src/librustc_typeck/check/wfcheck.rs

   1 use crate::check::{Inherited, FnCtxt};
   2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
   3
   4 use crate::hir::def_id::DefId;
   5 use rustc::traits::{self, ObligationCauseCode};
   6 use rustc::ty::{self, Lift, Ty, TyCtxt, 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 syntax::symbol::sym;
  17 use errors::{DiagnosticBuilder, DiagnosticId};
  18
  19 use rustc::hir::itemlikevisit::ParItemLikeVisitor;
  20 use rustc::hir;
  21
  22 /// Helper type of a temporary returned by `.for_item(...)`.
  23 /// Necessary because we can't write the following bound:
  24 /// `F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>)`.
  25 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  26     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  27     id: hir::HirId,
  28     span: Span,
  29     param_env: ty::ParamEnv<'tcx>,
  30 }
  31
  32 impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
  33     fn with_fcx<F>(&'tcx mut self, f: F) where
  34         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
  35                          TyCtxt<'b, 'gcx, 'gcx>) -> Vec<Ty<'tcx>>
  36     {
  37         let id = self.id;
  38         let span = self.span;
  39         let param_env = self.param_env;
  40         self.inherited.enter(|inh| {
  41             let fcx = FnCtxt::new(&inh, param_env, id);
  42             if !inh.tcx.features().trivial_bounds {
  43                 // As predicates are cached rather than obligations, this
  44                 // needsto be called first so that they are checked with an
  45                 // empty param_env.
  46                 check_false_global_bounds(&fcx, span, id);
  47             }
  48             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  49             fcx.select_all_obligations_or_error();
  50             fcx.regionck_item(id, span, &wf_tys);
  51         });
  52     }
  53 }
  54
  55 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  56 /// well-formed, meaning that they do not require any constraints not declared in the struct
  57 /// definition itself. For example, this definition would be illegal:
  58 ///
  59 ///     struct Ref<'a, T> { x: &'a T }
  60 ///
  61 /// because the type did not declare that `T:'a`.
  62 ///
  63 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  64 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  65 /// the types first.
  66 pub fn check_item_well_formed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
  67     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  68     let item = tcx.hir().expect_item_by_hir_id(hir_id);
  69
  70     debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
  71            item.hir_id,
  72            tcx.def_path_str(def_id));
  73
  74     match item.node {
  75         // Right now we check that every default trait implementation
  76         // has an implementation of itself. Basically, a case like:
  77         //
  78         // `impl Trait for T {}`
  79         //
  80         // has a requirement of `T: Trait` which was required for default
  81         // method implementations. Although this could be improved now that
  82         // there's a better infrastructure in place for this, it's being left
  83         // for a follow-up work.
  84         //
  85         // Since there's such a requirement, we need to check *just* positive
  86         // implementations, otherwise things like:
  87         //
  88         // impl !Send for T {}
  89         //
  90         // won't be allowed unless there's an *explicit* implementation of `Send`
  91         // for `T`
  92         hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
  93             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id_from_hir_id(item.hir_id))
  94                                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
  95             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
  96                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
  97             }
  98             if polarity == hir::ImplPolarity::Positive {
  99                 check_impl(tcx, item, self_ty, trait_ref);
 100             } else {
 101                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 102                 if trait_ref.is_some() && !is_auto {
 103                     span_err!(tcx.sess, item.span, E0192,
 104                               "negative impls are only allowed for \
 105                                auto traits (e.g., `Send` and `Sync`)")
 106                 }
 107             }
 108         }
 109         hir::ItemKind::Fn(..) => {
 110             check_item_fn(tcx, item);
 111         }
 112         hir::ItemKind::Static(ref ty, ..) => {
 113             check_item_type(tcx, item.hir_id, ty.span, false);
 114         }
 115         hir::ItemKind::Const(ref ty, ..) => {
 116             check_item_type(tcx, item.hir_id, ty.span, false);
 117         }
 118         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 119             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 120                 check_item_type(tcx, it.hir_id, ty.span, true);
 121             }
 122         },
 123         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 124             check_type_defn(tcx, item, false, |fcx| {
 125                 vec![fcx.non_enum_variant(struct_def)]
 126             });
 127
 128             check_variances_for_type_defn(tcx, item, ast_generics);
 129         }
 130         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 131             check_type_defn(tcx, item, true, |fcx| {
 132                 vec![fcx.non_enum_variant(struct_def)]
 133             });
 134
 135             check_variances_for_type_defn(tcx, item, ast_generics);
 136         }
 137         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 138             check_type_defn(tcx, item, true, |fcx| {
 139                 fcx.enum_variants(enum_def)
 140             });
 141
 142             check_variances_for_type_defn(tcx, item, ast_generics);
 143         }
 144         hir::ItemKind::Trait(..) => {
 145             check_trait(tcx, item);
 146         }
 147         hir::ItemKind::TraitAlias(..) => {
 148             check_trait(tcx, item);
 149         }
 150         _ => {}
 151     }
 152 }
 153
 154 pub fn check_trait_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 155     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 156     let trait_item = tcx.hir().expect_trait_item(hir_id);
 157
 158     let method_sig = match trait_item.node {
 159         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 160         _ => None
 161     };
 162     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 163 }
 164
 165 pub fn check_impl_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 166     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 167     let impl_item = tcx.hir().expect_impl_item(hir_id);
 168
 169     let method_sig = match impl_item.node {
 170         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 171         _ => None
 172     };
 173     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 174 }
 175
 176 fn check_associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 177                                    item_id: hir::HirId,
 178                                    span: Span,
 179                                    sig_if_method: Option<&hir::MethodSig>) {
 180     debug!("check_associated_item: {:?}", item_id);
 181
 182     let code = ObligationCauseCode::MiscObligation;
 183     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 184         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id_from_hir_id(item_id));
 185
 186         let (mut implied_bounds, self_ty) = match item.container {
 187             ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 188             ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 189                                           fcx.tcx.type_of(def_id))
 190         };
 191
 192         match item.kind {
 193             ty::AssocKind::Const => {
 194                 let ty = fcx.tcx.type_of(item.def_id);
 195                 let ty = fcx.normalize_associated_types_in(span, &ty);
 196                 fcx.register_wf_obligation(ty, span, code.clone());
 197             }
 198             ty::AssocKind::Method => {
 199                 reject_shadowing_parameters(fcx.tcx, item.def_id);
 200                 let sig = fcx.tcx.fn_sig(item.def_id);
 201                 let sig = fcx.normalize_associated_types_in(span, &sig);
 202                 check_fn_or_method(tcx, fcx, span, sig,
 203                                    item.def_id, &mut implied_bounds);
 204                 let sig_if_method = sig_if_method.expect("bad signature for method");
 205                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 206             }
 207             ty::AssocKind::Type => {
 208                 if item.defaultness.has_value() {
 209                     let ty = fcx.tcx.type_of(item.def_id);
 210                     let ty = fcx.normalize_associated_types_in(span, &ty);
 211                     fcx.register_wf_obligation(ty, span, code.clone());
 212                 }
 213             }
 214             ty::AssocKind::Existential => {
 215                 // do nothing, existential types check themselves
 216             }
 217         }
 218
 219         implied_bounds
 220     })
 221 }
 222
 223 fn for_item<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, item: &hir::Item)
 224                             -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 225     for_id(tcx, item.hir_id, item.span)
 226 }
 227
 228 fn for_id<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, id: hir::HirId, span: Span)
 229                           -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 230     let def_id = tcx.hir().local_def_id_from_hir_id(id);
 231     CheckWfFcxBuilder {
 232         inherited: Inherited::build(tcx, def_id),
 233         id,
 234         span,
 235         param_env: tcx.param_env(def_id),
 236     }
 237 }
 238
 239 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 240 fn check_type_defn<'a, 'tcx, F>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 241                                 item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 242     where F: for<'fcx, 'gcx, 'tcx2> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx2>) -> Vec<AdtVariant<'tcx2>>
 243 {
 244     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 245         let variants = lookup_fields(fcx);
 246         let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 247         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 248
 249         for variant in &variants {
 250             // For DST, or when drop needs to copy things around, all
 251             // intermediate types must be sized.
 252             let needs_drop_copy = || {
 253                 packed && {
 254                     let ty = variant.fields.last().unwrap().ty;
 255                     fcx.tcx.erase_regions(&ty).lift_to_tcx(fcx_tcx)
 256                         .map(|ty| ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id)))
 257                         .unwrap_or_else(|| {
 258                             fcx_tcx.sess.delay_span_bug(
 259                                 item.span, &format!("inference variables in {:?}", ty));
 260                             // Just treat unresolved type expression as if it needs drop.
 261                             true
 262                         })
 263                 }
 264             };
 265             let all_sized =
 266                 all_sized ||
 267                 variant.fields.is_empty() ||
 268                 needs_drop_copy();
 269             let unsized_len = if all_sized {
 270                 0
 271             } else {
 272                 1
 273             };
 274             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 275                 .iter()
 276                 .enumerate()
 277             {
 278                 let last = idx == variant.fields.len() - 1;
 279                 fcx.register_bound(
 280                     field.ty,
 281                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 282                     traits::ObligationCause::new(
 283                         field.span,
 284                         fcx.body_id,
 285                         traits::FieldSized {
 286                             adt_kind: match item.node.adt_kind() {
 287                                 Some(i) => i,
 288                                 None => bug!(),
 289                             },
 290                             last
 291                         }
 292                     )
 293                 );
 294             }
 295
 296             // All field types must be well-formed.
 297             for field in &variant.fields {
 298                 fcx.register_wf_obligation(field.ty, field.span,
 299                     ObligationCauseCode::MiscObligation)
 300             }
 301         }
 302
 303         check_where_clauses(tcx, fcx, item.span, def_id, None);
 304
 305         vec![] // no implied bounds in a struct def'n
 306     });
 307 }
 308
 309 fn check_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 310     debug!("check_trait: {:?}", item.hir_id);
 311
 312     let trait_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
 313
 314     let trait_def = tcx.trait_def(trait_def_id);
 315     if trait_def.is_marker {
 316         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 317             struct_span_err!(
 318                 tcx.sess,
 319                 tcx.def_span(*associated_def_id),
 320                 E0714,
 321                 "marker traits cannot have associated items",
 322             ).emit();
 323         }
 324     }
 325
 326     for_item(tcx, item).with_fcx(|fcx, _| {
 327         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 328         vec![]
 329     });
 330 }
 331
 332 fn check_item_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 333     for_item(tcx, item).with_fcx(|fcx, tcx| {
 334         let def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 335         let sig = fcx.tcx.fn_sig(def_id);
 336         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 337         let mut implied_bounds = vec![];
 338         check_fn_or_method(tcx, fcx, item.span, sig,
 339                            def_id, &mut implied_bounds);
 340         implied_bounds
 341     })
 342 }
 343
 344 fn check_item_type<'a, 'tcx>(
 345     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 346     item_id: hir::HirId,
 347     ty_span: Span,
 348     allow_foreign_ty: bool,
 349 ) {
 350     debug!("check_item_type: {:?}", item_id);
 351
 352     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 353         let ty = gcx.type_of(gcx.hir().local_def_id_from_hir_id(item_id));
 354         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 355
 356         let mut forbid_unsized = true;
 357         if allow_foreign_ty {
 358             if let ty::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
 359                 forbid_unsized = false;
 360             }
 361         }
 362
 363         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 364         if forbid_unsized {
 365             fcx.register_bound(
 366                 item_ty,
 367                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 368                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 369             );
 370         }
 371
 372         vec![] // no implied bounds in a const etc
 373     });
 374 }
 375
 376 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 377                         item: &hir::Item,
 378                         ast_self_ty: &hir::Ty,
 379                         ast_trait_ref: &Option<hir::TraitRef>)
 380 {
 381     debug!("check_impl: {:?}", item);
 382
 383     for_item(tcx, item).with_fcx(|fcx, tcx| {
 384         let item_def_id = fcx.tcx.hir().local_def_id_from_hir_id(item.hir_id);
 385
 386         match *ast_trait_ref {
 387             Some(ref ast_trait_ref) => {
 388                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 389                 let trait_ref =
 390                     fcx.normalize_associated_types_in(
 391                         ast_trait_ref.path.span, &trait_ref);
 392                 let obligations =
 393                     ty::wf::trait_obligations(fcx,
 394                                                 fcx.param_env,
 395                                                 fcx.body_id,
 396                                                 &trait_ref,
 397                                                 ast_trait_ref.path.span);
 398                 for obligation in obligations {
 399                     fcx.register_predicate(obligation);
 400                 }
 401             }
 402             None => {
 403                 let self_ty = fcx.tcx.type_of(item_def_id);
 404                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 405                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 406                     ObligationCauseCode::MiscObligation);
 407             }
 408         }
 409
 410         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 411
 412         fcx.impl_implied_bounds(item_def_id, item.span)
 413     });
 414 }
 415
 416 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 417 fn check_where_clauses<'a, 'gcx, 'fcx, 'tcx>(
 418     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 419     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 420     span: Span,
 421     def_id: DefId,
 422     return_ty: Option<Ty<'tcx>>,
 423 ) {
 424     let predicates = fcx.tcx.predicates_of(def_id);
 425     let generics = tcx.generics_of(def_id);
 426
 427     let is_our_default = |def: &ty::GenericParamDef| {
 428         match def.kind {
 429             GenericParamDefKind::Type { has_default, .. } => {
 430                 has_default && def.index >= generics.parent_count as u32
 431             }
 432             _ => unreachable!()
 433         }
 434     };
 435
 436     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 437     // For example this forbids the declaration:
 438     // struct Foo<T = Vec<[u32]>> { .. }
 439     // Here the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 440     for param in &generics.params {
 441         if let GenericParamDefKind::Type { .. } = param.kind {
 442             if is_our_default(&param) {
 443                 let ty = fcx.tcx.type_of(param.def_id);
 444                 // ignore dependent defaults -- that is, where the default of one type
 445                 // parameter includes another (e.g., <T, U = T>). In those cases, we can't
 446                 // be sure if it will error or not as user might always specify the other.
 447                 if !ty.needs_subst() {
 448                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 449                         ObligationCauseCode::MiscObligation);
 450                 }
 451             }
 452         }
 453     }
 454
 455     // Check that trait predicates are WF when params are substituted by their defaults.
 456     // We don't want to overly constrain the predicates that may be written but we want to
 457     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 458     // Therefore we check if a predicate which contains a single type param
 459     // with a concrete default is WF with that default substituted.
 460     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 461     //
 462     // First we build the defaulted substitution.
 463     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 464         match param.kind {
 465             GenericParamDefKind::Lifetime => {
 466                 // All regions are identity.
 467                 fcx.tcx.mk_param_from_def(param)
 468             }
 469
 470             GenericParamDefKind::Type { .. } => {
 471                 // If the param has a default,
 472                 if is_our_default(param) {
 473                     let default_ty = fcx.tcx.type_of(param.def_id);
 474                     // and it's not a dependent default
 475                     if !default_ty.needs_subst() {
 476                         // then substitute with the default.
 477                         return default_ty.into();
 478                     }
 479                 }
 480                 // Mark unwanted params as err.
 481                 fcx.tcx.types.err.into()
 482             }
 483
 484             GenericParamDefKind::Const => {
 485                 // FIXME(const_generics:defaults)
 486                 fcx.tcx.consts.err.into()
 487             }
 488         }
 489     });
 490
 491     // Now we build the substituted predicates.
 492     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 493         #[derive(Default)]
 494         struct CountParams { params: FxHashSet<u32> }
 495         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 496             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 497                 if let ty::Param(param) = t.sty {
 498                     self.params.insert(param.index);
 499                 }
 500                 t.super_visit_with(self)
 501             }
 502
 503             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 504                 true
 505             }
 506
 507             fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 508                 if let ConstValue::Param(param) = c.val {
 509                     self.params.insert(param.index);
 510                 }
 511                 c.super_visit_with(self)
 512             }
 513         }
 514         let mut param_count = CountParams::default();
 515         let has_region = pred.visit_with(&mut param_count);
 516         let substituted_pred = pred.subst(fcx.tcx, substs);
 517         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 518         // or preds with multiple params.
 519         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 520             None
 521         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 522             // Avoid duplication of predicates that contain no parameters, for example.
 523             None
 524         } else {
 525             Some(substituted_pred)
 526         }
 527     }).map(|pred| {
 528         // convert each of those into an obligation. So if you have
 529         // something like `struct Foo<T: Copy = String>`, we would
 530         // take that predicate `T: Copy`, substitute to `String: Copy`
 531         // (actually that happens in the previous `flat_map` call),
 532         // and then try to prove it (in this case, we'll fail).
 533         //
 534         // Note the subtle difference from how we handle `predicates`
 535         // below: there, we are not trying to prove those predicates
 536         // to be *true* but merely *well-formed*.
 537         let pred = fcx.normalize_associated_types_in(span, &pred);
 538         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 539         traits::Obligation::new(cause, fcx.param_env, pred)
 540     });
 541
 542     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 543
 544     if let Some(return_ty) = return_ty {
 545         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 546     }
 547
 548     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 549
 550     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 551     let wf_obligations =
 552         predicates.predicates
 553                     .iter()
 554                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 555                                                                 fcx.param_env,
 556                                                                 fcx.body_id,
 557                                                                 p,
 558                                                                 span));
 559
 560     for obligation in wf_obligations.chain(default_obligations) {
 561         debug!("next obligation cause: {:?}", obligation.cause);
 562         fcx.register_predicate(obligation);
 563     }
 564 }
 565
 566 fn check_fn_or_method<'a, 'fcx, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
 567                                             fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 568                                             span: Span,
 569                                             sig: ty::PolyFnSig<'tcx>,
 570                                             def_id: DefId,
 571                                             implied_bounds: &mut Vec<Ty<'tcx>>)
 572 {
 573     let sig = fcx.normalize_associated_types_in(span, &sig);
 574     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 575
 576     for input_ty in sig.inputs() {
 577         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 578     }
 579     implied_bounds.extend(sig.inputs());
 580
 581     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 582
 583     // FIXME(#25759) return types should not be implied bounds
 584     implied_bounds.push(sig.output());
 585
 586     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 587 }
 588
 589 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 590 /// "higher-order pattern unification".
 591 /// This ensures that inference is tractable.
 592 /// In particular, definitions of existential types can only use other generics as arguments,
 593 /// and they cannot repeat an argument. Example:
 594 ///
 595 /// ```rust
 596 /// existential type Foo<A, B>;
 597 ///
 598 /// // ok -- `Foo` is applied to two distinct, generic types.
 599 /// fn a<T, U>() -> Foo<T, U> { .. }
 600 ///
 601 /// // not ok -- `Foo` is applied to `T` twice.
 602 /// fn b<T>() -> Foo<T, T> { .. }
 603 ///
 604 ///
 605 /// // not ok -- `Foo` is applied to a non-generic type.
 606 /// fn b<T>() -> Foo<T, u32> { .. }
 607 /// ```
 608 ///
 609 fn check_existential_types<'a, 'fcx, 'gcx, 'tcx>(
 610     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 611     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 612     fn_def_id: DefId,
 613     span: Span,
 614     ty: Ty<'tcx>,
 615 ) -> Vec<ty::Predicate<'tcx>> {
 616     trace!("check_existential_types: {:?}", ty);
 617     let mut substituted_predicates = Vec::new();
 618     ty.fold_with(&mut ty::fold::BottomUpFolder {
 619         tcx: fcx.tcx,
 620         ty_op: |ty| {
 621             if let ty::Opaque(def_id, substs) = ty.sty {
 622                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 623                 let generics = tcx.generics_of(def_id);
 624                 // only check named existential types defined in this crate
 625                 if generics.parent.is_none() && def_id.is_local() {
 626                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 627                     if may_define_existential_type(tcx, fn_def_id, opaque_hir_id) {
 628                         trace!("check_existential_types may define. Generics: {:#?}", generics);
 629                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 630                         for (subst, param) in substs.iter().zip(&generics.params) {
 631                             match subst.unpack() {
 632                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 633                                     ty::Param(..) => {}
 634                                     // prevent `fn foo() -> Foo<u32>` from being defining
 635                                     _ => {
 636                                         tcx.sess
 637                                             .struct_span_err(
 638                                                 span,
 639                                                 "non-defining existential type use \
 640                                                  in defining scope",
 641                                             )
 642                                             .span_note(
 643                                                 tcx.def_span(param.def_id),
 644                                                 &format!(
 645                                                     "used non-generic type {} for \
 646                                                      generic parameter",
 647                                                     ty,
 648                                                 ),
 649                                             )
 650                                             .emit();
 651                                     }
 652                                 }
 653
 654                                 ty::subst::UnpackedKind::Lifetime(region) => {
 655                                     let param_span = tcx.def_span(param.def_id);
 656                                     if let ty::ReStatic = region {
 657                                         tcx
 658                                             .sess
 659                                             .struct_span_err(
 660                                                 span,
 661                                                 "non-defining existential type use \
 662                                                     in defining scope",
 663                                             )
 664                                             .span_label(
 665                                                 param_span,
 666                                                 "cannot use static lifetime, use a bound lifetime \
 667                                                 instead or remove the lifetime parameter from the \
 668                                                 existential type",
 669                                             )
 670                                             .emit();
 671                                     } else {
 672                                         seen.entry(region).or_default().push(param_span);
 673                                     }
 674                                 }
 675
 676                                 ty::subst::UnpackedKind::Const(ct) => match ct.val {
 677                                     ConstValue::Param(_) => {}
 678                                     _ => {
 679                                         tcx.sess
 680                                             .struct_span_err(
 681                                                 span,
 682                                                 "non-defining existential type use \
 683                                                 in defining scope",
 684                                             )
 685                                             .span_note(
 686                                                 tcx.def_span(param.def_id),
 687                                                 &format!(
 688                                                     "used non-generic const {} for \
 689                                                     generic parameter",
 690                                                     ty,
 691                                                 ),
 692                                             )
 693                                             .emit();
 694                                     }
 695                                 }
 696                             } // match subst
 697                         } // for (subst, param)
 698                         for (_, spans) in seen {
 699                             if spans.len() > 1 {
 700                                 tcx
 701                                     .sess
 702                                     .struct_span_err(
 703                                         span,
 704                                         "non-defining existential type use \
 705                                             in defining scope",
 706                                     ).
 707                                     span_note(
 708                                         spans,
 709                                         "lifetime used multiple times",
 710                                     )
 711                                     .emit();
 712                             }
 713                         }
 714                     } // if may_define_existential_type
 715
 716                     // now register the bounds on the parameters of the existential type
 717                     // so the parameters given by the function need to fulfill them
 718                     // ```rust
 719                     // existential type Foo<T: Bar>: 'static;
 720                     // fn foo<U>() -> Foo<U> { .. *}
 721                     // ```
 722                     // becomes
 723                     // ```rust
 724                     // existential type Foo<T: Bar>: 'static;
 725                     // fn foo<U: Bar>() -> Foo<U> { .. *}
 726                     // ```
 727                     let predicates = tcx.predicates_of(def_id);
 728                     trace!(
 729                         "check_existential_types may define. adding predicates: {:#?}",
 730                         predicates,
 731                     );
 732                     for &(pred, _) in predicates.predicates.iter() {
 733                         let substituted_pred = pred.subst(fcx.tcx, substs);
 734                         // Avoid duplication of predicates that contain no parameters, for example.
 735                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 736                             substituted_predicates.push(substituted_pred);
 737                         }
 738                     }
 739                 } // if is_named_existential_type
 740             } // if let Opaque
 741             ty
 742         },
 743         lt_op: |lt| lt,
 744         ct_op: |ct| ct,
 745     });
 746     substituted_predicates
 747 }
 748
 749 fn check_method_receiver<'fcx, 'gcx, 'tcx>(fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 750                                            method_sig: &hir::MethodSig,
 751                                            method: &ty::AssocItem,
 752                                            self_ty: Ty<'tcx>)
 753 {
 754     // check that the method has a valid receiver type, given the type `Self`
 755     debug!("check_method_receiver({:?}, self_ty={:?})",
 756            method, self_ty);
 757
 758     if !method.method_has_self_argument {
 759         return;
 760     }
 761
 762     let span = method_sig.decl.inputs[0].span;
 763
 764     let sig = fcx.tcx.fn_sig(method.def_id);
 765     let sig = fcx.normalize_associated_types_in(span, &sig);
 766     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 767
 768     debug!("check_method_receiver: sig={:?}", sig);
 769
 770     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 771     let self_ty = fcx.tcx.liberate_late_bound_regions(
 772         method.def_id,
 773         &ty::Binder::bind(self_ty)
 774     );
 775
 776     let receiver_ty = sig.inputs()[0];
 777
 778     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 779     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 780         method.def_id,
 781         &ty::Binder::bind(receiver_ty)
 782     );
 783
 784     if fcx.tcx.features().arbitrary_self_types {
 785         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 786             // report error, arbitrary_self_types was enabled
 787             fcx.tcx.sess.diagnostic().mut_span_err(
 788                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 789             ).note("type of `self` must be `Self` or a type that dereferences to it")
 790             .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 791             .code(DiagnosticId::Error("E0307".into()))
 792             .emit();
 793         }
 794     } else {
 795         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 796             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 797                 // report error, would have worked with arbitrary_self_types
 798                 feature_gate::feature_err(
 799                     &fcx.tcx.sess.parse_sess,
 800                     sym::arbitrary_self_types,
 801                     span,
 802                     GateIssue::Language,
 803                     &format!(
 804                         "`{}` cannot be used as the type of `self` without \
 805                             the `arbitrary_self_types` feature",
 806                         receiver_ty,
 807                     ),
 808                 ).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 809                 .emit();
 810             } else {
 811                 // report error, would not have worked with arbitrary_self_types
 812                 fcx.tcx.sess.diagnostic().mut_span_err(
 813                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 814                 ).note("type must be `Self` or a type that dereferences to it")
 815                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 816                 .code(DiagnosticId::Error("E0307".into()))
 817                 .emit();
 818             }
 819         }
 820     }
 821 }
 822
 823 /// returns true if `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 824 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 825 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 826 /// strict: `receiver_ty` must implement `Receiver` and directly implement `Deref<Target=self_ty>`.
 827 ///
 828 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 829 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 830 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 831 fn receiver_is_valid<'fcx, 'tcx, 'gcx>(
 832     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 833     span: Span,
 834     receiver_ty: Ty<'tcx>,
 835     self_ty: Ty<'tcx>,
 836     arbitrary_self_types_enabled: bool,
 837 ) -> bool {
 838     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 839
 840     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 841
 842     // `self: Self` is always valid
 843     if can_eq_self(receiver_ty) {
 844         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 845             err.emit();
 846         }
 847         return true
 848     }
 849
 850     let mut autoderef = fcx.autoderef(span, receiver_ty);
 851
 852     // the `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`
 853     if arbitrary_self_types_enabled {
 854         autoderef = autoderef.include_raw_pointers();
 855     }
 856
 857     // the first type is `receiver_ty`, which we know its not equal to `self_ty`. skip it.
 858     autoderef.next();
 859
 860     // keep dereferencing `receiver_ty` until we get to `self_ty`
 861     loop {
 862         if let Some((potential_self_ty, _)) = autoderef.next() {
 863             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 864                 potential_self_ty, self_ty);
 865
 866             if can_eq_self(potential_self_ty) {
 867                 autoderef.finalize(fcx);
 868
 869                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 870                     &cause, self_ty, potential_self_ty
 871                 ) {
 872                     err.emit();
 873                 }
 874
 875                 break
 876             }
 877         } else {
 878             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 879                 receiver_ty, self_ty);
 880             // If he receiver already has errors reported due to it, consider it valid to avoid
 881             // unecessary errors (#58712).
 882             return receiver_ty.references_error();
 883         }
 884
 885         // without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 886         // `self_ty`. Enforce this by only doing one iteration of the loop
 887         if !arbitrary_self_types_enabled {
 888             return false
 889         }
 890     }
 891
 892     // without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`
 893     if !arbitrary_self_types_enabled {
 894         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 895             Some(did) => did,
 896             None => {
 897                 debug!("receiver_is_valid: missing Receiver trait");
 898                 return false
 899             }
 900         };
 901
 902         let trait_ref = ty::TraitRef{
 903             def_id: trait_def_id,
 904             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 905         };
 906
 907         let obligation = traits::Obligation::new(
 908             cause.clone(),
 909             fcx.param_env,
 910             trait_ref.to_predicate()
 911         );
 912
 913         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 914             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 915                 receiver_ty);
 916             return false
 917         }
 918     }
 919
 920     true
 921 }
 922
 923 fn check_variances_for_type_defn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 924                                            item: &hir::Item,
 925                                            hir_generics: &hir::Generics)
 926 {
 927     let item_def_id = tcx.hir().local_def_id_from_hir_id(item.hir_id);
 928     let ty = tcx.type_of(item_def_id);
 929     if tcx.has_error_field(ty) {
 930         return;
 931     }
 932
 933     let ty_predicates = tcx.predicates_of(item_def_id);
 934     assert_eq!(ty_predicates.parent, None);
 935     let variances = tcx.variances_of(item_def_id);
 936
 937     let mut constrained_parameters: FxHashSet<_> =
 938         variances.iter().enumerate()
 939                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 940                         .map(|(index, _)| Parameter(index as u32))
 941                         .collect();
 942
 943     identify_constrained_generic_params(
 944         tcx,
 945         &ty_predicates,
 946         None,
 947         &mut constrained_parameters,
 948     );
 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
 957         match param.name {
 958             hir::ParamName::Error => { }
 959             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 960         }
 961     }
 962 }
 963
 964 fn report_bivariance<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 965                                span: Span,
 966                                param_name: ast::Name)
 967 {
 968     let mut err = error_392(tcx, span, param_name);
 969
 970     let suggested_marker_id = tcx.lang_items().phantom_data();
 971     // help is available only in presence of lang items
 972     if let Some(def_id) = suggested_marker_id {
 973         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 974                           param_name,
 975                           tcx.def_path_str(def_id)));
 976     }
 977     err.emit();
 978 }
 979
 980 fn reject_shadowing_parameters(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) {
 981     let generics = tcx.generics_of(def_id);
 982     let parent = tcx.generics_of(generics.parent.unwrap());
 983     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
 984         GenericParamDefKind::Lifetime => None,
 985         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
 986             Some((param.name, param.def_id))
 987         }
 988     }).collect();
 989
 990     for method_param in &generics.params {
 991         // Shadowing is checked in resolve_lifetime.
 992         if let GenericParamDefKind::Lifetime = method_param.kind {
 993             continue
 994         }
 995         if impl_params.contains_key(&method_param.name) {
 996             // Tighten up the span to focus on only the shadowing type
 997             let type_span = tcx.def_span(method_param.def_id);
 998
 999             // The expectation here is that the original trait declaration is
1000             // local so it should be okay to just unwrap everything.
1001             let trait_def_id = impl_params[&method_param.name];
1002             let trait_decl_span = tcx.def_span(trait_def_id);
1003             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
1004         }
1005     }
1006 }
1007
1008 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1009 /// aren't true.
1010 fn check_false_global_bounds<'a, 'gcx, 'tcx>(
1011     fcx: &FnCtxt<'a, 'gcx, 'tcx>,
1012     span: Span,
1013     id: hir::HirId)
1014 {
1015     let empty_env = ty::ParamEnv::empty();
1016
1017     let def_id = fcx.tcx.hir().local_def_id_from_hir_id(id);
1018     let predicates = fcx.tcx.predicates_of(def_id).predicates
1019         .iter()
1020         .map(|(p, _)| *p)
1021         .collect();
1022     // Check elaborated bounds.
1023     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1024
1025     for pred in implied_obligations {
1026         // Match the existing behavior.
1027         if pred.is_global() && !pred.has_late_bound_regions() {
1028             let pred = fcx.normalize_associated_types_in(span, &pred);
1029             let obligation = traits::Obligation::new(
1030                 traits::ObligationCause::new(
1031                     span,
1032                     id,
1033                     traits::TrivialBound,
1034                 ),
1035                 empty_env,
1036                 pred,
1037             );
1038             fcx.register_predicate(obligation);
1039         }
1040     }
1041
1042     fcx.select_all_obligations_or_error();
1043 }
1044
1045 pub struct CheckTypeWellFormedVisitor<'a, 'tcx: 'a> {
1046     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1047 }
1048
1049 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
1050     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
1051                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
1052         CheckTypeWellFormedVisitor {
1053             tcx,
1054         }
1055     }
1056 }
1057
1058 impl<'a, 'tcx> ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'a, 'tcx> {
1059     fn visit_item(&self, i: &'tcx hir::Item) {
1060         debug!("visit_item: {:?}", i);
1061         let def_id = self.tcx.hir().local_def_id_from_hir_id(i.hir_id);
1062         self.tcx.ensure().check_item_well_formed(def_id);
1063     }
1064
1065     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem) {
1066         debug!("visit_trait_item: {:?}", trait_item);
1067         let def_id = self.tcx.hir().local_def_id_from_hir_id(trait_item.hir_id);
1068         self.tcx.ensure().check_trait_item_well_formed(def_id);
1069     }
1070
1071     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem) {
1072         debug!("visit_impl_item: {:?}", impl_item);
1073         let def_id = self.tcx.hir().local_def_id_from_hir_id(impl_item.hir_id);
1074         self.tcx.ensure().check_impl_item_well_formed(def_id);
1075     }
1076 }
1077
1078 ///////////////////////////////////////////////////////////////////////////
1079 // ADT
1080
1081 struct AdtVariant<'tcx> {
1082     fields: Vec<AdtField<'tcx>>,
1083 }
1084
1085 struct AdtField<'tcx> {
1086     ty: Ty<'tcx>,
1087     span: Span,
1088 }
1089
1090 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
1091     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1092         let fields = struct_def.fields().iter().map(|field| {
1093             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id_from_hir_id(field.hir_id));
1094             let field_ty = self.normalize_associated_types_in(field.span,
1095                                                               &field_ty);
1096             AdtField { ty: field_ty, span: field.span }
1097         })
1098         .collect();
1099         AdtVariant { fields }
1100     }
1101
1102     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1103         enum_def.variants.iter()
1104             .map(|variant| self.non_enum_variant(&variant.node.data))
1105             .collect()
1106     }
1107
1108     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1109         match self.tcx.impl_trait_ref(impl_def_id) {
1110             Some(ref trait_ref) => {
1111                 // Trait impl: take implied bounds from all types that
1112                 // appear in the trait reference.
1113                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1114                 trait_ref.substs.types().collect()
1115             }
1116
1117             None => {
1118                 // Inherent impl: take implied bounds from the `self` type.
1119                 let self_ty = self.tcx.type_of(impl_def_id);
1120                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1121                 vec![self_ty]
1122             }
1123         }
1124     }
1125 }
1126
1127 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
1128                        -> DiagnosticBuilder<'tcx> {
1129     let mut err = struct_span_err!(tcx.sess, span, E0392,
1130                   "parameter `{}` is never used", param_name);
1131     err.span_label(span, "unused parameter");
1132     err
1133 }
1134
1135 fn error_194(tcx: TyCtxt<'_, '_, '_>, span: Span, trait_decl_span: Span, name: &str) {
1136     struct_span_err!(tcx.sess, span, E0194,
1137                      "type parameter `{}` shadows another type parameter of the same name",
1138                      name)
1139         .span_label(span, "shadows another type parameter")
1140         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1141         .emit();
1142 }