[HTML search] include partially-matched document titles in search results (#12041)

Co-authored-by: William Lachance <wlach@protonmail.com>

CHANGES.rst

@@ -139,6 +139,9 @@ Bugs fixed
 * #10786: improve the error message when a file to be copied (e.g., an asset)
   is removed during Sphinx execution.
   Patch by Bénédikt Tran.
+* #12040: HTML Search: Ensure that document titles that are partially-matched by
+  the user search query are included in search results.
+  Patch by James Addison.
 
 Testing
 -------

sphinx/themes/basic/static/searchtools.js

@@ -508,7 +508,7 @@ const Search = {
         if (!titleTerms.hasOwnProperty(word)) {
           Object.keys(titleTerms).forEach((term) => {
             if (term.match(escapedWord))
-              arr.push({ files: titleTerms[word], score: Scorer.partialTitle });
+              arr.push({ files: titleTerms[term], score: Scorer.partialTitle });
           });
         }
       }

tests/js/searchtools.js

@@ -54,6 +54,31 @@ 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);
+    });
+
   });
 
 });