add regression tests

Author: lcnr

tests/ui/traits/next-solver/assembly/candidates-equal-modulo-norm-1.rs

@@ -0,0 +1,26 @@
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#84.
+//
+// We try to infer `T::Rigid: Into<?0>` and have 2 candidates from where-clauses:
+//
+// - `Into<String>`
+// - `Into<<T::Rigid as Elaborate>::Assoc>`
+//
+// This causes ambiguity unless we normalize the alias in the second candidate
+// to detect that they actually result in the same constraints.
+trait Trait {
+    type Rigid: Elaborate<Assoc = String> + Into<String> + Default;
+}
+
+trait Elaborate: Into<Self::Assoc> {
+    type Assoc;
+}
+
+fn test<T: Trait>() {
+    let rigid: T::Rigid = Default::default();
+    drop(rigid.into());
+}
+
+fn main() {}

tests/ui/traits/next-solver/assembly/candidates-equal-modulo-norm-2.rs

@@ -0,0 +1,26 @@
+//@ compile-flags: -Znext-solver
+//@ check-pass
+
+// Regression test for trait-system-refactor-initiative#86. This previously
+// failed with ambiguity due to multiple candidates with different
+// normalization.
+
+trait Bar {
+    type Item;
+    type Assoc: AsRef<[Self::Item]>;
+}
+
+struct Foo<T: Bar> {
+    t: <T as Bar>::Assoc,
+}
+
+impl<T: Bar<Item = u32>> Foo<T>
+where
+    <T as Bar>::Assoc: AsRef<[u32]>,
+{
+    fn hello(&self) {
+        println!("{}", self.t.as_ref().len());
+    }
+}
+
+fn main() {}