src/librustc_typeck/check/wfcheck.rs

   1 use crate::check::{Inherited, FnCtxt};
   2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
   3
   4 use crate::hir::def_id::DefId;
   5 use rustc::traits::{self, ObligationCauseCode};
   6 use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind, TypeFoldable, ToPredicate};
   7 use rustc::ty::subst::{Subst, InternalSubsts};
   8 use rustc::util::nodemap::{FxHashSet, FxHashMap};
   9 use rustc::mir::interpret::ConstValue;
  10 use rustc::middle::lang_items;
  11 use rustc::infer::opaque_types::may_define_opaque_type;
  12
  13 use syntax::ast;
  14 use syntax::feature_gate::{self, GateIssue};
  15 use syntax_pos::Span;
  16 use syntax::symbol::sym;
  17 use errors::{DiagnosticBuilder, DiagnosticId};
  18
  19 use rustc::hir::itemlikevisit::ParItemLikeVisitor;
  20 use rustc::hir;
  21
  22 /// Helper type of a temporary returned by `.for_item(...)`.
  23 /// This is necessary because we can't write the following bound:
  24 ///
  25 /// ```rust
  26 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
  27 /// ```
  28 struct CheckWfFcxBuilder<'tcx> {
  29     inherited: super::InheritedBuilder<'tcx>,
  30     id: hir::HirId,
  31     span: Span,
  32     param_env: ty::ParamEnv<'tcx>,
  33 }
  34
  35 impl<'tcx> CheckWfFcxBuilder<'tcx> {
  36     fn with_fcx<F>(&mut self, f: F)
  37     where
  38         F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
  39     {
  40         let id = self.id;
  41         let span = self.span;
  42         let param_env = self.param_env;
  43         self.inherited.enter(|inh| {
  44             let fcx = FnCtxt::new(&inh, param_env, id);
  45             if !inh.tcx.features().trivial_bounds {
  46                 // As predicates are cached rather than obligations, this
  47                 // needsto be called first so that they are checked with an
  48                 // empty `param_env`.
  49                 check_false_global_bounds(&fcx, span, id);
  50             }
  51             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  52             fcx.select_all_obligations_or_error();
  53             fcx.regionck_item(id, span, &wf_tys);
  54         });
  55     }
  56 }
  57
  58 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  59 /// well-formed, meaning that they do not require any constraints not declared in the struct
  60 /// definition itself. For example, this definition would be illegal:
  61 ///
  62 /// ```rust
  63 /// struct Ref<'a, T> { x: &'a T }
  64 /// ```
  65 ///
  66 /// because the type did not declare that `T:'a`.
  67 ///
  68 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  69 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  70 /// the types first.
  71 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: DefId) {
  72     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  73     let item = tcx.hir().expect_item(hir_id);
  74
  75     debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
  76            item.hir_id,
  77            tcx.def_path_str(def_id));
  78
  79     match item.node {
  80         // Right now we check that every default trait implementation
  81         // has an implementation of itself. Basically, a case like:
  82         //
  83         //     impl Trait for T {}
  84         //
  85         // has a requirement of `T: Trait` which was required for default
  86         // method implementations. Although this could be improved now that
  87         // there's a better infrastructure in place for this, it's being left
  88         // for a follow-up work.
  89         //
  90         // Since there's such a requirement, we need to check *just* positive
  91         // implementations, otherwise things like:
  92         //
  93         //     impl !Send for T {}
  94         //
  95         // won't be allowed unless there's an *explicit* implementation of `Send`
  96         // for `T`
  97         hir::ItemKind::Impl(_, _, defaultness, _, ref trait_ref, ref self_ty, _) => {
  98             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
  99                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 100             let polarity = tcx.impl_polarity(def_id);
 101             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 102                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 103             }
 104             match polarity {
 105                 ty::ImplPolarity::Positive => {
 106                     check_impl(tcx, item, self_ty, trait_ref);
 107                 }
 108                 ty::ImplPolarity::Negative => {
 109                     // FIXME(#27579): what amount of WF checking do we need for neg impls?
 110                     if trait_ref.is_some() && !is_auto {
 111                         span_err!(tcx.sess, item.span, E0192,
 112                                   "negative impls are only allowed for \
 113                                    auto traits (e.g., `Send` and `Sync`)")
 114                     }
 115                 }
 116                 ty::ImplPolarity::Reservation => {
 117                     // FIXME: what amount of WF checking do we need for reservation impls?
 118                 }
 119             }
 120         }
 121         hir::ItemKind::Fn(..) => {
 122             check_item_fn(tcx, item);
 123         }
 124         hir::ItemKind::Static(ref ty, ..) => {
 125             check_item_type(tcx, item.hir_id, ty.span, false);
 126         }
 127         hir::ItemKind::Const(ref ty, ..) => {
 128             check_item_type(tcx, item.hir_id, ty.span, false);
 129         }
 130         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 131             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 132                 check_item_type(tcx, it.hir_id, ty.span, true);
 133             }
 134         },
 135         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 136             check_type_defn(tcx, item, false, |fcx| {
 137                 vec![fcx.non_enum_variant(struct_def)]
 138             });
 139
 140             check_variances_for_type_defn(tcx, item, ast_generics);
 141         }
 142         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 143             check_type_defn(tcx, item, true, |fcx| {
 144                 vec![fcx.non_enum_variant(struct_def)]
 145             });
 146
 147             check_variances_for_type_defn(tcx, item, ast_generics);
 148         }
 149         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 150             check_type_defn(tcx, item, true, |fcx| {
 151                 fcx.enum_variants(enum_def)
 152             });
 153
 154             check_variances_for_type_defn(tcx, item, ast_generics);
 155         }
 156         hir::ItemKind::Trait(..) => {
 157             check_trait(tcx, item);
 158         }
 159         hir::ItemKind::TraitAlias(..) => {
 160             check_trait(tcx, item);
 161         }
 162         _ => {}
 163     }
 164 }
 165
 166 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: DefId) {
 167     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 168     let trait_item = tcx.hir().expect_trait_item(hir_id);
 169
 170     let method_sig = match trait_item.kind {
 171         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 172         _ => None
 173     };
 174     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 175 }
 176
 177 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: DefId) {
 178     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 179     let impl_item = tcx.hir().expect_impl_item(hir_id);
 180
 181     let method_sig = match impl_item.kind {
 182         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 183         _ => None
 184     };
 185     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 186 }
 187
 188 fn check_associated_item(
 189     tcx: TyCtxt<'_>,
 190     item_id: hir::HirId,
 191     span: Span,
 192     sig_if_method: Option<&hir::MethodSig>,
 193 ) {
 194     debug!("check_associated_item: {:?}", item_id);
 195
 196     let code = ObligationCauseCode::MiscObligation;
 197     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 198         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
 199
 200         let (mut implied_bounds, self_ty) = match item.container {
 201             ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
 202             ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 203                                           fcx.tcx.type_of(def_id))
 204         };
 205
 206         match item.kind {
 207             ty::AssocKind::Const => {
 208                 let ty = fcx.tcx.type_of(item.def_id);
 209                 let ty = fcx.normalize_associated_types_in(span, &ty);
 210                 fcx.register_wf_obligation(ty, span, code.clone());
 211             }
 212             ty::AssocKind::Method => {
 213                 let sig = fcx.tcx.fn_sig(item.def_id);
 214                 let sig = fcx.normalize_associated_types_in(span, &sig);
 215                 check_fn_or_method(tcx, fcx, span, sig,
 216                                    item.def_id, &mut implied_bounds);
 217                 let sig_if_method = sig_if_method.expect("bad signature for method");
 218                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 219             }
 220             ty::AssocKind::Type => {
 221                 if item.defaultness.has_value() {
 222                     let ty = fcx.tcx.type_of(item.def_id);
 223                     let ty = fcx.normalize_associated_types_in(span, &ty);
 224                     fcx.register_wf_obligation(ty, span, code.clone());
 225                 }
 226             }
 227             ty::AssocKind::OpaqueTy => {
 228                 // Do nothing: opaque types check themselves.
 229             }
 230         }
 231
 232         implied_bounds
 233     })
 234 }
 235
 236 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item) -> CheckWfFcxBuilder<'tcx> {
 237     for_id(tcx, item.hir_id, item.span)
 238 }
 239
 240 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
 241     let def_id = tcx.hir().local_def_id(id);
 242     CheckWfFcxBuilder {
 243         inherited: Inherited::build(tcx, def_id),
 244         id,
 245         span,
 246         param_env: tcx.param_env(def_id),
 247     }
 248 }
 249
 250 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 251 fn check_type_defn<'tcx, F>(
 252     tcx: TyCtxt<'tcx>,
 253     item: &hir::Item,
 254     all_sized: bool,
 255     mut lookup_fields: F,
 256 ) where
 257     F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
 258 {
 259     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 260         let variants = lookup_fields(fcx);
 261         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 262         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 263
 264         for variant in &variants {
 265             // For DST, or when drop needs to copy things around, all
 266             // intermediate types must be sized.
 267             let needs_drop_copy = || {
 268                 packed && {
 269                     let ty = variant.fields.last().unwrap().ty;
 270                     let ty = fcx.tcx.erase_regions(&ty);
 271                     if ty.has_local_value() {
 272                             fcx_tcx.sess.delay_span_bug(
 273                                 item.span, &format!("inference variables in {:?}", ty));
 274                             // Just treat unresolved type expression as if it needs drop.
 275                             true
 276                     } else {
 277                         ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
 278                     }
 279                 }
 280             };
 281             let all_sized =
 282                 all_sized ||
 283                 variant.fields.is_empty() ||
 284                 needs_drop_copy();
 285             let unsized_len = if all_sized {
 286                 0
 287             } else {
 288                 1
 289             };
 290             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 291                 .iter()
 292                 .enumerate()
 293             {
 294                 let last = idx == variant.fields.len() - 1;
 295                 fcx.register_bound(
 296                     field.ty,
 297                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
 298                     traits::ObligationCause::new(
 299                         field.span,
 300                         fcx.body_id,
 301                         traits::FieldSized {
 302                             adt_kind: match item.node.adt_kind() {
 303                                 Some(i) => i,
 304                                 None => bug!(),
 305                             },
 306                             last
 307                         }
 308                     )
 309                 );
 310             }
 311
 312             // All field types must be well-formed.
 313             for field in &variant.fields {
 314                 fcx.register_wf_obligation(field.ty, field.span,
 315                     ObligationCauseCode::MiscObligation)
 316             }
 317         }
 318
 319         check_where_clauses(tcx, fcx, item.span, def_id, None);
 320
 321         // No implied bounds in a struct definition.
 322         vec![]
 323     });
 324 }
 325
 326 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item) {
 327     debug!("check_trait: {:?}", item.hir_id);
 328
 329     let trait_def_id = tcx.hir().local_def_id(item.hir_id);
 330
 331     let trait_def = tcx.trait_def(trait_def_id);
 332     if trait_def.is_marker {
 333         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 334             struct_span_err!(
 335                 tcx.sess,
 336                 tcx.def_span(*associated_def_id),
 337                 E0714,
 338                 "marker traits cannot have associated items",
 339             ).emit();
 340         }
 341     }
 342
 343     for_item(tcx, item).with_fcx(|fcx, _| {
 344         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 345         vec![]
 346     });
 347 }
 348
 349 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item) {
 350     for_item(tcx, item).with_fcx(|fcx, tcx| {
 351         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 352         let sig = fcx.tcx.fn_sig(def_id);
 353         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 354         let mut implied_bounds = vec![];
 355         check_fn_or_method(tcx, fcx, item.span, sig,
 356                            def_id, &mut implied_bounds);
 357         implied_bounds
 358     })
 359 }
 360
 361 fn check_item_type(
 362     tcx: TyCtxt<'_>,
 363     item_id: hir::HirId,
 364     ty_span: Span,
 365     allow_foreign_ty: bool,
 366 ) {
 367     debug!("check_item_type: {:?}", item_id);
 368
 369     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 370         let ty = gcx.type_of(gcx.hir().local_def_id(item_id));
 371         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 372
 373         let mut forbid_unsized = true;
 374         if allow_foreign_ty {
 375             let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
 376             if let ty::Foreign(_) = tail.kind {
 377                 forbid_unsized = false;
 378             }
 379         }
 380
 381         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 382         if forbid_unsized {
 383             fcx.register_bound(
 384                 item_ty,
 385                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
 386                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 387             );
 388         }
 389
 390         // No implied bounds in a const, etc.
 391         vec![]
 392     });
 393 }
 394
 395 fn check_impl<'tcx>(
 396     tcx: TyCtxt<'tcx>,
 397     item: &hir::Item,
 398     ast_self_ty: &hir::Ty,
 399     ast_trait_ref: &Option<hir::TraitRef>,
 400 ) {
 401     debug!("check_impl: {:?}", item);
 402
 403     for_item(tcx, item).with_fcx(|fcx, tcx| {
 404         let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 405
 406         match *ast_trait_ref {
 407             Some(ref ast_trait_ref) => {
 408                 // `#[rustc_reservation_impl]` impls are not real impls and
 409                 // therefore don't need to be WF (the trait's `Self: Trait` predicate
 410                 // won't hold).
 411                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 412                 let trait_ref =
 413                     fcx.normalize_associated_types_in(
 414                         ast_trait_ref.path.span, &trait_ref);
 415                 let obligations =
 416                     ty::wf::trait_obligations(fcx,
 417                                               fcx.param_env,
 418                                               fcx.body_id,
 419                                               &trait_ref,
 420                                               ast_trait_ref.path.span);
 421                 for obligation in obligations {
 422                     fcx.register_predicate(obligation);
 423                 }
 424             }
 425             None => {
 426                 let self_ty = fcx.tcx.type_of(item_def_id);
 427                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 428                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 429                     ObligationCauseCode::MiscObligation);
 430             }
 431         }
 432
 433         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 434
 435         fcx.impl_implied_bounds(item_def_id, item.span)
 436     });
 437 }
 438
 439 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 440 fn check_where_clauses<'tcx, 'fcx>(
 441     tcx: TyCtxt<'tcx>,
 442     fcx: &FnCtxt<'fcx, 'tcx>,
 443     span: Span,
 444     def_id: DefId,
 445     return_ty: Option<Ty<'tcx>>,
 446 ) {
 447     debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
 448
 449     let predicates = fcx.tcx.predicates_of(def_id);
 450     let generics = tcx.generics_of(def_id);
 451
 452     let is_our_default = |def: &ty::GenericParamDef| {
 453         match def.kind {
 454             GenericParamDefKind::Type { has_default, .. } => {
 455                 has_default && def.index >= generics.parent_count as u32
 456             }
 457             _ => unreachable!()
 458         }
 459     };
 460
 461     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 462     // For example, this forbids the declaration:
 463     //
 464     //     struct Foo<T = Vec<[u32]>> { .. }
 465     //
 466     // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 467     for param in &generics.params {
 468         if let GenericParamDefKind::Type { .. } = param.kind {
 469             if is_our_default(&param) {
 470                 let ty = fcx.tcx.type_of(param.def_id);
 471                 // Ignore dependent defaults -- that is, where the default of one type
 472                 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
 473                 // be sure if it will error or not as user might always specify the other.
 474                 if !ty.needs_subst() {
 475                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 476                         ObligationCauseCode::MiscObligation);
 477                 }
 478             }
 479         }
 480     }
 481
 482     // Check that trait predicates are WF when params are substituted by their defaults.
 483     // We don't want to overly constrain the predicates that may be written but we want to
 484     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 485     // Therefore we check if a predicate which contains a single type param
 486     // with a concrete default is WF with that default substituted.
 487     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 488     //
 489     // First we build the defaulted substitution.
 490     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 491         match param.kind {
 492             GenericParamDefKind::Lifetime => {
 493                 // All regions are identity.
 494                 fcx.tcx.mk_param_from_def(param)
 495             }
 496
 497             GenericParamDefKind::Type { .. } => {
 498                 // If the param has a default, ...
 499                 if is_our_default(param) {
 500                     let default_ty = fcx.tcx.type_of(param.def_id);
 501                     // ... and it's not a dependent default, ...
 502                     if !default_ty.needs_subst() {
 503                         // ... then substitute it with the default.
 504                         return default_ty.into();
 505                     }
 506                 }
 507                 // Mark unwanted params as error.
 508                 fcx.tcx.types.err.into()
 509             }
 510
 511             GenericParamDefKind::Const => {
 512                 // FIXME(const_generics:defaults)
 513                 fcx.tcx.consts.err.into()
 514             }
 515         }
 516     });
 517
 518     // Now we build the substituted predicates.
 519     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, sp)| {
 520         #[derive(Default)]
 521         struct CountParams { params: FxHashSet<u32> }
 522         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 523             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 524                 if let ty::Param(param) = t.kind {
 525                     self.params.insert(param.index);
 526                 }
 527                 t.super_visit_with(self)
 528             }
 529
 530             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 531                 true
 532             }
 533
 534             fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 535                 if let ConstValue::Param(param) = c.val {
 536                     self.params.insert(param.index);
 537                 }
 538                 c.super_visit_with(self)
 539             }
 540         }
 541         let mut param_count = CountParams::default();
 542         let has_region = pred.visit_with(&mut param_count);
 543         let substituted_pred = pred.subst(fcx.tcx, substs);
 544         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 545         // or preds with multiple params.
 546         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 547             None
 548         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 549             // Avoid duplication of predicates that contain no parameters, for example.
 550             None
 551         } else {
 552             Some((substituted_pred, sp))
 553         }
 554     }).map(|(pred, sp)| {
 555         // Convert each of those into an obligation. So if you have
 556         // something like `struct Foo<T: Copy = String>`, we would
 557         // take that predicate `T: Copy`, substitute to `String: Copy`
 558         // (actually that happens in the previous `flat_map` call),
 559         // and then try to prove it (in this case, we'll fail).
 560         //
 561         // Note the subtle difference from how we handle `predicates`
 562         // below: there, we are not trying to prove those predicates
 563         // to be *true* but merely *well-formed*.
 564         let pred = fcx.normalize_associated_types_in(sp, &pred);
 565         let cause = traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
 566         traits::Obligation::new(cause, fcx.param_env, pred)
 567     });
 568
 569     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 570
 571     if let Some(return_ty) = return_ty {
 572         predicates.predicates.extend(check_opaque_types(tcx, fcx, def_id, span, return_ty));
 573     }
 574
 575     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 576
 577     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 578     let wf_obligations =
 579         predicates.predicates
 580                     .iter()
 581                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 582                                                                 fcx.param_env,
 583                                                                 fcx.body_id,
 584                                                                 p,
 585                                                                 span));
 586
 587     for obligation in wf_obligations.chain(default_obligations) {
 588         debug!("next obligation cause: {:?}", obligation.cause);
 589         fcx.register_predicate(obligation);
 590     }
 591 }
 592
 593 fn check_fn_or_method<'fcx, 'tcx>(
 594     tcx: TyCtxt<'tcx>,
 595     fcx: &FnCtxt<'fcx, 'tcx>,
 596     span: Span,
 597     sig: ty::PolyFnSig<'tcx>,
 598     def_id: DefId,
 599     implied_bounds: &mut Vec<Ty<'tcx>>,
 600 ) {
 601     let sig = fcx.normalize_associated_types_in(span, &sig);
 602     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 603
 604     for input_ty in sig.inputs() {
 605         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 606     }
 607     implied_bounds.extend(sig.inputs());
 608
 609     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::ReturnType);
 610
 611     // FIXME(#25759) return types should not be implied bounds
 612     implied_bounds.push(sig.output());
 613
 614     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 615 }
 616
 617 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
 618 /// laid for "higher-order pattern unification".
 619 /// This ensures that inference is tractable.
 620 /// In particular, definitions of opaque types can only use other generics as arguments,
 621 /// and they cannot repeat an argument. Example:
 622 ///
 623 /// ```rust
 624 /// type Foo<A, B> = impl Bar<A, B>;
 625 ///
 626 /// // Okay -- `Foo` is applied to two distinct, generic types.
 627 /// fn a<T, U>() -> Foo<T, U> { .. }
 628 ///
 629 /// // Not okay -- `Foo` is applied to `T` twice.
 630 /// fn b<T>() -> Foo<T, T> { .. }
 631 ///
 632 /// // Not okay -- `Foo` is applied to a non-generic type.
 633 /// fn b<T>() -> Foo<T, u32> { .. }
 634 /// ```
 635 ///
 636 fn check_opaque_types<'fcx, 'tcx>(
 637     tcx: TyCtxt<'tcx>,
 638     fcx: &FnCtxt<'fcx, 'tcx>,
 639     fn_def_id: DefId,
 640     span: Span,
 641     ty: Ty<'tcx>,
 642 ) -> Vec<ty::Predicate<'tcx>> {
 643     trace!("check_opaque_types(ty={:?})", ty);
 644     let mut substituted_predicates = Vec::new();
 645     ty.fold_with(&mut ty::fold::BottomUpFolder {
 646         tcx: fcx.tcx,
 647         ty_op: |ty| {
 648             if let ty::Opaque(def_id, substs) = ty.kind {
 649                 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
 650                 let generics = tcx.generics_of(def_id);
 651                 // Only check named `impl Trait` types defined in this crate.
 652                 if generics.parent.is_none() && def_id.is_local() {
 653                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 654                     if may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
 655                         trace!("check_opaque_types: may define, generics={:#?}", generics);
 656                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 657                         for (subst, param) in substs.iter().zip(&generics.params) {
 658                             match subst.unpack() {
 659                                 ty::subst::GenericArgKind::Type(ty) => match ty.kind {
 660                                     ty::Param(..) => {}
 661                                     // Prevent `fn foo() -> Foo<u32>` from being defining.
 662                                     _ => {
 663                                         tcx.sess
 664                                             .struct_span_err(
 665                                                 span,
 666                                                 "non-defining opaque type use \
 667                                                  in defining scope",
 668                                             )
 669                                             .span_note(
 670                                                 tcx.def_span(param.def_id),
 671                                                 &format!(
 672                                                     "used non-generic type {} for \
 673                                                      generic parameter",
 674                                                     ty,
 675                                                 ),
 676                                             )
 677                                             .emit();
 678                                     }
 679                                 }
 680
 681                                 ty::subst::GenericArgKind::Lifetime(region) => {
 682                                     let param_span = tcx.def_span(param.def_id);
 683                                     if let ty::ReStatic = region {
 684                                         tcx
 685                                             .sess
 686                                             .struct_span_err(
 687                                                 span,
 688                                                 "non-defining opaque type use \
 689                                                     in defining scope",
 690                                             )
 691                                             .span_label(
 692                                                 param_span,
 693                                                 "cannot use static lifetime; use a bound lifetime \
 694                                                 instead or remove the lifetime parameter from the \
 695                                                 opaque type",
 696                                             )
 697                                             .emit();
 698                                     } else {
 699                                         seen.entry(region).or_default().push(param_span);
 700                                     }
 701                                 }
 702
 703                                 ty::subst::GenericArgKind::Const(ct) => match ct.val {
 704                                     ConstValue::Param(_) => {}
 705                                     _ => {
 706                                         tcx.sess
 707                                             .struct_span_err(
 708                                                 span,
 709                                                 "non-defining opaque type use \
 710                                                 in defining scope",
 711                                             )
 712                                             .span_note(
 713                                                 tcx.def_span(param.def_id),
 714                                                 &format!(
 715                                                     "used non-generic const {} for \
 716                                                     generic parameter",
 717                                                     ty,
 718                                                 ),
 719                                             )
 720                                             .emit();
 721                                     }
 722                                 }
 723                             } // match subst
 724                         } // for (subst, param)
 725                         for (_, spans) in seen {
 726                             if spans.len() > 1 {
 727                                 tcx
 728                                     .sess
 729                                     .struct_span_err(
 730                                         span,
 731                                         "non-defining opaque type use \
 732                                             in defining scope",
 733                                     ).
 734                                     span_note(
 735                                         spans,
 736                                         "lifetime used multiple times",
 737                                     )
 738                                     .emit();
 739                             }
 740                         }
 741                     } // if may_define_opaque_type
 742
 743                     // Now register the bounds on the parameters of the opaque type
 744                     // so the parameters given by the function need to fulfill them.
 745                     //
 746                     //     type Foo<T: Bar> = impl Baz + 'static;
 747                     //     fn foo<U>() -> Foo<U> { .. *}
 748                     //
 749                     // becomes
 750                     //
 751                     //     type Foo<T: Bar> = impl Baz + 'static;
 752                     //     fn foo<U: Bar>() -> Foo<U> { .. *}
 753                     let predicates = tcx.predicates_of(def_id);
 754                     trace!(
 755                         "check_opaque_types: may define, predicates={:#?}",
 756                         predicates,
 757                     );
 758                     for &(pred, _) in predicates.predicates.iter() {
 759                         let substituted_pred = pred.subst(fcx.tcx, substs);
 760                         // Avoid duplication of predicates that contain no parameters, for example.
 761                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 762                             substituted_predicates.push(substituted_pred);
 763                         }
 764                     }
 765                 } // if is_named_opaque_type
 766             } // if let Opaque
 767             ty
 768         },
 769         lt_op: |lt| lt,
 770         ct_op: |ct| ct,
 771     });
 772     substituted_predicates
 773 }
 774
 775 const HELP_FOR_SELF_TYPE: &str =
 776     "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
 777      `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
 778      of the previous types except `Self`)";
 779
 780 fn check_method_receiver<'fcx, 'tcx>(
 781     fcx: &FnCtxt<'fcx, 'tcx>,
 782     method_sig: &hir::MethodSig,
 783     method: &ty::AssocItem,
 784     self_ty: Ty<'tcx>,
 785 ) {
 786     // Check that the method has a valid receiver type, given the type `Self`.
 787     debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
 788
 789     if !method.method_has_self_argument {
 790         return;
 791     }
 792
 793     let span = method_sig.decl.inputs[0].span;
 794
 795     let sig = fcx.tcx.fn_sig(method.def_id);
 796     let sig = fcx.normalize_associated_types_in(span, &sig);
 797     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 798
 799     debug!("check_method_receiver: sig={:?}", sig);
 800
 801     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 802     let self_ty = fcx.tcx.liberate_late_bound_regions(
 803         method.def_id,
 804         &ty::Binder::bind(self_ty)
 805     );
 806
 807     let receiver_ty = sig.inputs()[0];
 808
 809     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 810     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 811         method.def_id,
 812         &ty::Binder::bind(receiver_ty)
 813     );
 814
 815     if fcx.tcx.features().arbitrary_self_types {
 816         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 817             // Report error; `arbitrary_self_types` was enabled.
 818             e0307(fcx, span, receiver_ty);
 819         }
 820     } else {
 821         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 822             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 823                 // Report error; would have worked with `arbitrary_self_types`.
 824                 feature_gate::feature_err(
 825                     &fcx.tcx.sess.parse_sess,
 826                     sym::arbitrary_self_types,
 827                     span,
 828                     GateIssue::Language,
 829                     &format!(
 830                         "`{}` cannot be used as the type of `self` without \
 831                             the `arbitrary_self_types` feature",
 832                         receiver_ty,
 833                     ),
 834                 ).help(HELP_FOR_SELF_TYPE)
 835                 .emit();
 836             } else {
 837                 // Report error; would not have worked with `arbitrary_self_types`.
 838                 e0307(fcx, span, receiver_ty);
 839             }
 840         }
 841     }
 842 }
 843
 844 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
 845     fcx.tcx.sess.diagnostic().struct_span_err(
 846         span,
 847         &format!("invalid `self` parameter type: {:?}", receiver_ty)
 848     ).note("type of `self` must be `Self` or a type that dereferences to it")
 849     .help(HELP_FOR_SELF_TYPE)
 850     .code(DiagnosticId::Error("E0307".into()))
 851     .emit();
 852 }
 853
 854 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 855 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 856 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 857 /// strict: `receiver_ty` must implement `Receiver` and directly implement
 858 /// `Deref<Target = self_ty>`.
 859 ///
 860 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 861 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 862 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 863 fn receiver_is_valid<'fcx, 'tcx>(
 864     fcx: &FnCtxt<'fcx, 'tcx>,
 865     span: Span,
 866     receiver_ty: Ty<'tcx>,
 867     self_ty: Ty<'tcx>,
 868     arbitrary_self_types_enabled: bool,
 869 ) -> bool {
 870     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 871
 872     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 873
 874     // `self: Self` is always valid.
 875     if can_eq_self(receiver_ty) {
 876         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 877             err.emit();
 878         }
 879         return true
 880     }
 881
 882     let mut autoderef = fcx.autoderef(span, receiver_ty);
 883
 884     // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
 885     if arbitrary_self_types_enabled {
 886         autoderef = autoderef.include_raw_pointers();
 887     }
 888
 889     // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
 890     autoderef.next();
 891
 892     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
 893     loop {
 894         if let Some((potential_self_ty, _)) = autoderef.next() {
 895             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 896                 potential_self_ty, self_ty);
 897
 898             if can_eq_self(potential_self_ty) {
 899                 autoderef.finalize(fcx);
 900
 901                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 902                     &cause, self_ty, potential_self_ty
 903                 ) {
 904                     err.emit();
 905                 }
 906
 907                 break
 908             }
 909         } else {
 910             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 911                 receiver_ty, self_ty);
 912             // If he receiver already has errors reported due to it, consider it valid to avoid
 913             // unecessary errors (#58712).
 914             return receiver_ty.references_error();
 915         }
 916
 917         // Without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 918         // `self_ty`. Enforce this by only doing one iteration of the loop.
 919         if !arbitrary_self_types_enabled {
 920             return false
 921         }
 922     }
 923
 924     // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
 925     if !arbitrary_self_types_enabled {
 926         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 927             Some(did) => did,
 928             None => {
 929                 debug!("receiver_is_valid: missing Receiver trait");
 930                 return false
 931             }
 932         };
 933
 934         let trait_ref = ty::TraitRef{
 935             def_id: trait_def_id,
 936             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 937         };
 938
 939         let obligation = traits::Obligation::new(
 940             cause,
 941             fcx.param_env,
 942             trait_ref.to_predicate()
 943         );
 944
 945         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 946             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 947                 receiver_ty);
 948             return false
 949         }
 950     }
 951
 952     true
 953 }
 954
 955 fn check_variances_for_type_defn<'tcx>(
 956     tcx: TyCtxt<'tcx>,
 957     item: &hir::Item,
 958     hir_generics: &hir::Generics,
 959 ) {
 960     let item_def_id = tcx.hir().local_def_id(item.hir_id);
 961     let ty = tcx.type_of(item_def_id);
 962     if tcx.has_error_field(ty) {
 963         return;
 964     }
 965
 966     let ty_predicates = tcx.predicates_of(item_def_id);
 967     assert_eq!(ty_predicates.parent, None);
 968     let variances = tcx.variances_of(item_def_id);
 969
 970     let mut constrained_parameters: FxHashSet<_> =
 971         variances.iter().enumerate()
 972                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 973                         .map(|(index, _)| Parameter(index as u32))
 974                         .collect();
 975
 976     identify_constrained_generic_params(
 977         tcx,
 978         &ty_predicates,
 979         None,
 980         &mut constrained_parameters,
 981     );
 982
 983     for (index, _) in variances.iter().enumerate() {
 984         if constrained_parameters.contains(&Parameter(index as u32)) {
 985             continue;
 986         }
 987
 988         let param = &hir_generics.params[index];
 989
 990         match param.name {
 991             hir::ParamName::Error => { }
 992             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 993         }
 994     }
 995 }
 996
 997 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
 998     let mut err = error_392(tcx, span, param_name);
 999
1000     let suggested_marker_id = tcx.lang_items().phantom_data();
1001     // Help is available only in presence of lang items.
1002     if let Some(def_id) = suggested_marker_id {
1003         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
1004                           param_name,
1005                           tcx.def_path_str(def_id)));
1006     }
1007     err.emit();
1008 }
1009
1010 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1011 /// aren't true.
1012 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1013     let empty_env = ty::ParamEnv::empty();
1014
1015     let def_id = fcx.tcx.hir().local_def_id(id);
1016     let predicates = fcx.tcx.predicates_of(def_id).predicates
1017         .iter()
1018         .map(|(p, _)| *p)
1019         .collect();
1020     // Check elaborated bounds.
1021     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1022
1023     for pred in implied_obligations {
1024         // Match the existing behavior.
1025         if pred.is_global() && !pred.has_late_bound_regions() {
1026             let pred = fcx.normalize_associated_types_in(span, &pred);
1027             let obligation = traits::Obligation::new(
1028                 traits::ObligationCause::new(
1029                     span,
1030                     id,
1031                     traits::TrivialBound,
1032                 ),
1033                 empty_env,
1034                 pred,
1035             );
1036             fcx.register_predicate(obligation);
1037         }
1038     }
1039
1040     fcx.select_all_obligations_or_error();
1041 }
1042
1043 pub struct CheckTypeWellFormedVisitor<'tcx> {
1044     tcx: TyCtxt<'tcx>,
1045 }
1046
1047 impl CheckTypeWellFormedVisitor<'tcx> {
1048     pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1049         CheckTypeWellFormedVisitor {
1050             tcx,
1051         }
1052     }
1053 }
1054
1055 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1056     fn visit_item(&self, i: &'tcx hir::Item) {
1057         debug!("visit_item: {:?}", i);
1058         let def_id = self.tcx.hir().local_def_id(i.hir_id);
1059         self.tcx.ensure().check_item_well_formed(def_id);
1060     }
1061
1062     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem) {
1063         debug!("visit_trait_item: {:?}", trait_item);
1064         let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1065         self.tcx.ensure().check_trait_item_well_formed(def_id);
1066     }
1067
1068     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem) {
1069         debug!("visit_impl_item: {:?}", impl_item);
1070         let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1071         self.tcx.ensure().check_impl_item_well_formed(def_id);
1072     }
1073 }
1074
1075 ///////////////////////////////////////////////////////////////////////////
1076 // ADT
1077
1078 struct AdtVariant<'tcx> {
1079     fields: Vec<AdtField<'tcx>>,
1080 }
1081
1082 struct AdtField<'tcx> {
1083     ty: Ty<'tcx>,
1084     span: Span,
1085 }
1086
1087 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1088     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1089         let fields = struct_def.fields().iter().map(|field| {
1090             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1091             let field_ty = self.normalize_associated_types_in(field.span,
1092                                                               &field_ty);
1093             let field_ty = self.resolve_vars_if_possible(&field_ty);
1094             debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1095             AdtField { ty: field_ty, span: field.span }
1096         })
1097         .collect();
1098         AdtVariant { fields }
1099     }
1100
1101     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1102         enum_def.variants.iter()
1103             .map(|variant| self.non_enum_variant(&variant.data))
1104             .collect()
1105     }
1106
1107     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1108         match self.tcx.impl_trait_ref(impl_def_id) {
1109             Some(ref trait_ref) => {
1110                 // Trait impl: take implied bounds from all types that
1111                 // appear in the trait reference.
1112                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1113                 trait_ref.substs.types().collect()
1114             }
1115
1116             None => {
1117                 // Inherent impl: take implied bounds from the `self` type.
1118                 let self_ty = self.tcx.type_of(impl_def_id);
1119                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1120                 vec![self_ty]
1121             }
1122         }
1123     }
1124 }
1125
1126 fn error_392(
1127     tcx: TyCtxt<'_>,
1128     span: Span,
1129     param_name: ast::Name,
1130 ) -> DiagnosticBuilder<'_> {
1131     let mut err = struct_span_err!(tcx.sess, span, E0392,
1132                   "parameter `{}` is never used", param_name);
1133     err.span_label(span, "unused parameter");
1134     err
1135 }