Rollup merge of #133768 - compiler-errors:gate, r=lcnr,jackh726

Remove `generic_associated_types_extended` feature gate

This PR retires nightly support for the `generic_associated_types_extended` feature. This feature hasn't received much attention in the last two years or so, and I believe the feature still remains both unsound and ICEy to use. I think that if we were to redesign and reimplement it, we'd want to first figure out how to implement it soundly, but in the mean time I'd prefer to clean this up.

r? ``@lcnr`` cc ``@jackh726`` who added this feature gate I think

compiler/rustc_feature/src/removed.rs

@@ -119,6 +119,13 @@ declare_features! (
     (removed, generator_clone, "1.65.0", Some(95360), Some("renamed to `coroutine_clone`")),
     /// Allows defining generators.
     (removed, generators, "1.21.0", Some(43122), Some("renamed to `coroutines`")),
+    /// An extension to the `generic_associated_types` feature, allowing incomplete features.
+    (removed, generic_associated_types_extended, "CURRENT_RUSTC_VERSION", Some(95451),
+        Some(
+            "feature needs overhaul and reimplementation pending \
+            better implied higher-ranked implied bounds support"
+        )
+    ),
     /// Allows `impl Trait` in bindings (`let`, `const`, `static`).
     (removed, impl_trait_in_bindings, "1.55.0", Some(63065),
      Some("the implementation was not maintainable, the feature may get reintroduced once the current refactorings are done")),

compiler/rustc_feature/src/unstable.rs

@@ -497,8 +497,6 @@ declare_features! (
     (unstable, gen_blocks, "1.75.0", Some(117078)),
     /// Infer generic args for both consts and types.
     (unstable, generic_arg_infer, "1.55.0", Some(85077)),
-    /// An extension to the `generic_associated_types` feature, allowing incomplete features.
-    (incomplete, generic_associated_types_extended, "1.61.0", Some(95451)),
     /// Allows non-trivial generic constants which have to have wfness manually propagated to callers
     (incomplete, generic_const_exprs, "1.56.0", Some(76560)),
     /// Allows generic parameters and where-clauses on free & associated const items.

compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs

@@ -329,10 +329,7 @@ pub fn dyn_compatibility_violations_for_assoc_item(
             .collect(),
         // Associated types can only be dyn-compatible if they have `Self: Sized` bounds.
         ty::AssocKind::Type => {
-            if !tcx.features().generic_associated_types_extended()
-                && !tcx.generics_of(item.def_id).is_own_empty()
-                && !item.is_impl_trait_in_trait()
-            {
+            if !tcx.generics_of(item.def_id).is_own_empty() && !item.is_impl_trait_in_trait() {
                 vec![DynCompatibilityViolation::GAT(item.name, item.ident(tcx).span)]
             } else {
                 // We will permit associated types if they are explicitly mentioned in the trait object.

compiler/rustc_trait_selection/src/traits/project.rs

@@ -14,7 +14,7 @@ use rustc_middle::traits::select::OverflowError;
 use rustc_middle::traits::{BuiltinImplSource, ImplSource, ImplSourceUserDefinedData};
 use rustc_middle::ty::fast_reject::DeepRejectCtxt;
 use rustc_middle::ty::fold::TypeFoldable;
-use rustc_middle::ty::visit::{MaxUniverse, TypeVisitable, TypeVisitableExt};
+use rustc_middle::ty::visit::TypeVisitableExt;
 use rustc_middle::ty::{self, Term, Ty, TyCtxt, TypingMode, Upcast};
 use rustc_middle::{bug, span_bug};
 use rustc_span::symbol::sym;
@@ -179,35 +179,11 @@ pub(super) fn poly_project_and_unify_term<'cx, 'tcx>(
 ) -> ProjectAndUnifyResult<'tcx> {
     let infcx = selcx.infcx;
     let r = infcx.commit_if_ok(|_snapshot| {
-        let old_universe = infcx.universe();
         let placeholder_predicate = infcx.enter_forall_and_leak_universe(obligation.predicate);
-        let new_universe = infcx.universe();
 
         let placeholder_obligation = obligation.with(infcx.tcx, placeholder_predicate);
         match project_and_unify_term(selcx, &placeholder_obligation) {
             ProjectAndUnifyResult::MismatchedProjectionTypes(e) => Err(e),
-            ProjectAndUnifyResult::Holds(obligations)
-                if old_universe != new_universe
-                    && selcx.tcx().features().generic_associated_types_extended() =>
-            {
-                // If the `generic_associated_types_extended` feature is active, then we ignore any
-                // obligations references lifetimes from any universe greater than or equal to the
-                // universe just created. Otherwise, we can end up with something like `for<'a> I: 'a`,
-                // which isn't quite what we want. Ideally, we want either an implied
-                // `for<'a where I: 'a> I: 'a` or we want to "lazily" check these hold when we
-                // instantiate concrete regions. There is design work to be done here; until then,
-                // however, this allows experimenting potential GAT features without running into
-                // well-formedness issues.
-                let new_obligations = obligations
-                    .into_iter()
-                    .filter(|obligation| {
-                        let mut visitor = MaxUniverse::new();
-                        obligation.predicate.visit_with(&mut visitor);
-                        visitor.max_universe() < new_universe
-                    })
-                    .collect();
-                Ok(ProjectAndUnifyResult::Holds(new_obligations))
-            }
             other => Ok(other),
         }
     });

compiler/rustc_trait_selection/src/traits/select/confirmation.rs

@@ -626,7 +626,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
         for assoc_type in assoc_types {
             let defs: &ty::Generics = tcx.generics_of(assoc_type);
 
-            if !defs.own_params.is_empty() && !tcx.features().generic_associated_types_extended() {
+            if !defs.own_params.is_empty() {
                 tcx.dcx().span_delayed_bug(
                     obligation.cause.span,
                     "GATs in trait object shouldn't have been considered",

tests/ui/generic-associated-types/extended/lending_iterator.rs

@@ -1,17 +1,11 @@
-//@ revisions: base extended
-//@[base] check-fail
-//@[extended] check-pass
-
-#![cfg_attr(extended, feature(generic_associated_types_extended))]
-#![cfg_attr(extended, allow(incomplete_features))]
+//@ known-bug: #133805
 
 pub trait FromLendingIterator<A>: Sized {
     fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
 }
 
 impl<A> FromLendingIterator<A> for Vec<A> {
     fn from_iter<I: for<'x> LendingIterator<Item<'x> = A>>(mut iter: I) -> Self {
-        //[base]~^ impl has stricter
         let mut v = vec![];
         while let Some(item) = iter.next() {
             v.push(item);
@@ -32,7 +26,6 @@ pub trait LendingIterator {
         Self: for<'q> LendingIterator<Item<'q> = A>,
     {
         <B as FromLendingIterator<A>>::from_iter(self)
-        //[base]~^ ERROR: does not live long enough
     }
 }
 

tests/ui/generic-associated-types/extended/lending_iterator.base.stderr → tests/ui/generic-associated-types/extended/lending_iterator.stderr

@@ -1,5 +1,5 @@
 error[E0276]: impl has stricter requirements than trait
-  --> $DIR/lending_iterator.rs:13:45
+  --> $DIR/lending_iterator.rs:8:45
    |
 LL |     fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
    |     ------------------------------------------------------------------------ definition of `from_iter` from trait
@@ -8,7 +8,7 @@ LL |     fn from_iter<I: for<'x> LendingIterator<Item<'x> = A>>(mut iter: I) ->
    |                                             ^^^^^^^^^^^^ impl has extra requirement `I: 'x`
 
 error: `Self` does not live long enough
-  --> $DIR/lending_iterator.rs:34:9
+  --> $DIR/lending_iterator.rs:28:9
    |
 LL |         <B as FromLendingIterator<A>>::from_iter(self)
    |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

tests/ui/generic-associated-types/extended/lending_iterator_2.rs

@@ -1,17 +1,11 @@
-//@ revisions: base extended
-//@[base] check-fail
-//@[extended] check-pass
-
-#![cfg_attr(extended, feature(generic_associated_types_extended))]
-#![cfg_attr(extended, allow(incomplete_features))]
+//@ known-bug: #133805
 
 pub trait FromLendingIterator<A>: Sized {
     fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
 }
 
 impl<A> FromLendingIterator<A> for Vec<A> {
     fn from_iter<I: for<'x> LendingIterator<Item<'x> = A>>(mut iter: I) -> Self {
-        //[base]~^ impl has stricter
         let mut v = vec![];
         while let Some(item) = iter.next() {
             v.push(item);

tests/ui/generic-associated-types/extended/lending_iterator_2.base.stderr → tests/ui/generic-associated-types/extended/lending_iterator_2.stderr

@@ -1,5 +1,5 @@
 error[E0276]: impl has stricter requirements than trait
-  --> $DIR/lending_iterator_2.rs:13:45
+  --> $DIR/lending_iterator_2.rs:8:45
    |
 LL |     fn from_iter<T: for<'x> LendingIterator<Item<'x> = A>>(iter: T) -> Self;
    |     ------------------------------------------------------------------------ definition of `from_iter` from trait

tests/ui/generic-associated-types/gat-in-trait-path.rs

@@ -1,10 +1,6 @@
-//@ revisions: base extended
-//@[base] check-fail
-//@[extended] check-pass
+//@ check-fail
 
 #![feature(associated_type_defaults)]
-#![cfg_attr(extended, feature(generic_associated_types_extended))]
-#![cfg_attr(extended, allow(incomplete_features))]
 
 trait Foo {
     type A<'a> where Self: 'a;
@@ -24,12 +20,12 @@ impl<T> Foo for Fooer<T> {
 }
 
 fn f(_arg : Box<dyn for<'a> Foo<A<'a> = &'a ()>>) {}
-//[base]~^ the trait `Foo` cannot be made into an object
+//~^ the trait `Foo` cannot be made into an object
 
 
 fn main() {
   let foo = Fooer(5);
   f(Box::new(foo));
-  //[base]~^ the trait `Foo` cannot be made into an object
-  //[base]~| the trait `Foo` cannot be made into an object
+  //~^ the trait `Foo` cannot be made into an object
+  //~| the trait `Foo` cannot be made into an object
 }

tests/ui/generic-associated-types/gat-in-trait-path.stderr

@@ -0,0 +1,58 @@
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/gat-in-trait-path.rs:22:17
+   |
+LL | fn f(_arg : Box<dyn for<'a> Foo<A<'a> = &'a ()>>) {}
+   |                 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/gat-in-trait-path.rs:6:10
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     type A<'a> where Self: 'a;
+   |          ^ ...because it contains the generic associated type `A`
+   = help: consider moving `A` to another trait
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `Foo` for this new enum and using it instead:
+             Fooy
+             Fooer<T>
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/gat-in-trait-path.rs:28:5
+   |
+LL |   f(Box::new(foo));
+   |     ^^^^^^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/gat-in-trait-path.rs:6:10
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     type A<'a> where Self: 'a;
+   |          ^ ...because it contains the generic associated type `A`
+   = help: consider moving `A` to another trait
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `Foo` for this new enum and using it instead:
+             Fooy
+             Fooer<T>
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/gat-in-trait-path.rs:28:5
+   |
+LL |   f(Box::new(foo));
+   |     ^^^^^^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/gat-in-trait-path.rs:6:10
+   |
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     type A<'a> where Self: 'a;
+   |          ^ ...because it contains the generic associated type `A`
+   = help: consider moving `A` to another trait
+   = help: the following types implement the trait, consider defining an enum where each variant holds one of these types, implementing `Foo` for this new enum and using it instead:
+             Fooy
+             Fooer<T>
+   = note: required for the cast from `Box<Fooer<{integer}>>` to `Box<(dyn Foo<A<'a> = &'a ()> + 'static)>`
+
+error: aborting due to 3 previous errors
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/generic-associated-types/issue-67510-pass.rs

@@ -1,15 +1,10 @@
-//@ revisions: base extended
-//@[base] check-fail
-//@[extended] check-pass
-
-#![cfg_attr(extended, feature(generic_associated_types_extended))]
-#![cfg_attr(extended, allow(incomplete_features))]
+//@ check-fail
 
 trait X {
     type Y<'a>;
 }
 
 fn _func1<'a>(_x: Box<dyn X<Y<'a>=&'a ()>>) {}
-//[base]~^ ERROR the trait `X` cannot be made into an object
+//~^ ERROR the trait `X` cannot be made into an object
 
 fn main() {}

tests/ui/generic-associated-types/issue-67510-pass.stderr

@@ -0,0 +1,18 @@
+error[E0038]: the trait `X` cannot be made into an object
+  --> $DIR/issue-67510-pass.rs:7:23
+   |
+LL | fn _func1<'a>(_x: Box<dyn X<Y<'a>=&'a ()>>) {}
+   |                       ^^^^^^^^^^^^^^^^^^^ `X` cannot be made into an object
+   |
+note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/issue-67510-pass.rs:4:10
+   |
+LL | trait X {
+   |       - this trait cannot be made into an object...
+LL |     type Y<'a>;
+   |          ^ ...because it contains the generic associated type `Y`
+   = help: consider moving `Y` to another trait
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/generic-associated-types/issue-76535.rs

@@ -1,8 +1,3 @@
-//@ revisions: base extended
-
-#![cfg_attr(extended, feature(generic_associated_types_extended))]
-#![cfg_attr(extended, allow(incomplete_features))]
-
 pub trait SubTrait {}
 
 pub trait SuperTrait {
@@ -38,6 +33,6 @@ impl SuperTrait for SuperStruct {
 fn main() {
     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
       //~^ ERROR missing generics for associated type
-      //[base]~^^ ERROR the trait
-      //[base]~| ERROR the trait
+      //~^^ ERROR the trait
+      //~| ERROR the trait
 }

tests/ui/generic-associated-types/issue-76535.stderr

@@ -0,0 +1,55 @@
+error[E0107]: missing generics for associated type `SuperTrait::SubType`
+  --> $DIR/issue-76535.rs:34:33
+   |
+LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
+   |                                 ^^^^^^^ expected 1 lifetime argument
+   |
+note: associated type defined here, with 1 lifetime parameter: `'a`
+  --> $DIR/issue-76535.rs:4:10
+   |
+LL |     type SubType<'a>: SubTrait where Self: 'a;
+   |          ^^^^^^^ --
+help: add missing lifetime argument
+   |
+LL |     let sub: Box<dyn SuperTrait<SubType<'a> = SubStruct>> = Box::new(SuperStruct::new(0));
+   |                                        ++++
+
+error[E0038]: the trait `SuperTrait` cannot be made into an object
+  --> $DIR/issue-76535.rs:34:14
+   |
+LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
+   |              ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` cannot be made into an object
+   |
+note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/issue-76535.rs:4:10
+   |
+LL | pub trait SuperTrait {
+   |           ---------- this trait cannot be made into an object...
+LL |     type SubType<'a>: SubTrait where Self: 'a;
+   |          ^^^^^^^ ...because it contains the generic associated type `SubType`
+   = help: consider moving `SubType` to another trait
+   = help: only type `SuperStruct` is seen to implement the trait in this crate, consider using it directly instead
+   = note: `SuperTrait` can be implemented in other crates; if you want to support your users passing their own types here, you can't refer to a specific type
+
+error[E0038]: the trait `SuperTrait` cannot be made into an object
+  --> $DIR/issue-76535.rs:34:57
+   |
+LL |     let sub: Box<dyn SuperTrait<SubType = SubStruct>> = Box::new(SuperStruct::new(0));
+   |                                                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ `SuperTrait` cannot be made into an object
+   |
+note: for a trait to be "dyn-compatible" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/issue-76535.rs:4:10
+   |
+LL | pub trait SuperTrait {
+   |           ---------- this trait cannot be made into an object...
+LL |     type SubType<'a>: SubTrait where Self: 'a;
+   |          ^^^^^^^ ...because it contains the generic associated type `SubType`
+   = help: consider moving `SubType` to another trait
+   = help: only type `SuperStruct` is seen to implement the trait in this crate, consider using it directly instead
+   = note: `SuperTrait` can be implemented in other crates; if you want to support your users passing their own types here, you can't refer to a specific type
+   = note: required for the cast from `Box<SuperStruct>` to `Box<dyn SuperTrait<SubType<'_> = SubStruct<'_>>>`
+
+error: aborting due to 3 previous errors
+
+Some errors have detailed explanations: E0038, E0107.
+For more information about an error, try `rustc --explain E0038`.