src/librustc_typeck/check/writeback.rs

   1 // Copyright 2014 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 // Type resolution: the phase that finds all the types in the AST with
  12 // unresolved type variables and replaces "ty_var" types with their
  13 // substitutions.
  14
  15 use check::FnCtxt;
  16 use rustc::hir;
  17 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  18 use rustc::infer::{InferCtxt};
  19 use rustc::ty::{self, Ty, TyCtxt, MethodCall, MethodCallee};
  20 use rustc::ty::adjustment;
  21 use rustc::ty::fold::{TypeFolder,TypeFoldable};
  22 use rustc::util::nodemap::{DefIdMap, DefIdSet};
  23 use syntax::ast;
  24 use syntax_pos::Span;
  25 use std::mem;
  26
  27 ///////////////////////////////////////////////////////////////////////////
  28 // Entry point
  29
  30 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
  31     pub fn resolve_type_vars_in_body(&self, body: &'gcx hir::Body)
  32                                      -> &'gcx ty::TypeckTables<'gcx> {
  33         let item_id = self.tcx.hir.body_owner(body.id());
  34         let item_def_id = self.tcx.hir.local_def_id(item_id);
  35
  36         let mut wbcx = WritebackCx::new(self, body);
  37         for arg in &body.arguments {
  38             wbcx.visit_node_id(arg.pat.span, arg.id);
  39         }
  40         wbcx.visit_body(body);
  41         wbcx.visit_upvar_borrow_map();
  42         wbcx.visit_closures();
  43         wbcx.visit_liberated_fn_sigs();
  44         wbcx.visit_fru_field_types();
  45         wbcx.visit_anon_types();
  46         wbcx.visit_type_nodes();
  47         wbcx.visit_cast_types();
  48         wbcx.visit_lints();
  49         wbcx.visit_free_region_map();
  50
  51         let used_trait_imports = mem::replace(&mut self.tables.borrow_mut().used_trait_imports,
  52                                               DefIdSet());
  53         debug!("used_trait_imports({:?}) = {:?}", item_def_id, used_trait_imports);
  54         wbcx.tables.used_trait_imports = used_trait_imports;
  55
  56         wbcx.tables.tainted_by_errors = self.is_tainted_by_errors();
  57
  58         self.tcx.alloc_tables(wbcx.tables)
  59     }
  60 }
  61
  62 ///////////////////////////////////////////////////////////////////////////
  63 // The Writerback context. This visitor walks the AST, checking the
  64 // fn-specific tables to find references to types or regions. It
  65 // resolves those regions to remove inference variables and writes the
  66 // final result back into the master tables in the tcx. Here and
  67 // there, it applies a few ad-hoc checks that were not convenient to
  68 // do elsewhere.
  69
  70 struct WritebackCx<'cx, 'gcx: 'cx+'tcx, 'tcx: 'cx> {
  71     fcx: &'cx FnCtxt<'cx, 'gcx, 'tcx>,
  72
  73     tables: ty::TypeckTables<'gcx>,
  74
  75     // Mapping from free regions of the function to the
  76     // early-bound versions of them, visible from the
  77     // outside of the function. This is needed by, and
  78     // only populated if there are any `impl Trait`.
  79     free_to_bound_regions: DefIdMap<&'gcx ty::Region>,
  80
  81     body: &'gcx hir::Body,
  82 }
  83
  84 impl<'cx, 'gcx, 'tcx> WritebackCx<'cx, 'gcx, 'tcx> {
  85     fn new(fcx: &'cx FnCtxt<'cx, 'gcx, 'tcx>, body: &'gcx hir::Body)
  86         -> WritebackCx<'cx, 'gcx, 'tcx> {
  87         let mut wbcx = WritebackCx {
  88             fcx: fcx,
  89             tables: ty::TypeckTables::empty(),
  90             free_to_bound_regions: DefIdMap(),
  91             body: body
  92         };
  93
  94         // Only build the reverse mapping if `impl Trait` is used.
  95         if fcx.anon_types.borrow().is_empty() {
  96             return wbcx;
  97         }
  98
  99         let gcx = fcx.tcx.global_tcx();
 100         let free_substs = fcx.parameter_environment.free_substs;
 101         for (i, k) in free_substs.iter().enumerate() {
 102             let r = if let Some(r) = k.as_region() {
 103                 r
 104             } else {
 105                 continue;
 106             };
 107             match *r {
 108                 ty::ReFree(ty::FreeRegion {
 109                     bound_region: ty::BoundRegion::BrNamed(def_id, name), ..
 110                 }) => {
 111                     let bound_region = gcx.mk_region(ty::ReEarlyBound(ty::EarlyBoundRegion {
 112                         index: i as u32,
 113                         name: name,
 114                     }));
 115                     wbcx.free_to_bound_regions.insert(def_id, bound_region);
 116                 }
 117                 _ => {
 118                     bug!("{:?} is not a free region for an early-bound lifetime", r);
 119                 }
 120             }
 121         }
 122
 123         wbcx
 124     }
 125
 126     fn tcx(&self) -> TyCtxt<'cx, 'gcx, 'tcx> {
 127         self.fcx.tcx
 128     }
 129
 130     fn write_ty_to_tables(&mut self, node_id: ast::NodeId, ty: Ty<'gcx>) {
 131         debug!("write_ty_to_tables({}, {:?})", node_id,  ty);
 132         assert!(!ty.needs_infer());
 133         self.tables.node_types.insert(node_id, ty);
 134     }
 135
 136     // Hacky hack: During type-checking, we treat *all* operators
 137     // as potentially overloaded. But then, during writeback, if
 138     // we observe that something like `a+b` is (known to be)
 139     // operating on scalars, we clear the overload.
 140     fn fix_scalar_builtin_expr(&mut self, e: &hir::Expr) {
 141         match e.node {
 142             hir::ExprUnary(hir::UnNeg, ref inner) |
 143             hir::ExprUnary(hir::UnNot, ref inner)  => {
 144                 let inner_ty = self.fcx.node_ty(inner.id);
 145                 let inner_ty = self.fcx.resolve_type_vars_if_possible(&inner_ty);
 146
 147                 if inner_ty.is_scalar() {
 148                     self.fcx.tables.borrow_mut().method_map.remove(&MethodCall::expr(e.id));
 149                 }
 150             }
 151             hir::ExprBinary(ref op, ref lhs, ref rhs) |
 152             hir::ExprAssignOp(ref op, ref lhs, ref rhs) => {
 153                 let lhs_ty = self.fcx.node_ty(lhs.id);
 154                 let lhs_ty = self.fcx.resolve_type_vars_if_possible(&lhs_ty);
 155
 156                 let rhs_ty = self.fcx.node_ty(rhs.id);
 157                 let rhs_ty = self.fcx.resolve_type_vars_if_possible(&rhs_ty);
 158
 159                 if lhs_ty.is_scalar() && rhs_ty.is_scalar() {
 160                     self.fcx.tables.borrow_mut().method_map.remove(&MethodCall::expr(e.id));
 161
 162                     // weird but true: the by-ref binops put an
 163                     // adjustment on the lhs but not the rhs; the
 164                     // adjustment for rhs is kind of baked into the
 165                     // system.
 166                     match e.node {
 167                         hir::ExprBinary(..) => {
 168                             if !op.node.is_by_value() {
 169                                 self.fcx.tables.borrow_mut().adjustments.remove(&lhs.id);
 170                             }
 171                         },
 172                         hir::ExprAssignOp(..) => {
 173                             self.fcx.tables.borrow_mut().adjustments.remove(&lhs.id);
 174                         },
 175                         _ => {},
 176                     }
 177                 }
 178             }
 179             _ => {},
 180         }
 181     }
 182 }
 183
 184 ///////////////////////////////////////////////////////////////////////////
 185 // Impl of Visitor for Resolver
 186 //
 187 // This is the master code which walks the AST. It delegates most of
 188 // the heavy lifting to the generic visit and resolve functions
 189 // below. In general, a function is made into a `visitor` if it must
 190 // traffic in node-ids or update tables in the type context etc.
 191
 192 impl<'cx, 'gcx, 'tcx> Visitor<'gcx> for WritebackCx<'cx, 'gcx, 'tcx> {
 193     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'gcx> {
 194         NestedVisitorMap::None
 195     }
 196
 197     fn visit_stmt(&mut self, s: &'gcx hir::Stmt) {
 198         self.visit_node_id(s.span, s.node.id());
 199         intravisit::walk_stmt(self, s);
 200     }
 201
 202     fn visit_expr(&mut self, e: &'gcx hir::Expr) {
 203         self.fix_scalar_builtin_expr(e);
 204
 205         self.visit_node_id(e.span, e.id);
 206         self.visit_method_map_entry(e.span, MethodCall::expr(e.id));
 207
 208         if let hir::ExprClosure(_, _, body, _) = e.node {
 209             let body = self.fcx.tcx.hir.body(body);
 210             for arg in &body.arguments {
 211                 self.visit_node_id(e.span, arg.id);
 212             }
 213
 214             self.visit_body(body);
 215         }
 216
 217         intravisit::walk_expr(self, e);
 218     }
 219
 220     fn visit_block(&mut self, b: &'gcx hir::Block) {
 221         self.visit_node_id(b.span, b.id);
 222         intravisit::walk_block(self, b);
 223     }
 224
 225     fn visit_pat(&mut self, p: &'gcx hir::Pat) {
 226         self.visit_node_id(p.span, p.id);
 227         intravisit::walk_pat(self, p);
 228     }
 229
 230     fn visit_local(&mut self, l: &'gcx hir::Local) {
 231         intravisit::walk_local(self, l);
 232         let var_ty = self.fcx.local_ty(l.span, l.id);
 233         let var_ty = self.resolve(&var_ty, &l.span);
 234         self.write_ty_to_tables(l.id, var_ty);
 235     }
 236 }
 237
 238 impl<'cx, 'gcx, 'tcx> WritebackCx<'cx, 'gcx, 'tcx> {
 239     fn visit_upvar_borrow_map(&mut self) {
 240         for (upvar_id, upvar_capture) in self.fcx.tables.borrow().upvar_capture_map.iter() {
 241             let new_upvar_capture = match *upvar_capture {
 242                 ty::UpvarCapture::ByValue => ty::UpvarCapture::ByValue,
 243                 ty::UpvarCapture::ByRef(ref upvar_borrow) => {
 244                     let r = upvar_borrow.region;
 245                     let r = self.resolve(&r, &upvar_id.var_id);
 246                     ty::UpvarCapture::ByRef(
 247                         ty::UpvarBorrow { kind: upvar_borrow.kind, region: r })
 248                 }
 249             };
 250             debug!("Upvar capture for {:?} resolved to {:?}",
 251                    upvar_id,
 252                    new_upvar_capture);
 253             self.tables.upvar_capture_map.insert(*upvar_id, new_upvar_capture);
 254         }
 255     }
 256
 257     fn visit_closures(&mut self) {
 258         for (&id, closure_ty) in self.fcx.tables.borrow().closure_tys.iter() {
 259             let closure_ty = self.resolve(closure_ty, &id);
 260             self.tables.closure_tys.insert(id, closure_ty);
 261         }
 262
 263         for (&id, &closure_kind) in self.fcx.tables.borrow().closure_kinds.iter() {
 264             self.tables.closure_kinds.insert(id, closure_kind);
 265         }
 266     }
 267
 268     fn visit_cast_types(&mut self) {
 269         self.tables.cast_kinds.extend(
 270             self.fcx.tables.borrow().cast_kinds.iter().map(|(&key, &value)| (key, value)));
 271     }
 272
 273     fn visit_lints(&mut self) {
 274         self.fcx.tables.borrow_mut().lints.transfer(&mut self.tables.lints);
 275     }
 276
 277     fn visit_free_region_map(&mut self) {
 278         self.tables.free_region_map = self.fcx.tables.borrow().free_region_map.clone();
 279     }
 280
 281     fn visit_anon_types(&mut self) {
 282         let gcx = self.tcx().global_tcx();
 283         for (&node_id, &concrete_ty) in self.fcx.anon_types.borrow().iter() {
 284             let inside_ty = self.resolve(&concrete_ty, &node_id);
 285
 286             // Convert the type from the function into a type valid outside
 287             // the function, by replacing free regions with early-bound ones.
 288             let outside_ty = gcx.fold_regions(&inside_ty, &mut false, |r, _| {
 289                 match *r {
 290                     // 'static is valid everywhere.
 291                     ty::ReStatic => gcx.types.re_static,
 292                     ty::ReEmpty => gcx.types.re_empty,
 293
 294                     // Free regions that come from early-bound regions are valid.
 295                     ty::ReFree(ty::FreeRegion {
 296                         bound_region: ty::BoundRegion::BrNamed(def_id, ..), ..
 297                     }) if self.free_to_bound_regions.contains_key(&def_id) => {
 298                         self.free_to_bound_regions[&def_id]
 299                     }
 300
 301                     ty::ReFree(_) |
 302                     ty::ReEarlyBound(_) |
 303                     ty::ReLateBound(..) |
 304                     ty::ReScope(_) |
 305                     ty::ReSkolemized(..) => {
 306                         let span = node_id.to_span(&self.fcx.tcx);
 307                         span_err!(self.tcx().sess, span, E0564,
 308                                   "only named lifetimes are allowed in `impl Trait`, \
 309                                    but `{}` was found in the type `{}`", r, inside_ty);
 310                         gcx.types.re_static
 311                     }
 312
 313                     ty::ReVar(_) |
 314                     ty::ReErased => {
 315                         let span = node_id.to_span(&self.fcx.tcx);
 316                         span_bug!(span, "invalid region in impl Trait: {:?}", r);
 317                     }
 318                 }
 319             });
 320
 321             self.tables.node_types.insert(node_id, outside_ty);
 322         }
 323     }
 324
 325     fn visit_node_id(&mut self, span: Span, node_id: ast::NodeId) {
 326         // Export associated path extensions.
 327         if let Some(def) = self.fcx.tables.borrow_mut().type_relative_path_defs.remove(&node_id) {
 328             self.tables.type_relative_path_defs.insert(node_id, def);
 329         }
 330
 331         // Resolve any borrowings for the node with id `node_id`
 332         self.visit_adjustments(span, node_id);
 333
 334         // Resolve the type of the node with id `node_id`
 335         let n_ty = self.fcx.node_ty(node_id);
 336         let n_ty = self.resolve(&n_ty, &span);
 337         self.write_ty_to_tables(node_id, n_ty);
 338         debug!("Node {} has type {:?}", node_id, n_ty);
 339
 340         // Resolve any substitutions
 341         self.fcx.opt_node_ty_substs(node_id, |item_substs| {
 342             let item_substs = self.resolve(item_substs, &span);
 343             if !item_substs.is_noop() {
 344                 debug!("write_substs_to_tcx({}, {:?})", node_id, item_substs);
 345                 assert!(!item_substs.substs.needs_infer());
 346                 self.tables.item_substs.insert(node_id, item_substs);
 347             }
 348         });
 349     }
 350
 351     fn visit_adjustments(&mut self, span: Span, node_id: ast::NodeId) {
 352         let adjustments = self.fcx.tables.borrow_mut().adjustments.remove(&node_id);
 353         match adjustments {
 354             None => {
 355                 debug!("No adjustments for node {}", node_id);
 356             }
 357
 358             Some(adjustment) => {
 359                 let resolved_adjustment = match adjustment.kind {
 360                     adjustment::Adjust::NeverToAny => {
 361                         adjustment::Adjust::NeverToAny
 362                     }
 363
 364                     adjustment::Adjust::ReifyFnPointer => {
 365                         adjustment::Adjust::ReifyFnPointer
 366                     }
 367
 368                     adjustment::Adjust::MutToConstPointer => {
 369                         adjustment::Adjust::MutToConstPointer
 370                     }
 371
 372                     adjustment::Adjust::ClosureFnPointer => {
 373                         adjustment::Adjust::ClosureFnPointer
 374                     }
 375
 376                     adjustment::Adjust::UnsafeFnPointer => {
 377                         adjustment::Adjust::UnsafeFnPointer
 378                     }
 379
 380                     adjustment::Adjust::DerefRef { autoderefs, autoref, unsize } => {
 381                         for autoderef in 0..autoderefs {
 382                             let method_call = MethodCall::autoderef(node_id, autoderef as u32);
 383                             self.visit_method_map_entry(span, method_call);
 384                         }
 385
 386                         adjustment::Adjust::DerefRef {
 387                             autoderefs: autoderefs,
 388                             autoref: self.resolve(&autoref, &span),
 389                             unsize: unsize,
 390                         }
 391                     }
 392                 };
 393                 let resolved_adjustment = adjustment::Adjustment {
 394                     kind: resolved_adjustment,
 395                     target: self.resolve(&adjustment.target, &span)
 396                 };
 397                 debug!("Adjustments for node {}: {:?}", node_id, resolved_adjustment);
 398                 self.tables.adjustments.insert(node_id, resolved_adjustment);
 399             }
 400         }
 401     }
 402
 403     fn visit_method_map_entry(&mut self,
 404                               method_span: Span,
 405                               method_call: MethodCall) {
 406         // Resolve any method map entry
 407         let new_method = match self.fcx.tables.borrow_mut().method_map.remove(&method_call) {
 408             Some(method) => {
 409                 debug!("writeback::resolve_method_map_entry(call={:?}, entry={:?})",
 410                        method_call,
 411                        method);
 412                 let new_method = MethodCallee {
 413                     def_id: method.def_id,
 414                     ty: self.resolve(&method.ty, &method_span),
 415                     substs: self.resolve(&method.substs, &method_span),
 416                 };
 417
 418                 Some(new_method)
 419             }
 420             None => None
 421         };
 422
 423         //NB(jroesch): We need to match twice to avoid a double borrow which would cause an ICE
 424         if let Some(method) = new_method {
 425             self.tables.method_map.insert(method_call, method);
 426         }
 427     }
 428
 429     fn visit_liberated_fn_sigs(&mut self) {
 430         for (&node_id, fn_sig) in self.fcx.tables.borrow().liberated_fn_sigs.iter() {
 431             let fn_sig = self.resolve(fn_sig, &node_id);
 432             self.tables.liberated_fn_sigs.insert(node_id, fn_sig.clone());
 433         }
 434     }
 435
 436     fn visit_fru_field_types(&mut self) {
 437         for (&node_id, ftys) in self.fcx.tables.borrow().fru_field_types.iter() {
 438             let ftys = self.resolve(ftys, &node_id);
 439             self.tables.fru_field_types.insert(node_id, ftys);
 440         }
 441     }
 442
 443     fn visit_type_nodes(&self) {
 444         for (&id, ty) in self.fcx.ast_ty_to_ty_cache.borrow().iter() {
 445             let ty = self.resolve(ty, &id);
 446             self.fcx.tcx.ast_ty_to_ty_cache.borrow_mut().insert(id, ty);
 447         }
 448     }
 449
 450     fn resolve<T>(&self, x: &T, span: &Locatable) -> T::Lifted
 451         where T: TypeFoldable<'tcx> + ty::Lift<'gcx>
 452     {
 453         let x = x.fold_with(&mut Resolver::new(self.fcx, span, self.body));
 454         if let Some(lifted) = self.tcx().lift_to_global(&x) {
 455             lifted
 456         } else {
 457             span_bug!(span.to_span(&self.fcx.tcx),
 458                       "writeback: `{:?}` missing from the global type context",
 459                       x);
 460         }
 461     }
 462 }
 463
 464 trait Locatable {
 465     fn to_span(&self, tcx: &TyCtxt) -> Span;
 466 }
 467
 468 impl Locatable for Span {
 469     fn to_span(&self, _: &TyCtxt) -> Span { *self }
 470 }
 471
 472 impl Locatable for ast::NodeId {
 473     fn to_span(&self, tcx: &TyCtxt) -> Span { tcx.hir.span(*self) }
 474 }
 475
 476 ///////////////////////////////////////////////////////////////////////////
 477 // The Resolver. This is the type folding engine that detects
 478 // unresolved types and so forth.
 479
 480 struct Resolver<'cx, 'gcx: 'cx+'tcx, 'tcx: 'cx> {
 481     tcx: TyCtxt<'cx, 'gcx, 'tcx>,
 482     infcx: &'cx InferCtxt<'cx, 'gcx, 'tcx>,
 483     span: &'cx Locatable,
 484     body: &'gcx hir::Body,
 485 }
 486
 487 impl<'cx, 'gcx, 'tcx> Resolver<'cx, 'gcx, 'tcx> {
 488     fn new(fcx: &'cx FnCtxt<'cx, 'gcx, 'tcx>, span: &'cx Locatable, body: &'gcx hir::Body)
 489         -> Resolver<'cx, 'gcx, 'tcx>
 490     {
 491         Resolver {
 492             tcx: fcx.tcx,
 493             infcx: fcx,
 494             span: span,
 495             body: body,
 496         }
 497     }
 498
 499     fn report_error(&self, t: Ty<'tcx>) {
 500         if !self.tcx.sess.has_errors() {
 501             self.infcx.need_type_info(self.body.id(), self.span.to_span(&self.tcx), t);
 502         }
 503     }
 504 }
 505
 506 impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for Resolver<'cx, 'gcx, 'tcx> {
 507     fn tcx<'a>(&'a self) -> TyCtxt<'a, 'gcx, 'tcx> {
 508         self.tcx
 509     }
 510
 511     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 512         match self.infcx.fully_resolve(&t) {
 513             Ok(t) => t,
 514             Err(_) => {
 515                 debug!("Resolver::fold_ty: input type `{:?}` not fully resolvable",
 516                        t);
 517                 self.report_error(t);
 518                 self.tcx().types.err
 519             }
 520         }
 521     }
 522
 523     // FIXME This should be carefully checked
 524     // We could use `self.report_error` but it doesn't accept a ty::Region, right now.
 525     fn fold_region(&mut self, r: &'tcx ty::Region) -> &'tcx ty::Region {
 526         match self.infcx.fully_resolve(&r) {
 527             Ok(r) => r,
 528             Err(_) => {
 529                 self.tcx.types.re_static
 530             }
 531         }
 532     }
 533 }
 534
 535 ///////////////////////////////////////////////////////////////////////////
 536 // During type check, we store promises with the result of trait
 537 // lookup rather than the actual results (because the results are not
 538 // necessarily available immediately). These routines unwind the
 539 // promises. It is expected that we will have already reported any
 540 // errors that may be encountered, so if the promises store an error,
 541 // a dummy result is returned.