src/librustc/hir/lowering/item.rs

   1 use super::LoweringContext;
   2 use super::ImplTraitContext;
   3 use super::ImplTraitPosition;
   4 use super::ImplTraitTypeIdVisitor;
   5 use super::AnonymousLifetimeMode;
   6 use super::ParamMode;
   7
   8 use crate::hir::{self, HirVec};
   9 use crate::hir::ptr::P;
  10 use crate::hir::def_id::DefId;
  11 use crate::hir::def::{Res, DefKind};
  12 use crate::util::nodemap::NodeMap;
  13
  14 use rustc_data_structures::thin_vec::ThinVec;
  15
  16 use std::collections::BTreeSet;
  17 use smallvec::SmallVec;
  18 use syntax::attr;
  19 use syntax::ast::*;
  20 use syntax::visit::{self, Visitor};
  21 use syntax::ext::base::SpecialDerives;
  22 use syntax::source_map::{respan, DesugaringKind, Spanned};
  23 use syntax::symbol::{kw, sym};
  24 use syntax_pos::Span;
  25
  26 pub(super) struct ItemLowerer<'tcx, 'interner> {
  27     pub(super) lctx: &'tcx mut LoweringContext<'interner>,
  28 }
  29
  30 impl<'tcx, 'interner> ItemLowerer<'tcx, 'interner> {
  31     fn with_trait_impl_ref<F>(&mut self, trait_impl_ref: &Option<TraitRef>, f: F)
  32     where
  33         F: FnOnce(&mut Self),
  34     {
  35         let old = self.lctx.is_in_trait_impl;
  36         self.lctx.is_in_trait_impl = if let &None = trait_impl_ref {
  37             false
  38         } else {
  39             true
  40         };
  41         f(self);
  42         self.lctx.is_in_trait_impl = old;
  43     }
  44 }
  45
  46 impl<'tcx, 'interner> Visitor<'tcx> for ItemLowerer<'tcx, 'interner> {
  47     fn visit_mod(&mut self, m: &'tcx Mod, _s: Span, _attrs: &[Attribute], n: NodeId) {
  48         self.lctx.modules.insert(n, hir::ModuleItems {
  49             items: BTreeSet::new(),
  50             trait_items: BTreeSet::new(),
  51             impl_items: BTreeSet::new(),
  52         });
  53
  54         let old = self.lctx.current_module;
  55         self.lctx.current_module = n;
  56         visit::walk_mod(self, m);
  57         self.lctx.current_module = old;
  58     }
  59
  60     fn visit_item(&mut self, item: &'tcx Item) {
  61         let mut item_hir_id = None;
  62         self.lctx.with_hir_id_owner(item.id, |lctx| {
  63             if let Some(hir_item) = lctx.lower_item(item) {
  64                 item_hir_id = Some(hir_item.hir_id);
  65                 lctx.insert_item(hir_item);
  66             }
  67         });
  68
  69         if let Some(hir_id) = item_hir_id {
  70             self.lctx.with_parent_item_lifetime_defs(hir_id, |this| {
  71                 let this = &mut ItemLowerer { lctx: this };
  72                 if let ItemKind::Impl(.., ref opt_trait_ref, _, _) = item.node {
  73                     this.with_trait_impl_ref(opt_trait_ref, |this| {
  74                         visit::walk_item(this, item)
  75                     });
  76                 } else {
  77                     visit::walk_item(this, item);
  78                 }
  79             });
  80         }
  81     }
  82
  83     fn visit_trait_item(&mut self, item: &'tcx TraitItem) {
  84         self.lctx.with_hir_id_owner(item.id, |lctx| {
  85             let hir_item = lctx.lower_trait_item(item);
  86             let id = hir::TraitItemId { hir_id: hir_item.hir_id };
  87             lctx.trait_items.insert(id, hir_item);
  88             lctx.modules.get_mut(&lctx.current_module).unwrap().trait_items.insert(id);
  89         });
  90
  91         visit::walk_trait_item(self, item);
  92     }
  93
  94     fn visit_impl_item(&mut self, item: &'tcx ImplItem) {
  95         self.lctx.with_hir_id_owner(item.id, |lctx| {
  96             let hir_item = lctx.lower_impl_item(item);
  97             let id = hir::ImplItemId { hir_id: hir_item.hir_id };
  98             lctx.impl_items.insert(id, hir_item);
  99             lctx.modules.get_mut(&lctx.current_module).unwrap().impl_items.insert(id);
 100         });
 101         visit::walk_impl_item(self, item);
 102     }
 103 }
 104
 105 impl LoweringContext<'_> {
 106     // Same as the method above, but accepts `hir::GenericParam`s
 107     // instead of `ast::GenericParam`s.
 108     // This should only be used with generics that have already had their
 109     // in-band lifetimes added. In practice, this means that this function is
 110     // only used when lowering a child item of a trait or impl.
 111     fn with_parent_item_lifetime_defs<T>(
 112         &mut self,
 113         parent_hir_id: hir::HirId,
 114         f: impl FnOnce(&mut LoweringContext<'_>) -> T,
 115     ) -> T {
 116         let old_len = self.in_scope_lifetimes.len();
 117
 118         let parent_generics = match self.items.get(&parent_hir_id).unwrap().node {
 119             hir::ItemKind::Impl(_, _, _, ref generics, ..)
 120             | hir::ItemKind::Trait(_, _, ref generics, ..) => {
 121                 &generics.params[..]
 122             }
 123             _ => &[],
 124         };
 125         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
 126             hir::GenericParamKind::Lifetime { .. } => Some(param.name.ident().modern()),
 127             _ => None,
 128         });
 129         self.in_scope_lifetimes.extend(lt_def_names);
 130
 131         let res = f(self);
 132
 133         self.in_scope_lifetimes.truncate(old_len);
 134         res
 135     }
 136
 137     pub(super) fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
 138         hir::Mod {
 139             inner: m.inner,
 140             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
 141         }
 142     }
 143
 144     pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
 145         let node_ids = match i.node {
 146             ItemKind::Use(ref use_tree) => {
 147                 let mut vec = smallvec![i.id];
 148                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
 149                 vec
 150             }
 151             ItemKind::MacroDef(..) => SmallVec::new(),
 152             ItemKind::Fn(..) |
 153             ItemKind::Impl(.., None, _, _) => smallvec![i.id],
 154             ItemKind::Static(ref ty, ..) => {
 155                 let mut ids = smallvec![i.id];
 156                 if self.sess.features_untracked().impl_trait_in_bindings {
 157                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 158                     visitor.visit_ty(ty);
 159                 }
 160                 ids
 161             },
 162             ItemKind::Const(ref ty, ..) => {
 163                 let mut ids = smallvec![i.id];
 164                 if self.sess.features_untracked().impl_trait_in_bindings {
 165                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 166                     visitor.visit_ty(ty);
 167                 }
 168                 ids
 169             },
 170             _ => smallvec![i.id],
 171         };
 172
 173         node_ids.into_iter().map(|node_id| hir::ItemId {
 174             id: self.allocate_hir_id_counter(node_id)
 175         }).collect()
 176     }
 177
 178     fn lower_item_id_use_tree(
 179         &mut self,
 180         tree: &UseTree,
 181         base_id: NodeId,
 182         vec: &mut SmallVec<[NodeId; 1]>
 183     ) {
 184         match tree.kind {
 185             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
 186                 vec.push(id);
 187                 self.lower_item_id_use_tree(nested, id, vec);
 188             },
 189             UseTreeKind::Glob => {}
 190             UseTreeKind::Simple(_, id1, id2) => {
 191                 for (_, &id) in self.expect_full_res_from_use(base_id)
 192                                     .skip(1)
 193                                     .zip([id1, id2].iter())
 194                 {
 195                     vec.push(id);
 196                 }
 197             },
 198         }
 199     }
 200
 201     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item> {
 202         let mut ident = i.ident;
 203         let mut vis = self.lower_visibility(&i.vis, None);
 204         let mut attrs = self.lower_attrs_extendable(&i.attrs);
 205         if self.resolver.has_derives(i.id, SpecialDerives::PARTIAL_EQ | SpecialDerives::EQ) {
 206             // Add `#[structural_match]` if the item derived both `PartialEq` and `Eq`.
 207             let ident = Ident::new(sym::structural_match, i.span);
 208             attrs.push(attr::mk_attr_outer(attr::mk_word_item(ident)));
 209         }
 210         let attrs = attrs.into();
 211
 212         if let ItemKind::MacroDef(ref def) = i.node {
 213             if !def.legacy || attr::contains_name(&i.attrs, sym::macro_export) {
 214                 let body = self.lower_token_stream(def.stream());
 215                 let hir_id = self.lower_node_id(i.id);
 216                 self.exported_macros.push(hir::MacroDef {
 217                     name: ident.name,
 218                     vis,
 219                     attrs,
 220                     hir_id,
 221                     span: i.span,
 222                     body,
 223                     legacy: def.legacy,
 224                 });
 225             } else {
 226                 self.non_exported_macro_attrs.extend(attrs.into_iter());
 227             }
 228             return None;
 229         }
 230
 231         let node = self.lower_item_kind(i.id, &mut ident, &attrs, &mut vis, &i.node);
 232
 233         Some(hir::Item {
 234             hir_id: self.lower_node_id(i.id),
 235             ident,
 236             attrs,
 237             node,
 238             vis,
 239             span: i.span,
 240         })
 241     }
 242
 243     fn lower_item_kind(
 244         &mut self,
 245         id: NodeId,
 246         ident: &mut Ident,
 247         attrs: &hir::HirVec<Attribute>,
 248         vis: &mut hir::Visibility,
 249         i: &ItemKind,
 250     ) -> hir::ItemKind {
 251         match *i {
 252             ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
 253             ItemKind::Use(ref use_tree) => {
 254                 // Start with an empty prefix.
 255                 let prefix = Path {
 256                     segments: vec![],
 257                     span: use_tree.span,
 258                 };
 259
 260                 self.lower_use_tree(use_tree, &prefix, id, vis, ident, attrs)
 261             }
 262             ItemKind::Static(ref t, m, ref e) => {
 263                 hir::ItemKind::Static(
 264                     self.lower_ty(
 265                         t,
 266                         if self.sess.features_untracked().impl_trait_in_bindings {
 267                             ImplTraitContext::OpaqueTy(None)
 268                         } else {
 269                             ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 270                         }
 271                     ),
 272                     self.lower_mutability(m),
 273                     self.lower_const_body(e),
 274                 )
 275             }
 276             ItemKind::Const(ref t, ref e) => {
 277                 hir::ItemKind::Const(
 278                     self.lower_ty(
 279                         t,
 280                         if self.sess.features_untracked().impl_trait_in_bindings {
 281                             ImplTraitContext::OpaqueTy(None)
 282                         } else {
 283                             ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 284                         }
 285                     ),
 286                     self.lower_const_body(e)
 287                 )
 288             }
 289             ItemKind::Fn(ref decl, header, ref generics, ref body) => {
 290                 let fn_def_id = self.resolver.definitions().local_def_id(id);
 291                 self.with_new_scopes(|this| {
 292                     this.current_item = Some(ident.span);
 293
 294                     // Note: we don't need to change the return type from `T` to
 295                     // `impl Future<Output = T>` here because lower_body
 296                     // only cares about the input argument patterns in the function
 297                     // declaration (decl), not the return types.
 298                     let body_id = this.lower_maybe_async_body(&decl, header.asyncness.node, body);
 299
 300                     let (generics, fn_decl) = this.add_in_band_defs(
 301                         generics,
 302                         fn_def_id,
 303                         AnonymousLifetimeMode::PassThrough,
 304                         |this, idty| this.lower_fn_decl(
 305                             &decl,
 306                             Some((fn_def_id, idty)),
 307                             true,
 308                             header.asyncness.node.opt_return_id()
 309                         ),
 310                     );
 311
 312                     hir::ItemKind::Fn(
 313                         fn_decl,
 314                         this.lower_fn_header(header),
 315                         generics,
 316                         body_id,
 317                     )
 318                 })
 319             }
 320             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
 321             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
 322             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
 323             ItemKind::TyAlias(ref t, ref generics) => hir::ItemKind::TyAlias(
 324                 self.lower_ty(t, ImplTraitContext::disallowed()),
 325                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 326             ),
 327             ItemKind::OpaqueTy(ref b, ref generics) => hir::ItemKind::OpaqueTy(
 328                 hir::OpaqueTy {
 329                     generics: self.lower_generics(generics,
 330                         ImplTraitContext::OpaqueTy(None)),
 331                     bounds: self.lower_param_bounds(b,
 332                         ImplTraitContext::OpaqueTy(None)),
 333                     impl_trait_fn: None,
 334                     origin: hir::OpaqueTyOrigin::TypeAlias,
 335                 },
 336             ),
 337             ItemKind::Enum(ref enum_definition, ref generics) => {
 338                 hir::ItemKind::Enum(
 339                     hir::EnumDef {
 340                         variants: enum_definition
 341                             .variants
 342                             .iter()
 343                             .map(|x| self.lower_variant(x))
 344                             .collect(),
 345                     },
 346                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 347                 )
 348             },
 349             ItemKind::Struct(ref struct_def, ref generics) => {
 350                 let struct_def = self.lower_variant_data(struct_def);
 351                 hir::ItemKind::Struct(
 352                     struct_def,
 353                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 354                 )
 355             }
 356             ItemKind::Union(ref vdata, ref generics) => {
 357                 let vdata = self.lower_variant_data(vdata);
 358                 hir::ItemKind::Union(
 359                     vdata,
 360                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 361                 )
 362             }
 363             ItemKind::Impl(
 364                 unsafety,
 365                 polarity,
 366                 defaultness,
 367                 ref ast_generics,
 368                 ref trait_ref,
 369                 ref ty,
 370                 ref impl_items,
 371             ) => {
 372                 let def_id = self.resolver.definitions().local_def_id(id);
 373
 374                 // Lower the "impl header" first. This ordering is important
 375                 // for in-band lifetimes! Consider `'a` here:
 376                 //
 377                 //     impl Foo<'a> for u32 {
 378                 //         fn method(&'a self) { .. }
 379                 //     }
 380                 //
 381                 // Because we start by lowering the `Foo<'a> for u32`
 382                 // part, we will add `'a` to the list of generics on
 383                 // the impl. When we then encounter it later in the
 384                 // method, it will not be considered an in-band
 385                 // lifetime to be added, but rather a reference to a
 386                 // parent lifetime.
 387                 let lowered_trait_impl_id = self.lower_node_id(id);
 388                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
 389                     ast_generics,
 390                     def_id,
 391                     AnonymousLifetimeMode::CreateParameter,
 392                     |this, _| {
 393                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
 394                             this.lower_trait_ref(trait_ref, ImplTraitContext::disallowed())
 395                         });
 396
 397                         if let Some(ref trait_ref) = trait_ref {
 398                             if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res {
 399                                 this.trait_impls.entry(def_id).or_default().push(
 400                                     lowered_trait_impl_id);
 401                             }
 402                         }
 403
 404                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::disallowed());
 405
 406                         (trait_ref, lowered_ty)
 407                     },
 408                 );
 409
 410                 let new_impl_items = self.with_in_scope_lifetime_defs(
 411                     &ast_generics.params,
 412                     |this| {
 413                         impl_items
 414                             .iter()
 415                             .map(|item| this.lower_impl_item_ref(item))
 416                             .collect()
 417                     },
 418                 );
 419
 420                 hir::ItemKind::Impl(
 421                     self.lower_unsafety(unsafety),
 422                     self.lower_impl_polarity(polarity),
 423                     self.lower_defaultness(defaultness, true /* [1] */),
 424                     generics,
 425                     trait_ref,
 426                     lowered_ty,
 427                     new_impl_items,
 428                 )
 429             }
 430             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
 431                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::disallowed());
 432                 let items = items
 433                     .iter()
 434                     .map(|item| self.lower_trait_item_ref(item))
 435                     .collect();
 436                 hir::ItemKind::Trait(
 437                     self.lower_is_auto(is_auto),
 438                     self.lower_unsafety(unsafety),
 439                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 440                     bounds,
 441                     items,
 442                 )
 443             }
 444             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemKind::TraitAlias(
 445                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 446                 self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 447             ),
 448             ItemKind::MacroDef(..)
 449             | ItemKind::Mac(..) => bug!("`TyMac` should have been expanded by now"),
 450         }
 451
 452         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
 453         //     not cause an assertion failure inside the `lower_defaultness` function.
 454     }
 455
 456     fn lower_use_tree(
 457         &mut self,
 458         tree: &UseTree,
 459         prefix: &Path,
 460         id: NodeId,
 461         vis: &mut hir::Visibility,
 462         ident: &mut Ident,
 463         attrs: &hir::HirVec<Attribute>,
 464     ) -> hir::ItemKind {
 465         debug!("lower_use_tree(tree={:?})", tree);
 466         debug!("lower_use_tree: vis = {:?}", vis);
 467
 468         let path = &tree.prefix;
 469         let segments = prefix
 470             .segments
 471             .iter()
 472             .chain(path.segments.iter())
 473             .cloned()
 474             .collect();
 475
 476         match tree.kind {
 477             UseTreeKind::Simple(rename, id1, id2) => {
 478                 *ident = tree.ident();
 479
 480                 // First, apply the prefix to the path.
 481                 let mut path = Path {
 482                     segments,
 483                     span: path.span,
 484                 };
 485
 486                 // Correctly resolve `self` imports.
 487                 if path.segments.len() > 1
 488                     && path.segments.last().unwrap().ident.name == kw::SelfLower
 489                 {
 490                     let _ = path.segments.pop();
 491                     if rename.is_none() {
 492                         *ident = path.segments.last().unwrap().ident;
 493                     }
 494                 }
 495
 496                 let mut resolutions = self.expect_full_res_from_use(id);
 497                 // We want to return *something* from this function, so hold onto the first item
 498                 // for later.
 499                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
 500
 501                 // Here, we are looping over namespaces, if they exist for the definition
 502                 // being imported. We only handle type and value namespaces because we
 503                 // won't be dealing with macros in the rest of the compiler.
 504                 // Essentially a single `use` which imports two names is desugared into
 505                 // two imports.
 506                 for (res, &new_node_id) in resolutions.zip([id1, id2].iter()) {
 507                     let ident = *ident;
 508                     let mut path = path.clone();
 509                     for seg in &mut path.segments {
 510                         seg.id = self.sess.next_node_id();
 511                     }
 512                     let span = path.span;
 513
 514                     self.with_hir_id_owner(new_node_id, |this| {
 515                         let new_id = this.lower_node_id(new_node_id);
 516                         let res = this.lower_res(res);
 517                         let path =
 518                             this.lower_path_extra(res, &path, ParamMode::Explicit, None);
 519                         let item = hir::ItemKind::Use(P(path), hir::UseKind::Single);
 520                         let vis = this.rebuild_vis(&vis);
 521
 522                         this.insert_item(
 523                             hir::Item {
 524                                 hir_id: new_id,
 525                                 ident,
 526                                 attrs: attrs.into_iter().cloned().collect(),
 527                                 node: item,
 528                                 vis,
 529                                 span,
 530                             },
 531                         );
 532                     });
 533                 }
 534
 535                 let path =
 536                     P(self.lower_path_extra(ret_res, &path, ParamMode::Explicit, None));
 537                 hir::ItemKind::Use(path, hir::UseKind::Single)
 538             }
 539             UseTreeKind::Glob => {
 540                 let path = P(self.lower_path(
 541                     id,
 542                     &Path {
 543                         segments,
 544                         span: path.span,
 545                     },
 546                     ParamMode::Explicit,
 547                 ));
 548                 hir::ItemKind::Use(path, hir::UseKind::Glob)
 549             }
 550             UseTreeKind::Nested(ref trees) => {
 551                 // Nested imports are desugared into simple imports.
 552                 // So, if we start with
 553                 //
 554                 // ```
 555                 // pub(x) use foo::{a, b};
 556                 // ```
 557                 //
 558                 // we will create three items:
 559                 //
 560                 // ```
 561                 // pub(x) use foo::a;
 562                 // pub(x) use foo::b;
 563                 // pub(x) use foo::{}; // <-- this is called the `ListStem`
 564                 // ```
 565                 //
 566                 // The first two are produced by recursively invoking
 567                 // `lower_use_tree` (and indeed there may be things
 568                 // like `use foo::{a::{b, c}}` and so forth).  They
 569                 // wind up being directly added to
 570                 // `self.items`. However, the structure of this
 571                 // function also requires us to return one item, and
 572                 // for that we return the `{}` import (called the
 573                 // `ListStem`).
 574
 575                 let prefix = Path {
 576                     segments,
 577                     span: prefix.span.to(path.span),
 578                 };
 579
 580                 // Add all the nested `PathListItem`s to the HIR.
 581                 for &(ref use_tree, id) in trees {
 582                     let new_hir_id = self.lower_node_id(id);
 583
 584                     let mut prefix = prefix.clone();
 585
 586                     // Give the segments new node-ids since they are being cloned.
 587                     for seg in &mut prefix.segments {
 588                         seg.id = self.sess.next_node_id();
 589                     }
 590
 591                     // Each `use` import is an item and thus are owners of the
 592                     // names in the path. Up to this point the nested import is
 593                     // the current owner, since we want each desugared import to
 594                     // own its own names, we have to adjust the owner before
 595                     // lowering the rest of the import.
 596                     self.with_hir_id_owner(id, |this| {
 597                         let mut vis = this.rebuild_vis(&vis);
 598                         let mut ident = *ident;
 599
 600                         let item = this.lower_use_tree(use_tree,
 601                                                        &prefix,
 602                                                        id,
 603                                                        &mut vis,
 604                                                        &mut ident,
 605                                                        attrs);
 606
 607                         this.insert_item(
 608                             hir::Item {
 609                                 hir_id: new_hir_id,
 610                                 ident,
 611                                 attrs: attrs.into_iter().cloned().collect(),
 612                                 node: item,
 613                                 vis,
 614                                 span: use_tree.span,
 615                             },
 616                         );
 617                     });
 618                 }
 619
 620                 // Subtle and a bit hacky: we lower the privacy level
 621                 // of the list stem to "private" most of the time, but
 622                 // not for "restricted" paths. The key thing is that
 623                 // we don't want it to stay as `pub` (with no caveats)
 624                 // because that affects rustdoc and also the lints
 625                 // about `pub` items. But we can't *always* make it
 626                 // private -- particularly not for restricted paths --
 627                 // because it contains node-ids that would then be
 628                 // unused, failing the check that HirIds are "densely
 629                 // assigned".
 630                 match vis.node {
 631                     hir::VisibilityKind::Public |
 632                     hir::VisibilityKind::Crate(_) |
 633                     hir::VisibilityKind::Inherited => {
 634                         *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
 635                     }
 636                     hir::VisibilityKind::Restricted { .. } => {
 637                         // Do nothing here, as described in the comment on the match.
 638                     }
 639                 }
 640
 641                 let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
 642                 let res = self.lower_res(res);
 643                 let path = P(self.lower_path_extra(res, &prefix, ParamMode::Explicit, None));
 644                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
 645             }
 646         }
 647     }
 648
 649     /// Paths like the visibility path in `pub(super) use foo::{bar, baz}` are repeated
 650     /// many times in the HIR tree; for each occurrence, we need to assign distinct
 651     /// `NodeId`s. (See, e.g., #56128.)
 652     fn rebuild_use_path(&mut self, path: &hir::Path) -> hir::Path {
 653         debug!("rebuild_use_path(path = {:?})", path);
 654         let segments = path.segments.iter().map(|seg| hir::PathSegment {
 655             ident: seg.ident,
 656             hir_id: seg.hir_id.map(|_| self.next_id()),
 657             res: seg.res,
 658             args: None,
 659             infer_args: seg.infer_args,
 660         }).collect();
 661         hir::Path {
 662             span: path.span,
 663             res: path.res,
 664             segments,
 665         }
 666     }
 667
 668     fn rebuild_vis(&mut self, vis: &hir::Visibility) -> hir::Visibility {
 669         let vis_kind = match vis.node {
 670             hir::VisibilityKind::Public => hir::VisibilityKind::Public,
 671             hir::VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 672             hir::VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 673             hir::VisibilityKind::Restricted { ref path, hir_id: _ } => {
 674                 hir::VisibilityKind::Restricted {
 675                     path: P(self.rebuild_use_path(path)),
 676                     hir_id: self.next_id(),
 677                 }
 678             }
 679         };
 680         respan(vis.span, vis_kind)
 681     }
 682
 683     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
 684         let def_id = self.resolver.definitions().local_def_id(i.id);
 685         hir::ForeignItem {
 686             hir_id: self.lower_node_id(i.id),
 687             ident: i.ident,
 688             attrs: self.lower_attrs(&i.attrs),
 689             node: match i.node {
 690                 ForeignItemKind::Fn(ref fdec, ref generics) => {
 691                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
 692                         generics,
 693                         def_id,
 694                         AnonymousLifetimeMode::PassThrough,
 695                         |this, _| {
 696                             (
 697                                 // Disallow impl Trait in foreign items
 698                                 this.lower_fn_decl(fdec, None, false, None),
 699                                 this.lower_fn_args_to_names(fdec),
 700                             )
 701                         },
 702                     );
 703
 704                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
 705                 }
 706                 ForeignItemKind::Static(ref t, m) => {
 707                     hir::ForeignItemKind::Static(
 708                         self.lower_ty(t, ImplTraitContext::disallowed()), self.lower_mutability(m))
 709                 }
 710                 ForeignItemKind::Ty => hir::ForeignItemKind::Type,
 711                 ForeignItemKind::Macro(_) => panic!("shouldn't exist here"),
 712             },
 713             vis: self.lower_visibility(&i.vis, None),
 714             span: i.span,
 715         }
 716     }
 717
 718     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
 719         hir::ForeignMod {
 720             abi: fm.abi,
 721             items: fm.items
 722                 .iter()
 723                 .map(|x| self.lower_foreign_item(x))
 724                 .collect(),
 725         }
 726     }
 727
 728     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
 729         P(hir::GlobalAsm {
 730             asm: ga.asm,
 731             ctxt: ga.ctxt,
 732         })
 733     }
 734
 735     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
 736         Spanned {
 737             node: hir::VariantKind {
 738                 ident: v.node.ident,
 739                 id: self.lower_node_id(v.node.id),
 740                 attrs: self.lower_attrs(&v.node.attrs),
 741                 data: self.lower_variant_data(&v.node.data),
 742                 disr_expr: v.node.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
 743             },
 744             span: v.span,
 745         }
 746     }
 747
 748     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
 749         match *vdata {
 750             VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
 751                 fields.iter().enumerate().map(|f| self.lower_struct_field(f)).collect(),
 752                 recovered,
 753             ),
 754             VariantData::Tuple(ref fields, id) => {
 755                 hir::VariantData::Tuple(
 756                     fields
 757                         .iter()
 758                         .enumerate()
 759                         .map(|f| self.lower_struct_field(f))
 760                         .collect(),
 761                     self.lower_node_id(id),
 762                 )
 763             },
 764             VariantData::Unit(id) => {
 765                 hir::VariantData::Unit(self.lower_node_id(id))
 766             },
 767         }
 768     }
 769
 770     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
 771         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.node {
 772             let t = self.lower_path_ty(
 773                 &f.ty,
 774                 qself,
 775                 path,
 776                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
 777                 ImplTraitContext::disallowed()
 778             );
 779             P(t)
 780         } else {
 781             self.lower_ty(&f.ty, ImplTraitContext::disallowed())
 782         };
 783         hir::StructField {
 784             span: f.span,
 785             hir_id: self.lower_node_id(f.id),
 786             ident: match f.ident {
 787                 Some(ident) => ident,
 788                 // FIXME(jseyfried): positional field hygiene.
 789                 None => Ident::new(sym::integer(index), f.span),
 790             },
 791             vis: self.lower_visibility(&f.vis, None),
 792             ty,
 793             attrs: self.lower_attrs(&f.attrs),
 794         }
 795     }
 796
 797     fn lower_trait_item(&mut self, i: &TraitItem) -> hir::TraitItem {
 798         let trait_item_def_id = self.resolver.definitions().local_def_id(i.id);
 799
 800         let (generics, node) = match i.node {
 801             TraitItemKind::Const(ref ty, ref default) => (
 802                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 803                 hir::TraitItemKind::Const(
 804                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 805                     default
 806                         .as_ref()
 807                         .map(|x| self.lower_const_body(x)),
 808                 ),
 809             ),
 810             TraitItemKind::Method(ref sig, None) => {
 811                 let names = self.lower_fn_args_to_names(&sig.decl);
 812                 let (generics, sig) = self.lower_method_sig(
 813                     &i.generics,
 814                     sig,
 815                     trait_item_def_id,
 816                     false,
 817                     None,
 818                 );
 819                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
 820             }
 821             TraitItemKind::Method(ref sig, Some(ref body)) => {
 822                 let body_id = self.lower_fn_body_block(&sig.decl, body);
 823                 let (generics, sig) = self.lower_method_sig(
 824                     &i.generics,
 825                     sig,
 826                     trait_item_def_id,
 827                     false,
 828                     None,
 829                 );
 830                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
 831             }
 832             TraitItemKind::Type(ref bounds, ref default) => {
 833                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 834                 let node = hir::TraitItemKind::Type(
 835                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 836                     default
 837                         .as_ref()
 838                         .map(|x| self.lower_ty(x, ImplTraitContext::disallowed())),
 839                 );
 840
 841                 (generics, node)
 842             },
 843             TraitItemKind::Macro(..) => bug!("macro item shouldn't exist at this point"),
 844         };
 845
 846         hir::TraitItem {
 847             hir_id: self.lower_node_id(i.id),
 848             ident: i.ident,
 849             attrs: self.lower_attrs(&i.attrs),
 850             generics,
 851             node,
 852             span: i.span,
 853         }
 854     }
 855
 856     fn lower_trait_item_ref(&mut self, i: &TraitItem) -> hir::TraitItemRef {
 857         let (kind, has_default) = match i.node {
 858             TraitItemKind::Const(_, ref default) => {
 859                 (hir::AssocItemKind::Const, default.is_some())
 860             }
 861             TraitItemKind::Type(_, ref default) => {
 862                 (hir::AssocItemKind::Type, default.is_some())
 863             }
 864             TraitItemKind::Method(ref sig, ref default) => (
 865                 hir::AssocItemKind::Method {
 866                     has_self: sig.decl.has_self(),
 867                 },
 868                 default.is_some(),
 869             ),
 870             TraitItemKind::Macro(..) => unimplemented!(),
 871         };
 872         hir::TraitItemRef {
 873             id: hir::TraitItemId { hir_id: self.lower_node_id(i.id) },
 874             ident: i.ident,
 875             span: i.span,
 876             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
 877             kind,
 878         }
 879     }
 880
 881     fn lower_impl_item(&mut self, i: &ImplItem) -> hir::ImplItem {
 882         let impl_item_def_id = self.resolver.definitions().local_def_id(i.id);
 883
 884         let (generics, node) = match i.node {
 885             ImplItemKind::Const(ref ty, ref expr) => (
 886                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 887                 hir::ImplItemKind::Const(
 888                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 889                     self.lower_const_body(expr),
 890                 ),
 891             ),
 892             ImplItemKind::Method(ref sig, ref body) => {
 893                 self.current_item = Some(i.span);
 894                 let body_id = self.lower_maybe_async_body(
 895                     &sig.decl, sig.header.asyncness.node, body
 896                 );
 897                 let impl_trait_return_allow = !self.is_in_trait_impl;
 898                 let (generics, sig) = self.lower_method_sig(
 899                     &i.generics,
 900                     sig,
 901                     impl_item_def_id,
 902                     impl_trait_return_allow,
 903                     sig.header.asyncness.node.opt_return_id(),
 904                 );
 905
 906                 (generics, hir::ImplItemKind::Method(sig, body_id))
 907             }
 908             ImplItemKind::TyAlias(ref ty) => (
 909                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 910                 hir::ImplItemKind::TyAlias(self.lower_ty(ty, ImplTraitContext::disallowed())),
 911             ),
 912             ImplItemKind::OpaqueTy(ref bounds) => (
 913                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 914                 hir::ImplItemKind::OpaqueTy(
 915                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 916                 ),
 917             ),
 918             ImplItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
 919         };
 920
 921         hir::ImplItem {
 922             hir_id: self.lower_node_id(i.id),
 923             ident: i.ident,
 924             attrs: self.lower_attrs(&i.attrs),
 925             generics,
 926             vis: self.lower_visibility(&i.vis, None),
 927             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 928             node,
 929             span: i.span,
 930         }
 931
 932         // [1] since `default impl` is not yet implemented, this is always true in impls
 933     }
 934
 935     fn lower_impl_item_ref(&mut self, i: &ImplItem) -> hir::ImplItemRef {
 936         hir::ImplItemRef {
 937             id: hir::ImplItemId { hir_id: self.lower_node_id(i.id) },
 938             ident: i.ident,
 939             span: i.span,
 940             vis: self.lower_visibility(&i.vis, Some(i.id)),
 941             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 942             kind: match i.node {
 943                 ImplItemKind::Const(..) => hir::AssocItemKind::Const,
 944                 ImplItemKind::TyAlias(..) => hir::AssocItemKind::Type,
 945                 ImplItemKind::OpaqueTy(..) => hir::AssocItemKind::OpaqueTy,
 946                 ImplItemKind::Method(ref sig, _) => hir::AssocItemKind::Method {
 947                     has_self: sig.decl.has_self(),
 948                 },
 949                 ImplItemKind::Macro(..) => unimplemented!(),
 950             },
 951         }
 952
 953         // [1] since `default impl` is not yet implemented, this is always true in impls
 954     }
 955
 956     /// If an `explicit_owner` is given, this method allocates the `HirId` in
 957     /// the address space of that item instead of the item currently being
 958     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
 959     /// lower a `Visibility` value although we haven't lowered the owning
 960     /// `ImplItem` in question yet.
 961     fn lower_visibility(
 962         &mut self,
 963         v: &Visibility,
 964         explicit_owner: Option<NodeId>,
 965     ) -> hir::Visibility {
 966         let node = match v.node {
 967             VisibilityKind::Public => hir::VisibilityKind::Public,
 968             VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 969             VisibilityKind::Restricted { ref path, id } => {
 970                 debug!("lower_visibility: restricted path id = {:?}", id);
 971                 let lowered_id = if let Some(owner) = explicit_owner {
 972                     self.lower_node_id_with_owner(id, owner)
 973                 } else {
 974                     self.lower_node_id(id)
 975                 };
 976                 let res = self.expect_full_res(id);
 977                 let res = self.lower_res(res);
 978                 hir::VisibilityKind::Restricted {
 979                     path: P(self.lower_path_extra(
 980                         res,
 981                         path,
 982                         ParamMode::Explicit,
 983                         explicit_owner,
 984                     )),
 985                     hir_id: lowered_id,
 986                 }
 987             },
 988             VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 989         };
 990         respan(v.span, node)
 991     }
 992
 993     fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
 994         match d {
 995             Defaultness::Default => hir::Defaultness::Default {
 996                 has_value: has_value,
 997             },
 998             Defaultness::Final => {
 999                 assert!(has_value);
1000                 hir::Defaultness::Final
1001             }
1002         }
1003     }
1004
1005     fn lower_impl_polarity(&mut self, i: ImplPolarity) -> hir::ImplPolarity {
1006         match i {
1007             ImplPolarity::Positive => hir::ImplPolarity::Positive,
1008             ImplPolarity::Negative => hir::ImplPolarity::Negative,
1009         }
1010     }
1011
1012     fn record_body(&mut self, arguments: HirVec<hir::Arg>, value: hir::Expr) -> hir::BodyId {
1013         let body = hir::Body {
1014             generator_kind: self.generator_kind,
1015             arguments,
1016             value,
1017         };
1018         let id = body.id();
1019         self.bodies.insert(id, body);
1020         id
1021     }
1022
1023     fn lower_body(
1024         &mut self,
1025         f: impl FnOnce(&mut LoweringContext<'_>) -> (HirVec<hir::Arg>, hir::Expr),
1026     ) -> hir::BodyId {
1027         let prev_gen_kind = self.generator_kind.take();
1028         let (arguments, result) = f(self);
1029         let body_id = self.record_body(arguments, result);
1030         self.generator_kind = prev_gen_kind;
1031         body_id
1032     }
1033
1034     fn lower_arg(&mut self, arg: &Arg) -> hir::Arg {
1035         hir::Arg {
1036             attrs: self.lower_attrs(&arg.attrs),
1037             hir_id: self.lower_node_id(arg.id),
1038             pat: self.lower_pat(&arg.pat),
1039             span: arg.span,
1040         }
1041     }
1042
1043     pub(super) fn lower_fn_body(
1044         &mut self,
1045         decl: &FnDecl,
1046         body: impl FnOnce(&mut LoweringContext<'_>) -> hir::Expr,
1047     ) -> hir::BodyId {
1048         self.lower_body(|this| (
1049             decl.inputs.iter().map(|x| this.lower_arg(x)).collect(),
1050             body(this),
1051         ))
1052     }
1053
1054     fn lower_fn_body_block(&mut self, decl: &FnDecl, body: &Block) -> hir::BodyId {
1055         self.lower_fn_body(decl, |this| {
1056             let body = this.lower_block(body, false);
1057             this.expr_block(body, ThinVec::new())
1058         })
1059     }
1060
1061     pub(super) fn lower_const_body(&mut self, expr: &Expr) -> hir::BodyId {
1062         self.lower_body(|this| (hir_vec![], this.lower_expr(expr)))
1063     }
1064
1065     fn lower_maybe_async_body(
1066         &mut self,
1067         decl: &FnDecl,
1068         asyncness: IsAsync,
1069         body: &Block,
1070     ) -> hir::BodyId {
1071         let closure_id = match asyncness {
1072             IsAsync::Async { closure_id, .. } => closure_id,
1073             IsAsync::NotAsync => return self.lower_fn_body_block(decl, body),
1074         };
1075
1076         self.lower_body(|this| {
1077             let mut arguments: Vec<hir::Arg> = Vec::new();
1078             let mut statements: Vec<hir::Stmt> = Vec::new();
1079
1080             // Async function arguments are lowered into the closure body so that they are
1081             // captured and so that the drop order matches the equivalent non-async functions.
1082             //
1083             // from:
1084             //
1085             //     async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
1086             //       async move {
1087             //       }
1088             //     }
1089             //
1090             // into:
1091             //
1092             //     fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) {
1093             //       async move {
1094             //         let __arg2 = __arg2;
1095             //         let <pattern> = __arg2;
1096             //         let __arg1 = __arg1;
1097             //         let <pattern> = __arg1;
1098             //         let __arg0 = __arg0;
1099             //         let <pattern> = __arg0;
1100             //       }
1101             //     }
1102             //
1103             // If `<pattern>` is a simple ident, then it is lowered to a single
1104             // `let <pattern> = <pattern>;` statement as an optimization.
1105             for (index, argument) in decl.inputs.iter().enumerate() {
1106                 let argument = this.lower_arg(argument);
1107                 let span = argument.pat.span;
1108
1109                 // Check if this is a binding pattern, if so, we can optimize and avoid adding a
1110                 // `let <pat> = __argN;` statement. In this case, we do not rename the argument.
1111                 let (ident, is_simple_argument) = match argument.pat.node {
1112                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, _) =>
1113                         (ident, true),
1114                     _ => {
1115                         // Replace the ident for bindings that aren't simple.
1116                         let name = format!("__arg{}", index);
1117                         let ident = Ident::from_str(&name);
1118
1119                         (ident, false)
1120                     },
1121                 };
1122
1123                 let desugared_span =
1124                     this.mark_span_with_reason(DesugaringKind::Async, span, None);
1125
1126                 // Construct an argument representing `__argN: <ty>` to replace the argument of the
1127                 // async function.
1128                 //
1129                 // If this is the simple case, this argument will end up being the same as the
1130                 // original argument, but with a different pattern id.
1131                 let mut stmt_attrs = ThinVec::new();
1132                 stmt_attrs.extend(argument.attrs.iter().cloned());
1133                 let (new_argument_pat, new_argument_id) = this.pat_ident(desugared_span, ident);
1134                 let new_argument = hir::Arg {
1135                     attrs: argument.attrs,
1136                     hir_id: argument.hir_id,
1137                     pat: new_argument_pat,
1138                     span: argument.span,
1139                 };
1140
1141
1142                 if is_simple_argument {
1143                     // If this is the simple case, then we only insert one statement that is
1144                     // `let <pat> = <pat>;`. We re-use the original argument's pattern so that
1145                     // `HirId`s are densely assigned.
1146                     let expr = this.expr_ident(desugared_span, ident, new_argument_id);
1147                     let stmt = this.stmt_let_pat(
1148                         stmt_attrs,
1149                         desugared_span,
1150                         Some(P(expr)),
1151                         argument.pat,
1152                         hir::LocalSource::AsyncFn
1153                     );
1154                     statements.push(stmt);
1155                 } else {
1156                     // If this is not the simple case, then we construct two statements:
1157                     //
1158                     // ```
1159                     // let __argN = __argN;
1160                     // let <pat> = __argN;
1161                     // ```
1162                     //
1163                     // The first statement moves the argument into the closure and thus ensures
1164                     // that the drop order is correct.
1165                     //
1166                     // The second statement creates the bindings that the user wrote.
1167
1168                     // Construct the `let mut __argN = __argN;` statement. It must be a mut binding
1169                     // because the user may have specified a `ref mut` binding in the next
1170                     // statement.
1171                     let (move_pat, move_id) = this.pat_ident_binding_mode(
1172                         desugared_span, ident, hir::BindingAnnotation::Mutable);
1173                     let move_expr = this.expr_ident(desugared_span, ident, new_argument_id);
1174                     let move_stmt = this.stmt_let_pat(
1175                         ThinVec::new(),
1176                         desugared_span,
1177                         Some(P(move_expr)),
1178                         move_pat,
1179                         hir::LocalSource::AsyncFn
1180                     );
1181
1182                     // Construct the `let <pat> = __argN;` statement. We re-use the original
1183                     // argument's pattern so that `HirId`s are densely assigned.
1184                     let pattern_expr = this.expr_ident(desugared_span, ident, move_id);
1185                     let pattern_stmt = this.stmt_let_pat(
1186                         stmt_attrs,
1187                         desugared_span,
1188                         Some(P(pattern_expr)),
1189                         argument.pat,
1190                         hir::LocalSource::AsyncFn
1191                     );
1192
1193                     statements.push(move_stmt);
1194                     statements.push(pattern_stmt);
1195                 };
1196
1197                 arguments.push(new_argument);
1198             }
1199
1200             let async_expr = this.make_async_expr(
1201                 CaptureBy::Value, closure_id, None, body.span,
1202                 |this| {
1203                     let body = this.lower_block_with_stmts(body, false, statements);
1204                     this.expr_block(body, ThinVec::new())
1205                 });
1206             (HirVec::from(arguments), this.expr(body.span, async_expr, ThinVec::new()))
1207         })
1208     }
1209
1210     fn lower_method_sig(
1211         &mut self,
1212         generics: &Generics,
1213         sig: &MethodSig,
1214         fn_def_id: DefId,
1215         impl_trait_return_allow: bool,
1216         is_async: Option<NodeId>,
1217     ) -> (hir::Generics, hir::MethodSig) {
1218         let header = self.lower_fn_header(sig.header);
1219         let (generics, decl) = self.add_in_band_defs(
1220             generics,
1221             fn_def_id,
1222             AnonymousLifetimeMode::PassThrough,
1223             |this, idty| this.lower_fn_decl(
1224                 &sig.decl,
1225                 Some((fn_def_id, idty)),
1226                 impl_trait_return_allow,
1227                 is_async,
1228             ),
1229         );
1230         (generics, hir::MethodSig { header, decl })
1231     }
1232
1233     fn lower_is_auto(&mut self, a: IsAuto) -> hir::IsAuto {
1234         match a {
1235             IsAuto::Yes => hir::IsAuto::Yes,
1236             IsAuto::No => hir::IsAuto::No,
1237         }
1238     }
1239
1240     fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
1241         hir::FnHeader {
1242             unsafety: self.lower_unsafety(h.unsafety),
1243             asyncness: self.lower_asyncness(h.asyncness.node),
1244             constness: self.lower_constness(h.constness),
1245             abi: h.abi,
1246         }
1247     }
1248
1249     pub(super) fn lower_unsafety(&mut self, u: Unsafety) -> hir::Unsafety {
1250         match u {
1251             Unsafety::Unsafe => hir::Unsafety::Unsafe,
1252             Unsafety::Normal => hir::Unsafety::Normal,
1253         }
1254     }
1255
1256     fn lower_constness(&mut self, c: Spanned<Constness>) -> hir::Constness {
1257         match c.node {
1258             Constness::Const => hir::Constness::Const,
1259             Constness::NotConst => hir::Constness::NotConst,
1260         }
1261     }
1262
1263     fn lower_asyncness(&mut self, a: IsAsync) -> hir::IsAsync {
1264         match a {
1265             IsAsync::Async { .. } => hir::IsAsync::Async,
1266             IsAsync::NotAsync => hir::IsAsync::NotAsync,
1267         }
1268     }
1269
1270     pub(super) fn lower_generics(
1271         &mut self,
1272         generics: &Generics,
1273         itctx: ImplTraitContext<'_>)
1274         -> hir::Generics
1275     {
1276         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1277         // FIXME: this could probably be done with less rightward drift. It also looks like two
1278         // control paths where `report_error` is called are the only paths that advance to after the
1279         // match statement, so the error reporting could probably just be moved there.
1280         let mut add_bounds: NodeMap<Vec<_>> = Default::default();
1281         for pred in &generics.where_clause.predicates {
1282             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1283                 'next_bound: for bound in &bound_pred.bounds {
1284                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
1285                         let report_error = |this: &mut Self| {
1286                             this.diagnostic().span_err(
1287                                 bound_pred.bounded_ty.span,
1288                                 "`?Trait` bounds are only permitted at the \
1289                                  point where a type parameter is declared",
1290                             );
1291                         };
1292                         // Check if the where clause type is a plain type parameter.
1293                         match bound_pred.bounded_ty.node {
1294                             TyKind::Path(None, ref path)
1295                                 if path.segments.len() == 1
1296                                     && bound_pred.bound_generic_params.is_empty() =>
1297                             {
1298                                 if let Some(Res::Def(DefKind::TyParam, def_id)) = self.resolver
1299                                     .get_partial_res(bound_pred.bounded_ty.id)
1300                                     .map(|d| d.base_res())
1301                                 {
1302                                     if let Some(node_id) =
1303                                         self.resolver.definitions().as_local_node_id(def_id)
1304                                     {
1305                                         for param in &generics.params {
1306                                             match param.kind {
1307                                                 GenericParamKind::Type { .. } => {
1308                                                     if node_id == param.id {
1309                                                         add_bounds.entry(param.id)
1310                                                             .or_default()
1311                                                             .push(bound.clone());
1312                                                         continue 'next_bound;
1313                                                     }
1314                                                 }
1315                                                 _ => {}
1316                                             }
1317                                         }
1318                                     }
1319                                 }
1320                                 report_error(self)
1321                             }
1322                             _ => report_error(self),
1323                         }
1324                     }
1325                 }
1326             }
1327         }
1328
1329         hir::Generics {
1330             params: self.lower_generic_params(&generics.params, &add_bounds, itctx),
1331             where_clause: self.lower_where_clause(&generics.where_clause),
1332             span: generics.span,
1333         }
1334     }
1335
1336     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
1337         self.with_anonymous_lifetime_mode(
1338             AnonymousLifetimeMode::ReportError,
1339             |this| {
1340                 hir::WhereClause {
1341                     predicates: wc.predicates
1342                         .iter()
1343                         .map(|predicate| this.lower_where_predicate(predicate))
1344                         .collect(),
1345                     span: wc.span,
1346                 }
1347             },
1348         )
1349     }
1350
1351     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
1352         match *pred {
1353             WherePredicate::BoundPredicate(WhereBoundPredicate {
1354                 ref bound_generic_params,
1355                 ref bounded_ty,
1356                 ref bounds,
1357                 span,
1358             }) => {
1359                 self.with_in_scope_lifetime_defs(
1360                     &bound_generic_params,
1361                     |this| {
1362                         hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1363                             bound_generic_params: this.lower_generic_params(
1364                                 bound_generic_params,
1365                                 &NodeMap::default(),
1366                                 ImplTraitContext::disallowed(),
1367                             ),
1368                             bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::disallowed()),
1369                             bounds: bounds
1370                                 .iter()
1371                                 .filter_map(|bound| match *bound {
1372                                     // Ignore `?Trait` bounds.
1373                                     // They were copied into type parameters already.
1374                                     GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1375                                     _ => Some(this.lower_param_bound(
1376                                         bound,
1377                                         ImplTraitContext::disallowed(),
1378                                     )),
1379                                 })
1380                                 .collect(),
1381                             span,
1382                         })
1383                     },
1384                 )
1385             }
1386             WherePredicate::RegionPredicate(WhereRegionPredicate {
1387                 ref lifetime,
1388                 ref bounds,
1389                 span,
1390             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1391                 span,
1392                 lifetime: self.lower_lifetime(lifetime),
1393                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
1394             }),
1395             WherePredicate::EqPredicate(WhereEqPredicate {
1396                 id,
1397                 ref lhs_ty,
1398                 ref rhs_ty,
1399                 span,
1400             }) => {
1401                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1402                     hir_id: self.lower_node_id(id),
1403                     lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::disallowed()),
1404                     rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::disallowed()),
1405                     span,
1406                 })
1407             },
1408         }
1409     }
1410 }