Replace compiletest suite by doc-tests with compile_fail

compiletest-rs use internal rustc APIs and is broken in today’s Nightly.
rustdoc however is maintained with rustc and so much less fragile.

tests/unit/script_plugins/lib.rs

@@ -0,0 +1,63 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+pub mod unrooted_must_root {
+    /**
+    ```
+    #![feature(plugin)]
+    #![plugin(script_plugins)]
+
+    #[must_root] struct Foo(i32);
+    #[must_root] struct Bar(Foo);
+
+    fn foo1(_: &Foo) {}
+    fn foo2(_: &()) -> &Foo { unimplemented!() }
+
+    fn main() {}
+    ```
+    */
+    pub fn ok() {}
+
+    /**
+    ```compile_fail
+    #![feature(plugin)]
+    #![plugin(script_plugins)]
+
+    #[must_root] struct Foo(i32);
+    struct Bar(Foo);
+
+    fn main() {}
+    ```
+    */
+    pub fn struct_field() {}
+
+    /**
+    ```compile_fail
+    #![feature(plugin)]
+    #![plugin(script_plugins)]
+
+    #[must_root] struct Foo(i32);
+
+    fn foo1(_: Foo) {}
+
+    fn main() {}
+    ```
+    */
+    pub fn parameter() {}
+
+    /**
+    ```compile_fail
+    #![feature(plugin)]
+    #![plugin(script_plugins)]
+
+    #[must_root] struct Foo(i32);
+
+    fn foo2() -> Foo { unimplemented!() }
+
+    fn main() {}
+    ```
+    */
+    pub fn return_type() {}
+
+}