src/interpreter/terminator.rs

   1 use rustc::hir::def_id::DefId;
   2 use rustc::mir::repr as mir;
   3 use rustc::traits::{self, ProjectionMode};
   4 use rustc::ty::fold::TypeFoldable;
   5 use rustc::ty::layout::Layout;
   6 use rustc::ty::subst::{self, Substs};
   7 use rustc::ty::{self, Ty, TyCtxt, BareFnTy};
   8 use std::rc::Rc;
   9 use std::iter;
  10 use syntax::{ast, attr};
  11 use syntax::codemap::{DUMMY_SP, Span};
  12
  13 use super::{EvalContext, IntegerExt};
  14 use error::{EvalError, EvalResult};
  15 use memory::{Pointer, FunctionDefinition};
  16
  17 impl<'a, 'tcx> EvalContext<'a, 'tcx> {
  18     pub(super) fn eval_terminator(
  19         &mut self,
  20         terminator: &mir::Terminator<'tcx>,
  21     ) -> EvalResult<'tcx, ()> {
  22         use rustc::mir::repr::TerminatorKind::*;
  23         match terminator.kind {
  24             Return => self.pop_stack_frame(),
  25
  26             Goto { target } => {
  27                 self.frame_mut().block = target;
  28             },
  29
  30             If { ref cond, targets: (then_target, else_target) } => {
  31                 let cond_ptr = self.eval_operand(cond)?;
  32                 let cond_val = self.memory.read_bool(cond_ptr)?;
  33                 self.frame_mut().block = if cond_val { then_target } else { else_target };
  34             }
  35
  36             SwitchInt { ref discr, ref values, ref targets, .. } => {
  37                 let discr_ptr = self.eval_lvalue(discr)?.to_ptr();
  38                 let discr_ty = self.lvalue_ty(discr);
  39                 let discr_size = self
  40                     .type_layout(discr_ty)
  41                     .size(&self.tcx.data_layout)
  42                     .bytes() as usize;
  43                 let discr_val = self.memory.read_uint(discr_ptr, discr_size)?;
  44                 if let ty::TyChar = discr_ty.sty {
  45                     if ::std::char::from_u32(discr_val as u32).is_none() {
  46                         return Err(EvalError::InvalidChar(discr_val as u32));
  47                     }
  48                 }
  49
  50                 // Branch to the `otherwise` case by default, if no match is found.
  51                 let mut target_block = targets[targets.len() - 1];
  52
  53                 for (index, val_const) in values.iter().enumerate() {
  54                     let ptr = self.const_to_ptr(val_const)?;
  55                     let val = self.memory.read_uint(ptr, discr_size)?;
  56                     if discr_val == val {
  57                         target_block = targets[index];
  58                         break;
  59                     }
  60                 }
  61
  62                 self.frame_mut().block = target_block;
  63             }
  64
  65             Switch { ref discr, ref targets, adt_def } => {
  66                 let adt_ptr = self.eval_lvalue(discr)?.to_ptr();
  67                 let adt_ty = self.lvalue_ty(discr);
  68                 let discr_val = self.read_discriminant_value(adt_ptr, adt_ty)?;
  69                 let matching = adt_def.variants.iter()
  70                     .position(|v| discr_val == v.disr_val.to_u64_unchecked());
  71
  72                 match matching {
  73                     Some(i) => {
  74                         self.frame_mut().block = targets[i];
  75                     },
  76                     None => return Err(EvalError::InvalidDiscriminant),
  77                 }
  78             }
  79
  80             Call { ref func, ref args, ref destination, .. } => {
  81                 let mut return_ptr = None;
  82                 if let Some((ref lv, target)) = *destination {
  83                     self.frame_mut().block = target;
  84                     return_ptr = Some(self.eval_lvalue(lv)?.to_ptr());
  85                 }
  86
  87                 let func_ty = self.operand_ty(func);
  88                 match func_ty.sty {
  89                     ty::TyFnPtr(bare_fn_ty) => {
  90                         let ptr = self.eval_operand(func)?;
  91                         let fn_ptr = self.memory.read_ptr(ptr)?;
  92                         let FunctionDefinition { def_id, substs, fn_ty } = self.memory.get_fn(fn_ptr.alloc_id)?;
  93                         if fn_ty != bare_fn_ty {
  94                             return Err(EvalError::FunctionPointerTyMismatch(fn_ty, bare_fn_ty));
  95                         }
  96                         self.eval_fn_call(def_id, substs, bare_fn_ty, return_ptr, args,
  97                                           terminator.source_info.span)?
  98                     },
  99                     ty::TyFnDef(def_id, substs, fn_ty) => {
 100                         self.eval_fn_call(def_id, substs, fn_ty, return_ptr, args,
 101                                           terminator.source_info.span)?
 102                     }
 103
 104                     _ => return Err(EvalError::Unimplemented(format!("can't handle callee of type {:?}", func_ty))),
 105                 }
 106             }
 107
 108             Drop { ref location, target, .. } => {
 109                 let ptr = self.eval_lvalue(location)?.to_ptr();
 110                 let ty = self.lvalue_ty(location);
 111                 self.drop(ptr, ty)?;
 112                 self.frame_mut().block = target;
 113             }
 114
 115             Assert { ref cond, expected, ref msg, target, .. } => {
 116                 let cond_ptr = self.eval_operand(cond)?;
 117                 if expected == self.memory.read_bool(cond_ptr)? {
 118                     self.frame_mut().block = target;
 119                 } else {
 120                     return match *msg {
 121                         mir::AssertMessage::BoundsCheck { ref len, ref index } => {
 122                             let len = self.eval_operand(len).expect("can't eval len");
 123                             let len = self.memory.read_usize(len).expect("can't read len");
 124                             let index = self.eval_operand(index).expect("can't eval index");
 125                             let index = self.memory.read_usize(index).expect("can't read index");
 126                             Err(EvalError::ArrayIndexOutOfBounds(terminator.source_info.span, len, index))
 127                         },
 128                         mir::AssertMessage::Math(ref err) => Err(EvalError::Math(terminator.source_info.span, err.clone())),
 129                     }
 130                 }
 131             },
 132
 133             DropAndReplace { .. } => unimplemented!(),
 134             Resume => unimplemented!(),
 135             Unreachable => unimplemented!(),
 136         }
 137
 138         Ok(())
 139     }
 140
 141     fn eval_fn_call(
 142         &mut self,
 143         def_id: DefId,
 144         substs: &'tcx Substs<'tcx>,
 145         fn_ty: &'tcx BareFnTy,
 146         return_ptr: Option<Pointer>,
 147         args: &[mir::Operand<'tcx>],
 148         span: Span,
 149     ) -> EvalResult<'tcx, ()> {
 150         use syntax::abi::Abi;
 151         match fn_ty.abi {
 152             Abi::RustIntrinsic => {
 153                 let name = self.tcx.item_name(def_id).as_str();
 154                 match fn_ty.sig.0.output {
 155                     ty::FnConverging(ty) => {
 156                         let layout = self.type_layout(ty);
 157                         let ret = return_ptr.unwrap();
 158                         self.call_intrinsic(&name, substs, args, ret, layout)
 159                     }
 160                     ty::FnDiverging => unimplemented!(),
 161                 }
 162             }
 163
 164             Abi::C => {
 165                 match fn_ty.sig.0.output {
 166                     ty::FnConverging(ty) => {
 167                         let size = self.type_size(ty);
 168                         self.call_c_abi(def_id, args, return_ptr.unwrap(), size)
 169                     }
 170                     ty::FnDiverging => unimplemented!(),
 171                 }
 172             }
 173
 174             Abi::Rust | Abi::RustCall => {
 175                 // TODO(solson): Adjust the first argument when calling a Fn or
 176                 // FnMut closure via FnOnce::call_once.
 177
 178                 // Only trait methods can have a Self parameter.
 179                 let (resolved_def_id, resolved_substs) = if substs.self_ty().is_some() {
 180                     self.trait_method(def_id, substs)
 181                 } else {
 182                     (def_id, substs)
 183                 };
 184
 185                 let mut arg_srcs = Vec::new();
 186                 for arg in args {
 187                     let src = self.eval_operand(arg)?;
 188                     let src_ty = self.operand_ty(arg);
 189                     arg_srcs.push((src, src_ty));
 190                 }
 191
 192                 if fn_ty.abi == Abi::RustCall && !args.is_empty() {
 193                     arg_srcs.pop();
 194                     let last_arg = args.last().unwrap();
 195                     let last = self.eval_operand(last_arg)?;
 196                     let last_ty = self.operand_ty(last_arg);
 197                     let last_layout = self.type_layout(last_ty);
 198                     match (&last_ty.sty, last_layout) {
 199                         (&ty::TyTuple(fields),
 200                          &Layout::Univariant { ref variant, .. }) => {
 201                             let offsets = iter::once(0)
 202                                 .chain(variant.offset_after_field.iter()
 203                                     .map(|s| s.bytes()));
 204                             for (offset, ty) in offsets.zip(fields) {
 205                                 let src = last.offset(offset as isize);
 206                                 arg_srcs.push((src, ty));
 207                             }
 208                         }
 209                         ty => panic!("expected tuple as last argument in function with 'rust-call' ABI, got {:?}", ty),
 210                     }
 211                 }
 212
 213                 let mir = self.load_mir(resolved_def_id);
 214                 self.push_stack_frame(def_id, span, mir, resolved_substs, return_ptr)?;
 215
 216                 for (i, (src, src_ty)) in arg_srcs.into_iter().enumerate() {
 217                     let dest = self.frame().locals[i];
 218                     self.move_(src, dest, src_ty)?;
 219                 }
 220
 221                 Ok(())
 222             }
 223
 224             abi => Err(EvalError::Unimplemented(format!("can't handle function with {:?} ABI", abi))),
 225         }
 226     }
 227
 228     fn read_discriminant_value(&self, adt_ptr: Pointer, adt_ty: Ty<'tcx>) -> EvalResult<'tcx, u64> {
 229         use rustc::ty::layout::Layout::*;
 230         let adt_layout = self.type_layout(adt_ty);
 231
 232         let discr_val = match *adt_layout {
 233             General { discr, .. } | CEnum { discr, .. } => {
 234                 let discr_size = discr.size().bytes();
 235                 self.memory.read_uint(adt_ptr, discr_size as usize)?
 236             }
 237
 238             RawNullablePointer { nndiscr, .. } => {
 239                 self.read_nonnull_discriminant_value(adt_ptr, nndiscr)?
 240             }
 241
 242             StructWrappedNullablePointer { nndiscr, ref discrfield, .. } => {
 243                 let offset = self.nonnull_offset(adt_ty, nndiscr, discrfield)?;
 244                 let nonnull = adt_ptr.offset(offset.bytes() as isize);
 245                 self.read_nonnull_discriminant_value(nonnull, nndiscr)?
 246             }
 247
 248             // The discriminant_value intrinsic returns 0 for non-sum types.
 249             Array { .. } | FatPointer { .. } | Scalar { .. } | Univariant { .. } |
 250             Vector { .. } => 0,
 251         };
 252
 253         Ok(discr_val)
 254     }
 255
 256     fn read_nonnull_discriminant_value(&self, ptr: Pointer, nndiscr: u64) -> EvalResult<'tcx, u64> {
 257         let not_null = match self.memory.read_usize(ptr) {
 258             Ok(0) => false,
 259             Ok(_) | Err(EvalError::ReadPointerAsBytes) => true,
 260             Err(e) => return Err(e),
 261         };
 262         assert!(nndiscr == 0 || nndiscr == 1);
 263         Ok(if not_null { nndiscr } else { 1 - nndiscr })
 264     }
 265
 266     fn call_intrinsic(
 267         &mut self,
 268         name: &str,
 269         substs: &'tcx Substs<'tcx>,
 270         args: &[mir::Operand<'tcx>],
 271         dest: Pointer,
 272         dest_layout: &'tcx Layout,
 273     ) -> EvalResult<'tcx, ()> {
 274         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 275             .map(|arg| self.eval_operand(arg))
 276             .collect();
 277         let args_ptrs = args_res?;
 278
 279         let pointer_size = self.memory.pointer_size();
 280
 281         match name {
 282             "add_with_overflow" => self.intrinsic_with_overflow(mir::BinOp::Add, &args[0], &args[1], dest, dest_layout)?,
 283             "sub_with_overflow" => self.intrinsic_with_overflow(mir::BinOp::Sub, &args[0], &args[1], dest, dest_layout)?,
 284             "mul_with_overflow" => self.intrinsic_with_overflow(mir::BinOp::Mul, &args[0], &args[1], dest, dest_layout)?,
 285
 286             // FIXME: turn into an assertion to catch wrong `assume` that would cause UB in llvm
 287             "assume" => {}
 288
 289             "copy_nonoverlapping" => {
 290                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 291                 let elem_size = self.type_size(elem_ty);
 292                 let elem_align = self.type_align(elem_ty);
 293                 let src = self.memory.read_ptr(args_ptrs[0])?;
 294                 let dest = self.memory.read_ptr(args_ptrs[1])?;
 295                 let count = self.memory.read_isize(args_ptrs[2])?;
 296                 self.memory.copy(src, dest, count as usize * elem_size, elem_align)?;
 297             }
 298
 299             "discriminant_value" => {
 300                 let ty = *substs.types.get(subst::FnSpace, 0);
 301                 let adt_ptr = self.memory.read_ptr(args_ptrs[0])?;
 302                 let discr_val = self.read_discriminant_value(adt_ptr, ty)?;
 303                 self.memory.write_uint(dest, discr_val, 8)?;
 304             }
 305
 306             "forget" => {}
 307
 308             "init" => self.memory.write_repeat(dest, 0, dest_layout.size(&self.tcx.data_layout).bytes() as usize)?,
 309
 310             "min_align_of" => {
 311                 let elem_ty = *substs.types.get(subst::FnSpace, 0);
 312                 let elem_align = self.type_align(elem_ty);
 313                 self.memory.write_uint(dest, elem_align as u64, pointer_size)?;
 314             }
 315
 316             "move_val_init" => {
 317                 let ty = *substs.types.get(subst::FnSpace, 0);
 318                 let ptr = self.memory.read_ptr(args_ptrs[0])?;
 319                 self.move_(args_ptrs[1], ptr, ty)?;
 320             }
 321
 322             "offset" => {
 323                 let pointee_ty = *substs.types.get(subst::FnSpace, 0);
 324                 let pointee_size = self.type_size(pointee_ty) as isize;
 325                 let ptr_arg = args_ptrs[0];
 326                 let offset = self.memory.read_isize(args_ptrs[1])?;
 327
 328                 match self.memory.read_ptr(ptr_arg) {
 329                     Ok(ptr) => {
 330                         let result_ptr = ptr.offset(offset as isize * pointee_size);
 331                         self.memory.write_ptr(dest, result_ptr)?;
 332                     }
 333                     Err(EvalError::ReadBytesAsPointer) => {
 334                         let addr = self.memory.read_isize(ptr_arg)?;
 335                         let result_addr = addr + offset * pointee_size as i64;
 336                         self.memory.write_isize(dest, result_addr)?;
 337                     }
 338                     Err(e) => return Err(e),
 339                 }
 340             }
 341
 342             "overflowing_sub" => {
 343                 self.intrinsic_overflowing(mir::BinOp::Sub, &args[0], &args[1], dest)?;
 344             }
 345             "overflowing_mul" => {
 346                 self.intrinsic_overflowing(mir::BinOp::Mul, &args[0], &args[1], dest)?;
 347             }
 348             "overflowing_add" => {
 349                 self.intrinsic_overflowing(mir::BinOp::Add, &args[0], &args[1], dest)?;
 350             }
 351
 352             "size_of" => {
 353                 let ty = *substs.types.get(subst::FnSpace, 0);
 354                 let size = self.type_size(ty) as u64;
 355                 self.memory.write_uint(dest, size, pointer_size)?;
 356             }
 357
 358             "size_of_val" => {
 359                 let ty = *substs.types.get(subst::FnSpace, 0);
 360                 if self.type_is_sized(ty) {
 361                     let size = self.type_size(ty) as u64;
 362                     self.memory.write_uint(dest, size, pointer_size)?;
 363                 } else {
 364                     match ty.sty {
 365                         ty::TySlice(_) | ty::TyStr => {
 366                             let elem_ty = ty.sequence_element_type(self.tcx);
 367                             let elem_size = self.type_size(elem_ty) as u64;
 368                             let ptr_size = self.memory.pointer_size() as isize;
 369                             let n = self.memory.read_usize(args_ptrs[0].offset(ptr_size))?;
 370                             self.memory.write_uint(dest, n * elem_size, pointer_size)?;
 371                         }
 372
 373                         _ => return Err(EvalError::Unimplemented(format!("unimplemented: size_of_val::<{:?}>", ty))),
 374                     }
 375                 }
 376             }
 377
 378             "transmute" => {
 379                 let ty = *substs.types.get(subst::FnSpace, 0);
 380                 self.move_(args_ptrs[0], dest, ty)?;
 381             }
 382             "uninit" => self.memory.mark_definedness(dest, dest_layout.size(&self.tcx.data_layout).bytes() as usize, false)?,
 383
 384             name => return Err(EvalError::Unimplemented(format!("unimplemented intrinsic: {}", name))),
 385         }
 386
 387         // Since we pushed no stack frame, the main loop will act
 388         // as if the call just completed and it's returning to the
 389         // current frame.
 390         Ok(())
 391     }
 392
 393     fn call_c_abi(
 394         &mut self,
 395         def_id: DefId,
 396         args: &[mir::Operand<'tcx>],
 397         dest: Pointer,
 398         dest_size: usize,
 399     ) -> EvalResult<'tcx, ()> {
 400         let name = self.tcx.item_name(def_id);
 401         let attrs = self.tcx.get_attrs(def_id);
 402         let link_name = match attr::first_attr_value_str_by_name(&attrs, "link_name") {
 403             Some(ln) => ln.clone(),
 404             None => name.as_str(),
 405         };
 406
 407         let args_res: EvalResult<Vec<Pointer>> = args.iter()
 408             .map(|arg| self.eval_operand(arg))
 409             .collect();
 410         let args = args_res?;
 411
 412         if link_name.starts_with("pthread_") {
 413             warn!("ignoring C ABI call: {}", link_name);
 414             return Ok(());
 415         }
 416
 417         match &link_name[..] {
 418             "__rust_allocate" => {
 419                 let size = self.memory.read_usize(args[0])?;
 420                 let align = self.memory.read_usize(args[1])?;
 421                 let ptr = self.memory.allocate(size as usize, align as usize)?;
 422                 self.memory.write_ptr(dest, ptr)?;
 423             }
 424
 425             "__rust_reallocate" => {
 426                 let ptr = self.memory.read_ptr(args[0])?;
 427                 let size = self.memory.read_usize(args[2])?;
 428                 let align = self.memory.read_usize(args[3])?;
 429                 let new_ptr = self.memory.reallocate(ptr, size as usize, align as usize)?;
 430                 self.memory.write_ptr(dest, new_ptr)?;
 431             }
 432
 433             "memcmp" => {
 434                 let left = self.memory.read_ptr(args[0])?;
 435                 let right = self.memory.read_ptr(args[1])?;
 436                 let n = self.memory.read_usize(args[2])? as usize;
 437
 438                 let result = {
 439                     let left_bytes = self.memory.read_bytes(left, n)?;
 440                     let right_bytes = self.memory.read_bytes(right, n)?;
 441
 442                     use std::cmp::Ordering::*;
 443                     match left_bytes.cmp(right_bytes) {
 444                         Less => -1,
 445                         Equal => 0,
 446                         Greater => 1,
 447                     }
 448                 };
 449
 450                 self.memory.write_int(dest, result, dest_size)?;
 451             }
 452
 453             _ => {
 454                 return Err(EvalError::Unimplemented(format!("can't call C ABI function: {}", link_name)));
 455             }
 456         }
 457
 458         // Since we pushed no stack frame, the main loop will act
 459         // as if the call just completed and it's returning to the
 460         // current frame.
 461         Ok(())
 462     }
 463
 464     fn fulfill_obligation(&self, trait_ref: ty::PolyTraitRef<'tcx>) -> traits::Vtable<'tcx, ()> {
 465         // Do the initial selection for the obligation. This yields the shallow result we are
 466         // looking for -- that is, what specific impl.
 467         self.tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 468             let mut selcx = traits::SelectionContext::new(&infcx);
 469
 470             let obligation = traits::Obligation::new(
 471                 traits::ObligationCause::misc(DUMMY_SP, ast::DUMMY_NODE_ID),
 472                 trait_ref.to_poly_trait_predicate(),
 473             );
 474             let selection = selcx.select(&obligation).unwrap().unwrap();
 475
 476             // Currently, we use a fulfillment context to completely resolve all nested obligations.
 477             // This is because they can inform the inference of the impl's type parameters.
 478             let mut fulfill_cx = traits::FulfillmentContext::new();
 479             let vtable = selection.map(|predicate| {
 480                 fulfill_cx.register_predicate_obligation(&infcx, predicate);
 481             });
 482             infcx.drain_fulfillment_cx_or_panic(DUMMY_SP, &mut fulfill_cx, &vtable)
 483         })
 484     }
 485
 486     /// Trait method, which has to be resolved to an impl method.
 487     fn trait_method(
 488         &self,
 489         def_id: DefId,
 490         substs: &'tcx Substs<'tcx>
 491     ) -> (DefId, &'tcx Substs<'tcx>) {
 492         let method_item = self.tcx.impl_or_trait_item(def_id);
 493         let trait_id = method_item.container().id();
 494         let trait_ref = ty::Binder(substs.to_trait_ref(self.tcx, trait_id));
 495         match self.fulfill_obligation(trait_ref) {
 496             traits::VtableImpl(vtable_impl) => {
 497                 let impl_did = vtable_impl.impl_def_id;
 498                 let mname = self.tcx.item_name(def_id);
 499                 // Create a concatenated set of substitutions which includes those from the impl
 500                 // and those from the method:
 501                 let impl_substs = vtable_impl.substs.with_method_from(substs);
 502                 let substs = self.tcx.mk_substs(impl_substs);
 503                 let mth = get_impl_method(self.tcx, impl_did, substs, mname);
 504
 505                 (mth.method.def_id, mth.substs)
 506             }
 507
 508             traits::VtableClosure(vtable_closure) =>
 509                 (vtable_closure.closure_def_id, vtable_closure.substs.func_substs),
 510
 511             traits::VtableFnPointer(_fn_ty) => {
 512                 let _trait_closure_kind = self.tcx.lang_items.fn_trait_kind(trait_id).unwrap();
 513                 unimplemented!()
 514                 // let llfn = trans_fn_pointer_shim(ccx, trait_closure_kind, fn_ty);
 515
 516                 // let method_ty = def_ty(tcx, def_id, substs);
 517                 // let fn_ptr_ty = match method_ty.sty {
 518                 //     ty::TyFnDef(_, _, fty) => tcx.mk_ty(ty::TyFnPtr(fty)),
 519                 //     _ => unreachable!("expected fn item type, found {}",
 520                 //                       method_ty)
 521                 // };
 522                 // Callee::ptr(immediate_rvalue(llfn, fn_ptr_ty))
 523             }
 524
 525             traits::VtableObject(ref _data) => {
 526                 unimplemented!()
 527                 // Callee {
 528                 //     data: Virtual(traits::get_vtable_index_of_object_method(
 529                 //                   tcx, data, def_id)),
 530                 //                   ty: def_ty(tcx, def_id, substs)
 531                 // }
 532             }
 533             vtable => unreachable!("resolved vtable bad vtable {:?} in trans", vtable),
 534         }
 535     }
 536
 537     pub(super) fn type_needs_drop(&self, ty: Ty<'tcx>) -> bool {
 538         self.tcx.type_needs_drop_given_env(ty, &self.tcx.empty_parameter_environment())
 539     }
 540
 541     fn drop(&mut self, ptr: Pointer, ty: Ty<'tcx>) -> EvalResult<'tcx, ()> {
 542         if !self.type_needs_drop(ty) {
 543             debug!("no need to drop {:?}", ty);
 544             return Ok(());
 545         }
 546         trace!("-need to drop {:?}", ty);
 547
 548         // TODO(solson): Call user-defined Drop::drop impls.
 549
 550         match ty.sty {
 551             ty::TyBox(_contents_ty) => {
 552                 let contents_ptr = self.memory.read_ptr(ptr)?;
 553                 // self.drop(contents_ptr, contents_ty)?;
 554                 trace!("-deallocating box");
 555                 self.memory.deallocate(contents_ptr)?;
 556             }
 557
 558             // TODO(solson): Implement drop for other relevant types (e.g. aggregates).
 559             _ => {}
 560         }
 561
 562         Ok(())
 563     }
 564 }
 565
 566 #[derive(Debug)]
 567 struct ImplMethod<'tcx> {
 568     method: Rc<ty::Method<'tcx>>,
 569     substs: &'tcx Substs<'tcx>,
 570     is_provided: bool,
 571 }
 572
 573 /// Locates the applicable definition of a method, given its name.
 574 fn get_impl_method<'a, 'tcx>(
 575     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 576     impl_def_id: DefId,
 577     substs: &'tcx Substs<'tcx>,
 578     name: ast::Name,
 579 ) -> ImplMethod<'tcx> {
 580     assert!(!substs.types.needs_infer());
 581
 582     let trait_def_id = tcx.trait_id_of_impl(impl_def_id).unwrap();
 583     let trait_def = tcx.lookup_trait_def(trait_def_id);
 584
 585     match trait_def.ancestors(impl_def_id).fn_defs(tcx, name).next() {
 586         Some(node_item) => {
 587             let substs = tcx.normalizing_infer_ctxt(ProjectionMode::Any).enter(|infcx| {
 588                 let substs = traits::translate_substs(&infcx, impl_def_id,
 589                                                       substs, node_item.node);
 590                 tcx.lift(&substs).unwrap_or_else(|| {
 591                     bug!("trans::meth::get_impl_method: translate_substs \
 592                           returned {:?} which contains inference types/regions",
 593                          substs);
 594                 })
 595             });
 596             ImplMethod {
 597                 method: node_item.item,
 598                 substs: substs,
 599                 is_provided: node_item.node.is_from_trait(),
 600             }
 601         }
 602         None => {
 603             bug!("method {:?} not found in {:?}", name, impl_def_id)
 604         }
 605     }
 606 }