Auto merge of #32169 - mitaa:anon-tip, r=nrc

Allow custom filenames for anonymous inputs

This came out of #29253 but doesn't fix it.

I thought it might be worth merging on its own nonetheless.

src/librustdoc/clean/mod.rs

@@ -205,7 +205,7 @@ impl<'a, 'tcx> Clean<Crate> for visit_ast::RustdocVisitor<'a, 'tcx> {
                     current_dir().unwrap().join(path)
                 }
             },
-            Input::Str(_) => PathBuf::new() // FIXME: this is wrong
+            Input::Str { ref name, .. } => PathBuf::from(name.clone()),
         };
 
         Crate {