Rollup merge of #81223 - GuillaumeGomez:generate-redirect-map, r=jyn514

[rustdoc] Generate redirect map file

Fixes #81134.

So with this code:

```rust
#![crate_name = "foo"]

pub use private::Quz;
pub use hidden::Bar;

mod private {
    pub struct Quz;
}

#[doc(hidden)]
pub mod hidden {
    pub struct Bar;
}

#[macro_export]
macro_rules! foo {
() => {}
}
```

It generates:

```json
{
  "foo/macro.foo!.html": "foo/macro.foo.html",
  "foo/private/struct.Quz.html": "foo/struct.Quz.html",
  "foo/hidden/struct.Bar.html": "foo/struct.Bar.html"
}
```

Do the pathes look as you expected ````@pietroalbini?````

r? ````@jyn514````

2 files changed, 29 insertions, 0 deletions

diff --git a/src/test/rustdoc/redirect-map-empty.rs b/src/test/rustdoc/redirect-map-empty.rs
new file mode 100644
index 00000000000..e9d021e0fa8
--- /dev/null
+++ b/src/test/rustdoc/redirect-map-empty.rs
@@ -0,0 +1,6 @@
+// compile-flags: -Z unstable-options --generate-redirect-map
+
+#![crate_name = "foo"]
+
+// @!has foo/redirect-map.json
+pub struct Foo;
diff --git a/src/test/rustdoc/redirect-map.rs b/src/test/rustdoc/redirect-map.rs
new file mode 100644
index 00000000000..b7f16b64e38
--- /dev/null
+++ b/src/test/rustdoc/redirect-map.rs
@@ -0,0 +1,23 @@
+// compile-flags: -Z unstable-options --generate-redirect-map
+
+#![crate_name = "foo"]
+
+// @!has foo/private/struct.Quz.html
+// @!has foo/hidden/struct.Bar.html
+// @has foo/redirect-map.json
+pub use private::Quz;
+pub use hidden::Bar;
+
+mod private {
+    pub struct Quz;
+}
+
+#[doc(hidden)]
+pub mod hidden {
+    pub struct Bar;
+}
+
+#[macro_export]
+macro_rules! foo {
+  () => {}
+}