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::traits::{self, ObligationCause, ObligationCauseCode};
   7 use rustc::ty::subst::{InternalSubsts, Subst};
   8 use rustc::ty::{self, AdtKind, GenericParamDefKind, ToPredicate, Ty, TyCtxt, TypeFoldable};
   9 use rustc_data_structures::fx::{FxHashMap, FxHashSet};
  10 use rustc_hir::def_id::DefId;
  11 use rustc_hir::ItemKind;
  12
  13 use errors::DiagnosticBuilder;
  14 use rustc_span::symbol::sym;
  15 use rustc_span::Span;
  16 use syntax::ast;
  17 use syntax::feature_gate;
  18
  19 use rustc_hir as hir;
  20 use rustc_hir::itemlikevisit::ParItemLikeVisitor;
  21
  22 use rustc_error_codes::*;
  23
  24 /// Helper type of a temporary returned by `.for_item(...)`.
  25 /// This is necessary because we can't write the following bound:
  26 ///
  27 /// ```rust
  28 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
  29 /// ```
  30 struct CheckWfFcxBuilder<'tcx> {
  31     inherited: super::InheritedBuilder<'tcx>,
  32     id: hir::HirId,
  33     span: Span,
  34     param_env: ty::ParamEnv<'tcx>,
  35 }
  36
  37 impl<'tcx> CheckWfFcxBuilder<'tcx> {
  38     fn with_fcx<F>(&mut self, f: F)
  39     where
  40         F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
  41     {
  42         let id = self.id;
  43         let span = self.span;
  44         let param_env = self.param_env;
  45         self.inherited.enter(|inh| {
  46             let fcx = FnCtxt::new(&inh, param_env, id);
  47             if !inh.tcx.features().trivial_bounds {
  48                 // As predicates are cached rather than obligations, this
  49                 // needsto be called first so that they are checked with an
  50                 // empty `param_env`.
  51                 check_false_global_bounds(&fcx, span, id);
  52             }
  53             let wf_tys = f(&fcx, fcx.tcx);
  54             fcx.select_all_obligations_or_error();
  55             fcx.regionck_item(id, span, &wf_tys);
  56         });
  57     }
  58 }
  59
  60 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  61 /// well-formed, meaning that they do not require any constraints not declared in the struct
  62 /// definition itself. For example, this definition would be illegal:
  63 ///
  64 /// ```rust
  65 /// struct Ref<'a, T> { x: &'a T }
  66 /// ```
  67 ///
  68 /// because the type did not declare that `T:'a`.
  69 ///
  70 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  71 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  72 /// the types first.
  73 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: DefId) {
  74     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  75     let item = tcx.hir().expect_item(hir_id);
  76
  77     debug!(
  78         "check_item_well_formed(it.hir_id={:?}, it.name={})",
  79         item.hir_id,
  80         tcx.def_path_str(def_id)
  81     );
  82
  83     match item.kind {
  84         // Right now we check that every default trait implementation
  85         // has an implementation of itself. Basically, a case like:
  86         //
  87         //     impl Trait for T {}
  88         //
  89         // has a requirement of `T: Trait` which was required for default
  90         // method implementations. Although this could be improved now that
  91         // there's a better infrastructure in place for this, it's being left
  92         // for a follow-up work.
  93         //
  94         // Since there's such a requirement, we need to check *just* positive
  95         // implementations, otherwise things like:
  96         //
  97         //     impl !Send for T {}
  98         //
  99         // won't be allowed unless there's an *explicit* implementation of `Send`
 100         // for `T`
 101         hir::ItemKind::Impl(_, _, defaultness, _, ref trait_ref, ref self_ty, _) => {
 102             let is_auto = tcx
 103                 .impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
 104                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 105             let polarity = tcx.impl_polarity(def_id);
 106             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 107                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 108             }
 109             match polarity {
 110                 ty::ImplPolarity::Positive => {
 111                     check_impl(tcx, item, self_ty, trait_ref);
 112                 }
 113                 ty::ImplPolarity::Negative => {
 114                     // FIXME(#27579): what amount of WF checking do we need for neg impls?
 115                     if trait_ref.is_some() && !is_auto {
 116                         span_err!(
 117                             tcx.sess,
 118                             item.span,
 119                             E0192,
 120                             "negative impls are only allowed for \
 121                                    auto traits (e.g., `Send` and `Sync`)"
 122                         )
 123                     }
 124                 }
 125                 ty::ImplPolarity::Reservation => {
 126                     // FIXME: what amount of WF checking do we need for reservation impls?
 127                 }
 128             }
 129         }
 130         hir::ItemKind::Fn(..) => {
 131             check_item_fn(tcx, item);
 132         }
 133         hir::ItemKind::Static(ref ty, ..) => {
 134             check_item_type(tcx, item.hir_id, ty.span, false);
 135         }
 136         hir::ItemKind::Const(ref ty, ..) => {
 137             check_item_type(tcx, item.hir_id, ty.span, false);
 138         }
 139         hir::ItemKind::ForeignMod(ref module) => {
 140             for it in module.items.iter() {
 141                 if let hir::ForeignItemKind::Static(ref ty, ..) = it.kind {
 142                     check_item_type(tcx, it.hir_id, ty.span, true);
 143                 }
 144             }
 145         }
 146         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 147             check_type_defn(tcx, item, false, |fcx| vec![fcx.non_enum_variant(struct_def)]);
 148
 149             check_variances_for_type_defn(tcx, item, ast_generics);
 150         }
 151         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 152             check_type_defn(tcx, item, true, |fcx| vec![fcx.non_enum_variant(struct_def)]);
 153
 154             check_variances_for_type_defn(tcx, item, ast_generics);
 155         }
 156         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 157             check_type_defn(tcx, item, true, |fcx| fcx.enum_variants(enum_def));
 158
 159             check_variances_for_type_defn(tcx, item, ast_generics);
 160         }
 161         hir::ItemKind::Trait(..) => {
 162             check_trait(tcx, item);
 163         }
 164         hir::ItemKind::TraitAlias(..) => {
 165             check_trait(tcx, item);
 166         }
 167         _ => {}
 168     }
 169 }
 170
 171 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: DefId) {
 172     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 173     let trait_item = tcx.hir().expect_trait_item(hir_id);
 174
 175     let method_sig = match trait_item.kind {
 176         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 177         _ => None,
 178     };
 179     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 180 }
 181
 182 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: DefId) {
 183     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 184     let impl_item = tcx.hir().expect_impl_item(hir_id);
 185
 186     let method_sig = match impl_item.kind {
 187         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 188         _ => None,
 189     };
 190
 191     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 192 }
 193
 194 fn check_associated_item(
 195     tcx: TyCtxt<'_>,
 196     item_id: hir::HirId,
 197     span: Span,
 198     sig_if_method: Option<&hir::FnSig<'_>>,
 199 ) {
 200     debug!("check_associated_item: {:?}", item_id);
 201
 202     let code = ObligationCauseCode::MiscObligation;
 203     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 204         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
 205
 206         let (mut implied_bounds, self_ty) = match item.container {
 207             ty::TraitContainer(_) => (vec![], fcx.tcx.types.self_param),
 208             ty::ImplContainer(def_id) => {
 209                 (fcx.impl_implied_bounds(def_id, span), fcx.tcx.type_of(def_id))
 210             }
 211         };
 212
 213         match item.kind {
 214             ty::AssocKind::Const => {
 215                 let ty = fcx.tcx.type_of(item.def_id);
 216                 let ty = fcx.normalize_associated_types_in(span, &ty);
 217                 fcx.register_wf_obligation(ty, span, code.clone());
 218             }
 219             ty::AssocKind::Method => {
 220                 let sig = fcx.tcx.fn_sig(item.def_id);
 221                 let sig = fcx.normalize_associated_types_in(span, &sig);
 222                 check_fn_or_method(tcx, fcx, span, sig, item.def_id, &mut implied_bounds);
 223                 let sig_if_method = sig_if_method.expect("bad signature for method");
 224                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 225             }
 226             ty::AssocKind::Type => {
 227                 if item.defaultness.has_value() {
 228                     let ty = fcx.tcx.type_of(item.def_id);
 229                     let ty = fcx.normalize_associated_types_in(span, &ty);
 230                     fcx.register_wf_obligation(ty, span, code.clone());
 231                 }
 232             }
 233             ty::AssocKind::OpaqueTy => {
 234                 // Do nothing: opaque types check themselves.
 235             }
 236         }
 237
 238         implied_bounds
 239     })
 240 }
 241
 242 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item<'_>) -> CheckWfFcxBuilder<'tcx> {
 243     for_id(tcx, item.hir_id, item.span)
 244 }
 245
 246 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
 247     let def_id = tcx.hir().local_def_id(id);
 248     CheckWfFcxBuilder {
 249         inherited: Inherited::build(tcx, def_id),
 250         id,
 251         span,
 252         param_env: tcx.param_env(def_id),
 253     }
 254 }
 255
 256 fn item_adt_kind(kind: &ItemKind<'_>) -> Option<AdtKind> {
 257     match kind {
 258         ItemKind::Struct(..) => Some(AdtKind::Struct),
 259         ItemKind::Union(..) => Some(AdtKind::Union),
 260         ItemKind::Enum(..) => Some(AdtKind::Enum),
 261         _ => None,
 262     }
 263 }
 264
 265 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 266 fn check_type_defn<'tcx, F>(
 267     tcx: TyCtxt<'tcx>,
 268     item: &hir::Item<'tcx>,
 269     all_sized: bool,
 270     mut lookup_fields: F,
 271 ) where
 272     F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
 273 {
 274     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 275         let variants = lookup_fields(fcx);
 276         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 277         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 278
 279         for variant in &variants {
 280             // For DST, or when drop needs to copy things around, all
 281             // intermediate types must be sized.
 282             let needs_drop_copy = || {
 283                 packed && {
 284                     let ty = variant.fields.last().unwrap().ty;
 285                     let ty = fcx.tcx.erase_regions(&ty);
 286                     if ty.has_local_value() {
 287                         fcx_tcx
 288                             .sess
 289                             .delay_span_bug(item.span, &format!("inference variables in {:?}", ty));
 290                         // Just treat unresolved type expression as if it needs drop.
 291                         true
 292                     } else {
 293                         ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
 294                     }
 295                 }
 296             };
 297             let all_sized = all_sized || variant.fields.is_empty() || needs_drop_copy();
 298             let unsized_len = if all_sized { 0 } else { 1 };
 299             for (idx, field) in
 300                 variant.fields[..variant.fields.len() - unsized_len].iter().enumerate()
 301             {
 302                 let last = idx == variant.fields.len() - 1;
 303                 fcx.register_bound(
 304                     field.ty,
 305                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
 306                     traits::ObligationCause::new(
 307                         field.span,
 308                         fcx.body_id,
 309                         traits::FieldSized {
 310                             adt_kind: match item_adt_kind(&item.kind) {
 311                                 Some(i) => i,
 312                                 None => bug!(),
 313                             },
 314                             last,
 315                         },
 316                     ),
 317                 );
 318             }
 319
 320             // All field types must be well-formed.
 321             for field in &variant.fields {
 322                 fcx.register_wf_obligation(
 323                     field.ty,
 324                     field.span,
 325                     ObligationCauseCode::MiscObligation,
 326                 )
 327             }
 328         }
 329
 330         check_where_clauses(tcx, fcx, item.span, def_id, None);
 331
 332         // No implied bounds in a struct definition.
 333         vec![]
 334     });
 335 }
 336
 337 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
 338     debug!("check_trait: {:?}", item.hir_id);
 339
 340     let trait_def_id = tcx.hir().local_def_id(item.hir_id);
 341
 342     let trait_def = tcx.trait_def(trait_def_id);
 343     if trait_def.is_marker {
 344         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 345             struct_span_err!(
 346                 tcx.sess,
 347                 tcx.def_span(*associated_def_id),
 348                 E0714,
 349                 "marker traits cannot have associated items",
 350             )
 351             .emit();
 352         }
 353     }
 354
 355     for_item(tcx, item).with_fcx(|fcx, _| {
 356         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 357         vec![]
 358     });
 359 }
 360
 361 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item<'_>) {
 362     for_item(tcx, item).with_fcx(|fcx, tcx| {
 363         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 364         let sig = fcx.tcx.fn_sig(def_id);
 365         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 366         let mut implied_bounds = vec![];
 367         check_fn_or_method(tcx, fcx, item.span, sig, def_id, &mut implied_bounds);
 368         implied_bounds
 369     })
 370 }
 371
 372 fn check_item_type(tcx: TyCtxt<'_>, item_id: hir::HirId, ty_span: Span, allow_foreign_ty: bool) {
 373     debug!("check_item_type: {:?}", item_id);
 374
 375     for_id(tcx, item_id, ty_span).with_fcx(|fcx, tcx| {
 376         let ty = tcx.type_of(tcx.hir().local_def_id(item_id));
 377         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 378
 379         let mut forbid_unsized = true;
 380         if allow_foreign_ty {
 381             let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
 382             if let ty::Foreign(_) = tail.kind {
 383                 forbid_unsized = false;
 384             }
 385         }
 386
 387         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 388         if forbid_unsized {
 389             fcx.register_bound(
 390                 item_ty,
 391                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem, None),
 392                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 393             );
 394         }
 395
 396         // No implied bounds in a const, etc.
 397         vec![]
 398     });
 399 }
 400
 401 fn check_impl<'tcx>(
 402     tcx: TyCtxt<'tcx>,
 403     item: &'tcx hir::Item<'tcx>,
 404     ast_self_ty: &hir::Ty<'_>,
 405     ast_trait_ref: &Option<hir::TraitRef<'_>>,
 406 ) {
 407     debug!("check_impl: {:?}", item);
 408
 409     for_item(tcx, item).with_fcx(|fcx, tcx| {
 410         let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 411
 412         match *ast_trait_ref {
 413             Some(ref ast_trait_ref) => {
 414                 // `#[rustc_reservation_impl]` impls are not real impls and
 415                 // therefore don't need to be WF (the trait's `Self: Trait` predicate
 416                 // won't hold).
 417                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 418                 let trait_ref =
 419                     fcx.normalize_associated_types_in(ast_trait_ref.path.span, &trait_ref);
 420                 let obligations = traits::wf::trait_obligations(
 421                     fcx,
 422                     fcx.param_env,
 423                     fcx.body_id,
 424                     &trait_ref,
 425                     ast_trait_ref.path.span,
 426                     Some(item),
 427                 );
 428                 for obligation in obligations {
 429                     fcx.register_predicate(obligation);
 430                 }
 431             }
 432             None => {
 433                 let self_ty = fcx.tcx.type_of(item_def_id);
 434                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 435                 fcx.register_wf_obligation(
 436                     self_ty,
 437                     ast_self_ty.span,
 438                     ObligationCauseCode::MiscObligation,
 439                 );
 440             }
 441         }
 442
 443         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 444
 445         fcx.impl_implied_bounds(item_def_id, item.span)
 446     });
 447 }
 448
 449 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 450 fn check_where_clauses<'tcx, 'fcx>(
 451     tcx: TyCtxt<'tcx>,
 452     fcx: &FnCtxt<'fcx, 'tcx>,
 453     span: Span,
 454     def_id: DefId,
 455     return_ty: Option<Ty<'tcx>>,
 456 ) {
 457     debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
 458
 459     let predicates = fcx.tcx.predicates_of(def_id);
 460     let generics = tcx.generics_of(def_id);
 461
 462     let is_our_default = |def: &ty::GenericParamDef| match def.kind {
 463         GenericParamDefKind::Type { has_default, .. } => {
 464             has_default && def.index >= generics.parent_count as u32
 465         }
 466         _ => unreachable!(),
 467     };
 468
 469     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 470     // For example, this forbids the declaration:
 471     //
 472     //     struct Foo<T = Vec<[u32]>> { .. }
 473     //
 474     // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 475     for param in &generics.params {
 476         if let GenericParamDefKind::Type { .. } = param.kind {
 477             if is_our_default(&param) {
 478                 let ty = fcx.tcx.type_of(param.def_id);
 479                 // Ignore dependent defaults -- that is, where the default of one type
 480                 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
 481                 // be sure if it will error or not as user might always specify the other.
 482                 if !ty.needs_subst() {
 483                     fcx.register_wf_obligation(
 484                         ty,
 485                         fcx.tcx.def_span(param.def_id),
 486                         ObligationCauseCode::MiscObligation,
 487                     );
 488                 }
 489             }
 490         }
 491     }
 492
 493     // Check that trait predicates are WF when params are substituted by their defaults.
 494     // We don't want to overly constrain the predicates that may be written but we want to
 495     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 496     // Therefore we check if a predicate which contains a single type param
 497     // with a concrete default is WF with that default substituted.
 498     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 499     //
 500     // First we build the defaulted substitution.
 501     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 502         match param.kind {
 503             GenericParamDefKind::Lifetime => {
 504                 // All regions are identity.
 505                 fcx.tcx.mk_param_from_def(param)
 506             }
 507
 508             GenericParamDefKind::Type { .. } => {
 509                 // If the param has a default, ...
 510                 if is_our_default(param) {
 511                     let default_ty = fcx.tcx.type_of(param.def_id);
 512                     // ... and it's not a dependent default, ...
 513                     if !default_ty.needs_subst() {
 514                         // ... then substitute it with the default.
 515                         return default_ty.into();
 516                     }
 517                 }
 518                 // Mark unwanted params as error.
 519                 fcx.tcx.types.err.into()
 520             }
 521
 522             GenericParamDefKind::Const => {
 523                 // FIXME(const_generics:defaults)
 524                 fcx.tcx.consts.err.into()
 525             }
 526         }
 527     });
 528
 529     // Now we build the substituted predicates.
 530     let default_obligations = predicates
 531         .predicates
 532         .iter()
 533         .flat_map(|&(pred, sp)| {
 534             #[derive(Default)]
 535             struct CountParams {
 536                 params: FxHashSet<u32>,
 537             }
 538             impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 539                 fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 540                     if let ty::Param(param) = t.kind {
 541                         self.params.insert(param.index);
 542                     }
 543                     t.super_visit_with(self)
 544                 }
 545
 546                 fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 547                     true
 548                 }
 549
 550                 fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 551                     if let ty::ConstKind::Param(param) = c.val {
 552                         self.params.insert(param.index);
 553                     }
 554                     c.super_visit_with(self)
 555                 }
 556             }
 557             let mut param_count = CountParams::default();
 558             let has_region = pred.visit_with(&mut param_count);
 559             let substituted_pred = pred.subst(fcx.tcx, substs);
 560             // Don't check non-defaulted params, dependent defaults (including lifetimes)
 561             // or preds with multiple params.
 562             if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 563                 None
 564             } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 565                 // Avoid duplication of predicates that contain no parameters, for example.
 566                 None
 567             } else {
 568                 Some((substituted_pred, sp))
 569             }
 570         })
 571         .map(|(pred, sp)| {
 572             // Convert each of those into an obligation. So if you have
 573             // something like `struct Foo<T: Copy = String>`, we would
 574             // take that predicate `T: Copy`, substitute to `String: Copy`
 575             // (actually that happens in the previous `flat_map` call),
 576             // and then try to prove it (in this case, we'll fail).
 577             //
 578             // Note the subtle difference from how we handle `predicates`
 579             // below: there, we are not trying to prove those predicates
 580             // to be *true* but merely *well-formed*.
 581             let pred = fcx.normalize_associated_types_in(sp, &pred);
 582             let cause =
 583                 traits::ObligationCause::new(sp, fcx.body_id, traits::ItemObligation(def_id));
 584             traits::Obligation::new(cause, fcx.param_env, pred)
 585         });
 586
 587     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 588
 589     if let Some(return_ty) = return_ty {
 590         predicates.predicates.extend(check_opaque_types(tcx, fcx, def_id, span, return_ty));
 591     }
 592
 593     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 594
 595     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 596     let wf_obligations = predicates
 597         .predicates
 598         .iter()
 599         .flat_map(|p| traits::wf::predicate_obligations(fcx, fcx.param_env, fcx.body_id, p, span));
 600
 601     for obligation in wf_obligations.chain(default_obligations) {
 602         debug!("next obligation cause: {:?}", obligation.cause);
 603         fcx.register_predicate(obligation);
 604     }
 605 }
 606
 607 fn check_fn_or_method<'fcx, 'tcx>(
 608     tcx: TyCtxt<'tcx>,
 609     fcx: &FnCtxt<'fcx, 'tcx>,
 610     span: Span,
 611     sig: ty::PolyFnSig<'tcx>,
 612     def_id: DefId,
 613     implied_bounds: &mut Vec<Ty<'tcx>>,
 614 ) {
 615     let sig = fcx.normalize_associated_types_in(span, &sig);
 616     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 617
 618     for input_ty in sig.inputs() {
 619         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 620     }
 621     implied_bounds.extend(sig.inputs());
 622
 623     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::ReturnType);
 624
 625     // FIXME(#25759) return types should not be implied bounds
 626     implied_bounds.push(sig.output());
 627
 628     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 629 }
 630
 631 /// Checks "defining uses" of opaque `impl Trait` types to ensure that they meet the restrictions
 632 /// laid for "higher-order pattern unification".
 633 /// This ensures that inference is tractable.
 634 /// In particular, definitions of opaque types can only use other generics as arguments,
 635 /// and they cannot repeat an argument. Example:
 636 ///
 637 /// ```rust
 638 /// type Foo<A, B> = impl Bar<A, B>;
 639 ///
 640 /// // Okay -- `Foo` is applied to two distinct, generic types.
 641 /// fn a<T, U>() -> Foo<T, U> { .. }
 642 ///
 643 /// // Not okay -- `Foo` is applied to `T` twice.
 644 /// fn b<T>() -> Foo<T, T> { .. }
 645 ///
 646 /// // Not okay -- `Foo` is applied to a non-generic type.
 647 /// fn b<T>() -> Foo<T, u32> { .. }
 648 /// ```
 649 ///
 650 fn check_opaque_types<'fcx, 'tcx>(
 651     tcx: TyCtxt<'tcx>,
 652     fcx: &FnCtxt<'fcx, 'tcx>,
 653     fn_def_id: DefId,
 654     span: Span,
 655     ty: Ty<'tcx>,
 656 ) -> Vec<ty::Predicate<'tcx>> {
 657     trace!("check_opaque_types(ty={:?})", ty);
 658     let mut substituted_predicates = Vec::new();
 659     ty.fold_with(&mut ty::fold::BottomUpFolder {
 660         tcx: fcx.tcx,
 661         ty_op: |ty| {
 662             if let ty::Opaque(def_id, substs) = ty.kind {
 663                 trace!("check_opaque_types: opaque_ty, {:?}, {:?}", def_id, substs);
 664                 let generics = tcx.generics_of(def_id);
 665                 // Only check named `impl Trait` types defined in this crate.
 666                 if generics.parent.is_none() && def_id.is_local() {
 667                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 668                     if may_define_opaque_type(tcx, fn_def_id, opaque_hir_id) {
 669                         trace!("check_opaque_types: may define, generics={:#?}", generics);
 670                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 671                         for (subst, param) in substs.iter().zip(&generics.params) {
 672                             match subst.unpack() {
 673                                 ty::subst::GenericArgKind::Type(ty) => match ty.kind {
 674                                     ty::Param(..) => {}
 675                                     // Prevent `fn foo() -> Foo<u32>` from being defining.
 676                                     _ => {
 677                                         tcx.sess
 678                                             .struct_span_err(
 679                                                 span,
 680                                                 "non-defining opaque type use \
 681                                                  in defining scope",
 682                                             )
 683                                             .span_note(
 684                                                 tcx.def_span(param.def_id),
 685                                                 &format!(
 686                                                     "used non-generic type {} for \
 687                                                      generic parameter",
 688                                                     ty,
 689                                                 ),
 690                                             )
 691                                             .emit();
 692                                     }
 693                                 },
 694
 695                                 ty::subst::GenericArgKind::Lifetime(region) => {
 696                                     let param_span = tcx.def_span(param.def_id);
 697                                     if let ty::ReStatic = region {
 698                                         tcx.sess
 699                                             .struct_span_err(
 700                                                 span,
 701                                                 "non-defining opaque type use \
 702                                                     in defining scope",
 703                                             )
 704                                             .span_label(
 705                                                 param_span,
 706                                                 "cannot use static lifetime; use a bound lifetime \
 707                                                 instead or remove the lifetime parameter from the \
 708                                                 opaque type",
 709                                             )
 710                                             .emit();
 711                                     } else {
 712                                         seen.entry(region).or_default().push(param_span);
 713                                     }
 714                                 }
 715
 716                                 ty::subst::GenericArgKind::Const(ct) => match ct.val {
 717                                     ty::ConstKind::Param(_) => {}
 718                                     _ => {
 719                                         tcx.sess
 720                                             .struct_span_err(
 721                                                 span,
 722                                                 "non-defining opaque type use \
 723                                                 in defining scope",
 724                                             )
 725                                             .span_note(
 726                                                 tcx.def_span(param.def_id),
 727                                                 &format!(
 728                                                     "used non-generic const {} for \
 729                                                     generic parameter",
 730                                                     ty,
 731                                                 ),
 732                                             )
 733                                             .emit();
 734                                     }
 735                                 },
 736                             } // match subst
 737                         } // for (subst, param)
 738                         for (_, spans) in seen {
 739                             if spans.len() > 1 {
 740                                 tcx.sess
 741                                     .struct_span_err(
 742                                         span,
 743                                         "non-defining opaque type use \
 744                                             in defining scope",
 745                                     )
 746                                     .span_note(spans, "lifetime used multiple times")
 747                                     .emit();
 748                             }
 749                         }
 750                     } // if may_define_opaque_type
 751
 752                     // Now register the bounds on the parameters of the opaque type
 753                     // so the parameters given by the function need to fulfill them.
 754                     //
 755                     //     type Foo<T: Bar> = impl Baz + 'static;
 756                     //     fn foo<U>() -> Foo<U> { .. *}
 757                     //
 758                     // becomes
 759                     //
 760                     //     type Foo<T: Bar> = impl Baz + 'static;
 761                     //     fn foo<U: Bar>() -> Foo<U> { .. *}
 762                     let predicates = tcx.predicates_of(def_id);
 763                     trace!("check_opaque_types: may define, predicates={:#?}", predicates,);
 764                     for &(pred, _) in predicates.predicates {
 765                         let substituted_pred = pred.subst(fcx.tcx, substs);
 766                         // Avoid duplication of predicates that contain no parameters, for example.
 767                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 768                             substituted_predicates.push(substituted_pred);
 769                         }
 770                     }
 771                 } // if is_named_opaque_type
 772             } // if let Opaque
 773             ty
 774         },
 775         lt_op: |lt| lt,
 776         ct_op: |ct| ct,
 777     });
 778     substituted_predicates
 779 }
 780
 781 const HELP_FOR_SELF_TYPE: &str = "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
 782      `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
 783      of the previous types except `Self`)";
 784
 785 fn check_method_receiver<'fcx, 'tcx>(
 786     fcx: &FnCtxt<'fcx, 'tcx>,
 787     fn_sig: &hir::FnSig<'_>,
 788     method: &ty::AssocItem,
 789     self_ty: Ty<'tcx>,
 790 ) {
 791     // Check that the method has a valid receiver type, given the type `Self`.
 792     debug!("check_method_receiver({:?}, self_ty={:?})", method, self_ty);
 793
 794     if !method.method_has_self_argument {
 795         return;
 796     }
 797
 798     let span = fn_sig.decl.inputs[0].span;
 799
 800     let sig = fcx.tcx.fn_sig(method.def_id);
 801     let sig = fcx.normalize_associated_types_in(span, &sig);
 802     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 803
 804     debug!("check_method_receiver: sig={:?}", sig);
 805
 806     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 807     let self_ty = fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(self_ty));
 808
 809     let receiver_ty = sig.inputs()[0];
 810
 811     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 812     let receiver_ty =
 813         fcx.tcx.liberate_late_bound_regions(method.def_id, &ty::Binder::bind(receiver_ty));
 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                     &format!(
 829                         "`{}` cannot be used as the type of `self` without \
 830                             the `arbitrary_self_types` feature",
 831                         receiver_ty,
 832                     ),
 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     struct_span_err!(
 846         fcx.tcx.sess.diagnostic(),
 847         span,
 848         E0307,
 849         "invalid `self` parameter type: {:?}",
 850         receiver_ty,
 851     )
 852     .note("type of `self` must be `Self` or a type that dereferences to it")
 853     .help(HELP_FOR_SELF_TYPE)
 854     .emit();
 855 }
 856
 857 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 858 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 859 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 860 /// strict: `receiver_ty` must implement `Receiver` and directly implement
 861 /// `Deref<Target = self_ty>`.
 862 ///
 863 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 864 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 865 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 866 fn receiver_is_valid<'fcx, 'tcx>(
 867     fcx: &FnCtxt<'fcx, 'tcx>,
 868     span: Span,
 869     receiver_ty: Ty<'tcx>,
 870     self_ty: Ty<'tcx>,
 871     arbitrary_self_types_enabled: bool,
 872 ) -> bool {
 873     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 874
 875     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 876
 877     // `self: Self` is always valid.
 878     if can_eq_self(receiver_ty) {
 879         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 880             err.emit();
 881         }
 882         return true;
 883     }
 884
 885     let mut autoderef = fcx.autoderef(span, receiver_ty);
 886
 887     // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
 888     if arbitrary_self_types_enabled {
 889         autoderef = autoderef.include_raw_pointers();
 890     }
 891
 892     // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
 893     autoderef.next();
 894
 895     let receiver_trait_def_id = fcx.tcx.require_lang_item(lang_items::ReceiverTraitLangItem, None);
 896
 897     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
 898     loop {
 899         if let Some((potential_self_ty, _)) = autoderef.next() {
 900             debug!(
 901                 "receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 902                 potential_self_ty, self_ty
 903             );
 904
 905             if can_eq_self(potential_self_ty) {
 906                 autoderef.finalize(fcx);
 907
 908                 if let Some(mut err) =
 909                     fcx.demand_eqtype_with_origin(&cause, self_ty, potential_self_ty)
 910                 {
 911                     err.emit();
 912                 }
 913
 914                 break;
 915             } else {
 916                 // Without `feature(arbitrary_self_types)`, we require that each step in the
 917                 // deref chain implement `receiver`
 918                 if !arbitrary_self_types_enabled
 919                     && !receiver_is_implemented(
 920                         fcx,
 921                         receiver_trait_def_id,
 922                         cause.clone(),
 923                         potential_self_ty,
 924                     )
 925                 {
 926                     return false;
 927                 }
 928             }
 929         } else {
 930             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`", receiver_ty, self_ty);
 931             // If he receiver already has errors reported due to it, consider it valid to avoid
 932             // unnecessary errors (#58712).
 933             return receiver_ty.references_error();
 934         }
 935     }
 936
 937     // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
 938     if !arbitrary_self_types_enabled
 939         && !receiver_is_implemented(fcx, receiver_trait_def_id, cause.clone(), receiver_ty)
 940     {
 941         return false;
 942     }
 943
 944     true
 945 }
 946
 947 fn receiver_is_implemented(
 948     fcx: &FnCtxt<'_, 'tcx>,
 949     receiver_trait_def_id: DefId,
 950     cause: ObligationCause<'tcx>,
 951     receiver_ty: Ty<'tcx>,
 952 ) -> bool {
 953     let trait_ref = ty::TraitRef {
 954         def_id: receiver_trait_def_id,
 955         substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 956     };
 957
 958     let obligation = traits::Obligation::new(cause, fcx.param_env, trait_ref.to_predicate());
 959
 960     if fcx.predicate_must_hold_modulo_regions(&obligation) {
 961         true
 962     } else {
 963         debug!(
 964             "receiver_is_implemented: type `{:?}` does not implement `Receiver` trait",
 965             receiver_ty
 966         );
 967         false
 968     }
 969 }
 970
 971 fn check_variances_for_type_defn<'tcx>(
 972     tcx: TyCtxt<'tcx>,
 973     item: &hir::Item<'tcx>,
 974     hir_generics: &hir::Generics<'_>,
 975 ) {
 976     let item_def_id = tcx.hir().local_def_id(item.hir_id);
 977     let ty = tcx.type_of(item_def_id);
 978     if tcx.has_error_field(ty) {
 979         return;
 980     }
 981
 982     let ty_predicates = tcx.predicates_of(item_def_id);
 983     assert_eq!(ty_predicates.parent, None);
 984     let variances = tcx.variances_of(item_def_id);
 985
 986     let mut constrained_parameters: FxHashSet<_> = variances
 987         .iter()
 988         .enumerate()
 989         .filter(|&(_, &variance)| variance != ty::Bivariant)
 990         .map(|(index, _)| Parameter(index as u32))
 991         .collect();
 992
 993     identify_constrained_generic_params(tcx, ty_predicates, None, &mut constrained_parameters);
 994
 995     for (index, _) in variances.iter().enumerate() {
 996         if constrained_parameters.contains(&Parameter(index as u32)) {
 997             continue;
 998         }
 999
1000         let param = &hir_generics.params[index];
1001
1002         match param.name {
1003             hir::ParamName::Error => {}
1004             _ => report_bivariance(tcx, param.span, param.name.ident().name),
1005         }
1006     }
1007 }
1008
1009 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
1010     let mut err = error_392(tcx, span, param_name);
1011
1012     let suggested_marker_id = tcx.lang_items().phantom_data();
1013     // Help is available only in presence of lang items.
1014     let msg = if let Some(def_id) = suggested_marker_id {
1015         format!(
1016             "consider removing `{}`, referring to it in a field, or using a marker such as `{}`",
1017             param_name,
1018             tcx.def_path_str(def_id),
1019         )
1020     } else {
1021         format!("consider removing `{}` or referring to it in a field", param_name)
1022     };
1023     err.help(&msg);
1024     err.emit();
1025 }
1026
1027 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1028 /// aren't true.
1029 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1030     let empty_env = ty::ParamEnv::empty();
1031
1032     let def_id = fcx.tcx.hir().local_def_id(id);
1033     let predicates = fcx.tcx.predicates_of(def_id).predicates.iter().map(|(p, _)| *p).collect();
1034     // Check elaborated bounds.
1035     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1036
1037     for pred in implied_obligations {
1038         // Match the existing behavior.
1039         if pred.is_global() && !pred.has_late_bound_regions() {
1040             let pred = fcx.normalize_associated_types_in(span, &pred);
1041             let obligation = traits::Obligation::new(
1042                 traits::ObligationCause::new(span, id, traits::TrivialBound),
1043                 empty_env,
1044                 pred,
1045             );
1046             fcx.register_predicate(obligation);
1047         }
1048     }
1049
1050     fcx.select_all_obligations_or_error();
1051 }
1052
1053 pub struct CheckTypeWellFormedVisitor<'tcx> {
1054     tcx: TyCtxt<'tcx>,
1055 }
1056
1057 impl CheckTypeWellFormedVisitor<'tcx> {
1058     pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1059         CheckTypeWellFormedVisitor { tcx }
1060     }
1061 }
1062
1063 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1064     fn visit_item(&self, i: &'tcx hir::Item<'tcx>) {
1065         debug!("visit_item: {:?}", i);
1066         let def_id = self.tcx.hir().local_def_id(i.hir_id);
1067         self.tcx.ensure().check_item_well_formed(def_id);
1068     }
1069
1070     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem<'tcx>) {
1071         debug!("visit_trait_item: {:?}", trait_item);
1072         let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1073         self.tcx.ensure().check_trait_item_well_formed(def_id);
1074     }
1075
1076     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem<'tcx>) {
1077         debug!("visit_impl_item: {:?}", impl_item);
1078         let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1079         self.tcx.ensure().check_impl_item_well_formed(def_id);
1080     }
1081 }
1082
1083 ///////////////////////////////////////////////////////////////////////////
1084 // ADT
1085
1086 struct AdtVariant<'tcx> {
1087     fields: Vec<AdtField<'tcx>>,
1088 }
1089
1090 struct AdtField<'tcx> {
1091     ty: Ty<'tcx>,
1092     span: Span,
1093 }
1094
1095 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1096     fn non_enum_variant(&self, struct_def: &hir::VariantData<'_>) -> AdtVariant<'tcx> {
1097         let fields = struct_def
1098             .fields()
1099             .iter()
1100             .map(|field| {
1101                 let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1102                 let field_ty = self.normalize_associated_types_in(field.span, &field_ty);
1103                 let field_ty = self.resolve_vars_if_possible(&field_ty);
1104                 debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1105                 AdtField { ty: field_ty, span: field.span }
1106             })
1107             .collect();
1108         AdtVariant { fields }
1109     }
1110
1111     fn enum_variants(&self, enum_def: &hir::EnumDef<'_>) -> Vec<AdtVariant<'tcx>> {
1112         enum_def.variants.iter().map(|variant| self.non_enum_variant(&variant.data)).collect()
1113     }
1114
1115     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1116         match self.tcx.impl_trait_ref(impl_def_id) {
1117             Some(ref trait_ref) => {
1118                 // Trait impl: take implied bounds from all types that
1119                 // appear in the trait reference.
1120                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1121                 trait_ref.substs.types().collect()
1122             }
1123
1124             None => {
1125                 // Inherent impl: take implied bounds from the `self` type.
1126                 let self_ty = self.tcx.type_of(impl_def_id);
1127                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1128                 vec![self_ty]
1129             }
1130         }
1131     }
1132 }
1133
1134 fn error_392(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) -> DiagnosticBuilder<'_> {
1135     let mut err =
1136         struct_span_err!(tcx.sess, span, E0392, "parameter `{}` is never used", param_name);
1137     err.span_label(span, "unused parameter");
1138     err
1139 }