Change RTN to use .. again

Author: compiler-errors

compiler/rustc_ast/src/ast.rs

@@ -176,6 +176,8 @@ pub enum GenericArgs {
     AngleBracketed(AngleBracketedArgs),
     /// The `(A, B)` and `C` in `Foo(A, B) -> C`.
     Parenthesized(ParenthesizedArgs),
+    /// `(..)` in return type notation
+    ParenthesizedElided(Span),
 }
 
 impl GenericArgs {
@@ -187,6 +189,7 @@ impl GenericArgs {
         match self {
             AngleBracketed(data) => data.span,
             Parenthesized(data) => data.span,
+            ParenthesizedElided(span) => *span,
         }
     }
 }
@@ -2051,7 +2054,7 @@ impl UintTy {
 /// * the `A: Bound` in `Trait<A: Bound>`
 /// * the `RetTy` in `Trait(ArgTy, ArgTy) -> RetTy`
 /// * the `C = { Ct }` in `Trait<C = { Ct }>` (feature `associated_const_equality`)
-/// * the `f(): Bound` in `Trait<f(): Bound>` (feature `return_type_notation`)
+/// * the `f(..): Bound` in `Trait<f(..): Bound>` (feature `return_type_notation`)
 #[derive(Clone, Encodable, Decodable, Debug)]
 pub struct AssocItemConstraint {
     pub id: NodeId,

compiler/rustc_ast/src/mut_visit.rs

@@ -582,6 +582,7 @@ fn noop_visit_generic_args<T: MutVisitor>(generic_args: &mut GenericArgs, vis: &
     match generic_args {
         GenericArgs::AngleBracketed(data) => vis.visit_angle_bracketed_parameter_data(data),
         GenericArgs::Parenthesized(data) => vis.visit_parenthesized_parameter_data(data),
+        GenericArgs::ParenthesizedElided(span) => vis.visit_span(span),
     }
 }
 

compiler/rustc_ast/src/util/classify.rs

@@ -234,6 +234,6 @@ fn path_return_type(path: &ast::Path) -> Option<&ast::Ty> {
             ast::FnRetTy::Default(_) => None,
             ast::FnRetTy::Ty(ret) => Some(ret),
         },
-        ast::GenericArgs::AngleBracketed(_) => None,
+        ast::GenericArgs::AngleBracketed(_) | ast::GenericArgs::ParenthesizedElided(_) => None,
     }
 }

compiler/rustc_ast/src/visit.rs

@@ -609,6 +609,7 @@ where
             walk_list!(visitor, visit_ty, inputs);
             try_visit!(visitor.visit_fn_ret_ty(output));
         }
+        GenericArgs::ParenthesizedElided(_span) => {}
     }
     V::Result::output()
 }

compiler/rustc_ast_lowering/messages.ftl

@@ -36,6 +36,9 @@ ast_lowering_bad_return_type_notation_inputs =
     argument types not allowed with return type notation
     .suggestion = remove the input types
 
+ast_lowering_bad_return_type_notation_needs_dots = return type notation arguments must be elided with `..`
+    .suggestion = add `..`
+
 ast_lowering_bad_return_type_notation_output =
     return type not allowed with return type notation
     .suggestion = remove the return type

compiler/rustc_ast_lowering/src/errors.rs

@@ -393,6 +393,12 @@ pub enum BadReturnTypeNotation {
         #[suggestion(code = "", applicability = "maybe-incorrect")]
         span: Span,
     },
+    #[diag(ast_lowering_bad_return_type_notation_needs_dots)]
+    NeedsDots {
+        #[primary_span]
+        #[suggestion(code = "(..)", applicability = "maybe-incorrect")]
+        span: Span,
+    },
 }
 
 #[derive(Diagnostic)]

compiler/rustc_ast_lowering/src/lib.rs

@@ -979,20 +979,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     self.lower_angle_bracketed_parameter_data(data, ParamMode::Explicit, itctx).0
                 }
                 GenericArgs::Parenthesized(data) => {
-                    if data.inputs.is_empty() && matches!(data.output, FnRetTy::Default(..)) {
-                        let parenthesized = if self.tcx.features().return_type_notation {
-                            hir::GenericArgsParentheses::ReturnTypeNotation
-                        } else {
-                            self.emit_bad_parenthesized_trait_in_assoc_ty(data);
-                            hir::GenericArgsParentheses::No
-                        };
-                        GenericArgsCtor {
-                            args: Default::default(),
-                            constraints: &[],
-                            parenthesized,
-                            span: data.inputs_span,
-                        }
-                    } else if let Some(first_char) = constraint.ident.as_str().chars().next()
+                    if let Some(first_char) = constraint.ident.as_str().chars().next()
                         && first_char.is_ascii_lowercase()
                     {
                         let mut err = if !data.inputs.is_empty() {
@@ -1004,7 +991,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                                 span: data.inputs_span.shrink_to_hi().to(ty.span),
                             })
                         } else {
-                            unreachable!("inputs are empty and return type is not provided")
+                            self.dcx().create_err(errors::BadReturnTypeNotation::NeedsDots {
+                                span: data.inputs_span,
+                            })
                         };
                         if !self.tcx.features().return_type_notation
                             && self.tcx.sess.is_nightly_build()
@@ -1034,6 +1023,12 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         .0
                     }
                 }
+                GenericArgs::ParenthesizedElided(span) => GenericArgsCtor {
+                    args: Default::default(),
+                    constraints: &[],
+                    parenthesized: hir::GenericArgsParentheses::ReturnTypeNotation,
+                    span: *span,
+                },
             };
             gen_args_ctor.into_generic_args(self)
         } else {

compiler/rustc_ast_lowering/src/path.rs

@@ -276,6 +276,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         )
                     }
                 },
+                GenericArgs::ParenthesizedElided(_span) => {
+                    todo!()
+                }
             }
         } else {
             (

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1289,6 +1289,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                     self.with_impl_trait(None, |this| this.visit_ty(ty));
                 }
             }
+            GenericArgs::ParenthesizedElided(_span) => {}
         }
     }
 
@@ -1445,7 +1446,7 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
                                 span: args.span,
                             });
                         }
-                        None => {}
+                        Some(ast::GenericArgs::ParenthesizedElided(_)) | None => {}
                     }
                 }
             }
@@ -1693,7 +1694,9 @@ fn deny_equality_constraints(
                 // Add `<Bar = RhsTy>` to `Foo`.
                 match &mut assoc_path.segments[len].args {
                     Some(args) => match args.deref_mut() {
-                        GenericArgs::Parenthesized(_) => continue,
+                        GenericArgs::Parenthesized(_) | GenericArgs::ParenthesizedElided(..) => {
+                            continue;
+                        }
                         GenericArgs::AngleBracketed(args) => {
                             args.args.push(arg);
                         }

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -1,6 +1,6 @@
 use rustc_ast as ast;
 use rustc_ast::visit::{self, AssocCtxt, FnCtxt, FnKind, Visitor};
-use rustc_ast::{attr, AssocItemConstraint, AssocItemConstraintKind, NodeId};
+use rustc_ast::{attr, NodeId};
 use rustc_ast::{token, PatKind};
 use rustc_feature::{AttributeGate, BuiltinAttribute, Features, GateIssue, BUILTIN_ATTRIBUTE_MAP};
 use rustc_session::parse::{feature_err, feature_err_issue, feature_warn};
@@ -445,23 +445,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
         visit::walk_fn(self, fn_kind)
     }
 
-    fn visit_assoc_item_constraint(&mut self, constraint: &'a AssocItemConstraint) {
-        if let AssocItemConstraintKind::Bound { .. } = constraint.kind
-            && let Some(ast::GenericArgs::Parenthesized(args)) = constraint.gen_args.as_ref()
-            && args.inputs.is_empty()
-            && let ast::FnRetTy::Default(..) = args.output
-        {
-            gate!(
-                &self,
-                return_type_notation,
-                constraint.span,
-                "return type notation is experimental"
-            );
-        }
-
-        visit::walk_assoc_item_constraint(self, constraint)
-    }
-
     fn visit_assoc_item(&mut self, i: &'a ast::AssocItem, ctxt: AssocCtxt) {
         let is_fn = match &i.kind {
             ast::AssocItemKind::Fn(_) => true,
@@ -566,6 +549,7 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
         unsafe_extern_blocks,
         "`unsafe extern {}` blocks and `safe` keyword are experimental"
     );
+    gate_all!(return_type_notation, "return type notation is experimental");
 
     if !visitor.features.never_patterns {
         if let Some(spans) = spans.get(&sym::never_patterns) {
@@ -611,10 +595,6 @@ pub fn check_crate(krate: &ast::Crate, sess: &Session, features: &Features) {
 
     gate_all_legacy_dont_use!(box_patterns, "box pattern syntax is experimental");
     gate_all_legacy_dont_use!(trait_alias, "trait aliases are experimental");
-    // Despite being a new feature, `where T: Trait<Assoc(): Sized>`, which is RTN syntax now,
-    // used to be gated under associated_type_bounds, which are right above, so RTN needs to
-    // be too.
-    gate_all_legacy_dont_use!(return_type_notation, "return type notation is experimental");
     gate_all_legacy_dont_use!(decl_macro, "`macro` is experimental");
     gate_all_legacy_dont_use!(try_blocks, "`try` blocks are unstable");
     gate_all_legacy_dont_use!(auto_traits, "`auto` traits are unstable");