src/librustc_typeck/check/wfcheck.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 use check::{Inherited, FnCtxt};
  12 use constrained_type_params::{identify_constrained_type_params, Parameter};
  13
  14 use hir::def_id::DefId;
  15 use rustc::traits::{self, ObligationCauseCode};
  16 use rustc::ty::{self, Lift, Ty, TyCtxt, TyKind, GenericParamDefKind, TypeFoldable, ToPredicate};
  17 use rustc::ty::subst::{Subst, Substs};
  18 use rustc::util::nodemap::{FxHashSet, FxHashMap};
  19 use rustc::middle::lang_items;
  20 use rustc::infer::opaque_types::may_define_existential_type;
  21
  22 use syntax::ast;
  23 use syntax::feature_gate::{self, GateIssue};
  24 use syntax_pos::Span;
  25 use errors::{DiagnosticBuilder, DiagnosticId};
  26
  27 use rustc::hir::intravisit::{self, Visitor, NestedVisitorMap};
  28 use rustc::hir;
  29
  30 /// Helper type of a temporary returned by `.for_item(...)`.
  31 /// Necessary because we can't write the following bound:
  32 /// `F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>)`.
  33 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  34     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  35     id: ast::NodeId,
  36     span: Span,
  37     param_env: ty::ParamEnv<'tcx>,
  38 }
  39
  40 impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
  41     fn with_fcx<F>(&'tcx mut self, f: F) where
  42         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
  43                          TyCtxt<'b, 'gcx, 'gcx>) -> Vec<Ty<'tcx>>
  44     {
  45         let id = self.id;
  46         let span = self.span;
  47         let param_env = self.param_env;
  48         self.inherited.enter(|inh| {
  49             let fcx = FnCtxt::new(&inh, param_env, id);
  50             if !inh.tcx.features().trivial_bounds {
  51                 // As predicates are cached rather than obligations, this
  52                 // needsto be called first so that they are checked with an
  53                 // empty param_env.
  54                 check_false_global_bounds(&fcx, span, id);
  55             }
  56             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  57             fcx.select_all_obligations_or_error();
  58             fcx.regionck_item(id, span, &wf_tys);
  59         });
  60     }
  61 }
  62
  63 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  64 /// well-formed, meaning that they do not require any constraints not declared in the struct
  65 /// definition itself. For example, this definition would be illegal:
  66 ///
  67 ///     struct Ref<'a, T> { x: &'a T }
  68 ///
  69 /// because the type did not declare that `T:'a`.
  70 ///
  71 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  72 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  73 /// the types first.
  74 pub fn check_item_well_formed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
  75     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
  76     let item = tcx.hir().expect_item(node_id);
  77
  78     debug!("check_item_well_formed(it.id={}, it.name={})",
  79            item.id,
  80            tcx.item_path_str(def_id));
  81
  82     match item.node {
  83         // Right now we check that every default trait implementation
  84         // has an implementation of itself. Basically, a case like:
  85         //
  86         // `impl Trait for T {}`
  87         //
  88         // has a requirement of `T: Trait` which was required for default
  89         // method implementations. Although this could be improved now that
  90         // there's a better infrastructure in place for this, it's being left
  91         // for a follow-up work.
  92         //
  93         // Since there's such a requirement, we need to check *just* positive
  94         // implementations, otherwise things like:
  95         //
  96         // impl !Send for T {}
  97         //
  98         // won't be allowed unless there's an *explicit* implementation of `Send`
  99         // for `T`
 100         hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
 101             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id(item.id))
 102                                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 103             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 104                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 105             }
 106             if polarity == hir::ImplPolarity::Positive {
 107                 check_impl(tcx, item, self_ty, trait_ref);
 108             } else {
 109                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 110                 if trait_ref.is_some() && !is_auto {
 111                     span_err!(tcx.sess, item.span, E0192,
 112                               "negative impls are only allowed for \
 113                                auto traits (e.g., `Send` and `Sync`)")
 114                 }
 115             }
 116         }
 117         hir::ItemKind::Fn(..) => {
 118             check_item_fn(tcx, item);
 119         }
 120         hir::ItemKind::Static(ref ty, ..) => {
 121             check_item_type(tcx, item.id, ty.span, false);
 122         }
 123         hir::ItemKind::Const(ref ty, ..) => {
 124             check_item_type(tcx, item.id, ty.span, false);
 125         }
 126         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 127             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 128                 check_item_type(tcx, it.id, ty.span, true);
 129             }
 130         },
 131         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 132             check_type_defn(tcx, item, false, |fcx| {
 133                 vec![fcx.non_enum_variant(struct_def)]
 134             });
 135
 136             check_variances_for_type_defn(tcx, item, ast_generics);
 137         }
 138         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 139             check_type_defn(tcx, item, true, |fcx| {
 140                 vec![fcx.non_enum_variant(struct_def)]
 141             });
 142
 143             check_variances_for_type_defn(tcx, item, ast_generics);
 144         }
 145         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 146             check_type_defn(tcx, item, true, |fcx| {
 147                 fcx.enum_variants(enum_def)
 148             });
 149
 150             check_variances_for_type_defn(tcx, item, ast_generics);
 151         }
 152         hir::ItemKind::Trait(..) => {
 153             check_trait(tcx, item);
 154         }
 155         hir::ItemKind::TraitAlias(..) => {
 156             check_trait(tcx, item);
 157         }
 158         _ => {}
 159     }
 160 }
 161
 162 pub fn check_trait_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 163     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 164     let trait_item = tcx.hir().expect_trait_item(node_id);
 165
 166     let method_sig = match trait_item.node {
 167         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 168         _ => None
 169     };
 170     check_associated_item(tcx, trait_item.id, trait_item.span, method_sig);
 171 }
 172
 173 pub fn check_impl_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 174     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 175     let impl_item = tcx.hir().expect_impl_item(node_id);
 176
 177     let method_sig = match impl_item.node {
 178         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 179         _ => None
 180     };
 181     check_associated_item(tcx, impl_item.id, impl_item.span, method_sig);
 182 }
 183
 184 fn check_associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 185                                    item_id: ast::NodeId,
 186                                    span: Span,
 187                                    sig_if_method: Option<&hir::MethodSig>) {
 188     debug!("check_associated_item: {:?}", item_id);
 189
 190     let code = ObligationCauseCode::MiscObligation;
 191     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 192         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
 193
 194         let (mut implied_bounds, self_ty) = match item.container {
 195             ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 196             ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 197                                           fcx.tcx.type_of(def_id))
 198         };
 199
 200         match item.kind {
 201             ty::AssociatedKind::Const => {
 202                 let ty = fcx.tcx.type_of(item.def_id);
 203                 let ty = fcx.normalize_associated_types_in(span, &ty);
 204                 fcx.register_wf_obligation(ty, span, code.clone());
 205             }
 206             ty::AssociatedKind::Method => {
 207                 reject_shadowing_parameters(fcx.tcx, item.def_id);
 208                 let sig = fcx.tcx.fn_sig(item.def_id);
 209                 let sig = fcx.normalize_associated_types_in(span, &sig);
 210                 check_fn_or_method(tcx, fcx, span, sig,
 211                                    item.def_id, &mut implied_bounds);
 212                 let sig_if_method = sig_if_method.expect("bad signature for method");
 213                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 214             }
 215             ty::AssociatedKind::Type => {
 216                 if item.defaultness.has_value() {
 217                     let ty = fcx.tcx.type_of(item.def_id);
 218                     let ty = fcx.normalize_associated_types_in(span, &ty);
 219                     fcx.register_wf_obligation(ty, span, code.clone());
 220                 }
 221             }
 222             ty::AssociatedKind::Existential => {
 223                 // do nothing, existential types check themselves
 224             }
 225         }
 226
 227         implied_bounds
 228     })
 229 }
 230
 231 fn for_item<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, item: &hir::Item)
 232                             -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 233     for_id(tcx, item.id, item.span)
 234 }
 235
 236 fn for_id<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, id: ast::NodeId, span: Span)
 237                           -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 238     let def_id = tcx.hir().local_def_id(id);
 239     CheckWfFcxBuilder {
 240         inherited: Inherited::build(tcx, def_id),
 241         id,
 242         span,
 243         param_env: tcx.param_env(def_id),
 244     }
 245 }
 246
 247 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 248 fn check_type_defn<'a, 'tcx, F>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 249                                 item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 250     where F: for<'fcx, 'gcx, 'tcx2> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx2>) -> Vec<AdtVariant<'tcx2>>
 251 {
 252     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 253         let variants = lookup_fields(fcx);
 254         let def_id = fcx.tcx.hir().local_def_id(item.id);
 255         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 256
 257         for variant in &variants {
 258             // For DST, or when drop needs to copy things around, all
 259             // intermediate types must be sized.
 260             let needs_drop_copy = || {
 261                 packed && {
 262                     let ty = variant.fields.last().unwrap().ty;
 263                     let ty = fcx.tcx.erase_regions(&ty).lift_to_tcx(fcx_tcx)
 264                         .unwrap_or_else(|| {
 265                             span_bug!(item.span, "inference variables in {:?}", ty)
 266                         });
 267                     ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
 268                 }
 269             };
 270             let all_sized =
 271                 all_sized ||
 272                 variant.fields.is_empty() ||
 273                 needs_drop_copy();
 274             let unsized_len = if all_sized {
 275                 0
 276             } else {
 277                 1
 278             };
 279             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 280                 .iter()
 281                 .enumerate()
 282             {
 283                 let last = idx == variant.fields.len() - 1;
 284                 fcx.register_bound(
 285                     field.ty,
 286                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 287                     traits::ObligationCause::new(
 288                         field.span,
 289                         fcx.body_id,
 290                         traits::FieldSized {
 291                             adt_kind: match item.node.adt_kind() {
 292                                 Some(i) => i,
 293                                 None => bug!(),
 294                             },
 295                             last
 296                         }
 297                     )
 298                 );
 299             }
 300
 301             // All field types must be well-formed.
 302             for field in &variant.fields {
 303                 fcx.register_wf_obligation(field.ty, field.span,
 304                     ObligationCauseCode::MiscObligation)
 305             }
 306         }
 307
 308         check_where_clauses(tcx, fcx, item.span, def_id, None);
 309
 310         vec![] // no implied bounds in a struct def'n
 311     });
 312 }
 313
 314 fn check_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 315     debug!("check_trait: {:?}", item.id);
 316
 317     let trait_def_id = tcx.hir().local_def_id(item.id);
 318
 319     let trait_def = tcx.trait_def(trait_def_id);
 320     if trait_def.is_marker {
 321         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 322             struct_span_err!(
 323                 tcx.sess,
 324                 tcx.def_span(*associated_def_id),
 325                 E0714,
 326                 "marker traits cannot have associated items",
 327             ).emit();
 328         }
 329     }
 330
 331     for_item(tcx, item).with_fcx(|fcx, _| {
 332         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 333         vec![]
 334     });
 335 }
 336
 337 fn check_item_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 338     for_item(tcx, item).with_fcx(|fcx, tcx| {
 339         let def_id = fcx.tcx.hir().local_def_id(item.id);
 340         let sig = fcx.tcx.fn_sig(def_id);
 341         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 342         let mut implied_bounds = vec![];
 343         check_fn_or_method(tcx, fcx, item.span, sig,
 344                            def_id, &mut implied_bounds);
 345         implied_bounds
 346     })
 347 }
 348
 349 fn check_item_type<'a, 'tcx>(
 350     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 351     item_id: ast::NodeId,
 352     ty_span: Span,
 353     allow_foreign_ty: bool,
 354 ) {
 355     debug!("check_item_type: {:?}", item_id);
 356
 357     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 358         let ty = gcx.type_of(gcx.hir().local_def_id(item_id));
 359         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 360
 361         let mut forbid_unsized = true;
 362         if allow_foreign_ty {
 363             if let TyKind::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
 364                 forbid_unsized = false;
 365             }
 366         }
 367
 368         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 369         if forbid_unsized {
 370             fcx.register_bound(
 371                 item_ty,
 372                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 373                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 374             );
 375         }
 376
 377         vec![] // no implied bounds in a const etc
 378     });
 379 }
 380
 381 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 382                         item: &hir::Item,
 383                         ast_self_ty: &hir::Ty,
 384                         ast_trait_ref: &Option<hir::TraitRef>)
 385 {
 386     debug!("check_impl: {:?}", item);
 387
 388     for_item(tcx, item).with_fcx(|fcx, tcx| {
 389         let item_def_id = fcx.tcx.hir().local_def_id(item.id);
 390
 391         match *ast_trait_ref {
 392             Some(ref ast_trait_ref) => {
 393                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 394                 let trait_ref =
 395                     fcx.normalize_associated_types_in(
 396                         ast_trait_ref.path.span, &trait_ref);
 397                 let obligations =
 398                     ty::wf::trait_obligations(fcx,
 399                                                 fcx.param_env,
 400                                                 fcx.body_id,
 401                                                 &trait_ref,
 402                                                 ast_trait_ref.path.span);
 403                 for obligation in obligations {
 404                     fcx.register_predicate(obligation);
 405                 }
 406             }
 407             None => {
 408                 let self_ty = fcx.tcx.type_of(item_def_id);
 409                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 410                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 411                     ObligationCauseCode::MiscObligation);
 412             }
 413         }
 414
 415         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 416
 417         fcx.impl_implied_bounds(item_def_id, item.span)
 418     });
 419 }
 420
 421 /// Checks where clauses and inline bounds that are declared on def_id.
 422 fn check_where_clauses<'a, 'gcx, 'fcx, 'tcx>(
 423     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 424     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 425     span: Span,
 426     def_id: DefId,
 427     return_ty: Option<Ty<'tcx>>,
 428 ) {
 429     use ty::subst::Subst;
 430     use rustc::ty::TypeFoldable;
 431
 432     let predicates = fcx.tcx.predicates_of(def_id);
 433
 434     let generics = tcx.generics_of(def_id);
 435     let is_our_default = |def: &ty::GenericParamDef| {
 436         match def.kind {
 437             GenericParamDefKind::Type { has_default, .. } => {
 438                 has_default && def.index >= generics.parent_count as u32
 439             }
 440             _ => unreachable!()
 441         }
 442     };
 443
 444     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 445     // For example this forbids the declaration:
 446     // struct Foo<T = Vec<[u32]>> { .. }
 447     // Here the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 448     for param in &generics.params {
 449         if let GenericParamDefKind::Type {..} = param.kind {
 450             if is_our_default(&param) {
 451                 let ty = fcx.tcx.type_of(param.def_id);
 452                 // ignore dependent defaults -- that is, where the default of one type
 453                 // parameter includes another (e.g., <T, U = T>). In those cases, we can't
 454                 // be sure if it will error or not as user might always specify the other.
 455                 if !ty.needs_subst() {
 456                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 457                         ObligationCauseCode::MiscObligation);
 458                 }
 459             }
 460         }
 461     }
 462
 463     // Check that trait predicates are WF when params are substituted by their defaults.
 464     // We don't want to overly constrain the predicates that may be written but we want to
 465     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 466     // Therefore we check if a predicate which contains a single type param
 467     // with a concrete default is WF with that default substituted.
 468     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 469     //
 470     // First we build the defaulted substitution.
 471     let substs = Substs::for_item(fcx.tcx, def_id, |param, _| {
 472         match param.kind {
 473             GenericParamDefKind::Lifetime => {
 474                 // All regions are identity.
 475                 fcx.tcx.mk_param_from_def(param)
 476             }
 477             GenericParamDefKind::Type {..} => {
 478                 // If the param has a default,
 479                 if is_our_default(param) {
 480                     let default_ty = fcx.tcx.type_of(param.def_id);
 481                     // and it's not a dependent default
 482                     if !default_ty.needs_subst() {
 483                         // then substitute with the default.
 484                         return default_ty.into();
 485                     }
 486                 }
 487                 // Mark unwanted params as err.
 488                 fcx.tcx.types.err.into()
 489             }
 490         }
 491     });
 492     // Now we build the substituted predicates.
 493     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 494         #[derive(Default)]
 495         struct CountParams { params: FxHashSet<u32> }
 496         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 497             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 498                 match t.sty {
 499                     ty::Param(p) => {
 500                         self.params.insert(p.idx);
 501                         t.super_visit_with(self)
 502                     }
 503                     _ => t.super_visit_with(self)
 504                 }
 505             }
 506
 507             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 508                 true
 509             }
 510         }
 511         let mut param_count = CountParams::default();
 512         let has_region = pred.visit_with(&mut param_count);
 513         let substituted_pred = pred.subst(fcx.tcx, substs);
 514         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 515         // or preds with multiple params.
 516         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 517             None
 518         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 519             // Avoid duplication of predicates that contain no parameters, for example.
 520             None
 521         } else {
 522             Some(substituted_pred)
 523         }
 524     }).map(|pred| {
 525         // convert each of those into an obligation. So if you have
 526         // something like `struct Foo<T: Copy = String>`, we would
 527         // take that predicate `T: Copy`, substitute to `String: Copy`
 528         // (actually that happens in the previous `flat_map` call),
 529         // and then try to prove it (in this case, we'll fail).
 530         //
 531         // Note the subtle difference from how we handle `predicates`
 532         // below: there, we are not trying to prove those predicates
 533         // to be *true* but merely *well-formed*.
 534         let pred = fcx.normalize_associated_types_in(span, &pred);
 535         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 536         traits::Obligation::new(cause, fcx.param_env, pred)
 537     });
 538
 539     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 540
 541     if let Some(return_ty) = return_ty {
 542         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 543     }
 544
 545     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 546
 547     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 548     let wf_obligations =
 549         predicates.predicates
 550                     .iter()
 551                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 552                                                                 fcx.param_env,
 553                                                                 fcx.body_id,
 554                                                                 p,
 555                                                                 span));
 556
 557     for obligation in wf_obligations.chain(default_obligations) {
 558         debug!("next obligation cause: {:?}", obligation.cause);
 559         fcx.register_predicate(obligation);
 560     }
 561 }
 562
 563 fn check_fn_or_method<'a, 'fcx, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
 564                                             fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 565                                             span: Span,
 566                                             sig: ty::PolyFnSig<'tcx>,
 567                                             def_id: DefId,
 568                                             implied_bounds: &mut Vec<Ty<'tcx>>)
 569 {
 570     let sig = fcx.normalize_associated_types_in(span, &sig);
 571     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 572
 573     for input_ty in sig.inputs() {
 574         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 575     }
 576     implied_bounds.extend(sig.inputs());
 577
 578     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 579
 580     // FIXME(#25759) return types should not be implied bounds
 581     implied_bounds.push(sig.output());
 582
 583     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 584 }
 585
 586 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 587 /// "higher-order pattern unification".
 588 /// This ensures that inference is tractable.
 589 /// In particular, definitions of existential types can only use other generics as arguments,
 590 /// and they cannot repeat an argument. Example:
 591 ///
 592 /// ```rust
 593 /// existential type Foo<A, B>;
 594 ///
 595 /// // ok -- `Foo` is applied to two distinct, generic types.
 596 /// fn a<T, U>() -> Foo<T, U> { .. }
 597 ///
 598 /// // not ok -- `Foo` is applied to `T` twice.
 599 /// fn b<T>() -> Foo<T, T> { .. }
 600 ///
 601 ///
 602 /// // not ok -- `Foo` is applied to a non-generic type.
 603 /// fn b<T>() -> Foo<T, u32> { .. }
 604 /// ```
 605 ///
 606 fn check_existential_types<'a, 'fcx, 'gcx, 'tcx>(
 607     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 608     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 609     fn_def_id: DefId,
 610     span: Span,
 611     ty: Ty<'tcx>,
 612 ) -> Vec<ty::Predicate<'tcx>> {
 613     trace!("check_existential_types: {:?}, {:?}", ty, ty.sty);
 614     let mut substituted_predicates = Vec::new();
 615     ty.fold_with(&mut ty::fold::BottomUpFolder {
 616         tcx: fcx.tcx,
 617         fldop: |ty| {
 618             if let ty::Opaque(def_id, substs) = ty.sty {
 619                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 620                 let generics = tcx.generics_of(def_id);
 621                 // only check named existential types
 622                 if generics.parent.is_none() {
 623                     let opaque_node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 624                     if may_define_existential_type(tcx, fn_def_id, opaque_node_id) {
 625                         trace!("check_existential_types may define. Generics: {:#?}", generics);
 626                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 627                         for (subst, param) in substs.iter().zip(&generics.params) {
 628                             match subst.unpack() {
 629                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 630                                     ty::Param(..) => {},
 631                                     // prevent `fn foo() -> Foo<u32>` from being defining
 632                                     _ => {
 633                                         tcx
 634                                             .sess
 635                                             .struct_span_err(
 636                                                 span,
 637                                                 "non-defining existential type use \
 638                                                  in defining scope",
 639                                             )
 640                                             .span_note(
 641                                                 tcx.def_span(param.def_id),
 642                                                 &format!(
 643                                                     "used non-generic type {} for \
 644                                                      generic parameter",
 645                                                     ty,
 646                                                 ),
 647                                             )
 648                                             .emit();
 649                                     },
 650                                 }, // match ty
 651                                 ty::subst::UnpackedKind::Lifetime(region) => {
 652                                     let param_span = tcx.def_span(param.def_id);
 653                                     if let ty::ReStatic = region {
 654                                         tcx
 655                                             .sess
 656                                             .struct_span_err(
 657                                                 span,
 658                                                 "non-defining existential type use \
 659                                                     in defining scope",
 660                                             )
 661                                             .span_label(
 662                                                 param_span,
 663                                                 "cannot use static lifetime, use a bound lifetime \
 664                                                 instead or remove the lifetime parameter from the \
 665                                                 existential type",
 666                                             )
 667                                             .emit();
 668                                     } else {
 669                                         seen.entry(region).or_default().push(param_span);
 670                                     }
 671                                 },
 672                             } // match subst
 673                         } // for (subst, param)
 674                         for (_, spans) in seen {
 675                             if spans.len() > 1 {
 676                                 tcx
 677                                     .sess
 678                                     .struct_span_err(
 679                                         span,
 680                                         "non-defining existential type use \
 681                                             in defining scope",
 682                                     ).
 683                                     span_note(
 684                                         spans,
 685                                         "lifetime used multiple times",
 686                                     )
 687                                     .emit();
 688                             }
 689                         }
 690                     } // if may_define_existential_type
 691
 692                     // now register the bounds on the parameters of the existential type
 693                     // so the parameters given by the function need to fulfill them
 694                     // ```rust
 695                     // existential type Foo<T: Bar>: 'static;
 696                     // fn foo<U>() -> Foo<U> { .. *}
 697                     // ```
 698                     // becomes
 699                     // ```rust
 700                     // existential type Foo<T: Bar>: 'static;
 701                     // fn foo<U: Bar>() -> Foo<U> { .. *}
 702                     // ```
 703                     let predicates = tcx.predicates_of(def_id);
 704                     trace!(
 705                         "check_existential_types may define. adding predicates: {:#?}",
 706                         predicates,
 707                     );
 708                     for &(pred, _) in predicates.predicates.iter() {
 709                         let substituted_pred = pred.subst(fcx.tcx, substs);
 710                         // Avoid duplication of predicates that contain no parameters, for example.
 711                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 712                             substituted_predicates.push(substituted_pred);
 713                         }
 714                     }
 715                 } // if is_named_existential_type
 716             } // if let Opaque
 717             ty
 718         },
 719         reg_op: |reg| reg,
 720     });
 721     substituted_predicates
 722 }
 723
 724 fn check_method_receiver<'fcx, 'gcx, 'tcx>(fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 725                                            method_sig: &hir::MethodSig,
 726                                            method: &ty::AssociatedItem,
 727                                            self_ty: Ty<'tcx>)
 728 {
 729     // check that the method has a valid receiver type, given the type `Self`
 730     debug!("check_method_receiver({:?}, self_ty={:?})",
 731            method, self_ty);
 732
 733     if !method.method_has_self_argument {
 734         return;
 735     }
 736
 737     let span = method_sig.decl.inputs[0].span;
 738
 739     let sig = fcx.tcx.fn_sig(method.def_id);
 740     let sig = fcx.normalize_associated_types_in(span, &sig);
 741     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 742
 743     debug!("check_method_receiver: sig={:?}", sig);
 744
 745     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 746     let self_ty = fcx.tcx.liberate_late_bound_regions(
 747         method.def_id,
 748         &ty::Binder::bind(self_ty)
 749     );
 750
 751     let receiver_ty = sig.inputs()[0];
 752
 753     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 754     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 755         method.def_id,
 756         &ty::Binder::bind(receiver_ty)
 757     );
 758
 759     if fcx.tcx.features().arbitrary_self_types {
 760         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 761             // report error, arbitrary_self_types was enabled
 762             fcx.tcx.sess.diagnostic().mut_span_err(
 763                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 764             ).note("type of `self` must be `Self` or a type that dereferences to it")
 765             .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 766             .code(DiagnosticId::Error("E0307".into()))
 767             .emit();
 768         }
 769     } else {
 770         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 771             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 772                 // report error, would have worked with arbitrary_self_types
 773                 feature_gate::feature_err(
 774                     &fcx.tcx.sess.parse_sess,
 775                     "arbitrary_self_types",
 776                     span,
 777                     GateIssue::Language,
 778                     &format!(
 779                         "`{}` cannot be used as the type of `self` without \
 780                             the `arbitrary_self_types` feature",
 781                         receiver_ty,
 782                     ),
 783                 ).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 784                 .emit();
 785             } else {
 786                 // report error, would not have worked with arbitrary_self_types
 787                 fcx.tcx.sess.diagnostic().mut_span_err(
 788                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 789                 ).note("type must be `Self` or a type that dereferences to it")
 790                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 791                 .code(DiagnosticId::Error("E0307".into()))
 792                 .emit();
 793             }
 794         }
 795     }
 796 }
 797
 798 /// returns true if `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 799 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 800 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 801 /// strict: `receiver_ty` must implement `Receiver` and directly implement `Deref<Target=self_ty>`.
 802 ///
 803 /// NB: there are cases this function returns `true` but causes an error to be emitted,
 804 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 805 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 806 fn receiver_is_valid<'fcx, 'tcx, 'gcx>(
 807     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 808     span: Span,
 809     receiver_ty: Ty<'tcx>,
 810     self_ty: Ty<'tcx>,
 811     arbitrary_self_types_enabled: bool,
 812 ) -> bool {
 813     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 814
 815     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 816
 817     // `self: Self` is always valid
 818     if can_eq_self(receiver_ty) {
 819         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 820             err.emit();
 821         }
 822         return true
 823     }
 824
 825     let mut autoderef = fcx.autoderef(span, receiver_ty);
 826
 827     // the `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`
 828     if arbitrary_self_types_enabled {
 829         autoderef = autoderef.include_raw_pointers();
 830     }
 831
 832     // the first type is `receiver_ty`, which we know its not equal to `self_ty`. skip it.
 833     autoderef.next();
 834
 835     // keep dereferencing `receiver_ty` until we get to `self_ty`
 836     loop {
 837         if let Some((potential_self_ty, _)) = autoderef.next() {
 838             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 839                 potential_self_ty, self_ty);
 840
 841             if can_eq_self(potential_self_ty) {
 842                 autoderef.finalize(fcx);
 843
 844                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 845                     &cause, self_ty, potential_self_ty
 846                 ) {
 847                     err.emit();
 848                 }
 849
 850                 break
 851             }
 852         } else {
 853             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 854                 receiver_ty, self_ty);
 855             return false
 856         }
 857
 858         // without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 859         // `self_ty`. Enforce this by only doing one iteration of the loop
 860         if !arbitrary_self_types_enabled {
 861             return false
 862         }
 863     }
 864
 865     // without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`
 866     if !arbitrary_self_types_enabled {
 867         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 868             Some(did) => did,
 869             None => {
 870                 debug!("receiver_is_valid: missing Receiver trait");
 871                 return false
 872             }
 873         };
 874
 875         let trait_ref = ty::TraitRef{
 876             def_id: trait_def_id,
 877             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 878         };
 879
 880         let obligation = traits::Obligation::new(
 881             cause.clone(),
 882             fcx.param_env,
 883             trait_ref.to_predicate()
 884         );
 885
 886         if !fcx.predicate_must_hold(&obligation) {
 887             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 888                 receiver_ty);
 889             return false
 890         }
 891     }
 892
 893     true
 894 }
 895
 896 fn check_variances_for_type_defn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 897                                            item: &hir::Item,
 898                                            hir_generics: &hir::Generics)
 899 {
 900     let item_def_id = tcx.hir().local_def_id(item.id);
 901     let ty = tcx.type_of(item_def_id);
 902     if tcx.has_error_field(ty) {
 903         return;
 904     }
 905
 906     let ty_predicates = tcx.predicates_of(item_def_id);
 907     assert_eq!(ty_predicates.parent, None);
 908     let variances = tcx.variances_of(item_def_id);
 909
 910     let mut constrained_parameters: FxHashSet<_> =
 911         variances.iter().enumerate()
 912                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 913                         .map(|(index, _)| Parameter(index as u32))
 914                         .collect();
 915
 916     identify_constrained_type_params(tcx,
 917                                      &ty_predicates,
 918                                      None,
 919                                      &mut constrained_parameters);
 920
 921     for (index, _) in variances.iter().enumerate() {
 922         if constrained_parameters.contains(&Parameter(index as u32)) {
 923             continue;
 924         }
 925
 926         let param = &hir_generics.params[index];
 927         match param.name {
 928             hir::ParamName::Error => { }
 929             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 930         }
 931     }
 932 }
 933
 934 fn report_bivariance<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 935                                span: Span,
 936                                param_name: ast::Name)
 937 {
 938     let mut err = error_392(tcx, span, param_name);
 939
 940     let suggested_marker_id = tcx.lang_items().phantom_data();
 941     // help is available only in presence of lang items
 942     if let Some(def_id) = suggested_marker_id {
 943         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 944                           param_name,
 945                           tcx.item_path_str(def_id)));
 946     }
 947     err.emit();
 948 }
 949
 950 fn reject_shadowing_parameters(tcx: TyCtxt, def_id: DefId) {
 951     let generics = tcx.generics_of(def_id);
 952     let parent = tcx.generics_of(generics.parent.unwrap());
 953     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
 954         GenericParamDefKind::Lifetime => None,
 955         GenericParamDefKind::Type {..} => Some((param.name, param.def_id)),
 956     }).collect();
 957
 958     for method_param in &generics.params {
 959         // Shadowing is checked in resolve_lifetime.
 960         if let GenericParamDefKind::Lifetime = method_param.kind {
 961             continue
 962         }
 963         if impl_params.contains_key(&method_param.name) {
 964             // Tighten up the span to focus on only the shadowing type
 965             let type_span = tcx.def_span(method_param.def_id);
 966
 967             // The expectation here is that the original trait declaration is
 968             // local so it should be okay to just unwrap everything.
 969             let trait_def_id = impl_params[&method_param.name];
 970             let trait_decl_span = tcx.def_span(trait_def_id);
 971             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
 972         }
 973     }
 974 }
 975
 976 /// Feature gates RFC 2056 - trivial bounds, checking for global bounds that
 977 /// aren't true.
 978 fn check_false_global_bounds<'a, 'gcx, 'tcx>(
 979     fcx: &FnCtxt<'a, 'gcx, 'tcx>,
 980     span: Span,
 981     id: ast::NodeId)
 982 {
 983     use rustc::ty::TypeFoldable;
 984
 985     let empty_env = ty::ParamEnv::empty();
 986
 987     let def_id = fcx.tcx.hir().local_def_id(id);
 988     let predicates = fcx.tcx.predicates_of(def_id).predicates
 989         .iter()
 990         .map(|(p, _)| *p)
 991         .collect();
 992     // Check elaborated bounds
 993     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
 994
 995     for pred in implied_obligations {
 996         // Match the existing behavior.
 997         if pred.is_global() && !pred.has_late_bound_regions() {
 998             let pred = fcx.normalize_associated_types_in(span, &pred);
 999             let obligation = traits::Obligation::new(
1000                 traits::ObligationCause::new(
1001                     span,
1002                     id,
1003                     traits::TrivialBound,
1004                 ),
1005                 empty_env,
1006                 pred,
1007             );
1008             fcx.register_predicate(obligation);
1009         }
1010     }
1011
1012     fcx.select_all_obligations_or_error();
1013 }
1014
1015 pub struct CheckTypeWellFormedVisitor<'a, 'tcx: 'a> {
1016     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1017 }
1018
1019 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
1020     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
1021                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
1022         CheckTypeWellFormedVisitor {
1023             tcx,
1024         }
1025     }
1026 }
1027
1028 impl<'a, 'tcx, 'v> Visitor<'v> for CheckTypeWellFormedVisitor<'a, 'tcx> {
1029     fn nested_visit_map<'this>(&'this mut self) -> NestedVisitorMap<'this, 'v> {
1030         NestedVisitorMap::None
1031     }
1032
1033     fn visit_item(&mut self, i: &hir::Item) {
1034         debug!("visit_item: {:?}", i);
1035         let def_id = self.tcx.hir().local_def_id(i.id);
1036         ty::query::queries::check_item_well_formed::ensure(self.tcx, def_id);
1037         intravisit::walk_item(self, i);
1038     }
1039
1040     fn visit_trait_item(&mut self, trait_item: &'v hir::TraitItem) {
1041         debug!("visit_trait_item: {:?}", trait_item);
1042         let def_id = self.tcx.hir().local_def_id(trait_item.id);
1043         ty::query::queries::check_trait_item_well_formed::ensure(self.tcx, def_id);
1044         intravisit::walk_trait_item(self, trait_item)
1045     }
1046
1047     fn visit_impl_item(&mut self, impl_item: &'v hir::ImplItem) {
1048         debug!("visit_impl_item: {:?}", impl_item);
1049         let def_id = self.tcx.hir().local_def_id(impl_item.id);
1050         ty::query::queries::check_impl_item_well_formed::ensure(self.tcx, def_id);
1051         intravisit::walk_impl_item(self, impl_item)
1052     }
1053 }
1054
1055 ///////////////////////////////////////////////////////////////////////////
1056 // ADT
1057
1058 struct AdtVariant<'tcx> {
1059     fields: Vec<AdtField<'tcx>>,
1060 }
1061
1062 struct AdtField<'tcx> {
1063     ty: Ty<'tcx>,
1064     span: Span,
1065 }
1066
1067 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
1068     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1069         let fields = struct_def.fields().iter().map(|field| {
1070             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.id));
1071             let field_ty = self.normalize_associated_types_in(field.span,
1072                                                               &field_ty);
1073             AdtField { ty: field_ty, span: field.span }
1074         })
1075         .collect();
1076         AdtVariant { fields }
1077     }
1078
1079     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1080         enum_def.variants.iter()
1081             .map(|variant| self.non_enum_variant(&variant.node.data))
1082             .collect()
1083     }
1084
1085     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1086         match self.tcx.impl_trait_ref(impl_def_id) {
1087             Some(ref trait_ref) => {
1088                 // Trait impl: take implied bounds from all types that
1089                 // appear in the trait reference.
1090                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1091                 trait_ref.substs.types().collect()
1092             }
1093
1094             None => {
1095                 // Inherent impl: take implied bounds from the `self` type.
1096                 let self_ty = self.tcx.type_of(impl_def_id);
1097                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1098                 vec![self_ty]
1099             }
1100         }
1101     }
1102 }
1103
1104 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
1105                        -> DiagnosticBuilder<'tcx> {
1106     let mut err = struct_span_err!(tcx.sess, span, E0392,
1107                   "parameter `{}` is never used", param_name);
1108     err.span_label(span, "unused type parameter");
1109     err
1110 }
1111
1112 fn error_194(tcx: TyCtxt, span: Span, trait_decl_span: Span, name: &str) {
1113     struct_span_err!(tcx.sess, span, E0194,
1114                      "type parameter `{}` shadows another type parameter of the same name",
1115                      name)
1116         .span_label(span, "shadows another type parameter")
1117         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1118         .emit();
1119 }