Regression test for trait-system-refactor#7

tests/ui/traits/next-solver/alias-relate/transitive-inference.rs

@@ -0,0 +1,42 @@
+//@ revisions: old next
+//@[next] compile-flags: -Znext-solver=globally
+//@ ignore-compare-mode-next-solver (explicit revisions)
+//@ check-pass
+// Regression test for trait-system-refactor-initiative#7. This test
+// would error if we were to rely on lazy normalization here.
+//
+// We eagerly normalize the associated types, here, causing this to
+// compile.
+
+use std::marker::PhantomData;
+
+#[derive(Default)]
+struct Foo<T, U>(PhantomData<(T, U)>);
+
+trait Trait {
+    type Assoc;
+
+    fn to_assoc(self) -> Self::Assoc;
+}
+
+impl Trait for Foo<u32, i32> {
+    type Assoc = Foo<u32, i32>;
+    fn to_assoc(self) -> Self::Assoc {
+        Foo(PhantomData)
+    }
+}
+impl Trait for Foo<i32, u32> {
+    type Assoc = Foo<i32, u32>;
+    fn to_assoc(self) -> Self::Assoc {
+        Foo(PhantomData)
+    }
+}
+
+#[allow(unused_assignments)]
+fn main() {
+    let mut x: Foo<_, _> = Default::default();
+    let mut assoc = x.to_assoc();
+    assoc = Foo::<u32, _>(PhantomData);
+    assoc = Foo::<_, i32>(PhantomData);
+    x = assoc;
+}