Re-apply "remove unit-test and fix code related to sphinx-doc#12040"

This reverts commit 23da660.

sphinx/themes/basic/static/searchtools.js

@@ -483,7 +483,7 @@ const Search = {
         });
         Object.keys(titleTerms).forEach((term) => {
           if (term.match(escapedWord) && titleTerms[word] === undefined)
-            arr.push({ files: titleTerms[word], score: Scorer.partialTitle });
+            arr.push({ files: titleTerms[term], score: Scorer.partialTitle });
         });
       }
 

tests/js/searchtools.js

@@ -27,6 +27,31 @@ describe('Basic html theme search', function() {
       expect(Search.performTermsSearch(searchterms, excluded, terms, titleterms)).toEqual(hits);
     });
 
+    it('should partially-match "sphinx" when in title index', function() {
+      index = {
+        docnames:["index"],
+        filenames:["index.rst"],
+        terms:{'useful': 0, 'utilities': 0},
+        titles:["sphinx_utils module"],
+        titleterms:{'sphinx_utils': 0}
+      }
+      Search.setIndex(index);
+      searchterms = ['sphinx'];
+      excluded = [];
+      terms = index.terms;
+      titleterms = index.titleterms;
+
+      hits = [[
+        "index",
+        "sphinx_utils module",
+        "",
+        null,
+        7,
+        "index.rst"
+      ]];
+      expect(Search.performTermsSearch(searchterms, excluded, terms, titleterms)).toEqual(hits);
+    });
+
   });
 
 });