src/librustc_typeck/check/wfcheck.rs

   1 use crate::check::{Inherited, FnCtxt};
   2 use crate::constrained_type_params::{identify_constrained_type_params, Parameter};
   3
   4 use crate::hir::def_id::DefId;
   5 use rustc::traits::{self, ObligationCauseCode};
   6 use rustc::ty::{self, Lift, Ty, TyCtxt, TyKind, GenericParamDefKind, TypeFoldable, ToPredicate};
   7 use rustc::ty::subst::{Subst, InternalSubsts};
   8 use rustc::util::nodemap::{FxHashSet, FxHashMap};
   9 use rustc::mir::interpret::ConstValue;
  10 use rustc::middle::lang_items;
  11 use rustc::infer::opaque_types::may_define_existential_type;
  12
  13 use syntax::ast;
  14 use syntax::feature_gate::{self, GateIssue};
  15 use syntax_pos::Span;
  16 use errors::{DiagnosticBuilder, DiagnosticId};
  17
  18 use rustc::hir::itemlikevisit::ItemLikeVisitor;
  19 use rustc::hir;
  20
  21 /// Helper type of a temporary returned by `.for_item(...)`.
  22 /// Necessary because we can't write the following bound:
  23 /// `F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>)`.
  24 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  25     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  26     id: hir::HirId,
  27     span: Span,
  28     param_env: ty::ParamEnv<'tcx>,
  29 }
  30
  31 impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
  32     fn with_fcx<F>(&'tcx mut self, f: F) where
  33         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
  34                          TyCtxt<'b, 'gcx, 'gcx>) -> Vec<Ty<'tcx>>
  35     {
  36         let id = self.id;
  37         let span = self.span;
  38         let param_env = self.param_env;
  39         self.inherited.enter(|inh| {
  40             let fcx = FnCtxt::new(&inh, param_env, id);
  41             if !inh.tcx.features().trivial_bounds {
  42                 // As predicates are cached rather than obligations, this
  43                 // needsto be called first so that they are checked with an
  44                 // empty param_env.
  45                 check_false_global_bounds(&fcx, span, id);
  46             }
  47             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  48             fcx.select_all_obligations_or_error();
  49             fcx.regionck_item(id, span, &wf_tys);
  50         });
  51     }
  52 }
  53
  54 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  55 /// well-formed, meaning that they do not require any constraints not declared in the struct
  56 /// definition itself. For example, this definition would be illegal:
  57 ///
  58 ///     struct Ref<'a, T> { x: &'a T }
  59 ///
  60 /// because the type did not declare that `T:'a`.
  61 ///
  62 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  63 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  64 /// the types first.
  65 pub fn check_item_well_formed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
  66     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  67     let item = tcx.hir().expect_item_by_hir_id(hir_id);
  68
  69     debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
  70            item.hir_id,
  71            tcx.item_path_str(def_id));
  72
  73     match item.node {
  74         // Right now we check that every default trait implementation
  75         // has an implementation of itself. Basically, a case like:
  76         //
  77         // `impl Trait for T {}`
  78         //
  79         // has a requirement of `T: Trait` which was required for default
  80         // method implementations. Although this could be improved now that
  81         // there's a better infrastructure in place for this, it's being left
  82         // for a follow-up work.
  83         //
  84         // Since there's such a requirement, we need to check *just* positive
  85         // implementations, otherwise things like:
  86         //
  87         // impl !Send for T {}
  88         //
  89         // won't be allowed unless there's an *explicit* implementation of `Send`
  90         // for `T`
  91         hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
  92             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id_from_hir_id(item.hir_id))
  93                                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
  94             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
  95                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
  96             }
  97             if polarity == hir::ImplPolarity::Positive {
  98                 check_impl(tcx, item, self_ty, trait_ref);
  99             } else {
 100                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 101                 if trait_ref.is_some() && !is_auto {
 102                     span_err!(tcx.sess, item.span, E0192,
 103                               "negative impls are only allowed for \
 104                                auto traits (e.g., `Send` and `Sync`)")
 105                 }
 106             }
 107         }
 108         hir::ItemKind::Fn(..) => {
 109             check_item_fn(tcx, item);
 110         }
 111         hir::ItemKind::Static(ref ty, ..) => {
 112             check_item_type(tcx, item.hir_id, ty.span, false);
 113         }
 114         hir::ItemKind::Const(ref ty, ..) => {
 115             check_item_type(tcx, item.hir_id, ty.span, false);
 116         }
 117         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 118             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 119                 check_item_type(tcx, it.hir_id, ty.span, true);
 120             }
 121         },
 122         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 123             check_type_defn(tcx, item, false, |fcx| {
 124                 vec![fcx.non_enum_variant(struct_def)]
 125             });
 126
 127             check_variances_for_type_defn(tcx, item, ast_generics);
 128         }
 129         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 130             check_type_defn(tcx, item, true, |fcx| {
 131                 vec![fcx.non_enum_variant(struct_def)]
 132             });
 133
 134             check_variances_for_type_defn(tcx, item, ast_generics);
 135         }
 136         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 137             check_type_defn(tcx, item, true, |fcx| {
 138                 fcx.enum_variants(enum_def)
 139             });
 140
 141             check_variances_for_type_defn(tcx, item, ast_generics);
 142         }
 143         hir::ItemKind::Trait(..) => {
 144             check_trait(tcx, item);
 145         }
 146         hir::ItemKind::TraitAlias(..) => {
 147             check_trait(tcx, item);
 148         }
 149         _ => {}
 150     }
 151 }
 152
 153 pub fn check_trait_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 154     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 155     let trait_item = tcx.hir().expect_trait_item(node_id);
 156
 157     let method_sig = match trait_item.node {
 158         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 159         _ => None
 160     };
 161     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 162 }
 163
 164 pub fn check_impl_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 165     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 166     let impl_item = tcx.hir().expect_impl_item(node_id);
 167
 168     let method_sig = match impl_item.node {
 169         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 170         _ => None
 171     };
 172     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 173 }
 174
 175 fn check_associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 176                                    item_id: hir::HirId,
 177                                    span: Span,
 178                                    sig_if_method: Option<&hir::MethodSig>) {
 179     debug!("check_associated_item: {:?}", item_id);
 180
 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_from_hir_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.hir_id, item.span)
 225 }
 226
 227 fn for_id<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, id: hir::HirId, span: Span)
 228                           -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 229     let def_id = tcx.hir().local_def_id_from_hir_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_from_hir_id(item.hir_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 all_sized =
 262                 all_sized ||
 263                 variant.fields.is_empty() ||
 264                 needs_drop_copy();
 265             let unsized_len = if all_sized {
 266                 0
 267             } else {
 268                 1
 269             };
 270             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 271                 .iter()
 272                 .enumerate()
 273             {
 274                 let last = idx == variant.fields.len() - 1;
 275                 fcx.register_bound(
 276                     field.ty,
 277                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 278                     traits::ObligationCause::new(
 279                         field.span,
 280                         fcx.body_id,
 281                         traits::FieldSized {
 282                             adt_kind: match item.node.adt_kind() {
 283                                 Some(i) => i,
 284                                 None => bug!(),
 285                             },
 286                             last
 287                         }
 288                     )
 289                 );
 290             }
 291
 292             // All field types must be well-formed.
 293             for field in &variant.fields {
 294                 fcx.register_wf_obligation(field.ty, field.span,
 295                     ObligationCauseCode::MiscObligation)
 296             }
 297         }
 298
 299         check_where_clauses(tcx, fcx, item.span, def_id, None);
 300
 301         vec![] // no implied bounds in a struct def'n
 302     });
 303 }
 304
 305 fn check_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 306     debug!("check_trait: {:?}", item.hir_id);
 307
 308     let trait_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
 309
 310     let trait_def = tcx.trait_def(trait_def_id);
 311     if trait_def.is_marker {
 312         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 313             struct_span_err!(
 314                 tcx.sess,
 315                 tcx.def_span(*associated_def_id),
 316                 E0714,
 317                 "marker traits cannot have associated items",
 318             ).emit();
 319         }
 320     }
 321
 322     for_item(tcx, item).with_fcx(|fcx, _| {
 323         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 324         vec![]
 325     });
 326 }
 327
 328 fn check_item_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 329     for_item(tcx, item).with_fcx(|fcx, tcx| {
 330         let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 331         let sig = fcx.tcx.fn_sig(def_id);
 332         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 333         let mut implied_bounds = vec![];
 334         check_fn_or_method(tcx, fcx, item.span, sig,
 335                            def_id, &mut implied_bounds);
 336         implied_bounds
 337     })
 338 }
 339
 340 fn check_item_type<'a, 'tcx>(
 341     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 342     item_id: hir::HirId,
 343     ty_span: Span,
 344     allow_foreign_ty: bool,
 345 ) {
 346     debug!("check_item_type: {:?}", item_id);
 347
 348     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 349         let ty = gcx.type_of(gcx.hir().local_def_id_from_hir_id(item_id));
 350         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 351
 352         let mut forbid_unsized = true;
 353         if allow_foreign_ty {
 354             if let TyKind::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
 355                 forbid_unsized = false;
 356             }
 357         }
 358
 359         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 360         if forbid_unsized {
 361             fcx.register_bound(
 362                 item_ty,
 363                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 364                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 365             );
 366         }
 367
 368         vec![] // no implied bounds in a const etc
 369     });
 370 }
 371
 372 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 373                         item: &hir::Item,
 374                         ast_self_ty: &hir::Ty,
 375                         ast_trait_ref: &Option<hir::TraitRef>)
 376 {
 377     debug!("check_impl: {:?}", item);
 378
 379     for_item(tcx, item).with_fcx(|fcx, tcx| {
 380         let item_def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 381
 382         match *ast_trait_ref {
 383             Some(ref ast_trait_ref) => {
 384                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 385                 let trait_ref =
 386                     fcx.normalize_associated_types_in(
 387                         ast_trait_ref.path.span, &trait_ref);
 388                 let obligations =
 389                     ty::wf::trait_obligations(fcx,
 390                                                 fcx.param_env,
 391                                                 fcx.body_id,
 392                                                 &trait_ref,
 393                                                 ast_trait_ref.path.span);
 394                 for obligation in obligations {
 395                     fcx.register_predicate(obligation);
 396                 }
 397             }
 398             None => {
 399                 let self_ty = fcx.tcx.type_of(item_def_id);
 400                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 401                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 402                     ObligationCauseCode::MiscObligation);
 403             }
 404         }
 405
 406         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 407
 408         fcx.impl_implied_bounds(item_def_id, item.span)
 409     });
 410 }
 411
 412 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 413 fn check_where_clauses<'a, 'gcx, 'fcx, 'tcx>(
 414     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 415     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 416     span: Span,
 417     def_id: DefId,
 418     return_ty: Option<Ty<'tcx>>,
 419 ) {
 420     use ty::subst::Subst;
 421     use rustc::ty::TypeFoldable;
 422
 423     let predicates = fcx.tcx.predicates_of(def_id);
 424
 425     let generics = tcx.generics_of(def_id);
 426     let is_our_default = |def: &ty::GenericParamDef| {
 427         match def.kind {
 428             GenericParamDefKind::Type { has_default, .. } => {
 429                 has_default && def.index >= generics.parent_count as u32
 430             }
 431             _ => unreachable!()
 432         }
 433     };
 434
 435     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 436     // For example this forbids the declaration:
 437     // struct Foo<T = Vec<[u32]>> { .. }
 438     // Here the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 439     for param in &generics.params {
 440         if let GenericParamDefKind::Type { .. } = param.kind {
 441             if is_our_default(&param) {
 442                 let ty = fcx.tcx.type_of(param.def_id);
 443                 // ignore dependent defaults -- that is, where the default of one type
 444                 // parameter includes another (e.g., <T, U = T>). In those cases, we can't
 445                 // be sure if it will error or not as user might always specify the other.
 446                 if !ty.needs_subst() {
 447                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 448                         ObligationCauseCode::MiscObligation);
 449                 }
 450             }
 451         }
 452     }
 453
 454     // Check that trait predicates are WF when params are substituted by their defaults.
 455     // We don't want to overly constrain the predicates that may be written but we want to
 456     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 457     // Therefore we check if a predicate which contains a single type param
 458     // with a concrete default is WF with that default substituted.
 459     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 460     //
 461     // First we build the defaulted substitution.
 462     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 463         match param.kind {
 464             GenericParamDefKind::Lifetime => {
 465                 // All regions are identity.
 466                 fcx.tcx.mk_param_from_def(param)
 467             }
 468             GenericParamDefKind::Type { .. } => {
 469                 // If the param has a default,
 470                 if is_our_default(param) {
 471                     let default_ty = fcx.tcx.type_of(param.def_id);
 472                     // and it's not a dependent default
 473                     if !default_ty.needs_subst() {
 474                         // then substitute with the default.
 475                         return default_ty.into();
 476                     }
 477                 }
 478                 // Mark unwanted params as err.
 479                 fcx.tcx.types.err.into()
 480             }
 481             GenericParamDefKind::Const => {
 482                 // FIXME(const_generics:defaults)
 483                 fcx.tcx.types.err.into()
 484             }
 485         }
 486     });
 487     // Now we build the substituted predicates.
 488     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 489         #[derive(Default)]
 490         struct CountParams { params: FxHashSet<u32> }
 491         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 492             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 493                 match t.sty {
 494                     ty::Param(p) => {
 495                         self.params.insert(p.idx);
 496                         t.super_visit_with(self)
 497                     }
 498                     _ => t.super_visit_with(self)
 499                 }
 500             }
 501
 502             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 503                 true
 504             }
 505
 506             fn visit_const(&mut self, c: &'tcx ty::LazyConst<'tcx>) -> bool {
 507                 if let ty::LazyConst::Evaluated(ty::Const {
 508                     val: ConstValue::Param(param),
 509                     ..
 510                 }) = c {
 511                     self.params.insert(param.index);
 512                 }
 513                 c.super_visit_with(self)
 514             }
 515         }
 516         let mut param_count = CountParams::default();
 517         let has_region = pred.visit_with(&mut param_count);
 518         let substituted_pred = pred.subst(fcx.tcx, substs);
 519         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 520         // or preds with multiple params.
 521         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 522             None
 523         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 524             // Avoid duplication of predicates that contain no parameters, for example.
 525             None
 526         } else {
 527             Some(substituted_pred)
 528         }
 529     }).map(|pred| {
 530         // convert each of those into an obligation. So if you have
 531         // something like `struct Foo<T: Copy = String>`, we would
 532         // take that predicate `T: Copy`, substitute to `String: Copy`
 533         // (actually that happens in the previous `flat_map` call),
 534         // and then try to prove it (in this case, we'll fail).
 535         //
 536         // Note the subtle difference from how we handle `predicates`
 537         // below: there, we are not trying to prove those predicates
 538         // to be *true* but merely *well-formed*.
 539         let pred = fcx.normalize_associated_types_in(span, &pred);
 540         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 541         traits::Obligation::new(cause, fcx.param_env, pred)
 542     });
 543
 544     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 545
 546     if let Some(return_ty) = return_ty {
 547         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 548     }
 549
 550     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 551
 552     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 553     let wf_obligations =
 554         predicates.predicates
 555                     .iter()
 556                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 557                                                                 fcx.param_env,
 558                                                                 fcx.body_id,
 559                                                                 p,
 560                                                                 span));
 561
 562     for obligation in wf_obligations.chain(default_obligations) {
 563         debug!("next obligation cause: {:?}", obligation.cause);
 564         fcx.register_predicate(obligation);
 565     }
 566 }
 567
 568 fn check_fn_or_method<'a, 'fcx, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
 569                                             fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 570                                             span: Span,
 571                                             sig: ty::PolyFnSig<'tcx>,
 572                                             def_id: DefId,
 573                                             implied_bounds: &mut Vec<Ty<'tcx>>)
 574 {
 575     let sig = fcx.normalize_associated_types_in(span, &sig);
 576     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 577
 578     for input_ty in sig.inputs() {
 579         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 580     }
 581     implied_bounds.extend(sig.inputs());
 582
 583     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 584
 585     // FIXME(#25759) return types should not be implied bounds
 586     implied_bounds.push(sig.output());
 587
 588     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 589 }
 590
 591 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 592 /// "higher-order pattern unification".
 593 /// This ensures that inference is tractable.
 594 /// In particular, definitions of existential types can only use other generics as arguments,
 595 /// and they cannot repeat an argument. Example:
 596 ///
 597 /// ```rust
 598 /// existential type Foo<A, B>;
 599 ///
 600 /// // ok -- `Foo` is applied to two distinct, generic types.
 601 /// fn a<T, U>() -> Foo<T, U> { .. }
 602 ///
 603 /// // not ok -- `Foo` is applied to `T` twice.
 604 /// fn b<T>() -> Foo<T, T> { .. }
 605 ///
 606 ///
 607 /// // not ok -- `Foo` is applied to a non-generic type.
 608 /// fn b<T>() -> Foo<T, u32> { .. }
 609 /// ```
 610 ///
 611 fn check_existential_types<'a, 'fcx, 'gcx, 'tcx>(
 612     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 613     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 614     fn_def_id: DefId,
 615     span: Span,
 616     ty: Ty<'tcx>,
 617 ) -> Vec<ty::Predicate<'tcx>> {
 618     trace!("check_existential_types: {:?}, {:?}", ty, ty.sty);
 619     let mut substituted_predicates = Vec::new();
 620     ty.fold_with(&mut ty::fold::BottomUpFolder {
 621         tcx: fcx.tcx,
 622         fldop: |ty| {
 623             if let ty::Opaque(def_id, substs) = ty.sty {
 624                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 625                 let generics = tcx.generics_of(def_id);
 626                 // only check named existential types defined in this crate
 627                 if generics.parent.is_none() && def_id.is_local() {
 628                     let opaque_node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 629                     if may_define_existential_type(tcx, fn_def_id, opaque_node_id) {
 630                         trace!("check_existential_types may define. Generics: {:#?}", generics);
 631                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 632                         for (subst, param) in substs.iter().zip(&generics.params) {
 633                             match subst.unpack() {
 634                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 635                                     ty::Param(..) => {}
 636                                     // prevent `fn foo() -> Foo<u32>` from being defining
 637                                     _ => {
 638                                         tcx.sess
 639                                             .struct_span_err(
 640                                                 span,
 641                                                 "non-defining existential type use \
 642                                                  in defining scope",
 643                                             )
 644                                             .span_note(
 645                                                 tcx.def_span(param.def_id),
 646                                                 &format!(
 647                                                     "used non-generic type {} for \
 648                                                      generic parameter",
 649                                                     ty,
 650                                                 ),
 651                                             )
 652                                             .emit();
 653                                     }
 654                                 }
 655
 656                                 ty::subst::UnpackedKind::Lifetime(region) => {
 657                                     let param_span = tcx.def_span(param.def_id);
 658                                     if let ty::ReStatic = region {
 659                                         tcx
 660                                             .sess
 661                                             .struct_span_err(
 662                                                 span,
 663                                                 "non-defining existential type use \
 664                                                     in defining scope",
 665                                             )
 666                                             .span_label(
 667                                                 param_span,
 668                                                 "cannot use static lifetime, use a bound lifetime \
 669                                                 instead or remove the lifetime parameter from the \
 670                                                 existential type",
 671                                             )
 672                                             .emit();
 673                                     } else {
 674                                         seen.entry(region).or_default().push(param_span);
 675                                     }
 676                                 }
 677
 678                                 ty::subst::UnpackedKind::Const(ct) => match ct {
 679                                     ty::LazyConst::Evaluated(ty::Const {
 680                                         val: ConstValue::Param(_),
 681                                         ..
 682                                     }) => {}
 683                                     _ => {
 684                                         tcx.sess
 685                                             .struct_span_err(
 686                                                 span,
 687                                                 "non-defining existential type use \
 688                                                 in defining scope",
 689                                             )
 690                                             .span_note(
 691                                                 tcx.def_span(param.def_id),
 692                                                 &format!(
 693                                                     "used non-generic const {} for \
 694                                                     generic parameter",
 695                                                     ty,
 696                                                 ),
 697                                             )
 698                                             .emit();
 699                                     }
 700                                 }
 701                             } // match subst
 702                         } // for (subst, param)
 703                         for (_, spans) in seen {
 704                             if spans.len() > 1 {
 705                                 tcx
 706                                     .sess
 707                                     .struct_span_err(
 708                                         span,
 709                                         "non-defining existential type use \
 710                                             in defining scope",
 711                                     ).
 712                                     span_note(
 713                                         spans,
 714                                         "lifetime used multiple times",
 715                                     )
 716                                     .emit();
 717                             }
 718                         }
 719                     } // if may_define_existential_type
 720
 721                     // now register the bounds on the parameters of the existential type
 722                     // so the parameters given by the function need to fulfill them
 723                     // ```rust
 724                     // existential type Foo<T: Bar>: 'static;
 725                     // fn foo<U>() -> Foo<U> { .. *}
 726                     // ```
 727                     // becomes
 728                     // ```rust
 729                     // existential type Foo<T: Bar>: 'static;
 730                     // fn foo<U: Bar>() -> Foo<U> { .. *}
 731                     // ```
 732                     let predicates = tcx.predicates_of(def_id);
 733                     trace!(
 734                         "check_existential_types may define. adding predicates: {:#?}",
 735                         predicates,
 736                     );
 737                     for &(pred, _) in predicates.predicates.iter() {
 738                         let substituted_pred = pred.subst(fcx.tcx, substs);
 739                         // Avoid duplication of predicates that contain no parameters, for example.
 740                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 741                             substituted_predicates.push(substituted_pred);
 742                         }
 743                     }
 744                 } // if is_named_existential_type
 745             } // if let Opaque
 746             ty
 747         },
 748         reg_op: |reg| reg,
 749     });
 750     substituted_predicates
 751 }
 752
 753 fn check_method_receiver<'fcx, 'gcx, 'tcx>(fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 754                                            method_sig: &hir::MethodSig,
 755                                            method: &ty::AssociatedItem,
 756                                            self_ty: Ty<'tcx>)
 757 {
 758     // check that the method has a valid receiver type, given the type `Self`
 759     debug!("check_method_receiver({:?}, self_ty={:?})",
 760            method, self_ty);
 761
 762     if !method.method_has_self_argument {
 763         return;
 764     }
 765
 766     let span = method_sig.decl.inputs[0].span;
 767
 768     let sig = fcx.tcx.fn_sig(method.def_id);
 769     let sig = fcx.normalize_associated_types_in(span, &sig);
 770     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 771
 772     debug!("check_method_receiver: sig={:?}", sig);
 773
 774     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 775     let self_ty = fcx.tcx.liberate_late_bound_regions(
 776         method.def_id,
 777         &ty::Binder::bind(self_ty)
 778     );
 779
 780     let receiver_ty = sig.inputs()[0];
 781
 782     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 783     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 784         method.def_id,
 785         &ty::Binder::bind(receiver_ty)
 786     );
 787
 788     if fcx.tcx.features().arbitrary_self_types {
 789         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 790             // report error, arbitrary_self_types was enabled
 791             fcx.tcx.sess.diagnostic().mut_span_err(
 792                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 793             ).note("type of `self` must be `Self` or a type that dereferences to it")
 794             .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 795             .code(DiagnosticId::Error("E0307".into()))
 796             .emit();
 797         }
 798     } else {
 799         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 800             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 801                 // report error, would have worked with arbitrary_self_types
 802                 feature_gate::feature_err(
 803                     &fcx.tcx.sess.parse_sess,
 804                     "arbitrary_self_types",
 805                     span,
 806                     GateIssue::Language,
 807                     &format!(
 808                         "`{}` cannot be used as the type of `self` without \
 809                             the `arbitrary_self_types` feature",
 810                         receiver_ty,
 811                     ),
 812                 ).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 813                 .emit();
 814             } else {
 815                 // report error, would not have worked with arbitrary_self_types
 816                 fcx.tcx.sess.diagnostic().mut_span_err(
 817                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 818                 ).note("type must be `Self` or a type that dereferences to it")
 819                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 820                 .code(DiagnosticId::Error("E0307".into()))
 821                 .emit();
 822             }
 823         }
 824     }
 825 }
 826
 827 /// returns true if `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 828 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 829 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 830 /// strict: `receiver_ty` must implement `Receiver` and directly implement `Deref<Target=self_ty>`.
 831 ///
 832 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 833 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 834 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 835 fn receiver_is_valid<'fcx, 'tcx, 'gcx>(
 836     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 837     span: Span,
 838     receiver_ty: Ty<'tcx>,
 839     self_ty: Ty<'tcx>,
 840     arbitrary_self_types_enabled: bool,
 841 ) -> bool {
 842     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 843
 844     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 845
 846     // `self: Self` is always valid
 847     if can_eq_self(receiver_ty) {
 848         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 849             err.emit();
 850         }
 851         return true
 852     }
 853
 854     let mut autoderef = fcx.autoderef(span, receiver_ty);
 855
 856     // the `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`
 857     if arbitrary_self_types_enabled {
 858         autoderef = autoderef.include_raw_pointers();
 859     }
 860
 861     // the first type is `receiver_ty`, which we know its not equal to `self_ty`. skip it.
 862     autoderef.next();
 863
 864     // keep dereferencing `receiver_ty` until we get to `self_ty`
 865     loop {
 866         if let Some((potential_self_ty, _)) = autoderef.next() {
 867             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 868                 potential_self_ty, self_ty);
 869
 870             if can_eq_self(potential_self_ty) {
 871                 autoderef.finalize(fcx);
 872
 873                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 874                     &cause, self_ty, potential_self_ty
 875                 ) {
 876                     err.emit();
 877                 }
 878
 879                 break
 880             }
 881         } else {
 882             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 883                 receiver_ty, self_ty);
 884             return false
 885         }
 886
 887         // without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 888         // `self_ty`. Enforce this by only doing one iteration of the loop
 889         if !arbitrary_self_types_enabled {
 890             return false
 891         }
 892     }
 893
 894     // without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`
 895     if !arbitrary_self_types_enabled {
 896         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 897             Some(did) => did,
 898             None => {
 899                 debug!("receiver_is_valid: missing Receiver trait");
 900                 return false
 901             }
 902         };
 903
 904         let trait_ref = ty::TraitRef{
 905             def_id: trait_def_id,
 906             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 907         };
 908
 909         let obligation = traits::Obligation::new(
 910             cause.clone(),
 911             fcx.param_env,
 912             trait_ref.to_predicate()
 913         );
 914
 915         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 916             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 917                 receiver_ty);
 918             return false
 919         }
 920     }
 921
 922     true
 923 }
 924
 925 fn check_variances_for_type_defn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 926                                            item: &hir::Item,
 927                                            hir_generics: &hir::Generics)
 928 {
 929     let item_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
 930     let ty = tcx.type_of(item_def_id);
 931     if tcx.has_error_field(ty) {
 932         return;
 933     }
 934
 935     let ty_predicates = tcx.predicates_of(item_def_id);
 936     assert_eq!(ty_predicates.parent, None);
 937     let variances = tcx.variances_of(item_def_id);
 938
 939     let mut constrained_parameters: FxHashSet<_> =
 940         variances.iter().enumerate()
 941                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 942                         .map(|(index, _)| Parameter(index as u32))
 943                         .collect();
 944
 945     identify_constrained_type_params(tcx,
 946                                      &ty_predicates,
 947                                      None,
 948                                      &mut constrained_parameters);
 949
 950     for (index, _) in variances.iter().enumerate() {
 951         if constrained_parameters.contains(&Parameter(index as u32)) {
 952             continue;
 953         }
 954
 955         let param = &hir_generics.params[index];
 956         match param.name {
 957             hir::ParamName::Error => { }
 958             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 959         }
 960     }
 961 }
 962
 963 fn report_bivariance<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 964                                span: Span,
 965                                param_name: ast::Name)
 966 {
 967     let mut err = error_392(tcx, span, param_name);
 968
 969     let suggested_marker_id = tcx.lang_items().phantom_data();
 970     // help is available only in presence of lang items
 971     if let Some(def_id) = suggested_marker_id {
 972         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 973                           param_name,
 974                           tcx.item_path_str(def_id)));
 975     }
 976     err.emit();
 977 }
 978
 979 fn reject_shadowing_parameters(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) {
 980     let generics = tcx.generics_of(def_id);
 981     let parent = tcx.generics_of(generics.parent.unwrap());
 982     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
 983         GenericParamDefKind::Lifetime => None,
 984         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
 985             Some((param.name, param.def_id))
 986         }
 987     }).collect();
 988
 989     for method_param in &generics.params {
 990         // Shadowing is checked in resolve_lifetime.
 991         if let GenericParamDefKind::Lifetime = method_param.kind {
 992             continue
 993         }
 994         if impl_params.contains_key(&method_param.name) {
 995             // Tighten up the span to focus on only the shadowing type
 996             let type_span = tcx.def_span(method_param.def_id);
 997
 998             // The expectation here is that the original trait declaration is
 999             // local so it should be okay to just unwrap everything.
1000             let trait_def_id = impl_params[&method_param.name];
1001             let trait_decl_span = tcx.def_span(trait_def_id);
1002             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
1003         }
1004     }
1005 }
1006
1007 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1008 /// aren't true.
1009 fn check_false_global_bounds<'a, 'gcx, 'tcx>(
1010     fcx: &FnCtxt<'a, 'gcx, 'tcx>,
1011     span: Span,
1012     id: hir::HirId)
1013 {
1014     use rustc::ty::TypeFoldable;
1015
1016     let empty_env = ty::ParamEnv::empty();
1017
1018     let def_id = fcx.tcx.hir().local_def_id_from_hir_id(id);
1019     let predicates = fcx.tcx.predicates_of(def_id).predicates
1020         .iter()
1021         .map(|(p, _)| *p)
1022         .collect();
1023     // Check elaborated bounds
1024     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1025
1026     for pred in implied_obligations {
1027         // Match the existing behavior.
1028         if pred.is_global() && !pred.has_late_bound_regions() {
1029             let pred = fcx.normalize_associated_types_in(span, &pred);
1030             let obligation = traits::Obligation::new(
1031                 traits::ObligationCause::new(
1032                     span,
1033                     id,
1034                     traits::TrivialBound,
1035                 ),
1036                 empty_env,
1037                 pred,
1038             );
1039             fcx.register_predicate(obligation);
1040         }
1041     }
1042
1043     fcx.select_all_obligations_or_error();
1044 }
1045
1046 pub struct CheckTypeWellFormedVisitor<'a, 'tcx: 'a> {
1047     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1048 }
1049
1050 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
1051     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
1052                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
1053         CheckTypeWellFormedVisitor {
1054             tcx,
1055         }
1056     }
1057 }
1058
1059 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'a, 'tcx> {
1060     fn visit_item(&mut self, i: &'tcx hir::Item) {
1061         debug!("visit_item: {:?}", i);
1062         let def_id = self.tcx.hir().local_def_id_from_hir_id(i.hir_id);
1063         self.tcx.ensure().check_item_well_formed(def_id);
1064     }
1065
1066     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
1067         debug!("visit_trait_item: {:?}", trait_item);
1068         let def_id = self.tcx.hir().local_def_id_from_hir_id(trait_item.hir_id);
1069         self.tcx.ensure().check_trait_item_well_formed(def_id);
1070     }
1071
1072     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
1073         debug!("visit_impl_item: {:?}", impl_item);
1074         let def_id = self.tcx.hir().local_def_id_from_hir_id(impl_item.hir_id);
1075         self.tcx.ensure().check_impl_item_well_formed(def_id);
1076     }
1077 }
1078
1079 ///////////////////////////////////////////////////////////////////////////
1080 // ADT
1081
1082 struct AdtVariant<'tcx> {
1083     fields: Vec<AdtField<'tcx>>,
1084 }
1085
1086 struct AdtField<'tcx> {
1087     ty: Ty<'tcx>,
1088     span: Span,
1089 }
1090
1091 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
1092     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1093         let fields = struct_def.fields().iter().map(|field| {
1094             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id_from_hir_id(field.hir_id));
1095             let field_ty = self.normalize_associated_types_in(field.span,
1096                                                               &field_ty);
1097             AdtField { ty: field_ty, span: field.span }
1098         })
1099         .collect();
1100         AdtVariant { fields }
1101     }
1102
1103     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1104         enum_def.variants.iter()
1105             .map(|variant| self.non_enum_variant(&variant.node.data))
1106             .collect()
1107     }
1108
1109     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1110         match self.tcx.impl_trait_ref(impl_def_id) {
1111             Some(ref trait_ref) => {
1112                 // Trait impl: take implied bounds from all types that
1113                 // appear in the trait reference.
1114                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1115                 trait_ref.substs.types().collect()
1116             }
1117
1118             None => {
1119                 // Inherent impl: take implied bounds from the `self` type.
1120                 let self_ty = self.tcx.type_of(impl_def_id);
1121                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1122                 vec![self_ty]
1123             }
1124         }
1125     }
1126 }
1127
1128 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
1129                        -> DiagnosticBuilder<'tcx> {
1130     let mut err = struct_span_err!(tcx.sess, span, E0392,
1131                   "parameter `{}` is never used", param_name);
1132     err.span_label(span, "unused type parameter");
1133     err
1134 }
1135
1136 fn error_194(tcx: TyCtxt<'_, '_, '_>, span: Span, trait_decl_span: Span, name: &str) {
1137     struct_span_err!(tcx.sess, span, E0194,
1138                      "type parameter `{}` shadows another type parameter of the same name",
1139                      name)
1140         .span_label(span, "shadows another type parameter")
1141         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1142         .emit();
1143 }