API: Add generator non-continuation data

Some generators (e.g. generator=recentchanges) in their default mode of
operation are particularly prone to not generating the same result set
on subsequent requests due to intervening activity on the wiki adding
new entries to the start of the list. We can mitigate this effect by
allowing such generators to provide "non-continuation" data to be used
if the generator isn't being continued.

ApiQueryRecentChanges and ApiQueryAllRevisions are updated to set this
new property. Other generators can easily be updated in the same way as
needed.

There isn't anything we can do about generators prone to having entries
added at random positions in the list rather than the beginning,
unfortunately.

Bug: T146176
Change-Id: I8308d6aa2c89fd2a85e74c7dd8a0a2a9ec927490

includes/api/ApiContinuationManager.php

@@ -31,6 +31,7 @@ class ApiContinuationManager {
 
 	private $continuationData = [];
 	private $generatorContinuationData = [];
+	private $generatorNonContinuationData = [];
 
 	private $generatorParams = [];
 	private $generatorDone = false;
@@ -142,6 +143,26 @@ class ApiContinuationManager {
 		$this->continuationData[$name][$paramName] = $paramValue;
 	}
 
+	/**
+	 * Set the non-continuation parameter for the generator module
+	 *
+	 * In case the generator isn't going to be continued, this sets the fields
+	 * to return.
+	 *
+	 * @since 1.28
+	 * @param ApiBase $module
+	 * @param string $paramName
+	 * @param string|array $paramValue
+	 */
+	public function addGeneratorNonContinueParam( ApiBase $module, $paramName, $paramValue ) {
+		$name = $module->getModuleName();
+		$paramName = $module->encodeParamName( $paramName );
+		if ( is_array( $paramValue ) ) {
+			$paramValue = implode( '|', $paramValue );
+		}
+		$this->generatorNonContinuationData[$name][$paramName] = $paramValue;
+	}
+
 	/**
 	 * Set the continuation parameter for the generator module
 	 * @param ApiBase $module
@@ -165,6 +186,15 @@ class ApiContinuationManager {
 		return array_merge_recursive( $this->continuationData, $this->generatorContinuationData );
 	}
 
+	/**
+	 * Fetch raw non-continuation data
+	 * @since 1.28
+	 * @return array
+	 */
+	public function getRawNonContinuation() {
+		return $this->generatorNonContinuationData;
+	}
+
 	/**
 	 * Fetch continuation result data
 	 * @return array [ (array)$data, (bool)$batchcomplete ]
@@ -192,8 +222,13 @@ class ApiContinuationManager {
 			foreach ( $continuationData as $module => $kvp ) {
 				$data += $kvp;
 			}
-			$data += $this->generatorParams;
-			$generatorKeys = implode( '|', array_keys( $this->generatorParams ) );
+			$generatorParams = [];
+			foreach ( $this->generatorNonContinuationData as $kvp ) {
+				$generatorParams += $kvp;
+			}
+			$generatorParams += $this->generatorParams;
+			$data += $generatorParams;
+			$generatorKeys = implode( '|', array_keys( $generatorParams ) );
 		} elseif ( $this->generatorContinuationData ) {
 			// All the generator-using modules are complete, but the
 			// generator isn't. Continue the generator and restart the

includes/api/ApiQuery.php

@@ -258,6 +258,11 @@ class ApiQuery extends ApiBase {
 		// Write the continuation data into the result
 		$this->setContinuationManager( null );
 		if ( $this->mParams['rawcontinue'] ) {
+			$data = $continuationManager->getRawNonContinuation();
+			if ( $data ) {
+				$this->getResult()->addValue( null, 'query-noncontinue', $data,
+					ApiResult::ADD_ON_TOP | ApiResult::NO_SIZE_CHECK );
+			}
 			$data = $continuationManager->getRawContinuation();
 			if ( $data ) {
 				$this->getResult()->addValue( null, 'query-continue', $data,

includes/api/ApiQueryAllRevisions.php

@@ -172,6 +172,13 @@ class ApiQueryAllRevisions extends ApiQueryRevisionsBase {
 		$nextIndex = 0;
 		$generated = [];
 		foreach ( $res as $row ) {
+			if ( $count === 0 && $resultPageSet !== null ) {
+				// Set the non-continue since the list of all revisions is
+				// prone to having entries added at the start frequently.
+				$this->getContinuationManager()->addGeneratorNonContinueParam(
+					$this, 'continue', "$row->rev_timestamp|$row->rev_id"
+				);
+			}
 			if ( ++$count > $this->limit ) {
 				// We've had enough
 				$this->setContinueEnumParameter( 'continue', "$row->rev_timestamp|$row->rev_id" );

includes/api/ApiQueryRecentChanges.php

@@ -372,6 +372,13 @@ class ApiQueryRecentChanges extends ApiQueryGeneratorBase {
 
 		/* Iterate through the rows, adding data extracted from them to our query result. */
 		foreach ( $res as $row ) {
+			if ( $count === 0 && $resultPageSet !== null ) {
+				// Set the non-continue since the list of recentchanges is
+				// prone to having entries added at the start frequently.
+				$this->getContinuationManager()->addGeneratorNonContinueParam(
+					$this, 'continue', "$row->rc_timestamp|$row->rc_id"
+				);
+			}
 			if ( ++$count > $params['limit'] ) {
 				// We've reached the one extra which shows that there are
 				// additional pages to be had. Stop here...