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 use self::ResolveReason::*;
  15
  16 use astconv::AstConv;
  17 use check::FnCtxt;
  18 use middle::def_id::DefId;
  19 use middle::pat_util;
  20 use middle::ty::{self, Ty, MethodCall, MethodCallee, HasTypeFlags};
  21 use middle::ty::adjustment;
  22 use middle::ty::fold::{TypeFolder,TypeFoldable};
  23 use middle::infer;
  24 use write_substs_to_tcx;
  25 use write_ty_to_tcx;
  26
  27 use std::cell::Cell;
  28
  29 use syntax::ast;
  30 use syntax::codemap::{DUMMY_SP, Span};
  31 use rustc_front::print::pprust::pat_to_string;
  32 use rustc_front::visit;
  33 use rustc_front::visit::Visitor;
  34 use rustc_front::util as hir_util;
  35 use rustc_front::hir;
  36
  37 ///////////////////////////////////////////////////////////////////////////
  38 // Entry point functions
  39
  40 pub fn resolve_type_vars_in_expr(fcx: &FnCtxt, e: &hir::Expr) {
  41     assert_eq!(fcx.writeback_errors.get(), false);
  42     let mut wbcx = WritebackCx::new(fcx);
  43     wbcx.visit_expr(e);
  44     wbcx.visit_upvar_borrow_map();
  45     wbcx.visit_closures();
  46 }
  47
  48 pub fn resolve_type_vars_in_fn(fcx: &FnCtxt,
  49                                decl: &hir::FnDecl,
  50                                blk: &hir::Block) {
  51     assert_eq!(fcx.writeback_errors.get(), false);
  52     let mut wbcx = WritebackCx::new(fcx);
  53     wbcx.visit_block(blk);
  54     for arg in &decl.inputs {
  55         wbcx.visit_node_id(ResolvingPattern(arg.pat.span), arg.id);
  56         wbcx.visit_pat(&*arg.pat);
  57
  58         // Privacy needs the type for the whole pattern, not just each binding
  59         if !pat_util::pat_is_binding(&fcx.tcx().def_map, &*arg.pat) {
  60             wbcx.visit_node_id(ResolvingPattern(arg.pat.span),
  61                                arg.pat.id);
  62         }
  63     }
  64     wbcx.visit_upvar_borrow_map();
  65     wbcx.visit_closures();
  66 }
  67
  68 ///////////////////////////////////////////////////////////////////////////
  69 // The Writerback context. This visitor walks the AST, checking the
  70 // fn-specific tables to find references to types or regions. It
  71 // resolves those regions to remove inference variables and writes the
  72 // final result back into the master tables in the tcx. Here and
  73 // there, it applies a few ad-hoc checks that were not convenient to
  74 // do elsewhere.
  75
  76 struct WritebackCx<'cx, 'tcx: 'cx> {
  77     fcx: &'cx FnCtxt<'cx, 'tcx>,
  78 }
  79
  80 impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
  81     fn new(fcx: &'cx FnCtxt<'cx, 'tcx>) -> WritebackCx<'cx, 'tcx> {
  82         WritebackCx { fcx: fcx }
  83     }
  84
  85     fn tcx(&self) -> &'cx ty::ctxt<'tcx> {
  86         self.fcx.tcx()
  87     }
  88
  89     // Hacky hack: During type-checking, we treat *all* operators
  90     // as potentially overloaded. But then, during writeback, if
  91     // we observe that something like `a+b` is (known to be)
  92     // operating on scalars, we clear the overload.
  93     fn fix_scalar_binary_expr(&mut self, e: &hir::Expr) {
  94         match e.node {
  95             hir::ExprBinary(ref op, ref lhs, ref rhs) |
  96             hir::ExprAssignOp(ref op, ref lhs, ref rhs) => {
  97                 let lhs_ty = self.fcx.node_ty(lhs.id);
  98                 let lhs_ty = self.fcx.infcx().resolve_type_vars_if_possible(&lhs_ty);
  99
 100                 let rhs_ty = self.fcx.node_ty(rhs.id);
 101                 let rhs_ty = self.fcx.infcx().resolve_type_vars_if_possible(&rhs_ty);
 102
 103                 if lhs_ty.is_scalar() && rhs_ty.is_scalar() {
 104                     self.fcx.inh.tables.borrow_mut().method_map.remove(&MethodCall::expr(e.id));
 105
 106                     // weird but true: the by-ref binops put an
 107                     // adjustment on the lhs but not the rhs; the
 108                     // adjustment for rhs is kind of baked into the
 109                     // system.
 110                     match e.node {
 111                         hir::ExprBinary(..) => {
 112                             if !hir_util::is_by_value_binop(op.node) {
 113                                 self.fcx.inh.tables.borrow_mut().adjustments.remove(&lhs.id);
 114                             }
 115                         },
 116                         hir::ExprAssignOp(..) => {
 117                             self.fcx.inh.tables.borrow_mut().adjustments.remove(&lhs.id);
 118                         },
 119                         _ => {},
 120                     }
 121                 } else {
 122                     let tcx = self.tcx();
 123
 124                     if let hir::ExprAssignOp(..) = e.node {
 125                         if
 126                             !tcx.sess.features.borrow().augmented_assignments &&
 127                             !self.fcx.expr_ty(e).references_error()
 128                         {
 129                             tcx.sess.span_err(
 130                                 e.span,
 131                                 "overloaded augmented assignments are not stable");
 132                             fileline_help!(
 133                                 tcx.sess, e.span,
 134                                 "add #![feature(augmented_assignments)] to the crate features \
 135                                  to enable");
 136                         }
 137                     }
 138                 }
 139             }
 140             _ => {},
 141         }
 142     }
 143 }
 144
 145 ///////////////////////////////////////////////////////////////////////////
 146 // Impl of Visitor for Resolver
 147 //
 148 // This is the master code which walks the AST. It delegates most of
 149 // the heavy lifting to the generic visit and resolve functions
 150 // below. In general, a function is made into a `visitor` if it must
 151 // traffic in node-ids or update tables in the type context etc.
 152
 153 impl<'cx, 'tcx, 'v> Visitor<'v> for WritebackCx<'cx, 'tcx> {
 154     fn visit_item(&mut self, _: &hir::Item) {
 155         // Ignore items
 156     }
 157
 158     fn visit_stmt(&mut self, s: &hir::Stmt) {
 159         if self.fcx.writeback_errors.get() {
 160             return;
 161         }
 162
 163         self.visit_node_id(ResolvingExpr(s.span), hir_util::stmt_id(s));
 164         visit::walk_stmt(self, s);
 165     }
 166
 167     fn visit_expr(&mut self, e: &hir::Expr) {
 168         if self.fcx.writeback_errors.get() {
 169             return;
 170         }
 171
 172         self.fix_scalar_binary_expr(e);
 173
 174         self.visit_node_id(ResolvingExpr(e.span), e.id);
 175         self.visit_method_map_entry(ResolvingExpr(e.span),
 176                                     MethodCall::expr(e.id));
 177
 178         if let hir::ExprClosure(_, ref decl, _) = e.node {
 179             for input in &decl.inputs {
 180                 self.visit_node_id(ResolvingExpr(e.span), input.id);
 181             }
 182         }
 183
 184         visit::walk_expr(self, e);
 185     }
 186
 187     fn visit_block(&mut self, b: &hir::Block) {
 188         if self.fcx.writeback_errors.get() {
 189             return;
 190         }
 191
 192         self.visit_node_id(ResolvingExpr(b.span), b.id);
 193         visit::walk_block(self, b);
 194     }
 195
 196     fn visit_pat(&mut self, p: &hir::Pat) {
 197         if self.fcx.writeback_errors.get() {
 198             return;
 199         }
 200
 201         self.visit_node_id(ResolvingPattern(p.span), p.id);
 202
 203         debug!("Type for pattern binding {} (id {}) resolved to {:?}",
 204                pat_to_string(p),
 205                p.id,
 206                self.tcx().node_id_to_type(p.id));
 207
 208         visit::walk_pat(self, p);
 209     }
 210
 211     fn visit_local(&mut self, l: &hir::Local) {
 212         if self.fcx.writeback_errors.get() {
 213             return;
 214         }
 215
 216         let var_ty = self.fcx.local_ty(l.span, l.id);
 217         let var_ty = self.resolve(&var_ty, ResolvingLocal(l.span));
 218         write_ty_to_tcx(self.tcx(), l.id, var_ty);
 219         visit::walk_local(self, l);
 220     }
 221
 222     fn visit_ty(&mut self, t: &hir::Ty) {
 223         match t.node {
 224             hir::TyFixedLengthVec(ref ty, ref count_expr) => {
 225                 self.visit_ty(&**ty);
 226                 write_ty_to_tcx(self.tcx(), count_expr.id, self.tcx().types.usize);
 227             }
 228             hir::TyBareFn(ref function_declaration) => {
 229                 visit::walk_fn_decl_nopat(self, &function_declaration.decl);
 230                 walk_list!(self, visit_lifetime_def, &function_declaration.lifetimes);
 231             }
 232             _ => visit::walk_ty(self, t)
 233         }
 234     }
 235 }
 236
 237 impl<'cx, 'tcx> WritebackCx<'cx, 'tcx> {
 238     fn visit_upvar_borrow_map(&self) {
 239         if self.fcx.writeback_errors.get() {
 240             return;
 241         }
 242
 243         for (upvar_id, upvar_capture) in self.fcx.inh.tables.borrow().upvar_capture_map.iter() {
 244             let new_upvar_capture = match *upvar_capture {
 245                 ty::UpvarCapture::ByValue => ty::UpvarCapture::ByValue,
 246                 ty::UpvarCapture::ByRef(ref upvar_borrow) => {
 247                     let r = upvar_borrow.region;
 248                     let r = self.resolve(&r, ResolvingUpvar(*upvar_id));
 249                     ty::UpvarCapture::ByRef(
 250                         ty::UpvarBorrow { kind: upvar_borrow.kind, region: r })
 251                 }
 252             };
 253             debug!("Upvar capture for {:?} resolved to {:?}",
 254                    upvar_id,
 255                    new_upvar_capture);
 256             self.fcx.tcx()
 257                     .tables
 258                     .borrow_mut()
 259                     .upvar_capture_map
 260                     .insert(*upvar_id, new_upvar_capture);
 261         }
 262     }
 263
 264     fn visit_closures(&self) {
 265         if self.fcx.writeback_errors.get() {
 266             return
 267         }
 268
 269         for (def_id, closure_ty) in self.fcx.inh.tables.borrow().closure_tys.iter() {
 270             let closure_ty = self.resolve(closure_ty, ResolvingClosure(*def_id));
 271             self.fcx.tcx().tables.borrow_mut().closure_tys.insert(*def_id, closure_ty);
 272         }
 273
 274         for (def_id, &closure_kind) in self.fcx.inh.tables.borrow().closure_kinds.iter() {
 275             self.fcx.tcx().tables.borrow_mut().closure_kinds.insert(*def_id, closure_kind);
 276         }
 277     }
 278
 279     fn visit_node_id(&self, reason: ResolveReason, id: ast::NodeId) {
 280         // Resolve any borrowings for the node with id `id`
 281         self.visit_adjustments(reason, id);
 282
 283         // Resolve the type of the node with id `id`
 284         let n_ty = self.fcx.node_ty(id);
 285         let n_ty = self.resolve(&n_ty, reason);
 286         write_ty_to_tcx(self.tcx(), id, n_ty);
 287         debug!("Node {} has type {:?}", id, n_ty);
 288
 289         // Resolve any substitutions
 290         self.fcx.opt_node_ty_substs(id, |item_substs| {
 291             write_substs_to_tcx(self.tcx(), id,
 292                                 self.resolve(item_substs, reason));
 293         });
 294     }
 295
 296     fn visit_adjustments(&self, reason: ResolveReason, id: ast::NodeId) {
 297         let adjustments = self.fcx.inh.tables.borrow_mut().adjustments.remove(&id);
 298         match adjustments {
 299             None => {
 300                 debug!("No adjustments for node {}", id);
 301             }
 302
 303             Some(adjustment) => {
 304                 let resolved_adjustment = match adjustment {
 305                     adjustment::AdjustReifyFnPointer => {
 306                         adjustment::AdjustReifyFnPointer
 307                     }
 308
 309                     adjustment::AdjustUnsafeFnPointer => {
 310                         adjustment::AdjustUnsafeFnPointer
 311                     }
 312
 313                     adjustment::AdjustDerefRef(adj) => {
 314                         for autoderef in 0..adj.autoderefs {
 315                             let method_call = MethodCall::autoderef(id, autoderef as u32);
 316                             self.visit_method_map_entry(reason, method_call);
 317                         }
 318
 319                         adjustment::AdjustDerefRef(adjustment::AutoDerefRef {
 320                             autoderefs: adj.autoderefs,
 321                             autoref: self.resolve(&adj.autoref, reason),
 322                             unsize: self.resolve(&adj.unsize, reason),
 323                         })
 324                     }
 325                 };
 326                 debug!("Adjustments for node {}: {:?}", id, resolved_adjustment);
 327                 self.tcx().tables.borrow_mut().adjustments.insert(
 328                     id, resolved_adjustment);
 329             }
 330         }
 331     }
 332
 333     fn visit_method_map_entry(&self,
 334                               reason: ResolveReason,
 335                               method_call: MethodCall) {
 336         // Resolve any method map entry
 337         let new_method = match self.fcx.inh.tables.borrow_mut().method_map.remove(&method_call) {
 338             Some(method) => {
 339                 debug!("writeback::resolve_method_map_entry(call={:?}, entry={:?})",
 340                        method_call,
 341                        method);
 342                 let new_method = MethodCallee {
 343                     def_id: method.def_id,
 344                     ty: self.resolve(&method.ty, reason),
 345                     substs: self.tcx().mk_substs(self.resolve(method.substs, reason)),
 346                 };
 347
 348                 Some(new_method)
 349             }
 350             None => None
 351         };
 352
 353         //NB(jroesch): We need to match twice to avoid a double borrow which would cause an ICE
 354         match new_method {
 355             Some(method) => {
 356                 self.tcx().tables.borrow_mut().method_map.insert(
 357                     method_call,
 358                     method);
 359             }
 360             None => {}
 361         }
 362     }
 363
 364     fn resolve<T:TypeFoldable<'tcx>>(&self, t: &T, reason: ResolveReason) -> T {
 365         t.fold_with(&mut Resolver::new(self.fcx, reason))
 366     }
 367 }
 368
 369 ///////////////////////////////////////////////////////////////////////////
 370 // Resolution reason.
 371
 372 #[derive(Copy, Clone)]
 373 enum ResolveReason {
 374     ResolvingExpr(Span),
 375     ResolvingLocal(Span),
 376     ResolvingPattern(Span),
 377     ResolvingUpvar(ty::UpvarId),
 378     ResolvingClosure(DefId),
 379 }
 380
 381 impl ResolveReason {
 382     fn span(&self, tcx: &ty::ctxt) -> Span {
 383         match *self {
 384             ResolvingExpr(s) => s,
 385             ResolvingLocal(s) => s,
 386             ResolvingPattern(s) => s,
 387             ResolvingUpvar(upvar_id) => {
 388                 tcx.expr_span(upvar_id.closure_expr_id)
 389             }
 390             ResolvingClosure(did) => {
 391                 if did.is_local() {
 392                     tcx.expr_span(did.node)
 393                 } else {
 394                     DUMMY_SP
 395                 }
 396             }
 397         }
 398     }
 399 }
 400
 401 ///////////////////////////////////////////////////////////////////////////
 402 // The Resolver. This is the type folding engine that detects
 403 // unresolved types and so forth.
 404
 405 struct Resolver<'cx, 'tcx: 'cx> {
 406     tcx: &'cx ty::ctxt<'tcx>,
 407     infcx: &'cx infer::InferCtxt<'cx, 'tcx>,
 408     writeback_errors: &'cx Cell<bool>,
 409     reason: ResolveReason,
 410 }
 411
 412 impl<'cx, 'tcx> Resolver<'cx, 'tcx> {
 413     fn new(fcx: &'cx FnCtxt<'cx, 'tcx>,
 414            reason: ResolveReason)
 415            -> Resolver<'cx, 'tcx>
 416     {
 417         Resolver::from_infcx(fcx.infcx(), &fcx.writeback_errors, reason)
 418     }
 419
 420     fn from_infcx(infcx: &'cx infer::InferCtxt<'cx, 'tcx>,
 421                   writeback_errors: &'cx Cell<bool>,
 422                   reason: ResolveReason)
 423                   -> Resolver<'cx, 'tcx>
 424     {
 425         Resolver { infcx: infcx,
 426                    tcx: infcx.tcx,
 427                    writeback_errors: writeback_errors,
 428                    reason: reason }
 429     }
 430
 431     fn report_error(&self, e: infer::FixupError) {
 432         self.writeback_errors.set(true);
 433         if !self.tcx.sess.has_errors() {
 434             match self.reason {
 435                 ResolvingExpr(span) => {
 436                     span_err!(self.tcx.sess, span, E0101,
 437                         "cannot determine a type for this expression: {}",
 438                         infer::fixup_err_to_string(e));
 439                 }
 440
 441                 ResolvingLocal(span) => {
 442                     span_err!(self.tcx.sess, span, E0102,
 443                         "cannot determine a type for this local variable: {}",
 444                         infer::fixup_err_to_string(e));
 445                 }
 446
 447                 ResolvingPattern(span) => {
 448                     span_err!(self.tcx.sess, span, E0103,
 449                         "cannot determine a type for this pattern binding: {}",
 450                         infer::fixup_err_to_string(e));
 451                 }
 452
 453                 ResolvingUpvar(upvar_id) => {
 454                     let span = self.reason.span(self.tcx);
 455                     span_err!(self.tcx.sess, span, E0104,
 456                         "cannot resolve lifetime for captured variable `{}`: {}",
 457                         self.tcx.local_var_name_str(upvar_id.var_id).to_string(),
 458                         infer::fixup_err_to_string(e));
 459                 }
 460
 461                 ResolvingClosure(_) => {
 462                     let span = self.reason.span(self.tcx);
 463                     span_err!(self.tcx.sess, span, E0196,
 464                               "cannot determine a type for this closure")
 465                 }
 466             }
 467         }
 468     }
 469 }
 470
 471 impl<'cx, 'tcx> TypeFolder<'tcx> for Resolver<'cx, 'tcx> {
 472     fn tcx<'a>(&'a self) -> &'a ty::ctxt<'tcx> {
 473         self.tcx
 474     }
 475
 476     fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
 477         match self.infcx.fully_resolve(&t) {
 478             Ok(t) => t,
 479             Err(e) => {
 480                 debug!("Resolver::fold_ty: input type `{:?}` not fully resolvable",
 481                        t);
 482                 self.report_error(e);
 483                 self.tcx().types.err
 484             }
 485         }
 486     }
 487
 488     fn fold_region(&mut self, r: ty::Region) -> ty::Region {
 489         match self.infcx.fully_resolve(&r) {
 490             Ok(r) => r,
 491             Err(e) => {
 492                 self.report_error(e);
 493                 ty::ReStatic
 494             }
 495         }
 496     }
 497 }
 498
 499 ///////////////////////////////////////////////////////////////////////////
 500 // During type check, we store promises with the result of trait
 501 // lookup rather than the actual results (because the results are not
 502 // necessarily available immediately). These routines unwind the
 503 // promises. It is expected that we will have already reported any
 504 // errors that may be encountered, so if the promises store an error,
 505 // a dummy result is returned.