Add regression test for remap-path-prefix handling in rustdoc for deps

Author: Urgau

tests/rustdoc/auxiliary/remapped-paths.rs

@@ -0,0 +1,11 @@
+//@ compile-flags:-Zunstable-options --remap-path-prefix={{src-base}}=
+
+pub struct MyStruct {
+    field: u32,
+}
+
+impl MyStruct {
+    pub fn new() -> MyStruct {
+        MyStruct { field: 3 }
+    }
+}

tests/rustdoc/import-remapped-paths.rs

@@ -0,0 +1,20 @@
+// This is a regression for `--remap-path-prefix` in an auxiliary dependency.
+//
+// We want to make sure that we can still have the "Source" links to the dependency
+// even if it's paths are remapped.
+//
+// See also rust-lang/rust#150100
+
+//@ aux-build:remapped-paths.rs
+//@ build-aux-docs
+
+#![crate_name = "foo"]
+
+extern crate remapped_paths;
+
+//@ has foo/struct.MyStruct.html
+// FIXME: Doesn't work!
+//@ has - '//a[@href="../src/remapped_paths/remapped-paths.rs.html#3"]' 'Source'
+//@ has - '//a[@href="../src/remapped_paths/remapped-paths.rs.html#8"]' 'Source'
+
+pub use remapped_paths::MyStruct;