Add queryTerms to the search results (#241)

The `queryTerms` field is useful to know which query terms matched in
the search result. When performing an exact search, `terms` and
`queryTerms` are identical. In case of prefix or fuzzy match though,
they can be different.

For example, if one searches for "moto" using prefix search, and a
result matches with the word "motorcycle", then for that result the
`terms` array will include "motorcycle", while the `queryTerms` array
will include "moto".

src/MiniSearch.test.js

@@ -1349,6 +1349,10 @@ describe('MiniSearch', () => {
           ['vita', 'nova'],
           ['vita']
         ])
+        expect(results.map(({ queryTerms }) => queryTerms)).toEqual([
+          ['vita', 'nova'],
+          ['vita']
+        ])
       })
 
       it('reports correct info when combining terms with AND', () => {
@@ -1359,6 +1363,9 @@ describe('MiniSearch', () => {
         expect(results.map(({ terms }) => terms)).toEqual([
           ['vita', 'nova']
         ])
+        expect(results.map(({ queryTerms }) => queryTerms)).toEqual([
+          ['vita', 'nova']
+        ])
       })
 
       it('reports correct info for fuzzy and prefix queries', () => {
@@ -1371,6 +1378,10 @@ describe('MiniSearch', () => {
           ['vita', 'nova'],
           ['vita']
         ])
+        expect(results.map(({ queryTerms }) => queryTerms)).toEqual([
+          ['vi', 'nuova'],
+          ['vi']
+        ])
       })
 
       it('reports correct info for many fuzzy and prefix queries', () => {
@@ -1385,6 +1396,11 @@ describe('MiniSearch', () => {
           ['vita', 'mezzo', 'del'],
           ['del']
         ])
+        expect(results.map(({ queryTerms }) => queryTerms)).toEqual([
+          ['vi', 'nuova', 'm', 'de'],
+          ['vi', 'm', 'de'],
+          ['de']
+        ])
       })
 
       it('passes only the query to tokenize', () => {

src/MiniSearch.ts

@@ -288,10 +288,17 @@ export type SearchResult = {
   id: any,
 
   /**
-   * List of terms that matched
+   * List of document terms that matched. For example, if a prefix search for
+   * `"moto"` matches `"motorcycle"`, `terms` will contain `"motorcycle"`.
    */
   terms: string[],
 
+  /**
+   * List of query terms that matched. For example, if a prefix search for
+   * `"moto"` matches `"motorcycle"`, `queryTerms` will contain `"moto"`.
+   */
+  queryTerms: string[],
+
   /**
    * Score of the search results
    */
@@ -1229,14 +1236,17 @@ export default class MiniSearch<T = any> {
     const results = []
 
     for (const [docId, { score, terms, match }] of rawResults) {
-      // Final score takes into account the number of matching QUERY terms.
-      // The end user will only receive the MATCHED terms.
+      // terms are the matched query terms, which will be returned to the user
+      // as queryTerms. The quality is calculated based on them, as opposed to
+      // the matched terms in the document (which can be different due to
+      // prefix and fuzzy match)
       const quality = terms.length || 1
 
       const result = {
         id: this._documentIds.get(docId),
         score: score * quality,
         terms: Object.keys(match),
+        queryTerms: terms,
         match
       }