Immutable and mutable? are covariant on their inner types

Whereas [mutable T] is invariant with respect to T, [T] and [mutable? T]
are covariant with respect to T.

2 files changed, 26 insertions, 0 deletions

diff --git a/src/test/run-pass/mutable-huh-variance-vec1.rs b/src/test/run-pass/mutable-huh-variance-vec1.rs
new file mode 100644
index 00000000000..5fb49cf88ce
--- /dev/null
+++ b/src/test/run-pass/mutable-huh-variance-vec1.rs
@@ -0,0 +1,13 @@
+// error-pattern: mismatched types
+
+fn main() {
+    let v = [[0]];
+
+    // This is ok because the outer vec is covariant with respect
+    // to the inner vec. If the outer vec was mutable then we
+    // couldn't do this.
+    fn f(&&v: [[mutable? int]]) {
+    }
+
+    f(v);
+}
diff --git a/src/test/run-pass/mutable-huh-variance-vec2.rs b/src/test/run-pass/mutable-huh-variance-vec2.rs
new file mode 100644
index 00000000000..1e254e86806
--- /dev/null
+++ b/src/test/run-pass/mutable-huh-variance-vec2.rs
@@ -0,0 +1,13 @@
+// error-pattern: mismatched types
+
+fn main() {
+    let v = [[0]];
+
+    // This is ok because the outer vec is covariant with respect
+    // to the inner vec. If the outer vec was mutable then we
+    // couldn't do this.
+    fn f(&&v: [mutable? [mutable? int]]) {
+    }
+
+    f(v);
+}