new test which features conflicting variance requirements

src/test/compile-fail/mutable-huh-variance-vec4.rs

@@ -0,0 +1,46 @@
+fn main() {
+
+    // Note: here we do not have any type annotations
+    // but we do express conflicting requirements:
+
+    let v = [mut [0]];
+    let w = [mut [mut 0]];
+    let x = [mut [mut 0]];
+
+    fn f(&&v: [mut [int]]) {
+        v[0] = [3]
+    }
+
+    fn g(&&v: [const [const int]]) {
+    }
+
+    fn h(&&v: [mut [mut int]]) {
+        v[0] = [mut 3]
+    }
+
+    fn i(&&v: [mut [const int]]) {
+        v[0] = [mut 3]
+    }
+
+    fn j(&&v: [[const int]]) {
+    }
+
+    f(v);
+    g(v);
+    h(v); //! ERROR (values differ in mutability)
+    i(v); //! ERROR (values differ in mutability)
+    j(v); //! ERROR (values differ in mutability)
+
+    f(w); //! ERROR (values differ in mutability)
+    g(w);
+    h(w);
+    i(w); //! ERROR (values differ in mutability)
+    j(w); //! ERROR (values differ in mutability)
+
+    // Note that without adding f() or h() to the mix, it is valid for
+    // x to have the type [mut [const int]], and thus we can safely
+    // call g() and i() but not j():
+    g(x);
+    i(x);
+    j(x); //! ERROR (values differ in mutability)
+}