src/librustc_typeck/check/wfcheck.rs

   1 use crate::check::{FnCtxt, Inherited};
   2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
   3
   4 use rustc::infer::opaque_types::may_define_opaque_type;
   5 use rustc::middle::lang_items;
   6 use rustc::session::parse::feature_err;
   7 use rustc::traits::{self, ObligationCause, ObligationCauseCode};
   8 use rustc::ty::subst::{InternalSubsts, Subst};
   9 use rustc::ty::{self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable};
  10 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  11 use rustc_errors::{struct_span_err, DiagnosticBuilder};
  12 use rustc_hir::def_id::DefId;
  13 use rustc_hir::ItemKind;
  14 use rustc_span::symbol::sym;
  15 use rustc_span::Span;
  16 use syntax::ast;
  17
  18 use rustc_hir as hir;
  19 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
  20
  21 /// Helper type of a temporary returned by `.for_item(...)`.
  22 /// This is necessary because we can't write the following bound:
  23 ///
  24 /// ```rust
  25 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
  26 /// ```
  27 struct CheckWfFcxBuilder<'tcx> {
  28     inherited: super::InheritedBuilder<'tcx>,
  29     id: hir::HirId,
  30     span: Span,
  31     param_env: ty::ParamEnv<'tcx>,
  32 }
  33
  34 impl<'tcx> CheckWfFcxBuilder<'tcx> {
  35     fn with_fcx<F>(&mut self, f: F)
  36     where
  37         F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
  38     {
  39         let id = self.id;
  40         let span = self.span;
  41         let param_env = self.param_env;
  42         self.inherited.enter(|inh| {
  43             let fcx = FnCtxt::new(&inh, param_env, id);
  44             if !inh.tcx.features().trivial_bounds {
  45                 // As predicates are cached rather than obligations, this
  46                 // needsto be called first so that they are checked with an
  47                 // empty `param_env`.
  48                 check_false_global_bounds(&fcx, span, id);
  49             }
  50             let wf_tys = f(&fcx, fcx.tcx);
  51             fcx.select_all_obligations_or_error();
  52             fcx.regionck_item(id, span, &wf_tys);
  53         });
  54     }
  55 }
  56
  57 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  58 /// well-formed, meaning that they do not require any constraints not declared in the struct
  59 /// definition itself. For example, this definition would be illegal:
  60 ///
  61 /// ```rust
  62 /// struct Ref<'a, T> { x: &'a T }
  63 /// ```
  64 ///
  65 /// because the type did not declare that `T:'a`.
  66 ///
  67 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  68 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  69 /// the types first.
  70 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: DefId) {
  71     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  72     let item = tcx.hir().expect_item(hir_id);
  73
  74     debug!(
  75         "check_item_well_formed(it.hir_id={:?}, it.name={})",
  76         item.hir_id,
  77         tcx.def_path_str(def_id)
  78     );
  79
  80     match item.kind {
  81         // Right now we check that every default trait implementation
  82         // has an implementation of itself. Basically, a case like:
  83         //
  84         //     impl Trait for T {}
  85         //
  86         // has a requirement of `T: Trait` which was required for default
  87         // method implementations. Although this could be improved now that
  88         // there's a better infrastructure in place for this, it's being left
  89         // for a follow-up work.
  90         //
  91         // Since there's such a requirement, we need to check *just* positive
  92         // implementations, otherwise things like:
  93         //
  94         //     impl !Send for T {}
  95         //
  96         // won't be allowed unless there's an *explicit* implementation of `Send`
  97         // for `T`
  98         hir::ItemKind::Impl { defaultness, ref of_trait, ref self_ty, .. } => {
  99             let is_auto = tcx
 100                 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
 101                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 102             let polarity = tcx.impl_polarity(def_id);
 103             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 104                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 105             }
 106             match polarity {
 107                 ty::ImplPolarity::Positive => {
 108                     check_impl(tcx, item, self_ty, of_trait);
 109                 }
 110                 ty::ImplPolarity::Negative => {
 111                     // FIXME(#27579): what amount of WF checking do we need for neg impls?
 112                     if of_trait.is_some() && !is_auto {
 113                         struct_span_err!(
 114                             tcx.sess,
 115                             item.span,
 116                             E0192,
 117                             "negative impls are only allowed for \
 118                                    auto traits (e.g., `Send` and `Sync`)"
 119                         )
 120                         .emit()
 121                     }
 122                 }
 123                 ty::ImplPolarity::Reservation => {
 124                     // FIXME: what amount of WF checking do we need for reservation impls?
 125                 }
 126             }
 127         }
 128         hir::ItemKind::Fn(..) => {
 129             check_item_fn(tcx, item);
 130         }
 131         hir::ItemKind::Static(ref ty, ..) => {
 132             check_item_type(tcx, item.hir_id, ty.span, false);
 133         }
 134         hir::ItemKind::Const(ref ty, ..) => {
 135             check_item_type(tcx, item.hir_id, ty.span, false);
 136         }
 137         hir::ItemKind::ForeignMod(ref module) => {
 138             for it in module.items.iter() {
 139                 if let hir::ForeignItemKind::Static(ref ty, ..) = it.kind {
 140                     check_item_type(tcx, it.hir_id, ty.span, true);
 141                 }
 142             }
 143         }
 144         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 145             check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
 146
 147             check_variances_for_type_defn(tcx, item, ast_generics);
 148         }
 149         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 150             check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
 151
 152             check_variances_for_type_defn(tcx, item, ast_generics);
 153         }
 154         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 155             check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
 156
 157             check_variances_for_type_defn(tcx, item, ast_generics);
 158         }
 159         hir::ItemKind::Trait(..) => {
 160             check_trait(tcx, item);
 161         }
 162         hir::ItemKind::TraitAlias(..) => {
 163             check_trait(tcx, item);
 164         }
 165         _ => {}
 166     }
 167 }
 168
 169 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: DefId) {
 170     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 171     let trait_item = tcx.hir().expect_trait_item(hir_id);
 172
 173     let method_sig = match trait_item.kind {
 174         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 175         _ => None,
 176     };
 177     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 178 }
 179
 180 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: DefId) {
 181     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 182     let impl_item = tcx.hir().expect_impl_item(hir_id);
 183
 184     let method_sig = match impl_item.kind {
 185         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 186         _ => None,
 187     };
 188
 189     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 190 }
 191
 192 fn check_associated_item(
 193     tcx: TyCtxt<'_>,
 194     item_id: hir::HirId,
 195     span: Span,
 196     sig_if_method: Option<&hir::FnSig<'_>>,
 197 ) {
 198     debug!("check_associated_item: {:?}", item_id);
 199
 200     let code = ObligationCauseCode::MiscObligation;
 201     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 202         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
 203
 204         let (mut implied_bounds, self_ty) = match item.container {
 205             ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
 206             ty::ImplContainer(def_id) => {
 207                 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
 208             }
 209         };
 210
 211         match item.kind {
 212             ty::AssocKind::Const => {
 213                 let ty = fcx.tcx.type_of(item.def_id);
 214                 let ty = fcx.normalize_associated_types_in(span, &ty);
 215                 fcx.register_wf_obligation(ty, span, code.clone());
 216             }
 217             ty::AssocKind::Method => {
 218                 let sig = fcx.tcx.fn_sig(item.def_id);
 219                 let sig = fcx.normalize_associated_types_in(span, &sig);
 220                 check_fn_or_method(tcx, fcx, span, sig, item.def_id, &mut implied_bounds);
 221                 let sig_if_method = sig_if_method.expect("bad signature for method");
 222                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 223             }
 224             ty::AssocKind::Type => {
 225                 if item.defaultness.has_value() {
 226                     let ty = fcx.tcx.type_of(item.def_id);
 227                     let ty = fcx.normalize_associated_types_in(span, &ty);
 228                     fcx.register_wf_obligation(ty, span, code.clone());
 229                 }
 230             }
 231             ty::AssocKind::OpaqueTy => {
 232                 // Do nothing: opaque types check themselves.
 233             }
 234         }
 235
 236         implied_bounds
 237     })
 238 }
 239
 240 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
 241     for_id(tcx, item.hir_id, item.span)
 242 }
 243
 244 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
 245     let def_id = tcx.hir().local_def_id(id);
 246     CheckWfFcxBuilder {
 247         inherited: Inherited::build(tcx, def_id),
 248         id,
 249         span,
 250         param_env: tcx.param_env(def_id),
 251     }
 252 }
 253
 254 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
 255     match kind {
 256         ItemKind::Struct(..) => Some(AdtKind::Struct),
 257         ItemKind::Union(..) => Some(AdtKind::Union),
 258         ItemKind::Enum(..) => Some(AdtKind::Enum),
 259         _ => None,
 260     }
 261 }
 262
 263 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 264 fn check_type_defn<'tcx, F>(
 265     tcx: TyCtxt<'tcx>,
 266     item: &hir::Item<'tcx>,
 267     all_sized: bool,
 268     mut lookup_fields: F,
 269 ) where
 270     F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
 271 {
 272     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 273         let variants = lookup_fields(fcx);
 274         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 275         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 276
 277         for variant in &variants {
 278             // For DST, or when drop needs to copy things around, all
 279             // intermediate types must be sized.
 280             let needs_drop_copy = || {
 281                 packed && {
 282                     let ty = variant.fields.last().unwrap().ty;
 283                     let ty = fcx.tcx.erase_regions(&ty);
 284                     if ty.has_local_value() {
 285                         fcx_tcx
 286                             .sess
 287                             .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
 288                         // Just treat unresolved type expression as if it needs drop.
 289                         true
 290                     } else {
 291                         ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
 292                     }
 293                 }
 294             };
 295             let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
 296             let unsized_len = if all_sized { 0 } else { 1 };
 297             for (idx, field) in
 298                 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
 299             {
 300                 let last = idx == variant.fields.len() - 1;
 301                 fcx.register_bound(
 302                     field.ty,
 303                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
 304                     traits::ObligationCause::new(
 305                         field.span,
 306                         fcx.body_id,
 307                         traits::FieldSized {
 308                             adt_kind: match item_adt_kind(&item.kind) {
 309                                 Some(i) => i,
 310                                 None => bug!(),
 311                             },
 312                             last,
 313                         },
 314                     ),
 315                 );
 316             }
 317
 318             // All field types must be well-formed.
 319             for field in &variant.fields {
 320                 fcx.register_wf_obligation(
 321                     field.ty,
 322                     field.span,
 323                     ObligationCauseCode::MiscObligation,
 324                 )
 325             }
 326         }
 327
 328         check_where_clauses(tcx, fcx, item.span, def_id, None);
 329
 330         // No implied bounds in a struct definition.
 331         vec![]
 332     });
 333 }
 334
 335 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
 336     debug!("check_trait: {:?}", item.hir_id);
 337
 338     let trait_def_id = tcx.hir().local_def_id(item.hir_id);
 339
 340     let trait_def = tcx.trait_def(trait_def_id);
 341     if trait_def.is_marker {
 342         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 343             struct_span_err!(
 344                 tcx.sess,
 345                 tcx.def_span(*associated_def_id),
 346                 E0714,
 347                 "marker traits cannot have associated items",
 348             )
 349             .emit();
 350         }
 351     }
 352
 353     for_item(tcx, item).with_fcx(|fcx, _| {
 354         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 355         vec![]
 356     });
 357 }
 358
 359 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
 360     for_item(tcx, item).with_fcx(|fcx, tcx| {
 361         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 362         let sig = fcx.tcx.fn_sig(def_id);
 363         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 364         let mut implied_bounds = vec![];
 365         check_fn_or_method(tcx, fcx, item.span, sig, def_id, &mut implied_bounds);
 366         implied_bounds
 367     })
 368 }
 369
 370 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
 371     debug!("check_item_type: {:?}", item_id);
 372
 373     for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
 374         let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
 375         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 376
 377         let mut forbid_unsized = true;
 378         if allow_foreign_ty {
 379             let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
 380             if let ty::Foreign(_) = tail.kind {
 381                 forbid_unsized = false;
 382             }
 383         }
 384
 385         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 386         if forbid_unsized {
 387             fcx.register_bound(
 388                 item_ty,
 389                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
 390                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 391             );
 392         }
 393
 394         // No implied bounds in a const, etc.
 395         vec![]
 396     });
 397 }
 398
 399 fn check_impl<'tcx>(
 400     tcx: TyCtxt<'tcx>,
 401     item: &'tcx hir::Item<'tcx>,
 402     ast_self_ty: &hir::Ty<'_>,
 403     ast_trait_ref: &Option<hir::TraitRef<'_>>,
 404 ) {
 405     debug!("check_impl: {:?}", item);
 406
 407     for_item(tcx, item).with_fcx(|fcx, tcx| {
 408         let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 409
 410         match *ast_trait_ref {
 411             Some(ref ast_trait_ref) => {
 412                 // `#[rustc_reservation_impl]` impls are not real impls and
 413                 // therefore don't need to be WF (the trait's `Self: Trait` predicate
 414                 // won't hold).
 415                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 416                 let trait_ref =
 417                     fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
 418                 let obligations = traits::wf::trait_obligations(
 419                     fcx,
 420                     fcx.param_env,
 421                     fcx.body_id,
 422                     &trait_ref,
 423                     ast_trait_ref.path.span,
 424                     Some(item),
 425                 );
 426                 for obligation in obligations {
 427                     fcx.register_predicate(obligation);
 428                 }
 429             }
 430             None => {
 431                 let self_ty = fcx.tcx.type_of(item_def_id);
 432                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 433                 fcx.register_wf_obligation(
 434                     self_ty,
 435                     ast_self_ty.span,
 436                     ObligationCauseCode::MiscObligation,
 437                 );
 438             }
 439         }
 440
 441         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 442
 443         fcx.impl_implied_bounds(item_def_id, item.span)
 444     });
 445 }
 446
 447 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 448 fn check_where_clauses<'tcx, 'fcx>(
 449     tcx: TyCtxt<'tcx>,
 450     fcx: &FnCtxt<'fcx, 'tcx>,
 451     span: Span,
 452     def_id: DefId,
 453     return_ty: Option<Ty<'tcx>>,
 454 ) {
 455     debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
 456
 457     let predicates = fcx.tcx.predicates_of(def_id);
 458     let generics = tcx.generics_of(def_id);
 459
 460     let is_our_default = |def: &ty::GenericParamDef| match def.kind {
 461         GenericParamDefKind::Type { has_default, .. } => {
 462             has_default && def.index >= generics.parent_count as u32
 463         }
 464         _ => unreachable!(),
 465     };
 466
 467     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 468     // For example, this forbids the declaration:
 469     //
 470     //     struct Foo<T = Vec<[u32]>> { .. }
 471     //
 472     // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 473     for param in &generics.params {
 474         if let GenericParamDefKind::Type { .. } = param.kind {
 475             if is_our_default(&param) {
 476                 let ty = fcx.tcx.type_of(param.def_id);
 477                 // Ignore dependent defaults -- that is, where the default of one type
 478                 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
 479                 // be sure if it will error or not as user might always specify the other.
 480                 if !ty.needs_subst() {
 481                     fcx.register_wf_obligation(
 482                         ty,
 483                         fcx.tcx.def_span(param.def_id),
 484                         ObligationCauseCode::MiscObligation,
 485                     );
 486                 }
 487             }
 488         }
 489     }
 490
 491     // Check that trait predicates are WF when params are substituted by their defaults.
 492     // We don't want to overly constrain the predicates that may be written but we want to
 493     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 494     // Therefore we check if a predicate which contains a single type param
 495     // with a concrete default is WF with that default substituted.
 496     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 497     //
 498     // First we build the defaulted substitution.
 499     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 500         match param.kind {
 501             GenericParamDefKind::Lifetime => {
 502                 // All regions are identity.
 503                 fcx.tcx.mk_param_from_def(param)
 504             }
 505
 506             GenericParamDefKind::Type { .. } => {
 507                 // If the param has a default, ...
 508                 if is_our_default(param) {
 509                     let default_ty = fcx.tcx.type_of(param.def_id);
 510                     // ... and it's not a dependent default, ...
 511                     if !default_ty.needs_subst() {
 512                         // ... then substitute it with the default.
 513                         return default_ty.into();
 514                     }
 515                 }
 516                 // Mark unwanted params as error.
 517                 fcx.tcx.types.err.into()
 518             }
 519
 520             GenericParamDefKind::Const => {
 521                 // FIXME(const_generics:defaults)
 522                 fcx.tcx.consts.err.into()
 523             }
 524         }
 525     });
 526
 527     // Now we build the substituted predicates.
 528     let default_obligations = predicates
 529         .predicates
 530         .iter()
 531         .flat_map(|&(pred, sp)| {
 532             #[derive(Default)]
 533             struct CountParams {
 534                 params: FxHashSet<u32>,
 535             }
 536             impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 537                 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 538                     if let ty::Param(param) = t.kind {
 539                         self.params.insert(param.index);
 540                     }
 541                     t.super_visit_with(self)
 542                 }
 543
 544                 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 545                     true
 546                 }
 547
 548                 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 549                     if let ty::ConstKind::Param(param) = c.val {
 550                         self.params.insert(param.index);
 551                     }
 552                     c.super_visit_with(self)
 553                 }
 554             }
 555             let mut param_count = CountParams::default();
 556             let has_region = pred.visit_with(&mut param_count);
 557             let substituted_pred = pred.subst(fcx.tcx, substs);
 558             // Don't check non-defaulted params, dependent defaults (including lifetimes)
 559             // or preds with multiple params.
 560             if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 561                 None
 562             } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 563                 // Avoid duplication of predicates that contain no parameters, for example.
 564                 None
 565             } else {
 566                 Some((substituted_pred, sp))
 567             }
 568         })
 569         .map(|(pred, sp)| {
 570             // Convert each of those into an obligation. So if you have
 571             // something like `struct Foo<T: Copy = String>`, we would
 572             // take that predicate `T: Copy`, substitute to `String: Copy`
 573             // (actually that happens in the previous `flat_map` call),
 574             // and then try to prove it (in this case, we'll fail).
 575             //
 576             // Note the subtle difference from how we handle `predicates`
 577             // below: there, we are not trying to prove those predicates
 578             // to be *true* but merely *well-formed*.
 579             let pred = fcx.normalize_associated_types_in(sp, &pred);
 580             let cause =
 581                 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
 582             traits::Obligation::new(cause, fcx.param_env, pred)
 583         });
 584
 585     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 586
 587     if let Some(return_ty) = return_ty {
 588         predicates.predicates.extend(check_opaque_types(tcx, fcx, def_id, span, return_ty));
 589     }
 590
 591     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 592
 593     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 594     let wf_obligations = predicates
 595         .predicates
 596         .iter()
 597         .flat_map(|p| traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, span));
 598
 599     for obligation in wf_obligations.chain(default_obligations) {
 600         debug!("next obligation cause: {:?}", obligation.cause);
 601         fcx.register_predicate(obligation);
 602     }
 603 }
 604
 605 fn check_fn_or_method<'fcx, 'tcx>(
 606     tcx: TyCtxt<'tcx>,
 607     fcx: &FnCtxt<'fcx, 'tcx>,
 608     span: Span,
 609     sig: ty::PolyFnSig<'tcx>,
 610     def_id: DefId,
 611     implied_bounds: &mut Vec<Ty<'tcx>>,
 612 ) {
 613     let sig = fcx.normalize_associated_types_in(span, &sig);
 614     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 615
 616     for input_ty in sig.inputs() {
 617         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 618     }
 619     implied_bounds.extend(sig.inputs());
 620
 621     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::ReturnType);
 622
 623     // FIXME(#25759) return types should not be implied bounds
 624     implied_bounds.push(sig.output());
 625
 626     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 627 }
 628
 629 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
 630 /// laid for "higher-order pattern unification".
 631 /// This ensures that inference is tractable.
 632 /// In particular, definitions of opaque types can only use other generics as arguments,
 633 /// and they cannot repeat an argument. Example:
 634 ///
 635 /// ```rust
 636 /// type Foo<A, B> = impl Bar<A, B>;
 637 ///
 638 /// // Okay -- `Foo` is applied to two distinct, generic types.
 639 /// fn a<T, U>() -> Foo<T, U> { .. }
 640 ///
 641 /// // Not okay -- `Foo` is applied to `T` twice.
 642 /// fn b<T>() -> Foo<T, T> { .. }
 643 ///
 644 /// // Not okay -- `Foo` is applied to a non-generic type.
 645 /// fn b<T>() -> Foo<T, u32> { .. }
 646 /// ```
 647 ///
 648 fn check_opaque_types<'fcx, 'tcx>(
 649     tcx: TyCtxt<'tcx>,
 650     fcx: &FnCtxt<'fcx, 'tcx>,
 651     fn_def_id: DefId,
 652     span: Span,
 653     ty: Ty<'tcx>,
 654 ) -> Vec<ty::Predicate<'tcx>> {
 655     trace!("check_opaque_types(ty={:?})", ty);
 656     let mut substituted_predicates = Vec::new();
 657     ty.fold_with(&mut ty::fold::BottomUpFolder {
 658         tcx: fcx.tcx,
 659         ty_op: |ty| {
 660             if let ty::Opaque(def_id, substs) = ty.kind {
 661                 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
 662                 let generics = tcx.generics_of(def_id);
 663                 // Only check named `impl Trait` types defined in this crate.
 664                 if generics.parent.is_none() && def_id.is_local() {
 665                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 666                     if may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
 667                         trace!("check_opaque_types: may define, generics={:#?}", generics);
 668                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 669                         for (subst, param) in substs.iter().zip(&generics.params) {
 670                             match subst.unpack() {
 671                                 ty::subst::GenericArgKind::Type(ty) => match ty.kind {
 672                                     ty::Param(..) => {}
 673                                     // Prevent `fn foo() -> Foo<u32>` from being defining.
 674                                     _ => {
 675                                         tcx.sess
 676                                             .struct_span_err(
 677                                                 span,
 678                                                 "non-defining opaque type use \
 679                                                  in defining scope",
 680                                             )
 681                                             .span_note(
 682                                                 tcx.def_span(param.def_id),
 683                                                 &format!(
 684                                                     "used non-generic type {} for \
 685                                                      generic parameter",
 686                                                     ty,
 687                                                 ),
 688                                             )
 689                                             .emit();
 690                                     }
 691                                 },
 692
 693                                 ty::subst::GenericArgKind::Lifetime(region) => {
 694                                     let param_span = tcx.def_span(param.def_id);
 695                                     if let ty::ReStatic = region {
 696                                         tcx.sess
 697                                             .struct_span_err(
 698                                                 span,
 699                                                 "non-defining opaque type use \
 700                                                     in defining scope",
 701                                             )
 702                                             .span_label(
 703                                                 param_span,
 704                                                 "cannot use static lifetime; use a bound lifetime \
 705                                                 instead or remove the lifetime parameter from the \
 706                                                 opaque type",
 707                                             )
 708                                             .emit();
 709                                     } else {
 710                                         seen.entry(region).or_default().push(param_span);
 711                                     }
 712                                 }
 713
 714                                 ty::subst::GenericArgKind::Const(ct) => match ct.val {
 715                                     ty::ConstKind::Param(_) => {}
 716                                     _ => {
 717                                         tcx.sess
 718                                             .struct_span_err(
 719                                                 span,
 720                                                 "non-defining opaque type use \
 721                                                 in defining scope",
 722                                             )
 723                                             .span_note(
 724                                                 tcx.def_span(param.def_id),
 725                                                 &format!(
 726                                                     "used non-generic const {} for \
 727                                                     generic parameter",
 728                                                     ty,
 729                                                 ),
 730                                             )
 731                                             .emit();
 732                                     }
 733                                 },
 734                             } // match subst
 735                         } // for (subst, param)
 736                         for (_, spans) in seen {
 737                             if spans.len() > 1 {
 738                                 tcx.sess
 739                                     .struct_span_err(
 740                                         span,
 741                                         "non-defining opaque type use \
 742                                             in defining scope",
 743                                     )
 744                                     .span_note(spans, "lifetime used multiple times")
 745                                     .emit();
 746                             }
 747                         }
 748                     } // if may_define_opaque_type
 749
 750                     // Now register the bounds on the parameters of the opaque type
 751                     // so the parameters given by the function need to fulfill them.
 752                     //
 753                     //     type Foo<T: Bar> = impl Baz + 'static;
 754                     //     fn foo<U>() -> Foo<U> { .. *}
 755                     //
 756                     // becomes
 757                     //
 758                     //     type Foo<T: Bar> = impl Baz + 'static;
 759                     //     fn foo<U: Bar>() -> Foo<U> { .. *}
 760                     let predicates = tcx.predicates_of(def_id);
 761                     trace!("check_opaque_types: may define, predicates={:#?}", predicates,);
 762                     for &(pred, _) in predicates.predicates {
 763                         let substituted_pred = pred.subst(fcx.tcx, substs);
 764                         // Avoid duplication of predicates that contain no parameters, for example.
 765                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 766                             substituted_predicates.push(substituted_pred);
 767                         }
 768                     }
 769                 } // if is_named_opaque_type
 770             } // if let Opaque
 771             ty
 772         },
 773         lt_op: |lt| lt,
 774         ct_op: |ct| ct,
 775     });
 776     substituted_predicates
 777 }
 778
 779 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
 780      `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
 781      of the previous types except `Self`)";
 782
 783 fn check_method_receiver<'fcx, 'tcx>(
 784     fcx: &FnCtxt<'fcx, 'tcx>,
 785     fn_sig: &hir::FnSig<'_>,
 786     method: &ty::AssocItem,
 787     self_ty: Ty<'tcx>,
 788 ) {
 789     // Check that the method has a valid receiver type, given the type `Self`.
 790     debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
 791
 792     if !method.method_has_self_argument {
 793         return;
 794     }
 795
 796     let span = fn_sig.decl.inputs[0].span;
 797
 798     let sig = fcx.tcx.fn_sig(method.def_id);
 799     let sig = fcx.normalize_associated_types_in(span, &sig);
 800     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 801
 802     debug!("check_method_receiver: sig={:?}", sig);
 803
 804     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 805     let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
 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 =
 811         fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
 812
 813     if fcx.tcx.features().arbitrary_self_types {
 814         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 815             // Report error; `arbitrary_self_types` was enabled.
 816             e0307(fcx, span, receiver_ty);
 817         }
 818     } else {
 819         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 820             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 821                 // Report error; would have worked with `arbitrary_self_types`.
 822                 feature_err(
 823                     &fcx.tcx.sess.parse_sess,
 824                     sym::arbitrary_self_types,
 825                     span,
 826                     &format!(
 827                         "`{}` cannot be used as the type of `self` without \
 828                             the `arbitrary_self_types` feature",
 829                         receiver_ty,
 830                     ),
 831                 )
 832                 .help(HELP_FOR_SELF_TYPE)
 833                 .emit();
 834             } else {
 835                 // Report error; would not have worked with `arbitrary_self_types`.
 836                 e0307(fcx, span, receiver_ty);
 837             }
 838         }
 839     }
 840 }
 841
 842 fn e0307(fcx: &FnCtxt<'fcx, 'tcx>, span: Span, receiver_ty: Ty<'_>) {
 843     struct_span_err!(
 844         fcx.tcx.sess.diagnostic(),
 845         span,
 846         E0307,
 847         "invalid `self` parameter type: {:?}",
 848         receiver_ty,
 849     )
 850     .note("type of `self` must be `Self` or a type that dereferences to it")
 851     .help(HELP_FOR_SELF_TYPE)
 852     .emit();
 853 }
 854
 855 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 856 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 857 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 858 /// strict: `receiver_ty` must implement `Receiver` and directly implement
 859 /// `Deref<Target = self_ty>`.
 860 ///
 861 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 862 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 863 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 864 fn receiver_is_valid<'fcx, 'tcx>(
 865     fcx: &FnCtxt<'fcx, 'tcx>,
 866     span: Span,
 867     receiver_ty: Ty<'tcx>,
 868     self_ty: Ty<'tcx>,
 869     arbitrary_self_types_enabled: bool,
 870 ) -> bool {
 871     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 872
 873     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 874
 875     // `self: Self` is always valid.
 876     if can_eq_self(receiver_ty) {
 877         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 878             err.emit();
 879         }
 880         return true;
 881     }
 882
 883     let mut autoderef = fcx.autoderef(span, receiver_ty);
 884
 885     // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
 886     if arbitrary_self_types_enabled {
 887         autoderef = autoderef.include_raw_pointers();
 888     }
 889
 890     // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
 891     autoderef.next();
 892
 893     let receiver_trait_def_id = fcx.tcx.require_lang_item(lang_items::ReceiverTraitLangItem, None);
 894
 895     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
 896     loop {
 897         if let Some((potential_self_ty, _)) = autoderef.next() {
 898             debug!(
 899                 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 900                 potential_self_ty, self_ty
 901             );
 902
 903             if can_eq_self(potential_self_ty) {
 904                 autoderef.finalize(fcx);
 905
 906                 if let Some(mut err) =
 907                     fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
 908                 {
 909                     err.emit();
 910                 }
 911
 912                 break;
 913             } else {
 914                 // Without `feature(arbitrary_self_types)`, we require that each step in the
 915                 // deref chain implement `receiver`
 916                 if !arbitrary_self_types_enabled
 917                     && !receiver_is_implemented(
 918                         fcx,
 919                         receiver_trait_def_id,
 920                         cause.clone(),
 921                         potential_self_ty,
 922                     )
 923                 {
 924                     return false;
 925                 }
 926             }
 927         } else {
 928             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
 929             // If he receiver already has errors reported due to it, consider it valid to avoid
 930             // unnecessary errors (#58712).
 931             return receiver_ty.references_error();
 932         }
 933     }
 934
 935     // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
 936     if !arbitrary_self_types_enabled
 937         && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
 938     {
 939         return false;
 940     }
 941
 942     true
 943 }
 944
 945 fn receiver_is_implemented(
 946     fcx: &FnCtxt<'_, 'tcx>,
 947     receiver_trait_def_id: DefId,
 948     cause: ObligationCause<'tcx>,
 949     receiver_ty: Ty<'tcx>,
 950 ) -> bool {
 951     let trait_ref = ty::TraitRef {
 952         def_id: receiver_trait_def_id,
 953         substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 954     };
 955
 956     let obligation = traits::Obligation::new(cause, fcx.param_env, trait_ref.to_predicate());
 957
 958     if fcx.predicate_must_hold_modulo_regions(&obligation) {
 959         true
 960     } else {
 961         debug!(
 962             "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
 963             receiver_ty
 964         );
 965         false
 966     }
 967 }
 968
 969 fn check_variances_for_type_defn<'tcx>(
 970     tcx: TyCtxt<'tcx>,
 971     item: &hir::Item<'tcx>,
 972     hir_generics: &hir::Generics<'_>,
 973 ) {
 974     let item_def_id = tcx.hir().local_def_id(item.hir_id);
 975     let ty = tcx.type_of(item_def_id);
 976     if tcx.has_error_field(ty) {
 977         return;
 978     }
 979
 980     let ty_predicates = tcx.predicates_of(item_def_id);
 981     assert_eq!(ty_predicates.parent, None);
 982     let variances = tcx.variances_of(item_def_id);
 983
 984     let mut constrained_parameters: FxHashSet<_> = variances
 985         .iter()
 986         .enumerate()
 987         .filter(|&(_, &variance)| variance != ty::Bivariant)
 988         .map(|(index, _)| Parameter(index as u32))
 989         .collect();
 990
 991     identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
 992
 993     for (index, _) in variances.iter().enumerate() {
 994         if constrained_parameters.contains(&Parameter(index as u32)) {
 995             continue;
 996         }
 997
 998         let param = &hir_generics.params[index];
 999
1000         match param.name {
1001             hir::ParamName::Error => {}
1002             _ => report_bivariance(tcx, param.span, param.name.ident().name),
1003         }
1004     }
1005 }
1006
1007 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
1008     let mut err = error_392(tcx, span, param_name);
1009
1010     let suggested_marker_id = tcx.lang_items().phantom_data();
1011     // Help is available only in presence of lang items.
1012     let msg = if let Some(def_id) = suggested_marker_id {
1013         format!(
1014             "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1015             param_name,
1016             tcx.def_path_str(def_id),
1017         )
1018     } else {
1019         format!("consider removing `{}` or referring to it in a field", param_name)
1020     };
1021     err.help(&msg);
1022     err.emit();
1023 }
1024
1025 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1026 /// aren't true.
1027 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1028     let empty_env = ty::ParamEnv::empty();
1029
1030     let def_id = fcx.tcx.hir().local_def_id(id);
1031     let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p).collect();
1032     // Check elaborated bounds.
1033     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1034
1035     for pred in implied_obligations {
1036         // Match the existing behavior.
1037         if pred.is_global() && !pred.has_late_bound_regions() {
1038             let pred = fcx.normalize_associated_types_in(span, &pred);
1039             let obligation = traits::Obligation::new(
1040                 traits::ObligationCause::new(span, id, traits::TrivialBound),
1041                 empty_env,
1042                 pred,
1043             );
1044             fcx.register_predicate(obligation);
1045         }
1046     }
1047
1048     fcx.select_all_obligations_or_error();
1049 }
1050
1051 pub struct CheckTypeWellFormedVisitor<'tcx> {
1052     tcx: TyCtxt<'tcx>,
1053 }
1054
1055 impl CheckTypeWellFormedVisitor<'tcx> {
1056     pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1057         CheckTypeWellFormedVisitor { tcx }
1058     }
1059 }
1060
1061 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1062     fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1063         debug!("visit_item: {:?}", i);
1064         let def_id = self.tcx.hir().local_def_id(i.hir_id);
1065         self.tcx.ensure().check_item_well_formed(def_id);
1066     }
1067
1068     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1069         debug!("visit_trait_item: {:?}", trait_item);
1070         let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1071         self.tcx.ensure().check_trait_item_well_formed(def_id);
1072     }
1073
1074     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1075         debug!("visit_impl_item: {:?}", impl_item);
1076         let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1077         self.tcx.ensure().check_impl_item_well_formed(def_id);
1078     }
1079 }
1080
1081 ///////////////////////////////////////////////////////////////////////////
1082 // ADT
1083
1084 struct AdtVariant<'tcx> {
1085     fields: Vec<AdtField<'tcx>>,
1086 }
1087
1088 struct AdtField<'tcx> {
1089     ty: Ty<'tcx>,
1090     span: Span,
1091 }
1092
1093 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1094     fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1095         let fields = struct_def
1096             .fields()
1097             .iter()
1098             .map(|field| {
1099                 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1100                 let field_ty = self.normalize_associated_types_in(field.span, &field_ty);
1101                 let field_ty = self.resolve_vars_if_possible(&field_ty);
1102                 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1103                 AdtField { ty: field_ty, span: field.span }
1104             })
1105             .collect();
1106         AdtVariant { fields }
1107     }
1108
1109     fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1110         enum_def.variants.iter().map(|variant| self.non_enum_variant(&variant.data)).collect()
1111     }
1112
1113     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1114         match self.tcx.impl_trait_ref(impl_def_id) {
1115             Some(ref trait_ref) => {
1116                 // Trait impl: take implied bounds from all types that
1117                 // appear in the trait reference.
1118                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1119                 trait_ref.substs.types().collect()
1120             }
1121
1122             None => {
1123                 // Inherent impl: take implied bounds from the `self` type.
1124                 let self_ty = self.tcx.type_of(impl_def_id);
1125                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1126                 vec![self_ty]
1127             }
1128         }
1129     }
1130 }
1131
1132 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) -> DiagnosticBuilder<'_> {
1133     let mut err =
1134         struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1135     err.span_label(span, "unused parameter");
1136     err
1137 }