rustdoc search: allow queries to end in an empty path segment

fixes rust-lang#129707

this can be used to show all items in a module,
or all associated items for a type.
currently sufferes slightly due to case insensitivity,
so `Option::` will also show items in the `option::` module.

it disables the checking of the last path element,
otherwise only items with short names will be shown

src/librustdoc/html/static/js/search.js

@@ -681,8 +681,6 @@ function createQueryElement(query, parserState, name, generics, isInGenerics) {
     const quadcolon = /::\s*::/.exec(path);
     if (path.startsWith("::")) {
         throw ["Paths cannot start with ", "::"];
-    } else if (path.endsWith("::")) {
-        throw ["Paths cannot end with ", "::"];
     } else if (quadcolon !== null) {
         throw ["Unexpected ", quadcolon[0]];
     }
@@ -3029,11 +3027,17 @@ class DocSearch {
                 return;
             }
 
-            const dist = editDistance(row.normalizedName, elem.normalizedPathLast, maxEditDistance);
-
-            if (index === -1 && dist > maxEditDistance) {
-                return;
-            }
+            let dist = 0;
+            if (elem.pathLast === "") {
+	            if (path_dist > 0) {
+		            return;
+		        }
+		    } else {
+	            dist = editDistance(row.normalizedName, elem.normalizedPathLast, maxEditDistance);
+	            if (index === -1 && dist > maxEditDistance) {
+	                return;
+	            }
+	        }
 
             addIntoResults(results_others, fullId, pos, index, dist, path_dist, maxEditDistance);
         }

tests/rustdoc-js-std/path-end-empty.js

@@ -0,0 +1,6 @@
+const EXPECTED = {
+    'query': 'Option::',
+    'others': [
+        { 'path': 'std::option::Option', 'name': 'get_or_insert_default' },
+    ],
+}