rustdoc: clean up method path index

This removes a special case that doesn't seem to do anything
any more.

src/librustdoc/formats/cache.rs

@@ -288,15 +288,7 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
                             // for where the type was defined. On the other
                             // hand, `paths` always has the right
                             // information if present.
-                            Some(&(
-                                ref fqp,
-                                ItemType::Trait
-                                | ItemType::Struct
-                                | ItemType::Union
-                                | ItemType::Enum
-                                | ItemType::Typedef,
-                            )) => Some(&fqp[..fqp.len() - 1]),
-                            Some(..) => Some(&*self.cache.stack),
+                            Some(&(ref fqp, _)) => Some(&fqp[..fqp.len() - 1]),
                             None => None,
                         };
                         ((Some(*last), path), true)

src/test/rustdoc-js/foreign-type-path.js

@@ -0,0 +1,9 @@
+const QUERY = 'MyForeignType::my_method';
+
+const EXPECTED = {
+    'others': [
+        // Test case for https://github.com/rust-lang/rust/pull/96887#pullrequestreview-967154358
+        // Validates that the parent path for a foreign type method is correct.
+        { 'path': 'foreign_type_path::aaaaaaa::MyForeignType', 'name': 'my_method' },
+    ],
+};

src/test/rustdoc-js/foreign-type-path.rs

@@ -0,0 +1,13 @@
+#![feature(extern_types)]
+
+pub mod aaaaaaa {
+
+    extern {
+        pub type MyForeignType;
+    }
+
+    impl MyForeignType {
+        pub fn my_method() {}
+    }
+
+}