src/librustc/hir/lowering/item.rs

   1 use super::LoweringContext;
   2 use super::ImplTraitContext;
   3 use super::ImplTraitPosition;
   4 use super::ImplTraitTypeIdVisitor;
   5 use super::AnonymousLifetimeMode;
   6 use super::ParamMode;
   7
   8 use crate::hir::{self, HirVec};
   9 use crate::hir::ptr::P;
  10 use crate::hir::def_id::DefId;
  11 use crate::hir::def::{Res, DefKind};
  12 use crate::util::nodemap::NodeMap;
  13
  14 use rustc_data_structures::thin_vec::ThinVec;
  15 use rustc_target::spec::abi;
  16
  17 use std::collections::BTreeSet;
  18 use smallvec::SmallVec;
  19 use syntax::attr;
  20 use syntax::ast::*;
  21 use syntax::visit::{self, Visitor};
  22 use syntax::source_map::{respan, DesugaringKind};
  23 use syntax::symbol::{kw, sym};
  24 use syntax_pos::Span;
  25
  26 use rustc_error_codes::*;
  27
  28 pub(super) struct ItemLowerer<'tcx, 'interner> {
  29     pub(super) lctx: &'tcx mut LoweringContext<'interner>,
  30 }
  31
  32 impl<'tcx, 'interner> ItemLowerer<'tcx, 'interner> {
  33     fn with_trait_impl_ref<F>(&mut self, trait_impl_ref: &Option<TraitRef>, f: F)
  34     where
  35         F: FnOnce(&mut Self),
  36     {
  37         let old = self.lctx.is_in_trait_impl;
  38         self.lctx.is_in_trait_impl = if let &None = trait_impl_ref {
  39             false
  40         } else {
  41             true
  42         };
  43         f(self);
  44         self.lctx.is_in_trait_impl = old;
  45     }
  46 }
  47
  48 impl<'tcx, 'interner> Visitor<'tcx> for ItemLowerer<'tcx, 'interner> {
  49     fn visit_mod(&mut self, m: &'tcx Mod, _s: Span, _attrs: &[Attribute], n: NodeId) {
  50         let hir_id = self.lctx.lower_node_id(n);
  51
  52         self.lctx.modules.insert(hir_id, hir::ModuleItems {
  53             items: BTreeSet::new(),
  54             trait_items: BTreeSet::new(),
  55             impl_items: BTreeSet::new(),
  56         });
  57
  58         let old = self.lctx.current_module;
  59         self.lctx.current_module = hir_id;
  60         visit::walk_mod(self, m);
  61         self.lctx.current_module = old;
  62     }
  63
  64     fn visit_item(&mut self, item: &'tcx Item) {
  65         let mut item_hir_id = None;
  66         self.lctx.with_hir_id_owner(item.id, |lctx| {
  67             lctx.without_in_scope_lifetime_defs(|lctx| {
  68                 if let Some(hir_item) = lctx.lower_item(item) {
  69                     item_hir_id = Some(hir_item.hir_id);
  70                     lctx.insert_item(hir_item);
  71                 }
  72             })
  73         });
  74
  75         if let Some(hir_id) = item_hir_id {
  76             self.lctx.with_parent_item_lifetime_defs(hir_id, |this| {
  77                 let this = &mut ItemLowerer { lctx: this };
  78                 if let ItemKind::Impl(.., ref opt_trait_ref, _, _) = item.kind {
  79                     this.with_trait_impl_ref(opt_trait_ref, |this| {
  80                         visit::walk_item(this, item)
  81                     });
  82                 } else {
  83                     visit::walk_item(this, item);
  84                 }
  85             });
  86         }
  87     }
  88
  89     fn visit_trait_item(&mut self, item: &'tcx TraitItem) {
  90         self.lctx.with_hir_id_owner(item.id, |lctx| {
  91             let hir_item = lctx.lower_trait_item(item);
  92             let id = hir::TraitItemId { hir_id: hir_item.hir_id };
  93             lctx.trait_items.insert(id, hir_item);
  94             lctx.modules.get_mut(&lctx.current_module).unwrap().trait_items.insert(id);
  95         });
  96
  97         visit::walk_trait_item(self, item);
  98     }
  99
 100     fn visit_impl_item(&mut self, item: &'tcx ImplItem) {
 101         self.lctx.with_hir_id_owner(item.id, |lctx| {
 102             let hir_item = lctx.lower_impl_item(item);
 103             let id = hir::ImplItemId { hir_id: hir_item.hir_id };
 104             lctx.impl_items.insert(id, hir_item);
 105             lctx.modules.get_mut(&lctx.current_module).unwrap().impl_items.insert(id);
 106         });
 107         visit::walk_impl_item(self, item);
 108     }
 109 }
 110
 111 impl LoweringContext<'_> {
 112     // Same as the method above, but accepts `hir::GenericParam`s
 113     // instead of `ast::GenericParam`s.
 114     // This should only be used with generics that have already had their
 115     // in-band lifetimes added. In practice, this means that this function is
 116     // only used when lowering a child item of a trait or impl.
 117     fn with_parent_item_lifetime_defs<T>(
 118         &mut self,
 119         parent_hir_id: hir::HirId,
 120         f: impl FnOnce(&mut LoweringContext<'_>) -> T,
 121     ) -> T {
 122         let old_len = self.in_scope_lifetimes.len();
 123
 124         let parent_generics = match self.items.get(&parent_hir_id).unwrap().kind {
 125             hir::ItemKind::Impl(_, _, _, ref generics, ..)
 126             | hir::ItemKind::Trait(_, _, ref generics, ..) => {
 127                 &generics.params[..]
 128             }
 129             _ => &[],
 130         };
 131         let lt_def_names = parent_generics.iter().filter_map(|param| match param.kind {
 132             hir::GenericParamKind::Lifetime { .. } => Some(param.name.modern()),
 133             _ => None,
 134         });
 135         self.in_scope_lifetimes.extend(lt_def_names);
 136
 137         let res = f(self);
 138
 139         self.in_scope_lifetimes.truncate(old_len);
 140         res
 141     }
 142
 143     // Clears (and restores) the `in_scope_lifetimes` field. Used when
 144     // visiting nested items, which never inherit in-scope lifetimes
 145     // from their surrounding environment.
 146     fn without_in_scope_lifetime_defs<T>(
 147         &mut self,
 148         f: impl FnOnce(&mut LoweringContext<'_>) -> T,
 149     ) -> T {
 150         let old_in_scope_lifetimes = std::mem::replace(&mut self.in_scope_lifetimes, vec![]);
 151
 152         // this vector is only used when walking over impl headers,
 153         // input types, and the like, and should not be non-empty in
 154         // between items
 155         assert!(self.lifetimes_to_define.is_empty());
 156
 157         let res = f(self);
 158
 159         assert!(self.in_scope_lifetimes.is_empty());
 160         self.in_scope_lifetimes = old_in_scope_lifetimes;
 161
 162         res
 163     }
 164
 165     pub(super) fn lower_mod(&mut self, m: &Mod) -> hir::Mod {
 166         hir::Mod {
 167             inner: m.inner,
 168             item_ids: m.items.iter().flat_map(|x| self.lower_item_id(x)).collect(),
 169         }
 170     }
 171
 172     pub(super) fn lower_item_id(&mut self, i: &Item) -> SmallVec<[hir::ItemId; 1]> {
 173         let node_ids = match i.kind {
 174             ItemKind::Use(ref use_tree) => {
 175                 let mut vec = smallvec![i.id];
 176                 self.lower_item_id_use_tree(use_tree, i.id, &mut vec);
 177                 vec
 178             }
 179             ItemKind::MacroDef(..) => SmallVec::new(),
 180             ItemKind::Fn(..) |
 181             ItemKind::Impl(.., None, _, _) => smallvec![i.id],
 182             ItemKind::Static(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             ItemKind::Const(ref ty, ..) => {
 191                 let mut ids = smallvec![i.id];
 192                 if self.sess.features_untracked().impl_trait_in_bindings {
 193                     let mut visitor = ImplTraitTypeIdVisitor { ids: &mut ids };
 194                     visitor.visit_ty(ty);
 195                 }
 196                 ids
 197             },
 198             _ => smallvec![i.id],
 199         };
 200
 201         node_ids.into_iter().map(|node_id| hir::ItemId {
 202             id: self.allocate_hir_id_counter(node_id)
 203         }).collect()
 204     }
 205
 206     fn lower_item_id_use_tree(
 207         &mut self,
 208         tree: &UseTree,
 209         base_id: NodeId,
 210         vec: &mut SmallVec<[NodeId; 1]>
 211     ) {
 212         match tree.kind {
 213             UseTreeKind::Nested(ref nested_vec) => for &(ref nested, id) in nested_vec {
 214                 vec.push(id);
 215                 self.lower_item_id_use_tree(nested, id, vec);
 216             },
 217             UseTreeKind::Glob => {}
 218             UseTreeKind::Simple(_, id1, id2) => {
 219                 for (_, &id) in self.expect_full_res_from_use(base_id)
 220                                     .skip(1)
 221                                     .zip([id1, id2].iter())
 222                 {
 223                     vec.push(id);
 224                 }
 225             },
 226         }
 227     }
 228
 229     pub fn lower_item(&mut self, i: &Item) -> Option<hir::Item> {
 230         let mut ident = i.ident;
 231         let mut vis = self.lower_visibility(&i.vis, None);
 232         let attrs = self.lower_attrs(&i.attrs);
 233
 234         if let ItemKind::MacroDef(ref def) = i.kind {
 235             if !def.legacy || attr::contains_name(&i.attrs, sym::macro_export) {
 236                 let body = self.lower_token_stream(def.stream());
 237                 let hir_id = self.lower_node_id(i.id);
 238                 self.exported_macros.push(hir::MacroDef {
 239                     name: ident.name,
 240                     vis,
 241                     attrs,
 242                     hir_id,
 243                     span: i.span,
 244                     body,
 245                     legacy: def.legacy,
 246                 });
 247             } else {
 248                 self.non_exported_macro_attrs.extend(attrs.into_iter());
 249             }
 250             return None;
 251         }
 252
 253         let kind = self.lower_item_kind(i.id, &mut ident, &attrs, &mut vis, &i.kind);
 254
 255         Some(hir::Item {
 256             hir_id: self.lower_node_id(i.id),
 257             ident,
 258             attrs,
 259             kind,
 260             vis,
 261             span: i.span,
 262         })
 263     }
 264
 265     fn lower_item_kind(
 266         &mut self,
 267         id: NodeId,
 268         ident: &mut Ident,
 269         attrs: &hir::HirVec<Attribute>,
 270         vis: &mut hir::Visibility,
 271         i: &ItemKind,
 272     ) -> hir::ItemKind {
 273         match *i {
 274             ItemKind::ExternCrate(orig_name) => hir::ItemKind::ExternCrate(orig_name),
 275             ItemKind::Use(ref use_tree) => {
 276                 // Start with an empty prefix.
 277                 let prefix = Path {
 278                     segments: vec![],
 279                     span: use_tree.span,
 280                 };
 281
 282                 self.lower_use_tree(use_tree, &prefix, id, vis, ident, attrs)
 283             }
 284             ItemKind::Static(ref t, m, ref e) => {
 285                 hir::ItemKind::Static(
 286                     self.lower_ty(
 287                         t,
 288                         if self.sess.features_untracked().impl_trait_in_bindings {
 289                             ImplTraitContext::OpaqueTy(None)
 290                         } else {
 291                             ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 292                         }
 293                     ),
 294                     m,
 295                     self.lower_const_body(e),
 296                 )
 297             }
 298             ItemKind::Const(ref t, ref e) => {
 299                 hir::ItemKind::Const(
 300                     self.lower_ty(
 301                         t,
 302                         if self.sess.features_untracked().impl_trait_in_bindings {
 303                             ImplTraitContext::OpaqueTy(None)
 304                         } else {
 305                             ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
 306                         }
 307                     ),
 308                     self.lower_const_body(e)
 309                 )
 310             }
 311             ItemKind::Fn(FnSig { ref decl, header }, ref generics, ref body) => {
 312                 let fn_def_id = self.resolver.definitions().local_def_id(id);
 313                 self.with_new_scopes(|this| {
 314                     this.current_item = Some(ident.span);
 315
 316                     // Note: we don't need to change the return type from `T` to
 317                     // `impl Future<Output = T>` here because lower_body
 318                     // only cares about the input argument patterns in the function
 319                     // declaration (decl), not the return types.
 320                     let body_id = this.lower_maybe_async_body(&decl, header.asyncness.node, body);
 321
 322                     let (generics, decl) = this.add_in_band_defs(
 323                         generics,
 324                         fn_def_id,
 325                         AnonymousLifetimeMode::PassThrough,
 326                         |this, idty| this.lower_fn_decl(
 327                             &decl,
 328                             Some((fn_def_id, idty)),
 329                             true,
 330                             header.asyncness.node.opt_return_id()
 331                         ),
 332                     );
 333                     let sig = hir::FnSig { decl, header: this.lower_fn_header(header) };
 334                     hir::ItemKind::Fn(sig, generics, body_id)
 335                 })
 336             }
 337             ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
 338             ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
 339             ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
 340             ItemKind::TyAlias(ref ty, ref generics) => match ty.kind.opaque_top_hack() {
 341                 None => {
 342                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 343                     let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
 344                     hir::ItemKind::TyAlias(ty, generics)
 345                 },
 346                 Some(bounds) => {
 347                     let ty = hir::OpaqueTy {
 348                         generics: self.lower_generics(generics, ImplTraitContext::OpaqueTy(None)),
 349                         bounds: self.lower_param_bounds(bounds, ImplTraitContext::OpaqueTy(None)),
 350                         impl_trait_fn: None,
 351                         origin: hir::OpaqueTyOrigin::TypeAlias,
 352                     };
 353                     hir::ItemKind::OpaqueTy(ty)
 354                 }
 355             }
 356             ItemKind::Enum(ref enum_definition, ref generics) => {
 357                 hir::ItemKind::Enum(
 358                     hir::EnumDef {
 359                         variants: enum_definition
 360                             .variants
 361                             .iter()
 362                             .map(|x| self.lower_variant(x))
 363                             .collect(),
 364                     },
 365                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 366                 )
 367             },
 368             ItemKind::Struct(ref struct_def, ref generics) => {
 369                 let struct_def = self.lower_variant_data(struct_def);
 370                 hir::ItemKind::Struct(
 371                     struct_def,
 372                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 373                 )
 374             }
 375             ItemKind::Union(ref vdata, ref generics) => {
 376                 let vdata = self.lower_variant_data(vdata);
 377                 hir::ItemKind::Union(
 378                     vdata,
 379                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 380                 )
 381             }
 382             ItemKind::Impl(
 383                 unsafety,
 384                 polarity,
 385                 defaultness,
 386                 ref ast_generics,
 387                 ref trait_ref,
 388                 ref ty,
 389                 ref impl_items,
 390             ) => {
 391                 let def_id = self.resolver.definitions().local_def_id(id);
 392
 393                 // Lower the "impl header" first. This ordering is important
 394                 // for in-band lifetimes! Consider `'a` here:
 395                 //
 396                 //     impl Foo<'a> for u32 {
 397                 //         fn method(&'a self) { .. }
 398                 //     }
 399                 //
 400                 // Because we start by lowering the `Foo<'a> for u32`
 401                 // part, we will add `'a` to the list of generics on
 402                 // the impl. When we then encounter it later in the
 403                 // method, it will not be considered an in-band
 404                 // lifetime to be added, but rather a reference to a
 405                 // parent lifetime.
 406                 let lowered_trait_impl_id = self.lower_node_id(id);
 407                 let (generics, (trait_ref, lowered_ty)) = self.add_in_band_defs(
 408                     ast_generics,
 409                     def_id,
 410                     AnonymousLifetimeMode::CreateParameter,
 411                     |this, _| {
 412                         let trait_ref = trait_ref.as_ref().map(|trait_ref| {
 413                             this.lower_trait_ref(trait_ref, ImplTraitContext::disallowed())
 414                         });
 415
 416                         if let Some(ref trait_ref) = trait_ref {
 417                             if let Res::Def(DefKind::Trait, def_id) = trait_ref.path.res {
 418                                 this.trait_impls.entry(def_id).or_default().push(
 419                                     lowered_trait_impl_id);
 420                             }
 421                         }
 422
 423                         let lowered_ty = this.lower_ty(ty, ImplTraitContext::disallowed());
 424
 425                         (trait_ref, lowered_ty)
 426                     },
 427                 );
 428
 429                 let new_impl_items = self.with_in_scope_lifetime_defs(
 430                     &ast_generics.params,
 431                     |this| {
 432                         impl_items
 433                             .iter()
 434                             .map(|item| this.lower_impl_item_ref(item))
 435                             .collect()
 436                     },
 437                 );
 438
 439                 hir::ItemKind::Impl(
 440                     unsafety,
 441                     polarity,
 442                     self.lower_defaultness(defaultness, true /* [1] */),
 443                     generics,
 444                     trait_ref,
 445                     lowered_ty,
 446                     new_impl_items,
 447                 )
 448             }
 449             ItemKind::Trait(is_auto, unsafety, ref generics, ref bounds, ref items) => {
 450                 let bounds = self.lower_param_bounds(bounds, ImplTraitContext::disallowed());
 451                 let items = items
 452                     .iter()
 453                     .map(|item| self.lower_trait_item_ref(item))
 454                     .collect();
 455                 hir::ItemKind::Trait(
 456                     is_auto,
 457                     unsafety,
 458                     self.lower_generics(generics, ImplTraitContext::disallowed()),
 459                     bounds,
 460                     items,
 461                 )
 462             }
 463             ItemKind::TraitAlias(ref generics, ref bounds) => hir::ItemKind::TraitAlias(
 464                 self.lower_generics(generics, ImplTraitContext::disallowed()),
 465                 self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 466             ),
 467             ItemKind::MacroDef(..)
 468             | ItemKind::Mac(..) => bug!("`TyMac` should have been expanded by now"),
 469         }
 470
 471         // [1] `defaultness.has_value()` is never called for an `impl`, always `true` in order to
 472         //     not cause an assertion failure inside the `lower_defaultness` function.
 473     }
 474
 475     fn lower_use_tree(
 476         &mut self,
 477         tree: &UseTree,
 478         prefix: &Path,
 479         id: NodeId,
 480         vis: &mut hir::Visibility,
 481         ident: &mut Ident,
 482         attrs: &hir::HirVec<Attribute>,
 483     ) -> hir::ItemKind {
 484         debug!("lower_use_tree(tree={:?})", tree);
 485         debug!("lower_use_tree: vis = {:?}", vis);
 486
 487         let path = &tree.prefix;
 488         let segments = prefix
 489             .segments
 490             .iter()
 491             .chain(path.segments.iter())
 492             .cloned()
 493             .collect();
 494
 495         match tree.kind {
 496             UseTreeKind::Simple(rename, id1, id2) => {
 497                 *ident = tree.ident();
 498
 499                 // First, apply the prefix to the path.
 500                 let mut path = Path {
 501                     segments,
 502                     span: path.span,
 503                 };
 504
 505                 // Correctly resolve `self` imports.
 506                 if path.segments.len() > 1
 507                     && path.segments.last().unwrap().ident.name == kw::SelfLower
 508                 {
 509                     let _ = path.segments.pop();
 510                     if rename.is_none() {
 511                         *ident = path.segments.last().unwrap().ident;
 512                     }
 513                 }
 514
 515                 let mut resolutions = self.expect_full_res_from_use(id);
 516                 // We want to return *something* from this function, so hold onto the first item
 517                 // for later.
 518                 let ret_res = self.lower_res(resolutions.next().unwrap_or(Res::Err));
 519
 520                 // Here, we are looping over namespaces, if they exist for the definition
 521                 // being imported. We only handle type and value namespaces because we
 522                 // won't be dealing with macros in the rest of the compiler.
 523                 // Essentially a single `use` which imports two names is desugared into
 524                 // two imports.
 525                 for (res, &new_node_id) in resolutions.zip([id1, id2].iter()) {
 526                     let ident = *ident;
 527                     let mut path = path.clone();
 528                     for seg in &mut path.segments {
 529                         seg.id = self.resolver.next_node_id();
 530                     }
 531                     let span = path.span;
 532
 533                     self.with_hir_id_owner(new_node_id, |this| {
 534                         let new_id = this.lower_node_id(new_node_id);
 535                         let res = this.lower_res(res);
 536                         let path =
 537                             this.lower_path_extra(res, &path, ParamMode::Explicit, None);
 538                         let kind = hir::ItemKind::Use(P(path), hir::UseKind::Single);
 539                         let vis = this.rebuild_vis(&vis);
 540
 541                         this.insert_item(
 542                             hir::Item {
 543                                 hir_id: new_id,
 544                                 ident,
 545                                 attrs: attrs.into_iter().cloned().collect(),
 546                                 kind,
 547                                 vis,
 548                                 span,
 549                             },
 550                         );
 551                     });
 552                 }
 553
 554                 let path = P(self.lower_path_extra(ret_res, &path, ParamMode::Explicit, None));
 555                 hir::ItemKind::Use(path, hir::UseKind::Single)
 556             }
 557             UseTreeKind::Glob => {
 558                 let path = P(self.lower_path(
 559                     id,
 560                     &Path {
 561                         segments,
 562                         span: path.span,
 563                     },
 564                     ParamMode::Explicit,
 565                 ));
 566                 hir::ItemKind::Use(path, hir::UseKind::Glob)
 567             }
 568             UseTreeKind::Nested(ref trees) => {
 569                 // Nested imports are desugared into simple imports.
 570                 // So, if we start with
 571                 //
 572                 // ```
 573                 // pub(x) use foo::{a, b};
 574                 // ```
 575                 //
 576                 // we will create three items:
 577                 //
 578                 // ```
 579                 // pub(x) use foo::a;
 580                 // pub(x) use foo::b;
 581                 // pub(x) use foo::{}; // <-- this is called the `ListStem`
 582                 // ```
 583                 //
 584                 // The first two are produced by recursively invoking
 585                 // `lower_use_tree` (and indeed there may be things
 586                 // like `use foo::{a::{b, c}}` and so forth).  They
 587                 // wind up being directly added to
 588                 // `self.items`. However, the structure of this
 589                 // function also requires us to return one item, and
 590                 // for that we return the `{}` import (called the
 591                 // `ListStem`).
 592
 593                 let prefix = Path {
 594                     segments,
 595                     span: prefix.span.to(path.span),
 596                 };
 597
 598                 // Add all the nested `PathListItem`s to the HIR.
 599                 for &(ref use_tree, id) in trees {
 600                     let new_hir_id = self.lower_node_id(id);
 601
 602                     let mut prefix = prefix.clone();
 603
 604                     // Give the segments new node-ids since they are being cloned.
 605                     for seg in &mut prefix.segments {
 606                         seg.id = self.resolver.next_node_id();
 607                     }
 608
 609                     // Each `use` import is an item and thus are owners of the
 610                     // names in the path. Up to this point the nested import is
 611                     // the current owner, since we want each desugared import to
 612                     // own its own names, we have to adjust the owner before
 613                     // lowering the rest of the import.
 614                     self.with_hir_id_owner(id, |this| {
 615                         let mut vis = this.rebuild_vis(&vis);
 616                         let mut ident = *ident;
 617
 618                         let kind = this.lower_use_tree(use_tree,
 619                                                        &prefix,
 620                                                        id,
 621                                                        &mut vis,
 622                                                        &mut ident,
 623                                                        attrs);
 624
 625                         this.insert_item(
 626                             hir::Item {
 627                                 hir_id: new_hir_id,
 628                                 ident,
 629                                 attrs: attrs.into_iter().cloned().collect(),
 630                                 kind,
 631                                 vis,
 632                                 span: use_tree.span,
 633                             },
 634                         );
 635                     });
 636                 }
 637
 638                 // Subtle and a bit hacky: we lower the privacy level
 639                 // of the list stem to "private" most of the time, but
 640                 // not for "restricted" paths. The key thing is that
 641                 // we don't want it to stay as `pub` (with no caveats)
 642                 // because that affects rustdoc and also the lints
 643                 // about `pub` items. But we can't *always* make it
 644                 // private -- particularly not for restricted paths --
 645                 // because it contains node-ids that would then be
 646                 // unused, failing the check that HirIds are "densely
 647                 // assigned".
 648                 match vis.node {
 649                     hir::VisibilityKind::Public |
 650                     hir::VisibilityKind::Crate(_) |
 651                     hir::VisibilityKind::Inherited => {
 652                         *vis = respan(prefix.span.shrink_to_lo(), hir::VisibilityKind::Inherited);
 653                     }
 654                     hir::VisibilityKind::Restricted { .. } => {
 655                         // Do nothing here, as described in the comment on the match.
 656                     }
 657                 }
 658
 659                 let res = self.expect_full_res_from_use(id).next().unwrap_or(Res::Err);
 660                 let res = self.lower_res(res);
 661                 let path = P(self.lower_path_extra(res, &prefix, ParamMode::Explicit, None));
 662                 hir::ItemKind::Use(path, hir::UseKind::ListStem)
 663             }
 664         }
 665     }
 666
 667     /// Paths like the visibility path in `pub(super) use foo::{bar, baz}` are repeated
 668     /// many times in the HIR tree; for each occurrence, we need to assign distinct
 669     /// `NodeId`s. (See, e.g., #56128.)
 670     fn rebuild_use_path(&mut self, path: &hir::Path) -> hir::Path {
 671         debug!("rebuild_use_path(path = {:?})", path);
 672         let segments = path.segments.iter().map(|seg| hir::PathSegment {
 673             ident: seg.ident,
 674             hir_id: seg.hir_id.map(|_| self.next_id()),
 675             res: seg.res,
 676             args: None,
 677             infer_args: seg.infer_args,
 678         }).collect();
 679         hir::Path {
 680             span: path.span,
 681             res: path.res,
 682             segments,
 683         }
 684     }
 685
 686     fn rebuild_vis(&mut self, vis: &hir::Visibility) -> hir::Visibility {
 687         let vis_kind = match vis.node {
 688             hir::VisibilityKind::Public => hir::VisibilityKind::Public,
 689             hir::VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 690             hir::VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
 691             hir::VisibilityKind::Restricted { ref path, hir_id: _ } => {
 692                 hir::VisibilityKind::Restricted {
 693                     path: P(self.rebuild_use_path(path)),
 694                     hir_id: self.next_id(),
 695                 }
 696             }
 697         };
 698         respan(vis.span, vis_kind)
 699     }
 700
 701     fn lower_foreign_item(&mut self, i: &ForeignItem) -> hir::ForeignItem {
 702         let def_id = self.resolver.definitions().local_def_id(i.id);
 703         hir::ForeignItem {
 704             hir_id: self.lower_node_id(i.id),
 705             ident: i.ident,
 706             attrs: self.lower_attrs(&i.attrs),
 707             kind: match i.kind {
 708                 ForeignItemKind::Fn(ref fdec, ref generics) => {
 709                     let (generics, (fn_dec, fn_args)) = self.add_in_band_defs(
 710                         generics,
 711                         def_id,
 712                         AnonymousLifetimeMode::PassThrough,
 713                         |this, _| {
 714                             (
 715                                 // Disallow `impl Trait` in foreign items.
 716                                 this.lower_fn_decl(fdec, None, false, None),
 717                                 this.lower_fn_params_to_names(fdec),
 718                             )
 719                         },
 720                     );
 721
 722                     hir::ForeignItemKind::Fn(fn_dec, fn_args, generics)
 723                 }
 724                 ForeignItemKind::Static(ref t, m) => {
 725                     hir::ForeignItemKind::Static(
 726                         self.lower_ty(t, ImplTraitContext::disallowed()), m)
 727                 }
 728                 ForeignItemKind::Ty => hir::ForeignItemKind::Type,
 729                 ForeignItemKind::Macro(_) => panic!("macro shouldn't exist here"),
 730             },
 731             vis: self.lower_visibility(&i.vis, None),
 732             span: i.span,
 733         }
 734     }
 735
 736     fn lower_foreign_mod(&mut self, fm: &ForeignMod) -> hir::ForeignMod {
 737         hir::ForeignMod {
 738             abi: self.lower_abi(fm.abi),
 739             items: fm.items
 740                 .iter()
 741                 .map(|x| self.lower_foreign_item(x))
 742                 .collect(),
 743         }
 744     }
 745
 746     fn lower_global_asm(&mut self, ga: &GlobalAsm) -> P<hir::GlobalAsm> {
 747         P(hir::GlobalAsm { asm: ga.asm })
 748     }
 749
 750     fn lower_variant(&mut self, v: &Variant) -> hir::Variant {
 751         hir::Variant {
 752             attrs: self.lower_attrs(&v.attrs),
 753             data: self.lower_variant_data(&v.data),
 754             disr_expr: v.disr_expr.as_ref().map(|e| self.lower_anon_const(e)),
 755             id: self.lower_node_id(v.id),
 756             ident: v.ident,
 757             span: v.span,
 758         }
 759     }
 760
 761     fn lower_variant_data(&mut self, vdata: &VariantData) -> hir::VariantData {
 762         match *vdata {
 763             VariantData::Struct(ref fields, recovered) => hir::VariantData::Struct(
 764                 fields.iter().enumerate().map(|f| self.lower_struct_field(f)).collect(),
 765                 recovered,
 766             ),
 767             VariantData::Tuple(ref fields, id) => {
 768                 hir::VariantData::Tuple(
 769                     fields
 770                         .iter()
 771                         .enumerate()
 772                         .map(|f| self.lower_struct_field(f))
 773                         .collect(),
 774                     self.lower_node_id(id),
 775                 )
 776             },
 777             VariantData::Unit(id) => {
 778                 hir::VariantData::Unit(self.lower_node_id(id))
 779             },
 780         }
 781     }
 782
 783     fn lower_struct_field(&mut self, (index, f): (usize, &StructField)) -> hir::StructField {
 784         let ty = if let TyKind::Path(ref qself, ref path) = f.ty.kind {
 785             let t = self.lower_path_ty(
 786                 &f.ty,
 787                 qself,
 788                 path,
 789                 ParamMode::ExplicitNamed, // no `'_` in declarations (Issue #61124)
 790                 ImplTraitContext::disallowed()
 791             );
 792             P(t)
 793         } else {
 794             self.lower_ty(&f.ty, ImplTraitContext::disallowed())
 795         };
 796         hir::StructField {
 797             span: f.span,
 798             hir_id: self.lower_node_id(f.id),
 799             ident: match f.ident {
 800                 Some(ident) => ident,
 801                 // FIXME(jseyfried): positional field hygiene.
 802                 None => Ident::new(sym::integer(index), f.span),
 803             },
 804             vis: self.lower_visibility(&f.vis, None),
 805             ty,
 806             attrs: self.lower_attrs(&f.attrs),
 807         }
 808     }
 809
 810     fn lower_trait_item(&mut self, i: &TraitItem) -> hir::TraitItem {
 811         let trait_item_def_id = self.resolver.definitions().local_def_id(i.id);
 812
 813         let (generics, kind) = match i.kind {
 814             TraitItemKind::Const(ref ty, ref default) => (
 815                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 816                 hir::TraitItemKind::Const(
 817                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 818                     default
 819                         .as_ref()
 820                         .map(|x| self.lower_const_body(x)),
 821                 ),
 822             ),
 823             TraitItemKind::Method(ref sig, None) => {
 824                 let names = self.lower_fn_params_to_names(&sig.decl);
 825                 let (generics, sig) = self.lower_method_sig(
 826                     &i.generics,
 827                     sig,
 828                     trait_item_def_id,
 829                     false,
 830                     None,
 831                 );
 832                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Required(names)))
 833             }
 834             TraitItemKind::Method(ref sig, Some(ref body)) => {
 835                 let body_id = self.lower_fn_body_block(&sig.decl, body);
 836                 let (generics, sig) = self.lower_method_sig(
 837                     &i.generics,
 838                     sig,
 839                     trait_item_def_id,
 840                     false,
 841                     None,
 842                 );
 843                 (generics, hir::TraitItemKind::Method(sig, hir::TraitMethod::Provided(body_id)))
 844             }
 845             TraitItemKind::Type(ref bounds, ref default) => {
 846                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 847                 let kind = hir::TraitItemKind::Type(
 848                     self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
 849                     default
 850                         .as_ref()
 851                         .map(|x| self.lower_ty(x, ImplTraitContext::disallowed())),
 852                 );
 853
 854                 (generics, kind)
 855             },
 856             TraitItemKind::Macro(..) => bug!("macro item shouldn't exist at this point"),
 857         };
 858
 859         hir::TraitItem {
 860             hir_id: self.lower_node_id(i.id),
 861             ident: i.ident,
 862             attrs: self.lower_attrs(&i.attrs),
 863             generics,
 864             kind,
 865             span: i.span,
 866         }
 867     }
 868
 869     fn lower_trait_item_ref(&mut self, i: &TraitItem) -> hir::TraitItemRef {
 870         let (kind, has_default) = match i.kind {
 871             TraitItemKind::Const(_, ref default) => {
 872                 (hir::AssocItemKind::Const, default.is_some())
 873             }
 874             TraitItemKind::Type(_, ref default) => {
 875                 (hir::AssocItemKind::Type, default.is_some())
 876             }
 877             TraitItemKind::Method(ref sig, ref default) => (
 878                 hir::AssocItemKind::Method {
 879                     has_self: sig.decl.has_self(),
 880                 },
 881                 default.is_some(),
 882             ),
 883             TraitItemKind::Macro(..) => unimplemented!(),
 884         };
 885         hir::TraitItemRef {
 886             id: hir::TraitItemId { hir_id: self.lower_node_id(i.id) },
 887             ident: i.ident,
 888             span: i.span,
 889             defaultness: self.lower_defaultness(Defaultness::Default, has_default),
 890             kind,
 891         }
 892     }
 893
 894     fn lower_impl_item(&mut self, i: &ImplItem) -> hir::ImplItem {
 895         let impl_item_def_id = self.resolver.definitions().local_def_id(i.id);
 896
 897         let (generics, kind) = match i.kind {
 898             ImplItemKind::Const(ref ty, ref expr) => (
 899                 self.lower_generics(&i.generics, ImplTraitContext::disallowed()),
 900                 hir::ImplItemKind::Const(
 901                     self.lower_ty(ty, ImplTraitContext::disallowed()),
 902                     self.lower_const_body(expr),
 903                 ),
 904             ),
 905             ImplItemKind::Method(ref sig, ref body) => {
 906                 self.current_item = Some(i.span);
 907                 let body_id = self.lower_maybe_async_body(
 908                     &sig.decl, sig.header.asyncness.node, body
 909                 );
 910                 let impl_trait_return_allow = !self.is_in_trait_impl;
 911                 let (generics, sig) = self.lower_method_sig(
 912                     &i.generics,
 913                     sig,
 914                     impl_item_def_id,
 915                     impl_trait_return_allow,
 916                     sig.header.asyncness.node.opt_return_id(),
 917                 );
 918
 919                 (generics, hir::ImplItemKind::Method(sig, body_id))
 920             }
 921             ImplItemKind::TyAlias(ref ty) => {
 922                 let generics = self.lower_generics(&i.generics, ImplTraitContext::disallowed());
 923                 let kind = match ty.kind.opaque_top_hack() {
 924                     None => {
 925                         let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
 926                         hir::ImplItemKind::TyAlias(ty)
 927                     }
 928                     Some(bs) => {
 929                         let bounds = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
 930                         hir::ImplItemKind::OpaqueTy(bounds)
 931                     }
 932                 };
 933                 (generics, kind)
 934             },
 935             ImplItemKind::Macro(..) => bug!("`TyMac` should have been expanded by now"),
 936         };
 937
 938         hir::ImplItem {
 939             hir_id: self.lower_node_id(i.id),
 940             ident: i.ident,
 941             attrs: self.lower_attrs(&i.attrs),
 942             generics,
 943             vis: self.lower_visibility(&i.vis, None),
 944             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 945             kind,
 946             span: i.span,
 947         }
 948
 949         // [1] since `default impl` is not yet implemented, this is always true in impls
 950     }
 951
 952     fn lower_impl_item_ref(&mut self, i: &ImplItem) -> hir::ImplItemRef {
 953         hir::ImplItemRef {
 954             id: hir::ImplItemId { hir_id: self.lower_node_id(i.id) },
 955             ident: i.ident,
 956             span: i.span,
 957             vis: self.lower_visibility(&i.vis, Some(i.id)),
 958             defaultness: self.lower_defaultness(i.defaultness, true /* [1] */),
 959             kind: match &i.kind {
 960                 ImplItemKind::Const(..) => hir::AssocItemKind::Const,
 961                 ImplItemKind::TyAlias(ty) => match ty.kind.opaque_top_hack() {
 962                     None => hir::AssocItemKind::Type,
 963                     Some(_) => hir::AssocItemKind::OpaqueTy,
 964                 },
 965                 ImplItemKind::Method(sig, _) => hir::AssocItemKind::Method {
 966                     has_self: sig.decl.has_self(),
 967                 },
 968                 ImplItemKind::Macro(..) => unimplemented!(),
 969             },
 970         }
 971
 972         // [1] since `default impl` is not yet implemented, this is always true in impls
 973     }
 974
 975     /// If an `explicit_owner` is given, this method allocates the `HirId` in
 976     /// the address space of that item instead of the item currently being
 977     /// lowered. This can happen during `lower_impl_item_ref()` where we need to
 978     /// lower a `Visibility` value although we haven't lowered the owning
 979     /// `ImplItem` in question yet.
 980     fn lower_visibility(
 981         &mut self,
 982         v: &Visibility,
 983         explicit_owner: Option<NodeId>,
 984     ) -> hir::Visibility {
 985         let node = match v.node {
 986             VisibilityKind::Public => hir::VisibilityKind::Public,
 987             VisibilityKind::Crate(sugar) => hir::VisibilityKind::Crate(sugar),
 988             VisibilityKind::Restricted { ref path, id } => {
 989                 debug!("lower_visibility: restricted path id = {:?}", id);
 990                 let lowered_id = if let Some(owner) = explicit_owner {
 991                     self.lower_node_id_with_owner(id, owner)
 992                 } else {
 993                     self.lower_node_id(id)
 994                 };
 995                 let res = self.expect_full_res(id);
 996                 let res = self.lower_res(res);
 997                 hir::VisibilityKind::Restricted {
 998                     path: P(self.lower_path_extra(
 999                         res,
1000                         path,
1001                         ParamMode::Explicit,
1002                         explicit_owner,
1003                     )),
1004                     hir_id: lowered_id,
1005                 }
1006             },
1007             VisibilityKind::Inherited => hir::VisibilityKind::Inherited,
1008         };
1009         respan(v.span, node)
1010     }
1011
1012     fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
1013         match d {
1014             Defaultness::Default => hir::Defaultness::Default {
1015                 has_value: has_value,
1016             },
1017             Defaultness::Final => {
1018                 assert!(has_value);
1019                 hir::Defaultness::Final
1020             }
1021         }
1022     }
1023
1024     fn record_body(&mut self, params: HirVec<hir::Param>, value: hir::Expr) -> hir::BodyId {
1025         let body = hir::Body {
1026             generator_kind: self.generator_kind,
1027             params,
1028             value,
1029         };
1030         let id = body.id();
1031         self.bodies.insert(id, body);
1032         id
1033     }
1034
1035     fn lower_body(
1036         &mut self,
1037         f: impl FnOnce(&mut LoweringContext<'_>) -> (HirVec<hir::Param>, hir::Expr),
1038     ) -> hir::BodyId {
1039         let prev_gen_kind = self.generator_kind.take();
1040         let (parameters, result) = f(self);
1041         let body_id = self.record_body(parameters, result);
1042         self.generator_kind = prev_gen_kind;
1043         body_id
1044     }
1045
1046     fn lower_param(&mut self, param: &Param) -> hir::Param {
1047         hir::Param {
1048             attrs: self.lower_attrs(&param.attrs),
1049             hir_id: self.lower_node_id(param.id),
1050             pat: self.lower_pat(&param.pat),
1051             span: param.span,
1052         }
1053     }
1054
1055     pub(super) fn lower_fn_body(
1056         &mut self,
1057         decl: &FnDecl,
1058         body: impl FnOnce(&mut LoweringContext<'_>) -> hir::Expr,
1059     ) -> hir::BodyId {
1060         self.lower_body(|this| (
1061             decl.inputs.iter().map(|x| this.lower_param(x)).collect(),
1062             body(this),
1063         ))
1064     }
1065
1066     fn lower_fn_body_block(&mut self, decl: &FnDecl, body: &Block) -> hir::BodyId {
1067         self.lower_fn_body(decl, |this| this.lower_block_expr(body))
1068     }
1069
1070     pub(super) fn lower_const_body(&mut self, expr: &Expr) -> hir::BodyId {
1071         self.lower_body(|this| (hir_vec![], this.lower_expr(expr)))
1072     }
1073
1074     fn lower_maybe_async_body(
1075         &mut self,
1076         decl: &FnDecl,
1077         asyncness: IsAsync,
1078         body: &Block,
1079     ) -> hir::BodyId {
1080         let closure_id = match asyncness {
1081             IsAsync::Async { closure_id, .. } => closure_id,
1082             IsAsync::NotAsync => return self.lower_fn_body_block(decl, body),
1083         };
1084
1085         self.lower_body(|this| {
1086             let mut parameters: Vec<hir::Param> = Vec::new();
1087             let mut statements: Vec<hir::Stmt> = Vec::new();
1088
1089             // Async function parameters are lowered into the closure body so that they are
1090             // captured and so that the drop order matches the equivalent non-async functions.
1091             //
1092             // from:
1093             //
1094             //     async fn foo(<pattern>: <ty>, <pattern>: <ty>, <pattern>: <ty>) {
1095             //         <body>
1096             //     }
1097             //
1098             // into:
1099             //
1100             //     fn foo(__arg0: <ty>, __arg1: <ty>, __arg2: <ty>) {
1101             //       async move {
1102             //         let __arg2 = __arg2;
1103             //         let <pattern> = __arg2;
1104             //         let __arg1 = __arg1;
1105             //         let <pattern> = __arg1;
1106             //         let __arg0 = __arg0;
1107             //         let <pattern> = __arg0;
1108             //         drop-temps { <body> } // see comments later in fn for details
1109             //       }
1110             //     }
1111             //
1112             // If `<pattern>` is a simple ident, then it is lowered to a single
1113             // `let <pattern> = <pattern>;` statement as an optimization.
1114             //
1115             // Note that the body is embedded in `drop-temps`; an
1116             // equivalent desugaring would be `return { <body>
1117             // };`. The key point is that we wish to drop all the
1118             // let-bound variables and temporaries created in the body
1119             // (and its tail expression!) before we drop the
1120             // parameters (c.f. rust-lang/rust#64512).
1121             for (index, parameter) in decl.inputs.iter().enumerate() {
1122                 let parameter = this.lower_param(parameter);
1123                 let span = parameter.pat.span;
1124
1125                 // Check if this is a binding pattern, if so, we can optimize and avoid adding a
1126                 // `let <pat> = __argN;` statement. In this case, we do not rename the parameter.
1127                 let (ident, is_simple_parameter) = match parameter.pat.kind {
1128                     hir::PatKind::Binding(hir::BindingAnnotation::Unannotated, _, ident, _) =>
1129                         (ident, true),
1130                     _ => {
1131                         // Replace the ident for bindings that aren't simple.
1132                         let name = format!("__arg{}", index);
1133                         let ident = Ident::from_str(&name);
1134
1135                         (ident, false)
1136                     },
1137                 };
1138
1139                 let desugared_span =
1140                     this.mark_span_with_reason(DesugaringKind::Async, span, None);
1141
1142                 // Construct a parameter representing `__argN: <ty>` to replace the parameter of the
1143                 // async function.
1144                 //
1145                 // If this is the simple case, this parameter will end up being the same as the
1146                 // original parameter, but with a different pattern id.
1147                 let mut stmt_attrs = ThinVec::new();
1148                 stmt_attrs.extend(parameter.attrs.iter().cloned());
1149                 let (new_parameter_pat, new_parameter_id) = this.pat_ident(desugared_span, ident);
1150                 let new_parameter = hir::Param {
1151                     attrs: parameter.attrs,
1152                     hir_id: parameter.hir_id,
1153                     pat: new_parameter_pat,
1154                     span: parameter.span,
1155                 };
1156
1157
1158                 if is_simple_parameter {
1159                     // If this is the simple case, then we only insert one statement that is
1160                     // `let <pat> = <pat>;`. We re-use the original argument's pattern so that
1161                     // `HirId`s are densely assigned.
1162                     let expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1163                     let stmt = this.stmt_let_pat(
1164                         stmt_attrs,
1165                         desugared_span,
1166                         Some(P(expr)),
1167                         parameter.pat,
1168                         hir::LocalSource::AsyncFn
1169                     );
1170                     statements.push(stmt);
1171                 } else {
1172                     // If this is not the simple case, then we construct two statements:
1173                     //
1174                     // ```
1175                     // let __argN = __argN;
1176                     // let <pat> = __argN;
1177                     // ```
1178                     //
1179                     // The first statement moves the parameter into the closure and thus ensures
1180                     // that the drop order is correct.
1181                     //
1182                     // The second statement creates the bindings that the user wrote.
1183
1184                     // Construct the `let mut __argN = __argN;` statement. It must be a mut binding
1185                     // because the user may have specified a `ref mut` binding in the next
1186                     // statement.
1187                     let (move_pat, move_id) = this.pat_ident_binding_mode(
1188                         desugared_span, ident, hir::BindingAnnotation::Mutable);
1189                     let move_expr = this.expr_ident(desugared_span, ident, new_parameter_id);
1190                     let move_stmt = this.stmt_let_pat(
1191                         ThinVec::new(),
1192                         desugared_span,
1193                         Some(P(move_expr)),
1194                         move_pat,
1195                         hir::LocalSource::AsyncFn
1196                     );
1197
1198                     // Construct the `let <pat> = __argN;` statement. We re-use the original
1199                     // parameter's pattern so that `HirId`s are densely assigned.
1200                     let pattern_expr = this.expr_ident(desugared_span, ident, move_id);
1201                     let pattern_stmt = this.stmt_let_pat(
1202                         stmt_attrs,
1203                         desugared_span,
1204                         Some(P(pattern_expr)),
1205                         parameter.pat,
1206                         hir::LocalSource::AsyncFn
1207                     );
1208
1209                     statements.push(move_stmt);
1210                     statements.push(pattern_stmt);
1211                 };
1212
1213                 parameters.push(new_parameter);
1214             }
1215
1216             let async_expr = this.make_async_expr(
1217                 CaptureBy::Value,
1218                 closure_id,
1219                 None,
1220                 body.span,
1221                 hir::AsyncGeneratorKind::Fn,
1222                 |this| {
1223                     // Create a block from the user's function body:
1224                     let user_body = this.lower_block_expr(body);
1225
1226                     // Transform into `drop-temps { <user-body> }`, an expression:
1227                     let desugared_span = this.mark_span_with_reason(
1228                         DesugaringKind::Async,
1229                         user_body.span,
1230                         None,
1231                     );
1232                     let user_body = this.expr_drop_temps(
1233                         desugared_span,
1234                         P(user_body),
1235                         ThinVec::new(),
1236                     );
1237
1238                     // As noted above, create the final block like
1239                     //
1240                     // ```
1241                     // {
1242                     //   let $param_pattern = $raw_param;
1243                     //   ...
1244                     //   drop-temps { <user-body> }
1245                     // }
1246                     // ```
1247                     let body = this.block_all(
1248                         desugared_span,
1249                         statements.into(),
1250                         Some(P(user_body)),
1251                     );
1252                     this.expr_block(P(body), ThinVec::new())
1253                 });
1254             (HirVec::from(parameters), this.expr(body.span, async_expr, ThinVec::new()))
1255         })
1256     }
1257
1258     fn lower_method_sig(
1259         &mut self,
1260         generics: &Generics,
1261         sig: &FnSig,
1262         fn_def_id: DefId,
1263         impl_trait_return_allow: bool,
1264         is_async: Option<NodeId>,
1265     ) -> (hir::Generics, hir::FnSig) {
1266         let header = self.lower_fn_header(sig.header);
1267         let (generics, decl) = self.add_in_band_defs(
1268             generics,
1269             fn_def_id,
1270             AnonymousLifetimeMode::PassThrough,
1271             |this, idty| this.lower_fn_decl(
1272                 &sig.decl,
1273                 Some((fn_def_id, idty)),
1274                 impl_trait_return_allow,
1275                 is_async,
1276             ),
1277         );
1278         (generics, hir::FnSig { header, decl })
1279     }
1280
1281     fn lower_fn_header(&mut self, h: FnHeader) -> hir::FnHeader {
1282         hir::FnHeader {
1283             unsafety: h.unsafety,
1284             asyncness: self.lower_asyncness(h.asyncness.node),
1285             constness: h.constness.node,
1286             abi: self.lower_abi(h.abi),
1287         }
1288     }
1289
1290     pub(super) fn lower_abi(&mut self, abi: Abi) -> abi::Abi {
1291         abi::lookup(&abi.symbol.as_str()).unwrap_or_else(|| {
1292             self.error_on_invalid_abi(abi);
1293             abi::Abi::Rust
1294         })
1295     }
1296
1297     fn error_on_invalid_abi(&self, abi: Abi) {
1298         struct_span_err!(
1299             self.sess,
1300             abi.span,
1301             E0703,
1302             "invalid ABI: found `{}`",
1303             abi.symbol
1304         )
1305         .span_label(abi.span, "invalid ABI")
1306         .help(&format!("valid ABIs: {}", abi::all_names().join(", ")))
1307         .emit();
1308     }
1309
1310     fn lower_asyncness(&mut self, a: IsAsync) -> hir::IsAsync {
1311         match a {
1312             IsAsync::Async { .. } => hir::IsAsync::Async,
1313             IsAsync::NotAsync => hir::IsAsync::NotAsync,
1314         }
1315     }
1316
1317     pub(super) fn lower_generics(
1318         &mut self,
1319         generics: &Generics,
1320         itctx: ImplTraitContext<'_>)
1321         -> hir::Generics
1322     {
1323         // Collect `?Trait` bounds in where clause and move them to parameter definitions.
1324         // FIXME: this could probably be done with less rightward drift. It also looks like two
1325         // control paths where `report_error` is called are the only paths that advance to after the
1326         // match statement, so the error reporting could probably just be moved there.
1327         let mut add_bounds: NodeMap<Vec<_>> = Default::default();
1328         for pred in &generics.where_clause.predicates {
1329             if let WherePredicate::BoundPredicate(ref bound_pred) = *pred {
1330                 'next_bound: for bound in &bound_pred.bounds {
1331                     if let GenericBound::Trait(_, TraitBoundModifier::Maybe) = *bound {
1332                         let report_error = |this: &mut Self| {
1333                             this.diagnostic().span_err(
1334                                 bound_pred.bounded_ty.span,
1335                                 "`?Trait` bounds are only permitted at the \
1336                                  point where a type parameter is declared",
1337                             );
1338                         };
1339                         // Check if the where clause type is a plain type parameter.
1340                         match bound_pred.bounded_ty.kind {
1341                             TyKind::Path(None, ref path)
1342                                 if path.segments.len() == 1
1343                                     && bound_pred.bound_generic_params.is_empty() =>
1344                             {
1345                                 if let Some(Res::Def(DefKind::TyParam, def_id)) = self.resolver
1346                                     .get_partial_res(bound_pred.bounded_ty.id)
1347                                     .map(|d| d.base_res())
1348                                 {
1349                                     if let Some(node_id) =
1350                                         self.resolver.definitions().as_local_node_id(def_id)
1351                                     {
1352                                         for param in &generics.params {
1353                                             match param.kind {
1354                                                 GenericParamKind::Type { .. } => {
1355                                                     if node_id == param.id {
1356                                                         add_bounds.entry(param.id)
1357                                                             .or_default()
1358                                                             .push(bound.clone());
1359                                                         continue 'next_bound;
1360                                                     }
1361                                                 }
1362                                                 _ => {}
1363                                             }
1364                                         }
1365                                     }
1366                                 }
1367                                 report_error(self)
1368                             }
1369                             _ => report_error(self),
1370                         }
1371                     }
1372                 }
1373             }
1374         }
1375
1376         hir::Generics {
1377             params: self.lower_generic_params(&generics.params, &add_bounds, itctx),
1378             where_clause: self.lower_where_clause(&generics.where_clause),
1379             span: generics.span,
1380         }
1381     }
1382
1383     fn lower_where_clause(&mut self, wc: &WhereClause) -> hir::WhereClause {
1384         self.with_anonymous_lifetime_mode(
1385             AnonymousLifetimeMode::ReportError,
1386             |this| {
1387                 hir::WhereClause {
1388                     predicates: wc.predicates
1389                         .iter()
1390                         .map(|predicate| this.lower_where_predicate(predicate))
1391                         .collect(),
1392                     span: wc.span,
1393                 }
1394             },
1395         )
1396     }
1397
1398     fn lower_where_predicate(&mut self, pred: &WherePredicate) -> hir::WherePredicate {
1399         match *pred {
1400             WherePredicate::BoundPredicate(WhereBoundPredicate {
1401                 ref bound_generic_params,
1402                 ref bounded_ty,
1403                 ref bounds,
1404                 span,
1405             }) => {
1406                 self.with_in_scope_lifetime_defs(
1407                     &bound_generic_params,
1408                     |this| {
1409                         hir::WherePredicate::BoundPredicate(hir::WhereBoundPredicate {
1410                             bound_generic_params: this.lower_generic_params(
1411                                 bound_generic_params,
1412                                 &NodeMap::default(),
1413                                 ImplTraitContext::disallowed(),
1414                             ),
1415                             bounded_ty: this.lower_ty(bounded_ty, ImplTraitContext::disallowed()),
1416                             bounds: bounds
1417                                 .iter()
1418                                 .filter_map(|bound| match *bound {
1419                                     // Ignore `?Trait` bounds.
1420                                     // They were copied into type parameters already.
1421                                     GenericBound::Trait(_, TraitBoundModifier::Maybe) => None,
1422                                     _ => Some(this.lower_param_bound(
1423                                         bound,
1424                                         ImplTraitContext::disallowed(),
1425                                     )),
1426                                 })
1427                                 .collect(),
1428                             span,
1429                         })
1430                     },
1431                 )
1432             }
1433             WherePredicate::RegionPredicate(WhereRegionPredicate {
1434                 ref lifetime,
1435                 ref bounds,
1436                 span,
1437             }) => hir::WherePredicate::RegionPredicate(hir::WhereRegionPredicate {
1438                 span,
1439                 lifetime: self.lower_lifetime(lifetime),
1440                 bounds: self.lower_param_bounds(bounds, ImplTraitContext::disallowed()),
1441             }),
1442             WherePredicate::EqPredicate(WhereEqPredicate {
1443                 id,
1444                 ref lhs_ty,
1445                 ref rhs_ty,
1446                 span,
1447             }) => {
1448                 hir::WherePredicate::EqPredicate(hir::WhereEqPredicate {
1449                     hir_id: self.lower_node_id(id),
1450                     lhs_ty: self.lower_ty(lhs_ty, ImplTraitContext::disallowed()),
1451                     rhs_ty: self.lower_ty(rhs_ty, ImplTraitContext::disallowed()),
1452                     span,
1453                 })
1454             },
1455         }
1456     }
1457 }