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