test(rustdoc): show the wrong --emit precedence

It should have the same behavior as rustc, which the last wins.

Author: weihanglo

tests/run-make/rustdoc-dep-info/rmake.rs

@@ -33,4 +33,17 @@ fn main() {
     // Now we check that we can provide a file name to the `dep-info` argument.
     rustdoc().input("lib.rs").arg("-Zunstable-options").emit("dep-info=bla.d").run();
     assert!(path("bla.d").exists());
+
+    // The last emit-type wins. The same behavior as rustc.
+    // TODO: this shows the wrong behavior as a MRE, which will be fixed in the next commit
+    rustdoc()
+        .input("lib.rs")
+        .arg("-Zunstable-options")
+        .emit("dep-info=precedence1.d")
+        .emit("dep-info=precedence2.d")
+        .emit("dep-info=precedence3.d")
+        .run();
+    assert!(path("precedence1.d").exists());
+    assert!(!path("precedence2.d").exists());
+    assert!(!path("precedence3.d").exists());
 }