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Auto merge of #63180 - varkor:trait-alias-impl-trait, r=Centril

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Change opaque type syntax from `existential type` to type alias `impl Trait`

This implements a new feature gate `type_alias_impl_trait` (this is slightly different from the originally proposed feature name, but matches what has been used in discussion since), deprecating the old `existential_types` feature.

The syntax for opaque types has been changed. In addition, the "existential" terminology has been replaced with "opaque", as per previous discussion and the RFC.

This makes partial progress towards implementing https://github.com/rust-lang/rust/issues/63063.

r? @Centril
This commit is contained in:
bors 2019-08-03 02:21:23 +00:00
commit d7270712cb
202 changed files with 1050 additions and 1033 deletions
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14
src/libsyntax/ast.rs
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@ -1488,6 +1488,7 @@ pub enum TraitItemKind {
Macro(Mac),
}
/// Represents anything within an `impl` block.
#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
pub struct ImplItem {
pub id: NodeId,
@ -1502,12 +1503,13 @@ pub struct ImplItem {
pub tokens: Option<TokenStream>,
}
/// Represents various kinds of content within an `impl`.
#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
pub enum ImplItemKind {
Const(P<Ty>, P<Expr>),
Method(MethodSig, P<Block>),
Type(P<Ty>),
Existential(GenericBounds),
OpaqueTy(GenericBounds),
Macro(Mac),
}
@ -1710,7 +1712,7 @@ pub enum TyKind {
///
/// The `NodeId` exists to prevent lowering from having to
/// generate `NodeId`s on the fly, which would complicate
/// the generation of `existential type` items significantly.
/// the generation of opaque `type Foo = impl Trait` items significantly.
ImplTrait(NodeId, GenericBounds),
/// No-op; kept solely so that we can pretty-print faithfully.
Paren(P<Ty>),
@ -2334,10 +2336,10 @@ pub enum ItemKind {
///
/// E.g., `type Foo = Bar<u8>;`.
Ty(P<Ty>, Generics),
/// An existential type declaration (`existential type`).
/// An opaque `impl Trait` type alias.
///
/// E.g., `existential type Foo: Bar + Boo;`.
Existential(GenericBounds, Generics),
/// E.g., `type Foo = impl Bar + Boo;`.
OpaqueTy(GenericBounds, Generics),
/// An enum definition (`enum` or `pub enum`).
///
/// E.g., `enum Foo<A, B> { C<A>, D<B> }`.
@ -2391,7 +2393,7 @@ impl ItemKind {
ItemKind::ForeignMod(..) => "foreign module",
ItemKind::GlobalAsm(..) => "global asm",
ItemKind::Ty(..) => "type alias",
ItemKind::Existential(..) => "existential type",
ItemKind::OpaqueTy(..) => "opaque type",
ItemKind::Enum(..) => "enum",
ItemKind::Struct(..) => "struct",
ItemKind::Union(..) => "union",