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