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