for purely return-type based searches, deprioritize clone-like functions

A clone-like function in a function that takes as an argument the type
that it returns.

However, functions that return a type variable are not counted as
clone-line. Because we're not unifying the whole function at once,
a function like `U -> T` would otherwise be counted as "clone-like"
because the generics will just unify with anything when done seperatly.

Co-authored-by: Michael Howell <michael@notriddle.com>

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

@@ -2717,9 +2717,26 @@ class DocSearch {
             const normalizedUserQuery = parsedQuery.userQuery.toLowerCase();
             const isMixedCase = normalizedUserQuery !== userQuery;
             const result_list = [];
+            const isReturnTypeQuery = parsedQuery.elems.length === 0 ||
+                typeInfo === "returned";
             for (const result of results.values()) {
                 result.item = this.searchIndex[result.id];
                 result.word = this.searchIndex[result.id].word;
+                if (isReturnTypeQuery) {
+                    // we are doing a return-type based search,
+                    // deprioritize "clone-like" results,
+                    // ie. functions that also take the queried type as an argument.
+                    const hasType = result.item && result.item.type;
+                    if (!hasType) {
+                        continue;
+                    }
+                    const inputs = result.item.type.inputs;
+                    const where_clause = result.item.type.where_clause;
+                    if (containsTypeFromQuery(inputs, where_clause)) {
+                        result.path_dist *= 100;
+                        result.dist *= 100;
+                    }
+                }
                 result_list.push(result);
             }
 
@@ -3540,6 +3557,35 @@ class DocSearch {
             return false;
         }
 
+        /**
+         * This function checks if the given list contains any
+         * (non-generic) types mentioned in the query.
+         *
+         * @param {Array<FunctionType>} list    - A list of function types.
+         * @param {[FunctionType]} where_clause - Trait bounds for generic items.
+         */
+        function containsTypeFromQuery(list, where_clause) {
+            if (!list) return false;
+            for (const ty of parsedQuery.returned) {
+                // negative type ids are generics
+                if (ty.id < 0) {
+                    continue;
+                }
+                if (checkIfInList(list, ty, where_clause, null, 0)) {
+                    return true;
+                }
+            }
+            for (const ty of parsedQuery.elems) {
+                if (ty.id < 0) {
+                    continue;
+                }
+                if (checkIfInList(list, ty, where_clause, null, 0)) {
+                    return true;
+                }
+            }
+            return false;
+        }
+
         /**
          * This function checks if the object (`row`) matches the given type (`elem`) and its
          * generics (if any).

tests/rustdoc-js-std/return-based-sort.js

@@ -0,0 +1,30 @@
+// test that `clone`-like functions are sorted lower when
+// a search is based soley on return type
+
+const FILTER_CRATE = "core";
+
+const EXPECTED = [
+    {
+        'query': '-> AllocError',
+        'others': [
+            { 'path': 'core::alloc::Allocator', 'name': 'allocate' },
+            { 'path': 'core::alloc::AllocError', 'name': 'clone' },
+        ],
+    },
+    {
+        'query': 'AllocError',
+        'returned': [
+            { 'path': 'core::alloc::Allocator', 'name': 'allocate' },
+            { 'path': 'core::alloc::AllocError', 'name': 'clone' },
+         ],
+    },
+    {
+        'query': '-> &str',
+        'others': [
+            // type_name_of_val should not be consider clone-like
+            { 'path': 'core::any', 'name': 'type_name_of_val' },
+            // this returns `Option<&str>`, and thus should be sorted lower
+            { 'path': 'core::str::Split', 'name': 'next' },
+         ],
+    },
+]