Add test

Author: JohnTitor

src/test/ui/lint/lint-forbid-internal-unsafe.rs

@@ -0,0 +1,16 @@
+#![forbid(unsafe_code)]
+#![feature(allow_internal_unsafe)]
+
+#[allow_internal_unsafe]
+//~^ ERROR: cannot use `allow_internal_unsafe` with `forbid(unsafe_code)`
+macro_rules! evil {
+    ($e:expr) => {
+        unsafe {
+            $e
+        }
+    }
+}
+
+fn main() {
+    println!("{}", evil!(*(0 as *const u8)));
+}

src/test/ui/lint/lint-forbid-internal-unsafe.stderr

@@ -0,0 +1,14 @@
+error: cannot use `allow_internal_unsafe` with `forbid(unsafe_code)`
+  --> $DIR/lint-forbid-internal-unsafe.rs:4:1
+   |
+LL | #[allow_internal_unsafe]
+   | ^^^^^^^^^^^^^^^^^^^^^^^^
+   |
+note: lint level defined here
+  --> $DIR/lint-forbid-internal-unsafe.rs:1:11
+   |
+LL | #![forbid(unsafe_code)]
+   |           ^^^^^^^^^^^
+
+error: aborting due to previous error
+