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::middle::lang_items;
  10 use rustc::infer::opaque_types::may_define_existential_type;
  11
  12 use syntax::ast;
  13 use syntax::feature_gate::{self, GateIssue};
  14 use syntax_pos::Span;
  15 use errors::{DiagnosticBuilder, DiagnosticId};
  16
  17 use rustc::hir::itemlikevisit::ItemLikeVisitor;
  18 use rustc::hir;
  19
  20 /// Helper type of a temporary returned by `.for_item(...)`.
  21 /// Necessary because we can't write the following bound:
  22 /// `F: for<'b, 'tcx> where 'gcx: 'tcx FnOnce(FnCtxt<'b, 'gcx, 'tcx>)`.
  23 struct CheckWfFcxBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
  24     inherited: super::InheritedBuilder<'a, 'gcx, 'tcx>,
  25     id: hir::HirId,
  26     span: Span,
  27     param_env: ty::ParamEnv<'tcx>,
  28 }
  29
  30 impl<'a, 'gcx, 'tcx> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
  31     fn with_fcx<F>(&'tcx mut self, f: F) where
  32         F: for<'b> FnOnce(&FnCtxt<'b, 'gcx, 'tcx>,
  33                          TyCtxt<'b, 'gcx, 'gcx>) -> Vec<Ty<'tcx>>
  34     {
  35         let id = self.id;
  36         let span = self.span;
  37         let param_env = self.param_env;
  38         self.inherited.enter(|inh| {
  39             let fcx = FnCtxt::new(&inh, param_env, id);
  40             if !inh.tcx.features().trivial_bounds {
  41                 // As predicates are cached rather than obligations, this
  42                 // needsto be called first so that they are checked with an
  43                 // empty param_env.
  44                 check_false_global_bounds(&fcx, span, id);
  45             }
  46             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  47             fcx.select_all_obligations_or_error();
  48             fcx.regionck_item(id, span, &wf_tys);
  49         });
  50     }
  51 }
  52
  53 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  54 /// well-formed, meaning that they do not require any constraints not declared in the struct
  55 /// definition itself. For example, this definition would be illegal:
  56 ///
  57 ///     struct Ref<'a, T> { x: &'a T }
  58 ///
  59 /// because the type did not declare that `T:'a`.
  60 ///
  61 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  62 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  63 /// the types first.
  64 pub fn check_item_well_formed<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
  65     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  66     let item = tcx.hir().expect_item_by_hir_id(hir_id);
  67
  68     debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
  69            item.hir_id,
  70            tcx.item_path_str(def_id));
  71
  72     match item.node {
  73         // Right now we check that every default trait implementation
  74         // has an implementation of itself. Basically, a case like:
  75         //
  76         // `impl Trait for T {}`
  77         //
  78         // has a requirement of `T: Trait` which was required for default
  79         // method implementations. Although this could be improved now that
  80         // there's a better infrastructure in place for this, it's being left
  81         // for a follow-up work.
  82         //
  83         // Since there's such a requirement, we need to check *just* positive
  84         // implementations, otherwise things like:
  85         //
  86         // impl !Send for T {}
  87         //
  88         // won't be allowed unless there's an *explicit* implementation of `Send`
  89         // for `T`
  90         hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
  91             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id_from_hir_id(item.hir_id))
  92                                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
  93             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
  94                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
  95             }
  96             if polarity == hir::ImplPolarity::Positive {
  97                 check_impl(tcx, item, self_ty, trait_ref);
  98             } else {
  99                 // FIXME(#27579) what amount of WF checking do we need for neg impls?
 100                 if trait_ref.is_some() && !is_auto {
 101                     span_err!(tcx.sess, item.span, E0192,
 102                               "negative impls are only allowed for \
 103                                auto traits (e.g., `Send` and `Sync`)")
 104                 }
 105             }
 106         }
 107         hir::ItemKind::Fn(..) => {
 108             check_item_fn(tcx, item);
 109         }
 110         hir::ItemKind::Static(ref ty, ..) => {
 111             check_item_type(tcx, item.hir_id, ty.span, false);
 112         }
 113         hir::ItemKind::Const(ref ty, ..) => {
 114             check_item_type(tcx, item.hir_id, ty.span, false);
 115         }
 116         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 117             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 118                 check_item_type(tcx, it.hir_id, ty.span, true);
 119             }
 120         },
 121         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 122             check_type_defn(tcx, item, false, |fcx| {
 123                 vec![fcx.non_enum_variant(struct_def)]
 124             });
 125
 126             check_variances_for_type_defn(tcx, item, ast_generics);
 127         }
 128         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 129             check_type_defn(tcx, item, true, |fcx| {
 130                 vec![fcx.non_enum_variant(struct_def)]
 131             });
 132
 133             check_variances_for_type_defn(tcx, item, ast_generics);
 134         }
 135         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 136             check_type_defn(tcx, item, true, |fcx| {
 137                 fcx.enum_variants(enum_def)
 138             });
 139
 140             check_variances_for_type_defn(tcx, item, ast_generics);
 141         }
 142         hir::ItemKind::Trait(..) => {
 143             check_trait(tcx, item);
 144         }
 145         hir::ItemKind::TraitAlias(..) => {
 146             check_trait(tcx, item);
 147         }
 148         _ => {}
 149     }
 150 }
 151
 152 pub fn check_trait_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 153     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 154     let trait_item = tcx.hir().expect_trait_item(node_id);
 155
 156     let method_sig = match trait_item.node {
 157         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 158         _ => None
 159     };
 160     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 161 }
 162
 163 pub fn check_impl_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, def_id: DefId) {
 164     let node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 165     let impl_item = tcx.hir().expect_impl_item(node_id);
 166
 167     let method_sig = match impl_item.node {
 168         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 169         _ => None
 170     };
 171     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 172 }
 173
 174 fn check_associated_item<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 175                                    item_id: hir::HirId,
 176                                    span: Span,
 177                                    sig_if_method: Option<&hir::MethodSig>) {
 178     debug!("check_associated_item: {:?}", item_id);
 179
 180     let code = ObligationCauseCode::MiscObligation;
 181     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 182         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id_from_hir_id(item_id));
 183
 184         let (mut implied_bounds, self_ty) = match item.container {
 185             ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 186             ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 187                                           fcx.tcx.type_of(def_id))
 188         };
 189
 190         match item.kind {
 191             ty::AssociatedKind::Const => {
 192                 let ty = fcx.tcx.type_of(item.def_id);
 193                 let ty = fcx.normalize_associated_types_in(span, &ty);
 194                 fcx.register_wf_obligation(ty, span, code.clone());
 195             }
 196             ty::AssociatedKind::Method => {
 197                 reject_shadowing_parameters(fcx.tcx, item.def_id);
 198                 let sig = fcx.tcx.fn_sig(item.def_id);
 199                 let sig = fcx.normalize_associated_types_in(span, &sig);
 200                 check_fn_or_method(tcx, fcx, span, sig,
 201                                    item.def_id, &mut implied_bounds);
 202                 let sig_if_method = sig_if_method.expect("bad signature for method");
 203                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 204             }
 205             ty::AssociatedKind::Type => {
 206                 if item.defaultness.has_value() {
 207                     let ty = fcx.tcx.type_of(item.def_id);
 208                     let ty = fcx.normalize_associated_types_in(span, &ty);
 209                     fcx.register_wf_obligation(ty, span, code.clone());
 210                 }
 211             }
 212             ty::AssociatedKind::Existential => {
 213                 // do nothing, existential types check themselves
 214             }
 215         }
 216
 217         implied_bounds
 218     })
 219 }
 220
 221 fn for_item<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, item: &hir::Item)
 222                             -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 223     for_id(tcx, item.hir_id, item.span)
 224 }
 225
 226 fn for_id<'a, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>, id: hir::HirId, span: Span)
 227                           -> CheckWfFcxBuilder<'a, 'gcx, 'tcx> {
 228     let def_id = tcx.hir().local_def_id_from_hir_id(id);
 229     CheckWfFcxBuilder {
 230         inherited: Inherited::build(tcx, def_id),
 231         id,
 232         span,
 233         param_env: tcx.param_env(def_id),
 234     }
 235 }
 236
 237 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 238 fn check_type_defn<'a, 'tcx, F>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 239                                 item: &hir::Item, all_sized: bool, mut lookup_fields: F)
 240     where F: for<'fcx, 'gcx, 'tcx2> FnMut(&FnCtxt<'fcx, 'gcx, 'tcx2>) -> Vec<AdtVariant<'tcx2>>
 241 {
 242     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 243         let variants = lookup_fields(fcx);
 244         let def_id = fcx.tcx.hir().local_def_id(item.id);
 245         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 246
 247         for variant in &variants {
 248             // For DST, or when drop needs to copy things around, all
 249             // intermediate types must be sized.
 250             let needs_drop_copy = || {
 251                 packed && {
 252                     let ty = variant.fields.last().unwrap().ty;
 253                     let ty = fcx.tcx.erase_regions(&ty).lift_to_tcx(fcx_tcx)
 254                         .unwrap_or_else(|| {
 255                             span_bug!(item.span, "inference variables in {:?}", ty)
 256                         });
 257                     ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
 258                 }
 259             };
 260             let all_sized =
 261                 all_sized ||
 262                 variant.fields.is_empty() ||
 263                 needs_drop_copy();
 264             let unsized_len = if all_sized {
 265                 0
 266             } else {
 267                 1
 268             };
 269             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 270                 .iter()
 271                 .enumerate()
 272             {
 273                 let last = idx == variant.fields.len() - 1;
 274                 fcx.register_bound(
 275                     field.ty,
 276                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 277                     traits::ObligationCause::new(
 278                         field.span,
 279                         fcx.body_id,
 280                         traits::FieldSized {
 281                             adt_kind: match item.node.adt_kind() {
 282                                 Some(i) => i,
 283                                 None => bug!(),
 284                             },
 285                             last
 286                         }
 287                     )
 288                 );
 289             }
 290
 291             // All field types must be well-formed.
 292             for field in &variant.fields {
 293                 fcx.register_wf_obligation(field.ty, field.span,
 294                     ObligationCauseCode::MiscObligation)
 295             }
 296         }
 297
 298         check_where_clauses(tcx, fcx, item.span, def_id, None);
 299
 300         vec![] // no implied bounds in a struct def'n
 301     });
 302 }
 303
 304 fn check_trait<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 305     debug!("check_trait: {:?}", item.id);
 306
 307     let trait_def_id = tcx.hir().local_def_id(item.id);
 308
 309     let trait_def = tcx.trait_def(trait_def_id);
 310     if trait_def.is_marker {
 311         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 312             struct_span_err!(
 313                 tcx.sess,
 314                 tcx.def_span(*associated_def_id),
 315                 E0714,
 316                 "marker traits cannot have associated items",
 317             ).emit();
 318         }
 319     }
 320
 321     for_item(tcx, item).with_fcx(|fcx, _| {
 322         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 323         vec![]
 324     });
 325 }
 326
 327 fn check_item_fn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, item: &hir::Item) {
 328     for_item(tcx, item).with_fcx(|fcx, tcx| {
 329         let def_id = fcx.tcx.hir().local_def_id(item.id);
 330         let sig = fcx.tcx.fn_sig(def_id);
 331         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 332         let mut implied_bounds = vec![];
 333         check_fn_or_method(tcx, fcx, item.span, sig,
 334                            def_id, &mut implied_bounds);
 335         implied_bounds
 336     })
 337 }
 338
 339 fn check_item_type<'a, 'tcx>(
 340     tcx: TyCtxt<'a, 'tcx, 'tcx>,
 341     item_id: hir::HirId,
 342     ty_span: Span,
 343     allow_foreign_ty: bool,
 344 ) {
 345     debug!("check_item_type: {:?}", item_id);
 346
 347     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 348         let ty = gcx.type_of(gcx.hir().local_def_id_from_hir_id(item_id));
 349         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 350
 351         let mut forbid_unsized = true;
 352         if allow_foreign_ty {
 353             if let TyKind::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
 354                 forbid_unsized = false;
 355             }
 356         }
 357
 358         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 359         if forbid_unsized {
 360             fcx.register_bound(
 361                 item_ty,
 362                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 363                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 364             );
 365         }
 366
 367         vec![] // no implied bounds in a const etc
 368     });
 369 }
 370
 371 fn check_impl<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 372                         item: &hir::Item,
 373                         ast_self_ty: &hir::Ty,
 374                         ast_trait_ref: &Option<hir::TraitRef>)
 375 {
 376     debug!("check_impl: {:?}", item);
 377
 378     for_item(tcx, item).with_fcx(|fcx, tcx| {
 379         let item_def_id = fcx.tcx.hir().local_def_id(item.id);
 380
 381         match *ast_trait_ref {
 382             Some(ref ast_trait_ref) => {
 383                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 384                 let trait_ref =
 385                     fcx.normalize_associated_types_in(
 386                         ast_trait_ref.path.span, &trait_ref);
 387                 let obligations =
 388                     ty::wf::trait_obligations(fcx,
 389                                                 fcx.param_env,
 390                                                 fcx.body_id,
 391                                                 &trait_ref,
 392                                                 ast_trait_ref.path.span);
 393                 for obligation in obligations {
 394                     fcx.register_predicate(obligation);
 395                 }
 396             }
 397             None => {
 398                 let self_ty = fcx.tcx.type_of(item_def_id);
 399                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 400                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 401                     ObligationCauseCode::MiscObligation);
 402             }
 403         }
 404
 405         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 406
 407         fcx.impl_implied_bounds(item_def_id, item.span)
 408     });
 409 }
 410
 411 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 412 fn check_where_clauses<'a, 'gcx, 'fcx, 'tcx>(
 413     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 414     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 415     span: Span,
 416     def_id: DefId,
 417     return_ty: Option<Ty<'tcx>>,
 418 ) {
 419     use ty::subst::Subst;
 420     use rustc::ty::TypeFoldable;
 421
 422     let predicates = fcx.tcx.predicates_of(def_id);
 423
 424     let generics = tcx.generics_of(def_id);
 425     let is_our_default = |def: &ty::GenericParamDef| {
 426         match def.kind {
 427             GenericParamDefKind::Type { has_default, .. } => {
 428                 has_default && def.index >= generics.parent_count as u32
 429             }
 430             _ => unreachable!()
 431         }
 432     };
 433
 434     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 435     // For example this forbids the declaration:
 436     // struct Foo<T = Vec<[u32]>> { .. }
 437     // Here the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 438     for param in &generics.params {
 439         if let GenericParamDefKind::Type {..} = param.kind {
 440             if is_our_default(&param) {
 441                 let ty = fcx.tcx.type_of(param.def_id);
 442                 // ignore dependent defaults -- that is, where the default of one type
 443                 // parameter includes another (e.g., <T, U = T>). In those cases, we can't
 444                 // be sure if it will error or not as user might always specify the other.
 445                 if !ty.needs_subst() {
 446                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 447                         ObligationCauseCode::MiscObligation);
 448                 }
 449             }
 450         }
 451     }
 452
 453     // Check that trait predicates are WF when params are substituted by their defaults.
 454     // We don't want to overly constrain the predicates that may be written but we want to
 455     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 456     // Therefore we check if a predicate which contains a single type param
 457     // with a concrete default is WF with that default substituted.
 458     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 459     //
 460     // First we build the defaulted substitution.
 461     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 462         match param.kind {
 463             GenericParamDefKind::Lifetime => {
 464                 // All regions are identity.
 465                 fcx.tcx.mk_param_from_def(param)
 466             }
 467             GenericParamDefKind::Type {..} => {
 468                 // If the param has a default,
 469                 if is_our_default(param) {
 470                     let default_ty = fcx.tcx.type_of(param.def_id);
 471                     // and it's not a dependent default
 472                     if !default_ty.needs_subst() {
 473                         // then substitute with the default.
 474                         return default_ty.into();
 475                     }
 476                 }
 477                 // Mark unwanted params as err.
 478                 fcx.tcx.types.err.into()
 479             }
 480         }
 481     });
 482     // Now we build the substituted predicates.
 483     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 484         #[derive(Default)]
 485         struct CountParams { params: FxHashSet<u32> }
 486         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 487             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 488                 match t.sty {
 489                     ty::Param(p) => {
 490                         self.params.insert(p.idx);
 491                         t.super_visit_with(self)
 492                     }
 493                     _ => t.super_visit_with(self)
 494                 }
 495             }
 496
 497             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 498                 true
 499             }
 500         }
 501         let mut param_count = CountParams::default();
 502         let has_region = pred.visit_with(&mut param_count);
 503         let substituted_pred = pred.subst(fcx.tcx, substs);
 504         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 505         // or preds with multiple params.
 506         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 507             None
 508         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 509             // Avoid duplication of predicates that contain no parameters, for example.
 510             None
 511         } else {
 512             Some(substituted_pred)
 513         }
 514     }).map(|pred| {
 515         // convert each of those into an obligation. So if you have
 516         // something like `struct Foo<T: Copy = String>`, we would
 517         // take that predicate `T: Copy`, substitute to `String: Copy`
 518         // (actually that happens in the previous `flat_map` call),
 519         // and then try to prove it (in this case, we'll fail).
 520         //
 521         // Note the subtle difference from how we handle `predicates`
 522         // below: there, we are not trying to prove those predicates
 523         // to be *true* but merely *well-formed*.
 524         let pred = fcx.normalize_associated_types_in(span, &pred);
 525         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 526         traits::Obligation::new(cause, fcx.param_env, pred)
 527     });
 528
 529     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 530
 531     if let Some(return_ty) = return_ty {
 532         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 533     }
 534
 535     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 536
 537     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 538     let wf_obligations =
 539         predicates.predicates
 540                     .iter()
 541                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 542                                                                 fcx.param_env,
 543                                                                 fcx.body_id,
 544                                                                 p,
 545                                                                 span));
 546
 547     for obligation in wf_obligations.chain(default_obligations) {
 548         debug!("next obligation cause: {:?}", obligation.cause);
 549         fcx.register_predicate(obligation);
 550     }
 551 }
 552
 553 fn check_fn_or_method<'a, 'fcx, 'gcx, 'tcx>(tcx: TyCtxt<'a, 'gcx, 'gcx>,
 554                                             fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 555                                             span: Span,
 556                                             sig: ty::PolyFnSig<'tcx>,
 557                                             def_id: DefId,
 558                                             implied_bounds: &mut Vec<Ty<'tcx>>)
 559 {
 560     let sig = fcx.normalize_associated_types_in(span, &sig);
 561     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 562
 563     for input_ty in sig.inputs() {
 564         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 565     }
 566     implied_bounds.extend(sig.inputs());
 567
 568     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 569
 570     // FIXME(#25759) return types should not be implied bounds
 571     implied_bounds.push(sig.output());
 572
 573     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 574 }
 575
 576 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 577 /// "higher-order pattern unification".
 578 /// This ensures that inference is tractable.
 579 /// In particular, definitions of existential types can only use other generics as arguments,
 580 /// and they cannot repeat an argument. Example:
 581 ///
 582 /// ```rust
 583 /// existential type Foo<A, B>;
 584 ///
 585 /// // ok -- `Foo` is applied to two distinct, generic types.
 586 /// fn a<T, U>() -> Foo<T, U> { .. }
 587 ///
 588 /// // not ok -- `Foo` is applied to `T` twice.
 589 /// fn b<T>() -> Foo<T, T> { .. }
 590 ///
 591 ///
 592 /// // not ok -- `Foo` is applied to a non-generic type.
 593 /// fn b<T>() -> Foo<T, u32> { .. }
 594 /// ```
 595 ///
 596 fn check_existential_types<'a, 'fcx, 'gcx, 'tcx>(
 597     tcx: TyCtxt<'a, 'gcx, 'gcx>,
 598     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 599     fn_def_id: DefId,
 600     span: Span,
 601     ty: Ty<'tcx>,
 602 ) -> Vec<ty::Predicate<'tcx>> {
 603     trace!("check_existential_types: {:?}, {:?}", ty, ty.sty);
 604     let mut substituted_predicates = Vec::new();
 605     ty.fold_with(&mut ty::fold::BottomUpFolder {
 606         tcx: fcx.tcx,
 607         fldop: |ty| {
 608             if let ty::Opaque(def_id, substs) = ty.sty {
 609                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 610                 let generics = tcx.generics_of(def_id);
 611                 // only check named existential types defined in this crate
 612                 if generics.parent.is_none() && def_id.is_local() {
 613                     let opaque_node_id = tcx.hir().as_local_node_id(def_id).unwrap();
 614                     if may_define_existential_type(tcx, fn_def_id, opaque_node_id) {
 615                         trace!("check_existential_types may define. Generics: {:#?}", generics);
 616                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 617                         for (subst, param) in substs.iter().zip(&generics.params) {
 618                             match subst.unpack() {
 619                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 620                                     ty::Param(..) => {},
 621                                     // prevent `fn foo() -> Foo<u32>` from being defining
 622                                     _ => {
 623                                         tcx
 624                                             .sess
 625                                             .struct_span_err(
 626                                                 span,
 627                                                 "non-defining existential type use \
 628                                                  in defining scope",
 629                                             )
 630                                             .span_note(
 631                                                 tcx.def_span(param.def_id),
 632                                                 &format!(
 633                                                     "used non-generic type {} for \
 634                                                      generic parameter",
 635                                                     ty,
 636                                                 ),
 637                                             )
 638                                             .emit();
 639                                     },
 640                                 }, // match ty
 641                                 ty::subst::UnpackedKind::Lifetime(region) => {
 642                                     let param_span = tcx.def_span(param.def_id);
 643                                     if let ty::ReStatic = region {
 644                                         tcx
 645                                             .sess
 646                                             .struct_span_err(
 647                                                 span,
 648                                                 "non-defining existential type use \
 649                                                     in defining scope",
 650                                             )
 651                                             .span_label(
 652                                                 param_span,
 653                                                 "cannot use static lifetime, use a bound lifetime \
 654                                                 instead or remove the lifetime parameter from the \
 655                                                 existential type",
 656                                             )
 657                                             .emit();
 658                                     } else {
 659                                         seen.entry(region).or_default().push(param_span);
 660                                     }
 661                                 },
 662                             } // match subst
 663                         } // for (subst, param)
 664                         for (_, spans) in seen {
 665                             if spans.len() > 1 {
 666                                 tcx
 667                                     .sess
 668                                     .struct_span_err(
 669                                         span,
 670                                         "non-defining existential type use \
 671                                             in defining scope",
 672                                     ).
 673                                     span_note(
 674                                         spans,
 675                                         "lifetime used multiple times",
 676                                     )
 677                                     .emit();
 678                             }
 679                         }
 680                     } // if may_define_existential_type
 681
 682                     // now register the bounds on the parameters of the existential type
 683                     // so the parameters given by the function need to fulfill them
 684                     // ```rust
 685                     // existential type Foo<T: Bar>: 'static;
 686                     // fn foo<U>() -> Foo<U> { .. *}
 687                     // ```
 688                     // becomes
 689                     // ```rust
 690                     // existential type Foo<T: Bar>: 'static;
 691                     // fn foo<U: Bar>() -> Foo<U> { .. *}
 692                     // ```
 693                     let predicates = tcx.predicates_of(def_id);
 694                     trace!(
 695                         "check_existential_types may define. adding predicates: {:#?}",
 696                         predicates,
 697                     );
 698                     for &(pred, _) in predicates.predicates.iter() {
 699                         let substituted_pred = pred.subst(fcx.tcx, substs);
 700                         // Avoid duplication of predicates that contain no parameters, for example.
 701                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 702                             substituted_predicates.push(substituted_pred);
 703                         }
 704                     }
 705                 } // if is_named_existential_type
 706             } // if let Opaque
 707             ty
 708         },
 709         reg_op: |reg| reg,
 710     });
 711     substituted_predicates
 712 }
 713
 714 fn check_method_receiver<'fcx, 'gcx, 'tcx>(fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 715                                            method_sig: &hir::MethodSig,
 716                                            method: &ty::AssociatedItem,
 717                                            self_ty: Ty<'tcx>)
 718 {
 719     // check that the method has a valid receiver type, given the type `Self`
 720     debug!("check_method_receiver({:?}, self_ty={:?})",
 721            method, self_ty);
 722
 723     if !method.method_has_self_argument {
 724         return;
 725     }
 726
 727     let span = method_sig.decl.inputs[0].span;
 728
 729     let sig = fcx.tcx.fn_sig(method.def_id);
 730     let sig = fcx.normalize_associated_types_in(span, &sig);
 731     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 732
 733     debug!("check_method_receiver: sig={:?}", sig);
 734
 735     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 736     let self_ty = fcx.tcx.liberate_late_bound_regions(
 737         method.def_id,
 738         &ty::Binder::bind(self_ty)
 739     );
 740
 741     let receiver_ty = sig.inputs()[0];
 742
 743     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 744     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 745         method.def_id,
 746         &ty::Binder::bind(receiver_ty)
 747     );
 748
 749     if fcx.tcx.features().arbitrary_self_types {
 750         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 751             // report error, arbitrary_self_types was enabled
 752             fcx.tcx.sess.diagnostic().mut_span_err(
 753                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 754             ).note("type of `self` must be `Self` or a type that dereferences to it")
 755             .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 756             .code(DiagnosticId::Error("E0307".into()))
 757             .emit();
 758         }
 759     } else {
 760         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 761             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 762                 // report error, would have worked with arbitrary_self_types
 763                 feature_gate::feature_err(
 764                     &fcx.tcx.sess.parse_sess,
 765                     "arbitrary_self_types",
 766                     span,
 767                     GateIssue::Language,
 768                     &format!(
 769                         "`{}` cannot be used as the type of `self` without \
 770                             the `arbitrary_self_types` feature",
 771                         receiver_ty,
 772                     ),
 773                 ).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 774                 .emit();
 775             } else {
 776                 // report error, would not have worked with arbitrary_self_types
 777                 fcx.tcx.sess.diagnostic().mut_span_err(
 778                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 779                 ).note("type must be `Self` or a type that dereferences to it")
 780                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 781                 .code(DiagnosticId::Error("E0307".into()))
 782                 .emit();
 783             }
 784         }
 785     }
 786 }
 787
 788 /// returns true if `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 789 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 790 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 791 /// strict: `receiver_ty` must implement `Receiver` and directly implement `Deref<Target=self_ty>`.
 792 ///
 793 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 794 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 795 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 796 fn receiver_is_valid<'fcx, 'tcx, 'gcx>(
 797     fcx: &FnCtxt<'fcx, 'gcx, 'tcx>,
 798     span: Span,
 799     receiver_ty: Ty<'tcx>,
 800     self_ty: Ty<'tcx>,
 801     arbitrary_self_types_enabled: bool,
 802 ) -> bool {
 803     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 804
 805     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 806
 807     // `self: Self` is always valid
 808     if can_eq_self(receiver_ty) {
 809         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 810             err.emit();
 811         }
 812         return true
 813     }
 814
 815     let mut autoderef = fcx.autoderef(span, receiver_ty);
 816
 817     // the `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`
 818     if arbitrary_self_types_enabled {
 819         autoderef = autoderef.include_raw_pointers();
 820     }
 821
 822     // the first type is `receiver_ty`, which we know its not equal to `self_ty`. skip it.
 823     autoderef.next();
 824
 825     // keep dereferencing `receiver_ty` until we get to `self_ty`
 826     loop {
 827         if let Some((potential_self_ty, _)) = autoderef.next() {
 828             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 829                 potential_self_ty, self_ty);
 830
 831             if can_eq_self(potential_self_ty) {
 832                 autoderef.finalize(fcx);
 833
 834                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 835                     &cause, self_ty, potential_self_ty
 836                 ) {
 837                     err.emit();
 838                 }
 839
 840                 break
 841             }
 842         } else {
 843             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 844                 receiver_ty, self_ty);
 845             return false
 846         }
 847
 848         // without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 849         // `self_ty`. Enforce this by only doing one iteration of the loop
 850         if !arbitrary_self_types_enabled {
 851             return false
 852         }
 853     }
 854
 855     // without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`
 856     if !arbitrary_self_types_enabled {
 857         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 858             Some(did) => did,
 859             None => {
 860                 debug!("receiver_is_valid: missing Receiver trait");
 861                 return false
 862             }
 863         };
 864
 865         let trait_ref = ty::TraitRef{
 866             def_id: trait_def_id,
 867             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 868         };
 869
 870         let obligation = traits::Obligation::new(
 871             cause.clone(),
 872             fcx.param_env,
 873             trait_ref.to_predicate()
 874         );
 875
 876         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 877             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 878                 receiver_ty);
 879             return false
 880         }
 881     }
 882
 883     true
 884 }
 885
 886 fn check_variances_for_type_defn<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 887                                            item: &hir::Item,
 888                                            hir_generics: &hir::Generics)
 889 {
 890     let item_def_id = tcx.hir().local_def_id(item.id);
 891     let ty = tcx.type_of(item_def_id);
 892     if tcx.has_error_field(ty) {
 893         return;
 894     }
 895
 896     let ty_predicates = tcx.predicates_of(item_def_id);
 897     assert_eq!(ty_predicates.parent, None);
 898     let variances = tcx.variances_of(item_def_id);
 899
 900     let mut constrained_parameters: FxHashSet<_> =
 901         variances.iter().enumerate()
 902                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 903                         .map(|(index, _)| Parameter(index as u32))
 904                         .collect();
 905
 906     identify_constrained_type_params(tcx,
 907                                      &ty_predicates,
 908                                      None,
 909                                      &mut constrained_parameters);
 910
 911     for (index, _) in variances.iter().enumerate() {
 912         if constrained_parameters.contains(&Parameter(index as u32)) {
 913             continue;
 914         }
 915
 916         let param = &hir_generics.params[index];
 917         match param.name {
 918             hir::ParamName::Error => { }
 919             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 920         }
 921     }
 922 }
 923
 924 fn report_bivariance<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>,
 925                                span: Span,
 926                                param_name: ast::Name)
 927 {
 928     let mut err = error_392(tcx, span, param_name);
 929
 930     let suggested_marker_id = tcx.lang_items().phantom_data();
 931     // help is available only in presence of lang items
 932     if let Some(def_id) = suggested_marker_id {
 933         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 934                           param_name,
 935                           tcx.item_path_str(def_id)));
 936     }
 937     err.emit();
 938 }
 939
 940 fn reject_shadowing_parameters(tcx: TyCtxt<'_, '_, '_>, def_id: DefId) {
 941     let generics = tcx.generics_of(def_id);
 942     let parent = tcx.generics_of(generics.parent.unwrap());
 943     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
 944         GenericParamDefKind::Lifetime => None,
 945         GenericParamDefKind::Type {..} => Some((param.name, param.def_id)),
 946     }).collect();
 947
 948     for method_param in &generics.params {
 949         // Shadowing is checked in resolve_lifetime.
 950         if let GenericParamDefKind::Lifetime = method_param.kind {
 951             continue
 952         }
 953         if impl_params.contains_key(&method_param.name) {
 954             // Tighten up the span to focus on only the shadowing type
 955             let type_span = tcx.def_span(method_param.def_id);
 956
 957             // The expectation here is that the original trait declaration is
 958             // local so it should be okay to just unwrap everything.
 959             let trait_def_id = impl_params[&method_param.name];
 960             let trait_decl_span = tcx.def_span(trait_def_id);
 961             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
 962         }
 963     }
 964 }
 965
 966 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
 967 /// aren't true.
 968 fn check_false_global_bounds<'a, 'gcx, 'tcx>(
 969     fcx: &FnCtxt<'a, 'gcx, 'tcx>,
 970     span: Span,
 971     id: hir::HirId)
 972 {
 973     use rustc::ty::TypeFoldable;
 974
 975     let empty_env = ty::ParamEnv::empty();
 976
 977     let def_id = fcx.tcx.hir().local_def_id_from_hir_id(id);
 978     let predicates = fcx.tcx.predicates_of(def_id).predicates
 979         .iter()
 980         .map(|(p, _)| *p)
 981         .collect();
 982     // Check elaborated bounds
 983     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
 984
 985     for pred in implied_obligations {
 986         // Match the existing behavior.
 987         if pred.is_global() && !pred.has_late_bound_regions() {
 988             let pred = fcx.normalize_associated_types_in(span, &pred);
 989             let obligation = traits::Obligation::new(
 990                 traits::ObligationCause::new(
 991                     span,
 992                     id,
 993                     traits::TrivialBound,
 994                 ),
 995                 empty_env,
 996                 pred,
 997             );
 998             fcx.register_predicate(obligation);
 999         }
1000     }
1001
1002     fcx.select_all_obligations_or_error();
1003 }
1004
1005 pub struct CheckTypeWellFormedVisitor<'a, 'tcx: 'a> {
1006     tcx: TyCtxt<'a, 'tcx, 'tcx>,
1007 }
1008
1009 impl<'a, 'gcx> CheckTypeWellFormedVisitor<'a, 'gcx> {
1010     pub fn new(tcx: TyCtxt<'a, 'gcx, 'gcx>)
1011                -> CheckTypeWellFormedVisitor<'a, 'gcx> {
1012         CheckTypeWellFormedVisitor {
1013             tcx,
1014         }
1015     }
1016 }
1017
1018 impl<'a, 'tcx> ItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'a, 'tcx> {
1019     fn visit_item(&mut self, i: &'tcx hir::Item) {
1020         debug!("visit_item: {:?}", i);
1021         let def_id = self.tcx.hir().local_def_id(i.id);
1022         self.tcx.ensure().check_item_well_formed(def_id);
1023     }
1024
1025     fn visit_trait_item(&mut self, trait_item: &'tcx hir::TraitItem) {
1026         debug!("visit_trait_item: {:?}", trait_item);
1027         let def_id = self.tcx.hir().local_def_id_from_hir_id(trait_item.hir_id);
1028         self.tcx.ensure().check_trait_item_well_formed(def_id);
1029     }
1030
1031     fn visit_impl_item(&mut self, impl_item: &'tcx hir::ImplItem) {
1032         debug!("visit_impl_item: {:?}", impl_item);
1033         let def_id = self.tcx.hir().local_def_id_from_hir_id(impl_item.hir_id);
1034         self.tcx.ensure().check_impl_item_well_formed(def_id);
1035     }
1036 }
1037
1038 ///////////////////////////////////////////////////////////////////////////
1039 // ADT
1040
1041 struct AdtVariant<'tcx> {
1042     fields: Vec<AdtField<'tcx>>,
1043 }
1044
1045 struct AdtField<'tcx> {
1046     ty: Ty<'tcx>,
1047     span: Span,
1048 }
1049
1050 impl<'a, 'gcx, 'tcx> FnCtxt<'a, 'gcx, 'tcx> {
1051     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1052         let fields = struct_def.fields().iter().map(|field| {
1053             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.id));
1054             let field_ty = self.normalize_associated_types_in(field.span,
1055                                                               &field_ty);
1056             AdtField { ty: field_ty, span: field.span }
1057         })
1058         .collect();
1059         AdtVariant { fields }
1060     }
1061
1062     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1063         enum_def.variants.iter()
1064             .map(|variant| self.non_enum_variant(&variant.node.data))
1065             .collect()
1066     }
1067
1068     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1069         match self.tcx.impl_trait_ref(impl_def_id) {
1070             Some(ref trait_ref) => {
1071                 // Trait impl: take implied bounds from all types that
1072                 // appear in the trait reference.
1073                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1074                 trait_ref.substs.types().collect()
1075             }
1076
1077             None => {
1078                 // Inherent impl: take implied bounds from the `self` type.
1079                 let self_ty = self.tcx.type_of(impl_def_id);
1080                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1081                 vec![self_ty]
1082             }
1083         }
1084     }
1085 }
1086
1087 fn error_392<'a, 'tcx>(tcx: TyCtxt<'a, 'tcx, 'tcx>, span: Span, param_name: ast::Name)
1088                        -> DiagnosticBuilder<'tcx> {
1089     let mut err = struct_span_err!(tcx.sess, span, E0392,
1090                   "parameter `{}` is never used", param_name);
1091     err.span_label(span, "unused type parameter");
1092     err
1093 }
1094
1095 fn error_194(tcx: TyCtxt<'_, '_, '_>, span: Span, trait_decl_span: Span, name: &str) {
1096     struct_span_err!(tcx.sess, span, E0194,
1097                      "type parameter `{}` shadows another type parameter of the same name",
1098                      name)
1099         .span_label(span, "shadows another type parameter")
1100         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1101         .emit();
1102 }