope: region::Scope,
	pub span: Span,
	}

	#[derive(Clone, Debug)]
	pub enum Guard<'tcx> {
	If(ExprRef<'tcx>),
	}

	#[derive(Copy, Clone, Debug)]
	pub enum LogicalOp {
	And,
	Or,
	}

	impl<'tcx> ExprRef<'tcx> {
	pub fn span(&self) -> Span {
	match self {
	ExprRef::Hair(expr) => expr.span,
	ExprRef::Mirror(expr) => expr.span,
	}
	}
	}

	///////////////////////////////////////////////////////////////////////////
	// The Mirror trait

	/// "Mirroring" is the process of converting from a HIR type into one
	/// of the HAIR types defined in this file. This is basically a "on
	/// the fly" desugaring step that hides a lot of the messiness in the
	/// tcx. For example, the mirror of a `&'tcx hir::Expr` is an
	/// `Expr<'tcx>`.
	///
	/// Mirroring is gradual: when you mirror an outer expression like `e1
	/// + e2`, the references to the inner expressions `e1` and `e2` are
	/// `ExprRef<'tcx>` instances, and they may or may not be eagerly
	/// mirrored. This allows a single AST node from the compiler to
	/// expand into one or more Hair nodes, which lets the Hair nodes be
	/// simpler.
	pub trait Mirror<'tcx> {
	type Output;

	fn make_mirror(self, cx: &mut Cx<'_, 'tcx>) -> Self::Output;
	}

	impl<'tcx> Mirror<'tcx> for Expr<'tcx> {
	type Output = Expr<'tcx>;

	fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Expr<'tcx> {
	self
	}
	}

	impl<'tcx> Mirror<'tcx> for ExprRef<'tcx> {
	type Output = Expr<'tcx>;

	fn make_mirror(self, hir: &mut Cx<'a, 'tcx>) -> Expr<'tcx> {
	match self {
	ExprRef::Hair(h) => h.make_mirror(hir),
	ExprRef::Mirror(m) => *m,
	}
	}
	}

	impl<'tcx> Mirror<'tcx> for Stmt<'tcx> {
	type Output = Stmt<'tcx>;

	fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Stmt<'tcx> {
	self
	}
	}

	impl<'tcx> Mirror<'tcx> for StmtRef<'tcx> {
	type Output = Stmt<'tcx>;

	fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Stmt<'tcx> {
	match self {
	StmtRef::Mirror(m) => *m,
	}
	}
	}

	impl<'tcx> Mirror<'tcx> for Block<'tcx> {
	type Output = Block<'tcx>;

	fn make_mirror(self, _: &mut Cx<'_, 'tcx>) -> Block<'tcx> {
	self
	}
	}