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             if let ty::Foreign(_) = fcx.tcx.struct_tail(item_ty).sty {
 370                 forbid_unsized = false;
 371             }
 372         }
 373
 374         fcx.register_wf_obligation(item_ty, ty_span, ObligationCauseCode::MiscObligation);
 375         if forbid_unsized {
 376             fcx.register_bound(
 377                 item_ty,
 378                 fcx.tcx.require_lang_item(lang_items::SizedTraitLangItem),
 379                 traits::ObligationCause::new(ty_span, fcx.body_id, traits::MiscObligation),
 380             );
 381         }
 382
 383         // No implied bounds in a const, etc.
 384         vec![]
 385     });
 386 }
 387
 388 fn check_impl<'tcx>(
 389     tcx: TyCtxt<'tcx>,
 390     item: &hir::Item,
 391     ast_self_ty: &hir::Ty,
 392     ast_trait_ref: &Option<hir::TraitRef>,
 393 ) {
 394     debug!("check_impl: {:?}", item);
 395
 396     for_item(tcx, item).with_fcx(|fcx, tcx| {
 397         let item_def_id = fcx.tcx.hir().local_def_id(item.hir_id);
 398
 399         match *ast_trait_ref {
 400             Some(ref ast_trait_ref) => {
 401                 let trait_ref = fcx.tcx.impl_trait_ref(item_def_id).unwrap();
 402                 let trait_ref =
 403                     fcx.normalize_associated_types_in(
 404                         ast_trait_ref.path.span, &trait_ref);
 405                 let obligations =
 406                     ty::wf::trait_obligations(fcx,
 407                                                 fcx.param_env,
 408                                                 fcx.body_id,
 409                                                 &trait_ref,
 410                                                 ast_trait_ref.path.span);
 411                 for obligation in obligations {
 412                     fcx.register_predicate(obligation);
 413                 }
 414             }
 415             None => {
 416                 let self_ty = fcx.tcx.type_of(item_def_id);
 417                 let self_ty = fcx.normalize_associated_types_in(item.span, &self_ty);
 418                 fcx.register_wf_obligation(self_ty, ast_self_ty.span,
 419                     ObligationCauseCode::MiscObligation);
 420             }
 421         }
 422
 423         check_where_clauses(tcx, fcx, item.span, item_def_id, None);
 424
 425         fcx.impl_implied_bounds(item_def_id, item.span)
 426     });
 427 }
 428
 429 /// Checks where-clauses and inline bounds that are declared on `def_id`.
 430 fn check_where_clauses<'tcx, 'fcx>(
 431     tcx: TyCtxt<'tcx>,
 432     fcx: &FnCtxt<'fcx, 'tcx>,
 433     span: Span,
 434     def_id: DefId,
 435     return_ty: Option<Ty<'tcx>>,
 436 ) {
 437     debug!("check_where_clauses(def_id={:?}, return_ty={:?})", def_id, return_ty);
 438
 439     let predicates = fcx.tcx.predicates_of(def_id);
 440     let generics = tcx.generics_of(def_id);
 441
 442     let is_our_default = |def: &ty::GenericParamDef| {
 443         match def.kind {
 444             GenericParamDefKind::Type { has_default, .. } => {
 445                 has_default && def.index >= generics.parent_count as u32
 446             }
 447             _ => unreachable!()
 448         }
 449     };
 450
 451     // Check that concrete defaults are well-formed. See test `type-check-defaults.rs`.
 452     // For example, this forbids the declaration:
 453     //
 454     //     struct Foo<T = Vec<[u32]>> { .. }
 455     //
 456     // Here, the default `Vec<[u32]>` is not WF because `[u32]: Sized` does not hold.
 457     for param in &generics.params {
 458         if let GenericParamDefKind::Type { .. } = param.kind {
 459             if is_our_default(&param) {
 460                 let ty = fcx.tcx.type_of(param.def_id);
 461                 // Ignore dependent defaults -- that is, where the default of one type
 462                 // parameter includes another (e.g., `<T, U = T>`). In those cases, we can't
 463                 // be sure if it will error or not as user might always specify the other.
 464                 if !ty.needs_subst() {
 465                     fcx.register_wf_obligation(ty, fcx.tcx.def_span(param.def_id),
 466                         ObligationCauseCode::MiscObligation);
 467                 }
 468             }
 469         }
 470     }
 471
 472     // Check that trait predicates are WF when params are substituted by their defaults.
 473     // We don't want to overly constrain the predicates that may be written but we want to
 474     // catch cases where a default my never be applied such as `struct Foo<T: Copy = String>`.
 475     // Therefore we check if a predicate which contains a single type param
 476     // with a concrete default is WF with that default substituted.
 477     // For more examples see tests `defaults-well-formedness.rs` and `type-check-defaults.rs`.
 478     //
 479     // First we build the defaulted substitution.
 480     let substs = InternalSubsts::for_item(fcx.tcx, def_id, |param, _| {
 481         match param.kind {
 482             GenericParamDefKind::Lifetime => {
 483                 // All regions are identity.
 484                 fcx.tcx.mk_param_from_def(param)
 485             }
 486
 487             GenericParamDefKind::Type { .. } => {
 488                 // If the param has a default, ...
 489                 if is_our_default(param) {
 490                     let default_ty = fcx.tcx.type_of(param.def_id);
 491                     // ... and it's not a dependent default, ...
 492                     if !default_ty.needs_subst() {
 493                         // ... then substitute it with the default.
 494                         return default_ty.into();
 495                     }
 496                 }
 497                 // Mark unwanted params as error.
 498                 fcx.tcx.types.err.into()
 499             }
 500
 501             GenericParamDefKind::Const => {
 502                 // FIXME(const_generics:defaults)
 503                 fcx.tcx.consts.err.into()
 504             }
 505         }
 506     });
 507
 508     // Now we build the substituted predicates.
 509     let default_obligations = predicates.predicates.iter().flat_map(|&(pred, _)| {
 510         #[derive(Default)]
 511         struct CountParams { params: FxHashSet<u32> }
 512         impl<'tcx> ty::fold::TypeVisitor<'tcx> for CountParams {
 513             fn visit_ty(&mut self, t: Ty<'tcx>) -> bool {
 514                 if let ty::Param(param) = t.sty {
 515                     self.params.insert(param.index);
 516                 }
 517                 t.super_visit_with(self)
 518             }
 519
 520             fn visit_region(&mut self, _: ty::Region<'tcx>) -> bool {
 521                 true
 522             }
 523
 524             fn visit_const(&mut self, c: &'tcx ty::Const<'tcx>) -> bool {
 525                 if let ConstValue::Param(param) = c.val {
 526                     self.params.insert(param.index);
 527                 }
 528                 c.super_visit_with(self)
 529             }
 530         }
 531         let mut param_count = CountParams::default();
 532         let has_region = pred.visit_with(&mut param_count);
 533         let substituted_pred = pred.subst(fcx.tcx, substs);
 534         // Don't check non-defaulted params, dependent defaults (including lifetimes)
 535         // or preds with multiple params.
 536         if substituted_pred.references_error() || param_count.params.len() > 1 || has_region {
 537             None
 538         } else if predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 539             // Avoid duplication of predicates that contain no parameters, for example.
 540             None
 541         } else {
 542             Some(substituted_pred)
 543         }
 544     }).map(|pred| {
 545         // Convert each of those into an obligation. So if you have
 546         // something like `struct Foo<T: Copy = String>`, we would
 547         // take that predicate `T: Copy`, substitute to `String: Copy`
 548         // (actually that happens in the previous `flat_map` call),
 549         // and then try to prove it (in this case, we'll fail).
 550         //
 551         // Note the subtle difference from how we handle `predicates`
 552         // below: there, we are not trying to prove those predicates
 553         // to be *true* but merely *well-formed*.
 554         let pred = fcx.normalize_associated_types_in(span, &pred);
 555         let cause = traits::ObligationCause::new(span, fcx.body_id, traits::ItemObligation(def_id));
 556         traits::Obligation::new(cause, fcx.param_env, pred)
 557     });
 558
 559     let mut predicates = predicates.instantiate_identity(fcx.tcx);
 560
 561     if let Some(return_ty) = return_ty {
 562         predicates.predicates.extend(check_existential_types(tcx, fcx, def_id, span, return_ty));
 563     }
 564
 565     let predicates = fcx.normalize_associated_types_in(span, &predicates);
 566
 567     debug!("check_where_clauses: predicates={:?}", predicates.predicates);
 568     let wf_obligations =
 569         predicates.predicates
 570                     .iter()
 571                     .flat_map(|p| ty::wf::predicate_obligations(fcx,
 572                                                                 fcx.param_env,
 573                                                                 fcx.body_id,
 574                                                                 p,
 575                                                                 span));
 576
 577     for obligation in wf_obligations.chain(default_obligations) {
 578         debug!("next obligation cause: {:?}", obligation.cause);
 579         fcx.register_predicate(obligation);
 580     }
 581 }
 582
 583 fn check_fn_or_method<'fcx, 'tcx>(
 584     tcx: TyCtxt<'tcx>,
 585     fcx: &FnCtxt<'fcx, 'tcx>,
 586     span: Span,
 587     sig: ty::PolyFnSig<'tcx>,
 588     def_id: DefId,
 589     implied_bounds: &mut Vec<Ty<'tcx>>,
 590 ) {
 591     let sig = fcx.normalize_associated_types_in(span, &sig);
 592     let sig = fcx.tcx.liberate_late_bound_regions(def_id, &sig);
 593
 594     for input_ty in sig.inputs() {
 595         fcx.register_wf_obligation(&input_ty, span, ObligationCauseCode::MiscObligation);
 596     }
 597     implied_bounds.extend(sig.inputs());
 598
 599     fcx.register_wf_obligation(sig.output(), span, ObligationCauseCode::MiscObligation);
 600
 601     // FIXME(#25759) return types should not be implied bounds
 602     implied_bounds.push(sig.output());
 603
 604     check_where_clauses(tcx, fcx, span, def_id, Some(sig.output()));
 605 }
 606
 607 /// Checks "defining uses" of existential types to ensure that they meet the restrictions laid for
 608 /// "higher-order pattern unification".
 609 /// This ensures that inference is tractable.
 610 /// In particular, definitions of existential types can only use other generics as arguments,
 611 /// and they cannot repeat an argument. Example:
 612 ///
 613 /// ```rust
 614 /// existential type Foo<A, B>;
 615 ///
 616 /// // Okay -- `Foo` is applied to two distinct, generic types.
 617 /// fn a<T, U>() -> Foo<T, U> { .. }
 618 ///
 619 /// // Not okay -- `Foo` is applied to `T` twice.
 620 /// fn b<T>() -> Foo<T, T> { .. }
 621 ///
 622 /// // Not okay -- `Foo` is applied to a non-generic type.
 623 /// fn b<T>() -> Foo<T, u32> { .. }
 624 /// ```
 625 ///
 626 fn check_existential_types<'fcx, 'tcx>(
 627     tcx: TyCtxt<'tcx>,
 628     fcx: &FnCtxt<'fcx, 'tcx>,
 629     fn_def_id: DefId,
 630     span: Span,
 631     ty: Ty<'tcx>,
 632 ) -> Vec<ty::Predicate<'tcx>> {
 633     trace!("check_existential_types(ty={:?})", ty);
 634     let mut substituted_predicates = Vec::new();
 635     ty.fold_with(&mut ty::fold::BottomUpFolder {
 636         tcx: fcx.tcx,
 637         ty_op: |ty| {
 638             if let ty::Opaque(def_id, substs) = ty.sty {
 639                 trace!("check_existential_types: opaque_ty, {:?}, {:?}", def_id, substs);
 640                 let generics = tcx.generics_of(def_id);
 641                 // Only check named existential types defined in this crate.
 642                 if generics.parent.is_none() && def_id.is_local() {
 643                     let opaque_hir_id = tcx.hir().as_local_hir_id(def_id).unwrap();
 644                     if may_define_existential_type(tcx, fn_def_id, opaque_hir_id) {
 645                         trace!("check_existential_types: may define, generics={:#?}", generics);
 646                         let mut seen: FxHashMap<_, Vec<_>> = FxHashMap::default();
 647                         for (subst, param) in substs.iter().zip(&generics.params) {
 648                             match subst.unpack() {
 649                                 ty::subst::UnpackedKind::Type(ty) => match ty.sty {
 650                                     ty::Param(..) => {}
 651                                     // Prevent `fn foo() -> Foo<u32>` from being defining.
 652                                     _ => {
 653                                         tcx.sess
 654                                             .struct_span_err(
 655                                                 span,
 656                                                 "non-defining existential type use \
 657                                                  in defining scope",
 658                                             )
 659                                             .span_note(
 660                                                 tcx.def_span(param.def_id),
 661                                                 &format!(
 662                                                     "used non-generic type {} for \
 663                                                      generic parameter",
 664                                                     ty,
 665                                                 ),
 666                                             )
 667                                             .emit();
 668                                     }
 669                                 }
 670
 671                                 ty::subst::UnpackedKind::Lifetime(region) => {
 672                                     let param_span = tcx.def_span(param.def_id);
 673                                     if let ty::ReStatic = region {
 674                                         tcx
 675                                             .sess
 676                                             .struct_span_err(
 677                                                 span,
 678                                                 "non-defining existential type use \
 679                                                     in defining scope",
 680                                             )
 681                                             .span_label(
 682                                                 param_span,
 683                                                 "cannot use static lifetime, use a bound lifetime \
 684                                                 instead or remove the lifetime parameter from the \
 685                                                 existential type",
 686                                             )
 687                                             .emit();
 688                                     } else {
 689                                         seen.entry(region).or_default().push(param_span);
 690                                     }
 691                                 }
 692
 693                                 ty::subst::UnpackedKind::Const(ct) => match ct.val {
 694                                     ConstValue::Param(_) => {}
 695                                     _ => {
 696                                         tcx.sess
 697                                             .struct_span_err(
 698                                                 span,
 699                                                 "non-defining existential type use \
 700                                                 in defining scope",
 701                                             )
 702                                             .span_note(
 703                                                 tcx.def_span(param.def_id),
 704                                                 &format!(
 705                                                     "used non-generic const {} for \
 706                                                     generic parameter",
 707                                                     ty,
 708                                                 ),
 709                                             )
 710                                             .emit();
 711                                     }
 712                                 }
 713                             } // match subst
 714                         } // for (subst, param)
 715                         for (_, spans) in seen {
 716                             if spans.len() > 1 {
 717                                 tcx
 718                                     .sess
 719                                     .struct_span_err(
 720                                         span,
 721                                         "non-defining existential type use \
 722                                             in defining scope",
 723                                     ).
 724                                     span_note(
 725                                         spans,
 726                                         "lifetime used multiple times",
 727                                     )
 728                                     .emit();
 729                             }
 730                         }
 731                     } // if may_define_existential_type
 732
 733                     // Now register the bounds on the parameters of the existential type
 734                     // so the parameters given by the function need to fulfill them.
 735                     //
 736                     //     existential type Foo<T: Bar>: 'static;
 737                     //     fn foo<U>() -> Foo<U> { .. *}
 738                     //
 739                     // becomes
 740                     //
 741                     //     existential type Foo<T: Bar>: 'static;
 742                     //     fn foo<U: Bar>() -> Foo<U> { .. *}
 743                     let predicates = tcx.predicates_of(def_id);
 744                     trace!(
 745                         "check_existential_types: may define, predicates={:#?}",
 746                         predicates,
 747                     );
 748                     for &(pred, _) in predicates.predicates.iter() {
 749                         let substituted_pred = pred.subst(fcx.tcx, substs);
 750                         // Avoid duplication of predicates that contain no parameters, for example.
 751                         if !predicates.predicates.iter().any(|&(p, _)| p == substituted_pred) {
 752                             substituted_predicates.push(substituted_pred);
 753                         }
 754                     }
 755                 } // if is_named_existential_type
 756             } // if let Opaque
 757             ty
 758         },
 759         lt_op: |lt| lt,
 760         ct_op: |ct| ct,
 761     });
 762     substituted_predicates
 763 }
 764
 765 fn check_method_receiver<'fcx, 'tcx>(
 766     fcx: &FnCtxt<'fcx, 'tcx>,
 767     method_sig: &hir::MethodSig,
 768     method: &ty::AssocItem,
 769     self_ty: Ty<'tcx>,
 770 ) {
 771     // Check that the method has a valid receiver type, given the type `Self`.
 772     debug!("check_method_receiver({:?}, self_ty={:?})",
 773            method, self_ty);
 774
 775     if !method.method_has_self_argument {
 776         return;
 777     }
 778
 779     let span = method_sig.decl.inputs[0].span;
 780
 781     let sig = fcx.tcx.fn_sig(method.def_id);
 782     let sig = fcx.normalize_associated_types_in(span, &sig);
 783     let sig = fcx.tcx.liberate_late_bound_regions(method.def_id, &sig);
 784
 785     debug!("check_method_receiver: sig={:?}", sig);
 786
 787     let self_ty = fcx.normalize_associated_types_in(span, &self_ty);
 788     let self_ty = fcx.tcx.liberate_late_bound_regions(
 789         method.def_id,
 790         &ty::Binder::bind(self_ty)
 791     );
 792
 793     let receiver_ty = sig.inputs()[0];
 794
 795     let receiver_ty = fcx.normalize_associated_types_in(span, &receiver_ty);
 796     let receiver_ty = fcx.tcx.liberate_late_bound_regions(
 797         method.def_id,
 798         &ty::Binder::bind(receiver_ty)
 799     );
 800
 801     if fcx.tcx.features().arbitrary_self_types {
 802         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 803             // Report error; `arbitrary_self_types` was enabled.
 804             fcx.tcx.sess.diagnostic().mut_span_err(
 805                 span, &format!("invalid method receiver type: {:?}", receiver_ty)
 806             ).note("type of `self` must be `Self` or a type that dereferences to it")
 807             .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 808             .code(DiagnosticId::Error("E0307".into()))
 809             .emit();
 810         }
 811     } else {
 812         if !receiver_is_valid(fcx, span, receiver_ty, self_ty, false) {
 813             if receiver_is_valid(fcx, span, receiver_ty, self_ty, true) {
 814                 // Report error; would have worked with `arbitrary_self_types`.
 815                 feature_gate::feature_err(
 816                     &fcx.tcx.sess.parse_sess,
 817                     sym::arbitrary_self_types,
 818                     span,
 819                     GateIssue::Language,
 820                     &format!(
 821                         "`{}` cannot be used as the type of `self` without \
 822                             the `arbitrary_self_types` feature",
 823                         receiver_ty,
 824                     ),
 825                 ).help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 826                 .emit();
 827             } else {
 828                 // Report error; would not have worked with `arbitrary_self_types`.
 829                 fcx.tcx.sess.diagnostic().mut_span_err(
 830                     span, &format!("invalid method receiver type: {:?}", receiver_ty)
 831                 ).note("type must be `Self` or a type that dereferences to it")
 832                 .help("consider changing to `self`, `&self`, `&mut self`, or `self: Box<Self>`")
 833                 .code(DiagnosticId::Error("E0307".into()))
 834                 .emit();
 835             }
 836         }
 837     }
 838 }
 839
 840 /// Returns whether `receiver_ty` would be considered a valid receiver type for `self_ty`. If
 841 /// `arbitrary_self_types` is enabled, `receiver_ty` must transitively deref to `self_ty`, possibly
 842 /// through a `*const/mut T` raw pointer. If the feature is not enabled, the requirements are more
 843 /// strict: `receiver_ty` must implement `Receiver` and directly implement
 844 /// `Deref<Target = self_ty>`.
 845 ///
 846 /// N.B., there are cases this function returns `true` but causes an error to be emitted,
 847 /// particularly when `receiver_ty` derefs to a type that is the same as `self_ty` but has the
 848 /// wrong lifetime. Be careful of this if you are calling this function speculatively.
 849 fn receiver_is_valid<'fcx, 'tcx>(
 850     fcx: &FnCtxt<'fcx, 'tcx>,
 851     span: Span,
 852     receiver_ty: Ty<'tcx>,
 853     self_ty: Ty<'tcx>,
 854     arbitrary_self_types_enabled: bool,
 855 ) -> bool {
 856     let cause = fcx.cause(span, traits::ObligationCauseCode::MethodReceiver);
 857
 858     let can_eq_self = |ty| fcx.infcx.can_eq(fcx.param_env, self_ty, ty).is_ok();
 859
 860     // `self: Self` is always valid.
 861     if can_eq_self(receiver_ty) {
 862         if let Some(mut err) = fcx.demand_eqtype_with_origin(&cause, self_ty, receiver_ty) {
 863             err.emit();
 864         }
 865         return true
 866     }
 867
 868     let mut autoderef = fcx.autoderef(span, receiver_ty);
 869
 870     // The `arbitrary_self_types` feature allows raw pointer receivers like `self: *const Self`.
 871     if arbitrary_self_types_enabled {
 872         autoderef = autoderef.include_raw_pointers();
 873     }
 874
 875     // The first type is `receiver_ty`, which we know its not equal to `self_ty`; skip it.
 876     autoderef.next();
 877
 878     // Keep dereferencing `receiver_ty` until we get to `self_ty`.
 879     loop {
 880         if let Some((potential_self_ty, _)) = autoderef.next() {
 881             debug!("receiver_is_valid: potential self type `{:?}` to match `{:?}`",
 882                 potential_self_ty, self_ty);
 883
 884             if can_eq_self(potential_self_ty) {
 885                 autoderef.finalize(fcx);
 886
 887                 if let Some(mut err) = fcx.demand_eqtype_with_origin(
 888                     &cause, self_ty, potential_self_ty
 889                 ) {
 890                     err.emit();
 891                 }
 892
 893                 break
 894             }
 895         } else {
 896             debug!("receiver_is_valid: type `{:?}` does not deref to `{:?}`",
 897                 receiver_ty, self_ty);
 898             // If he receiver already has errors reported due to it, consider it valid to avoid
 899             // unecessary errors (#58712).
 900             return receiver_ty.references_error();
 901         }
 902
 903         // Without the `arbitrary_self_types` feature, `receiver_ty` must directly deref to
 904         // `self_ty`. Enforce this by only doing one iteration of the loop.
 905         if !arbitrary_self_types_enabled {
 906             return false
 907         }
 908     }
 909
 910     // Without `feature(arbitrary_self_types)`, we require that `receiver_ty` implements `Receiver`.
 911     if !arbitrary_self_types_enabled {
 912         let trait_def_id = match fcx.tcx.lang_items().receiver_trait() {
 913             Some(did) => did,
 914             None => {
 915                 debug!("receiver_is_valid: missing Receiver trait");
 916                 return false
 917             }
 918         };
 919
 920         let trait_ref = ty::TraitRef{
 921             def_id: trait_def_id,
 922             substs: fcx.tcx.mk_substs_trait(receiver_ty, &[]),
 923         };
 924
 925         let obligation = traits::Obligation::new(
 926             cause,
 927             fcx.param_env,
 928             trait_ref.to_predicate()
 929         );
 930
 931         if !fcx.predicate_must_hold_modulo_regions(&obligation) {
 932             debug!("receiver_is_valid: type `{:?}` does not implement `Receiver` trait",
 933                 receiver_ty);
 934             return false
 935         }
 936     }
 937
 938     true
 939 }
 940
 941 fn check_variances_for_type_defn<'tcx>(
 942     tcx: TyCtxt<'tcx>,
 943     item: &hir::Item,
 944     hir_generics: &hir::Generics,
 945 ) {
 946     let item_def_id = tcx.hir().local_def_id(item.hir_id);
 947     let ty = tcx.type_of(item_def_id);
 948     if tcx.has_error_field(ty) {
 949         return;
 950     }
 951
 952     let ty_predicates = tcx.predicates_of(item_def_id);
 953     assert_eq!(ty_predicates.parent, None);
 954     let variances = tcx.variances_of(item_def_id);
 955
 956     let mut constrained_parameters: FxHashSet<_> =
 957         variances.iter().enumerate()
 958                         .filter(|&(_, &variance)| variance != ty::Bivariant)
 959                         .map(|(index, _)| Parameter(index as u32))
 960                         .collect();
 961
 962     identify_constrained_generic_params(
 963         tcx,
 964         &ty_predicates,
 965         None,
 966         &mut constrained_parameters,
 967     );
 968
 969     for (index, _) in variances.iter().enumerate() {
 970         if constrained_parameters.contains(&Parameter(index as u32)) {
 971             continue;
 972         }
 973
 974         let param = &hir_generics.params[index];
 975
 976         match param.name {
 977             hir::ParamName::Error => { }
 978             _ => report_bivariance(tcx, param.span, param.name.ident().name),
 979         }
 980     }
 981 }
 982
 983 fn report_bivariance(tcx: TyCtxt<'_>, span: Span, param_name: ast::Name) {
 984     let mut err = error_392(tcx, span, param_name);
 985
 986     let suggested_marker_id = tcx.lang_items().phantom_data();
 987     // Help is available only in presence of lang items.
 988     if let Some(def_id) = suggested_marker_id {
 989         err.help(&format!("consider removing `{}` or using a marker such as `{}`",
 990                           param_name,
 991                           tcx.def_path_str(def_id)));
 992     }
 993     err.emit();
 994 }
 995
 996 fn reject_shadowing_parameters(tcx: TyCtxt<'_>, def_id: DefId) {
 997     let generics = tcx.generics_of(def_id);
 998     let parent = tcx.generics_of(generics.parent.unwrap());
 999     let impl_params: FxHashMap<_, _> = parent.params.iter().flat_map(|param| match param.kind {
1000         GenericParamDefKind::Lifetime => None,
1001         GenericParamDefKind::Type { .. } | GenericParamDefKind::Const => {
1002             Some((param.name, param.def_id))
1003         }
1004     }).collect();
1005
1006     for method_param in &generics.params {
1007         // Shadowing is checked in `resolve_lifetime`.
1008         if let GenericParamDefKind::Lifetime = method_param.kind {
1009             continue
1010         }
1011         if impl_params.contains_key(&method_param.name) {
1012             // Tighten up the span to focus on only the shadowing type.
1013             let type_span = tcx.def_span(method_param.def_id);
1014
1015             // The expectation here is that the original trait declaration is
1016             // local so it should be okay to just unwrap everything.
1017             let trait_def_id = impl_params[&method_param.name];
1018             let trait_decl_span = tcx.def_span(trait_def_id);
1019             error_194(tcx, type_span, trait_decl_span, &method_param.name.as_str()[..]);
1020         }
1021     }
1022 }
1023
1024 /// Feature gates RFC 2056 -- trivial bounds, checking for global bounds that
1025 /// aren't true.
1026 fn check_false_global_bounds(fcx: &FnCtxt<'_, '_>, span: Span, id: hir::HirId) {
1027     let empty_env = ty::ParamEnv::empty();
1028
1029     let def_id = fcx.tcx.hir().local_def_id(id);
1030     let predicates = fcx.tcx.predicates_of(def_id).predicates
1031         .iter()
1032         .map(|(p, _)| *p)
1033         .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(
1043                     span,
1044                     id,
1045                     traits::TrivialBound,
1046                 ),
1047                 empty_env,
1048                 pred,
1049             );
1050             fcx.register_predicate(obligation);
1051         }
1052     }
1053
1054     fcx.select_all_obligations_or_error();
1055 }
1056
1057 pub struct CheckTypeWellFormedVisitor<'tcx> {
1058     tcx: TyCtxt<'tcx>,
1059 }
1060
1061 impl CheckTypeWellFormedVisitor<'tcx> {
1062     pub fn new(tcx: TyCtxt<'tcx>) -> CheckTypeWellFormedVisitor<'tcx> {
1063         CheckTypeWellFormedVisitor {
1064             tcx,
1065         }
1066     }
1067 }
1068
1069 impl ParItemLikeVisitor<'tcx> for CheckTypeWellFormedVisitor<'tcx> {
1070     fn visit_item(&self, i: &'tcx hir::Item) {
1071         debug!("visit_item: {:?}", i);
1072         let def_id = self.tcx.hir().local_def_id(i.hir_id);
1073         self.tcx.ensure().check_item_well_formed(def_id);
1074     }
1075
1076     fn visit_trait_item(&self, trait_item: &'tcx hir::TraitItem) {
1077         debug!("visit_trait_item: {:?}", trait_item);
1078         let def_id = self.tcx.hir().local_def_id(trait_item.hir_id);
1079         self.tcx.ensure().check_trait_item_well_formed(def_id);
1080     }
1081
1082     fn visit_impl_item(&self, impl_item: &'tcx hir::ImplItem) {
1083         debug!("visit_impl_item: {:?}", impl_item);
1084         let def_id = self.tcx.hir().local_def_id(impl_item.hir_id);
1085         self.tcx.ensure().check_impl_item_well_formed(def_id);
1086     }
1087 }
1088
1089 ///////////////////////////////////////////////////////////////////////////
1090 // ADT
1091
1092 struct AdtVariant<'tcx> {
1093     fields: Vec<AdtField<'tcx>>,
1094 }
1095
1096 struct AdtField<'tcx> {
1097     ty: Ty<'tcx>,
1098     span: Span,
1099 }
1100
1101 impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
1102     fn non_enum_variant(&self, struct_def: &hir::VariantData) -> AdtVariant<'tcx> {
1103         let fields = struct_def.fields().iter().map(|field| {
1104             let field_ty = self.tcx.type_of(self.tcx.hir().local_def_id(field.hir_id));
1105             let field_ty = self.normalize_associated_types_in(field.span,
1106                                                               &field_ty);
1107             let field_ty = self.resolve_vars_if_possible(&field_ty);
1108             debug!("non_enum_variant: type of field {:?} is {:?}", field, field_ty);
1109             AdtField { ty: field_ty, span: field.span }
1110         })
1111         .collect();
1112         AdtVariant { fields }
1113     }
1114
1115     fn enum_variants(&self, enum_def: &hir::EnumDef) -> Vec<AdtVariant<'tcx>> {
1116         enum_def.variants.iter()
1117             .map(|variant| self.non_enum_variant(&variant.node.data))
1118             .collect()
1119     }
1120
1121     fn impl_implied_bounds(&self, impl_def_id: DefId, span: Span) -> Vec<Ty<'tcx>> {
1122         match self.tcx.impl_trait_ref(impl_def_id) {
1123             Some(ref trait_ref) => {
1124                 // Trait impl: take implied bounds from all types that
1125                 // appear in the trait reference.
1126                 let trait_ref = self.normalize_associated_types_in(span, trait_ref);
1127                 trait_ref.substs.types().collect()
1128             }
1129
1130             None => {
1131                 // Inherent impl: take implied bounds from the `self` type.
1132                 let self_ty = self.tcx.type_of(impl_def_id);
1133                 let self_ty = self.normalize_associated_types_in(span, &self_ty);
1134                 vec![self_ty]
1135             }
1136         }
1137     }
1138 }
1139
1140 fn error_392(
1141     tcx: TyCtxt<'_>,
1142     span: Span,
1143     param_name: ast::Name,
1144 ) -> DiagnosticBuilder<'_> {
1145     let mut err = struct_span_err!(tcx.sess, span, E0392,
1146                   "parameter `{}` is never used", param_name);
1147     err.span_label(span, "unused parameter");
1148     err
1149 }
1150
1151 fn error_194(tcx: TyCtxt<'_>, span: Span, trait_decl_span: Span, name: &str) {
1152     struct_span_err!(tcx.sess, span, E0194,
1153                      "type parameter `{}` shadows another type parameter of the same name",
1154                      name)
1155         .span_label(span, "shadows another type parameter")
1156         .span_label(trait_decl_span, format!("first `{}` declared here", name))
1157         .emit();
1158 }