Auto merge of rust-lang#125786 - compiler-errors:fold-item-bounds, r=lcnr

Fold item bounds before proving them in `check_type_bounds` in new solver

Vaguely confident that this is sufficient to prevent rust-lang/trait-system-refactor-initiative#46 and rust-lang/trait-system-refactor-initiative#62.

This is not the "correct" solution, but will probably suffice until coinduction, at which point we implement the right solution (`check_type_bounds` must prove `Assoc<...> alias-eq ConcreteType`, normalizing requires proving item bounds).

r? lcnr

Author: bors

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -2026,10 +2026,19 @@ pub(super) fn check_type_bounds<'tcx>(
     // to its definition type. This should be the param-env we use to *prove* the
     // predicate too, but we don't do that because of performance issues.
     // See <https://github.com/rust-lang/rust/pull/117542#issue-1976337685>.
+    let trait_projection_ty = Ty::new_projection(tcx, trait_ty.def_id, rebased_args);
+    let impl_identity_ty = tcx.type_of(impl_ty.def_id).instantiate_identity();
     let normalize_param_env = param_env_with_gat_bounds(tcx, impl_ty, impl_trait_ref);
     for mut obligation in util::elaborate(tcx, obligations) {
-        let normalized_predicate =
-            ocx.normalize(&normalize_cause, normalize_param_env, obligation.predicate);
+        let normalized_predicate = if infcx.next_trait_solver() {
+            obligation.predicate.fold_with(&mut ReplaceTy {
+                tcx,
+                from: trait_projection_ty,
+                to: impl_identity_ty,
+            })
+        } else {
+            ocx.normalize(&normalize_cause, normalize_param_env, obligation.predicate)
+        };
         debug!("compare_projection_bounds: normalized predicate = {:?}", normalized_predicate);
         obligation.predicate = normalized_predicate;
 
@@ -2050,6 +2059,22 @@ pub(super) fn check_type_bounds<'tcx>(
     ocx.resolve_regions_and_report_errors(impl_ty_def_id, &outlives_env)
 }
 
+struct ReplaceTy<'tcx> {
+    tcx: TyCtxt<'tcx>,
+    from: Ty<'tcx>,
+    to: Ty<'tcx>,
+}
+
+impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ReplaceTy<'tcx> {
+    fn interner(&self) -> TyCtxt<'tcx> {
+        self.tcx
+    }
+
+    fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
+        if self.from == ty { self.to } else { ty.super_fold_with(self) }
+    }
+}
+
 /// Install projection predicates that allow GATs to project to their own
 /// definition types. This is not allowed in general in cases of default
 /// associated types in trait definitions, or when specialization is involved,

tests/ui/associated-types/defaults-suitability.stderr tests/ui/associated-types/defaults-suitability.current.stderr

@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `NotClone: Clone` is not satisfied
-  --> $DIR/defaults-suitability.rs:13:22
+  --> $DIR/defaults-suitability.rs:16:22
    |
 LL |     type Ty: Clone = NotClone;
    |                      ^^^^^^^^ the trait `Clone` is not implemented for `NotClone`
    |
 note: required by a bound in `Tr::Ty`
-  --> $DIR/defaults-suitability.rs:13:14
+  --> $DIR/defaults-suitability.rs:16:14
    |
 LL |     type Ty: Clone = NotClone;
    |              ^^^^^ required by this bound in `Tr::Ty`
@@ -16,13 +16,13 @@ LL | struct NotClone;
    |
 
 error[E0277]: the trait bound `NotClone: Clone` is not satisfied
-  --> $DIR/defaults-suitability.rs:22:15
+  --> $DIR/defaults-suitability.rs:25:15
    |
 LL |     type Ty = NotClone;
    |               ^^^^^^^^ the trait `Clone` is not implemented for `NotClone`
    |
 note: required by a bound in `Tr2::Ty`
-  --> $DIR/defaults-suitability.rs:20:15
+  --> $DIR/defaults-suitability.rs:23:15
    |
 LL |     Self::Ty: Clone,
    |               ^^^^^ required by this bound in `Tr2::Ty`
@@ -36,14 +36,14 @@ LL | struct NotClone;
    |
 
 error[E0277]: the trait bound `T: Clone` is not satisfied
-  --> $DIR/defaults-suitability.rs:28:23
+  --> $DIR/defaults-suitability.rs:31:23
    |
 LL |     type Bar: Clone = Vec<T>;
    |                       ^^^^^^ the trait `Clone` is not implemented for `T`, which is required by `Vec<T>: Clone`
    |
    = note: required for `Vec<T>` to implement `Clone`
 note: required by a bound in `Foo::Bar`
-  --> $DIR/defaults-suitability.rs:28:15
+  --> $DIR/defaults-suitability.rs:31:15
    |
 LL |     type Bar: Clone = Vec<T>;
    |               ^^^^^ required by this bound in `Foo::Bar`
@@ -53,30 +53,30 @@ LL | trait Foo<T: std::clone::Clone> {
    |            +++++++++++++++++++
 
 error[E0277]: the trait bound `(): Foo<Self>` is not satisfied
-  --> $DIR/defaults-suitability.rs:34:29
+  --> $DIR/defaults-suitability.rs:37:29
    |
 LL |     type Assoc: Foo<Self> = ();
    |                             ^^ the trait `Foo<Self>` is not implemented for `()`
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/defaults-suitability.rs:27:1
+  --> $DIR/defaults-suitability.rs:30:1
    |
 LL | trait Foo<T> {
    | ^^^^^^^^^^^^
 note: required by a bound in `Bar::Assoc`
-  --> $DIR/defaults-suitability.rs:34:17
+  --> $DIR/defaults-suitability.rs:37:17
    |
 LL |     type Assoc: Foo<Self> = ();
    |                 ^^^^^^^^^ required by this bound in `Bar::Assoc`
 
 error[E0277]: the trait bound `NotClone: IsU8<NotClone>` is not satisfied
-  --> $DIR/defaults-suitability.rs:56:18
+  --> $DIR/defaults-suitability.rs:59:18
    |
 LL |     type Assoc = NotClone;
    |                  ^^^^^^^^ the trait `IsU8<NotClone>` is not implemented for `NotClone`
    |
 note: required by a bound in `D::Assoc`
-  --> $DIR/defaults-suitability.rs:53:18
+  --> $DIR/defaults-suitability.rs:56:18
    |
 LL |     Self::Assoc: IsU8<Self::Assoc>,
    |                  ^^^^^^^^^^^^^^^^^ required by this bound in `D::Assoc`
@@ -85,14 +85,14 @@ LL |     type Assoc = NotClone;
    |          ----- required by a bound in this associated type
 
 error[E0277]: the trait bound `<Self as Foo2<T>>::Baz: Clone` is not satisfied
-  --> $DIR/defaults-suitability.rs:65:23
+  --> $DIR/defaults-suitability.rs:68:23
    |
 LL |     type Bar: Clone = Vec<Self::Baz>;
    |                       ^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `<Self as Foo2<T>>::Baz`, which is required by `Vec<<Self as Foo2<T>>::Baz>: Clone`
    |
    = note: required for `Vec<<Self as Foo2<T>>::Baz>` to implement `Clone`
 note: required by a bound in `Foo2::Bar`
-  --> $DIR/defaults-suitability.rs:65:15
+  --> $DIR/defaults-suitability.rs:68:15
    |
 LL |     type Bar: Clone = Vec<Self::Baz>;
    |               ^^^^^ required by this bound in `Foo2::Bar`
@@ -102,14 +102,14 @@ LL | trait Foo2<T> where <Self as Foo2<T>>::Baz: Clone {
    |               +++++++++++++++++++++++++++++++++++
 
 error[E0277]: the trait bound `<Self as Foo25<T>>::Baz: Clone` is not satisfied
-  --> $DIR/defaults-suitability.rs:74:23
+  --> $DIR/defaults-suitability.rs:77:23
    |
 LL |     type Bar: Clone = Vec<Self::Baz>;
    |                       ^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `<Self as Foo25<T>>::Baz`, which is required by `Vec<<Self as Foo25<T>>::Baz>: Clone`
    |
    = note: required for `Vec<<Self as Foo25<T>>::Baz>` to implement `Clone`
 note: required by a bound in `Foo25::Bar`
-  --> $DIR/defaults-suitability.rs:74:15
+  --> $DIR/defaults-suitability.rs:77:15
    |
 LL |     type Bar: Clone = Vec<Self::Baz>;
    |               ^^^^^ required by this bound in `Foo25::Bar`
@@ -119,13 +119,13 @@ LL | trait Foo25<T: Clone> where <Self as Foo25<T>>::Baz: Clone {
    |                       ++++++++++++++++++++++++++++++++++++
 
 error[E0277]: the trait bound `T: Clone` is not satisfied
-  --> $DIR/defaults-suitability.rs:87:16
+  --> $DIR/defaults-suitability.rs:90:16
    |
 LL |     type Baz = T;
    |                ^ the trait `Clone` is not implemented for `T`
    |
 note: required by a bound in `Foo3::Baz`
-  --> $DIR/defaults-suitability.rs:84:16
+  --> $DIR/defaults-suitability.rs:87:16
    |
 LL |     Self::Baz: Clone,
    |                ^^^^^ required by this bound in `Foo3::Baz`

tests/ui/associated-types/defaults-suitability.next.stderr

@@ -0,0 +1,142 @@
+error[E0277]: the trait bound `NotClone: Clone` is not satisfied
+  --> $DIR/defaults-suitability.rs:16:22
+   |
+LL |     type Ty: Clone = NotClone;
+   |                      ^^^^^^^^ the trait `Clone` is not implemented for `NotClone`
+   |
+note: required by a bound in `Tr::Ty`
+  --> $DIR/defaults-suitability.rs:16:14
+   |
+LL |     type Ty: Clone = NotClone;
+   |              ^^^^^ required by this bound in `Tr::Ty`
+help: consider annotating `NotClone` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct NotClone;
+   |
+
+error[E0277]: the trait bound `NotClone: Clone` is not satisfied
+  --> $DIR/defaults-suitability.rs:25:15
+   |
+LL |     type Ty = NotClone;
+   |               ^^^^^^^^ the trait `Clone` is not implemented for `NotClone`
+   |
+note: required by a bound in `Tr2::Ty`
+  --> $DIR/defaults-suitability.rs:23:15
+   |
+LL |     Self::Ty: Clone,
+   |               ^^^^^ required by this bound in `Tr2::Ty`
+LL | {
+LL |     type Ty = NotClone;
+   |          -- required by a bound in this associated type
+help: consider annotating `NotClone` with `#[derive(Clone)]`
+   |
+LL + #[derive(Clone)]
+LL | struct NotClone;
+   |
+
+error[E0277]: the trait bound `T: Clone` is not satisfied
+  --> $DIR/defaults-suitability.rs:31:23
+   |
+LL |     type Bar: Clone = Vec<T>;
+   |                       ^^^^^^ the trait `Clone` is not implemented for `T`, which is required by `Vec<T>: Clone`
+   |
+   = note: required for `Vec<T>` to implement `Clone`
+note: required by a bound in `Foo::Bar`
+  --> $DIR/defaults-suitability.rs:31:15
+   |
+LL |     type Bar: Clone = Vec<T>;
+   |               ^^^^^ required by this bound in `Foo::Bar`
+help: consider restricting type parameter `T`
+   |
+LL | trait Foo<T: std::clone::Clone> {
+   |            +++++++++++++++++++
+
+error[E0277]: the trait bound `(): Foo<Self>` is not satisfied
+  --> $DIR/defaults-suitability.rs:37:29
+   |
+LL |     type Assoc: Foo<Self> = ();
+   |                             ^^ the trait `Foo<Self>` is not implemented for `()`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/defaults-suitability.rs:30:1
+   |
+LL | trait Foo<T> {
+   | ^^^^^^^^^^^^
+note: required by a bound in `Bar::Assoc`
+  --> $DIR/defaults-suitability.rs:37:17
+   |
+LL |     type Assoc: Foo<Self> = ();
+   |                 ^^^^^^^^^ required by this bound in `Bar::Assoc`
+
+error[E0277]: the trait bound `NotClone: IsU8<NotClone>` is not satisfied
+  --> $DIR/defaults-suitability.rs:59:18
+   |
+LL |     type Assoc = NotClone;
+   |                  ^^^^^^^^ the trait `IsU8<NotClone>` is not implemented for `NotClone`
+   |
+note: required by a bound in `D::Assoc`
+  --> $DIR/defaults-suitability.rs:56:18
+   |
+LL |     Self::Assoc: IsU8<Self::Assoc>,
+   |                  ^^^^^^^^^^^^^^^^^ required by this bound in `D::Assoc`
+...
+LL |     type Assoc = NotClone;
+   |          ----- required by a bound in this associated type
+
+error[E0277]: the trait bound `<Self as Foo2<T>>::Baz: Clone` is not satisfied
+  --> $DIR/defaults-suitability.rs:68:23
+   |
+LL |     type Bar: Clone = Vec<Self::Baz>;
+   |                       ^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `<Self as Foo2<T>>::Baz`, which is required by `Vec<<Self as Foo2<T>>::Baz>: Clone`
+   |
+   = note: required for `Vec<<Self as Foo2<T>>::Baz>` to implement `Clone`
+note: required by a bound in `Foo2::Bar`
+  --> $DIR/defaults-suitability.rs:68:15
+   |
+LL |     type Bar: Clone = Vec<Self::Baz>;
+   |               ^^^^^ required by this bound in `Foo2::Bar`
+help: consider further restricting the associated type
+   |
+LL | trait Foo2<T> where <Self as Foo2<T>>::Baz: Clone {
+   |               +++++++++++++++++++++++++++++++++++
+
+error[E0277]: the trait bound `<Self as Foo25<T>>::Baz: Clone` is not satisfied
+  --> $DIR/defaults-suitability.rs:77:23
+   |
+LL |     type Bar: Clone = Vec<Self::Baz>;
+   |                       ^^^^^^^^^^^^^^ the trait `Clone` is not implemented for `<Self as Foo25<T>>::Baz`, which is required by `Vec<<Self as Foo25<T>>::Baz>: Clone`
+   |
+   = note: required for `Vec<<Self as Foo25<T>>::Baz>` to implement `Clone`
+note: required by a bound in `Foo25::Bar`
+  --> $DIR/defaults-suitability.rs:77:15
+   |
+LL |     type Bar: Clone = Vec<Self::Baz>;
+   |               ^^^^^ required by this bound in `Foo25::Bar`
+help: consider further restricting the associated type
+   |
+LL | trait Foo25<T: Clone> where <Self as Foo25<T>>::Baz: Clone {
+   |                       ++++++++++++++++++++++++++++++++++++
+
+error[E0277]: the trait bound `T: Clone` is not satisfied
+  --> $DIR/defaults-suitability.rs:90:16
+   |
+LL |     type Baz = T;
+   |                ^ the trait `Clone` is not implemented for `T`
+   |
+note: required by a bound in `Foo3::Baz`
+  --> $DIR/defaults-suitability.rs:87:16
+   |
+LL |     Self::Baz: Clone,
+   |                ^^^^^ required by this bound in `Foo3::Baz`
+...
+LL |     type Baz = T;
+   |          --- required by a bound in this associated type
+help: consider further restricting type parameter `T`
+   |
+LL |     Self::Baz: Clone, T: std::clone::Clone
+   |                     ~~~~~~~~~~~~~~~~~~~~~~
+
+error: aborting due to 8 previous errors
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/associated-types/defaults-suitability.rs

@@ -1,3 +1,6 @@
+//@ revisions: current next
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@[next] compile-flags: -Znext-solver
 //! Checks that associated type defaults are properly validated.
 //!
 //! This means:

tests/ui/associated-types/defaults-unsound-62211-1.current.stderr

@@ -1,12 +1,12 @@
 error[E0277]: `Self` doesn't implement `std::fmt::Display`
-  --> $DIR/defaults-unsound-62211-1.rs:26:96
+  --> $DIR/defaults-unsound-62211-1.rs:24:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ `Self` cannot be formatted with the default formatter
    |
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:26:86
+  --> $DIR/defaults-unsound-62211-1.rs:24:86
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                      ^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -16,13 +16,13 @@ LL | trait UncheckedCopy: Sized + std::fmt::Display {
    |                            +++++++++++++++++++
 
 error[E0277]: cannot add-assign `&'static str` to `Self`
-  --> $DIR/defaults-unsound-62211-1.rs:26:96
+  --> $DIR/defaults-unsound-62211-1.rs:24:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ no implementation for `Self += &'static str`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:26:47
+  --> $DIR/defaults-unsound-62211-1.rs:24:47
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                               ^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -32,13 +32,13 @@ LL | trait UncheckedCopy: Sized + AddAssign<&'static str> {
    |                            +++++++++++++++++++++++++
 
 error[E0277]: the trait bound `Self: Deref` is not satisfied
-  --> $DIR/defaults-unsound-62211-1.rs:26:96
+  --> $DIR/defaults-unsound-62211-1.rs:24:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ the trait `Deref` is not implemented for `Self`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:26:25
+  --> $DIR/defaults-unsound-62211-1.rs:24:25
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                         ^^^^^^^^^^^^^^^^^^^ required by this bound in `UncheckedCopy::Output`
@@ -48,13 +48,13 @@ LL | trait UncheckedCopy: Sized + Deref {
    |                            +++++++
 
 error[E0277]: the trait bound `Self: Copy` is not satisfied
-  --> $DIR/defaults-unsound-62211-1.rs:26:96
+  --> $DIR/defaults-unsound-62211-1.rs:24:96
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                                                                                                ^^^^ the trait `Copy` is not implemented for `Self`
    |
 note: required by a bound in `UncheckedCopy::Output`
-  --> $DIR/defaults-unsound-62211-1.rs:26:18
+  --> $DIR/defaults-unsound-62211-1.rs:24:18
    |
 LL |     type Output: Copy + Deref<Target = str> + AddAssign<&'static str> + From<Self> + Display = Self;
    |                  ^^^^ required by this bound in `UncheckedCopy::Output`