src/librustc_typeck/check/wfcheck.rs

   1 use crate::check::{Inherited, FnCtxt};
   2 use crate::constrained_generic_params::{identify_constrained_generic_params, Parameter};
   3
   4 use crate::hir::def_id::DefId;
   5 use rustc::traits::{self, ObligationCauseCode};
   6 use rustc::ty::{self, Ty, TyCtxt, GenericParamDefKind, TypeFoldable, ToPredicate};
   7 use rustc::ty::subst::{Subst, InternalSubsts};
   8 use rustc::util::nodemap::{FxHashSet, FxHashMap};
   9 use rustc::mir::interpret::ConstValue;
  10 use rustc::middle::lang_items;
  11 use rustc::infer::opaque_types::may_define_existential_type;
  12
  13 use syntax::ast;
  14 use syntax::feature_gate::{self, GateIssue};
  15 use syntax_pos::Span;
  16 use syntax::symbol::sym;
  17 use errors::{DiagnosticBuilder, DiagnosticId};
  18
  19 use rustc::hir::itemlikevisit::ParItemLikeVisitor;
  20 use rustc::hir;
  21
  22 /// Helper type of a temporary returned by `.for_item(...)`.
  23 /// This is necessary because we can't write the following bound:
  24 ///
  25 /// ```rust
  26 /// F: for<'b, 'tcx> where 'tcx FnOnce(FnCtxt<'b, 'tcx>)
  27 /// ```
  28 struct CheckWfFcxBuilder<'tcx> {
  29     inherited: super::InheritedBuilder<'tcx>,
  30     id: hir::HirId,
  31     span: Span,
  32     param_env: ty::ParamEnv<'tcx>,
  33 }
  34
  35 impl<'tcx> CheckWfFcxBuilder<'tcx> {
  36     fn with_fcx<F>(&mut self, f: F)
  37     where
  38         F: for<'b> FnOnce(&FnCtxt<'b, 'tcx>, TyCtxt<'tcx>) -> Vec<Ty<'tcx>>,
  39     {
  40         let id = self.id;
  41         let span = self.span;
  42         let param_env = self.param_env;
  43         self.inherited.enter(|inh| {
  44             let fcx = FnCtxt::new(&inh, param_env, id);
  45             if !inh.tcx.features().trivial_bounds {
  46                 // As predicates are cached rather than obligations, this
  47                 // needsto be called first so that they are checked with an
  48                 // empty `param_env`.
  49                 check_false_global_bounds(&fcx, span, id);
  50             }
  51             let wf_tys = f(&fcx, fcx.tcx.global_tcx());
  52             fcx.select_all_obligations_or_error();
  53             fcx.regionck_item(id, span, &wf_tys);
  54         });
  55     }
  56 }
  57
  58 /// Checks that the field types (in a struct def'n) or argument types (in an enum def'n) are
  59 /// well-formed, meaning that they do not require any constraints not declared in the struct
  60 /// definition itself. For example, this definition would be illegal:
  61 ///
  62 /// ```rust
  63 /// struct Ref<'a, T> { x: &'a T }
  64 /// ```
  65 ///
  66 /// because the type did not declare that `T:'a`.
  67 ///
  68 /// We do this check as a pre-pass before checking fn bodies because if these constraints are
  69 /// not included it frequently leads to confusing errors in fn bodies. So it's better to check
  70 /// the types first.
  71 pub fn check_item_well_formed(tcx: TyCtxt<'_>, def_id: DefId) {
  72     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
  73     let item = tcx.hir().expect_item(hir_id);
  74
  75     debug!("check_item_well_formed(it.hir_id={:?}, it.name={})",
  76            item.hir_id,
  77            tcx.def_path_str(def_id));
  78
  79     match item.node {
  80         // Right now we check that every default trait implementation
  81         // has an implementation of itself. Basically, a case like:
  82         //
  83         //     impl Trait for T {}
  84         //
  85         // has a requirement of `T: Trait` which was required for default
  86         // method implementations. Although this could be improved now that
  87         // there's a better infrastructure in place for this, it's being left
  88         // for a follow-up work.
  89         //
  90         // Since there's such a requirement, we need to check *just* positive
  91         // implementations, otherwise things like:
  92         //
  93         //     impl !Send for T {}
  94         //
  95         // won't be allowed unless there's an *explicit* implementation of `Send`
  96         // for `T`
  97         hir::ItemKind::Impl(_, polarity, defaultness, _, ref trait_ref, ref self_ty, _) => {
  98             let is_auto = tcx.impl_trait_ref(tcx.hir().local_def_id(item.hir_id))
  99                                 .map_or(false, |trait_ref| tcx.trait_is_auto(trait_ref.def_id));
 100             if let (hir::Defaultness::Default { .. }, true) = (defaultness, is_auto) {
 101                 tcx.sess.span_err(item.span, "impls of auto traits cannot be default");
 102             }
 103             if polarity == hir::ImplPolarity::Positive {
 104                 check_impl(tcx, item, self_ty, trait_ref);
 105             } else {
 106                 // FIXME(#27579): what amount of WF checking do we need for neg impls?
 107                 if trait_ref.is_some() && !is_auto {
 108                     span_err!(tcx.sess, item.span, E0192,
 109                               "negative impls are only allowed for \
 110                                auto traits (e.g., `Send` and `Sync`)")
 111                 }
 112             }
 113         }
 114         hir::ItemKind::Fn(..) => {
 115             check_item_fn(tcx, item);
 116         }
 117         hir::ItemKind::Static(ref ty, ..) => {
 118             check_item_type(tcx, item.hir_id, ty.span, false);
 119         }
 120         hir::ItemKind::Const(ref ty, ..) => {
 121             check_item_type(tcx, item.hir_id, ty.span, false);
 122         }
 123         hir::ItemKind::ForeignMod(ref module) => for it in module.items.iter() {
 124             if let hir::ForeignItemKind::Static(ref ty, ..) = it.node {
 125                 check_item_type(tcx, it.hir_id, ty.span, true);
 126             }
 127         },
 128         hir::ItemKind::Struct(ref struct_def, ref ast_generics) => {
 129             check_type_defn(tcx, item, false, |fcx| {
 130                 vec![fcx.non_enum_variant(struct_def)]
 131             });
 132
 133             check_variances_for_type_defn(tcx, item, ast_generics);
 134         }
 135         hir::ItemKind::Union(ref struct_def, ref ast_generics) => {
 136             check_type_defn(tcx, item, true, |fcx| {
 137                 vec![fcx.non_enum_variant(struct_def)]
 138             });
 139
 140             check_variances_for_type_defn(tcx, item, ast_generics);
 141         }
 142         hir::ItemKind::Enum(ref enum_def, ref ast_generics) => {
 143             check_type_defn(tcx, item, true, |fcx| {
 144                 fcx.enum_variants(enum_def)
 145             });
 146
 147             check_variances_for_type_defn(tcx, item, ast_generics);
 148         }
 149         hir::ItemKind::Trait(..) => {
 150             check_trait(tcx, item);
 151         }
 152         hir::ItemKind::TraitAlias(..) => {
 153             check_trait(tcx, item);
 154         }
 155         _ => {}
 156     }
 157 }
 158
 159 pub fn check_trait_item(tcx: TyCtxt<'_>, def_id: DefId) {
 160     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 161     let trait_item = tcx.hir().expect_trait_item(hir_id);
 162
 163     let method_sig = match trait_item.node {
 164         hir::TraitItemKind::Method(ref sig, _) => Some(sig),
 165         _ => None
 166     };
 167     check_associated_item(tcx, trait_item.hir_id, trait_item.span, method_sig);
 168 }
 169
 170 pub fn check_impl_item(tcx: TyCtxt<'_>, def_id: DefId) {
 171     let hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 172     let impl_item = tcx.hir().expect_impl_item(hir_id);
 173
 174     let method_sig = match impl_item.node {
 175         hir::ImplItemKind::Method(ref sig, _) => Some(sig),
 176         _ => None
 177     };
 178     check_associated_item(tcx, impl_item.hir_id, impl_item.span, method_sig);
 179 }
 180
 181 fn check_associated_item(
 182     tcx: TyCtxt<'_>,
 183     item_id: hir::HirId,
 184     span: Span,
 185     sig_if_method: Option<&hir::MethodSig>,
 186 ) {
 187     debug!("check_associated_item: {:?}", item_id);
 188
 189     let code = ObligationCauseCode::MiscObligation;
 190     for_id(tcx, item_id, span).with_fcx(|fcx, tcx| {
 191         let item = fcx.tcx.associated_item(fcx.tcx.hir().local_def_id(item_id));
 192
 193         let (mut implied_bounds, self_ty) = match item.container {
 194             ty::TraitContainer(_) => (vec![], fcx.tcx.mk_self_type()),
 195             ty::ImplContainer(def_id) => (fcx.impl_implied_bounds(def_id, span),
 196                                           fcx.tcx.type_of(def_id))
 197         };
 198
 199         match item.kind {
 200             ty::AssocKind::Const => {
 201                 let ty = fcx.tcx.type_of(item.def_id);
 202                 let ty = fcx.normalize_associated_types_in(span, &ty);
 203                 fcx.register_wf_obligation(ty, span, code.clone());
 204             }
 205             ty::AssocKind::Method => {
 206                 reject_shadowing_parameters(fcx.tcx, item.def_id);
 207                 let sig = fcx.tcx.fn_sig(item.def_id);
 208                 let sig = fcx.normalize_associated_types_in(span, &sig);
 209                 check_fn_or_method(tcx, fcx, span, sig,
 210                                    item.def_id, &mut implied_bounds);
 211                 let sig_if_method = sig_if_method.expect("bad signature for method");
 212                 check_method_receiver(fcx, sig_if_method, &item, self_ty);
 213             }
 214             ty::AssocKind::Type => {
 215                 if item.defaultness.has_value() {
 216                     let ty = fcx.tcx.type_of(item.def_id);
 217                     let ty = fcx.normalize_associated_types_in(span, &ty);
 218                     fcx.register_wf_obligation(ty, span, code.clone());
 219                 }
 220             }
 221             ty::AssocKind::Existential => {
 222                 // do nothing, existential types check themselves
 223             }
 224         }
 225
 226         implied_bounds
 227     })
 228 }
 229
 230 fn for_item<'tcx>(tcx: TyCtxt<'tcx>, item: &hir::Item) -> CheckWfFcxBuilder<'tcx> {
 231     for_id(tcx, item.hir_id, item.span)
 232 }
 233
 234 fn for_id(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) -> CheckWfFcxBuilder<'_> {
 235     let def_id = tcx.hir().local_def_id(id);
 236     CheckWfFcxBuilder {
 237         inherited: Inherited::build(tcx, def_id),
 238         id,
 239         span,
 240         param_env: tcx.param_env(def_id),
 241     }
 242 }
 243
 244 /// In a type definition, we check that to ensure that the types of the fields are well-formed.
 245 fn check_type_defn<'tcx, F>(
 246     tcx: TyCtxt<'tcx>,
 247     item: &hir::Item,
 248     all_sized: bool,
 249     mut lookup_fields: F,
 250 ) where
 251     F: for<'fcx> FnMut(&FnCtxt<'fcx, 'tcx>) -> Vec<AdtVariant<'tcx>>,
 252 {
 253     for_item(tcx, item).with_fcx(|fcx, fcx_tcx| {
 254         let variants = lookup_fields(fcx);
 255         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 256         let packed = fcx.tcx.adt_def(def_id).repr.packed();
 257
 258         for variant in &variants {
 259             // For DST, or when drop needs to copy things around, all
 260             // intermediate types must be sized.
 261             let needs_drop_copy = || {
 262                 packed && {
 263                     let ty = variant.fields.last().unwrap().ty;
 264                     let ty = fcx.tcx.erase_regions(&ty);
 265                     if ty.has_local_value() {
 266                             fcx_tcx.sess.delay_span_bug(
 267                                 item.span, &format!("inference variables in {:?}", ty));
 268                             // Just treat unresolved type expression as if it needs drop.
 269                             true
 270                     } else {
 271                         ty.needs_drop(fcx_tcx, fcx_tcx.param_env(def_id))
 272                     }
 273                 }
 274             };
 275             let all_sized =
 276                 all_sized ||
 277                 variant.fields.is_empty() ||
 278                 needs_drop_copy();
 279             let unsized_len = if all_sized {
 280                 0
 281             } else {
 282                 1
 283             };
 284             for (idx, field) in variant.fields[..variant.fields.len() - unsized_len]
 285                 .iter()
 286                 .enumerate()
 287             {
 288                 let last = idx == variant.fields.len() - 1;
 289                 fcx.register_bound(
 290                     field.ty,
 291                     fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 292                     traits::ObligationCause::new(
 293                         field.span,
 294                         fcx.body_id,
 295                         traits::FieldSized {
 296                             adt_kind: match item.node.adt_kind() {
 297                                 Some(i) => i,
 298                                 None => bug!(),
 299                             },
 300                             last
 301                         }
 302                     )
 303                 );
 304             }
 305
 306             // All field types must be well-formed.
 307             for field in &variant.fields {
 308                 fcx.register_wf_obligation(field.ty, field.span,
 309                     ObligationCauseCode::MiscObligation)
 310             }
 311         }
 312
 313         check_where_clauses(tcx, fcx, item.span, def_id, None);
 314
 315         // No implied bounds in a struct definition.
 316         vec![]
 317     });
 318 }
 319
 320 fn check_trait(tcx: TyCtxt<'_>, item: &hir::Item) {
 321     debug!("check_trait: {:?}", item.hir_id);
 322
 323     let trait_def_id = tcx.hir().local_def_id(item.hir_id);
 324
 325     let trait_def = tcx.trait_def(trait_def_id);
 326     if trait_def.is_marker {
 327         for associated_def_id in &*tcx.associated_item_def_ids(trait_def_id) {
 328             struct_span_err!(
 329                 tcx.sess,
 330                 tcx.def_span(*associated_def_id),
 331                 E0714,
 332                 "marker traits cannot have associated items",
 333             ).emit();
 334         }
 335     }
 336
 337     for_item(tcx, item).with_fcx(|fcx, _| {
 338         check_where_clauses(tcx, fcx, item.span, trait_def_id, None);
 339         vec![]
 340     });
 341 }
 342
 343 fn check_item_fn(tcx: TyCtxt<'_>, item: &hir::Item) {
 344     for_item(tcx, item).with_fcx(|fcx, tcx| {
 345         let def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 346         let sig = fcx.tcx.fn_sig(def_id);
 347         let sig = fcx.normalize_associated_types_in(item.span, &sig);
 348         let mut implied_bounds = vec![];
 349         check_fn_or_method(tcx, fcx, item.span, sig,
 350                            def_id, &mut implied_bounds);
 351         implied_bounds
 352     })
 353 }
 354
 355 fn check_item_type(
 356     tcx: TyCtxt<'_>,
 357     item_id: hir::HirId,
 358     ty_span: Span,
 359     allow_foreign_ty: bool,
 360 ) {
 361     debug!("check_item_type: {:?}", item_id);
 362
 363     for_id(tcx, item_id, ty_span).with_fcx(|fcx, gcx| {
 364         let ty = gcx.type_of(gcx.hir().local_def_id(item_id));
 365         let item_ty = fcx.normalize_associated_types_in(ty_span, &ty);
 366
 367         let mut forbid_unsized = true;
 368         if allow_foreign_ty {
 369             let tail = fcx.tcx.struct_tail_erasing_lifetimes(item_ty, fcx.param_env);
 370             if let ty::Foreign(_) = tail.sty {
 371                 forbid_unsized = false;
 372             }
 373         }
 374
 375         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 376         if forbid_unsized {
 377             fcx.register_bound(
 378                 item_ty,
 379                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 380                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 381             );
 382         }
 383
 384         // No implied bounds in a const, etc.
 385         vec![]
 386     });
 387 }
 388
 389 fn check_impl<'tcx>(
 390     tcx: TyCtxt<'tcx>,
 391     item: &hir::Item,
 392     ast_self_ty: &hir::Ty,
 393     ast_trait_ref: &Option<hir::TraitRef>,
 394 ) {
 395     debug!("check_impl: {:?}", item);
 396
 397     for_item(tcx, item).with_fcx(|fcx, tcx| {
 398         let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 399
 400         match *ast_trait_ref {
 401             Some(ref ast_trait_ref) => {
 402                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 403                 let trait_ref =
 404                     fcx.normalize_associated_types_in(
 405                         ast_trait_ref.path.span, &trait_ref);
 406                 let obligations =
 407                     ty::wf::trait_obligations(fcx,
 408                                                 fcx.param_env,
 409                                                 fcx.body_id,
 410                                                 &trait_ref,
 411                                                 ast_trait_ref.path.span);
 412                 for obligation in obligations {
 413                     fcx.register_predicate(obligation);
 414                 }
 415             }
 416             None => {
 417                 let self_ty = fcx.tcx.type_of(item_def_id);
 418                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 419                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 420                     ObligationCauseCode::MiscObligation);
 421             }
 422         }
 423
 424         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 425
 426         fcx.impl_implied_bounds(item_def_id, item.span)
 427     });
 428 }
 429
 430 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 431 fn check_where_clauses<'tcx, 'fcx>(
 432     tcx: TyCtxt<'tcx>,
 433     fcx: &FnCtxt<'fcx, 'tcx>,
 434     span: Span,
 435     def_id: DefId,
 436     return_ty: Option<Ty<'tcx>>,
 437 ) {
 438     debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
 439
 440     let predicates = fcx.tcx.predicates_of(def_id);
 441     let generics = tcx.generics_of(def_id);
 442
 443     let is_our_default = |def: &ty::GenericParamDef| {
 444         match def.kind {
 445             GenericParamDefKind::Type { has_default, .. } => {
 446                 has_default && def.index >= generics.parent_count as u32
 447             }
 448             _ => unreachable!()
 449         }
 450     };
 451
 452     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 453     // For example, this forbids the declaration:
 454     //
 455     //     struct Foo<T = Vec<[u32]>> { .. }
 456     //
 457     // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 458     for param in &generics.params {
 459         if let GenericParamDefKind::Type { .. } = param.kind {
 460             if is_our_default(&param) {
 461                 let ty = fcx.tcx.type_of(param.def_id);
 462                 // Ignore dependent defaults -- that is, where the default of one type
 463                 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
 464                 // be sure if it will error or not as user might always specify the other.
 465                 if !ty.needs_subst() {
 466                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 467                         ObligationCauseCode::MiscObligation);
 468                 }
 469             }
 470         }
 471     }
 472
 473     // Check that trait predicates are WF when params are substituted by their defaults.
 474     // We don't want to overly constrain the predicates that may be written but we want to
 475     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 476     // Therefore we check if a predicate which contains a single type param
 477     // with a concrete default is WF with that default substituted.
 478     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 479     //
 480     // First we build the defaulted substitution.
 481     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 482         match param.kind {
 483             GenericParamDefKind::Lifetime => {
 484                 // All regions are identity.
 485                 fcx.tcx.mk_param_from_def(param)
 486             }
 487
 488             GenericParamDefKind::Type { .. } => {
 489                 // If the param has a default, ...
 490                 if is_our_default(param) {
 491                     let default_ty = fcx.tcx.type_of(param.def_id);
 492                     // ... and it's not a dependent default, ...
 493                     if !default_ty.needs_subst() {
 494                         // ... then substitute it with the default.
 495                         return default_ty.into();
 496                     }
 497                 }
 498                 // Mark unwanted params as error.
 499                 fcx.tcx.types.err.into()
 500             }
 501
 502             GenericParamDefKind::Const => {
 503                 // FIXME(const_generics:defaults)
 504                 fcx.tcx.consts.err.into()
 505             }
 506         }
 507     });
 508
 509     // Now we build the substituted predicates.
 510     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 511         #[derive(Default)]
 512         struct CountParams { params: FxHashSet<u32> }
 513         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 514             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 515                 if let ty::Param(param) = t.sty {
 516                     self.params.insert(param.index);
 517                 }
 518                 t.super_visit_with(self)
 519             }
 520
 521             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 522                 true
 523             }
 524
 525             fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 526                 if let ConstValue::Param(param) = c.val {
 527                     self.params.insert(param.index);
 528                 }
 529                 c.super_visit_with(self)
 530             }
 531         }
 532         let mut param_count = CountParams::default();
 533         let has_region = pred.visit_with(&mut param_count);
 534         let substituted_pred = pred.subst(fcx.tcx, substs);
 535         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 536         // or preds with multiple params.
 537         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 538             None
 539         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 540             // Avoid duplication of predicates that contain no parameters, for example.
 541             None
 542         } else {
 543             Some(substituted_pred)
 544         }
 545     }).map(|pred| {
 546         // Convert each of those into an obligation. So if you have
 547         // something like `struct Foo<T: Copy = String>`, we would
 548         // take that predicate `T: Copy`, substitute to `String: Copy`
 549         // (actually that happens in the previous `flat_map` call),
 550         // and then try to prove it (in this case, we'll fail).
 551         //
 552         // Note the subtle difference from how we handle `predicates`
 553         // below: there, we are not trying to prove those predicates
 554         // to be *true* but merely *well-formed*.
 555         let pred = fcx.normalize_associated_types_in(span, &pred);
 556         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 557         traits::Obligation::new(cause, fcx.param_env, pred)
 558     });
 559
 560     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 561
 562     if let Some(return_ty) = return_ty {
 563         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 564     }
 565
 566     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 567
 568     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 569     let wf_obligations =
 570         predicates.predicates
 571                     .iter()
 572                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 573                                                                 fcx.param_env,
 574                                                                 fcx.body_id,
 575                                                                 p,
 576                                                                 span));
 577
 578     for obligation in wf_obligations.chain(default_obligations) {
 579         debug!("next obligation cause: {:?}", obligation.cause);
 580         fcx.register_predicate(obligation);
 581     }
 582 }
 583
 584 fn check_fn_or_method<'fcx, 'tcx>(
 585     tcx: TyCtxt<'tcx>,
 586     fcx: &FnCtxt<'fcx, 'tcx>,
 587     span: Span,
 588     sig: ty::PolyFnSig<'tcx>,
 589     def_id: DefId,
 590     implied_bounds: &mut Vec<Ty<'tcx>>,
 591 ) {
 592     let sig = fcx.normalize_associated_types_in(span, &sig);
 593     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 594
 595     for input_ty in sig.inputs() {
 596         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 597     }
 598     implied_bounds.extend(sig.inputs());
 599
 600     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 601
 602     // FIXME(#25759) return types should not be implied bounds
 603     implied_bounds.push(sig.output());
 604
 605     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 606 }
 607
 608 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 609 /// "higher-order pattern unification".
 610 /// This ensures that inference is tractable.
 611 /// In particular, definitions of existential types can only use other generics as arguments,
 612 /// and they cannot repeat an argument. Example:
 613 ///
 614 /// ```rust
 615 /// existential type Foo<A, B>;
 616 ///
 617 /// // Okay -- `Foo` is applied to two distinct, generic types.
 618 /// fn a<T, U>() -> Foo<T, U> { .. }
 619 ///
 620 /// // Not okay -- `Foo` is applied to `T` twice.
 621 /// fn b<T>() -> Foo<T, T> { .. }
 622 ///
 623 /// // Not okay -- `Foo` is applied to a non-generic type.
 624 /// fn b<T>() -> Foo<T, u32> { .. }
 625 /// ```
 626 ///
 627 fn check_existential_types<'fcx, 'tcx>(
 628     tcx: TyCtxt<'tcx>,
 629     fcx: &FnCtxt<'fcx, 'tcx>,
 630     fn_def_id: DefId,
 631     span: Span,
 632     ty: Ty<'tcx>,
 633 ) -> Vec<ty::Predicate<'tcx>> {
 634     trace!("check_existential_types(ty={:?})", ty);
 635     let mut substituted_predicates = Vec::new();
 636     ty.fold_with(&mut ty::fold::BottomUpFolder {
 637         tcx: fcx.tcx,
 638         ty_op: |ty| {
 639             if let ty::Opaque(def_id, substs) = ty.sty {
 640                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 641                 let generics = tcx.generics_of(def_id);
 642                 // Only check named existential types defined in this crate.
 643                 if generics.parent.is_none() && def_id.is_local() {
 644                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 645                     if may_define_existential_type(tcx, fn_def_id, opaque_hir_id) {
 646                         trace!("check_existential_types: may define, generics={:#?}", generics);
 647                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 648                         for (subst, param) in substs.iter().zip(&generics.params) {
 649                             match subst.unpack() {
 650                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 651                                     ty::Param(..) => {}
 652                                     // Prevent `fn foo() -> Foo<u32>` from being defining.
 653                                     _ => {
 654                                         tcx.sess
 655                                             .struct_span_err(
 656                                                 span,
 657                                                 "non-defining existential type use \
 658                                                  in defining scope",
 659                                             )
 660                                             .span_note(
 661                                                 tcx.def_span(param.def_id),
 662                                                 &format!(
 663                                                     "used non-generic type {} for \
 664                                                      generic parameter",
 665                                                     ty,
 666                                                 ),
 667                                             )
 668                                             .emit();
 669                                     }
 670                                 }
 671
 672                                 ty::subst::UnpackedKind::Lifetime(region) => {
 673                                     let param_span = tcx.def_span(param.def_id);
 674                                     if let ty::ReStatic = region {
 675                                         tcx
 676                                             .sess
 677                                             .struct_span_err(
 678                                                 span,
 679                                                 "non-defining existential type use \
 680                                                     in defining scope",
 681                                             )
 682                                             .span_label(
 683                                                 param_span,
 684                                                 "cannot use static lifetime, use a bound lifetime \
 685                                                 instead or remove the lifetime parameter from the \
 686                                                 existential type",
 687                                             )
 688                                             .emit();
 689                                     } else {
 690                                         seen.entry(region).or_default().push(param_span);
 691                                     }
 692                                 }
 693
 694                                 ty::subst::UnpackedKind::Const(ct) => match ct.val {
 695                                     ConstValue::Param(_) => {}
 696                                     _ => {
 697                                         tcx.sess
 698                                             .struct_span_err(
 699                                                 span,
 700                                                 "non-defining existential type use \
 701                                                 in defining scope",
 702                                             )
 703                                             .span_note(
 704                                                 tcx.def_span(param.def_id),
 705                                                 &format!(
 706                                                     "used non-generic const {} for \
 707                                                     generic parameter",
 708                                                     ty,
 709                                                 ),
 710                                             )
 711                                             .emit();
 712                                     }
 713                                 }
 714                             } // match subst
 715                         } // for (subst, param)
 716                         for (_, spans) in seen {
 717                             if spans.len() > 1 {
 718                                 tcx
 719                                     .sess
 720                                     .struct_span_err(
 721                                         span,
 722                                         "non-defining existential type use \
 723                                             in defining scope",
 724                                     ).
 725                                     span_note(
 726                                         spans,
 727                                         "lifetime used multiple times",
 728                                     )
 729                                     .emit();
 730                             }
 731                         }
 732                     } // if may_define_existential_type
 733
 734                     // Now register the bounds on the parameters of the existential type
 735                     // so the parameters given by the function need to fulfill them.
 736                     //
 737                     //     existential type Foo<T: Bar>: 'static;
 738                     //     fn foo<U>() -> Foo<U> { .. *}
 739                     //
 740                     // becomes
 741                     //
 742                     //     existential type Foo<T: Bar>: 'static;
 743                     //     fn foo<U: Bar>() -> Foo<U> { .. *}
 744                     let predicates = tcx.predicates_of(def_id);
 745                     trace!(
 746                         "check_existential_types: may define, predicates={:#?}",
 747                         predicates,
 748                     );
 749                     for &(pred, _) in predicates.predicates.iter() {
 750                         let substituted_pred = pred.subst(fcx.tcx, substs);
 751                         // Avoid duplication of predicates that contain no parameters, for example.
 752                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 753                             substituted_predicates.push(substituted_pred);
 754                         }
 755                     }
 756                 } // if is_named_existential_type
 757             } // if let Opaque
 758             ty
 759         },
 760         lt_op: |lt| lt,
 761         ct_op: |ct| ct,
 762     });
 763     substituted_predicates
 764 }
 765
 766 fn check_method_receiver<'fcx, 'tcx>(
 767     fcx: &FnCtxt<'fcx, 'tcx>,
 768     method_sig: &hir::MethodSig,
 769     method: &ty::AssocItem,
 770     self_ty: Ty<'tcx>,
 771 ) {
 772     const HELP_FOR_SELF_TYPE: &str =
 773         "consider changing to `self`, `&self`, `&mut self`, `self: Box<Self>`, \
 774          `self: Rc<Self>`, `self: Arc<Self>`, or `self: Pin<P>` (where P is one \
 775          of the previous types except `Self`)";
 776     // Check that the method has a valid receiver type, given the type `Self`.
 777     debug!("check_method_receiver({:?}, self_ty={:?})",
 778            method, self_ty);
 779
 780     if !method.method_has_self_argument {
 781         return;
 782     }
 783
 784     let span = method_sig.decl.inputs[0].span;
 785
 786     let sig = fcx.tcx.fn_sig(method.def_id);
 787     let sig = fcx.normalize_associated_types_in(span, &sig);
 788     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 789
 790     debug!("check_method_receiver: sig={:?}", sig);
 791
 792     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 793     let self_ty = fcx.tcx.liberate_late_bound_regions(
 794         method.def_id,
 795         &ty::Binder::bind(self_ty)
 796     );
 797
 798     let receiver_ty = sig.inputs()[0];
 799
 800     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 801     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 802         method.def_id,
 803         &ty::Binder::bind(receiver_ty)
 804     );
 805
 806     if fcx.tcx.features().arbitrary_self_types {
 807         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 808             // Report error; `arbitrary_self_types` was enabled.
 809             fcx.tcx.sess.diagnostic().mut_span_err(
 810                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 811             ).note("type of `self` must be `Self` or a type that dereferences to it")
 812             .help(HELP_FOR_SELF_TYPE)
 813             .code(DiagnosticId::Error("E0307".into()))
 814             .emit();
 815         }
 816     } else {
 817         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 818             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 819                 // Report error; would have worked with `arbitrary_self_types`.
 820                 feature_gate::feature_err(
 821                     &fcx.tcx.sess.parse_sess,
 822                     sym::arbitrary_self_types,
 823                     span,
 824                     GateIssue::Language,
 825                     &format!(
 826                         "`{}` cannot be used as the type of `self` without \
 827                             the `arbitrary_self_types` feature",
 828                         receiver_ty,
 829                     ),
 830                 ).help(HELP_FOR_SELF_TYPE)
 831                 .emit();
 832             } else {
 833                 // Report error; would not have worked with `arbitrary_self_types`.
 834                 fcx.tcx.sess.diagnostic().mut_span_err(
 835                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 836                 ).note("type must be `Self` or a type that dereferences to it")
 837                 .help(HELP_FOR_SELF_TYPE)
 838                 .code(DiagnosticId::Error("E0307".into()))
 839                 .emit();
 840             }
 841         }
 842     }
 843 }
 844
 845 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 846 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 847 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 848 /// strict: `receiver_ty` must implement `Receiver` and directly implement
 849 /// `Deref<Target = self_ty>`.
 850 ///
 851 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 852 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 853 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 854 fn receiver_is_valid<'fcx, 'tcx>(
 855     fcx: &FnCtxt<'fcx, 'tcx>,
 856     span: Span,
 857     receiver_ty: Ty<'tcx>,
 858     self_ty: Ty<'tcx>,
 859     arbitrary_self_types_enabled: bool,
 860 ) -> bool {
 861     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 862
 863     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 864
 865     // `self: Self` is always valid.
 866     if can_eq_self(receiver_ty) {
 867         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 868             err.emit();
 869         }
 870         return true
 871     }
 872
 873     let mut autoderef = fcx.autoderef(span, receiver_ty);
 874
 875     // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
 876     if arbitrary_self_types_enabled {
 877         autoderef = autoderef.include_raw_pointers();
 878     }
 879
 880     // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
 881     autoderef.next();
 882
 883     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
 884     loop {
 885         if let Some((potential_self_ty, _)) = autoderef.next() {
 886             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 887                 potential_self_ty, self_ty);
 888
 889             if can_eq_self(potential_self_ty) {
 890                 autoderef.finalize(fcx);
 891
 892                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 893                     &cause, self_ty, potential_self_ty
 894                 ) {
 895                     err.emit();
 896                 }
 897
 898                 break
 899             }
 900         } else {
 901             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 902                 receiver_ty, self_ty);
 903             // If he receiver already has errors reported due to it, consider it valid to avoid
 904             // unecessary errors (#58712).
 905             return receiver_ty.references_error();
 906         }
 907
 908         // Without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 909         // `self_ty`. Enforce this by only doing one iteration of the loop.
 910         if !arbitrary_self_types_enabled {
 911             return false
 912         }
 913     }
 914
 915     // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
 916     if !arbitrary_self_types_enabled {
 917         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 918             Some(did) => did,
 919             None => {
 920                 debug!("receiver_is_valid: missing Receiver trait");
 921                 return false
 922             }
 923         };
 924
 925         let trait_ref = ty::TraitRef{
 926             def_id: trait_def_id,
 927             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 928         };
 929
 930         let obligation = traits::Obligation::new(
 931             cause,
 932             fcx.param_env,
 933             trait_ref.to_predicate()
 934         );
 935
 936         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 937             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 938                 receiver_ty);
 939             return false
 940         }
 941     }
 942
 943     true
 944 }
 945
 946 fn check_variances_for_type_defn<'tcx>(
 947     tcx: TyCtxt<'tcx>,
 948     item: &hir::Item,
 949     hir_generics: &hir::Generics,
 950 ) {
 951     let item_def_id = tcx.hir().local_def_id(item.hir_id);
 952     let ty = tcx.type_of(item_def_id);
 953     if tcx.has_error_field(ty) {
 954         return;
 955     }
 956
 957     let ty_predicates = tcx.predicates_of(item_def_id);
 958     assert_eq!(ty_predicates.parent, None);
 959     let variances = tcx.variances_of(item_def_id);
 960
 961     let mut constrained_parameters: FxHashSet<_> =
 962         variances.iter().enumerate()
 963                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 964                         .map(|(index, _)| Parameter(index as u32))
 965                         .collect();
 966
 967     identify_constrained_generic_params(
 968         tcx,
 969         &ty_predicates,
 970         None,
 971         &mut constrained_parameters,
 972     );
 973
 974     for (index, _) in variances.iter().enumerate() {
 975         if constrained_parameters.contains(&Parameter(index as u32)) {
 976             continue;
 977         }
 978
 979         let param = &hir_generics.params[index];
 980
 981         match param.name {
 982             hir::ParamName::Error => { }
 983             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 984         }
 985     }
 986 }
 987
 988 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
 989     let mut err = error_392(tcx, span, param_name);
 990
 991     let suggested_marker_id = tcx.lang_items().phantom_data();
 992     // Help is available only in presence of lang items.
 993     if let Some(def_id) = suggested_marker_id {
 994         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 995                           param_name,
 996                           tcx.def_path_str(def_id)));
 997     }
 998     err.emit();
 999 }
1000
1001 fn reject_shadowing_parameters(tcx: TyCtxt<'_>, def_id: DefId) {
1002     let generics = tcx.generics_of(def_id);
1003     let parent = tcx.generics_of(generics.parent.unwrap());
1004     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
1005         GenericParamDefKind::Lifetime => None,
1006         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1007             Some((param.name, param.def_id))
1008         }
1009     }).collect();
1010
1011     for method_param in &generics.params {
1012         // Shadowing is checked in `resolve_lifetime`.
1013         if let GenericParamDefKind::Lifetime = method_param.kind {
1014             continue
1015         }
1016         if impl_params.contains_key(&method_param.name) {
1017             // Tighten up the span to focus on only the shadowing type.
1018             let type_span = tcx.def_span(method_param.def_id);
1019
1020             // The expectation here is that the original trait declaration is
1021             // local so it should be okay to just unwrap everything.
1022             let trait_def_id = impl_params[&method_param.name];
1023             let trait_decl_span = tcx.def_span(trait_def_id);
1024             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
1025         }
1026     }
1027 }
1028
1029 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1030 /// aren't true.
1031 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1032     let empty_env = ty::ParamEnv::empty();
1033
1034     let def_id = fcx.tcx.hir().local_def_id(id);
1035     let predicates = fcx.tcx.predicates_of(def_id).predicates
1036         .iter()
1037         .map(|(p, _)| *p)
1038         .collect();
1039     // Check elaborated bounds.
1040     let implied_obligations = traits::elaborate_predicates(fcx.tcx, predicates);
1041
1042     for pred in implied_obligations {
1043         // Match the existing behavior.
1044         if pred.is_global() && !pred.has_late_bound_regions() {
1045             let pred = fcx.normalize_associated_types_in(span, &pred);
1046             let obligation = traits::Obligation::new(
1047                 traits::ObligationCause::new(
1048                     span,
1049                     id,
1050                     traits::TrivialBound,
1051                 ),
1052                 empty_env,
1053                 pred,
1054             );
1055             fcx.register_predicate(obligation);
1056         }
1057     }
1058
1059     fcx.select_all_obligations_or_error();
1060 }
1061
1062 pub struct CheckTypeWellFormedVisitor<'tcx> {
1063     tcx: TyCtxt<'tcx>,
1064 }
1065
1066 impl CheckTypeWellFormedVisitor<'tcx> {
1067     pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1068         CheckTypeWellFormedVisitor {
1069             tcx,
1070         }
1071     }
1072 }
1073
1074 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1075     fn visit_item(&self, i: &'tcx hir::Item) {
1076         debug!("visit_item: {:?}", i);
1077         let def_id = self.tcx.hir().local_def_id(i.hir_id);
1078         self.tcx.ensure().check_item_well_formed(def_id);
1079     }
1080
1081     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem) {
1082         debug!("visit_trait_item: {:?}", trait_item);
1083         let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1084         self.tcx.ensure().check_trait_item_well_formed(def_id);
1085     }
1086
1087     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem) {
1088         debug!("visit_impl_item: {:?}", impl_item);
1089         let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1090         self.tcx.ensure().check_impl_item_well_formed(def_id);
1091     }
1092 }
1093
1094 ///////////////////////////////////////////////////////////////////////////
1095 // ADT
1096
1097 struct AdtVariant<'tcx> {
1098     fields: Vec<AdtField<'tcx>>,
1099 }
1100
1101 struct AdtField<'tcx> {
1102     ty: Ty<'tcx>,
1103     span: Span,
1104 }
1105
1106 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1107     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1108         let fields = struct_def.fields().iter().map(|field| {
1109             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1110             let field_ty = self.normalize_associated_types_in(field.span,
1111                                                               &field_ty);
1112             let field_ty = self.resolve_vars_if_possible(&field_ty);
1113             debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1114             AdtField { ty: field_ty, span: field.span }
1115         })
1116         .collect();
1117         AdtVariant { fields }
1118     }
1119
1120     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1121         enum_def.variants.iter()
1122             .map(|variant| self.non_enum_variant(&variant.node.data))
1123             .collect()
1124     }
1125
1126     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1127         match self.tcx.impl_trait_ref(impl_def_id) {
1128             Some(ref trait_ref) => {
1129                 // Trait impl: take implied bounds from all types that
1130                 // appear in the trait reference.
1131                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1132                 trait_ref.substs.types().collect()
1133             }
1134
1135             None => {
1136                 // Inherent impl: take implied bounds from the `self` type.
1137                 let self_ty = self.tcx.type_of(impl_def_id);
1138                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1139                 vec![self_ty]
1140             }
1141         }
1142     }
1143 }
1144
1145 fn error_392(
1146     tcx: TyCtxt<'_>,
1147     span: Span,
1148     param_name: ast::Name,
1149 ) -> DiagnosticBuilder<'_> {
1150     let mut err = struct_span_err!(tcx.sess, span, E0392,
1151                   "parameter `{}` is never used", param_name);
1152     err.span_label(span, "unused parameter");
1153     err
1154 }
1155
1156 fn error_194(tcx: TyCtxt<'_>, span: Span, trait_decl_span: Span, name: &str) {
1157     struct_span_err!(tcx.sess, span, E0194,
1158                      "type parameter `{}` shadows another type parameter of the same name",
1159                      name)
1160         .span_label(span, "shadows another type parameter")
1161         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1162         .emit();
1163 }