src/librustc_ast_lowering/item.rs

   1 use super::{AnonymousLifetimeMode, LoweringContext, ParamMode};
   2 use super::{ImplTraitContext, ImplTraitPosition, ImplTraitTypeIdVisitor};
   3
   4 use rustc::arena::Arena;
   5 use rustc::bug;
   6 use rustc_error_codes::*;
   7 use rustc_errors::struct_span_err;
   8 use rustc_hir as hir;
   9 use rustc_hir::def::{DefKind, Res};
  10 use rustc_hir::def_id::DefId;
  11 use rustc_session::node_id::NodeMap;
  12 use rustc_span::source_map::{respan, DesugaringKind};
  13 use rustc_span::symbol::{kw, sym};
  14 use rustc_span::Span;
  15 use rustc_target::spec::abi;
  16 use syntax::ast::*;
  17 use syntax::attr;
  18 use syntax::visit::{self, Visitor};
  19
  20 use log::debug;
  21 use smallvec::{smallvec, SmallVec};
  22 use std::collections::BTreeSet;
  23
  24 pub(super) struct ItemLowerer<'a, 'lowering, 'hir> {
  25     pub(super) lctx: &'a mut LoweringContext<'lowering, 'hir>,
  26 }
  27
  28 impl ItemLowerer<'_, '_, '_> {
  29     fn with_trait_impl_ref(&mut self, impl_ref: &Option<TraitRef>, f: impl FnOnce(&mut Self)) {
  30         let old = self.lctx.is_in_trait_impl;
  31         self.lctx.is_in_trait_impl = if let &None = impl_ref { false } else { true };
  32         f(self);
  33         self.lctx.is_in_trait_impl = old;
  34     }
  35 }
  36
  37 impl<'a> Visitor<'a> for ItemLowerer<'a, '_, '_> {
  38     fn visit_mod(&mut self, m: &'a Mod, _s: Span, _attrs: &[Attribute], n: NodeId) {
  39         let hir_id = self.lctx.lower_node_id(n);
  40
  41         self.lctx.modules.insert(
  42             hir_id,
  43             hir::ModuleItems {
  44                 items: BTreeSet::new(),
  45                 trait_items: BTreeSet::new(),
  46                 impl_items: BTreeSet::new(),
  47             },
  48         );
  49
  50         let old = self.lctx.current_module;
  51         self.lctx.current_module = hir_id;
  52         visit::walk_mod(self, m);
  53         self.lctx.current_module = old;
  54     }
  55
  56     fn visit_item(&mut self, item: &'a Item) {
  57         let mut item_hir_id = None;
  58         self.lctx.with_hir_id_owner(item.id, |lctx| {
  59             lctx.without_in_scope_lifetime_defs(|lctx| {
  60                 if let Some(hir_item) = lctx.lower_item(item) {
  61                     item_hir_id = Some(hir_item.hir_id);
  62                     lctx.insert_item(hir_item);
  63                 }
  64             })
  65         });
  66
  67         if let Some(hir_id) = item_hir_id {
  68             self.lctx.with_parent_item_lifetime_defs(hir_id, |this| {
  69                 let this = &mut ItemLowerer { lctx: this };
  70                 if let ItemKind::Impl { constness, ref of_trait, .. } = item.kind {
  71                     if constness == Constness::Const {
  72                         this.lctx
  73                             .diagnostic()
  74                             .span_err(item.span, "const trait impls are not yet implemented");
  75                     }
  76
  77                     this.with_trait_impl_ref(of_trait, |this| visit::walk_item(this, item));
  78                 } else {
  79                     visit::walk_item(this, item);
  80                 }
  81             });
  82         }
  83     }
  84
  85     fn visit_trait_item(&mut self, item: &'a AssocItem) {
  86         self.lctx.with_hir_id_owner(item.id, |lctx| {
  87             let hir_item = lctx.lower_trait_item(item);
  88             let id = hir::TraitItemId { hir_id: hir_item.hir_id };
  89             lctx.trait_items.insert(id, hir_item);
  90             lctx.modules.get_mut(&lctx.current_module).unwrap().trait_items.insert(id);
  91         });
  92
  93         visit::walk_trait_item(self, item);
  94     }
  95
  96     fn visit_impl_item(&mut self, item: &'a AssocItem) {
  97         self.lctx.with_hir_id_owner(item.id, |lctx| {
  98             let hir_item = lctx.lower_impl_item(item);
  99             let id = hir::ImplItemId { hir_id: hir_item.hir_id };
 100             lctx.impl_items.insert(id, hir_item);
 101             lctx.modules.get_mut(&lctx.current_module).unwrap().impl_items.insert(id);
 102         });
 103         visit::walk_impl_item(self, item);
 104     }
 105 }
 106
 107 impl<'hir> LoweringContext<'_, 'hir> {
 108     // Same as the method above, but accepts `hir::GenericParam`s
 109     // instead of `ast::GenericParam`s.
 110     // This should only be used with generics that have already had their
 111     // in-band lifetimes added. In practice, this means that this function is
 112     // only used when lowering a child item of a trait or impl.
 113     fn with_parent_item_lifetime_defs<T>(
 114         &mut self,
 115         parent_hir_id: hir::HirId,
 116         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> T,
 117     ) -> T {
 118         let old_len = self.in_scope_lifetimes.len();
 119
 120         let parent_generics = match self.items.get(&parent_hir_id).unwrap().kind {
 121             hir::ItemKind::Impl { ref generics, .. }
 122             | hir::ItemKind::Trait(_, _, ref generics, ..) => &generics.params[..],
 123             _ => &[],
 124         };
 125         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
 126             hir::GenericParamKind::Lifetime { .. } => Some(param.name.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     // Clears (and restores) the `in_scope_lifetimes` field. Used when
 138     // visiting nested items, which never inherit in-scope lifetimes
 139     // from their surrounding environment.
 140     fn without_in_scope_lifetime_defs<T>(
 141         &mut self,
 142         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> T,
 143     ) -> T {
 144         let old_in_scope_lifetimes = std::mem::replace(&mut self.in_scope_lifetimes, vec![]);
 145
 146         // this vector is only used when walking over impl headers,
 147         // input types, and the like, and should not be non-empty in
 148         // between items
 149         assert!(self.lifetimes_to_define.is_empty());
 150
 151         let res = f(self);
 152
 153         assert!(self.in_scope_lifetimes.is_empty());
 154         self.in_scope_lifetimes = old_in_scope_lifetimes;
 155
 156         res
 157     }
 158
 159     pub(super) fn lower_mod(&mut self, m: &Mod) -> hir::Mod<'hir> {
 160         hir::Mod {
 161             inner: m.inner,
 162             item_ids: self
 163                 .arena
 164                 .alloc_from_iter(m.items.iter().flat_map(|x| self.lower_item_id(x))),
 165         }
 166     }
 167
 168     pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
 169         let node_ids = match i.kind {
 170             ItemKind::Use(ref use_tree) => {
 171                 let mut vec = smallvec![i.id];
 172                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
 173                 vec
 174             }
 175             ItemKind::MacroDef(..) => SmallVec::new(),
 176             ItemKind::Fn(..) | ItemKind::Impl { of_trait: None, .. } => smallvec![i.id],
 177             ItemKind::Static(ref ty, ..) => {
 178                 let mut ids = smallvec![i.id];
 179                 if self.sess.features_untracked().impl_trait_in_bindings {
 180                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 181                     visitor.visit_ty(ty);
 182                 }
 183                 ids
 184             }
 185             ItemKind::Const(ref ty, ..) => {
 186                 let mut ids = smallvec![i.id];
 187                 if self.sess.features_untracked().impl_trait_in_bindings {
 188                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 189                     visitor.visit_ty(ty);
 190                 }
 191                 ids
 192             }
 193             _ => smallvec![i.id],
 194         };
 195
 196         node_ids
 197             .into_iter()
 198             .map(|node_id| hir::ItemId { id: self.allocate_hir_id_counter(node_id) })
 199             .collect()
 200     }
 201
 202     fn lower_item_id_use_tree(
 203         &mut self,
 204         tree: &UseTree,
 205         base_id: NodeId,
 206         vec: &mut SmallVec<[NodeId; 1]>,
 207     ) {
 208         match tree.kind {
 209             UseTreeKind::Nested(ref nested_vec) => {
 210                 for &(ref nested, id) in nested_vec {
 211                     vec.push(id);
 212                     self.lower_item_id_use_tree(nested, id, vec);
 213                 }
 214             }
 215             UseTreeKind::Glob => {}
 216             UseTreeKind::Simple(_, id1, id2) => {
 217                 for (_, &id) in
 218                     self.expect_full_res_from_use(base_id).skip(1).zip([id1, id2].iter())
 219                 {
 220                     vec.push(id);
 221                 }
 222             }
 223         }
 224     }
 225
 226     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item<'hir>> {
 227         let mut ident = i.ident;
 228         let mut vis = self.lower_visibility(&i.vis, None);
 229         let attrs = self.lower_attrs(&i.attrs);
 230
 231         if let ItemKind::MacroDef(ref def) = i.kind {
 232             if !def.legacy || attr::contains_name(&i.attrs, sym::macro_export) {
 233                 let body = self.lower_token_stream(def.body.inner_tokens());
 234                 let hir_id = self.lower_node_id(i.id);
 235                 self.exported_macros.push(hir::MacroDef {
 236                     name: ident.name,
 237                     vis,
 238                     attrs,
 239                     hir_id,
 240                     span: i.span,
 241                     body,
 242                     legacy: def.legacy,
 243                 });
 244             } else {
 245                 self.non_exported_macro_attrs.extend(attrs.iter().cloned());
 246             }
 247             return None;
 248         }
 249
 250         let kind = self.lower_item_kind(i.span, i.id, &mut ident, attrs, &mut vis, &i.kind);
 251
 252         Some(hir::Item { hir_id: self.lower_node_id(i.id), ident, attrs, kind, vis, span: i.span })
 253     }
 254
 255     fn lower_item_kind(
 256         &mut self,
 257         span: Span,
 258         id: NodeId,
 259         ident: &mut Ident,
 260         attrs: &'hir [Attribute],
 261         vis: &mut hir::Visibility<'hir>,
 262         i: &ItemKind,
 263     ) -> hir::ItemKind<'hir> {
 264         match *i {
 265             ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
 266             ItemKind::Use(ref use_tree) => {
 267                 // Start with an empty prefix.
 268                 let prefix = Path { segments: vec![], span: use_tree.span };
 269
 270                 self.lower_use_tree(use_tree, &prefix, id, vis, ident, attrs)
 271             }
 272             ItemKind::Static(ref t, m, ref e) => {
 273                 let ty = self.lower_ty(
 274                     t,
 275                     if self.sess.features_untracked().impl_trait_in_bindings {
 276                         ImplTraitContext::OpaqueTy(None)
 277                     } else {
 278                         ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 279                     },
 280                 );
 281                 hir::ItemKind::Static(ty, m, self.lower_const_body(span, Some(e)))
 282             }
 283             ItemKind::Const(ref t, ref e) => {
 284                 let ty = self.lower_ty(
 285                     t,
 286                     if self.sess.features_untracked().impl_trait_in_bindings {
 287                         ImplTraitContext::OpaqueTy(None)
 288                     } else {
 289                         ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 290                     },
 291                 );
 292                 hir::ItemKind::Const(ty, self.lower_const_body(span, Some(e)))
 293             }
 294             ItemKind::Fn(FnSig { ref decl, header }, ref generics, ref body) => {
 295                 let fn_def_id = self.resolver.definitions().local_def_id(id);
 296                 self.with_new_scopes(|this| {
 297                     this.current_item = Some(ident.span);
 298
 299                     // Note: we don't need to change the return type from `T` to
 300                     // `impl Future<Output = T>` here because lower_body
 301                     // only cares about the input argument patterns in the function
 302                     // declaration (decl), not the return types.
 303                     let body_id =
 304                         this.lower_maybe_async_body(span, &decl, header.asyncness.node, Some(body));
 305
 306                     let (generics, decl) = this.add_in_band_defs(
 307                         generics,
 308                         fn_def_id,
 309                         AnonymousLifetimeMode::PassThrough,
 310                         |this, idty| {
 311                             this.lower_fn_decl(
 312                                 &decl,
 313                                 Some((fn_def_id, idty)),
 314                                 true,
 315                                 header.asyncness.node.opt_return_id(),
 316                             )
 317                         },
 318                     );
 319                     let sig = hir::FnSig { decl, header: this.lower_fn_header(header) };
 320                     hir::ItemKind::Fn(sig, generics, body_id)
 321                 })
 322             }
 323             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
 324             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
 325             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
 326             ItemKind::TyAlias(ref ty, ref generics) => match ty.kind.opaque_top_hack() {
 327                 None => {
 328                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 329                     let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
 330                     hir::ItemKind::TyAlias(ty, generics)
 331                 }
 332                 Some(bounds) => {
 333                     let ty = hir::OpaqueTy {
 334                         generics: self.lower_generics(generics, ImplTraitContext::OpaqueTy(None)),
 335                         bounds: self.lower_param_bounds(bounds, ImplTraitContext::OpaqueTy(None)),
 336                         impl_trait_fn: None,
 337                         origin: hir::OpaqueTyOrigin::TypeAlias,
 338                     };
 339                     hir::ItemKind::OpaqueTy(ty)
 340                 }
 341             },
 342             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemKind::Enum(
 343                 hir::EnumDef {
 344                     variants: self.arena.alloc_from_iter(
 345                         enum_definition.variants.iter().map(|x| self.lower_variant(x)),
 346                     ),
 347                 },
 348                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 349             ),
 350             ItemKind::Struct(ref struct_def, ref generics) => {
 351                 let struct_def = self.lower_variant_data(struct_def);
 352                 hir::ItemKind::Struct(
 353                     struct_def,
 354                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 355                 )
 356             }
 357             ItemKind::Union(ref vdata, ref generics) => {
 358                 let vdata = self.lower_variant_data(vdata);
 359                 hir::ItemKind::Union(
 360                     vdata,
 361                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 362                 )
 363             }
 364             ItemKind::Impl {
 365                 unsafety,
 366                 polarity,
 367                 defaultness,
 368                 constness,
 369                 generics: ref ast_generics,
 370                 of_trait: ref trait_ref,
 371                 self_ty: ref ty,
 372                 items: ref impl_items,
 373             } => {
 374                 let def_id = self.resolver.definitions().local_def_id(id);
 375
 376                 // Lower the "impl header" first. This ordering is important
 377                 // for in-band lifetimes! Consider `'a` here:
 378                 //
 379                 //     impl Foo<'a> for u32 {
 380                 //         fn method(&'a self) { .. }
 381                 //     }
 382                 //
 383                 // Because we start by lowering the `Foo<'a> for u32`
 384                 // part, we will add `'a` to the list of generics on
 385                 // the impl. When we then encounter it later in the
 386                 // method, it will not be considered an in-band
 387                 // lifetime to be added, but rather a reference to a
 388                 // parent lifetime.
 389                 let lowered_trait_impl_id = self.lower_node_id(id);
 390                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
 391                     ast_generics,
 392                     def_id,
 393                     AnonymousLifetimeMode::CreateParameter,
 394                     |this, _| {
 395                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
 396                             this.lower_trait_ref(trait_ref, ImplTraitContext::disallowed())
 397                         });
 398
 399                         if let Some(ref trait_ref) = trait_ref {
 400                             if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res {
 401                                 this.trait_impls
 402                                     .entry(def_id)
 403                                     .or_default()
 404                                     .push(lowered_trait_impl_id);
 405                             }
 406                         }
 407
 408                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::disallowed());
 409
 410                         (trait_ref, lowered_ty)
 411                     },
 412                 );
 413
 414                 let new_impl_items =
 415                     self.with_in_scope_lifetime_defs(&ast_generics.params, |this| {
 416                         this.arena.alloc_from_iter(
 417                             impl_items.iter().map(|item| this.lower_impl_item_ref(item)),
 418                         )
 419                     });
 420
 421                 hir::ItemKind::Impl {
 422                     unsafety,
 423                     polarity,
 424                     defaultness: self.lower_defaultness(defaultness, true /* [1] */),
 425                     constness,
 426                     generics,
 427                     of_trait: trait_ref,
 428                     self_ty: lowered_ty,
 429                     items: new_impl_items,
 430                 }
 431             }
 432             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
 433                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::disallowed());
 434                 let items = self
 435                     .arena
 436                     .alloc_from_iter(items.iter().map(|item| self.lower_trait_item_ref(item)));
 437                 hir::ItemKind::Trait(
 438                     is_auto,
 439                     unsafety,
 440                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 441                     bounds,
 442                     items,
 443                 )
 444             }
 445             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemKind::TraitAlias(
 446                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 447                 self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 448             ),
 449             ItemKind::MacroDef(..) | ItemKind::Mac(..) => {
 450                 bug!("`TyMac` should have been expanded by now")
 451             }
 452         }
 453
 454         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
 455         //     not cause an assertion failure inside the `lower_defaultness` function.
 456     }
 457
 458     fn lower_use_tree(
 459         &mut self,
 460         tree: &UseTree,
 461         prefix: &Path,
 462         id: NodeId,
 463         vis: &mut hir::Visibility<'hir>,
 464         ident: &mut Ident,
 465         attrs: &'hir [Attribute],
 466     ) -> hir::ItemKind<'hir> {
 467         debug!("lower_use_tree(tree={:?})", tree);
 468         debug!("lower_use_tree: vis = {:?}", vis);
 469
 470         let path = &tree.prefix;
 471         let segments = prefix.segments.iter().chain(path.segments.iter()).cloned().collect();
 472
 473         match tree.kind {
 474             UseTreeKind::Simple(rename, id1, id2) => {
 475                 *ident = tree.ident();
 476
 477                 // First, apply the prefix to the path.
 478                 let mut path = Path { segments, span: path.span };
 479
 480                 // Correctly resolve `self` imports.
 481                 if path.segments.len() > 1
 482                     && path.segments.last().unwrap().ident.name == kw::SelfLower
 483                 {
 484                     let _ = path.segments.pop();
 485                     if rename.is_none() {
 486                         *ident = path.segments.last().unwrap().ident;
 487                     }
 488                 }
 489
 490                 let mut resolutions = self.expect_full_res_from_use(id);
 491                 // We want to return *something* from this function, so hold onto the first item
 492                 // for later.
 493                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
 494
 495                 // Here, we are looping over namespaces, if they exist for the definition
 496                 // being imported. We only handle type and value namespaces because we
 497                 // won't be dealing with macros in the rest of the compiler.
 498                 // Essentially a single `use` which imports two names is desugared into
 499                 // two imports.
 500                 for (res, &new_node_id) in resolutions.zip([id1, id2].iter()) {
 501                     let ident = *ident;
 502                     let mut path = path.clone();
 503                     for seg in &mut path.segments {
 504                         seg.id = self.resolver.next_node_id();
 505                     }
 506                     let span = path.span;
 507
 508                     self.with_hir_id_owner(new_node_id, |this| {
 509                         let new_id = this.lower_node_id(new_node_id);
 510                         let res = this.lower_res(res);
 511                         let path = this.lower_path_extra(res, &path, ParamMode::Explicit, None);
 512                         let kind = hir::ItemKind::Use(path, hir::UseKind::Single);
 513                         let vis = this.rebuild_vis(&vis);
 514
 515                         this.insert_item(hir::Item {
 516                             hir_id: new_id,
 517                             ident,
 518                             attrs,
 519                             kind,
 520                             vis,
 521                             span,
 522                         });
 523                     });
 524                 }
 525
 526                 let path = self.lower_path_extra(ret_res, &path, ParamMode::Explicit, None);
 527                 hir::ItemKind::Use(path, hir::UseKind::Single)
 528             }
 529             UseTreeKind::Glob => {
 530                 let path =
 531                     self.lower_path(id, &Path { segments, span: path.span }, ParamMode::Explicit);
 532                 hir::ItemKind::Use(path, hir::UseKind::Glob)
 533             }
 534             UseTreeKind::Nested(ref trees) => {
 535                 // Nested imports are desugared into simple imports.
 536                 // So, if we start with
 537                 //
 538                 // ```
 539                 // pub(x) use foo::{a, b};
 540                 // ```
 541                 //
 542                 // we will create three items:
 543                 //
 544                 // ```
 545                 // pub(x) use foo::a;
 546                 // pub(x) use foo::b;
 547                 // pub(x) use foo::{}; // <-- this is called the `ListStem`
 548                 // ```
 549                 //
 550                 // The first two are produced by recursively invoking
 551                 // `lower_use_tree` (and indeed there may be things
 552                 // like `use foo::{a::{b, c}}` and so forth).  They
 553                 // wind up being directly added to
 554                 // `self.items`. However, the structure of this
 555                 // function also requires us to return one item, and
 556                 // for that we return the `{}` import (called the
 557                 // `ListStem`).
 558
 559                 let prefix = Path { segments, span: prefix.span.to(path.span) };
 560
 561                 // Add all the nested `PathListItem`s to the HIR.
 562                 for &(ref use_tree, id) in trees {
 563                     let new_hir_id = self.lower_node_id(id);
 564
 565                     let mut prefix = prefix.clone();
 566
 567                     // Give the segments new node-ids since they are being cloned.
 568                     for seg in &mut prefix.segments {
 569                         seg.id = self.resolver.next_node_id();
 570                     }
 571
 572                     // Each `use` import is an item and thus are owners of the
 573                     // names in the path. Up to this point the nested import is
 574                     // the current owner, since we want each desugared import to
 575                     // own its own names, we have to adjust the owner before
 576                     // lowering the rest of the import.
 577                     self.with_hir_id_owner(id, |this| {
 578                         let mut vis = this.rebuild_vis(&vis);
 579                         let mut ident = *ident;
 580
 581                         let kind =
 582                             this.lower_use_tree(use_tree, &prefix, id, &mut vis, &mut ident, attrs);
 583
 584                         this.insert_item(hir::Item {
 585                             hir_id: new_hir_id,
 586                             ident,
 587                             attrs,
 588                             kind,
 589                             vis,
 590                             span: use_tree.span,
 591                         });
 592                     });
 593                 }
 594
 595                 // Subtle and a bit hacky: we lower the privacy level
 596                 // of the list stem to "private" most of the time, but
 597                 // not for "restricted" paths. The key thing is that
 598                 // we don't want it to stay as `pub` (with no caveats)
 599                 // because that affects rustdoc and also the lints
 600                 // about `pub` items. But we can't *always* make it
 601                 // private -- particularly not for restricted paths --
 602                 // because it contains node-ids that would then be
 603                 // unused, failing the check that HirIds are "densely
 604                 // assigned".
 605                 match vis.node {
 606                     hir::VisibilityKind::Public
 607                     | hir::VisibilityKind::Crate(_)
 608                     | hir::VisibilityKind::Inherited => {
 609                         *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
 610                     }
 611                     hir::VisibilityKind::Restricted { .. } => {
 612                         // Do nothing here, as described in the comment on the match.
 613                     }
 614                 }
 615
 616                 let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
 617                 let res = self.lower_res(res);
 618                 let path = self.lower_path_extra(res, &prefix, ParamMode::Explicit, None);
 619                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
 620             }
 621         }
 622     }
 623
 624     /// Paths like the visibility path in `pub(super) use foo::{bar, baz}` are repeated
 625     /// many times in the HIR tree; for each occurrence, we need to assign distinct
 626     /// `NodeId`s. (See, e.g., #56128.)
 627     fn rebuild_use_path(&mut self, path: &hir::Path<'hir>) -> &'hir hir::Path<'hir> {
 628         debug!("rebuild_use_path(path = {:?})", path);
 629         let segments =
 630             self.arena.alloc_from_iter(path.segments.iter().map(|seg| hir::PathSegment {
 631                 ident: seg.ident,
 632                 hir_id: seg.hir_id.map(|_| self.next_id()),
 633                 res: seg.res,
 634                 args: None,
 635                 infer_args: seg.infer_args,
 636             }));
 637         self.arena.alloc(hir::Path { span: path.span, res: path.res, segments })
 638     }
 639
 640     fn rebuild_vis(&mut self, vis: &hir::Visibility<'hir>) -> hir::Visibility<'hir> {
 641         let vis_kind = match vis.node {
 642             hir::VisibilityKind::Public => hir::VisibilityKind::Public,
 643             hir::VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 644             hir::VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 645             hir::VisibilityKind::Restricted { ref path, hir_id: _ } => {
 646                 hir::VisibilityKind::Restricted {
 647                     path: self.rebuild_use_path(path),
 648                     hir_id: self.next_id(),
 649                 }
 650             }
 651         };
 652         respan(vis.span, vis_kind)
 653     }
 654
 655     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem<'hir> {
 656         let def_id = self.resolver.definitions().local_def_id(i.id);
 657         hir::ForeignItem {
 658             hir_id: self.lower_node_id(i.id),
 659             ident: i.ident,
 660             attrs: self.lower_attrs(&i.attrs),
 661             kind: match i.kind {
 662                 ForeignItemKind::Fn(ref fdec, ref generics) => {
 663                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
 664                         generics,
 665                         def_id,
 666                         AnonymousLifetimeMode::PassThrough,
 667                         |this, _| {
 668                             (
 669                                 // Disallow `impl Trait` in foreign items.
 670                                 this.lower_fn_decl(fdec, None, false, None),
 671                                 this.lower_fn_params_to_names(fdec),
 672                             )
 673                         },
 674                     );
 675
 676                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
 677                 }
 678                 ForeignItemKind::Static(ref t, m) => {
 679                     let ty = self.lower_ty(t, ImplTraitContext::disallowed());
 680                     hir::ForeignItemKind::Static(ty, m)
 681                 }
 682                 ForeignItemKind::Ty => hir::ForeignItemKind::Type,
 683                 ForeignItemKind::Macro(_) => panic!("macro shouldn't exist here"),
 684             },
 685             vis: self.lower_visibility(&i.vis, None),
 686             span: i.span,
 687         }
 688     }
 689
 690     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod<'hir> {
 691         hir::ForeignMod {
 692             abi: fm.abi.map_or(abi::Abi::C, |abi| self.lower_abi(abi)),
 693             items: self.arena.alloc_from_iter(fm.items.iter().map(|x| self.lower_foreign_item(x))),
 694         }
 695     }
 696
 697     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> &'hir hir::GlobalAsm {
 698         self.arena.alloc(hir::GlobalAsm { asm: ga.asm })
 699     }
 700
 701     fn lower_variant(&mut self, v: &Variant) -> hir::Variant<'hir> {
 702         hir::Variant {
 703             attrs: self.lower_attrs(&v.attrs),
 704             data: self.lower_variant_data(&v.data),
 705             disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
 706             id: self.lower_node_id(v.id),
 707             ident: v.ident,
 708             span: v.span,
 709         }
 710     }
 711
 712     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData<'hir> {
 713         match *vdata {
 714             VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
 715                 self.arena
 716                     .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_struct_field(f))),
 717                 recovered,
 718             ),
 719             VariantData::Tuple(ref fields, id) => hir::VariantData::Tuple(
 720                 self.arena
 721                     .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_struct_field(f))),
 722                 self.lower_node_id(id),
 723             ),
 724             VariantData::Unit(id) => hir::VariantData::Unit(self.lower_node_id(id)),
 725         }
 726     }
 727
 728     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField<'hir> {
 729         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
 730             let t = self.lower_path_ty(
 731                 &f.ty,
 732                 qself,
 733                 path,
 734                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
 735                 ImplTraitContext::disallowed(),
 736             );
 737             self.arena.alloc(t)
 738         } else {
 739             self.lower_ty(&f.ty, ImplTraitContext::disallowed())
 740         };
 741         hir::StructField {
 742             span: f.span,
 743             hir_id: self.lower_node_id(f.id),
 744             ident: match f.ident {
 745                 Some(ident) => ident,
 746                 // FIXME(jseyfried): positional field hygiene.
 747                 None => Ident::new(sym::integer(index), f.span),
 748             },
 749             vis: self.lower_visibility(&f.vis, None),
 750             ty,
 751             attrs: self.lower_attrs(&f.attrs),
 752         }
 753     }
 754
 755     fn lower_trait_item(&mut self, i: &AssocItem) -> hir::TraitItem<'hir> {
 756         let trait_item_def_id = self.resolver.definitions().local_def_id(i.id);
 757
 758         let (generics, kind) = match i.kind {
 759             AssocItemKind::Const(ref ty, ref default) => {
 760                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 761                 let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 762                 (
 763                     generics,
 764                     hir::TraitItemKind::Const(
 765                         ty,
 766                         default.as_ref().map(|x| self.lower_const_body(i.span, Some(x))),
 767                     ),
 768                 )
 769             }
 770             AssocItemKind::Fn(ref sig, None) => {
 771                 let names = self.lower_fn_params_to_names(&sig.decl);
 772                 let (generics, sig) =
 773                     self.lower_method_sig(&i.generics, sig, trait_item_def_id, false, None);
 774                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
 775             }
 776             AssocItemKind::Fn(ref sig, Some(ref body)) => {
 777                 let body_id = self.lower_fn_body_block(i.span, &sig.decl, Some(body));
 778                 let (generics, sig) =
 779                     self.lower_method_sig(&i.generics, sig, trait_item_def_id, false, None);
 780                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
 781             }
 782             AssocItemKind::TyAlias(ref bounds, ref default) => {
 783                 let ty = default.as_ref().map(|x| self.lower_ty(x, ImplTraitContext::disallowed()));
 784                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 785                 let kind = hir::TraitItemKind::Type(
 786                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 787                     ty,
 788                 );
 789
 790                 (generics, kind)
 791             }
 792             AssocItemKind::Macro(..) => bug!("macro item shouldn't exist at this point"),
 793         };
 794
 795         hir::TraitItem {
 796             hir_id: self.lower_node_id(i.id),
 797             ident: i.ident,
 798             attrs: self.lower_attrs(&i.attrs),
 799             generics,
 800             kind,
 801             span: i.span,
 802         }
 803     }
 804
 805     fn lower_trait_item_ref(&mut self, i: &AssocItem) -> hir::TraitItemRef {
 806         let (kind, has_default) = match i.kind {
 807             AssocItemKind::Const(_, ref default) => (hir::AssocItemKind::Const, default.is_some()),
 808             AssocItemKind::TyAlias(_, ref default) => (hir::AssocItemKind::Type, default.is_some()),
 809             AssocItemKind::Fn(ref sig, ref default) => {
 810                 (hir::AssocItemKind::Method { has_self: sig.decl.has_self() }, default.is_some())
 811             }
 812             AssocItemKind::Macro(..) => unimplemented!(),
 813         };
 814         hir::TraitItemRef {
 815             id: hir::TraitItemId { hir_id: self.lower_node_id(i.id) },
 816             ident: i.ident,
 817             span: i.span,
 818             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
 819             kind,
 820         }
 821     }
 822
 823     /// Construct `ExprKind::Err` for the given `span`.
 824     fn expr_err(&mut self, span: Span) -> hir::Expr<'hir> {
 825         self.expr(span, hir::ExprKind::Err, AttrVec::new())
 826     }
 827
 828     fn lower_impl_item(&mut self, i: &AssocItem) -> hir::ImplItem<'hir> {
 829         let impl_item_def_id = self.resolver.definitions().local_def_id(i.id);
 830
 831         let (generics, kind) = match i.kind {
 832             AssocItemKind::Const(ref ty, ref expr) => {
 833                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 834                 let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 835                 (
 836                     generics,
 837                     hir::ImplItemKind::Const(ty, self.lower_const_body(i.span, expr.as_deref())),
 838                 )
 839             }
 840             AssocItemKind::Fn(ref sig, ref body) => {
 841                 self.current_item = Some(i.span);
 842                 let body_id = self.lower_maybe_async_body(
 843                     i.span,
 844                     &sig.decl,
 845                     sig.header.asyncness.node,
 846                     body.as_deref(),
 847                 );
 848                 let impl_trait_return_allow = !self.is_in_trait_impl;
 849                 let (generics, sig) = self.lower_method_sig(
 850                     &i.generics,
 851                     sig,
 852                     impl_item_def_id,
 853                     impl_trait_return_allow,
 854                     sig.header.asyncness.node.opt_return_id(),
 855                 );
 856
 857                 (generics, hir::ImplItemKind::Method(sig, body_id))
 858             }
 859             AssocItemKind::TyAlias(_, ref ty) => {
 860                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 861                 let kind = match ty {
 862                     None => {
 863                         let ty = self.arena.alloc(self.ty(i.span, hir::TyKind::Err));
 864                         hir::ImplItemKind::TyAlias(ty)
 865                     }
 866                     Some(ty) => match ty.kind.opaque_top_hack() {
 867                         None => {
 868                             let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 869                             hir::ImplItemKind::TyAlias(ty)
 870                         }
 871                         Some(bs) => {
 872                             let bs = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
 873                             hir::ImplItemKind::OpaqueTy(bs)
 874                         }
 875                     },
 876                 };
 877                 (generics, kind)
 878             }
 879             AssocItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
 880         };
 881
 882         hir::ImplItem {
 883             hir_id: self.lower_node_id(i.id),
 884             ident: i.ident,
 885             attrs: self.lower_attrs(&i.attrs),
 886             generics,
 887             vis: self.lower_visibility(&i.vis, None),
 888             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 889             kind,
 890             span: i.span,
 891         }
 892
 893         // [1] since `default impl` is not yet implemented, this is always true in impls
 894     }
 895
 896     fn lower_impl_item_ref(&mut self, i: &AssocItem) -> hir::ImplItemRef<'hir> {
 897         hir::ImplItemRef {
 898             id: hir::ImplItemId { hir_id: self.lower_node_id(i.id) },
 899             ident: i.ident,
 900             span: i.span,
 901             vis: self.lower_visibility(&i.vis, Some(i.id)),
 902             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 903             kind: match &i.kind {
 904                 AssocItemKind::Const(..) => hir::AssocItemKind::Const,
 905                 AssocItemKind::TyAlias(_, ty) => {
 906                     match ty.as_deref().and_then(|ty| ty.kind.opaque_top_hack()) {
 907                         None => hir::AssocItemKind::Type,
 908                         Some(_) => hir::AssocItemKind::OpaqueTy,
 909                     }
 910                 }
 911                 AssocItemKind::Fn(sig, _) => {
 912                     hir::AssocItemKind::Method { has_self: sig.decl.has_self() }
 913                 }
 914                 AssocItemKind::Macro(..) => unimplemented!(),
 915             },
 916         }
 917
 918         // [1] since `default impl` is not yet implemented, this is always true in impls
 919     }
 920
 921     /// If an `explicit_owner` is given, this method allocates the `HirId` in
 922     /// the address space of that item instead of the item currently being
 923     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
 924     /// lower a `Visibility` value although we haven't lowered the owning
 925     /// `ImplItem` in question yet.
 926     fn lower_visibility(
 927         &mut self,
 928         v: &Visibility,
 929         explicit_owner: Option<NodeId>,
 930     ) -> hir::Visibility<'hir> {
 931         let node = match v.node {
 932             VisibilityKind::Public => hir::VisibilityKind::Public,
 933             VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 934             VisibilityKind::Restricted { ref path, id } => {
 935                 debug!("lower_visibility: restricted path id = {:?}", id);
 936                 let lowered_id = if let Some(owner) = explicit_owner {
 937                     self.lower_node_id_with_owner(id, owner)
 938                 } else {
 939                     self.lower_node_id(id)
 940                 };
 941                 let res = self.expect_full_res(id);
 942                 let res = self.lower_res(res);
 943                 hir::VisibilityKind::Restricted {
 944                     path: self.lower_path_extra(res, path, ParamMode::Explicit, explicit_owner),
 945                     hir_id: lowered_id,
 946                 }
 947             }
 948             VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 949         };
 950         respan(v.span, node)
 951     }
 952
 953     fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
 954         match d {
 955             Defaultness::Default => hir::Defaultness::Default { has_value: has_value },
 956             Defaultness::Final => {
 957                 assert!(has_value);
 958                 hir::Defaultness::Final
 959             }
 960         }
 961     }
 962
 963     fn record_body(
 964         &mut self,
 965         params: &'hir [hir::Param<'hir>],
 966         value: hir::Expr<'hir>,
 967     ) -> hir::BodyId {
 968         let body = hir::Body { generator_kind: self.generator_kind, params, value };
 969         let id = body.id();
 970         self.bodies.insert(id, body);
 971         id
 972     }
 973
 974     fn lower_body(
 975         &mut self,
 976         f: impl FnOnce(&mut Self) -> (&'hir [hir::Param<'hir>], hir::Expr<'hir>),
 977     ) -> hir::BodyId {
 978         let prev_gen_kind = self.generator_kind.take();
 979         let (parameters, result) = f(self);
 980         let body_id = self.record_body(parameters, result);
 981         self.generator_kind = prev_gen_kind;
 982         body_id
 983     }
 984
 985     fn lower_param(&mut self, param: &Param) -> hir::Param<'hir> {
 986         hir::Param {
 987             attrs: self.lower_attrs(&param.attrs),
 988             hir_id: self.lower_node_id(param.id),
 989             pat: self.lower_pat(&param.pat),
 990             span: param.span,
 991         }
 992     }
 993
 994     pub(super) fn lower_fn_body(
 995         &mut self,
 996         decl: &FnDecl,
 997         body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
 998     ) -> hir::BodyId {
 999         self.lower_body(|this| {
1000             (
1001                 this.arena.alloc_from_iter(decl.inputs.iter().map(|x| this.lower_param(x))),
1002                 body(this),
1003             )
1004         })
1005     }
1006
1007     fn lower_fn_body_block(
1008         &mut self,
1009         span: Span,
1010         decl: &FnDecl,
1011         body: Option<&Block>,
1012     ) -> hir::BodyId {
1013         self.lower_fn_body(decl, |this| this.lower_block_expr_opt(span, body))
1014     }
1015
1016     fn lower_block_expr_opt(&mut self, span: Span, block: Option<&Block>) -> hir::Expr<'hir> {
1017         match block {
1018             Some(block) => self.lower_block_expr(block),
1019             None => self.expr_err(span),
1020         }
1021     }
1022
1023     pub(super) fn lower_const_body(&mut self, span: Span, expr: Option<&Expr>) -> hir::BodyId {
1024         self.lower_body(|this| {
1025             (
1026                 &[],
1027                 match expr {
1028                     Some(expr) => this.lower_expr_mut(expr),
1029                     None => this.expr_err(span),
1030                 },
1031             )
1032         })
1033     }
1034
1035     fn lower_maybe_async_body(
1036         &mut self,
1037         span: Span,
1038         decl: &FnDecl,
1039         asyncness: IsAsync,
1040         body: Option<&Block>,
1041     ) -> hir::BodyId {
1042         let closure_id = match asyncness {
1043             IsAsync::Async { closure_id, .. } => closure_id,
1044             IsAsync::NotAsync => return self.lower_fn_body_block(span, decl, body),
1045         };
1046
1047         self.lower_body(|this| {
1048             let mut parameters: Vec<hir::Param<'_>> = Vec::new();
1049             let mut statements: Vec<hir::Stmt<'_>> = Vec::new();
1050
1051             // Async function parameters are lowered into the closure body so that they are
1052             // captured and so that the drop order matches the equivalent non-async functions.
1053             //
1054             // from:
1055             //
1056             //     async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
1057             //         <body>
1058             //     }
1059             //
1060             // into:
1061             //
1062             //     fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) {
1063             //       async move {
1064             //         let __arg2 = __arg2;
1065             //         let <pattern> = __arg2;
1066             //         let __arg1 = __arg1;
1067             //         let <pattern> = __arg1;
1068             //         let __arg0 = __arg0;
1069             //         let <pattern> = __arg0;
1070             //         drop-temps { <body> } // see comments later in fn for details
1071             //       }
1072             //     }
1073             //
1074             // If `<pattern>` is a simple ident, then it is lowered to a single
1075             // `let <pattern> = <pattern>;` statement as an optimization.
1076             //
1077             // Note that the body is embedded in `drop-temps`; an
1078             // equivalent desugaring would be `return { <body>
1079             // };`. The key point is that we wish to drop all the
1080             // let-bound variables and temporaries created in the body
1081             // (and its tail expression!) before we drop the
1082             // parameters (c.f. rust-lang/rust#64512).
1083             for (index, parameter) in decl.inputs.iter().enumerate() {
1084                 let parameter = this.lower_param(parameter);
1085                 let span = parameter.pat.span;
1086
1087                 // Check if this is a binding pattern, if so, we can optimize and avoid adding a
1088                 // `let <pat> = __argN;` statement. In this case, we do not rename the parameter.
1089                 let (ident, is_simple_parameter) = match parameter.pat.kind {
1090                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, _) => {
1091                         (ident, true)
1092                     }
1093                     _ => {
1094                         // Replace the ident for bindings that aren't simple.
1095                         let name = format!("__arg{}", index);
1096                         let ident = Ident::from_str(&name);
1097
1098                         (ident, false)
1099                     }
1100                 };
1101
1102                 let desugared_span = this.mark_span_with_reason(DesugaringKind::Async, span, None);
1103
1104                 // Construct a parameter representing `__argN: <ty>` to replace the parameter of the
1105                 // async function.
1106                 //
1107                 // If this is the simple case, this parameter will end up being the same as the
1108                 // original parameter, but with a different pattern id.
1109                 let mut stmt_attrs = AttrVec::new();
1110                 stmt_attrs.extend(parameter.attrs.iter().cloned());
1111                 let (new_parameter_pat, new_parameter_id) = this.pat_ident(desugared_span, ident);
1112                 let new_parameter = hir::Param {
1113                     attrs: parameter.attrs,
1114                     hir_id: parameter.hir_id,
1115                     pat: new_parameter_pat,
1116                     span: parameter.span,
1117                 };
1118
1119                 if is_simple_parameter {
1120                     // If this is the simple case, then we only insert one statement that is
1121                     // `let <pat> = <pat>;`. We re-use the original argument's pattern so that
1122                     // `HirId`s are densely assigned.
1123                     let expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1124                     let stmt = this.stmt_let_pat(
1125                         stmt_attrs,
1126                         desugared_span,
1127                         Some(expr),
1128                         parameter.pat,
1129                         hir::LocalSource::AsyncFn,
1130                     );
1131                     statements.push(stmt);
1132                 } else {
1133                     // If this is not the simple case, then we construct two statements:
1134                     //
1135                     // ```
1136                     // let __argN = __argN;
1137                     // let <pat> = __argN;
1138                     // ```
1139                     //
1140                     // The first statement moves the parameter into the closure and thus ensures
1141                     // that the drop order is correct.
1142                     //
1143                     // The second statement creates the bindings that the user wrote.
1144
1145                     // Construct the `let mut __argN = __argN;` statement. It must be a mut binding
1146                     // because the user may have specified a `ref mut` binding in the next
1147                     // statement.
1148                     let (move_pat, move_id) = this.pat_ident_binding_mode(
1149                         desugared_span,
1150                         ident,
1151                         hir::BindingAnnotation::Mutable,
1152                     );
1153                     let move_expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1154                     let move_stmt = this.stmt_let_pat(
1155                         AttrVec::new(),
1156                         desugared_span,
1157                         Some(move_expr),
1158                         move_pat,
1159                         hir::LocalSource::AsyncFn,
1160                     );
1161
1162                     // Construct the `let <pat> = __argN;` statement. We re-use the original
1163                     // parameter's pattern so that `HirId`s are densely assigned.
1164                     let pattern_expr = this.expr_ident(desugared_span, ident, move_id);
1165                     let pattern_stmt = this.stmt_let_pat(
1166                         stmt_attrs,
1167                         desugared_span,
1168                         Some(pattern_expr),
1169                         parameter.pat,
1170                         hir::LocalSource::AsyncFn,
1171                     );
1172
1173                     statements.push(move_stmt);
1174                     statements.push(pattern_stmt);
1175                 };
1176
1177                 parameters.push(new_parameter);
1178             }
1179
1180             let body_span = body.map_or(span, |b| b.span);
1181             let async_expr = this.make_async_expr(
1182                 CaptureBy::Value,
1183                 closure_id,
1184                 None,
1185                 body_span,
1186                 hir::AsyncGeneratorKind::Fn,
1187                 |this| {
1188                     // Create a block from the user's function body:
1189                     let user_body = this.lower_block_expr_opt(body_span, body);
1190
1191                     // Transform into `drop-temps { <user-body> }`, an expression:
1192                     let desugared_span =
1193                         this.mark_span_with_reason(DesugaringKind::Async, user_body.span, None);
1194                     let user_body = this.expr_drop_temps(
1195                         desugared_span,
1196                         this.arena.alloc(user_body),
1197                         AttrVec::new(),
1198                     );
1199
1200                     // As noted above, create the final block like
1201                     //
1202                     // ```
1203                     // {
1204                     //   let $param_pattern = $raw_param;
1205                     //   ...
1206                     //   drop-temps { <user-body> }
1207                     // }
1208                     // ```
1209                     let body = this.block_all(
1210                         desugared_span,
1211                         this.arena.alloc_from_iter(statements),
1212                         Some(user_body),
1213                     );
1214
1215                     this.expr_block(body, AttrVec::new())
1216                 },
1217             );
1218
1219             (
1220                 this.arena.alloc_from_iter(parameters),
1221                 this.expr(body_span, async_expr, AttrVec::new()),
1222             )
1223         })
1224     }
1225
1226     fn lower_method_sig(
1227         &mut self,
1228         generics: &Generics,
1229         sig: &FnSig,
1230         fn_def_id: DefId,
1231         impl_trait_return_allow: bool,
1232         is_async: Option<NodeId>,
1233     ) -> (hir::Generics<'hir>, hir::FnSig<'hir>) {
1234         let header = self.lower_fn_header(sig.header);
1235         let (generics, decl) = self.add_in_band_defs(
1236             generics,
1237             fn_def_id,
1238             AnonymousLifetimeMode::PassThrough,
1239             |this, idty| {
1240                 this.lower_fn_decl(
1241                     &sig.decl,
1242                     Some((fn_def_id, idty)),
1243                     impl_trait_return_allow,
1244                     is_async,
1245                 )
1246             },
1247         );
1248         (generics, hir::FnSig { header, decl })
1249     }
1250
1251     fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
1252         hir::FnHeader {
1253             unsafety: h.unsafety,
1254             asyncness: self.lower_asyncness(h.asyncness.node),
1255             constness: h.constness.node,
1256             abi: self.lower_extern(h.ext),
1257         }
1258     }
1259
1260     pub(super) fn lower_abi(&mut self, abi: StrLit) -> abi::Abi {
1261         abi::lookup(&abi.symbol_unescaped.as_str()).unwrap_or_else(|| {
1262             self.error_on_invalid_abi(abi);
1263             abi::Abi::Rust
1264         })
1265     }
1266
1267     pub(super) fn lower_extern(&mut self, ext: Extern) -> abi::Abi {
1268         match ext {
1269             Extern::None => abi::Abi::Rust,
1270             Extern::Implicit => abi::Abi::C,
1271             Extern::Explicit(abi) => self.lower_abi(abi),
1272         }
1273     }
1274
1275     fn error_on_invalid_abi(&self, abi: StrLit) {
1276         struct_span_err!(self.sess, abi.span, E0703, "invalid ABI: found `{}`", abi.symbol)
1277             .span_label(abi.span, "invalid ABI")
1278             .help(&format!("valid ABIs: {}", abi::all_names().join(", ")))
1279             .emit();
1280     }
1281
1282     fn lower_asyncness(&mut self, a: IsAsync) -> hir::IsAsync {
1283         match a {
1284             IsAsync::Async { .. } => hir::IsAsync::Async,
1285             IsAsync::NotAsync => hir::IsAsync::NotAsync,
1286         }
1287     }
1288
1289     pub(super) fn lower_generics_mut(
1290         &mut self,
1291         generics: &Generics,
1292         itctx: ImplTraitContext<'_, 'hir>,
1293     ) -> GenericsCtor<'hir> {
1294         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1295         // FIXME: this could probably be done with less rightward drift. It also looks like two
1296         // control paths where `report_error` is called are the only paths that advance to after the
1297         // match statement, so the error reporting could probably just be moved there.
1298         let mut add_bounds: NodeMap<Vec<_>> = Default::default();
1299         for pred in &generics.where_clause.predicates {
1300             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1301                 'next_bound: for bound in &bound_pred.bounds {
1302                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
1303                         let report_error = |this: &mut Self| {
1304                             this.diagnostic().span_err(
1305                                 bound_pred.bounded_ty.span,
1306                                 "`?Trait` bounds are only permitted at the \
1307                                  point where a type parameter is declared",
1308                             );
1309                         };
1310                         // Check if the where clause type is a plain type parameter.
1311                         match bound_pred.bounded_ty.kind {
1312                             TyKind::Path(None, ref path)
1313                                 if path.segments.len() == 1
1314                                     && bound_pred.bound_generic_params.is_empty() =>
1315                             {
1316                                 if let Some(Res::Def(DefKind::TyParam, def_id)) = self
1317                                     .resolver
1318                                     .get_partial_res(bound_pred.bounded_ty.id)
1319                                     .map(|d| d.base_res())
1320                                 {
1321                                     if let Some(node_id) =
1322                                         self.resolver.definitions().as_local_node_id(def_id)
1323                                     {
1324                                         for param in &generics.params {
1325                                             match param.kind {
1326                                                 GenericParamKind::Type { .. } => {
1327                                                     if node_id == param.id {
1328                                                         add_bounds
1329                                                             .entry(param.id)
1330                                                             .or_default()
1331                                                             .push(bound.clone());
1332                                                         continue 'next_bound;
1333                                                     }
1334                                                 }
1335                                                 _ => {}
1336                                             }
1337                                         }
1338                                     }
1339                                 }
1340                                 report_error(self)
1341                             }
1342                             _ => report_error(self),
1343                         }
1344                     }
1345                 }
1346             }
1347         }
1348
1349         GenericsCtor {
1350             params: self.lower_generic_params_mut(&generics.params, &add_bounds, itctx).collect(),
1351             where_clause: self.lower_where_clause(&generics.where_clause),
1352             span: generics.span,
1353         }
1354     }
1355
1356     pub(super) fn lower_generics(
1357         &mut self,
1358         generics: &Generics,
1359         itctx: ImplTraitContext<'_, 'hir>,
1360     ) -> hir::Generics<'hir> {
1361         let generics_ctor = self.lower_generics_mut(generics, itctx);
1362         generics_ctor.into_generics(self.arena)
1363     }
1364
1365     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause<'hir> {
1366         self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
1367             hir::WhereClause {
1368                 predicates: this.arena.alloc_from_iter(
1369                     wc.predicates.iter().map(|predicate| this.lower_where_predicate(predicate)),
1370                 ),
1371                 span: wc.span,
1372             }
1373         })
1374     }
1375
1376     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate<'hir> {
1377         match *pred {
1378             WherePredicate::BoundPredicate(WhereBoundPredicate {
1379                 ref bound_generic_params,
1380                 ref bounded_ty,
1381                 ref bounds,
1382                 span,
1383             }) => {
1384                 self.with_in_scope_lifetime_defs(&bound_generic_params, |this| {
1385                     hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1386                         bound_generic_params: this.lower_generic_params(
1387                             bound_generic_params,
1388                             &NodeMap::default(),
1389                             ImplTraitContext::disallowed(),
1390                         ),
1391                         bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::disallowed()),
1392                         bounds: this.arena.alloc_from_iter(bounds.iter().filter_map(|bound| {
1393                             match *bound {
1394                                 // Ignore `?Trait` bounds.
1395                                 // They were copied into type parameters already.
1396                                 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1397                                 _ => Some(
1398                                     this.lower_param_bound(bound, ImplTraitContext::disallowed()),
1399                                 ),
1400                             }
1401                         })),
1402                         span,
1403                     })
1404                 })
1405             }
1406             WherePredicate::RegionPredicate(WhereRegionPredicate {
1407                 ref lifetime,
1408                 ref bounds,
1409                 span,
1410             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1411                 span,
1412                 lifetime: self.lower_lifetime(lifetime),
1413                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
1414             }),
1415             WherePredicate::EqPredicate(WhereEqPredicate { id, ref lhs_ty, ref rhs_ty, span }) => {
1416                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1417                     hir_id: self.lower_node_id(id),
1418                     lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::disallowed()),
1419                     rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::disallowed()),
1420                     span,
1421                 })
1422             }
1423         }
1424     }
1425 }
1426
1427 /// Helper struct for delayed construction of Generics.
1428 pub(super) struct GenericsCtor<'hir> {
1429     pub(super) params: SmallVec<[hir::GenericParam<'hir>; 4]>,
1430     where_clause: hir::WhereClause<'hir>,
1431     span: Span,
1432 }
1433
1434 impl<'hir> GenericsCtor<'hir> {
1435     pub(super) fn into_generics(self, arena: &'hir Arena<'hir>) -> hir::Generics<'hir> {
1436         hir::Generics {
1437             params: arena.alloc_from_iter(self.params),
1438             where_clause: self.where_clause,
1439             span: self.span,
1440         }
1441     }
1442 }