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