rustdoc: add test case for the implementors JS file placement

src/test/rustdoc/inline_cross/auxiliary/implementors_inline.rs

@@ -0,0 +1,18 @@
+pub mod my_trait {
+    pub trait MyTrait {
+        fn my_fn(&self) -> Self;
+    }
+}
+
+pub mod prelude {
+    #[doc(inline)]
+    pub use crate::my_trait::MyTrait;
+}
+
+pub struct SomeStruct;
+
+impl my_trait::MyTrait for SomeStruct {
+    fn my_fn(&self) -> SomeStruct {
+        SomeStruct
+    }
+}

src/test/rustdoc/inline_cross/implementors-js.rs

@@ -0,0 +1,25 @@
+// aux-build:implementors_inline.rs
+// build-aux-docs
+// ignore-cross-compile
+
+extern crate implementors_inline;
+
+// @!has implementors/implementors_js/trait.MyTrait.js
+// @has implementors/implementors_inline/my_trait/trait.MyTrait.js
+// @!has implementors/implementors_inline/prelude/trait.MyTrait.js
+// @has implementors_inline/my_trait/trait.MyTrait.html
+// @has - '//script/@src' '../../implementors/implementors_inline/my_trait/trait.MyTrait.js'
+// @has implementors_js/trait.MyTrait.html
+// @has - '//script/@src' '../implementors/implementors_inline/my_trait/trait.MyTrait.js'
+/// When re-exporting this trait, the HTML will be inlined,
+/// but, vitally, the JavaScript will be located only at the
+/// one canonical path.
+pub use implementors_inline::prelude::MyTrait;
+
+pub struct OtherStruct;
+
+impl MyTrait for OtherStruct {
+    fn my_fn(&self) -> OtherStruct {
+        OtherStruct
+    }
+}