Work-in-progress: initial draft JavaScript implementation of ngram-ba…

…sed substring matching.

sphinx/themes/basic/static/searchtools.js

@@ -491,6 +491,7 @@ const Search = {
   performTermsSearch: (searchTerms, excludedTerms) => {
     // prepare search
     const terms = Search._index.terms;
+    const termsNgrams = Search._index.terms_ngrams;
     const titleTerms = Search._index.titleterms;
     const filenames = Search._index.filenames;
     const docNames = Search._index.docnames;
@@ -510,9 +511,40 @@ const Search = {
       if (word.length > 2) {
         const escapedWord = _escapeRegExp(word);
         if (!terms.hasOwnProperty(word)) {
-          Object.keys(terms).forEach((term) => {
-            if (term.match(escapedWord))
-              arr.push({ files: terms[term], score: Scorer.partialTerm });
+          // utility function to lookup superstrings of an ngram
+          let lookup = function (ngram) {
+            let node = termsNgrams;
+            for (const step of ngram) {
+              node = node[step];
+              if (!node) return [];
+            }
+            return node;
+          };
+
+          // retrieve the initial candidate superstrings
+          let start = 0;
+          let ngram = word.substring(start, start + 3);
+          const candidateTerms = new Set(lookup(ngram));
+
+          // iterate over each ngram in the word
+          while (candidateTerms.size && start + 3 <= word.length) {
+            ngram = word.substring(start, start + 3);
+
+            // remove candidate terms that aren't found for the ngram
+            const ngramTerms = new Set(lookup(ngram));
+            for (const candidateTerm of candidateTerms) {
+              if (!ngramTerms.has(candidateTerm)) {
+                candidateTerms.delete(candidateTerm);
+              }
+            }
+
+            // continue to the next ngram
+            start++;
+          }
+
+          // include matches in the results
+          candidateTerms.forEach((term) => {
+            arr.push({ files: terms[term], score: Scorer.partialTerm });
           });
         }
         if (!titleTerms.hasOwnProperty(word)) {