Rollup merge of #69361 - Centril:free-ty-alias, r=petrochenkov

parse: allow `type Foo: Ord` syntactically

This addresses:
> (Work still remains to fuse this with free type aliases, but this can be done later.)

in #69194.

r? @petrochenkov

Author: Dylan-DPC

src/librustc_ast_lowering/item.rs

@@ -297,28 +297,28 @@ 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 ty, ref generics) => match ty.kind.opaque_top_hack() {
+            ItemKind::TyAlias(ref generics, _, Some(ref ty)) => match ty.kind.opaque_top_hack() {
                 None => {
                     let ty = self.lower_ty(ty, ImplTraitContext::disallowed());
                     let generics = self.lower_generics(generics, 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(
-                            generics,
-                            ImplTraitContext::OpaqueTy(None, hir::OpaqueTyOrigin::Misc),
-                        ),
-                        bounds: self.lower_param_bounds(
-                            bounds,
-                            ImplTraitContext::OpaqueTy(None, hir::OpaqueTyOrigin::Misc),
-                        ),
+                        generics: self.lower_generics(generics, ctx()),
+                        bounds: self.lower_param_bounds(bounds, ctx()),
                         impl_trait_fn: None,
                         origin: hir::OpaqueTyOrigin::TypeAlias,
                     };
                     hir::ItemKind::OpaqueTy(ty)
                 }
             },
+            ItemKind::TyAlias(ref generics, _, None) => {
+                let ty = self.arena.alloc(self.ty(span, hir::TyKind::Err));
+                let generics = self.lower_generics(generics, ImplTraitContext::disallowed());
+                hir::ItemKind::TyAlias(ty, generics)
+            }
             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemKind::Enum(
                 hir::EnumDef {
                     variants: self.arena.alloc_from_iter(

src/librustc_ast_lowering/lib.rs

@@ -462,7 +462,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     ItemKind::Struct(_, ref generics)
                     | ItemKind::Union(_, ref generics)
                     | ItemKind::Enum(_, ref generics)
-                    | ItemKind::TyAlias(_, ref generics)
+                    | ItemKind::TyAlias(ref generics, ..)
                     | ItemKind::Trait(_, _, ref generics, ..) => {
                         let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
                         let count = generics

src/librustc_ast_passes/ast_validation.rs

@@ -969,6 +969,13 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                 let msg = "free static item without body";
                 self.error_item_without_body(item.span, "static", msg, " = <expr>;");
             }
+            ItemKind::TyAlias(_, ref bounds, ref body) => {
+                if body.is_none() {
+                    let msg = "free type alias without body";
+                    self.error_item_without_body(item.span, "type", msg, " = <type>;");
+                }
+                self.check_type_no_bounds(bounds, "this context");
+            }
             _ => {}
         }
 

src/librustc_ast_passes/feature_gate.rs

@@ -372,7 +372,7 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 gate_feature_post!(&self, decl_macro, i.span, msg);
             }
 
-            ast::ItemKind::TyAlias(ref ty, ..) => self.check_impl_trait(&ty),
+            ast::ItemKind::TyAlias(_, _, Some(ref ty)) => self.check_impl_trait(&ty),
 
             _ => {}
         }

src/librustc_ast_pretty/pprust.rs

@@ -2,7 +2,7 @@ use crate::pp::Breaks::{Consistent, Inconsistent};
 use crate::pp::{self, Breaks};
 
 use rustc_span::edition::Edition;
-use rustc_span::source_map::{dummy_spanned, SourceMap, Spanned};
+use rustc_span::source_map::{SourceMap, Spanned};
 use rustc_span::symbol::{kw, sym};
 use rustc_span::{BytePos, FileName, Span};
 use syntax::ast::{self, BlockCheckMode, PatKind, RangeEnd, RangeSyntax};
@@ -1026,27 +1026,26 @@ impl<'a> State<'a> {
         span: Span,
         ident: ast::Ident,
         attrs: &[Attribute],
-        defaultness: ast::Defaultness,
+        def: ast::Defaultness,
         kind: &ast::AssocItemKind,
         vis: &ast::Visibility,
     ) {
         self.ann.pre(self, AnnNode::SubItem(id));
         self.hardbreak_if_not_bol();
         self.maybe_print_comment(span.lo());
         self.print_outer_attributes(attrs);
-        self.print_defaultness(defaultness);
         match kind {
             ast::ForeignItemKind::Fn(sig, gen, body) => {
-                self.print_fn_full(sig, ident, gen, vis, body.as_deref(), attrs);
+                self.print_fn_full(sig, ident, gen, vis, def, body.as_deref(), attrs);
             }
             ast::ForeignItemKind::Const(ty, body) => {
-                self.print_item_const(ident, None, ty, body.as_deref(), vis);
+                self.print_item_const(ident, None, ty, body.as_deref(), vis, def);
             }
             ast::ForeignItemKind::Static(ty, mutbl, body) => {
-                self.print_item_const(ident, Some(*mutbl), ty, body.as_deref(), vis);
+                self.print_item_const(ident, Some(*mutbl), ty, body.as_deref(), vis, def);
             }
             ast::ForeignItemKind::TyAlias(generics, bounds, ty) => {
-                self.print_associated_type(ident, generics, bounds, ty.as_deref());
+                self.print_associated_type(ident, generics, bounds, ty.as_deref(), vis, def);
             }
             ast::ForeignItemKind::Macro(m) => {
                 self.print_mac(m);
@@ -1065,13 +1064,17 @@ impl<'a> State<'a> {
         ty: &ast::Ty,
         body: Option<&ast::Expr>,
         vis: &ast::Visibility,
+        defaultness: ast::Defaultness,
     ) {
+        self.head("");
+        self.print_visibility(vis);
+        self.print_defaultness(defaultness);
         let leading = match mutbl {
             None => "const",
             Some(ast::Mutability::Not) => "static",
             Some(ast::Mutability::Mut) => "static mut",
         };
-        self.head(visibility_qualified(vis, leading));
+        self.word_space(leading);
         self.print_ident(ident);
         self.word_space(":");
         self.print_type(ty);
@@ -1091,7 +1094,12 @@ impl<'a> State<'a> {
         generics: &ast::Generics,
         bounds: &ast::GenericBounds,
         ty: Option<&ast::Ty>,
+        vis: &ast::Visibility,
+        defaultness: ast::Defaultness,
     ) {
+        self.head("");
+        self.print_visibility(vis);
+        self.print_defaultness(defaultness);
         self.word_space("type");
         self.print_ident(ident);
         self.print_generic_params(&generics.params);
@@ -1102,7 +1110,9 @@ impl<'a> State<'a> {
             self.word_space("=");
             self.print_type(ty);
         }
-        self.s.word(";")
+        self.s.word(";");
+        self.end(); // end inner head-block
+        self.end(); // end outer head-block
     }
 
     /// Pretty-prints an item.
@@ -1133,13 +1143,17 @@ impl<'a> State<'a> {
                 self.end(); // end outer head-block
             }
             ast::ItemKind::Static(ref ty, mutbl, ref body) => {
-                self.print_item_const(item.ident, Some(mutbl), ty, body.as_deref(), &item.vis);
+                let def = ast::Defaultness::Final;
+                self.print_item_const(item.ident, Some(mutbl), ty, body.as_deref(), &item.vis, def);
             }
             ast::ItemKind::Const(ref ty, ref body) => {
-                self.print_item_const(item.ident, None, ty, body.as_deref(), &item.vis);
+                let def = ast::Defaultness::Final;
+                self.print_item_const(item.ident, None, ty, body.as_deref(), &item.vis, def);
             }
             ast::ItemKind::Fn(ref sig, ref gen, ref body) => {
-                self.print_fn_full(sig, item.ident, gen, &item.vis, body.as_deref(), &item.attrs);
+                let def = ast::Defaultness::Final;
+                let body = body.as_deref();
+                self.print_fn_full(sig, item.ident, gen, &item.vis, def, body, &item.attrs);
             }
             ast::ItemKind::Mod(ref _mod) => {
                 self.head(visibility_qualified(&item.vis, "mod"));
@@ -1171,18 +1185,10 @@ impl<'a> State<'a> {
                 self.s.word(ga.asm.to_string());
                 self.end();
             }
-            ast::ItemKind::TyAlias(ref ty, ref generics) => {
-                self.head(visibility_qualified(&item.vis, "type"));
-                self.print_ident(item.ident);
-                self.print_generic_params(&generics.params);
-                self.end(); // end the inner ibox
-
-                self.print_where_clause(&generics.where_clause);
-                self.s.space();
-                self.word_space("=");
-                self.print_type(ty);
-                self.s.word(";");
-                self.end(); // end the outer ibox
+            ast::ItemKind::TyAlias(ref generics, ref bounds, ref ty) => {
+                let def = ast::Defaultness::Final;
+                let ty = ty.as_deref();
+                self.print_associated_type(item.ident, generics, bounds, ty, &item.vis, def);
             }
             ast::ItemKind::Enum(ref enum_definition, ref params) => {
                 self.print_enum_def(enum_definition, params, item.ident, item.span, &item.vis);
@@ -2370,13 +2376,16 @@ impl<'a> State<'a> {
         name: ast::Ident,
         generics: &ast::Generics,
         vis: &ast::Visibility,
+        defaultness: ast::Defaultness,
         body: Option<&ast::Block>,
         attrs: &[ast::Attribute],
     ) {
         if body.is_some() {
             self.head("");
         }
-        self.print_fn(&sig.decl, sig.header, Some(name), generics, vis);
+        self.print_visibility(vis);
+        self.print_defaultness(defaultness);
+        self.print_fn(&sig.decl, sig.header, Some(name), generics);
         if let Some(body) = body {
             self.nbsp();
             self.print_block_with_attrs(body, attrs);
@@ -2391,10 +2400,8 @@ impl<'a> State<'a> {
         header: ast::FnHeader,
         name: Option<ast::Ident>,
         generics: &ast::Generics,
-        vis: &ast::Visibility,
     ) {
-        self.print_fn_header_info(header, vis);
-
+        self.print_fn_header_info(header);
         if let Some(name) = name {
             self.nbsp();
             self.print_ident(name);
@@ -2672,8 +2679,7 @@ impl<'a> State<'a> {
             span: rustc_span::DUMMY_SP,
         };
         let header = ast::FnHeader { unsafety, ext, ..ast::FnHeader::default() };
-        let vis = dummy_spanned(ast::VisibilityKind::Inherited);
-        self.print_fn(decl, header, name, &generics, &vis);
+        self.print_fn(decl, header, name, &generics);
         self.end();
     }
 
@@ -2700,9 +2706,7 @@ impl<'a> State<'a> {
         }
     }
 
-    crate fn print_fn_header_info(&mut self, header: ast::FnHeader, vis: &ast::Visibility) {
-        self.s.word(visibility_qualified(vis, ""));
-
+    crate fn print_fn_header_info(&mut self, header: ast::FnHeader) {
         self.print_constness(header.constness);
         self.print_asyncness(header.asyncness);
         self.print_unsafety(header.unsafety);

src/librustc_ast_pretty/pprust/tests.rs

@@ -1,7 +1,7 @@
 use super::*;
 
 use rustc_span;
-use rustc_span::source_map::{dummy_spanned, respan};
+use rustc_span::source_map::respan;
 use syntax::ast;
 use syntax::with_default_globals;
 
@@ -13,13 +13,7 @@ fn fun_to_string(
 ) -> String {
     to_string(|s| {
         s.head("");
-        s.print_fn(
-            decl,
-            header,
-            Some(name),
-            generics,
-            &dummy_spanned(ast::VisibilityKind::Inherited),
-        );
+        s.print_fn(decl, header, Some(name), generics);
         s.end(); // Close the head box.
         s.end(); // Close the outer box.
     })

src/librustc_parse/parser/item.rs

@@ -156,8 +156,7 @@ impl<'a> Parser<'a> {
             self.parse_item_mod(attrs)?
         } else if self.eat_keyword(kw::Type) {
             // TYPE ITEM
-            let (ident, ty, generics) = self.parse_type_alias()?;
-            (ident, ItemKind::TyAlias(ty, generics))
+            self.parse_type_alias()?
         } else if self.eat_keyword(kw::Enum) {
             // ENUM ITEM
             self.parse_item_enum()?
@@ -676,7 +675,10 @@ impl<'a> Parser<'a> {
         vis: &Visibility,
     ) -> PResult<'a, (Ident, AssocItemKind)> {
         if self.eat_keyword(kw::Type) {
-            self.parse_assoc_ty()
+            match self.parse_type_alias()? {
+                (ident, ItemKind::TyAlias(a, b, c)) => Ok((ident, AssocItemKind::TyAlias(a, b, c))),
+                _ => unreachable!(),
+            }
         } else if self.check_fn_front_matter() {
             let (ident, sig, generics, body) = self.parse_fn(at_end, attrs, req_name)?;
             Ok((ident, AssocItemKind::Fn(sig, generics, body)))
@@ -700,10 +702,12 @@ impl<'a> Parser<'a> {
         }
     }
 
-    /// Parses the following grammar:
-    ///
-    ///     AssocTy = Ident ["<"...">"] [":" [GenericBounds]] ["where" ...] ["=" Ty]
-    fn parse_assoc_ty(&mut self) -> PResult<'a, (Ident, AssocItemKind)> {
+    /// Parses a `type` alias with the following grammar:
+    /// ```
+    /// TypeAlias = "type" Ident Generics {":" GenericBounds}? {"=" Ty}? ";" ;
+    /// ```
+    /// The `"type"` has already been eaten.
+    fn parse_type_alias(&mut self) -> PResult<'a, (Ident, ItemKind)> {
         let ident = self.parse_ident()?;
         let mut generics = self.parse_generics()?;
 
@@ -715,7 +719,7 @@ impl<'a> Parser<'a> {
         let default = if self.eat(&token::Eq) { Some(self.parse_ty()?) } else { None };
         self.expect_semi()?;
 
-        Ok((ident, AssocItemKind::TyAlias(generics, bounds, default)))
+        Ok((ident, ItemKind::TyAlias(generics, bounds, default)))
     }
 
     /// Parses a `UseTree`.
@@ -989,18 +993,6 @@ impl<'a> Parser<'a> {
         P(Ty { kind: TyKind::Infer, span: id.span, id: ast::DUMMY_NODE_ID })
     }
 
-    /// 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 ty = self.parse_ty()?;
-        self.expect_semi()?;
-        Ok((ident, ty, tps))
-    }
-
     /// Parses an enum declaration.
     fn parse_item_enum(&mut self) -> PResult<'a, ItemInfo> {
         let id = self.parse_ident()?;

src/librustc_resolve/build_reduced_graph.rs

@@ -718,8 +718,8 @@ impl<'a, 'b> BuildReducedGraphVisitor<'a, 'b> {
             }
 
             // These items live in the type namespace.
-            ItemKind::TyAlias(ref ty, _) => {
-                let def_kind = match ty.kind.opaque_top_hack() {
+            ItemKind::TyAlias(_, _, ref ty) => {
+                let def_kind = match ty.as_deref().and_then(|ty| ty.kind.opaque_top_hack()) {
                     None => DefKind::TyAlias,
                     Some(_) => DefKind::OpaqueTy,
                 };

src/librustc_resolve/late.rs

@@ -797,7 +797,7 @@ impl<'a, 'b, 'ast> LateResolutionVisitor<'a, 'b, 'ast> {
         debug!("(resolving item) resolving {} ({:?})", name, item.kind);
 
         match item.kind {
-            ItemKind::TyAlias(_, ref generics) | ItemKind::Fn(_, ref generics, _) => {
+            ItemKind::TyAlias(ref generics, _, _) | ItemKind::Fn(_, ref generics, _) => {
                 self.with_generic_param_rib(generics, ItemRibKind(HasGenericParams::Yes), |this| {
                     visit::walk_item(this, item)
                 });

src/librustc_save_analysis/dump_visitor.rs

@@ -1311,12 +1311,15 @@ impl<'l, 'tcx> Visitor<'l> for DumpVisitor<'l, 'tcx> {
                 self.process_mod(item);
                 visit::walk_mod(self, m);
             }
-            TyAlias(ref ty, ref ty_params) => {
+            TyAlias(ref ty_params, _, ref ty) => {
                 let qualname = format!(
                     "::{}",
                     self.tcx.def_path_str(self.tcx.hir().local_def_id_from_node_id(item.id))
                 );
-                let value = ty_to_string(&ty);
+                let value = match ty {
+                    Some(ty) => ty_to_string(&ty),
+                    None => "_".to_string(),
+                };
                 if !self.span.filter_generated(item.ident.span) {
                     let span = self.span_from_span(item.ident.span);
                     let id = id_from_node_id(item.id, &self.save_ctxt);
@@ -1341,7 +1344,7 @@ impl<'l, 'tcx> Visitor<'l> for DumpVisitor<'l, 'tcx> {
                     );
                 }
 
-                self.visit_ty(&ty);
+                walk_list!(self, visit_ty, ty);
                 self.process_generic_params(ty_params, &qualname, item.id);
             }
             Mac(_) => (),