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