Clean up type alias impl trait implementation

src/librustc_ast/ast.rs

@@ -1858,15 +1858,6 @@ impl TyKind {
  pub fn is_unit(&self) -> bool {
  if let TyKind::Tup(ref tys) = *self { tys.is_empty() } else { false }
  }
-
- /// HACK(type_alias_impl_trait, Centril): A temporary crutch used
- /// in lowering to avoid making larger changes there and beyond.
- pub fn opaque_top_hack(&self) -> Option<&GenericBounds> {
- match self {
- Self::ImplTrait(_, bounds) => Some(bounds),
- _ => None,
- }
- }
 }
 
 /// Syntax used to declare a trait object.

src/librustc_ast_lowering/item.rs

@@ -1,12 +1,13 @@
 use super::{AnonymousLifetimeMode, LoweringContext, ParamMode};
-use super::{ImplTraitContext, ImplTraitPosition, ImplTraitTypeIdVisitor};
+use super::{ImplTraitContext, ImplTraitPosition};
 use crate::Arena;
 
 use rustc_ast::ast::*;
 use rustc_ast::attr;
 use rustc_ast::node_id::NodeMap;
 use rustc_ast::ptr::P;
 use rustc_ast::visit::{self, AssocCtxt, Visitor};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
@@ -165,13 +166,6 @@ impl<'hir> LoweringContext<'_, 'hir> {
  }
  ItemKind::MacroDef(..) => SmallVec::new(),
  ItemKind::Fn(..) | ItemKind::Impl { of_trait: None, .. } => smallvec![i.id],
- ItemKind::Static(ref ty, ..) | ItemKind::Const(_, ref ty, ..) => {
- let mut ids = smallvec![i.id];
- if self.sess.features_untracked().impl_trait_in_bindings {
- ImplTraitTypeIdVisitor { ids: &mut ids }.visit_ty(ty);
- }
- ids
- }
  _ => smallvec![i.id],
  };
 
@@ -292,23 +286,25 @@ impl<'hir> LoweringContext<'_, 'hir> {
  ItemKind::Mod(ref m) => hir::ItemKind::Mod(self.lower_mod(m)),
  ItemKind::ForeignMod(ref nm) => hir::ItemKind::ForeignMod(self.lower_foreign_mod(nm)),
  ItemKind::GlobalAsm(ref ga) => hir::ItemKind::GlobalAsm(self.lower_global_asm(ga)),
- ItemKind::TyAlias(_, ref gen, _, Some(ref ty)) => match ty.kind.opaque_top_hack() {
- None => {
- let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
- let generics = self.lower_generics(gen, ImplTraitContext::disallowed());
- hir::ItemKind::TyAlias(ty, generics)
- }
- Some(bounds) => {
- let ctx = || ImplTraitContext::OpaqueTy(None, hir::OpaqueTyOrigin::Misc);
- let ty = hir::OpaqueTy {
- generics: self.lower_generics(gen, ctx()),
- bounds: self.lower_param_bounds(bounds, ctx()),
- impl_trait_fn: None,
- origin: hir::OpaqueTyOrigin::TypeAlias,
- };
- hir::ItemKind::OpaqueTy(ty)
- }
- },
+ ItemKind::TyAlias(_, ref gen, _, Some(ref ty)) => {
+ // We lower
+ //
+ // type Foo = impl Trait
+ //
+ // to
+ //
+ // type Foo = Foo1
+ // opaque type Foo1: Trait
+ let ty = self.lower_ty(
+ ty,
+ ImplTraitContext::OtherOpaqueTy {
+ capturable_lifetimes: &mut FxHashSet::default(),
+ origin: hir::OpaqueTyOrigin::Misc,
+ },
+ );
+ let generics = self.lower_generics(gen, ImplTraitContext::disallowed());
+ hir::ItemKind::TyAlias(ty, generics)
+ }
  ItemKind::TyAlias(_, ref generics, _, None) => {
  let ty = self.arena.alloc(self.ty(span, hir::TyKind::Err));
  let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
@@ -438,8 +434,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
  span: Span,
  body: Option<&Expr>,
  ) -> (&'hir hir::Ty<'hir>, hir::BodyId) {
+ let mut capturable_lifetimes;
  let itctx = if self.sess.features_untracked().impl_trait_in_bindings {
- ImplTraitContext::OpaqueTy(None, hir::OpaqueTyOrigin::Misc)
+ capturable_lifetimes = FxHashSet::default();
+ ImplTraitContext::OtherOpaqueTy {
+ capturable_lifetimes: &mut capturable_lifetimes,
+ origin: hir::OpaqueTyOrigin::Misc,
+ }
  } else {
  ImplTraitContext::Disallowed(ImplTraitPosition::Binding)
  };
@@ -844,16 +845,16 @@ impl<'hir> LoweringContext<'_, 'hir> {
  let ty = self.arena.alloc(self.ty(i.span, hir::TyKind::Err));
  hir::ImplItemKind::TyAlias(ty)
  }
- Some(ty) => match ty.kind.opaque_top_hack() {
- None => {
- let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
- hir::ImplItemKind::TyAlias(ty)
- }
- Some(bs) => {
- let bs = self.lower_param_bounds(bs, ImplTraitContext::disallowed());
-  hir::ImplItemKind::OpaqueTy(bs)
- }
- },
+ Some(ty) => {
+ let ty = self.lower_ty(
+ ty,
+ ImplTraitContext::OtherOpaqueTy {
+  capturable_lifetimes: &mut FxHashSet::default(),
+  origin: hir::OpaqueTyOrigin::Misc,
+ },
+ );
+ hir::ImplItemKind::TyAlias(ty)
+ }
  };
  (generics, kind)
  }
@@ -887,12 +888,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  defaultness,
  kind: match &i.kind {
  AssocItemKind::Const(..) => hir::AssocItemKind::Const,
- AssocItemKind::TyAlias(.., ty) => {
- match ty.as_deref().and_then(|ty| ty.kind.opaque_top_hack()) {
- None => hir::AssocItemKind::Type,
- Some(_) => hir::AssocItemKind::OpaqueTy,
- }
- }
+ AssocItemKind::TyAlias(..) => hir::AssocItemKind::Type,
  AssocItemKind::Fn(_, sig, ..) => {
  hir::AssocItemKind::Fn { has_self: sig.decl.has_self() }
  }