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_errors::struct_span_err;
   7 use rustc_hir as hir;
   8 use rustc_hir::def::{DefKind, Res};
   9 use rustc_hir::def_id::DefId;
  10 use rustc_span::source_map::{respan, DesugaringKind};
  11 use rustc_span::symbol::{kw, sym};
  12 use rustc_span::Span;
  13 use rustc_target::spec::abi;
  14 use syntax::ast::*;
  15 use syntax::attr;
  16 use syntax::node_id::NodeMap;
  17 use syntax::visit::{self, AssocCtxt, Visitor};
  18
  19 use log::debug;
  20 use smallvec::{smallvec, SmallVec};
  21 use std::collections::BTreeSet;
  22
  23 pub(super) struct ItemLowerer<'a, 'lowering, 'hir> {
  24     pub(super) lctx: &'a mut LoweringContext<'lowering, 'hir>,
  25 }
  26
  27 impl ItemLowerer<'_, '_, '_> {
  28     fn with_trait_impl_ref(&mut self, impl_ref: &Option<TraitRef>, f: impl FnOnce(&mut Self)) {
  29         let old = self.lctx.is_in_trait_impl;
  30         self.lctx.is_in_trait_impl = if let &None = impl_ref { false } else { true };
  31         f(self);
  32         self.lctx.is_in_trait_impl = old;
  33     }
  34 }
  35
  36 impl<'a> Visitor<'a> for ItemLowerer<'a, '_, '_> {
  37     fn visit_mod(&mut self, m: &'a Mod, _s: Span, _attrs: &[Attribute], n: NodeId) {
  38         let hir_id = self.lctx.lower_node_id(n);
  39
  40         self.lctx.modules.insert(
  41             hir_id,
  42             hir::ModuleItems {
  43                 items: BTreeSet::new(),
  44                 trait_items: BTreeSet::new(),
  45                 impl_items: BTreeSet::new(),
  46             },
  47         );
  48
  49         let old = self.lctx.current_module;
  50         self.lctx.current_module = hir_id;
  51         visit::walk_mod(self, m);
  52         self.lctx.current_module = old;
  53     }
  54
  55     fn visit_item(&mut self, item: &'a Item) {
  56         let mut item_hir_id = None;
  57         self.lctx.with_hir_id_owner(item.id, |lctx| {
  58             lctx.without_in_scope_lifetime_defs(|lctx| {
  59                 if let Some(hir_item) = lctx.lower_item(item) {
  60                     item_hir_id = Some(hir_item.hir_id);
  61                     lctx.insert_item(hir_item);
  62                 }
  63             })
  64         });
  65
  66         if let Some(hir_id) = item_hir_id {
  67             self.lctx.with_parent_item_lifetime_defs(hir_id, |this| {
  68                 let this = &mut ItemLowerer { lctx: this };
  69                 if let ItemKind::Impl { constness, ref of_trait, .. } = item.kind {
  70                     if let Const::Yes(span) = constness {
  71                         this.lctx
  72                             .diagnostic()
  73                             .struct_span_err(item.span, "const trait impls are not yet implemented")
  74                             .span_label(span, "const because of this")
  75                             .emit();
  76                     }
  77
  78                     this.with_trait_impl_ref(of_trait, |this| visit::walk_item(this, item));
  79                 } else {
  80                     visit::walk_item(this, item);
  81                 }
  82             });
  83         }
  84     }
  85
  86     fn visit_assoc_item(&mut self, item: &'a AssocItem, ctxt: AssocCtxt) {
  87         self.lctx.with_hir_id_owner(item.id, |lctx| match ctxt {
  88             AssocCtxt::Trait => {
  89                 let hir_item = lctx.lower_trait_item(item);
  90                 let id = hir::TraitItemId { hir_id: hir_item.hir_id };
  91                 lctx.trait_items.insert(id, hir_item);
  92                 lctx.modules.get_mut(&lctx.current_module).unwrap().trait_items.insert(id);
  93             }
  94             AssocCtxt::Impl => {
  95                 let hir_item = lctx.lower_impl_item(item);
  96                 let id = hir::ImplItemId { hir_id: hir_item.hir_id };
  97                 lctx.impl_items.insert(id, hir_item);
  98                 lctx.modules.get_mut(&lctx.current_module).unwrap().impl_items.insert(id);
  99             }
 100         });
 101
 102         visit::walk_assoc_item(self, item, ctxt);
 103     }
 104 }
 105
 106 impl<'hir> LoweringContext<'_, 'hir> {
 107     // Same as the method above, but accepts `hir::GenericParam`s
 108     // instead of `ast::GenericParam`s.
 109     // This should only be used with generics that have already had their
 110     // in-band lifetimes added. In practice, this means that this function is
 111     // only used when lowering a child item of a trait or impl.
 112     fn with_parent_item_lifetime_defs<T>(
 113         &mut self,
 114         parent_hir_id: hir::HirId,
 115         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> T,
 116     ) -> T {
 117         let old_len = self.in_scope_lifetimes.len();
 118
 119         let parent_generics = match self.items.get(&parent_hir_id).unwrap().kind {
 120             hir::ItemKind::Impl { ref generics, .. }
 121             | hir::ItemKind::Trait(_, _, ref generics, ..) => &generics.params[..],
 122             _ => &[],
 123         };
 124         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
 125             hir::GenericParamKind::Lifetime { .. } => Some(param.name.modern()),
 126             _ => None,
 127         });
 128         self.in_scope_lifetimes.extend(lt_def_names);
 129
 130         let res = f(self);
 131
 132         self.in_scope_lifetimes.truncate(old_len);
 133         res
 134     }
 135
 136     // Clears (and restores) the `in_scope_lifetimes` field. Used when
 137     // visiting nested items, which never inherit in-scope lifetimes
 138     // from their surrounding environment.
 139     fn without_in_scope_lifetime_defs<T>(
 140         &mut self,
 141         f: impl FnOnce(&mut LoweringContext<'_, '_>) -> T,
 142     ) -> T {
 143         let old_in_scope_lifetimes = std::mem::replace(&mut self.in_scope_lifetimes, vec![]);
 144
 145         // this vector is only used when walking over impl headers,
 146         // input types, and the like, and should not be non-empty in
 147         // between items
 148         assert!(self.lifetimes_to_define.is_empty());
 149
 150         let res = f(self);
 151
 152         assert!(self.in_scope_lifetimes.is_empty());
 153         self.in_scope_lifetimes = old_in_scope_lifetimes;
 154
 155         res
 156     }
 157
 158     pub(super) fn lower_mod(&mut self, m: &Mod) -> hir::Mod<'hir> {
 159         hir::Mod {
 160             inner: m.inner,
 161             item_ids: self
 162                 .arena
 163                 .alloc_from_iter(m.items.iter().flat_map(|x| self.lower_item_id(x))),
 164         }
 165     }
 166
 167     pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
 168         let node_ids = match i.kind {
 169             ItemKind::Use(ref use_tree) => {
 170                 let mut vec = smallvec![i.id];
 171                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
 172                 vec
 173             }
 174             ItemKind::MacroDef(..) => SmallVec::new(),
 175             ItemKind::Fn(..) | ItemKind::Impl { of_trait: None, .. } => smallvec![i.id],
 176             ItemKind::Static(ref ty, ..) => {
 177                 let mut ids = smallvec![i.id];
 178                 if self.sess.features_untracked().impl_trait_in_bindings {
 179                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 180                     visitor.visit_ty(ty);
 181                 }
 182                 ids
 183             }
 184             ItemKind::Const(ref ty, ..) => {
 185                 let mut ids = smallvec![i.id];
 186                 if self.sess.features_untracked().impl_trait_in_bindings {
 187                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 188                     visitor.visit_ty(ty);
 189                 }
 190                 ids
 191             }
 192             _ => smallvec![i.id],
 193         };
 194
 195         node_ids
 196             .into_iter()
 197             .map(|node_id| hir::ItemId { id: self.allocate_hir_id_counter(node_id) })
 198             .collect()
 199     }
 200
 201     fn lower_item_id_use_tree(
 202         &mut self,
 203         tree: &UseTree,
 204         base_id: NodeId,
 205         vec: &mut SmallVec<[NodeId; 1]>,
 206     ) {
 207         match tree.kind {
 208             UseTreeKind::Nested(ref nested_vec) => {
 209                 for &(ref nested, id) in nested_vec {
 210                     vec.push(id);
 211                     self.lower_item_id_use_tree(nested, id, vec);
 212                 }
 213             }
 214             UseTreeKind::Glob => {}
 215             UseTreeKind::Simple(_, id1, id2) => {
 216                 for (_, &id) in
 217                     self.expect_full_res_from_use(base_id).skip(1).zip([id1, id2].iter())
 218                 {
 219                     vec.push(id);
 220                 }
 221             }
 222         }
 223     }
 224
 225     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item<'hir>> {
 226         let mut ident = i.ident;
 227         let mut vis = self.lower_visibility(&i.vis, None);
 228         let attrs = self.lower_attrs(&i.attrs);
 229
 230         if let ItemKind::MacroDef(ref def) = i.kind {
 231             if !def.legacy || attr::contains_name(&i.attrs, sym::macro_export) {
 232                 let body = self.lower_token_stream(def.body.inner_tokens());
 233                 let hir_id = self.lower_node_id(i.id);
 234                 self.exported_macros.push(hir::MacroDef {
 235                     name: ident.name,
 236                     vis,
 237                     attrs,
 238                     hir_id,
 239                     span: i.span,
 240                     body,
 241                     legacy: def.legacy,
 242                 });
 243             } else {
 244                 self.non_exported_macro_attrs.extend(attrs.iter().cloned());
 245             }
 246             return None;
 247         }
 248
 249         let kind = self.lower_item_kind(i.span, i.id, &mut ident, attrs, &mut vis, &i.kind);
 250
 251         Some(hir::Item { hir_id: self.lower_node_id(i.id), ident, attrs, kind, vis, span: i.span })
 252     }
 253
 254     fn lower_item_kind(
 255         &mut self,
 256         span: Span,
 257         id: NodeId,
 258         ident: &mut Ident,
 259         attrs: &'hir [Attribute],
 260         vis: &mut hir::Visibility<'hir>,
 261         i: &ItemKind,
 262     ) -> hir::ItemKind<'hir> {
 263         match *i {
 264             ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
 265             ItemKind::Use(ref use_tree) => {
 266                 // Start with an empty prefix.
 267                 let prefix = Path { segments: vec![], span: use_tree.span };
 268
 269                 self.lower_use_tree(use_tree, &prefix, id, vis, ident, attrs)
 270             }
 271             ItemKind::Static(ref t, m, ref e) => {
 272                 let ty = self.lower_ty(
 273                     t,
 274                     if self.sess.features_untracked().impl_trait_in_bindings {
 275                         ImplTraitContext::OpaqueTy(None)
 276                     } else {
 277                         ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 278                     },
 279                 );
 280                 hir::ItemKind::Static(ty, m, self.lower_const_body(span, Some(e)))
 281             }
 282             ItemKind::Const(ref t, ref e) => {
 283                 let ty = self.lower_ty(
 284                     t,
 285                     if self.sess.features_untracked().impl_trait_in_bindings {
 286                         ImplTraitContext::OpaqueTy(None)
 287                     } else {
 288                         ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 289                     },
 290                 );
 291                 hir::ItemKind::Const(ty, self.lower_const_body(span, Some(e)))
 292             }
 293             ItemKind::Fn(FnSig { ref decl, header }, ref generics, ref body) => {
 294                 let fn_def_id = self.resolver.definitions().local_def_id(id);
 295                 self.with_new_scopes(|this| {
 296                     this.current_item = Some(ident.span);
 297
 298                     // Note: we don't need to change the return type from `T` to
 299                     // `impl Future<Output = T>` here because lower_body
 300                     // only cares about the input argument patterns in the function
 301                     // declaration (decl), not the return types.
 302                     let asyncness = header.asyncness;
 303                     let body_id =
 304                         this.lower_maybe_async_body(span, &decl, asyncness, body.as_deref());
 305
 306                     let (generics, decl) = this.add_in_band_defs(
 307                         generics,
 308                         fn_def_id,
 309                         AnonymousLifetimeMode::PassThrough,
 310                         |this, idty| {
 311                             let ret_id = asyncness.opt_return_id();
 312                             this.lower_fn_decl(&decl, Some((fn_def_id, idty)), true, ret_id)
 313                         },
 314                     );
 315                     let sig = hir::FnSig { decl, header: this.lower_fn_header(header) };
 316                     hir::ItemKind::Fn(sig, generics, body_id)
 317                 })
 318             }
 319             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
 320             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
 321             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
 322             ItemKind::TyAlias(ref ty, ref generics) => match ty.kind.opaque_top_hack() {
 323                 None => {
 324                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 325                     let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
 326                     hir::ItemKind::TyAlias(ty, generics)
 327                 }
 328                 Some(bounds) => {
 329                     let ty = hir::OpaqueTy {
 330                         generics: self.lower_generics(generics, ImplTraitContext::OpaqueTy(None)),
 331                         bounds: self.lower_param_bounds(bounds, ImplTraitContext::OpaqueTy(None)),
 332                         impl_trait_fn: None,
 333                         origin: hir::OpaqueTyOrigin::TypeAlias,
 334                     };
 335                     hir::ItemKind::OpaqueTy(ty)
 336                 }
 337             },
 338             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemKind::Enum(
 339                 hir::EnumDef {
 340                     variants: self.arena.alloc_from_iter(
 341                         enum_definition.variants.iter().map(|x| self.lower_variant(x)),
 342                     ),
 343                 },
 344                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 345             ),
 346             ItemKind::Struct(ref struct_def, ref generics) => {
 347                 let struct_def = self.lower_variant_data(struct_def);
 348                 hir::ItemKind::Struct(
 349                     struct_def,
 350                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 351                 )
 352             }
 353             ItemKind::Union(ref vdata, ref generics) => {
 354                 let vdata = self.lower_variant_data(vdata);
 355                 hir::ItemKind::Union(
 356                     vdata,
 357                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 358                 )
 359             }
 360             ItemKind::Impl {
 361                 unsafety,
 362                 polarity,
 363                 defaultness,
 364                 constness,
 365                 generics: ref ast_generics,
 366                 of_trait: ref trait_ref,
 367                 self_ty: ref ty,
 368                 items: ref impl_items,
 369             } => {
 370                 let def_id = self.resolver.definitions().local_def_id(id);
 371
 372                 // Lower the "impl header" first. This ordering is important
 373                 // for in-band lifetimes! Consider `'a` here:
 374                 //
 375                 //     impl Foo<'a> for u32 {
 376                 //         fn method(&'a self) { .. }
 377                 //     }
 378                 //
 379                 // Because we start by lowering the `Foo<'a> for u32`
 380                 // part, we will add `'a` to the list of generics on
 381                 // the impl. When we then encounter it later in the
 382                 // method, it will not be considered an in-band
 383                 // lifetime to be added, but rather a reference to a
 384                 // parent lifetime.
 385                 let lowered_trait_impl_id = self.lower_node_id(id);
 386                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
 387                     ast_generics,
 388                     def_id,
 389                     AnonymousLifetimeMode::CreateParameter,
 390                     |this, _| {
 391                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
 392                             this.lower_trait_ref(trait_ref, ImplTraitContext::disallowed())
 393                         });
 394
 395                         if let Some(ref trait_ref) = trait_ref {
 396                             if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res {
 397                                 this.trait_impls
 398                                     .entry(def_id)
 399                                     .or_default()
 400                                     .push(lowered_trait_impl_id);
 401                             }
 402                         }
 403
 404                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::disallowed());
 405
 406                         (trait_ref, lowered_ty)
 407                     },
 408                 );
 409
 410                 let new_impl_items =
 411                     self.with_in_scope_lifetime_defs(&ast_generics.params, |this| {
 412                         this.arena.alloc_from_iter(
 413                             impl_items.iter().map(|item| this.lower_impl_item_ref(item)),
 414                         )
 415                     });
 416
 417                 hir::ItemKind::Impl {
 418                     unsafety: self.lower_unsafety(unsafety),
 419                     polarity,
 420                     defaultness: self.lower_defaultness(defaultness, true /* [1] */),
 421                     constness: self.lower_constness(constness),
 422                     generics,
 423                     of_trait: trait_ref,
 424                     self_ty: lowered_ty,
 425                     items: new_impl_items,
 426                 }
 427             }
 428             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
 429                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::disallowed());
 430                 let items = self
 431                     .arena
 432                     .alloc_from_iter(items.iter().map(|item| self.lower_trait_item_ref(item)));
 433                 hir::ItemKind::Trait(
 434                     is_auto,
 435                     self.lower_unsafety(unsafety),
 436                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 437                     bounds,
 438                     items,
 439                 )
 440             }
 441             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemKind::TraitAlias(
 442                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 443                 self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 444             ),
 445             ItemKind::MacroDef(..) | ItemKind::Mac(..) => {
 446                 bug!("`TyMac` should have been expanded by now")
 447             }
 448         }
 449
 450         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
 451         //     not cause an assertion failure inside the `lower_defaultness` function.
 452     }
 453
 454     fn lower_use_tree(
 455         &mut self,
 456         tree: &UseTree,
 457         prefix: &Path,
 458         id: NodeId,
 459         vis: &mut hir::Visibility<'hir>,
 460         ident: &mut Ident,
 461         attrs: &'hir [Attribute],
 462     ) -> hir::ItemKind<'hir> {
 463         debug!("lower_use_tree(tree={:?})", tree);
 464         debug!("lower_use_tree: vis = {:?}", vis);
 465
 466         let path = &tree.prefix;
 467         let segments = prefix.segments.iter().chain(path.segments.iter()).cloned().collect();
 468
 469         match tree.kind {
 470             UseTreeKind::Simple(rename, id1, id2) => {
 471                 *ident = tree.ident();
 472
 473                 // First, apply the prefix to the path.
 474                 let mut path = Path { segments, span: path.span };
 475
 476                 // Correctly resolve `self` imports.
 477                 if path.segments.len() > 1
 478                     && path.segments.last().unwrap().ident.name == kw::SelfLower
 479                 {
 480                     let _ = path.segments.pop();
 481                     if rename.is_none() {
 482                         *ident = path.segments.last().unwrap().ident;
 483                     }
 484                 }
 485
 486                 let mut resolutions = self.expect_full_res_from_use(id);
 487                 // We want to return *something* from this function, so hold onto the first item
 488                 // for later.
 489                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
 490
 491                 // Here, we are looping over namespaces, if they exist for the definition
 492                 // being imported. We only handle type and value namespaces because we
 493                 // won't be dealing with macros in the rest of the compiler.
 494                 // Essentially a single `use` which imports two names is desugared into
 495                 // two imports.
 496                 for (res, &new_node_id) in resolutions.zip([id1, id2].iter()) {
 497                     let ident = *ident;
 498                     let mut path = path.clone();
 499                     for seg in &mut path.segments {
 500                         seg.id = self.resolver.next_node_id();
 501                     }
 502                     let span = path.span;
 503
 504                     self.with_hir_id_owner(new_node_id, |this| {
 505                         let new_id = this.lower_node_id(new_node_id);
 506                         let res = this.lower_res(res);
 507                         let path = this.lower_path_extra(res, &path, ParamMode::Explicit, None);
 508                         let kind = hir::ItemKind::Use(path, hir::UseKind::Single);
 509                         let vis = this.rebuild_vis(&vis);
 510
 511                         this.insert_item(hir::Item {
 512                             hir_id: new_id,
 513                             ident,
 514                             attrs,
 515                             kind,
 516                             vis,
 517                             span,
 518                         });
 519                     });
 520                 }
 521
 522                 let path = self.lower_path_extra(ret_res, &path, ParamMode::Explicit, None);
 523                 hir::ItemKind::Use(path, hir::UseKind::Single)
 524             }
 525             UseTreeKind::Glob => {
 526                 let path =
 527                     self.lower_path(id, &Path { segments, span: path.span }, ParamMode::Explicit);
 528                 hir::ItemKind::Use(path, hir::UseKind::Glob)
 529             }
 530             UseTreeKind::Nested(ref trees) => {
 531                 // Nested imports are desugared into simple imports.
 532                 // So, if we start with
 533                 //
 534                 // ```
 535                 // pub(x) use foo::{a, b};
 536                 // ```
 537                 //
 538                 // we will create three items:
 539                 //
 540                 // ```
 541                 // pub(x) use foo::a;
 542                 // pub(x) use foo::b;
 543                 // pub(x) use foo::{}; // <-- this is called the `ListStem`
 544                 // ```
 545                 //
 546                 // The first two are produced by recursively invoking
 547                 // `lower_use_tree` (and indeed there may be things
 548                 // like `use foo::{a::{b, c}}` and so forth).  They
 549                 // wind up being directly added to
 550                 // `self.items`. However, the structure of this
 551                 // function also requires us to return one item, and
 552                 // for that we return the `{}` import (called the
 553                 // `ListStem`).
 554
 555                 let prefix = Path { segments, span: prefix.span.to(path.span) };
 556
 557                 // Add all the nested `PathListItem`s to the HIR.
 558                 for &(ref use_tree, id) in trees {
 559                     let new_hir_id = self.lower_node_id(id);
 560
 561                     let mut prefix = prefix.clone();
 562
 563                     // Give the segments new node-ids since they are being cloned.
 564                     for seg in &mut prefix.segments {
 565                         seg.id = self.resolver.next_node_id();
 566                     }
 567
 568                     // Each `use` import is an item and thus are owners of the
 569                     // names in the path. Up to this point the nested import is
 570                     // the current owner, since we want each desugared import to
 571                     // own its own names, we have to adjust the owner before
 572                     // lowering the rest of the import.
 573                     self.with_hir_id_owner(id, |this| {
 574                         let mut vis = this.rebuild_vis(&vis);
 575                         let mut ident = *ident;
 576
 577                         let kind =
 578                             this.lower_use_tree(use_tree, &prefix, id, &mut vis, &mut ident, attrs);
 579
 580                         this.insert_item(hir::Item {
 581                             hir_id: new_hir_id,
 582                             ident,
 583                             attrs,
 584                             kind,
 585                             vis,
 586                             span: use_tree.span,
 587                         });
 588                     });
 589                 }
 590
 591                 // Subtle and a bit hacky: we lower the privacy level
 592                 // of the list stem to "private" most of the time, but
 593                 // not for "restricted" paths. The key thing is that
 594                 // we don't want it to stay as `pub` (with no caveats)
 595                 // because that affects rustdoc and also the lints
 596                 // about `pub` items. But we can't *always* make it
 597                 // private -- particularly not for restricted paths --
 598                 // because it contains node-ids that would then be
 599                 // unused, failing the check that HirIds are "densely
 600                 // assigned".
 601                 match vis.node {
 602                     hir::VisibilityKind::Public
 603                     | hir::VisibilityKind::Crate(_)
 604                     | hir::VisibilityKind::Inherited => {
 605                         *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
 606                     }
 607                     hir::VisibilityKind::Restricted { .. } => {
 608                         // Do nothing here, as described in the comment on the match.
 609                     }
 610                 }
 611
 612                 let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
 613                 let res = self.lower_res(res);
 614                 let path = self.lower_path_extra(res, &prefix, ParamMode::Explicit, None);
 615                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
 616             }
 617         }
 618     }
 619
 620     /// Paths like the visibility path in `pub(super) use foo::{bar, baz}` are repeated
 621     /// many times in the HIR tree; for each occurrence, we need to assign distinct
 622     /// `NodeId`s. (See, e.g., #56128.)
 623     fn rebuild_use_path(&mut self, path: &hir::Path<'hir>) -> &'hir hir::Path<'hir> {
 624         debug!("rebuild_use_path(path = {:?})", path);
 625         let segments =
 626             self.arena.alloc_from_iter(path.segments.iter().map(|seg| hir::PathSegment {
 627                 ident: seg.ident,
 628                 hir_id: seg.hir_id.map(|_| self.next_id()),
 629                 res: seg.res,
 630                 args: None,
 631                 infer_args: seg.infer_args,
 632             }));
 633         self.arena.alloc(hir::Path { span: path.span, res: path.res, segments })
 634     }
 635
 636     fn rebuild_vis(&mut self, vis: &hir::Visibility<'hir>) -> hir::Visibility<'hir> {
 637         let vis_kind = match vis.node {
 638             hir::VisibilityKind::Public => hir::VisibilityKind::Public,
 639             hir::VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 640             hir::VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 641             hir::VisibilityKind::Restricted { ref path, hir_id: _ } => {
 642                 hir::VisibilityKind::Restricted {
 643                     path: self.rebuild_use_path(path),
 644                     hir_id: self.next_id(),
 645                 }
 646             }
 647         };
 648         respan(vis.span, vis_kind)
 649     }
 650
 651     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem<'hir> {
 652         let def_id = self.resolver.definitions().local_def_id(i.id);
 653         hir::ForeignItem {
 654             hir_id: self.lower_node_id(i.id),
 655             ident: i.ident,
 656             attrs: self.lower_attrs(&i.attrs),
 657             kind: match i.kind {
 658                 ForeignItemKind::Fn(ref sig, ref generics, _) => {
 659                     let fdec = &sig.decl;
 660                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
 661                         generics,
 662                         def_id,
 663                         AnonymousLifetimeMode::PassThrough,
 664                         |this, _| {
 665                             (
 666                                 // Disallow `impl Trait` in foreign items.
 667                                 this.lower_fn_decl(fdec, None, false, None),
 668                                 this.lower_fn_params_to_names(fdec),
 669                             )
 670                         },
 671                     );
 672
 673                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
 674                 }
 675                 ForeignItemKind::Static(ref t, m) => {
 676                     let ty = self.lower_ty(t, ImplTraitContext::disallowed());
 677                     hir::ForeignItemKind::Static(ty, m)
 678                 }
 679                 ForeignItemKind::Ty => hir::ForeignItemKind::Type,
 680                 ForeignItemKind::Macro(_) => panic!("macro shouldn't exist here"),
 681             },
 682             vis: self.lower_visibility(&i.vis, None),
 683             span: i.span,
 684         }
 685     }
 686
 687     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod<'hir> {
 688         hir::ForeignMod {
 689             abi: fm.abi.map_or(abi::Abi::C, |abi| self.lower_abi(abi)),
 690             items: self.arena.alloc_from_iter(fm.items.iter().map(|x| self.lower_foreign_item(x))),
 691         }
 692     }
 693
 694     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> &'hir hir::GlobalAsm {
 695         self.arena.alloc(hir::GlobalAsm { asm: ga.asm })
 696     }
 697
 698     fn lower_variant(&mut self, v: &Variant) -> hir::Variant<'hir> {
 699         hir::Variant {
 700             attrs: self.lower_attrs(&v.attrs),
 701             data: self.lower_variant_data(&v.data),
 702             disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
 703             id: self.lower_node_id(v.id),
 704             ident: v.ident,
 705             span: v.span,
 706         }
 707     }
 708
 709     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData<'hir> {
 710         match *vdata {
 711             VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
 712                 self.arena
 713                     .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_struct_field(f))),
 714                 recovered,
 715             ),
 716             VariantData::Tuple(ref fields, id) => hir::VariantData::Tuple(
 717                 self.arena
 718                     .alloc_from_iter(fields.iter().enumerate().map(|f| self.lower_struct_field(f))),
 719                 self.lower_node_id(id),
 720             ),
 721             VariantData::Unit(id) => hir::VariantData::Unit(self.lower_node_id(id)),
 722         }
 723     }
 724
 725     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField<'hir> {
 726         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
 727             let t = self.lower_path_ty(
 728                 &f.ty,
 729                 qself,
 730                 path,
 731                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
 732                 ImplTraitContext::disallowed(),
 733             );
 734             self.arena.alloc(t)
 735         } else {
 736             self.lower_ty(&f.ty, ImplTraitContext::disallowed())
 737         };
 738         hir::StructField {
 739             span: f.span,
 740             hir_id: self.lower_node_id(f.id),
 741             ident: match f.ident {
 742                 Some(ident) => ident,
 743                 // FIXME(jseyfried): positional field hygiene.
 744                 None => Ident::new(sym::integer(index), f.span),
 745             },
 746             vis: self.lower_visibility(&f.vis, None),
 747             ty,
 748             attrs: self.lower_attrs(&f.attrs),
 749         }
 750     }
 751
 752     fn lower_trait_item(&mut self, i: &AssocItem) -> hir::TraitItem<'hir> {
 753         let trait_item_def_id = self.resolver.definitions().local_def_id(i.id);
 754
 755         let (generics, kind) = match i.kind {
 756             AssocItemKind::Const(ref ty, ref default) => {
 757                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 758                 let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 759                 (
 760                     generics,
 761                     hir::TraitItemKind::Const(
 762                         ty,
 763                         default.as_ref().map(|x| self.lower_const_body(i.span, Some(x))),
 764                     ),
 765                 )
 766             }
 767             AssocItemKind::Fn(ref sig, None) => {
 768                 let names = self.lower_fn_params_to_names(&sig.decl);
 769                 let (generics, sig) =
 770                     self.lower_method_sig(&i.generics, sig, trait_item_def_id, false, None);
 771                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
 772             }
 773             AssocItemKind::Fn(ref sig, Some(ref body)) => {
 774                 let body_id = self.lower_fn_body_block(i.span, &sig.decl, Some(body));
 775                 let (generics, sig) =
 776                     self.lower_method_sig(&i.generics, sig, trait_item_def_id, false, None);
 777                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
 778             }
 779             AssocItemKind::TyAlias(ref bounds, ref default) => {
 780                 let ty = default.as_ref().map(|x| self.lower_ty(x, ImplTraitContext::disallowed()));
 781                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 782                 let kind = hir::TraitItemKind::Type(
 783                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 784                     ty,
 785                 );
 786
 787                 (generics, kind)
 788             }
 789             AssocItemKind::Macro(..) => bug!("macro item shouldn't exist at this point"),
 790         };
 791
 792         hir::TraitItem {
 793             hir_id: self.lower_node_id(i.id),
 794             ident: i.ident,
 795             attrs: self.lower_attrs(&i.attrs),
 796             generics,
 797             kind,
 798             span: i.span,
 799         }
 800     }
 801
 802     fn lower_trait_item_ref(&mut self, i: &AssocItem) -> hir::TraitItemRef {
 803         let (kind, has_default) = match i.kind {
 804             AssocItemKind::Const(_, ref default) => (hir::AssocItemKind::Const, default.is_some()),
 805             AssocItemKind::TyAlias(_, ref default) => (hir::AssocItemKind::Type, default.is_some()),
 806             AssocItemKind::Fn(ref sig, ref default) => {
 807                 (hir::AssocItemKind::Method { has_self: sig.decl.has_self() }, default.is_some())
 808             }
 809             AssocItemKind::Macro(..) => unimplemented!(),
 810         };
 811         hir::TraitItemRef {
 812             id: hir::TraitItemId { hir_id: self.lower_node_id(i.id) },
 813             ident: i.ident,
 814             span: i.span,
 815             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
 816             kind,
 817         }
 818     }
 819
 820     /// Construct `ExprKind::Err` for the given `span`.
 821     fn expr_err(&mut self, span: Span) -> hir::Expr<'hir> {
 822         self.expr(span, hir::ExprKind::Err, AttrVec::new())
 823     }
 824
 825     fn lower_impl_item(&mut self, i: &AssocItem) -> hir::ImplItem<'hir> {
 826         let impl_item_def_id = self.resolver.definitions().local_def_id(i.id);
 827
 828         let (generics, kind) = match i.kind {
 829             AssocItemKind::Const(ref ty, ref expr) => {
 830                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 831                 let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 832                 (
 833                     generics,
 834                     hir::ImplItemKind::Const(ty, self.lower_const_body(i.span, expr.as_deref())),
 835                 )
 836             }
 837             AssocItemKind::Fn(ref sig, ref body) => {
 838                 self.current_item = Some(i.span);
 839                 let asyncness = sig.header.asyncness;
 840                 let body_id =
 841                     self.lower_maybe_async_body(i.span, &sig.decl, asyncness, body.as_deref());
 842                 let impl_trait_return_allow = !self.is_in_trait_impl;
 843                 let (generics, sig) = self.lower_method_sig(
 844                     &i.generics,
 845                     sig,
 846                     impl_item_def_id,
 847                     impl_trait_return_allow,
 848                     asyncness.opt_return_id(),
 849                 );
 850
 851                 (generics, hir::ImplItemKind::Method(sig, body_id))
 852             }
 853             AssocItemKind::TyAlias(_, ref ty) => {
 854                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 855                 let kind = match ty {
 856                     None => {
 857                         let ty = self.arena.alloc(self.ty(i.span, hir::TyKind::Err));
 858                         hir::ImplItemKind::TyAlias(ty)
 859                     }
 860                     Some(ty) => match ty.kind.opaque_top_hack() {
 861                         None => {
 862                             let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 863                             hir::ImplItemKind::TyAlias(ty)
 864                         }
 865                         Some(bs) => {
 866                             let bs = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
 867                             hir::ImplItemKind::OpaqueTy(bs)
 868                         }
 869                     },
 870                 };
 871                 (generics, kind)
 872             }
 873             AssocItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
 874         };
 875
 876         hir::ImplItem {
 877             hir_id: self.lower_node_id(i.id),
 878             ident: i.ident,
 879             attrs: self.lower_attrs(&i.attrs),
 880             generics,
 881             vis: self.lower_visibility(&i.vis, None),
 882             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 883             kind,
 884             span: i.span,
 885         }
 886
 887         // [1] since `default impl` is not yet implemented, this is always true in impls
 888     }
 889
 890     fn lower_impl_item_ref(&mut self, i: &AssocItem) -> hir::ImplItemRef<'hir> {
 891         hir::ImplItemRef {
 892             id: hir::ImplItemId { hir_id: self.lower_node_id(i.id) },
 893             ident: i.ident,
 894             span: i.span,
 895             vis: self.lower_visibility(&i.vis, Some(i.id)),
 896             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 897             kind: match &i.kind {
 898                 AssocItemKind::Const(..) => hir::AssocItemKind::Const,
 899                 AssocItemKind::TyAlias(_, ty) => {
 900                     match ty.as_deref().and_then(|ty| ty.kind.opaque_top_hack()) {
 901                         None => hir::AssocItemKind::Type,
 902                         Some(_) => hir::AssocItemKind::OpaqueTy,
 903                     }
 904                 }
 905                 AssocItemKind::Fn(sig, _) => {
 906                     hir::AssocItemKind::Method { has_self: sig.decl.has_self() }
 907                 }
 908                 AssocItemKind::Macro(..) => unimplemented!(),
 909             },
 910         }
 911
 912         // [1] since `default impl` is not yet implemented, this is always true in impls
 913     }
 914
 915     /// If an `explicit_owner` is given, this method allocates the `HirId` in
 916     /// the address space of that item instead of the item currently being
 917     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
 918     /// lower a `Visibility` value although we haven't lowered the owning
 919     /// `ImplItem` in question yet.
 920     fn lower_visibility(
 921         &mut self,
 922         v: &Visibility,
 923         explicit_owner: Option<NodeId>,
 924     ) -> hir::Visibility<'hir> {
 925         let node = match v.node {
 926             VisibilityKind::Public => hir::VisibilityKind::Public,
 927             VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 928             VisibilityKind::Restricted { ref path, id } => {
 929                 debug!("lower_visibility: restricted path id = {:?}", id);
 930                 let lowered_id = if let Some(owner) = explicit_owner {
 931                     self.lower_node_id_with_owner(id, owner)
 932                 } else {
 933                     self.lower_node_id(id)
 934                 };
 935                 let res = self.expect_full_res(id);
 936                 let res = self.lower_res(res);
 937                 hir::VisibilityKind::Restricted {
 938                     path: self.lower_path_extra(res, path, ParamMode::Explicit, explicit_owner),
 939                     hir_id: lowered_id,
 940                 }
 941             }
 942             VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 943         };
 944         respan(v.span, node)
 945     }
 946
 947     fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
 948         match d {
 949             Defaultness::Default => hir::Defaultness::Default { has_value: has_value },
 950             Defaultness::Final => {
 951                 assert!(has_value);
 952                 hir::Defaultness::Final
 953             }
 954         }
 955     }
 956
 957     fn record_body(
 958         &mut self,
 959         params: &'hir [hir::Param<'hir>],
 960         value: hir::Expr<'hir>,
 961     ) -> hir::BodyId {
 962         let body = hir::Body { generator_kind: self.generator_kind, params, value };
 963         let id = body.id();
 964         self.bodies.insert(id, body);
 965         id
 966     }
 967
 968     fn lower_body(
 969         &mut self,
 970         f: impl FnOnce(&mut Self) -> (&'hir [hir::Param<'hir>], hir::Expr<'hir>),
 971     ) -> hir::BodyId {
 972         let prev_gen_kind = self.generator_kind.take();
 973         let (parameters, result) = f(self);
 974         let body_id = self.record_body(parameters, result);
 975         self.generator_kind = prev_gen_kind;
 976         body_id
 977     }
 978
 979     fn lower_param(&mut self, param: &Param) -> hir::Param<'hir> {
 980         hir::Param {
 981             attrs: self.lower_attrs(&param.attrs),
 982             hir_id: self.lower_node_id(param.id),
 983             pat: self.lower_pat(&param.pat),
 984             span: param.span,
 985         }
 986     }
 987
 988     pub(super) fn lower_fn_body(
 989         &mut self,
 990         decl: &FnDecl,
 991         body: impl FnOnce(&mut Self) -> hir::Expr<'hir>,
 992     ) -> hir::BodyId {
 993         self.lower_body(|this| {
 994             (
 995                 this.arena.alloc_from_iter(decl.inputs.iter().map(|x| this.lower_param(x))),
 996                 body(this),
 997             )
 998         })
 999     }
1000
1001     fn lower_fn_body_block(
1002         &mut self,
1003         span: Span,
1004         decl: &FnDecl,
1005         body: Option<&Block>,
1006     ) -> hir::BodyId {
1007         self.lower_fn_body(decl, |this| this.lower_block_expr_opt(span, body))
1008     }
1009
1010     fn lower_block_expr_opt(&mut self, span: Span, block: Option<&Block>) -> hir::Expr<'hir> {
1011         match block {
1012             Some(block) => self.lower_block_expr(block),
1013             None => self.expr_err(span),
1014         }
1015     }
1016
1017     pub(super) fn lower_const_body(&mut self, span: Span, expr: Option<&Expr>) -> hir::BodyId {
1018         self.lower_body(|this| {
1019             (
1020                 &[],
1021                 match expr {
1022                     Some(expr) => this.lower_expr_mut(expr),
1023                     None => this.expr_err(span),
1024                 },
1025             )
1026         })
1027     }
1028
1029     fn lower_maybe_async_body(
1030         &mut self,
1031         span: Span,
1032         decl: &FnDecl,
1033         asyncness: Async,
1034         body: Option<&Block>,
1035     ) -> hir::BodyId {
1036         let closure_id = match asyncness {
1037             Async::Yes { closure_id, .. } => closure_id,
1038             Async::No => return self.lower_fn_body_block(span, decl, body),
1039         };
1040
1041         self.lower_body(|this| {
1042             let mut parameters: Vec<hir::Param<'_>> = Vec::new();
1043             let mut statements: Vec<hir::Stmt<'_>> = Vec::new();
1044
1045             // Async function parameters are lowered into the closure body so that they are
1046             // captured and so that the drop order matches the equivalent non-async functions.
1047             //
1048             // from:
1049             //
1050             //     async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
1051             //         <body>
1052             //     }
1053             //
1054             // into:
1055             //
1056             //     fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) {
1057             //       async move {
1058             //         let __arg2 = __arg2;
1059             //         let <pattern> = __arg2;
1060             //         let __arg1 = __arg1;
1061             //         let <pattern> = __arg1;
1062             //         let __arg0 = __arg0;
1063             //         let <pattern> = __arg0;
1064             //         drop-temps { <body> } // see comments later in fn for details
1065             //       }
1066             //     }
1067             //
1068             // If `<pattern>` is a simple ident, then it is lowered to a single
1069             // `let <pattern> = <pattern>;` statement as an optimization.
1070             //
1071             // Note that the body is embedded in `drop-temps`; an
1072             // equivalent desugaring would be `return { <body>
1073             // };`. The key point is that we wish to drop all the
1074             // let-bound variables and temporaries created in the body
1075             // (and its tail expression!) before we drop the
1076             // parameters (c.f. rust-lang/rust#64512).
1077             for (index, parameter) in decl.inputs.iter().enumerate() {
1078                 let parameter = this.lower_param(parameter);
1079                 let span = parameter.pat.span;
1080
1081                 // Check if this is a binding pattern, if so, we can optimize and avoid adding a
1082                 // `let <pat> = __argN;` statement. In this case, we do not rename the parameter.
1083                 let (ident, is_simple_parameter) = match parameter.pat.kind {
1084                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, _) => {
1085                         (ident, true)
1086                     }
1087                     _ => {
1088                         // Replace the ident for bindings that aren't simple.
1089                         let name = format!("__arg{}", index);
1090                         let ident = Ident::from_str(&name);
1091
1092                         (ident, false)
1093                     }
1094                 };
1095
1096                 let desugared_span = this.mark_span_with_reason(DesugaringKind::Async, span, None);
1097
1098                 // Construct a parameter representing `__argN: <ty>` to replace the parameter of the
1099                 // async function.
1100                 //
1101                 // If this is the simple case, this parameter will end up being the same as the
1102                 // original parameter, but with a different pattern id.
1103                 let mut stmt_attrs = AttrVec::new();
1104                 stmt_attrs.extend(parameter.attrs.iter().cloned());
1105                 let (new_parameter_pat, new_parameter_id) = this.pat_ident(desugared_span, ident);
1106                 let new_parameter = hir::Param {
1107                     attrs: parameter.attrs,
1108                     hir_id: parameter.hir_id,
1109                     pat: new_parameter_pat,
1110                     span: parameter.span,
1111                 };
1112
1113                 if is_simple_parameter {
1114                     // If this is the simple case, then we only insert one statement that is
1115                     // `let <pat> = <pat>;`. We re-use the original argument's pattern so that
1116                     // `HirId`s are densely assigned.
1117                     let expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1118                     let stmt = this.stmt_let_pat(
1119                         stmt_attrs,
1120                         desugared_span,
1121                         Some(expr),
1122                         parameter.pat,
1123                         hir::LocalSource::AsyncFn,
1124                     );
1125                     statements.push(stmt);
1126                 } else {
1127                     // If this is not the simple case, then we construct two statements:
1128                     //
1129                     // ```
1130                     // let __argN = __argN;
1131                     // let <pat> = __argN;
1132                     // ```
1133                     //
1134                     // The first statement moves the parameter into the closure and thus ensures
1135                     // that the drop order is correct.
1136                     //
1137                     // The second statement creates the bindings that the user wrote.
1138
1139                     // Construct the `let mut __argN = __argN;` statement. It must be a mut binding
1140                     // because the user may have specified a `ref mut` binding in the next
1141                     // statement.
1142                     let (move_pat, move_id) = this.pat_ident_binding_mode(
1143                         desugared_span,
1144                         ident,
1145                         hir::BindingAnnotation::Mutable,
1146                     );
1147                     let move_expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1148                     let move_stmt = this.stmt_let_pat(
1149                         AttrVec::new(),
1150                         desugared_span,
1151                         Some(move_expr),
1152                         move_pat,
1153                         hir::LocalSource::AsyncFn,
1154                     );
1155
1156                     // Construct the `let <pat> = __argN;` statement. We re-use the original
1157                     // parameter's pattern so that `HirId`s are densely assigned.
1158                     let pattern_expr = this.expr_ident(desugared_span, ident, move_id);
1159                     let pattern_stmt = this.stmt_let_pat(
1160                         stmt_attrs,
1161                         desugared_span,
1162                         Some(pattern_expr),
1163                         parameter.pat,
1164                         hir::LocalSource::AsyncFn,
1165                     );
1166
1167                     statements.push(move_stmt);
1168                     statements.push(pattern_stmt);
1169                 };
1170
1171                 parameters.push(new_parameter);
1172             }
1173
1174             let body_span = body.map_or(span, |b| b.span);
1175             let async_expr = this.make_async_expr(
1176                 CaptureBy::Value,
1177                 closure_id,
1178                 None,
1179                 body_span,
1180                 hir::AsyncGeneratorKind::Fn,
1181                 |this| {
1182                     // Create a block from the user's function body:
1183                     let user_body = this.lower_block_expr_opt(body_span, body);
1184
1185                     // Transform into `drop-temps { <user-body> }`, an expression:
1186                     let desugared_span =
1187                         this.mark_span_with_reason(DesugaringKind::Async, user_body.span, None);
1188                     let user_body = this.expr_drop_temps(
1189                         desugared_span,
1190                         this.arena.alloc(user_body),
1191                         AttrVec::new(),
1192                     );
1193
1194                     // As noted above, create the final block like
1195                     //
1196                     // ```
1197                     // {
1198                     //   let $param_pattern = $raw_param;
1199                     //   ...
1200                     //   drop-temps { <user-body> }
1201                     // }
1202                     // ```
1203                     let body = this.block_all(
1204                         desugared_span,
1205                         this.arena.alloc_from_iter(statements),
1206                         Some(user_body),
1207                     );
1208
1209                     this.expr_block(body, AttrVec::new())
1210                 },
1211             );
1212
1213             (
1214                 this.arena.alloc_from_iter(parameters),
1215                 this.expr(body_span, async_expr, AttrVec::new()),
1216             )
1217         })
1218     }
1219
1220     fn lower_method_sig(
1221         &mut self,
1222         generics: &Generics,
1223         sig: &FnSig,
1224         fn_def_id: DefId,
1225         impl_trait_return_allow: bool,
1226         is_async: Option<NodeId>,
1227     ) -> (hir::Generics<'hir>, hir::FnSig<'hir>) {
1228         let header = self.lower_fn_header(sig.header);
1229         let (generics, decl) = self.add_in_band_defs(
1230             generics,
1231             fn_def_id,
1232             AnonymousLifetimeMode::PassThrough,
1233             |this, idty| {
1234                 this.lower_fn_decl(
1235                     &sig.decl,
1236                     Some((fn_def_id, idty)),
1237                     impl_trait_return_allow,
1238                     is_async,
1239                 )
1240             },
1241         );
1242         (generics, hir::FnSig { header, decl })
1243     }
1244
1245     fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
1246         hir::FnHeader {
1247             unsafety: self.lower_unsafety(h.unsafety),
1248             asyncness: self.lower_asyncness(h.asyncness),
1249             constness: self.lower_constness(h.constness),
1250             abi: self.lower_extern(h.ext),
1251         }
1252     }
1253
1254     pub(super) fn lower_abi(&mut self, abi: StrLit) -> abi::Abi {
1255         abi::lookup(&abi.symbol_unescaped.as_str()).unwrap_or_else(|| {
1256             self.error_on_invalid_abi(abi);
1257             abi::Abi::Rust
1258         })
1259     }
1260
1261     pub(super) fn lower_extern(&mut self, ext: Extern) -> abi::Abi {
1262         match ext {
1263             Extern::None => abi::Abi::Rust,
1264             Extern::Implicit => abi::Abi::C,
1265             Extern::Explicit(abi) => self.lower_abi(abi),
1266         }
1267     }
1268
1269     fn error_on_invalid_abi(&self, abi: StrLit) {
1270         struct_span_err!(self.sess, abi.span, E0703, "invalid ABI: found `{}`", abi.symbol)
1271             .span_label(abi.span, "invalid ABI")
1272             .help(&format!("valid ABIs: {}", abi::all_names().join(", ")))
1273             .emit();
1274     }
1275
1276     fn lower_asyncness(&mut self, a: Async) -> hir::IsAsync {
1277         match a {
1278             Async::Yes { .. } => hir::IsAsync::Async,
1279             Async::No => hir::IsAsync::NotAsync,
1280         }
1281     }
1282
1283     fn lower_constness(&mut self, c: Const) -> hir::Constness {
1284         match c {
1285             Const::Yes(_) => hir::Constness::Const,
1286             Const::No => hir::Constness::NotConst,
1287         }
1288     }
1289
1290     pub(super) fn lower_unsafety(&mut self, u: Unsafe) -> hir::Unsafety {
1291         match u {
1292             Unsafe::Yes(_) => hir::Unsafety::Unsafe,
1293             Unsafe::No => hir::Unsafety::Normal,
1294         }
1295     }
1296
1297     pub(super) fn lower_generics_mut(
1298         &mut self,
1299         generics: &Generics,
1300         itctx: ImplTraitContext<'_, 'hir>,
1301     ) -> GenericsCtor<'hir> {
1302         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1303         // FIXME: this could probably be done with less rightward drift. It also looks like two
1304         // control paths where `report_error` is called are the only paths that advance to after the
1305         // match statement, so the error reporting could probably just be moved there.
1306         let mut add_bounds: NodeMap<Vec<_>> = Default::default();
1307         for pred in &generics.where_clause.predicates {
1308             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1309                 'next_bound: for bound in &bound_pred.bounds {
1310                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
1311                         let report_error = |this: &mut Self| {
1312                             this.diagnostic().span_err(
1313                                 bound_pred.bounded_ty.span,
1314                                 "`?Trait` bounds are only permitted at the \
1315                                  point where a type parameter is declared",
1316                             );
1317                         };
1318                         // Check if the where clause type is a plain type parameter.
1319                         match bound_pred.bounded_ty.kind {
1320                             TyKind::Path(None, ref path)
1321                                 if path.segments.len() == 1
1322                                     && bound_pred.bound_generic_params.is_empty() =>
1323                             {
1324                                 if let Some(Res::Def(DefKind::TyParam, def_id)) = self
1325                                     .resolver
1326                                     .get_partial_res(bound_pred.bounded_ty.id)
1327                                     .map(|d| d.base_res())
1328                                 {
1329                                     if let Some(node_id) =
1330                                         self.resolver.definitions().as_local_node_id(def_id)
1331                                     {
1332                                         for param in &generics.params {
1333                                             match param.kind {
1334                                                 GenericParamKind::Type { .. } => {
1335                                                     if node_id == param.id {
1336                                                         add_bounds
1337                                                             .entry(param.id)
1338                                                             .or_default()
1339                                                             .push(bound.clone());
1340                                                         continue 'next_bound;
1341                                                     }
1342                                                 }
1343                                                 _ => {}
1344                                             }
1345                                         }
1346                                     }
1347                                 }
1348                                 report_error(self)
1349                             }
1350                             _ => report_error(self),
1351                         }
1352                     }
1353                 }
1354             }
1355         }
1356
1357         GenericsCtor {
1358             params: self.lower_generic_params_mut(&generics.params, &add_bounds, itctx).collect(),
1359             where_clause: self.lower_where_clause(&generics.where_clause),
1360             span: generics.span,
1361         }
1362     }
1363
1364     pub(super) fn lower_generics(
1365         &mut self,
1366         generics: &Generics,
1367         itctx: ImplTraitContext<'_, 'hir>,
1368     ) -> hir::Generics<'hir> {
1369         let generics_ctor = self.lower_generics_mut(generics, itctx);
1370         generics_ctor.into_generics(self.arena)
1371     }
1372
1373     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause<'hir> {
1374         self.with_anonymous_lifetime_mode(AnonymousLifetimeMode::ReportError, |this| {
1375             hir::WhereClause {
1376                 predicates: this.arena.alloc_from_iter(
1377                     wc.predicates.iter().map(|predicate| this.lower_where_predicate(predicate)),
1378                 ),
1379                 span: wc.span,
1380             }
1381         })
1382     }
1383
1384     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate<'hir> {
1385         match *pred {
1386             WherePredicate::BoundPredicate(WhereBoundPredicate {
1387                 ref bound_generic_params,
1388                 ref bounded_ty,
1389                 ref bounds,
1390                 span,
1391             }) => {
1392                 self.with_in_scope_lifetime_defs(&bound_generic_params, |this| {
1393                     hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1394                         bound_generic_params: this.lower_generic_params(
1395                             bound_generic_params,
1396                             &NodeMap::default(),
1397                             ImplTraitContext::disallowed(),
1398                         ),
1399                         bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::disallowed()),
1400                         bounds: this.arena.alloc_from_iter(bounds.iter().filter_map(|bound| {
1401                             match *bound {
1402                                 // Ignore `?Trait` bounds.
1403                                 // They were copied into type parameters already.
1404                                 GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1405                                 _ => Some(
1406                                     this.lower_param_bound(bound, ImplTraitContext::disallowed()),
1407                                 ),
1408                             }
1409                         })),
1410                         span,
1411                     })
1412                 })
1413             }
1414             WherePredicate::RegionPredicate(WhereRegionPredicate {
1415                 ref lifetime,
1416                 ref bounds,
1417                 span,
1418             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1419                 span,
1420                 lifetime: self.lower_lifetime(lifetime),
1421                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
1422             }),
1423             WherePredicate::EqPredicate(WhereEqPredicate { id, ref lhs_ty, ref rhs_ty, span }) => {
1424                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1425                     hir_id: self.lower_node_id(id),
1426                     lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::disallowed()),
1427                     rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::disallowed()),
1428                     span,
1429                 })
1430             }
1431         }
1432     }
1433 }
1434
1435 /// Helper struct for delayed construction of Generics.
1436 pub(super) struct GenericsCtor<'hir> {
1437     pub(super) params: SmallVec<[hir::GenericParam<'hir>; 4]>,
1438     where_clause: hir::WhereClause<'hir>,
1439     span: Span,
1440 }
1441
1442 impl<'hir> GenericsCtor<'hir> {
1443     pub(super) fn into_generics(self, arena: &'hir Arena<'hir>) -> hir::Generics<'hir> {
1444         hir::Generics {
1445             params: arena.alloc_from_iter(self.params),
1446             where_clause: self.where_clause,
1447             span: self.span,
1448         }
1449     }
1450 }