Add tests

tests/ui/traits/new-solver/alias_eq_cant_be_furthur_normalized.rs

@@ -0,0 +1,29 @@
+// check-pass
+// compile-flags: -Ztrait-solver=next
+
+// check that a goal such as `alias-eq(<T as TraitB>::Assoc<bool>, <T as TraitB>::Assoc<?0>)`
+// succeeds with a constraint that `?0 = bool`
+
+// FIXME(deferred_projection_equality): add a test that this is true during coherence
+
+trait TraitA {}
+
+trait TraitB {
+    type Assoc<T: ?Sized>;
+}
+
+impl<T: TraitB> TraitA for (T, T::Assoc<bool>) {}
+
+impl TraitB for i32 {
+    type Assoc<T: ?Sized> = u32;
+}
+
+fn needs_a<T: TraitA>() {}
+
+fn bar<T: TraitB>() {
+    needs_a::<(T, <T as TraitB>::Assoc<_>)>();
+}
+
+fn main() {
+    bar::<i32>();
+}

tests/ui/traits/new-solver/alias_eq_dont_use_normalizes_to_if_substs_eq.rs

@@ -0,0 +1,45 @@
+// compile-flags: -Ztrait-solver=next
+
+// check that when computing `alias-eq(<() as Foo<u16, T>>::Assoc, <() as Foo<?0, T>>::Assoc)`
+//  we do not infer `?0 = u8` via the `for<STOP> (): Foo<u8, STOP>` impl or `?0 = u16` by
+// relating substs as either could be a valid solution.
+
+trait Foo<T, STOP> {
+    type Assoc;
+}
+
+impl<STOP> Foo<u8, STOP> for ()
+where
+    (): Foo<u16, STOP>,
+{
+    type Assoc = <() as Foo<u16, STOP>>::Assoc;
+}
+
+impl Foo<u16, i8> for () {
+    type Assoc = u8;
+}
+
+impl Foo<u16, i16> for () {
+    type Assoc = u16;
+}
+
+fn output<T, U>() -> <() as Foo<T, U>>::Assoc
+where
+    (): Foo<T, U>,
+{
+    todo!()
+}
+
+fn incomplete<T>()
+where
+    (): Foo<u16, T>,
+{
+    // `<() as Foo<u16, STOP>>::Assoc == <() as Foo<_, STOP>>::Assoc`
+    let _: <() as Foo<u16, T>>::Assoc = output::<_, T>();
+    //~^ error: type annotations needed
+
+    // let _: <() as Foo<u16, T>>::Assoc = output::<u8, T>(); // OK
+    // let _: <() as Foo<u16, T>>::Assoc = output::<u16, T>(); // OK
+}
+
+fn main() {}

tests/ui/traits/new-solver/alias_eq_dont_use_normalizes_to_if_substs_eq.stderr

@@ -0,0 +1,9 @@
+error[E0282]: type annotations needed
+  --> $DIR/alias_eq_dont_use_normalizes_to_if_substs_eq.rs:38:41
+   |
+LL |     let _: <() as Foo<u16, T>>::Assoc = output::<_, T>();
+   |                                         ^^^^^^^^^^^^^^ cannot infer type of the type parameter `T` declared on the function `output`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.

tests/ui/traits/new-solver/alias_eq_simple.rs

@@ -0,0 +1,22 @@
+// check-pass
+// compile-flags: -Ztrait-solver=next
+
+// test that the new solver can handle `alias-eq(<i32 as TraitB>::Assoc, u32)`
+
+trait TraitA {}
+
+trait TraitB {
+    type Assoc;
+}
+
+impl<T: TraitB> TraitA for (T, T::Assoc) {}
+
+impl TraitB for i32 {
+    type Assoc = u32;
+}
+
+fn needs_a<T: TraitA>() {}
+
+fn main() {
+    needs_a::<(i32, u32)>();
+}

tests/ui/traits/new-solver/alias_eq_substs_eq_not_intercrate.rs

@@ -0,0 +1,20 @@
+// compile-flags: -Ztrait-solver=next
+
+// check that a `alias-eq(<?0 as TraitB>::Assoc, <T as TraitB>::Assoc)` goal fails.
+
+// FIXME(deferred_projection_equality): add a test that this is true during coherence
+
+trait TraitB {
+    type Assoc;
+}
+
+fn needs_a<T: TraitB>() -> T::Assoc {
+    unimplemented!()
+}
+
+fn bar<T: TraitB>() {
+    let _: <_ as TraitB>::Assoc = needs_a::<T>();
+    //~^ error: type annotations needed
+}
+
+fn main() {}

tests/ui/traits/new-solver/alias_eq_substs_eq_not_intercrate.stderr

@@ -0,0 +1,9 @@
+error[E0282]: type annotations needed
+  --> $DIR/alias_eq_substs_eq_not_intercrate.rs:16:12
+   |
+LL |     let _: <_ as TraitB>::Assoc = needs_a::<T>();
+   |            ^^^^^^^^^^^^^^^^^^^^ cannot infer type for associated type `<_ as TraitB>::Assoc`
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.

tests/ui/traits/new-solver/normalizes_to_ignores_unnormalizable_candidate.rs

@@ -0,0 +1,40 @@
+// [no_self_infer] check-pass
+// compile-flags: -Ztrait-solver=next
+// revisions: self_infer no_self_infer
+
+// checks that the new solver is smart enough to infer `?0 = U` when solving:
+// `normalizes-to(<Vec<?0> as Trait>::Assoc, u8)`
+// with `normalizes-to(<Vec<U> as Trait>::Assoc, u8)` in the paramenv even when
+// there is a separate `Vec<T>: Trait` bound  in the paramenv.
+//
+// FIXME(-Ztrait-solver=next)
+// This could also compile for `normalizes-to(<?0 as Trait>::Assoc, u8)` but
+// we currently immediately consider a goal ambiguous if the self type is an
+// inference variable.
+
+trait Trait {
+    type Assoc;
+}
+
+fn foo<T: Trait<Assoc = u8>>(x: T) {}
+
+#[cfg(self_infer)]
+fn unconstrained<T>() -> T {
+    todo!()
+}
+
+#[cfg(no_self_infer)]
+fn unconstrained<T>() -> Vec<T> {
+    todo!()
+}
+
+fn bar<T, U>()
+where
+    Vec<T>: Trait,
+    Vec<U>: Trait<Assoc = u8>,
+{
+    foo(unconstrained())
+    //[self_infer]~^ ERROR type annotations needed
+}
+
+fn main() {}

tests/ui/traits/new-solver/normalizes_to_ignores_unnormalizable_candidate.self_infer.stderr

@@ -0,0 +1,14 @@
+error[E0282]: type annotations needed
+  --> $DIR/normalizes_to_ignores_unnormalizable_candidate.rs:36:5
+   |
+LL |     foo(unconstrained())
+   |     ^^^ cannot infer type of the type parameter `T` declared on the function `foo`
+   |
+help: consider specifying the generic argument
+   |
+LL |     foo::<T>(unconstrained())
+   |        +++++
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0282`.