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Rollup merge of #66197 - Centril:transparent-ast, r=varkor

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Push `ast::{ItemKind, ImplItemKind}::OpaqueTy` hack down into lowering

We currently have a hack in the form of `ast::{ItemKind, ImplItemKind}::OpaqueTy` which is constructed literally when you write `type Alias = impl Trait;` but not e.g. `type Alias = Vec<impl Trait>;`. Per https://github.com/rust-lang/rfcs/pull/2515, this needs to change to allow `impl Trait` in nested positions.  This PR achieves this change for the syntactic aspect but not the semantic one, which will require changes in lowering and def collection. In the interim, `TyKind::opaque_top_hack` is introduced to avoid knock-on changes in lowering, collection, and resolve. These hacks can then be removed and fixed one by one until the desired semantics are supported.

r? @varkor
This commit is contained in:
Tyler Mandry 2019-11-15 14:44:47 +01:00 • committed by GitHub
commit c5bb2ec0dd
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27 changed files with 314 additions and 263 deletions
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61
src/librustc_parse/parser/item.rs
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@ -7,7 +7,7 @@ use syntax::ast::{self, Abi, DUMMY_NODE_ID, Ident, Attribute, AttrKind, AttrStyl
use syntax::ast::{ItemKind, ImplItem, ImplItemKind, TraitItem, TraitItemKind, UseTree, UseTreeKind};
use syntax::ast::{PathSegment, IsAuto, Constness, IsAsync, Unsafety, Defaultness};
use syntax::ast::{Visibility, VisibilityKind, Mutability, FnHeader, ForeignItem, ForeignItemKind};
use syntax::ast::{Ty, TyKind, Generics, GenericBounds, TraitRef, EnumDef, VariantData, StructField};
use syntax::ast::{Ty, TyKind, Generics, TraitRef, EnumDef, VariantData, StructField};
use syntax::ast::{Mac, MacDelimiter, Block, BindingMode, FnDecl, FnSig, SelfKind, Param};
use syntax::ptr::P;
use syntax::ThinVec;
@ -24,15 +24,6 @@ use log::debug;
use std::mem;
use errors::{PResult, Applicability, DiagnosticBuilder, StashKey};
/// Whether the type alias or associated type is a concrete type or an opaque type.
#[derive(Debug)]
pub(super) enum AliasKind {
/// Just a new name for the same type.
Weak(P<Ty>),
/// Only trait impls of the type will be usable, not the actual type itself.
OpaqueTy(GenericBounds),
}
pub(super) type ItemInfo = (Ident, ItemKind, Option<Vec<Attribute>>);
impl<'a> Parser<'a> {
@ -269,15 +260,11 @@ impl<'a> Parser<'a> {
return self.mk_item_with_info(attrs, lo, vis, info);
}
if let Some(type_) = self.eat_type() {
let (ident, alias, generics) = type_?;
if self.eat_keyword(kw::Type) {
// TYPE ITEM
let item_ = match alias {
AliasKind::Weak(ty) => ItemKind::TyAlias(ty, generics),
AliasKind::OpaqueTy(bounds) => ItemKind::OpaqueTy(bounds, generics),
};
let span = lo.to(self.prev_span);
return Ok(Some(self.mk_item(span, ident, item_, vis, attrs)));
let (ident, ty, generics) = self.parse_type_alias()?;
let kind = ItemKind::TyAlias(ty, generics);
return self.mk_item_with_info(attrs, lo, vis, (ident, kind, None));
}
if self.eat_keyword(kw::Enum) {
@ -711,13 +698,9 @@ impl<'a> Parser<'a> {
let lo = self.token.span;
let vis = self.parse_visibility(false)?;
let defaultness = self.parse_defaultness();
let (name, kind, generics) = if let Some(type_) = self.eat_type() {
let (name, alias, generics) = type_?;
let kind = match alias {
AliasKind::Weak(typ) => ast::ImplItemKind::TyAlias(typ),
AliasKind::OpaqueTy(bounds) => ast::ImplItemKind::OpaqueTy(bounds),
};
(name, kind, generics)
let (name, kind, generics) = if self.eat_keyword(kw::Type) {
let (name, ty, generics) = self.parse_type_alias()?;
(name, ast::ImplItemKind::TyAlias(ty), generics)
} else if self.is_const_item() {
self.parse_impl_const()?
} else if let Some(mac) = self.parse_assoc_macro_invoc("impl", Some(&vis), at_end)? {
@ -1322,34 +1305,16 @@ impl<'a> Parser<'a> {
})
}
/// Parses `type Foo = Bar;` or returns `None`
/// without modifying the parser state.
fn eat_type(&mut self) -> Option<PResult<'a, (Ident, AliasKind, Generics)>> {
// This parses the grammar:
// Ident ["<"...">"] ["where" ...] ("=" | ":") Ty ";"
if self.eat_keyword(kw::Type) {
Some(self.parse_type_alias())
} else {
None
}
}
/// Parses a type alias or opaque type.
fn parse_type_alias(&mut self) -> PResult<'a, (Ident, AliasKind, Generics)> {
/// Parses the grammar:
/// Ident ["<"...">"] ["where" ...] ("=" | ":") Ty ";"
fn parse_type_alias(&mut self) -> PResult<'a, (Ident, P<Ty>, Generics)> {
let ident = self.parse_ident()?;
let mut tps = self.parse_generics()?;
tps.where_clause = self.parse_where_clause()?;
self.expect(&token::Eq)?;
let alias = if self.check_keyword(kw::Impl) {
self.bump();
let bounds = self.parse_generic_bounds(Some(self.prev_span))?;
AliasKind::OpaqueTy(bounds)
} else {
let ty = self.parse_ty()?;
AliasKind::Weak(ty)
};
let ty = self.parse_ty()?;
self.expect_semi()?;
Ok((ident, alias, tps))
Ok((ident, ty, tps))
}
/// Parses an enum declaration.