src/librustc_mir/hair/mod.rs

   1 // Copyright 2015 The Rust Project Developers. See the COPYRIGHT
   2 // file at the top-level directory of this distribution and at
   3 // http://rust-lang.org/COPYRIGHT.
   4 //
   5 // Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
   6 // http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
   7 // <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
   8 // option. This file may not be copied, modified, or distributed
   9 // except according to those terms.
  10
  11 //! The MIR is translated from some high-level abstract IR
  12 //! (HAIR). This section defines the HAIR along with a trait for
  13 //! accessing it. The intention is to allow MIR construction to be
  14 //! unit-tested and separated from the Rust source and compiler data
  15 //! structures.
  16
  17 use rustc::mir::{BinOp, BorrowKind, Field, Literal, UnOp};
  18 use rustc::hir::def_id::DefId;
  19 use rustc::middle::region;
  20 use rustc::ty::subst::Substs;
  21 use rustc::ty::{AdtDef, ClosureSubsts, Region, Ty, GeneratorInterior};
  22 use rustc::hir;
  23 use syntax::ast;
  24 use syntax_pos::Span;
  25 use self::cx::Cx;
  26
  27 pub mod cx;
  28
  29 pub mod pattern;
  30 pub use self::pattern::{BindingMode, Pattern, PatternKind, FieldPattern};
  31
  32 #[derive(Copy, Clone, Debug)]
  33 pub enum LintLevel {
  34     Inherited,
  35     Explicit(ast::NodeId)
  36 }
  37
  38 impl LintLevel {
  39     pub fn is_explicit(self) -> bool {
  40         match self {
  41             LintLevel::Inherited => false,
  42             LintLevel::Explicit(_) => true
  43         }
  44     }
  45 }
  46
  47 #[derive(Clone, Debug)]
  48 pub struct Block<'tcx> {
  49     pub targeted_by_break: bool,
  50     pub region_scope: region::Scope,
  51     pub opt_destruction_scope: Option<region::Scope>,
  52     pub span: Span,
  53     pub stmts: Vec<StmtRef<'tcx>>,
  54     pub expr: Option<ExprRef<'tcx>>,
  55     pub safety_mode: BlockSafety,
  56 }
  57
  58 #[derive(Copy, Clone, Debug)]
  59 pub enum BlockSafety {
  60     Safe,
  61     ExplicitUnsafe(ast::NodeId),
  62     PushUnsafe,
  63     PopUnsafe
  64 }
  65
  66 #[derive(Clone, Debug)]
  67 pub enum StmtRef<'tcx> {
  68     Mirror(Box<Stmt<'tcx>>),
  69 }
  70
  71 #[derive(Clone, Debug)]
  72 pub struct Stmt<'tcx> {
  73     pub kind: StmtKind<'tcx>,
  74     pub opt_destruction_scope: Option<region::Scope>,
  75 }
  76
  77 #[derive(Clone, Debug)]
  78 pub enum StmtKind<'tcx> {
  79     Expr {
  80         /// scope for this statement; may be used as lifetime of temporaries
  81         scope: region::Scope,
  82
  83         /// expression being evaluated in this statement
  84         expr: ExprRef<'tcx>,
  85     },
  86
  87     Let {
  88         /// scope for variables bound in this let; covers this and
  89         /// remaining statements in block
  90         remainder_scope: region::Scope,
  91
  92         /// scope for the initialization itself; might be used as
  93         /// lifetime of temporaries
  94         init_scope: region::Scope,
  95
  96         /// let <PAT>: ty = ...
  97         pattern: Pattern<'tcx>,
  98
  99         /// let pat: <TY> = init ...
 100         ty: Option<hir::HirId>,
 101
 102         /// let pat: ty = <INIT> ...
 103         initializer: Option<ExprRef<'tcx>>,
 104
 105         /// the lint level for this let-statement
 106         lint_level: LintLevel,
 107     },
 108 }
 109
 110 /// The Hair trait implementor translates their expressions (`&'tcx H::Expr`)
 111 /// into instances of this `Expr` enum. This translation can be done
 112 /// basically as lazily or as eagerly as desired: every recursive
 113 /// reference to an expression in this enum is an `ExprRef<'tcx>`, which
 114 /// may in turn be another instance of this enum (boxed), or else an
 115 /// untranslated `&'tcx H::Expr`. Note that instances of `Expr` are very
 116 /// shortlived. They are created by `Hair::to_expr`, analyzed and
 117 /// converted into MIR, and then discarded.
 118 ///
 119 /// If you compare `Expr` to the full compiler AST, you will see it is
 120 /// a good bit simpler. In fact, a number of the more straight-forward
 121 /// MIR simplifications are already done in the impl of `Hair`. For
 122 /// example, method calls and overloaded operators are absent: they are
 123 /// expected to be converted into `Expr::Call` instances.
 124 #[derive(Clone, Debug)]
 125 pub struct Expr<'tcx> {
 126     /// type of this expression
 127     pub ty: Ty<'tcx>,
 128
 129     /// lifetime of this expression if it should be spilled into a
 130     /// temporary; should be None only if in a constant context
 131     pub temp_lifetime: Option<region::Scope>,
 132
 133     /// span of the expression in the source
 134     pub span: Span,
 135
 136     /// kind of expression
 137     pub kind: ExprKind<'tcx>,
 138 }
 139
 140 #[derive(Clone, Debug)]
 141 pub enum ExprKind<'tcx> {
 142     Scope {
 143         region_scope: region::Scope,
 144         lint_level: LintLevel,
 145         value: ExprRef<'tcx>,
 146     },
 147     Box {
 148         value: ExprRef<'tcx>,
 149     },
 150     Call {
 151         ty: Ty<'tcx>,
 152         fun: ExprRef<'tcx>,
 153         args: Vec<ExprRef<'tcx>>,
 154     },
 155     Deref {
 156         arg: ExprRef<'tcx>,
 157     }, // NOT overloaded!
 158     Binary {
 159         op: BinOp,
 160         lhs: ExprRef<'tcx>,
 161         rhs: ExprRef<'tcx>,
 162     }, // NOT overloaded!
 163     LogicalOp {
 164         op: LogicalOp,
 165         lhs: ExprRef<'tcx>,
 166         rhs: ExprRef<'tcx>,
 167     }, // NOT overloaded!
 168        // LogicalOp is distinct from BinaryOp because of lazy evaluation of the operands.
 169     Unary {
 170         op: UnOp,
 171         arg: ExprRef<'tcx>,
 172     }, // NOT overloaded!
 173     Cast {
 174         source: ExprRef<'tcx>,
 175     },
 176     Use {
 177         source: ExprRef<'tcx>,
 178     }, // Use a lexpr to get a vexpr.
 179     NeverToAny {
 180         source: ExprRef<'tcx>,
 181     },
 182     ReifyFnPointer {
 183         source: ExprRef<'tcx>,
 184     },
 185     ClosureFnPointer {
 186         source: ExprRef<'tcx>,
 187     },
 188     UnsafeFnPointer {
 189         source: ExprRef<'tcx>,
 190     },
 191     Unsize {
 192         source: ExprRef<'tcx>,
 193     },
 194     If {
 195         condition: ExprRef<'tcx>,
 196         then: ExprRef<'tcx>,
 197         otherwise: Option<ExprRef<'tcx>>,
 198     },
 199     Loop {
 200         condition: Option<ExprRef<'tcx>>,
 201         body: ExprRef<'tcx>,
 202     },
 203     Match {
 204         discriminant: ExprRef<'tcx>,
 205         arms: Vec<Arm<'tcx>>,
 206     },
 207     Block {
 208         body: &'tcx hir::Block,
 209     },
 210     Assign {
 211         lhs: ExprRef<'tcx>,
 212         rhs: ExprRef<'tcx>,
 213     },
 214     AssignOp {
 215         op: BinOp,
 216         lhs: ExprRef<'tcx>,
 217         rhs: ExprRef<'tcx>,
 218     },
 219     Field {
 220         lhs: ExprRef<'tcx>,
 221         name: Field,
 222     },
 223     Index {
 224         lhs: ExprRef<'tcx>,
 225         index: ExprRef<'tcx>,
 226     },
 227     VarRef {
 228         id: ast::NodeId,
 229     },
 230     /// first argument, used for self in a closure
 231     SelfRef,
 232     StaticRef {
 233         id: DefId,
 234     },
 235     Borrow {
 236         region: Region<'tcx>,
 237         borrow_kind: BorrowKind,
 238         arg: ExprRef<'tcx>,
 239     },
 240     Break {
 241         label: region::Scope,
 242         value: Option<ExprRef<'tcx>>,
 243     },
 244     Continue {
 245         label: region::Scope,
 246     },
 247     Return {
 248         value: Option<ExprRef<'tcx>>,
 249     },
 250     Repeat {
 251         value: ExprRef<'tcx>,
 252         count: u64,
 253     },
 254     Array {
 255         fields: Vec<ExprRef<'tcx>>,
 256     },
 257     Tuple {
 258         fields: Vec<ExprRef<'tcx>>,
 259     },
 260     Adt {
 261         adt_def: &'tcx AdtDef,
 262         variant_index: usize,
 263         substs: &'tcx Substs<'tcx>,
 264         fields: Vec<FieldExprRef<'tcx>>,
 265         base: Option<FruInfo<'tcx>>
 266     },
 267     Closure {
 268         closure_id: DefId,
 269         substs: ClosureSubsts<'tcx>,
 270         upvars: Vec<ExprRef<'tcx>>,
 271         interior: Option<GeneratorInterior<'tcx>>,
 272     },
 273     Literal {
 274         literal: Literal<'tcx>,
 275     },
 276     InlineAsm {
 277         asm: &'tcx hir::InlineAsm,
 278         outputs: Vec<ExprRef<'tcx>>,
 279         inputs: Vec<ExprRef<'tcx>>
 280     },
 281     Yield {
 282         value: ExprRef<'tcx>,
 283     },
 284 }
 285
 286 #[derive(Clone, Debug)]
 287 pub enum ExprRef<'tcx> {
 288     Hair(&'tcx hir::Expr),
 289     Mirror(Box<Expr<'tcx>>),
 290 }
 291
 292 #[derive(Clone, Debug)]
 293 pub struct FieldExprRef<'tcx> {
 294     pub name: Field,
 295     pub expr: ExprRef<'tcx>,
 296 }
 297
 298 #[derive(Clone, Debug)]
 299 pub struct FruInfo<'tcx> {
 300     pub base: ExprRef<'tcx>,
 301     pub field_types: Vec<Ty<'tcx>>
 302 }
 303
 304 #[derive(Clone, Debug)]
 305 pub struct Arm<'tcx> {
 306     pub patterns: Vec<Pattern<'tcx>>,
 307     pub guard: Option<ExprRef<'tcx>>,
 308     pub body: ExprRef<'tcx>,
 309     pub lint_level: LintLevel,
 310 }
 311
 312 #[derive(Copy, Clone, Debug)]
 313 pub enum LogicalOp {
 314     And,
 315     Or,
 316 }
 317
 318 ///////////////////////////////////////////////////////////////////////////
 319 // The Mirror trait
 320
 321 /// "Mirroring" is the process of converting from a HIR type into one
 322 /// of the HAIR types defined in this file. This is basically a "on
 323 /// the fly" desugaring step that hides a lot of the messiness in the
 324 /// tcx. For example, the mirror of a `&'tcx hir::Expr` is an
 325 /// `Expr<'tcx>`.
 326 ///
 327 /// Mirroring is gradual: when you mirror an outer expression like `e1
 328 /// + e2`, the references to the inner expressions `e1` and `e2` are
 329 /// `ExprRef<'tcx>` instances, and they may or may not be eagerly
 330 /// mirrored.  This allows a single AST node from the compiler to
 331 /// expand into one or more Hair nodes, which lets the Hair nodes be
 332 /// simpler.
 333 pub trait Mirror<'tcx> {
 334     type Output;
 335
 336     fn make_mirror<'a, 'gcx>(self, cx: &mut Cx<'a, 'gcx, 'tcx>) -> Self::Output;
 337 }
 338
 339 impl<'tcx> Mirror<'tcx> for Expr<'tcx> {
 340     type Output = Expr<'tcx>;
 341
 342     fn make_mirror<'a, 'gcx>(self, _: &mut Cx<'a, 'gcx, 'tcx>) -> Expr<'tcx> {
 343         self
 344     }
 345 }
 346
 347 impl<'tcx> Mirror<'tcx> for ExprRef<'tcx> {
 348     type Output = Expr<'tcx>;
 349
 350     fn make_mirror<'a, 'gcx>(self, hir: &mut Cx<'a, 'gcx, 'tcx>) -> Expr<'tcx> {
 351         match self {
 352             ExprRef::Hair(h) => h.make_mirror(hir),
 353             ExprRef::Mirror(m) => *m,
 354         }
 355     }
 356 }
 357
 358 impl<'tcx> Mirror<'tcx> for Stmt<'tcx> {
 359     type Output = Stmt<'tcx>;
 360
 361     fn make_mirror<'a, 'gcx>(self, _: &mut Cx<'a, 'gcx, 'tcx>) -> Stmt<'tcx> {
 362         self
 363     }
 364 }
 365
 366 impl<'tcx> Mirror<'tcx> for StmtRef<'tcx> {
 367     type Output = Stmt<'tcx>;
 368
 369     fn make_mirror<'a, 'gcx>(self, _: &mut Cx<'a, 'gcx, 'tcx>) -> Stmt<'tcx> {
 370         match self {
 371             StmtRef::Mirror(m) => *m,
 372         }
 373     }
 374 }
 375
 376 impl<'tcx> Mirror<'tcx> for Block<'tcx> {
 377     type Output = Block<'tcx>;
 378
 379     fn make_mirror<'a, 'gcx>(self, _: &mut Cx<'a, 'gcx, 'tcx>) -> Block<'tcx> {
 380         self
 381     }
 382 }