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_target::spec::abi;
  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::source_map::{respan, DesugaringKind};
  22 use syntax::symbol::{kw, sym};
  23 use syntax_pos::Span;
  24
  25 use rustc_error_codes::*;
  26
  27 pub(super) struct ItemLowerer<'a, 'lowering, 'hir> {
  28     pub(super) lctx: &'a mut LoweringContext<'lowering, 'hir>,
  29 }
  30
  31 impl<'a, 'lowering, 'hir> ItemLowerer<'a, 'lowering, 'hir> {
  32     fn with_trait_impl_ref<F>(&mut self, trait_impl_ref: &Option<TraitRef>, f: F)
  33     where
  34         F: FnOnce(&mut Self),
  35     {
  36         let old = self.lctx.is_in_trait_impl;
  37         self.lctx.is_in_trait_impl = if let &None = trait_impl_ref {
  38             false
  39         } else {
  40             true
  41         };
  42         f(self);
  43         self.lctx.is_in_trait_impl = old;
  44     }
  45 }
  46
  47 impl<'a, 'lowering, 'hir> Visitor<'a> for ItemLowerer<'a, 'lowering, 'hir> {
  48     fn visit_mod(&mut self, m: &'a Mod, _s: Span, _attrs: &[Attribute], n: NodeId) {
  49         let hir_id = self.lctx.lower_node_id(n);
  50
  51         self.lctx.modules.insert(hir_id, hir::ModuleItems {
  52             items: BTreeSet::new(),
  53             trait_items: BTreeSet::new(),
  54             impl_items: BTreeSet::new(),
  55         });
  56
  57         let old = self.lctx.current_module;
  58         self.lctx.current_module = hir_id;
  59         visit::walk_mod(self, m);
  60         self.lctx.current_module = old;
  61     }
  62
  63     fn visit_item(&mut self, item: &'a Item) {
  64         let mut item_hir_id = None;
  65         self.lctx.with_hir_id_owner(item.id, |lctx| {
  66             lctx.without_in_scope_lifetime_defs(|lctx| {
  67                 if let Some(hir_item) = lctx.lower_item(item) {
  68                     item_hir_id = Some(hir_item.hir_id);
  69                     lctx.insert_item(hir_item);
  70                 }
  71             })
  72         });
  73
  74         if let Some(hir_id) = item_hir_id {
  75             self.lctx.with_parent_item_lifetime_defs(hir_id, |this| {
  76                 let this = &mut ItemLowerer { lctx: this };
  77                 if let ItemKind::Impl(.., ref opt_trait_ref, _, _) = item.kind {
  78                     this.with_trait_impl_ref(opt_trait_ref, |this| {
  79                         visit::walk_item(this, item)
  80                     });
  81                 } else {
  82                     visit::walk_item(this, item);
  83                 }
  84             });
  85         }
  86     }
  87
  88     fn visit_trait_item(&mut self, item: &'a AssocItem) {
  89         self.lctx.with_hir_id_owner(item.id, |lctx| {
  90             let hir_item = lctx.lower_trait_item(item);
  91             let id = hir::TraitItemId { hir_id: hir_item.hir_id };
  92             lctx.trait_items.insert(id, hir_item);
  93             lctx.modules.get_mut(&lctx.current_module).unwrap().trait_items.insert(id);
  94         });
  95
  96         visit::walk_trait_item(self, item);
  97     }
  98
  99     fn visit_impl_item(&mut self, item: &'a AssocItem) {
 100         self.lctx.with_hir_id_owner(item.id, |lctx| {
 101             let hir_item = lctx.lower_impl_item(item);
 102             let id = hir::ImplItemId { hir_id: hir_item.hir_id };
 103             lctx.impl_items.insert(id, hir_item);
 104             lctx.modules.get_mut(&lctx.current_module).unwrap().impl_items.insert(id);
 105         });
 106         visit::walk_impl_item(self, item);
 107     }
 108 }
 109
 110 impl LoweringContext<'_, 'hir> {
 111     // Same as the method above, but accepts `hir::GenericParam`s
 112     // instead of `ast::GenericParam`s.
 113     // This should only be used with generics that have already had their
 114     // in-band lifetimes added. In practice, this means that this function is
 115     // only used when lowering a child item of a trait or impl.
 116     fn with_parent_item_lifetime_defs<T>(
 117         &mut self,
 118         parent_hir_id: hir::HirId,
 119         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> T,
 120     ) -> T {
 121         let old_len = self.in_scope_lifetimes.len();
 122
 123         let parent_generics = match self.items.get(&parent_hir_id).unwrap().kind {
 124             hir::ItemKind::Impl(_, _, _, ref generics, ..)
 125             | hir::ItemKind::Trait(_, _, ref generics, ..) => {
 126                 &generics.params[..]
 127             }
 128             _ => &[],
 129         };
 130         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
 131             hir::GenericParamKind::Lifetime { .. } => Some(param.name.modern()),
 132             _ => None,
 133         });
 134         self.in_scope_lifetimes.extend(lt_def_names);
 135
 136         let res = f(self);
 137
 138         self.in_scope_lifetimes.truncate(old_len);
 139         res
 140     }
 141
 142     // Clears (and restores) the `in_scope_lifetimes` field. Used when
 143     // visiting nested items, which never inherit in-scope lifetimes
 144     // from their surrounding environment.
 145     fn without_in_scope_lifetime_defs<T>(
 146         &mut self,
 147         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> T,
 148     ) -> T {
 149         let old_in_scope_lifetimes = std::mem::replace(&mut self.in_scope_lifetimes, vec![]);
 150
 151         // this vector is only used when walking over impl headers,
 152         // input types, and the like, and should not be non-empty in
 153         // between items
 154         assert!(self.lifetimes_to_define.is_empty());
 155
 156         let res = f(self);
 157
 158         assert!(self.in_scope_lifetimes.is_empty());
 159         self.in_scope_lifetimes = old_in_scope_lifetimes;
 160
 161         res
 162     }
 163
 164     pub(super) fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
 165         hir::Mod {
 166             inner: m.inner,
 167             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
 168         }
 169     }
 170
 171     pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
 172         let node_ids = match i.kind {
 173             ItemKind::Use(ref use_tree) => {
 174                 let mut vec = smallvec![i.id];
 175                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
 176                 vec
 177             }
 178             ItemKind::MacroDef(..) => SmallVec::new(),
 179             ItemKind::Fn(..) |
 180             ItemKind::Impl(.., None, _, _) => smallvec![i.id],
 181             ItemKind::Static(ref ty, ..) => {
 182                 let mut ids = smallvec![i.id];
 183                 if self.sess.features_untracked().impl_trait_in_bindings {
 184                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 185                     visitor.visit_ty(ty);
 186                 }
 187                 ids
 188             },
 189             ItemKind::Const(ref ty, ..) => {
 190                 let mut ids = smallvec![i.id];
 191                 if self.sess.features_untracked().impl_trait_in_bindings {
 192                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 193                     visitor.visit_ty(ty);
 194                 }
 195                 ids
 196             },
 197             _ => smallvec![i.id],
 198         };
 199
 200         node_ids.into_iter().map(|node_id| hir::ItemId {
 201             id: self.allocate_hir_id_counter(node_id)
 202         }).collect()
 203     }
 204
 205     fn lower_item_id_use_tree(
 206         &mut self,
 207         tree: &UseTree,
 208         base_id: NodeId,
 209         vec: &mut SmallVec<[NodeId; 1]>
 210     ) {
 211         match tree.kind {
 212             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
 213                 vec.push(id);
 214                 self.lower_item_id_use_tree(nested, id, vec);
 215             },
 216             UseTreeKind::Glob => {}
 217             UseTreeKind::Simple(_, id1, id2) => {
 218                 for (_, &id) in self.expect_full_res_from_use(base_id)
 219                                     .skip(1)
 220                                     .zip([id1, id2].iter())
 221                 {
 222                     vec.push(id);
 223                 }
 224             },
 225         }
 226     }
 227
 228     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item<'hir>> {
 229         let mut ident = i.ident;
 230         let mut vis = self.lower_visibility(&i.vis, None);
 231         let attrs = self.lower_attrs(&i.attrs);
 232
 233         if let ItemKind::MacroDef(ref def) = i.kind {
 234             if !def.legacy || attr::contains_name(&i.attrs, sym::macro_export) {
 235                 let body = self.lower_token_stream(def.body.inner_tokens());
 236                 let hir_id = self.lower_node_id(i.id);
 237                 self.exported_macros.push(hir::MacroDef {
 238                     name: ident.name,
 239                     vis,
 240                     attrs,
 241                     hir_id,
 242                     span: i.span,
 243                     body,
 244                     legacy: def.legacy,
 245                 });
 246             } else {
 247                 self.non_exported_macro_attrs.extend(attrs.into_iter());
 248             }
 249             return None;
 250         }
 251
 252         let kind = self.lower_item_kind(i.span, i.id, &mut ident, &attrs, &mut vis, &i.kind);
 253
 254         Some(hir::Item {
 255             hir_id: self.lower_node_id(i.id),
 256             ident,
 257             attrs,
 258             kind,
 259             vis,
 260             span: i.span,
 261         })
 262     }
 263
 264     fn lower_item_kind(
 265         &mut self,
 266         span: Span,
 267         id: NodeId,
 268         ident: &mut Ident,
 269         attrs: &hir::HirVec<Attribute>,
 270         vis: &mut hir::Visibility,
 271         i: &ItemKind,
 272     ) -> hir::ItemKind<'hir> {
 273         match *i {
 274             ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
 275             ItemKind::Use(ref use_tree) => {
 276                 // Start with an empty prefix.
 277                 let prefix = Path {
 278                     segments: vec![],
 279                     span: use_tree.span,
 280                 };
 281
 282                 self.lower_use_tree(use_tree, &prefix, id, vis, ident, attrs)
 283             }
 284             ItemKind::Static(ref t, m, ref e) => {
 285                 let ty = self.lower_ty(
 286                     t,
 287                     if self.sess.features_untracked().impl_trait_in_bindings {
 288                         ImplTraitContext::OpaqueTy(None)
 289                     } else {
 290                         ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 291                     }
 292                 );
 293                 hir::ItemKind::Static(
 294                     self.arena.alloc(ty.into_inner()),
 295                     m,
 296                     self.lower_const_body(span, Some(e)),
 297                 )
 298             }
 299             ItemKind::Const(ref t, ref e) => {
 300                 let ty = self.lower_ty(
 301                     t,
 302                     if self.sess.features_untracked().impl_trait_in_bindings {
 303                         ImplTraitContext::OpaqueTy(None)
 304                     } else {
 305                         ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 306                     }
 307                 );
 308                 hir::ItemKind::Const(
 309                     self.arena.alloc(ty.into_inner()),
 310                     self.lower_const_body(span, Some(e))
 311                 )
 312             }
 313             ItemKind::Fn(FnSig { ref decl, header }, ref generics, ref body) => {
 314                 let fn_def_id = self.resolver.definitions().local_def_id(id);
 315                 self.with_new_scopes(|this| {
 316                     this.current_item = Some(ident.span);
 317
 318                     // Note: we don't need to change the return type from `T` to
 319                     // `impl Future<Output = T>` here because lower_body
 320                     // only cares about the input argument patterns in the function
 321                     // declaration (decl), not the return types.
 322                     let body_id = this.lower_maybe_async_body(
 323                         span,
 324                         &decl,
 325                         header.asyncness.node,
 326                         Some(body),
 327                     );
 328
 329                     let (generics, decl) = this.add_in_band_defs(
 330                         generics,
 331                         fn_def_id,
 332                         AnonymousLifetimeMode::PassThrough,
 333                         |this, idty| this.lower_fn_decl(
 334                             &decl,
 335                             Some((fn_def_id, idty)),
 336                             true,
 337                             header.asyncness.node.opt_return_id()
 338                         ),
 339                     );
 340                     let sig = hir::FnSig { decl, header: this.lower_fn_header(header) };
 341                     hir::ItemKind::Fn(sig, generics, body_id)
 342                 })
 343             }
 344             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
 345             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
 346             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
 347             ItemKind::TyAlias(ref ty, ref generics) => match ty.kind.opaque_top_hack() {
 348                 None => {
 349                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 350                     let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
 351                     hir::ItemKind::TyAlias(self.arena.alloc(ty.into_inner()), generics)
 352                 },
 353                 Some(bounds) => {
 354                     let ty = hir::OpaqueTy {
 355                         generics: self.lower_generics(generics, ImplTraitContext::OpaqueTy(None)),
 356                         bounds: self.lower_param_bounds(bounds, ImplTraitContext::OpaqueTy(None)),
 357                         impl_trait_fn: None,
 358                         origin: hir::OpaqueTyOrigin::TypeAlias,
 359                     };
 360                     hir::ItemKind::OpaqueTy(ty)
 361                 }
 362             }
 363             ItemKind::Enum(ref enum_definition, ref generics) => {
 364                 hir::ItemKind::Enum(
 365                     hir::EnumDef {
 366                         variants: enum_definition
 367                             .variants
 368                             .iter()
 369                             .map(|x| self.lower_variant(x))
 370                             .collect(),
 371                     },
 372                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 373                 )
 374             },
 375             ItemKind::Struct(ref struct_def, ref generics) => {
 376                 let struct_def = self.lower_variant_data(struct_def);
 377                 hir::ItemKind::Struct(
 378                     struct_def,
 379                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 380                 )
 381             }
 382             ItemKind::Union(ref vdata, ref generics) => {
 383                 let vdata = self.lower_variant_data(vdata);
 384                 hir::ItemKind::Union(
 385                     vdata,
 386                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 387                 )
 388             }
 389             ItemKind::Impl(
 390                 unsafety,
 391                 polarity,
 392                 defaultness,
 393                 ref ast_generics,
 394                 ref trait_ref,
 395                 ref ty,
 396                 ref impl_items,
 397             ) => {
 398                 let def_id = self.resolver.definitions().local_def_id(id);
 399
 400                 // Lower the "impl header" first. This ordering is important
 401                 // for in-band lifetimes! Consider `'a` here:
 402                 //
 403                 //     impl Foo<'a> for u32 {
 404                 //         fn method(&'a self) { .. }
 405                 //     }
 406                 //
 407                 // Because we start by lowering the `Foo<'a> for u32`
 408                 // part, we will add `'a` to the list of generics on
 409                 // the impl. When we then encounter it later in the
 410                 // method, it will not be considered an in-band
 411                 // lifetime to be added, but rather a reference to a
 412                 // parent lifetime.
 413                 let lowered_trait_impl_id = self.lower_node_id(id);
 414                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
 415                     ast_generics,
 416                     def_id,
 417                     AnonymousLifetimeMode::CreateParameter,
 418                     |this, _| {
 419                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
 420                             this.lower_trait_ref(trait_ref, ImplTraitContext::disallowed())
 421                         });
 422
 423                         if let Some(ref trait_ref) = trait_ref {
 424                             if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res {
 425                                 this.trait_impls.entry(def_id).or_default().push(
 426                                     lowered_trait_impl_id);
 427                             }
 428                         }
 429
 430                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::disallowed());
 431
 432                         (trait_ref, lowered_ty)
 433                     },
 434                 );
 435
 436                 let new_impl_items = self.with_in_scope_lifetime_defs(
 437                     &ast_generics.params,
 438                     |this| {
 439                         this.arena.alloc_from_iter(
 440                             impl_items
 441                                 .iter()
 442                                 .map(|item| this.lower_impl_item_ref(item))
 443                         )
 444                     },
 445                 );
 446
 447                 hir::ItemKind::Impl(
 448                     unsafety,
 449                     polarity,
 450                     self.lower_defaultness(defaultness, true /* [1] */),
 451                     generics,
 452                     trait_ref,
 453                     self.arena.alloc(lowered_ty.into_inner()),
 454                     new_impl_items,
 455                 )
 456             }
 457             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
 458                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::disallowed());
 459                 let items = self.arena.alloc_from_iter(items
 460                     .iter()
 461                     .map(|item| self.lower_trait_item_ref(item))
 462                 );
 463                 hir::ItemKind::Trait(
 464                     is_auto,
 465                     unsafety,
 466                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 467                     bounds,
 468                     items,
 469                 )
 470             }
 471             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemKind::TraitAlias(
 472                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 473                 self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 474             ),
 475             ItemKind::MacroDef(..)
 476             | ItemKind::Mac(..) => bug!("`TyMac` should have been expanded by now"),
 477         }
 478
 479         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
 480         //     not cause an assertion failure inside the `lower_defaultness` function.
 481     }
 482
 483     fn lower_use_tree(
 484         &mut self,
 485         tree: &UseTree,
 486         prefix: &Path,
 487         id: NodeId,
 488         vis: &mut hir::Visibility,
 489         ident: &mut Ident,
 490         attrs: &hir::HirVec<Attribute>,
 491     ) -> hir::ItemKind<'hir> {
 492         debug!("lower_use_tree(tree={:?})", tree);
 493         debug!("lower_use_tree: vis = {:?}", vis);
 494
 495         let path = &tree.prefix;
 496         let segments = prefix
 497             .segments
 498             .iter()
 499             .chain(path.segments.iter())
 500             .cloned()
 501             .collect();
 502
 503         match tree.kind {
 504             UseTreeKind::Simple(rename, id1, id2) => {
 505                 *ident = tree.ident();
 506
 507                 // First, apply the prefix to the path.
 508                 let mut path = Path {
 509                     segments,
 510                     span: path.span,
 511                 };
 512
 513                 // Correctly resolve `self` imports.
 514                 if path.segments.len() > 1
 515                     && path.segments.last().unwrap().ident.name == kw::SelfLower
 516                 {
 517                     let _ = path.segments.pop();
 518                     if rename.is_none() {
 519                         *ident = path.segments.last().unwrap().ident;
 520                     }
 521                 }
 522
 523                 let mut resolutions = self.expect_full_res_from_use(id);
 524                 // We want to return *something* from this function, so hold onto the first item
 525                 // for later.
 526                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
 527
 528                 // Here, we are looping over namespaces, if they exist for the definition
 529                 // being imported. We only handle type and value namespaces because we
 530                 // won't be dealing with macros in the rest of the compiler.
 531                 // Essentially a single `use` which imports two names is desugared into
 532                 // two imports.
 533                 for (res, &new_node_id) in resolutions.zip([id1, id2].iter()) {
 534                     let ident = *ident;
 535                     let mut path = path.clone();
 536                     for seg in &mut path.segments {
 537                         seg.id = self.resolver.next_node_id();
 538                     }
 539                     let span = path.span;
 540
 541                     self.with_hir_id_owner(new_node_id, |this| {
 542                         let new_id = this.lower_node_id(new_node_id);
 543                         let res = this.lower_res(res);
 544                         let path =
 545                             this.lower_path_extra(res, &path, ParamMode::Explicit, None);
 546                         let kind = hir::ItemKind::Use(this.arena.alloc(path), hir::UseKind::Single);
 547                         let vis = this.rebuild_vis(&vis);
 548
 549                         this.insert_item(
 550                             hir::Item {
 551                                 hir_id: new_id,
 552                                 ident,
 553                                 attrs: attrs.into_iter().cloned().collect(),
 554                                 kind,
 555                                 vis,
 556                                 span,
 557                             },
 558                         );
 559                     });
 560                 }
 561
 562                 let path = self.arena.alloc(self.lower_path_extra(ret_res, &path, ParamMode::Explicit, None));
 563                 hir::ItemKind::Use(path, hir::UseKind::Single)
 564             }
 565             UseTreeKind::Glob => {
 566                 let path = self.arena.alloc(self.lower_path(
 567                     id,
 568                     &Path {
 569                         segments,
 570                         span: path.span,
 571                     },
 572                     ParamMode::Explicit,
 573                 ));
 574                 hir::ItemKind::Use(path, hir::UseKind::Glob)
 575             }
 576             UseTreeKind::Nested(ref trees) => {
 577                 // Nested imports are desugared into simple imports.
 578                 // So, if we start with
 579                 //
 580                 // ```
 581                 // pub(x) use foo::{a, b};
 582                 // ```
 583                 //
 584                 // we will create three items:
 585                 //
 586                 // ```
 587                 // pub(x) use foo::a;
 588                 // pub(x) use foo::b;
 589                 // pub(x) use foo::{}; // <-- this is called the `ListStem`
 590                 // ```
 591                 //
 592                 // The first two are produced by recursively invoking
 593                 // `lower_use_tree` (and indeed there may be things
 594                 // like `use foo::{a::{b, c}}` and so forth).  They
 595                 // wind up being directly added to
 596                 // `self.items`. However, the structure of this
 597                 // function also requires us to return one item, and
 598                 // for that we return the `{}` import (called the
 599                 // `ListStem`).
 600
 601                 let prefix = Path {
 602                     segments,
 603                     span: prefix.span.to(path.span),
 604                 };
 605
 606                 // Add all the nested `PathListItem`s to the HIR.
 607                 for &(ref use_tree, id) in trees {
 608                     let new_hir_id = self.lower_node_id(id);
 609
 610                     let mut prefix = prefix.clone();
 611
 612                     // Give the segments new node-ids since they are being cloned.
 613                     for seg in &mut prefix.segments {
 614                         seg.id = self.resolver.next_node_id();
 615                     }
 616
 617                     // Each `use` import is an item and thus are owners of the
 618                     // names in the path. Up to this point the nested import is
 619                     // the current owner, since we want each desugared import to
 620                     // own its own names, we have to adjust the owner before
 621                     // lowering the rest of the import.
 622                     self.with_hir_id_owner(id, |this| {
 623                         let mut vis = this.rebuild_vis(&vis);
 624                         let mut ident = *ident;
 625
 626                         let kind = this.lower_use_tree(use_tree,
 627                                                        &prefix,
 628                                                        id,
 629                                                        &mut vis,
 630                                                        &mut ident,
 631                                                        attrs);
 632
 633                         this.insert_item(
 634                             hir::Item {
 635                                 hir_id: new_hir_id,
 636                                 ident,
 637                                 attrs: attrs.into_iter().cloned().collect(),
 638                                 kind,
 639                                 vis,
 640                                 span: use_tree.span,
 641                             },
 642                         );
 643                     });
 644                 }
 645
 646                 // Subtle and a bit hacky: we lower the privacy level
 647                 // of the list stem to "private" most of the time, but
 648                 // not for "restricted" paths. The key thing is that
 649                 // we don't want it to stay as `pub` (with no caveats)
 650                 // because that affects rustdoc and also the lints
 651                 // about `pub` items. But we can't *always* make it
 652                 // private -- particularly not for restricted paths --
 653                 // because it contains node-ids that would then be
 654                 // unused, failing the check that HirIds are "densely
 655                 // assigned".
 656                 match vis.node {
 657                     hir::VisibilityKind::Public |
 658                     hir::VisibilityKind::Crate(_) |
 659                     hir::VisibilityKind::Inherited => {
 660                         *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
 661                     }
 662                     hir::VisibilityKind::Restricted { .. } => {
 663                         // Do nothing here, as described in the comment on the match.
 664                     }
 665                 }
 666
 667                 let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
 668                 let res = self.lower_res(res);
 669                 let path = self.arena.alloc(self.lower_path_extra(res, &prefix, ParamMode::Explicit, None));
 670                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
 671             }
 672         }
 673     }
 674
 675     /// Paths like the visibility path in `pub(super) use foo::{bar, baz}` are repeated
 676     /// many times in the HIR tree; for each occurrence, we need to assign distinct
 677     /// `NodeId`s. (See, e.g., #56128.)
 678     fn rebuild_use_path(&mut self, path: &hir::Path) -> hir::Path {
 679         debug!("rebuild_use_path(path = {:?})", path);
 680         let segments = path.segments.iter().map(|seg| hir::PathSegment {
 681             ident: seg.ident,
 682             hir_id: seg.hir_id.map(|_| self.next_id()),
 683             res: seg.res,
 684             args: None,
 685             infer_args: seg.infer_args,
 686         }).collect();
 687         hir::Path {
 688             span: path.span,
 689             res: path.res,
 690             segments,
 691         }
 692     }
 693
 694     fn rebuild_vis(&mut self, vis: &hir::Visibility) -> hir::Visibility {
 695         let vis_kind = match vis.node {
 696             hir::VisibilityKind::Public => hir::VisibilityKind::Public,
 697             hir::VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 698             hir::VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 699             hir::VisibilityKind::Restricted { ref path, hir_id: _ } => {
 700                 hir::VisibilityKind::Restricted {
 701                     path: P(self.rebuild_use_path(path)),
 702                     hir_id: self.next_id(),
 703                 }
 704             }
 705         };
 706         respan(vis.span, vis_kind)
 707     }
 708
 709     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
 710         let def_id = self.resolver.definitions().local_def_id(i.id);
 711         hir::ForeignItem {
 712             hir_id: self.lower_node_id(i.id),
 713             ident: i.ident,
 714             attrs: self.lower_attrs(&i.attrs),
 715             kind: match i.kind {
 716                 ForeignItemKind::Fn(ref fdec, ref generics) => {
 717                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
 718                         generics,
 719                         def_id,
 720                         AnonymousLifetimeMode::PassThrough,
 721                         |this, _| {
 722                             (
 723                                 // Disallow `impl Trait` in foreign items.
 724                                 this.lower_fn_decl(fdec, None, false, None),
 725                                 this.lower_fn_params_to_names(fdec),
 726                             )
 727                         },
 728                     );
 729
 730                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
 731                 }
 732                 ForeignItemKind::Static(ref t, m) => {
 733                     hir::ForeignItemKind::Static(
 734                         self.lower_ty(t, ImplTraitContext::disallowed()), m)
 735                 }
 736                 ForeignItemKind::Ty => hir::ForeignItemKind::Type,
 737                 ForeignItemKind::Macro(_) => panic!("macro shouldn't exist here"),
 738             },
 739             vis: self.lower_visibility(&i.vis, None),
 740             span: i.span,
 741         }
 742     }
 743
 744     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
 745         hir::ForeignMod {
 746             abi: fm.abi.map_or(abi::Abi::C, |abi| self.lower_abi(abi)),
 747             items: fm.items
 748                 .iter()
 749                 .map(|x| self.lower_foreign_item(x))
 750                 .collect(),
 751         }
 752     }
 753
 754     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> &'hir hir::GlobalAsm {
 755         self.arena.alloc(hir::GlobalAsm { asm: ga.asm })
 756     }
 757
 758     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
 759         hir::Variant {
 760             attrs: self.lower_attrs(&v.attrs),
 761             data: self.lower_variant_data(&v.data),
 762             disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
 763             id: self.lower_node_id(v.id),
 764             ident: v.ident,
 765             span: v.span,
 766         }
 767     }
 768
 769     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
 770         match *vdata {
 771             VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
 772                 fields.iter().enumerate().map(|f| self.lower_struct_field(f)).collect(),
 773                 recovered,
 774             ),
 775             VariantData::Tuple(ref fields, id) => {
 776                 hir::VariantData::Tuple(
 777                     fields
 778                         .iter()
 779                         .enumerate()
 780                         .map(|f| self.lower_struct_field(f))
 781                         .collect(),
 782                     self.lower_node_id(id),
 783                 )
 784             },
 785             VariantData::Unit(id) => {
 786                 hir::VariantData::Unit(self.lower_node_id(id))
 787             },
 788         }
 789     }
 790
 791     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
 792         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
 793             let t = self.lower_path_ty(
 794                 &f.ty,
 795                 qself,
 796                 path,
 797                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
 798                 ImplTraitContext::disallowed()
 799             );
 800             P(t)
 801         } else {
 802             self.lower_ty(&f.ty, ImplTraitContext::disallowed())
 803         };
 804         hir::StructField {
 805             span: f.span,
 806             hir_id: self.lower_node_id(f.id),
 807             ident: match f.ident {
 808                 Some(ident) => ident,
 809                 // FIXME(jseyfried): positional field hygiene.
 810                 None => Ident::new(sym::integer(index), f.span),
 811             },
 812             vis: self.lower_visibility(&f.vis, None),
 813             ty,
 814             attrs: self.lower_attrs(&f.attrs),
 815         }
 816     }
 817
 818     fn lower_trait_item(&mut self, i: &AssocItem) -> hir::TraitItem {
 819         let trait_item_def_id = self.resolver.definitions().local_def_id(i.id);
 820
 821         let (generics, kind) = match i.kind {
 822             AssocItemKind::Const(ref ty, ref default) => (
 823                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 824                 hir::TraitItemKind::Const(
 825                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 826                     default
 827                         .as_ref()
 828                         .map(|x| self.lower_const_body(i.span, Some(x))),
 829                 ),
 830             ),
 831             AssocItemKind::Fn(ref sig, None) => {
 832                 let names = self.lower_fn_params_to_names(&sig.decl);
 833                 let (generics, sig) = self.lower_method_sig(
 834                     &i.generics,
 835                     sig,
 836                     trait_item_def_id,
 837                     false,
 838                     None,
 839                 );
 840                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
 841             }
 842             AssocItemKind::Fn(ref sig, Some(ref body)) => {
 843                 let body_id = self.lower_fn_body_block(i.span, &sig.decl, Some(body));
 844                 let (generics, sig) = self.lower_method_sig(
 845                     &i.generics,
 846                     sig,
 847                     trait_item_def_id,
 848                     false,
 849                     None,
 850                 );
 851                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
 852             }
 853             AssocItemKind::TyAlias(ref bounds, ref default) => {
 854                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 855                 let kind = hir::TraitItemKind::Type(
 856                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 857                     default
 858                         .as_ref()
 859                         .map(|x| self.lower_ty(x, ImplTraitContext::disallowed())),
 860                 );
 861
 862                 (generics, kind)
 863             },
 864             AssocItemKind::Macro(..) => bug!("macro item shouldn't exist at this point"),
 865         };
 866
 867         hir::TraitItem {
 868             hir_id: self.lower_node_id(i.id),
 869             ident: i.ident,
 870             attrs: self.lower_attrs(&i.attrs),
 871             generics,
 872             kind,
 873             span: i.span,
 874         }
 875     }
 876
 877     fn lower_trait_item_ref(&mut self, i: &AssocItem) -> hir::TraitItemRef {
 878         let (kind, has_default) = match i.kind {
 879             AssocItemKind::Const(_, ref default) => {
 880                 (hir::AssocItemKind::Const, default.is_some())
 881             }
 882             AssocItemKind::TyAlias(_, ref default) => {
 883                 (hir::AssocItemKind::Type, default.is_some())
 884             }
 885             AssocItemKind::Fn(ref sig, ref default) => (
 886                 hir::AssocItemKind::Method {
 887                     has_self: sig.decl.has_self(),
 888                 },
 889                 default.is_some(),
 890             ),
 891             AssocItemKind::Macro(..) => unimplemented!(),
 892         };
 893         hir::TraitItemRef {
 894             id: hir::TraitItemId { hir_id: self.lower_node_id(i.id) },
 895             ident: i.ident,
 896             span: i.span,
 897             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
 898             kind,
 899         }
 900     }
 901
 902     /// Construct `ExprKind::Err` for the given `span`.
 903     fn expr_err(&mut self, span: Span) -> hir::Expr {
 904         self.expr(span, hir::ExprKind::Err, AttrVec::new())
 905     }
 906
 907     fn lower_impl_item(&mut self, i: &AssocItem) -> hir::ImplItem {
 908         let impl_item_def_id = self.resolver.definitions().local_def_id(i.id);
 909
 910         let (generics, kind) = match i.kind {
 911             AssocItemKind::Const(ref ty, ref expr) => (
 912                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 913                 hir::ImplItemKind::Const(
 914                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 915                     self.lower_const_body(i.span, expr.as_deref()),
 916                 ),
 917             ),
 918             AssocItemKind::Fn(ref sig, ref body) => {
 919                 self.current_item = Some(i.span);
 920                 let body_id = self.lower_maybe_async_body(
 921                     i.span,
 922                     &sig.decl,
 923                     sig.header.asyncness.node,
 924                     body.as_deref(),
 925                 );
 926                 let impl_trait_return_allow = !self.is_in_trait_impl;
 927                 let (generics, sig) = self.lower_method_sig(
 928                     &i.generics,
 929                     sig,
 930                     impl_item_def_id,
 931                     impl_trait_return_allow,
 932                     sig.header.asyncness.node.opt_return_id(),
 933                 );
 934
 935                 (generics, hir::ImplItemKind::Method(sig, body_id))
 936             }
 937             AssocItemKind::TyAlias(_, ref ty) => {
 938                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 939                 let kind = match ty {
 940                     None => {
 941                         hir::ImplItemKind::TyAlias(P(self.ty(i.span, hir::TyKind::Err)))
 942                     }
 943                     Some(ty) => match ty.kind.opaque_top_hack() {
 944                         None => {
 945                             let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 946                             hir::ImplItemKind::TyAlias(ty)
 947                         }
 948                         Some(bs) => {
 949                             let bs = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
 950                             hir::ImplItemKind::OpaqueTy(bs)
 951                         }
 952                     }
 953                 };
 954                 (generics, kind)
 955             },
 956             AssocItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
 957         };
 958
 959         hir::ImplItem {
 960             hir_id: self.lower_node_id(i.id),
 961             ident: i.ident,
 962             attrs: self.lower_attrs(&i.attrs),
 963             generics,
 964             vis: self.lower_visibility(&i.vis, None),
 965             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 966             kind,
 967             span: i.span,
 968         }
 969
 970         // [1] since `default impl` is not yet implemented, this is always true in impls
 971     }
 972
 973     fn lower_impl_item_ref(&mut self, i: &AssocItem) -> hir::ImplItemRef {
 974         hir::ImplItemRef {
 975             id: hir::ImplItemId { hir_id: self.lower_node_id(i.id) },
 976             ident: i.ident,
 977             span: i.span,
 978             vis: self.lower_visibility(&i.vis, Some(i.id)),
 979             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 980             kind: match &i.kind {
 981                 AssocItemKind::Const(..) => hir::AssocItemKind::Const,
 982                 AssocItemKind::TyAlias(_, ty) => match ty
 983                     .as_deref()
 984                     .and_then(|ty| ty.kind.opaque_top_hack())
 985                 {
 986                     None => hir::AssocItemKind::Type,
 987                     Some(_) => hir::AssocItemKind::OpaqueTy,
 988                 },
 989                 AssocItemKind::Fn(sig, _) => hir::AssocItemKind::Method {
 990                     has_self: sig.decl.has_self(),
 991                 },
 992                 AssocItemKind::Macro(..) => unimplemented!(),
 993             },
 994         }
 995
 996         // [1] since `default impl` is not yet implemented, this is always true in impls
 997     }
 998
 999     /// If an `explicit_owner` is given, this method allocates the `HirId` in
1000     /// the address space of that item instead of the item currently being
1001     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
1002     /// lower a `Visibility` value although we haven't lowered the owning
1003     /// `ImplItem` in question yet.
1004     fn lower_visibility(
1005         &mut self,
1006         v: &Visibility,
1007         explicit_owner: Option<NodeId>,
1008     ) -> hir::Visibility {
1009         let node = match v.node {
1010             VisibilityKind::Public => hir::VisibilityKind::Public,
1011             VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
1012             VisibilityKind::Restricted { ref path, id } => {
1013                 debug!("lower_visibility: restricted path id = {:?}", id);
1014                 let lowered_id = if let Some(owner) = explicit_owner {
1015                     self.lower_node_id_with_owner(id, owner)
1016                 } else {
1017                     self.lower_node_id(id)
1018                 };
1019                 let res = self.expect_full_res(id);
1020                 let res = self.lower_res(res);
1021                 hir::VisibilityKind::Restricted {
1022                     path: P(self.lower_path_extra(
1023                         res,
1024                         path,
1025                         ParamMode::Explicit,
1026                         explicit_owner,
1027                     )),
1028                     hir_id: lowered_id,
1029                 }
1030             },
1031             VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
1032         };
1033         respan(v.span, node)
1034     }
1035
1036     fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
1037         match d {
1038             Defaultness::Default => hir::Defaultness::Default {
1039                 has_value: has_value,
1040             },
1041             Defaultness::Final => {
1042                 assert!(has_value);
1043                 hir::Defaultness::Final
1044             }
1045         }
1046     }
1047
1048     fn record_body(&mut self, params: HirVec<hir::Param>, value: hir::Expr) -> hir::BodyId {
1049         let body = hir::Body {
1050             generator_kind: self.generator_kind,
1051             params,
1052             value,
1053         };
1054         let id = body.id();
1055         self.bodies.insert(id, body);
1056         id
1057     }
1058
1059     fn lower_body(
1060         &mut self,
1061         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> (HirVec<hir::Param>, hir::Expr),
1062     ) -> hir::BodyId {
1063         let prev_gen_kind = self.generator_kind.take();
1064         let (parameters, result) = f(self);
1065         let body_id = self.record_body(parameters, result);
1066         self.generator_kind = prev_gen_kind;
1067         body_id
1068     }
1069
1070     fn lower_param(&mut self, param: &Param) -> hir::Param {
1071         hir::Param {
1072             attrs: self.lower_attrs(&param.attrs),
1073             hir_id: self.lower_node_id(param.id),
1074             pat: self.lower_pat(&param.pat),
1075             span: param.span,
1076         }
1077     }
1078
1079     pub(super) fn lower_fn_body(
1080         &mut self,
1081         decl: &FnDecl,
1082         body: impl FnOnce(&mut LoweringContext<'_, '_>) -> hir::Expr,
1083     ) -> hir::BodyId {
1084         self.lower_body(|this| (
1085             decl.inputs.iter().map(|x| this.lower_param(x)).collect(),
1086             body(this),
1087         ))
1088     }
1089
1090     fn lower_fn_body_block(
1091         &mut self,
1092         span: Span,
1093         decl: &FnDecl,
1094         body: Option<&Block>,
1095     ) -> hir::BodyId {
1096         self.lower_fn_body(decl, |this| this.lower_block_expr_opt(span, body))
1097     }
1098
1099     fn lower_block_expr_opt(&mut self, span: Span, block: Option<&Block>) -> hir::Expr {
1100         match block {
1101             Some(block) => self.lower_block_expr(block),
1102             None => self.expr_err(span),
1103         }
1104     }
1105
1106     pub(super) fn lower_const_body(&mut self, span: Span, expr: Option<&Expr>) -> hir::BodyId {
1107         self.lower_body(|this| (hir_vec![], match expr {
1108             Some(expr) => this.lower_expr(expr),
1109             None => this.expr_err(span),
1110         }))
1111     }
1112
1113     fn lower_maybe_async_body(
1114         &mut self,
1115         span: Span,
1116         decl: &FnDecl,
1117         asyncness: IsAsync,
1118         body: Option<&Block>,
1119     ) -> hir::BodyId {
1120         let closure_id = match asyncness {
1121             IsAsync::Async { closure_id, .. } => closure_id,
1122             IsAsync::NotAsync => return self.lower_fn_body_block(span, decl, body),
1123         };
1124
1125         self.lower_body(|this| {
1126             let mut parameters: Vec<hir::Param> = Vec::new();
1127             let mut statements: Vec<hir::Stmt> = Vec::new();
1128
1129             // Async function parameters are lowered into the closure body so that they are
1130             // captured and so that the drop order matches the equivalent non-async functions.
1131             //
1132             // from:
1133             //
1134             //     async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
1135             //         <body>
1136             //     }
1137             //
1138             // into:
1139             //
1140             //     fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) {
1141             //       async move {
1142             //         let __arg2 = __arg2;
1143             //         let <pattern> = __arg2;
1144             //         let __arg1 = __arg1;
1145             //         let <pattern> = __arg1;
1146             //         let __arg0 = __arg0;
1147             //         let <pattern> = __arg0;
1148             //         drop-temps { <body> } // see comments later in fn for details
1149             //       }
1150             //     }
1151             //
1152             // If `<pattern>` is a simple ident, then it is lowered to a single
1153             // `let <pattern> = <pattern>;` statement as an optimization.
1154             //
1155             // Note that the body is embedded in `drop-temps`; an
1156             // equivalent desugaring would be `return { <body>
1157             // };`. The key point is that we wish to drop all the
1158             // let-bound variables and temporaries created in the body
1159             // (and its tail expression!) before we drop the
1160             // parameters (c.f. rust-lang/rust#64512).
1161             for (index, parameter) in decl.inputs.iter().enumerate() {
1162                 let parameter = this.lower_param(parameter);
1163                 let span = parameter.pat.span;
1164
1165                 // Check if this is a binding pattern, if so, we can optimize and avoid adding a
1166                 // `let <pat> = __argN;` statement. In this case, we do not rename the parameter.
1167                 let (ident, is_simple_parameter) = match parameter.pat.kind {
1168                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, _) =>
1169                         (ident, true),
1170                     _ => {
1171                         // Replace the ident for bindings that aren't simple.
1172                         let name = format!("__arg{}", index);
1173                         let ident = Ident::from_str(&name);
1174
1175                         (ident, false)
1176                     },
1177                 };
1178
1179                 let desugared_span =
1180                     this.mark_span_with_reason(DesugaringKind::Async, span, None);
1181
1182                 // Construct a parameter representing `__argN: <ty>` to replace the parameter of the
1183                 // async function.
1184                 //
1185                 // If this is the simple case, this parameter will end up being the same as the
1186                 // original parameter, but with a different pattern id.
1187                 let mut stmt_attrs = AttrVec::new();
1188                 stmt_attrs.extend(parameter.attrs.iter().cloned());
1189                 let (new_parameter_pat, new_parameter_id) = this.pat_ident(desugared_span, ident);
1190                 let new_parameter = hir::Param {
1191                     attrs: parameter.attrs,
1192                     hir_id: parameter.hir_id,
1193                     pat: new_parameter_pat,
1194                     span: parameter.span,
1195                 };
1196
1197
1198                 if is_simple_parameter {
1199                     // If this is the simple case, then we only insert one statement that is
1200                     // `let <pat> = <pat>;`. We re-use the original argument's pattern so that
1201                     // `HirId`s are densely assigned.
1202                     let expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1203                     let stmt = this.stmt_let_pat(
1204                         stmt_attrs,
1205                         desugared_span,
1206                         Some(P(expr)),
1207                         parameter.pat,
1208                         hir::LocalSource::AsyncFn
1209                     );
1210                     statements.push(stmt);
1211                 } else {
1212                     // If this is not the simple case, then we construct two statements:
1213                     //
1214                     // ```
1215                     // let __argN = __argN;
1216                     // let <pat> = __argN;
1217                     // ```
1218                     //
1219                     // The first statement moves the parameter into the closure and thus ensures
1220                     // that the drop order is correct.
1221                     //
1222                     // The second statement creates the bindings that the user wrote.
1223
1224                     // Construct the `let mut __argN = __argN;` statement. It must be a mut binding
1225                     // because the user may have specified a `ref mut` binding in the next
1226                     // statement.
1227                     let (move_pat, move_id) = this.pat_ident_binding_mode(
1228                         desugared_span, ident, hir::BindingAnnotation::Mutable);
1229                     let move_expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1230                     let move_stmt = this.stmt_let_pat(
1231                         AttrVec::new(),
1232                         desugared_span,
1233                         Some(P(move_expr)),
1234                         move_pat,
1235                         hir::LocalSource::AsyncFn
1236                     );
1237
1238                     // Construct the `let <pat> = __argN;` statement. We re-use the original
1239                     // parameter's pattern so that `HirId`s are densely assigned.
1240                     let pattern_expr = this.expr_ident(desugared_span, ident, move_id);
1241                     let pattern_stmt = this.stmt_let_pat(
1242                         stmt_attrs,
1243                         desugared_span,
1244                         Some(P(pattern_expr)),
1245                         parameter.pat,
1246                         hir::LocalSource::AsyncFn
1247                     );
1248
1249                     statements.push(move_stmt);
1250                     statements.push(pattern_stmt);
1251                 };
1252
1253                 parameters.push(new_parameter);
1254             }
1255
1256             let body_span = body.map_or(span, |b| b.span);
1257             let async_expr = this.make_async_expr(
1258                 CaptureBy::Value,
1259                 closure_id,
1260                 None,
1261                 body_span,
1262                 hir::AsyncGeneratorKind::Fn,
1263                 |this| {
1264                     // Create a block from the user's function body:
1265                     let user_body = this.lower_block_expr_opt(body_span, body);
1266
1267                     // Transform into `drop-temps { <user-body> }`, an expression:
1268                     let desugared_span = this.mark_span_with_reason(
1269                         DesugaringKind::Async,
1270                         user_body.span,
1271                         None,
1272                     );
1273                     let user_body = this.expr_drop_temps(
1274                         desugared_span,
1275                         P(user_body),
1276                         AttrVec::new(),
1277                     );
1278
1279                     // As noted above, create the final block like
1280                     //
1281                     // ```
1282                     // {
1283                     //   let $param_pattern = $raw_param;
1284                     //   ...
1285                     //   drop-temps { <user-body> }
1286                     // }
1287                     // ```
1288                     let body = this.block_all(
1289                         desugared_span,
1290                         statements.into(),
1291                         Some(P(user_body)),
1292                     );
1293                     this.expr_block(P(body), AttrVec::new())
1294                 });
1295             (HirVec::from(parameters), this.expr(body_span, async_expr, AttrVec::new()))
1296         })
1297     }
1298
1299     fn lower_method_sig(
1300         &mut self,
1301         generics: &Generics,
1302         sig: &FnSig,
1303         fn_def_id: DefId,
1304         impl_trait_return_allow: bool,
1305         is_async: Option<NodeId>,
1306     ) -> (hir::Generics, hir::FnSig) {
1307         let header = self.lower_fn_header(sig.header);
1308         let (generics, decl) = self.add_in_band_defs(
1309             generics,
1310             fn_def_id,
1311             AnonymousLifetimeMode::PassThrough,
1312             |this, idty| this.lower_fn_decl(
1313                 &sig.decl,
1314                 Some((fn_def_id, idty)),
1315                 impl_trait_return_allow,
1316                 is_async,
1317             ),
1318         );
1319         (generics, hir::FnSig { header, decl })
1320     }
1321
1322     fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
1323         hir::FnHeader {
1324             unsafety: h.unsafety,
1325             asyncness: self.lower_asyncness(h.asyncness.node),
1326             constness: h.constness.node,
1327             abi: self.lower_extern(h.ext),
1328         }
1329     }
1330
1331     pub(super) fn lower_abi(&mut self, abi: StrLit) -> abi::Abi {
1332         abi::lookup(&abi.symbol_unescaped.as_str()).unwrap_or_else(|| {
1333             self.error_on_invalid_abi(abi);
1334             abi::Abi::Rust
1335         })
1336     }
1337
1338     pub(super) fn lower_extern(&mut self, ext: Extern) -> abi::Abi {
1339         match ext {
1340             Extern::None => abi::Abi::Rust,
1341             Extern::Implicit => abi::Abi::C,
1342             Extern::Explicit(abi) => self.lower_abi(abi),
1343         }
1344     }
1345
1346     fn error_on_invalid_abi(&self, abi: StrLit) {
1347         struct_span_err!(
1348             self.sess,
1349             abi.span,
1350             E0703,
1351             "invalid ABI: found `{}`",
1352             abi.symbol
1353         )
1354         .span_label(abi.span, "invalid ABI")
1355         .help(&format!("valid ABIs: {}", abi::all_names().join(", ")))
1356         .emit();
1357     }
1358
1359     fn lower_asyncness(&mut self, a: IsAsync) -> hir::IsAsync {
1360         match a {
1361             IsAsync::Async { .. } => hir::IsAsync::Async,
1362             IsAsync::NotAsync => hir::IsAsync::NotAsync,
1363         }
1364     }
1365
1366     pub(super) fn lower_generics(
1367         &mut self,
1368         generics: &Generics,
1369         itctx: ImplTraitContext<'_>)
1370         -> hir::Generics
1371     {
1372         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1373         // FIXME: this could probably be done with less rightward drift. It also looks like two
1374         // control paths where `report_error` is called are the only paths that advance to after the
1375         // match statement, so the error reporting could probably just be moved there.
1376         let mut add_bounds: NodeMap<Vec<_>> = Default::default();
1377         for pred in &generics.where_clause.predicates {
1378             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1379                 'next_bound: for bound in &bound_pred.bounds {
1380                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
1381                         let report_error = |this: &mut Self| {
1382                             this.diagnostic().span_err(
1383                                 bound_pred.bounded_ty.span,
1384                                 "`?Trait` bounds are only permitted at the \
1385                                  point where a type parameter is declared",
1386                             );
1387                         };
1388                         // Check if the where clause type is a plain type parameter.
1389                         match bound_pred.bounded_ty.kind {
1390                             TyKind::Path(None, ref path)
1391                                 if path.segments.len() == 1
1392                                     && bound_pred.bound_generic_params.is_empty() =>
1393                             {
1394                                 if let Some(Res::Def(DefKind::TyParam, def_id)) = self.resolver
1395                                     .get_partial_res(bound_pred.bounded_ty.id)
1396                                     .map(|d| d.base_res())
1397                                 {
1398                                     if let Some(node_id) =
1399                                         self.resolver.definitions().as_local_node_id(def_id)
1400                                     {
1401                                         for param in &generics.params {
1402                                             match param.kind {
1403                                                 GenericParamKind::Type { .. } => {
1404                                                     if node_id == param.id {
1405                                                         add_bounds.entry(param.id)
1406                                                             .or_default()
1407                                                             .push(bound.clone());
1408                                                         continue 'next_bound;
1409                                                     }
1410                                                 }
1411                                                 _ => {}
1412                                             }
1413                                         }
1414                                     }
1415                                 }
1416                                 report_error(self)
1417                             }
1418                             _ => report_error(self),
1419                         }
1420                     }
1421                 }
1422             }
1423         }
1424
1425         hir::Generics {
1426             params: self.lower_generic_params(&generics.params, &add_bounds, itctx),
1427             where_clause: self.lower_where_clause(&generics.where_clause),
1428             span: generics.span,
1429         }
1430     }
1431
1432     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
1433         self.with_anonymous_lifetime_mode(
1434             AnonymousLifetimeMode::ReportError,
1435             |this| {
1436                 hir::WhereClause {
1437                     predicates: wc.predicates
1438                         .iter()
1439                         .map(|predicate| this.lower_where_predicate(predicate))
1440                         .collect(),
1441                     span: wc.span,
1442                 }
1443             },
1444         )
1445     }
1446
1447     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
1448         match *pred {
1449             WherePredicate::BoundPredicate(WhereBoundPredicate {
1450                 ref bound_generic_params,
1451                 ref bounded_ty,
1452                 ref bounds,
1453                 span,
1454             }) => {
1455                 self.with_in_scope_lifetime_defs(
1456                     &bound_generic_params,
1457                     |this| {
1458                         hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1459                             bound_generic_params: this.lower_generic_params(
1460                                 bound_generic_params,
1461                                 &NodeMap::default(),
1462                                 ImplTraitContext::disallowed(),
1463                             ),
1464                             bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::disallowed()),
1465                             bounds: bounds
1466                                 .iter()
1467                                 .filter_map(|bound| match *bound {
1468                                     // Ignore `?Trait` bounds.
1469                                     // They were copied into type parameters already.
1470                                     GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1471                                     _ => Some(this.lower_param_bound(
1472                                         bound,
1473                                         ImplTraitContext::disallowed(),
1474                                     )),
1475                                 })
1476                                 .collect(),
1477                             span,
1478                         })
1479                     },
1480                 )
1481             }
1482             WherePredicate::RegionPredicate(WhereRegionPredicate {
1483                 ref lifetime,
1484                 ref bounds,
1485                 span,
1486             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1487                 span,
1488                 lifetime: self.lower_lifetime(lifetime),
1489                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
1490             }),
1491             WherePredicate::EqPredicate(WhereEqPredicate {
1492                 id,
1493                 ref lhs_ty,
1494                 ref rhs_ty,
1495                 span,
1496             }) => {
1497                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1498                     hir_id: self.lower_node_id(id),
1499                     lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::disallowed()),
1500                     rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::disallowed()),
1501                     span,
1502                 })
1503             },
1504         }
1505     }
1506 }