rustdoc: sort search index items for compression

This should not affect the appearance of the docs pages themselves.

This makes the pre-compressed search index smaller, thanks to the
empty-string path duplication format, and also the gzipped version,
by giving the algorithm more structure to work with.

    rust$ wc -c search-index-old.js search-index-new.js
    2628334 search-index-old.js
    2586181 search-index-new.js
    5214515 total
    rust$ gzip search-index-*
    rust$ wc -c search-index-old.js.gz search-index-new.js.gz
    239486 search-index-old.js.gz
    237386 search-index-new.js.gz
    476872 total

1 files changed, 1 insertions, 8 deletions

diff --git a/src/librustdoc/formats/cache.rs b/src/librustdoc/formats/cache.rs
index 01bceb1d910..7100cc87b0c 100644
--- a/src/librustdoc/formats/cache.rs
+++ b/src/librustdoc/formats/cache.rs
@@ -309,15 +309,8 @@ impl<'a, 'tcx> DocFolder for CacheBuilder<'a, 'tcx> {
                             parent,
                             parent_idx: None,
                             search_type: get_index_search_type(&item, &self.empty_cache, self.tcx),
+                            aliases: item.attrs.get_doc_aliases(),
                         });
-
-                        for alias in item.attrs.get_doc_aliases() {
-                            self.cache
-                                .aliases
-                                .entry(alias.to_lowercase())
-                                .or_insert(Vec::new())
-                                .push(self.cache.search_index.len() - 1);
-                        }
                     }
                 }
                 (Some(parent), None) if is_inherent_impl_item => {