[HTML search] optimization: don't loop over all document terms and title terms during search.

[jayaddison]

Is your feature request related to a problem? Please describe.
There seems to be a potentially-large inefficiency in the Sphinx JavaScript search code: for any query word greater than length two (likely to be >90% of them, I'd guess!), we iterate through all document terms and all title terms in the client's search index to check for partial matches.

However, if an exact-match was already found on the query word, then we won't add any of those candidates, even when they do match. That means that we spend JavaScript compute resources iterating through items that are unused.

The relevant code is found here:

sphinx/sphinx/themes/basic/static/searchtools.js

Lines 469 to 476 in cf7d275

	Object.keys(terms).forEach((term) => {
	if (term.match(escapedWord) && !terms[word])
	arr.push({ files: terms[term], score: Scorer.partialTerm });
	});
	Object.keys(titleTerms).forEach((term) => {
	if (term.match(escapedWord) && !titleTerms[word])
	arr.push({ files: titleTerms[word], score: Scorer.partialTitle });
	});

I don't have any stats on the performance impact of this, but it feels like it may be significant, especially for large documentation projects.

Describe the solution you'd like

• If we've already found exact-matches for a document term, then do not iterate over all document terms to check for partial matches.
• If we've already found exact-matches for a document title term, then do not iterate over all document title terms to check for partial matches.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context

• Extracted from / resolved-by HTML Search: Partial matches can overwrite main matches in certain rare cases #11957.

[jayaddison]

Resolved by #11958.