src/librustc_const_eval/eval.rs

   1 // Copyright 2012-2016 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 use rustc::middle::const_val::ConstVal::*;
  12 use rustc::middle::const_val::ErrKind::*;
  13 use rustc::middle::const_val::{ConstVal, ConstEvalErr, EvalResult, ErrKind};
  14
  15 use rustc::hir::map as hir_map;
  16 use rustc::hir::map::blocks::FnLikeNode;
  17 use rustc::traits;
  18 use rustc::hir::def::{Def, CtorKind};
  19 use rustc::hir::def_id::DefId;
  20 use rustc::ty::{self, Ty, TyCtxt};
  21 use rustc::ty::maps::Providers;
  22 use rustc::ty::util::IntTypeExt;
  23 use rustc::ty::subst::{Substs, Subst};
  24 use rustc::traits::Reveal;
  25 use rustc::util::common::ErrorReported;
  26 use rustc::util::nodemap::DefIdMap;
  27
  28 use syntax::ast;
  29 use rustc::hir::{self, Expr};
  30 use syntax_pos::Span;
  31
  32 use std::cmp::Ordering;
  33
  34 use rustc_const_math::*;
  35
  36 macro_rules! signal {
  37     ($e:expr, $exn:expr) => {
  38         return Err(ConstEvalErr { span: $e.span, kind: $exn })
  39     }
  40 }
  41
  42 macro_rules! math {
  43     ($e:expr, $op:expr) => {
  44         match $op {
  45             Ok(val) => val,
  46             Err(e) => signal!($e, ErrKind::from(e)),
  47         }
  48     }
  49 }
  50
  51 /// * `def_id` is the id of the constant.
  52 /// * `substs` is the monomorphized substitutions for the expression.
  53 ///
  54 /// `substs` is optional and is used for associated constants.
  55 /// This generally happens in late/trans const evaluation.
  56 pub fn lookup_const_by_id<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
  57                                     def_id: DefId,
  58                                     substs: &'tcx Substs<'tcx>)
  59                                     -> Option<(DefId, &'tcx Substs<'tcx>)> {
  60     if let Some(node_id) = tcx.hir.as_local_node_id(def_id) {
  61         match tcx.hir.find(node_id) {
  62             Some(hir_map::NodeTraitItem(_)) => {
  63                 // If we have a trait item and the substitutions for it,
  64                 // `resolve_trait_associated_const` will select an impl
  65                 // or the default.
  66                 resolve_trait_associated_const(tcx, def_id, substs)
  67             }
  68             _ => Some((def_id, substs))
  69         }
  70     } else {
  71         match tcx.describe_def(def_id) {
  72             Some(Def::AssociatedConst(_)) => {
  73                 // As mentioned in the comments above for in-crate
  74                 // constants, we only try to find the expression for a
  75                 // trait-associated const if the caller gives us the
  76                 // substitutions for the reference to it.
  77                 if tcx.trait_of_item(def_id).is_some() {
  78                     resolve_trait_associated_const(tcx, def_id, substs)
  79                 } else {
  80                     Some((def_id, substs))
  81                 }
  82             }
  83             _ => Some((def_id, substs))
  84         }
  85     }
  86 }
  87
  88 pub struct ConstContext<'a, 'tcx: 'a> {
  89     tcx: TyCtxt<'a, 'tcx, 'tcx>,
  90     tables: &'a ty::TypeckTables<'tcx>,
  91     substs: &'tcx Substs<'tcx>,
  92     fn_args: Option<DefIdMap<ConstVal<'tcx>>>
  93 }
  94
  95 impl<'a, 'tcx> ConstContext<'a, 'tcx> {
  96     pub fn with_tables(tcx: TyCtxt<'a, 'tcx, 'tcx>, tables: &'a ty::TypeckTables<'tcx>) -> Self {
  97         ConstContext {
  98             tcx: tcx,
  99             tables: tables,
 100             substs: tcx.intern_substs(&[]),
 101             fn_args: None
 102         }
 103     }
 104
 105     /// Evaluate a constant expression in a context where the expression isn't
 106     /// guaranteed to be evaluatable.
 107     pub fn eval(&self, e: &Expr) -> EvalResult<'tcx> {
 108         if self.tables.tainted_by_errors {
 109             signal!(e, TypeckError);
 110         }
 111         eval_const_expr_partial(self, e)
 112     }
 113 }
 114
 115 type CastResult<'tcx> = Result<ConstVal<'tcx>, ErrKind<'tcx>>;
 116
 117 fn eval_const_expr_partial<'a, 'tcx>(cx: &ConstContext<'a, 'tcx>,
 118                                      e: &Expr) -> EvalResult<'tcx> {
 119     let tcx = cx.tcx;
 120     let ety = cx.tables.expr_ty(e);
 121
 122     // Avoid applying substitutions if they're empty, that'd ICE.
 123     let ety = if cx.substs.is_empty() {
 124         ety
 125     } else {
 126         ety.subst(tcx, cx.substs)
 127     };
 128
 129     let result = match e.node {
 130       hir::ExprUnary(hir::UnNeg, ref inner) => {
 131         // unary neg literals already got their sign during creation
 132         if let hir::ExprLit(ref lit) = inner.node {
 133             use syntax::ast::*;
 134             use syntax::ast::LitIntType::*;
 135             const I8_OVERFLOW: u128 = i8::min_value() as u8 as u128;
 136             const I16_OVERFLOW: u128 = i16::min_value() as u16 as u128;
 137             const I32_OVERFLOW: u128 = i32::min_value() as u32 as u128;
 138             const I64_OVERFLOW: u128 = i64::min_value() as u64 as u128;
 139             const I128_OVERFLOW: u128 = i128::min_value() as u128;
 140             match (&lit.node, &ety.sty) {
 141                 (&LitKind::Int(I8_OVERFLOW, _), &ty::TyInt(IntTy::I8)) |
 142                 (&LitKind::Int(I8_OVERFLOW, Signed(IntTy::I8)), _) => {
 143                     return Ok(Integral(I8(i8::min_value())))
 144                 },
 145                 (&LitKind::Int(I16_OVERFLOW, _), &ty::TyInt(IntTy::I16)) |
 146                 (&LitKind::Int(I16_OVERFLOW, Signed(IntTy::I16)), _) => {
 147                     return Ok(Integral(I16(i16::min_value())))
 148                 },
 149                 (&LitKind::Int(I32_OVERFLOW, _), &ty::TyInt(IntTy::I32)) |
 150                 (&LitKind::Int(I32_OVERFLOW, Signed(IntTy::I32)), _) => {
 151                     return Ok(Integral(I32(i32::min_value())))
 152                 },
 153                 (&LitKind::Int(I64_OVERFLOW, _), &ty::TyInt(IntTy::I64)) |
 154                 (&LitKind::Int(I64_OVERFLOW, Signed(IntTy::I64)), _) => {
 155                     return Ok(Integral(I64(i64::min_value())))
 156                 },
 157                 (&LitKind::Int(I128_OVERFLOW, _), &ty::TyInt(IntTy::I128)) |
 158                 (&LitKind::Int(I128_OVERFLOW, Signed(IntTy::I128)), _) => {
 159                     return Ok(Integral(I128(i128::min_value())))
 160                 },
 161                 (&LitKind::Int(n, _), &ty::TyInt(IntTy::Is)) |
 162                 (&LitKind::Int(n, Signed(IntTy::Is)), _) => {
 163                     match tcx.sess.target.int_type {
 164                         IntTy::I16 => if n == I16_OVERFLOW {
 165                             return Ok(Integral(Isize(Is16(i16::min_value()))));
 166                         },
 167                         IntTy::I32 => if n == I32_OVERFLOW {
 168                             return Ok(Integral(Isize(Is32(i32::min_value()))));
 169                         },
 170                         IntTy::I64 => if n == I64_OVERFLOW {
 171                             return Ok(Integral(Isize(Is64(i64::min_value()))));
 172                         },
 173                         _ => span_bug!(e.span, "typeck error")
 174                     }
 175                 },
 176                 _ => {},
 177             }
 178         }
 179         match cx.eval(inner)? {
 180           Float(f) => Float(-f),
 181           Integral(i) => Integral(math!(e, -i)),
 182           const_val => signal!(e, NegateOn(const_val)),
 183         }
 184       }
 185       hir::ExprUnary(hir::UnNot, ref inner) => {
 186         match cx.eval(inner)? {
 187           Integral(i) => Integral(math!(e, !i)),
 188           Bool(b) => Bool(!b),
 189           const_val => signal!(e, NotOn(const_val)),
 190         }
 191       }
 192       hir::ExprUnary(hir::UnDeref, _) => signal!(e, UnimplementedConstVal("deref operation")),
 193       hir::ExprBinary(op, ref a, ref b) => {
 194         // technically, if we don't have type hints, but integral eval
 195         // gives us a type through a type-suffix, cast or const def type
 196         // we need to re-eval the other value of the BinOp if it was
 197         // not inferred
 198         match (cx.eval(a)?, cx.eval(b)?) {
 199           (Float(a), Float(b)) => {
 200             use std::cmp::Ordering::*;
 201             match op.node {
 202               hir::BiAdd => Float(math!(e, a + b)),
 203               hir::BiSub => Float(math!(e, a - b)),
 204               hir::BiMul => Float(math!(e, a * b)),
 205               hir::BiDiv => Float(math!(e, a / b)),
 206               hir::BiRem => Float(math!(e, a % b)),
 207               hir::BiEq => Bool(math!(e, a.try_cmp(b)) == Equal),
 208               hir::BiLt => Bool(math!(e, a.try_cmp(b)) == Less),
 209               hir::BiLe => Bool(math!(e, a.try_cmp(b)) != Greater),
 210               hir::BiNe => Bool(math!(e, a.try_cmp(b)) != Equal),
 211               hir::BiGe => Bool(math!(e, a.try_cmp(b)) != Less),
 212               hir::BiGt => Bool(math!(e, a.try_cmp(b)) == Greater),
 213               _ => span_bug!(e.span, "typeck error"),
 214             }
 215           }
 216           (Integral(a), Integral(b)) => {
 217             use std::cmp::Ordering::*;
 218             match op.node {
 219               hir::BiAdd => Integral(math!(e, a + b)),
 220               hir::BiSub => Integral(math!(e, a - b)),
 221               hir::BiMul => Integral(math!(e, a * b)),
 222               hir::BiDiv => Integral(math!(e, a / b)),
 223               hir::BiRem => Integral(math!(e, a % b)),
 224               hir::BiBitAnd => Integral(math!(e, a & b)),
 225               hir::BiBitOr => Integral(math!(e, a | b)),
 226               hir::BiBitXor => Integral(math!(e, a ^ b)),
 227               hir::BiShl => Integral(math!(e, a << b)),
 228               hir::BiShr => Integral(math!(e, a >> b)),
 229               hir::BiEq => Bool(math!(e, a.try_cmp(b)) == Equal),
 230               hir::BiLt => Bool(math!(e, a.try_cmp(b)) == Less),
 231               hir::BiLe => Bool(math!(e, a.try_cmp(b)) != Greater),
 232               hir::BiNe => Bool(math!(e, a.try_cmp(b)) != Equal),
 233               hir::BiGe => Bool(math!(e, a.try_cmp(b)) != Less),
 234               hir::BiGt => Bool(math!(e, a.try_cmp(b)) == Greater),
 235               _ => span_bug!(e.span, "typeck error"),
 236             }
 237           }
 238           (Bool(a), Bool(b)) => {
 239             Bool(match op.node {
 240               hir::BiAnd => a && b,
 241               hir::BiOr => a || b,
 242               hir::BiBitXor => a ^ b,
 243               hir::BiBitAnd => a & b,
 244               hir::BiBitOr => a | b,
 245               hir::BiEq => a == b,
 246               hir::BiNe => a != b,
 247               hir::BiLt => a < b,
 248               hir::BiLe => a <= b,
 249               hir::BiGe => a >= b,
 250               hir::BiGt => a > b,
 251               _ => span_bug!(e.span, "typeck error"),
 252              })
 253           }
 254           (Char(a), Char(b)) => {
 255             Bool(match op.node {
 256               hir::BiEq => a == b,
 257               hir::BiNe => a != b,
 258               hir::BiLt => a < b,
 259               hir::BiLe => a <= b,
 260               hir::BiGe => a >= b,
 261               hir::BiGt => a > b,
 262               _ => span_bug!(e.span, "typeck error"),
 263              })
 264           }
 265
 266           _ => signal!(e, MiscBinaryOp),
 267         }
 268       }
 269       hir::ExprCast(ref base, _) => {
 270         let base_val = cx.eval(base)?;
 271         let base_ty = cx.tables.expr_ty(base);
 272
 273         // Avoid applying substitutions if they're empty, that'd ICE.
 274         let base_ty = if cx.substs.is_empty() {
 275             base_ty
 276         } else {
 277             base_ty.subst(tcx, cx.substs)
 278         };
 279         if ety == base_ty {
 280             base_val
 281         } else {
 282             match cast_const(tcx, base_val, ety) {
 283                 Ok(val) => val,
 284                 Err(kind) => signal!(e, kind),
 285             }
 286         }
 287       }
 288       hir::ExprPath(ref qpath) => {
 289         let substs = cx.tables.node_substs(e.id);
 290
 291         // Avoid applying substitutions if they're empty, that'd ICE.
 292         let substs = if cx.substs.is_empty() {
 293             substs
 294         } else {
 295             substs.subst(tcx, cx.substs)
 296         };
 297
 298           match cx.tables.qpath_def(qpath, e.id) {
 299               Def::Const(def_id) |
 300               Def::AssociatedConst(def_id) => {
 301                     match tcx.at(e.span).const_eval((def_id, substs)) {
 302                         Ok(val) => val,
 303                         Err(ConstEvalErr { kind: TypeckError, .. }) => {
 304                             signal!(e, TypeckError);
 305                         }
 306                         Err(err) => {
 307                             debug!("bad reference: {:?}, {:?}", err.description(), err.span);
 308                             signal!(e, ErroneousReferencedConstant(box err))
 309                         },
 310                     }
 311               },
 312               Def::VariantCtor(variant_def, CtorKind::Const) => {
 313                 Variant(variant_def)
 314               }
 315               Def::VariantCtor(_, CtorKind::Fn) => {
 316                   signal!(e, UnimplementedConstVal("enum variants"));
 317               }
 318               Def::StructCtor(_, CtorKind::Const) => {
 319                   ConstVal::Struct(Default::default())
 320               }
 321               Def::StructCtor(_, CtorKind::Fn) => {
 322                   signal!(e, UnimplementedConstVal("tuple struct constructors"))
 323               }
 324               Def::Local(def_id) => {
 325                   debug!("Def::Local({:?}): {:?}", def_id, cx.fn_args);
 326                   if let Some(val) = cx.fn_args.as_ref().and_then(|args| args.get(&def_id)) {
 327                       val.clone()
 328                   } else {
 329                       signal!(e, NonConstPath);
 330                   }
 331               },
 332               Def::Method(id) | Def::Fn(id) => Function(id, substs),
 333               Def::Err => span_bug!(e.span, "typeck error"),
 334               _ => signal!(e, NonConstPath),
 335           }
 336       }
 337       hir::ExprCall(ref callee, ref args) => {
 338           let (def_id, substs) = match cx.eval(callee)? {
 339               Function(def_id, substs) => (def_id, substs),
 340               _ => signal!(e, TypeckError),
 341           };
 342
 343           let body = if let Some(node_id) = tcx.hir.as_local_node_id(def_id) {
 344             if let Some(fn_like) = FnLikeNode::from_node(tcx.hir.get(node_id)) {
 345                 if fn_like.constness() == hir::Constness::Const {
 346                     tcx.hir.body(fn_like.body())
 347                 } else {
 348                     signal!(e, TypeckError)
 349                 }
 350             } else {
 351                 signal!(e, TypeckError)
 352             }
 353           } else {
 354             if tcx.is_const_fn(def_id) {
 355                 tcx.sess.cstore.item_body(tcx, def_id)
 356             } else {
 357                 signal!(e, TypeckError)
 358             }
 359           };
 360
 361           let arg_defs = body.arguments.iter().map(|arg| match arg.pat.node {
 362                hir::PatKind::Binding(_, def_id, _, _) => Some(def_id),
 363                _ => None
 364            }).collect::<Vec<_>>();
 365           assert_eq!(arg_defs.len(), args.len());
 366
 367           let mut call_args = DefIdMap();
 368           for (arg, arg_expr) in arg_defs.into_iter().zip(args.iter()) {
 369               let arg_val = cx.eval(arg_expr)?;
 370               debug!("const call arg: {:?}", arg);
 371               if let Some(def_id) = arg {
 372                 assert!(call_args.insert(def_id, arg_val).is_none());
 373               }
 374           }
 375           debug!("const call({:?})", call_args);
 376           let callee_cx = ConstContext {
 377             tcx: tcx,
 378             tables: tcx.typeck_tables_of(def_id),
 379             substs: substs,
 380             fn_args: Some(call_args)
 381           };
 382           callee_cx.eval(&body.value)?
 383       },
 384       hir::ExprLit(ref lit) => match lit_to_const(&lit.node, tcx, ety) {
 385           Ok(val) => val,
 386           Err(err) => signal!(e, err),
 387       },
 388       hir::ExprBlock(ref block) => {
 389         match block.expr {
 390             Some(ref expr) => cx.eval(expr)?,
 391             None => Tuple(vec![]),
 392         }
 393       }
 394       hir::ExprType(ref e, _) => cx.eval(e)?,
 395       hir::ExprTup(ref fields) => {
 396         Tuple(fields.iter().map(|e| cx.eval(e)).collect::<Result<_, _>>()?)
 397       }
 398       hir::ExprStruct(_, ref fields, _) => {
 399         Struct(fields.iter().map(|f| {
 400             cx.eval(&f.expr).map(|v| (f.name.node, v))
 401         }).collect::<Result<_, _>>()?)
 402       }
 403       hir::ExprIndex(ref arr, ref idx) => {
 404         if !tcx.sess.features.borrow().const_indexing {
 405             signal!(e, IndexOpFeatureGated);
 406         }
 407         let arr = cx.eval(arr)?;
 408         let idx = match cx.eval(idx)? {
 409             Integral(Usize(i)) => i.as_u64(tcx.sess.target.uint_type),
 410             _ => signal!(idx, IndexNotUsize),
 411         };
 412         assert_eq!(idx as usize as u64, idx);
 413         match arr {
 414             Array(ref v) => {
 415                 if let Some(elem) = v.get(idx as usize) {
 416                     elem.clone()
 417                 } else {
 418                     let n = v.len() as u64;
 419                     assert_eq!(n as usize as u64, n);
 420                     signal!(e, IndexOutOfBounds { len: n, index: idx })
 421                 }
 422             }
 423
 424             Repeat(.., n) if idx >= n => {
 425                 signal!(e, IndexOutOfBounds { len: n, index: idx })
 426             }
 427             Repeat(ref elem, _) => (**elem).clone(),
 428
 429             ByteStr(ref data) if idx >= data.len() as u64 => {
 430                 signal!(e, IndexOutOfBounds { len: data.len() as u64, index: idx })
 431             }
 432             ByteStr(data) => {
 433                 Integral(U8(data[idx as usize]))
 434             },
 435
 436             _ => signal!(e, IndexedNonVec),
 437         }
 438       }
 439       hir::ExprArray(ref v) => {
 440         Array(v.iter().map(|e| cx.eval(e)).collect::<Result<_, _>>()?)
 441       }
 442       hir::ExprRepeat(ref elem, _) => {
 443           let n = match ety.sty {
 444             ty::TyArray(_, n) => n as u64,
 445             _ => span_bug!(e.span, "typeck error")
 446           };
 447           Repeat(Box::new(cx.eval(elem)?), n)
 448       },
 449       hir::ExprTupField(ref base, index) => {
 450         let c = cx.eval(base)?;
 451         if let Tuple(ref fields) = c {
 452             fields[index.node].clone()
 453         } else {
 454             signal!(base, ExpectedConstTuple);
 455         }
 456       }
 457       hir::ExprField(ref base, field_name) => {
 458         let c = cx.eval(base)?;
 459         if let Struct(ref fields) = c {
 460             if let Some(f) = fields.get(&field_name.node) {
 461                 f.clone()
 462             } else {
 463                 signal!(e, MissingStructField);
 464             }
 465         } else {
 466             signal!(base, ExpectedConstStruct);
 467         }
 468       }
 469       hir::ExprAddrOf(..) => signal!(e, UnimplementedConstVal("address operator")),
 470       _ => signal!(e, MiscCatchAll)
 471     };
 472
 473     Ok(result)
 474 }
 475
 476 fn resolve_trait_associated_const<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 477                                             def_id: DefId,
 478                                             substs: &'tcx Substs<'tcx>)
 479                                             -> Option<(DefId, &'tcx Substs<'tcx>)> {
 480     let trait_item = tcx.associated_item(def_id);
 481     let trait_id = trait_item.container.id();
 482     let trait_ref = ty::Binder(ty::TraitRef::new(trait_id, substs));
 483     debug!("resolve_trait_associated_const: trait_ref={:?}",
 484            trait_ref);
 485
 486     tcx.infer_ctxt().enter(|infcx| {
 487         let param_env = ty::ParamEnv::empty(Reveal::UserFacing);
 488         let mut selcx = traits::SelectionContext::new(&infcx);
 489         let obligation = traits::Obligation::new(traits::ObligationCause::dummy(),
 490                                                  param_env,
 491                                                  trait_ref.to_poly_trait_predicate());
 492         let selection = match selcx.select(&obligation) {
 493             Ok(Some(vtable)) => vtable,
 494             // Still ambiguous, so give up and let the caller decide whether this
 495             // expression is really needed yet. Some associated constant values
 496             // can't be evaluated until monomorphization is done in trans.
 497             Ok(None) => {
 498                 return None
 499             }
 500             Err(_) => {
 501                 return None
 502             }
 503         };
 504
 505         // NOTE: this code does not currently account for specialization, but when
 506         // it does so, it should hook into the Reveal to determine when the
 507         // constant should resolve; this will also require plumbing through to this
 508         // function whether we are in "trans mode" to pick the right Reveal
 509         // when constructing the inference context above.
 510         match selection {
 511             traits::VtableImpl(ref impl_data) => {
 512                 let name = trait_item.name;
 513                 let ac = tcx.associated_items(impl_data.impl_def_id)
 514                     .find(|item| item.kind == ty::AssociatedKind::Const && item.name == name);
 515                 match ac {
 516                     // FIXME(eddyb) Use proper Instance resolution to
 517                     // get the correct Substs returned from here.
 518                     Some(ic) => Some((ic.def_id, Substs::empty())),
 519                     None => {
 520                         if trait_item.defaultness.has_value() {
 521                             Some((def_id, substs))
 522                         } else {
 523                             None
 524                         }
 525                     }
 526                 }
 527             }
 528             _ => {
 529                 bug!("resolve_trait_associated_const: unexpected vtable type")
 530             }
 531         }
 532     })
 533 }
 534
 535 fn cast_const_int<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 536                             val: ConstInt,
 537                             ty: Ty<'tcx>)
 538                             -> CastResult<'tcx> {
 539     let v = val.to_u128_unchecked();
 540     match ty.sty {
 541         ty::TyBool if v == 0 => Ok(Bool(false)),
 542         ty::TyBool if v == 1 => Ok(Bool(true)),
 543         ty::TyInt(ast::IntTy::I8) => Ok(Integral(I8(v as i128 as i8))),
 544         ty::TyInt(ast::IntTy::I16) => Ok(Integral(I16(v as i128 as i16))),
 545         ty::TyInt(ast::IntTy::I32) => Ok(Integral(I32(v as i128 as i32))),
 546         ty::TyInt(ast::IntTy::I64) => Ok(Integral(I64(v as i128 as i64))),
 547         ty::TyInt(ast::IntTy::I128) => Ok(Integral(I128(v as i128))),
 548         ty::TyInt(ast::IntTy::Is) => {
 549             Ok(Integral(Isize(ConstIsize::new_truncating(v as i128, tcx.sess.target.int_type))))
 550         },
 551         ty::TyUint(ast::UintTy::U8) => Ok(Integral(U8(v as u8))),
 552         ty::TyUint(ast::UintTy::U16) => Ok(Integral(U16(v as u16))),
 553         ty::TyUint(ast::UintTy::U32) => Ok(Integral(U32(v as u32))),
 554         ty::TyUint(ast::UintTy::U64) => Ok(Integral(U64(v as u64))),
 555         ty::TyUint(ast::UintTy::U128) => Ok(Integral(U128(v as u128))),
 556         ty::TyUint(ast::UintTy::Us) => {
 557             Ok(Integral(Usize(ConstUsize::new_truncating(v, tcx.sess.target.uint_type))))
 558         },
 559         ty::TyFloat(ast::FloatTy::F64) => Ok(Float(F64(val.to_f64()))),
 560         ty::TyFloat(ast::FloatTy::F32) => Ok(Float(F32(val.to_f32()))),
 561         ty::TyRawPtr(_) => Err(ErrKind::UnimplementedConstVal("casting an address to a raw ptr")),
 562         ty::TyChar => match val {
 563             U8(u) => Ok(Char(u as char)),
 564             _ => bug!(),
 565         },
 566         _ => Err(CannotCast),
 567     }
 568 }
 569
 570 fn cast_const_float<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 571                               val: ConstFloat,
 572                               ty: Ty<'tcx>) -> CastResult<'tcx> {
 573     match ty.sty {
 574         ty::TyInt(_) | ty::TyUint(_) => {
 575             let i = match val {
 576                 F32(f) if f >= 0.0 => U128(f as u128),
 577                 F64(f) if f >= 0.0 => U128(f as u128),
 578
 579                 F32(f) => I128(f as i128),
 580                 F64(f) => I128(f as i128)
 581             };
 582
 583             if let (I128(_), &ty::TyUint(_)) = (i, &ty.sty) {
 584                 return Err(CannotCast);
 585             }
 586
 587             cast_const_int(tcx, i, ty)
 588         }
 589         ty::TyFloat(ast::FloatTy::F64) => Ok(Float(F64(match val {
 590             F32(f) => f as f64,
 591             F64(f) => f
 592         }))),
 593         ty::TyFloat(ast::FloatTy::F32) => Ok(Float(F32(match val {
 594             F64(f) => f as f32,
 595             F32(f) => f
 596         }))),
 597         _ => Err(CannotCast),
 598     }
 599 }
 600
 601 fn cast_const<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 602                         val: ConstVal<'tcx>,
 603                         ty: Ty<'tcx>)
 604                         -> CastResult<'tcx> {
 605     match val {
 606         Integral(i) => cast_const_int(tcx, i, ty),
 607         Bool(b) => cast_const_int(tcx, U8(b as u8), ty),
 608         Float(f) => cast_const_float(tcx, f, ty),
 609         Char(c) => cast_const_int(tcx, U32(c as u32), ty),
 610         Variant(v) => {
 611             let adt = tcx.adt_def(tcx.parent_def_id(v).unwrap());
 612             let idx = adt.variant_index_with_id(v);
 613             cast_const_int(tcx, adt.discriminant_for_variant(tcx, idx), ty)
 614         }
 615         Function(..) => Err(UnimplementedConstVal("casting fn pointers")),
 616         ByteStr(b) => match ty.sty {
 617             ty::TyRawPtr(_) => {
 618                 Err(ErrKind::UnimplementedConstVal("casting a bytestr to a raw ptr"))
 619             },
 620             ty::TyRef(_, ty::TypeAndMut { ref ty, mutbl: hir::MutImmutable }) => match ty.sty {
 621                 ty::TyArray(ty, n) if ty == tcx.types.u8 && n == b.len() => Ok(ByteStr(b)),
 622                 ty::TySlice(_) => {
 623                     Err(ErrKind::UnimplementedConstVal("casting a bytestr to slice"))
 624                 },
 625                 _ => Err(CannotCast),
 626             },
 627             _ => Err(CannotCast),
 628         },
 629         Str(s) => match ty.sty {
 630             ty::TyRawPtr(_) => Err(ErrKind::UnimplementedConstVal("casting a str to a raw ptr")),
 631             ty::TyRef(_, ty::TypeAndMut { ref ty, mutbl: hir::MutImmutable }) => match ty.sty {
 632                 ty::TyStr => Ok(Str(s)),
 633                 _ => Err(CannotCast),
 634             },
 635             _ => Err(CannotCast),
 636         },
 637         _ => Err(CannotCast),
 638     }
 639 }
 640
 641 fn lit_to_const<'a, 'tcx>(lit: &ast::LitKind,
 642                           tcx: TyCtxt<'a, 'tcx, 'tcx>,
 643                           mut ty: Ty<'tcx>)
 644                           -> Result<ConstVal<'tcx>, ErrKind<'tcx>> {
 645     use syntax::ast::*;
 646     use syntax::ast::LitIntType::*;
 647
 648     if let ty::TyAdt(adt, _) = ty.sty {
 649         if adt.is_enum() {
 650             ty = adt.repr.discr_type().to_ty(tcx)
 651         }
 652     }
 653
 654     match *lit {
 655         LitKind::Str(ref s, _) => Ok(Str(s.as_str())),
 656         LitKind::ByteStr(ref data) => Ok(ByteStr(data.clone())),
 657         LitKind::Byte(n) => Ok(Integral(U8(n))),
 658         LitKind::Int(n, hint) => {
 659             match (&ty.sty, hint) {
 660                 (&ty::TyInt(ity), _) |
 661                 (_, Signed(ity)) => {
 662                     Ok(Integral(ConstInt::new_signed_truncating(n as i128,
 663                         ity, tcx.sess.target.int_type)))
 664                 }
 665                 (&ty::TyUint(uty), _) |
 666                 (_, Unsigned(uty)) => {
 667                     Ok(Integral(ConstInt::new_unsigned_truncating(n as u128,
 668                         uty, tcx.sess.target.uint_type)))
 669                 }
 670                 _ => bug!()
 671             }
 672         }
 673         LitKind::Float(n, fty) => {
 674             parse_float(&n.as_str(), fty).map(Float)
 675         }
 676         LitKind::FloatUnsuffixed(n) => {
 677             let fty = match ty.sty {
 678                 ty::TyFloat(fty) => fty,
 679                 _ => bug!()
 680             };
 681             parse_float(&n.as_str(), fty).map(Float)
 682         }
 683         LitKind::Bool(b) => Ok(Bool(b)),
 684         LitKind::Char(c) => Ok(Char(c)),
 685     }
 686 }
 687
 688 fn parse_float<'tcx>(num: &str, fty: ast::FloatTy)
 689                      -> Result<ConstFloat, ErrKind<'tcx>> {
 690     let val = match fty {
 691         ast::FloatTy::F32 => num.parse::<f32>().map(F32),
 692         ast::FloatTy::F64 => num.parse::<f64>().map(F64)
 693     };
 694     val.map_err(|_| {
 695         // FIXME(#31407) this is only necessary because float parsing is buggy
 696         UnimplementedConstVal("could not evaluate float literal (see issue #31407)")
 697     })
 698 }
 699
 700 pub fn compare_const_vals(tcx: TyCtxt, span: Span, a: &ConstVal, b: &ConstVal)
 701                           -> Result<Ordering, ErrorReported>
 702 {
 703     let result = match (a, b) {
 704         (&Integral(a), &Integral(b)) => a.try_cmp(b).ok(),
 705         (&Float(a), &Float(b)) => a.try_cmp(b).ok(),
 706         (&Str(ref a), &Str(ref b)) => Some(a.cmp(b)),
 707         (&Bool(a), &Bool(b)) => Some(a.cmp(&b)),
 708         (&ByteStr(ref a), &ByteStr(ref b)) => Some(a.cmp(b)),
 709         (&Char(a), &Char(ref b)) => Some(a.cmp(b)),
 710         _ => None,
 711     };
 712
 713     match result {
 714         Some(result) => Ok(result),
 715         None => {
 716             // FIXME: can this ever be reached?
 717             span_err!(tcx.sess, span, E0298,
 718                       "type mismatch comparing {} and {}",
 719                       a.description(),
 720                       b.description());
 721             Err(ErrorReported)
 722         }
 723     }
 724 }
 725
 726 impl<'a, 'tcx> ConstContext<'a, 'tcx> {
 727     pub fn compare_lit_exprs(&self,
 728                              span: Span,
 729                              a: &Expr,
 730                              b: &Expr) -> Result<Ordering, ErrorReported> {
 731         let tcx = self.tcx;
 732         let a = match self.eval(a) {
 733             Ok(a) => a,
 734             Err(e) => {
 735                 e.report(tcx, a.span, "expression");
 736                 return Err(ErrorReported);
 737             }
 738         };
 739         let b = match self.eval(b) {
 740             Ok(b) => b,
 741             Err(e) => {
 742                 e.report(tcx, b.span, "expression");
 743                 return Err(ErrorReported);
 744             }
 745         };
 746         compare_const_vals(tcx, span, &a, &b)
 747     }
 748 }
 749
 750 pub fn provide(providers: &mut Providers) {
 751     *providers = Providers {
 752         const_eval,
 753         ..*providers
 754     };
 755 }
 756
 757 fn const_eval<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 758                         (def_id, substs): (DefId, &'tcx Substs<'tcx>))
 759                         -> EvalResult<'tcx> {
 760     let (def_id, substs) = if let Some(resolved) = lookup_const_by_id(tcx, def_id, substs) {
 761         resolved
 762     } else {
 763         return Err(ConstEvalErr {
 764             span: tcx.def_span(def_id),
 765             kind: TypeckError
 766         });
 767     };
 768
 769     let cx = ConstContext {
 770         tcx,
 771         tables: tcx.typeck_tables_of(def_id),
 772         substs: substs,
 773         fn_args: None
 774     };
 775
 776     let body = if let Some(id) = tcx.hir.as_local_node_id(def_id) {
 777         tcx.mir_const_qualif(def_id);
 778         tcx.hir.body(tcx.hir.body_owned_by(id))
 779     } else {
 780         tcx.sess.cstore.item_body(tcx, def_id)
 781     };
 782     cx.eval(&body.value)
 783 }