Add regression tests

Author: oli-obk

src/test/ui/consts/self_normalization.rs

@@ -0,0 +1,16 @@
+// compile-pass
+
+fn testfn(_arr: &mut [();0]) {}
+
+trait TestTrait {
+    fn method();
+}
+
+impl TestTrait for [(); 0] {
+    fn method() {
+        let mut arr: Self = [(); 0];
+        testfn(&mut arr);
+    }
+}
+
+fn main() {}

src/test/ui/consts/self_normalization2.rs

@@ -0,0 +1,21 @@
+// compile-pass
+
+trait Gen<T> {
+    fn gen(x: Self) -> T;
+}
+
+struct A;
+
+impl Gen<[(); 0]> for A {
+    fn gen(x: Self) -> [(); 0] {
+        []
+    }
+}
+
+fn array() -> impl Gen<[(); 0]> {
+    A
+}
+
+fn main() {
+    let [] = Gen::gen(array());
+}