Make negative_bounds internal & fix some of its issues

compiler/rustc_ast_passes/messages.ftl

@@ -188,6 +188,9 @@ ast_passes_module_nonascii = trying to load file for module `{$name}` with non-a
 ast_passes_negative_bound_not_supported =
     negative bounds are not supported
 
+ast_passes_negative_bound_with_parenthetical_notation =
+    parenthetical notation may not be used for negative bounds
+
 ast_passes_nested_impl_trait = nested `impl Trait` is not allowed
     .outer = outer `impl Trait`
     .inner = nested `impl Trait` here

compiler/rustc_ast_passes/src/ast_validation.rs

@@ -1257,13 +1257,24 @@ impl<'a> Visitor<'a> for AstValidator<'a> {
         if let GenericBound::Trait(trait_ref, modifiers) = bound
             && let BoundPolarity::Negative(_) = modifiers.polarity
             && let Some(segment) = trait_ref.trait_ref.path.segments.last()
-            && let Some(ast::GenericArgs::AngleBracketed(args)) = segment.args.as_deref()
         {
-            for arg in &args.args {
-                if let ast::AngleBracketedArg::Constraint(constraint) = arg {
-                    self.dcx()
-                        .emit_err(errors::ConstraintOnNegativeBound { span: constraint.span });
+            match segment.args.as_deref() {
+                Some(ast::GenericArgs::AngleBracketed(args)) => {
+                    for arg in &args.args {
+                        if let ast::AngleBracketedArg::Constraint(constraint) = arg {
+                            self.dcx().emit_err(errors::ConstraintOnNegativeBound {
+                                span: constraint.span,
+                            });
+                        }
+                    }
+                }
+                // The lowered form of parenthesized generic args contains a type binding.
+                Some(ast::GenericArgs::Parenthesized(args)) => {
+                    self.dcx().emit_err(errors::NegativeBoundWithParentheticalNotation {
+                        span: args.span,
+                    });
                 }
+                None => {}
             }
         }
 

compiler/rustc_ast_passes/src/errors.rs

@@ -745,6 +745,13 @@ pub struct ConstraintOnNegativeBound {
     pub span: Span,
 }
 
+#[derive(Diagnostic)]
+#[diag(ast_passes_negative_bound_with_parenthetical_notation)]
+pub struct NegativeBoundWithParentheticalNotation {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(ast_passes_invalid_unnamed_field_ty)]
 pub struct InvalidUnnamedFieldTy {

compiler/rustc_feature/src/unstable.rs

@@ -210,7 +210,7 @@ declare_features! (
     /// Allows the `multiple_supertrait_upcastable` lint.
     (unstable, multiple_supertrait_upcastable, "1.69.0", None),
     /// Allow negative trait bounds. This is an internal-only feature for testing the trait solver!
-    (incomplete, negative_bounds, "1.71.0", None),
+    (internal, negative_bounds, "1.71.0", None),
     /// Allows using `#[omit_gdb_pretty_printer_section]`.
     (internal, omit_gdb_pretty_printer_section, "1.5.0", None),
     /// Allows using `#[prelude_import]` on glob `use` items.

compiler/rustc_hir_analysis/src/astconv/bounds.rs

@@ -26,23 +26,36 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
         span: Span,
     ) {
         let tcx = self.tcx();
+        let sized_def_id = tcx.lang_items().sized_trait();
+        let mut seen_negative_sized_bound = false;
 
         // Try to find an unbound in bounds.
         let mut unbounds: SmallVec<[_; 1]> = SmallVec::new();
         let mut search_bounds = |ast_bounds: &'tcx [hir::GenericBound<'tcx>]| {
             for ab in ast_bounds {
-                if let hir::GenericBound::Trait(ptr, hir::TraitBoundModifier::Maybe) = ab {
-                    unbounds.push(ptr)
+                let hir::GenericBound::Trait(ptr, modifier) = ab else {
+                    continue;
+                };
+                match modifier {
+                    hir::TraitBoundModifier::Maybe => unbounds.push(ptr),
+                    hir::TraitBoundModifier::Negative => {
+                        if let Some(sized_def_id) = sized_def_id
+                            && ptr.trait_ref.path.res == Res::Def(DefKind::Trait, sized_def_id)
+                        {
+                            seen_negative_sized_bound = true;
+                        }
+                    }
+                    _ => {}
                 }
             }
         };
         search_bounds(ast_bounds);
         if let Some((self_ty, where_clause)) = self_ty_where_predicates {
             for clause in where_clause {
-                if let hir::WherePredicate::BoundPredicate(pred) = clause {
-                    if pred.is_param_bound(self_ty.to_def_id()) {
-                        search_bounds(pred.bounds);
-                    }
+                if let hir::WherePredicate::BoundPredicate(pred) = clause
+                    && pred.is_param_bound(self_ty.to_def_id())
+                {
+                    search_bounds(pred.bounds);
                 }
             }
         }
@@ -53,15 +66,13 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             });
         }
 
-        let sized_def_id = tcx.lang_items().sized_trait();
-
         let mut seen_sized_unbound = false;
         for unbound in unbounds {
-            if let Some(sized_def_id) = sized_def_id {
-                if unbound.trait_ref.path.res == Res::Def(DefKind::Trait, sized_def_id) {
-                    seen_sized_unbound = true;
-                    continue;
-                }
+            if let Some(sized_def_id) = sized_def_id
+                && unbound.trait_ref.path.res == Res::Def(DefKind::Trait, sized_def_id)
+            {
+                seen_sized_unbound = true;
+                continue;
             }
             // There was a `?Trait` bound, but it was not `?Sized`; warn.
             tcx.dcx().span_warn(
@@ -71,15 +82,12 @@ impl<'tcx> dyn AstConv<'tcx> + '_ {
             );
         }
 
-        // If the above loop finished there was no `?Sized` bound; add implicitly sized if `Sized` is available.
-        if sized_def_id.is_none() {
-            // No lang item for `Sized`, so we can't add it as a bound.
-            return;
-        }
-        if seen_sized_unbound {
-            // There was in fact a `?Sized` bound, return without doing anything
-        } else {
-            // There was no `?Sized` bound; add implicitly sized if `Sized` is available.
+        if seen_sized_unbound || seen_negative_sized_bound {
+            // There was in fact a `?Sized` or `!Sized` bound;
+            // we don't need to do anything.
+        } else if sized_def_id.is_some() {
+            // There was no `?Sized` or `!Sized` bound;
+            // add `Sized` if it's available.
             bounds.push_sized(tcx, self_ty, span);
         }
     }

tests/ui/traits/negative-bounds/associated-constraints.rs

@@ -1,5 +1,4 @@
 #![feature(negative_bounds, associated_type_bounds)]
-//~^ WARN the feature `negative_bounds` is incomplete and may not be safe to use and/or cause compiler crashes
 
 trait Trait {
     type Assoc;
@@ -17,4 +16,7 @@ fn test3<T: !Trait<Assoc: Send>>() {}
 fn test4<T>() where T: !Trait<Assoc: Send> {}
 //~^ ERROR associated type constraints not allowed on negative bounds
 
+fn test5<T>() where T: !Fn() -> i32 {}
+//~^ ERROR parenthetical notation may not be used for negative bounds
+
 fn main() {}

tests/ui/traits/negative-bounds/associated-constraints.stderr

@@ -1,34 +1,32 @@
 error: associated type constraints not allowed on negative bounds
-  --> $DIR/associated-constraints.rs:8:19
+  --> $DIR/associated-constraints.rs:7:19
    |
 LL | fn test<T: !Trait<Assoc = i32>>() {}
    |                   ^^^^^^^^^^^
 
 error: associated type constraints not allowed on negative bounds
-  --> $DIR/associated-constraints.rs:11:31
+  --> $DIR/associated-constraints.rs:10:31
    |
 LL | fn test2<T>() where T: !Trait<Assoc = i32> {}
    |                               ^^^^^^^^^^^
 
 error: associated type constraints not allowed on negative bounds
-  --> $DIR/associated-constraints.rs:14:20
+  --> $DIR/associated-constraints.rs:13:20
    |
 LL | fn test3<T: !Trait<Assoc: Send>>() {}
    |                    ^^^^^^^^^^^
 
 error: associated type constraints not allowed on negative bounds
-  --> $DIR/associated-constraints.rs:17:31
+  --> $DIR/associated-constraints.rs:16:31
    |
 LL | fn test4<T>() where T: !Trait<Assoc: Send> {}
    |                               ^^^^^^^^^^^
 
-warning: the feature `negative_bounds` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/associated-constraints.rs:1:12
+error: parenthetical notation may not be used for negative bounds
+  --> $DIR/associated-constraints.rs:19:25
    |
-LL | #![feature(negative_bounds, associated_type_bounds)]
-   |            ^^^^^^^^^^^^^^^
-   |
-   = note: `#[warn(incomplete_features)]` on by default
+LL | fn test5<T>() where T: !Fn() -> i32 {}
+   |                         ^^^^^^^^^^^
 
-error: aborting due to 4 previous errors; 1 warning emitted
+error: aborting due to 5 previous errors
 

tests/ui/traits/negative-bounds/simple.rs

@@ -1,5 +1,4 @@
 #![feature(negative_bounds, negative_impls)]
-//~^ WARN the feature `negative_bounds` is incomplete and may not be safe to use and/or cause compiler crashes
 
 fn not_copy<T: !Copy>() {}
 

tests/ui/traits/negative-bounds/simple.stderr

@@ -1,44 +1,36 @@
-warning: the feature `negative_bounds` is incomplete and may not be safe to use and/or cause compiler crashes
-  --> $DIR/simple.rs:1:12
-   |
-LL | #![feature(negative_bounds, negative_impls)]
-   |            ^^^^^^^^^^^^^^^
-   |
-   = note: `#[warn(incomplete_features)]` on by default
-
 error[E0277]: the trait bound `T: !Copy` is not satisfied
-  --> $DIR/simple.rs:11:16
+  --> $DIR/simple.rs:10:16
    |
 LL |     not_copy::<T>();
    |                ^ the trait `!Copy` is not implemented for `T`
    |
 note: required by a bound in `not_copy`
-  --> $DIR/simple.rs:4:16
+  --> $DIR/simple.rs:3:16
    |
 LL | fn not_copy<T: !Copy>() {}
    |                ^^^^^ required by this bound in `not_copy`
 
 error[E0277]: the trait bound `T: !Copy` is not satisfied
-  --> $DIR/simple.rs:16:16
+  --> $DIR/simple.rs:15:16
    |
 LL |     not_copy::<T>();
    |                ^ the trait `!Copy` is not implemented for `T`
    |
 note: required by a bound in `not_copy`
-  --> $DIR/simple.rs:4:16
+  --> $DIR/simple.rs:3:16
    |
 LL | fn not_copy<T: !Copy>() {}
    |                ^^^^^ required by this bound in `not_copy`
 
 error[E0277]: the trait bound `Copyable: !Copy` is not satisfied
-  --> $DIR/simple.rs:31:16
+  --> $DIR/simple.rs:30:16
    |
 LL |     not_copy::<Copyable>();
    |                ^^^^^^^^ the trait `!Copy` is not implemented for `Copyable`
    |
    = help: the trait `Copy` is implemented for `Copyable`
 note: required by a bound in `not_copy`
-  --> $DIR/simple.rs:4:16
+  --> $DIR/simple.rs:3:16
    |
 LL | fn not_copy<T: !Copy>() {}
    |                ^^^^^ required by this bound in `not_copy`
@@ -49,13 +41,13 @@ LL | struct Copyable;
    |
 
 error[E0277]: the trait bound `NotNecessarilyCopyable: !Copy` is not satisfied
-  --> $DIR/simple.rs:38:16
+  --> $DIR/simple.rs:37:16
    |
 LL |     not_copy::<NotNecessarilyCopyable>();
    |                ^^^^^^^^^^^^^^^^^^^^^^ the trait `!Copy` is not implemented for `NotNecessarilyCopyable`
    |
 note: required by a bound in `not_copy`
-  --> $DIR/simple.rs:4:16
+  --> $DIR/simple.rs:3:16
    |
 LL | fn not_copy<T: !Copy>() {}
    |                ^^^^^ required by this bound in `not_copy`
@@ -65,6 +57,6 @@ LL + #[derive(Copy)]
 LL | struct NotNecessarilyCopyable;
    |
 
-error: aborting due to 4 previous errors; 1 warning emitted
+error: aborting due to 4 previous errors
 
 For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/negative-bounds/supertrait.rs

@@ -1,7 +1,6 @@
 // check-pass
 
 #![feature(negative_bounds)]
-//~^ WARN the feature `negative_bounds` is incomplete
 
 trait A: !B {}
 trait B: !A {}