Improve TitleWidget search results

Add the query value as a redlink in the result list,
as is already done if the query value is *not* a prefix
of some other (existing) title.

Bug: T291056
Change-Id: I1569ad5a57cd98fe7deb034512b46e948a3561e1

resources/src/mediawiki.widgets/mw.widgets.TitleWidget.js

@@ -148,8 +148,7 @@
 	 * @return {jQuery.Promise} Suggestions promise
 	 */
 	mw.widgets.TitleWidget.prototype.getSuggestionsPromise = function () {
-		var req,
-			api = this.getApi(),
+		var api = this.getApi(),
 			query = this.getQueryValue(),
 			widget = this,
 			promiseAbortObject = { abort: function () {
@@ -180,19 +179,67 @@
 					} } ).promise( promiseAbortObject );
 				}
 			}
-			// Not a interwiki: do an API lookup of the query
-			req = api.get( widget.getApiParams( query ) );
-			promiseAbortObject.abort = req.abort.bind( req ); // TODO ew
-			return req.then( function ( ret ) {
-				if ( widget.showMissing && ret.query === undefined ) {
-					ret = api.get( { action: 'query', titles: query } );
-					promiseAbortObject.abort = ret.abort.bind( ret );
+			// Not a interwiki: do a prefix-search API lookup of the query.
+			var prefixSearchRequest = api.get( widget.getApiParams( query ) );
+			promiseAbortObject.abort = prefixSearchRequest.abort.bind( prefixSearchRequest ); // TODO ew
+			return prefixSearchRequest.then( function ( prefixSearchResponse ) {
+				if ( !widget.showMissing ) {
+					return prefixSearchResponse;
 				}
-				return ret;
+				// Add the query title as the first result, after looking up its details.
+				var queryTitleRequest = api.get( { action: 'query', titles: query } );
+				promiseAbortObject.abort = queryTitleRequest.abort.bind( queryTitleRequest );
+				return queryTitleRequest.then( function ( queryTitleResponse ) {
+					// By default, return the prefix-search result.
+					var result = prefixSearchResponse;
+					if ( prefixSearchResponse.query === undefined ) {
+						// There are no prefix-search results, so make the only result the query title.
+						// The API response structures are identical because both API calls are action=query.
+						result.query = queryTitleResponse.query;
+					} else if ( queryTitleResponse.query.pages[ -1 ] !== undefined &&
+						!widget.responseContainsNonExistingTitle( prefixSearchResponse, queryTitleResponse.query.pages[ -1 ].title )
+					) {
+						// There are prefix-search results, but the query title isn't in them,
+						// so add it as a new result. It's under the new key 'queryTitle', because
+						// all other results will be under their page ID or a negative integer ID,
+						// and the keys aren't actually used for anything.
+						result.query.pages.queryTitle = queryTitleResponse.query.pages[ -1 ];
+						// Give it the lowest possible sort-index (the API only returns index > 0)
+						// to make this result be sorted at the top.
+						result.query.pages.queryTitle.index = 0;
+					}
+					return result;
+				} );
 			} );
 		} ).promise( promiseAbortObject );
 	};
 
+	/**
+	 * Check for the existence of a given title in an API result set.
+	 *
+	 * As the title is known not to exist, this doesn't check in apiResponse.query.pages,
+	 * but only in the redirect targets in apiResponse.query.redirects.
+	 *
+	 * @private
+	 * @param {Object} apiResponse The API result set to search in.
+	 * @param {string} title The page title to search for.
+	 * @return {boolean}
+	 */
+	mw.widgets.TitleWidget.prototype.responseContainsNonExistingTitle = function ( apiResponse, title ) {
+		// Make sure there are redirects in the data.
+		if ( apiResponse.query.redirects === undefined ) {
+			return false;
+		}
+		// Check the targets against the given title.
+		for ( var redirect in apiResponse.query.redirects ) {
+			if ( apiResponse.query.redirects[ redirect ].to === title ) {
+				return true;
+			}
+		}
+		// The title wasn't found.
+		return false;
+	};
+
 	/**
 	 * Get API params for a given query
 	 *
@@ -279,7 +326,7 @@
 				imageUrl: OO.getProp( suggestionPage, 'thumbnail', 'source' ),
 				description: suggestionPage.description,
 				// Sort index
-				index: suggestionPage.index || redirectIndices[ suggestionPage.title ],
+				index: suggestionPage.index !== undefined ? suggestionPage.index : redirectIndices[ suggestionPage.title ],
 				originalData: suggestionPage
 			};