Fix impedance mismatch with Parser::getRevisionRecordObject()

Parser::getRevisionRecordObject() returns `null` if the revision is
missing, but it invokes ParserOptions::getCurrentRevisionRecordCallback()
(ie, Parser::statelessFetchRevisionRecord() by default) which returns
`false` as its error condition.

This reverts commit ae74a29af3116eb73a4cb775736b3acee0a65c59, and instead
fixes the bug at its root.

Bug: T251952
Change-Id: If36b35391f7833a1aded8b5a0de706d44187d423

2 files changed, 9 insertions, 3 deletions

diff --git a/includes/parser/CoreParserFunctions.php b/includes/parser/CoreParserFunctions.php
index 427c8ca7857c..a96d873a3b62 100644
--- a/includes/parser/CoreParserFunctions.php
+++ b/includes/parser/CoreParserFunctions.php
@@ -1394,9 +1394,7 @@ class CoreParserFunctions {
 		}
 		// fetch revision from cache/database and return the value
 		$rev = self::getCachedRevisionObject( $parser, $t, 'vary-user' );
-
-		// TODO what can getCachedRevisionObject return other than RevisionRecord and null
-		if ( !( $rev instanceof RevisionRecord ) ) {
+		if ( $rev === null ) {
 			return '';
 		}
 		$user = $rev->getUser();
diff --git a/includes/parser/Parser.php b/includes/parser/Parser.php
index e9698527167e..92c0c2df4659 100644
--- a/includes/parser/Parser.php
+++ b/includes/parser/Parser.php
@@ -5778,6 +5778,14 @@ class Parser {
 			$this
 		);
 
+		if ( $rev === false ) {
+			// The revision record callback returns `false` (not null) to
+			// indicate that the revision is missing.  (See for example
+			// Parser::statelessFetchRevisionRecord(), the default callback.)
+			// This API expects `null` instead. (T251952)
+			$rev = null;
+		}
+
 		if ( $this->mRevisionId === null && $rev && $rev->getId() ) {
 			// We are in preview mode (mRevisionId is null), and the current revision callback
 			// returned an existing revision. Ignore it and return null, it's probably the page's