-Znext-solver Remove a problematic assertion from probing object bound candidates

compiler/rustc_next_trait_solver/src/solve/assembly/structural_traits.rs

@@ -962,8 +962,12 @@ where
             .iter()
             .filter(|source_projection| self.projection_may_match(**source_projection, alias_term));
         let Some(replacement) = matching_projections.next() else {
-            // This shouldn't happen.
-            panic!("could not replace {alias_term:?} with term from from {:?}", self.self_ty);
+            // This replacement is not the right one, i.e. we have projection which
+            // has the same `def_id` but cannot be normalized or should be normalized
+            // by other sources such as param env, not object bounds. This is as good
+            // as `replacement = None`, so just return like it.
+            // See https://github.com/rust-lang/rust/pull/152859.
+            return Ok(None);
         };
         // FIXME: This *may* have issues with duplicated projections.
         if matching_projections.next().is_some() {

tests/ui/traits/next-solver/object-projection-with-param-env-bound-1.rs

@@ -0,0 +1,24 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+// A regression test for https://github.com/rust-lang/rust/issues/152789.
+// Ensures we do not trigger an ICE or compilation error when normalizing
+// a projection on a trait object, where the matching trait predicate
+// (with the same trait id as the object bound) originates from another
+// source such as the param env, rather than from the object's own bounds.
+
+pub trait Trait<T> {
+    type Assoc;
+}
+
+pub trait Foo {
+    type FooAssoc;
+}
+
+pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc)
+where
+    dyn Trait<i32, Assoc = i64>: Trait<U::FooAssoc>;
+
+fn main() {}

tests/ui/traits/next-solver/object-projection-with-param-env-bound-2.rs

@@ -0,0 +1,35 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+
+// A regression test for https://github.com/rust-lang/rust/issues/152789.
+// Ensures we do not trigger an ICE or compilation error when normalizing
+// a projection on a trait object, where the matching trait predicate
+// (with the same trait id as the object bound) originates from another
+// source such as the param env, rather than from the object's own bounds.
+
+pub trait Trait<T> {
+    type Assoc;
+}
+
+pub trait Trait2<T> {
+    type Assoc2;
+}
+
+impl<T, U: ?Sized> Trait<T> for U
+where
+    U: Trait2<T>,
+{
+    type Assoc = <U as Trait2<T>>::Assoc2;
+}
+
+pub trait Foo {
+    type FooAssoc;
+}
+
+pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc)
+where
+    dyn Trait<i32, Assoc = i64>: Trait2<U::FooAssoc>;
+
+fn main() {}

tests/ui/traits/next-solver/object-projection-with-unsatisfied-bound-1.current.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the trait bound `(dyn Trait<i32, Assoc = i64> + 'static): Trait<<U as Foo>::FooAssoc>` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-1.rs:18:25
+   |
+LL | pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc);
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait<<U as Foo>::FooAssoc>` is not implemented for `(dyn Trait<i32, Assoc = i64> + 'static)`
+   |
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc) where (dyn Trait<i32, Assoc = i64> + 'static): Trait<<U as Foo>::FooAssoc>;
+   |                                                                                     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/next-solver/object-projection-with-unsatisfied-bound-1.next.stderr

@@ -0,0 +1,14 @@
+error[E0277]: the trait bound `(dyn Trait<i32, Assoc = i64> + 'static): Trait<<U as Foo>::FooAssoc>` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-1.rs:18:25
+   |
+LL | pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc);
+   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `Trait<<U as Foo>::FooAssoc>` is not implemented for `(dyn Trait<i32, Assoc = i64> + 'static)`
+   |
+help: consider introducing a `where` clause, but there might be an alternative better way to express this requirement
+   |
+LL | pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc) where (dyn Trait<i32, Assoc = i64> + 'static): Trait<<U as Foo>::FooAssoc>;
+   |                                                                                     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0277`.

tests/ui/traits/next-solver/object-projection-with-unsatisfied-bound-1.rs

@@ -0,0 +1,21 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+
+// A regression test for https://github.com/rust-lang/rust/issues/152789.
+// Ensures we do not trigger an ICE when normalization fails for a
+// projection on a trait object, even if the projection has the same
+// trait id as the object's bound.
+
+pub trait Trait<T> {
+    type Assoc;
+}
+
+pub trait Foo {
+    type FooAssoc;
+}
+
+pub struct Wrap<U: Foo>(<dyn Trait<i32, Assoc = i64> as Trait<U::FooAssoc>>::Assoc);
+//~^ ERROR: the trait bound `(dyn Trait<i32, Assoc = i64> + 'static): Trait<<U as Foo>::FooAssoc>` is not satisfied
+
+fn main() {}

tests/ui/traits/next-solver/object-projection-with-unsatisfied-bound-2.current.stderr

@@ -0,0 +1,58 @@
+error[E0277]: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:20:14
+   |
+LL | impl<T: Foo> Bar<dyn Callback<T>> {
+   |              ^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `(dyn Callback<T> + 'static)`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:10:1
+   |
+LL | trait Foo {
+   | ^^^^^^^^^
+note: required by a bound in `Bar`
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:16:15
+   |
+LL | struct Bar<T: Foo + ?Sized> {
+   |               ^^^ required by this bound in `Bar`
+
+error[E0277]: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:22:14
+   |
+LL |     fn event(&self) {
+   |              ^^^^^ the trait `Foo` is not implemented for `(dyn Callback<T> + 'static)`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:10:1
+   |
+LL | trait Foo {
+   | ^^^^^^^^^
+note: required by a bound in `Bar`
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:16:15
+   |
+LL | struct Bar<T: Foo + ?Sized> {
+   |               ^^^ required by this bound in `Bar`
+
+error[E0277]: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:24:9
+   |
+LL |         (self.callback)(any(), any());
+   |         ^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `(dyn Callback<T> + 'static)`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:10:1
+   |
+LL | trait Foo {
+   | ^^^^^^^^^
+
+error[E0618]: expected function, found `Box<(dyn Callback<(dyn Callback<T> + 'static), Output = ()> + 'static)>`
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:24:9
+   |
+LL |         (self.callback)(any(), any());
+   |         ^^^^^^^^^^^^^^^--------------
+   |         |
+   |         call expression requires function
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0277, E0618.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/traits/next-solver/object-projection-with-unsatisfied-bound-2.next.stderr

@@ -0,0 +1,58 @@
+error[E0277]: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:20:14
+   |
+LL | impl<T: Foo> Bar<dyn Callback<T>> {
+   |              ^^^^^^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `(dyn Callback<T> + 'static)`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:10:1
+   |
+LL | trait Foo {
+   | ^^^^^^^^^
+note: required by a bound in `Bar`
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:16:15
+   |
+LL | struct Bar<T: Foo + ?Sized> {
+   |               ^^^ required by this bound in `Bar`
+
+error[E0277]: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:22:14
+   |
+LL |     fn event(&self) {
+   |              ^^^^^ the trait `Foo` is not implemented for `(dyn Callback<T> + 'static)`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:10:1
+   |
+LL | trait Foo {
+   | ^^^^^^^^^
+note: required by a bound in `Bar`
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:16:15
+   |
+LL | struct Bar<T: Foo + ?Sized> {
+   |               ^^^ required by this bound in `Bar`
+
+error[E0618]: expected function, found `Box<(dyn Callback<(dyn Callback<T> + 'static)> + 'static)>`
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:24:9
+   |
+LL |         (self.callback)(any(), any());
+   |         ^^^^^^^^^^^^^^^--------------
+   |         |
+   |         call expression requires function
+
+error[E0277]: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:24:9
+   |
+LL |         (self.callback)(any(), any());
+   |         ^^^^^^^^^^^^^^^ the trait `Foo` is not implemented for `(dyn Callback<T> + 'static)`
+   |
+help: this trait has no implementations, consider adding one
+  --> $DIR/object-projection-with-unsatisfied-bound-2.rs:10:1
+   |
+LL | trait Foo {
+   | ^^^^^^^^^
+
+error: aborting due to 4 previous errors
+
+Some errors have detailed explanations: E0277, E0618.
+For more information about an error, try `rustc --explain E0277`.

tests/ui/traits/next-solver/object-projection-with-unsatisfied-bound-2.rs

@@ -0,0 +1,32 @@
+//@ revisions: current next
+//@[next] compile-flags: -Znext-solver
+//@ ignore-compare-mode-next-solver (explicit revisions)
+
+// A regression test for https://github.com/rust-lang/rust/issues/151329.
+// Ensures we do not trigger an ICE when normalization fails for a
+// projection on a trait object, even if the projection has the same
+// trait id as the object's bound.
+
+trait Foo {
+    type V;
+}
+
+trait Callback<T: Foo>: Fn(&T, &T::V) {}
+
+struct Bar<T: Foo + ?Sized> {
+    callback: Box<dyn Callback<T>>,
+}
+
+impl<T: Foo> Bar<dyn Callback<T>> {
+    //~^ ERROR: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+    fn event(&self) {
+        //~^ ERROR: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+        (self.callback)(any(), any());
+        //~^ ERROR: the trait bound `(dyn Callback<T> + 'static): Foo` is not satisfied
+        //~| ERROR: expected function
+    }
+}
+
+fn any() {}
+
+fn main() {}