Emit deprecation warnings reading from $wgUser

With this patch deprecation warnings will be emitted
if $wgUser is accessed or written into. The only pattern
of usage still allowed is

$oldUser = $wgUser;
$wgUser = $newUser;
// Do something
$wgUser = $oldUser;

Once there is no deprecation warnings, we know that nothing
legitimately depends on $wgUser being set, so we can safely
remove the code that's still allowed as well.

Bug: T267861
Change-Id: Ia1c42b3a32acd0e2bb9b0e93f1dc3c82640dcb22

.phpcs.xml

@@ -15,7 +15,6 @@
 		<exclude name="MediaWiki.NamingConventions.LowerCamelFunctionsName.FunctionName" />
 		<exclude name="MediaWiki.Usage.DbrQueryUsage.DbrQueryFound" />
 		<exclude name="MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgTitle" />
-		<exclude name="MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser" />
 		<exclude name="MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgVersion" />
 		<exclude name="MediaWiki.Usage.ExtendClassUsage.FunctionConfigUsage" />
 		<exclude name="MediaWiki.Usage.ExtendClassUsage.FunctionVarUsage" />
@@ -177,6 +176,7 @@
 	</rule>
 	<rule ref="PSR2.Methods.MethodDeclaration.Underscore">
 		<exclude-pattern>*/includes/StubObject\.php</exclude-pattern>
+		<exclude-pattern>*/includes/StubGlobalUser\.php</exclude-pattern>
 		<exclude-pattern>*/includes/StubUserLang\.php</exclude-pattern>
 	</rule>
 	<rule ref="MediaWiki.Usage.AssignmentInReturn.AssignmentInReturn">

RELEASE-NOTES-1.37

@@ -778,6 +778,11 @@ because of Phabricator reports.
    - PPDPart has been merged into PPDPart_Hash
    - PPDStack has been merged into PPDStack_Hash
    - PPDStackElement has been merged into PPDStackElement_Hash
+* By default, the global variable $wgUser is now an instance of the new class
+  StubGlobalUser rather than User, and the first time it is used it will emit
+  deprecation warnings (the $wgUser variable was deprecated in 1.35). For
+  extensions that read from this variable, please use a relevant ContextSource
+  instead, falling back to RequestContext::getMain() if none is available.
 * Collation::singleton and ::factory were deprecated, obtain an CollationFactory
   instance from MediaWikiServices instead.
 * Title::getDefaultNamespace() has been deprecated to be removed because

autoload.php

@@ -1610,6 +1610,7 @@ $wgAutoloadLocalClasses = [
 	'StringPrefixSearch' => __DIR__ . '/includes/search/StringPrefixSearch.php',
 	'StringUtils' => __DIR__ . '/includes/libs/StringUtils.php',
 	'StripState' => __DIR__ . '/includes/parser/StripState.php',
+	'StubGlobalUser' => __DIR__ . '/includes/StubGlobalUser.php',
 	'StubObject' => __DIR__ . '/includes/StubObject.php',
 	'StubUserLang' => __DIR__ . '/includes/StubUserLang.php',
 	'SubmitAction' => __DIR__ . '/includes/actions/SubmitAction.php',

includes/Setup.php

@@ -820,7 +820,10 @@ if ( !defined( 'MW_NO_SESSION' ) && !$wgCommandLineMode ) {
  * @deprecated since 1.35, use an available context source when possible, or, as a backup,
  * RequestContext::getMain()
  */
-$wgUser = RequestContext::getMain()->getUser(); // BackCompat
+$wgUser = new StubGlobalUser( RequestContext::getMain()->getUser() ); // BackCompat
+register_shutdown_function( static function () {
+	StubGlobalUser::$destructorDeprecationDisarmed = true;
+} );
 
 /**
  * @var Language|StubUserLang $wgLang

includes/StubGlobalUser.php

@@ -0,0 +1,148 @@
+<?php
+/**
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+/**
+ * Stub object for the global user ($wgUser) that makes it possible to change the
+ * relevant underlying object while still ensuring that deprecation warnings will
+ * be emitted upon method calls.
+ *
+ * @internal Will be removed in 1.38
+ *
+ * @since 1.37
+ * @author Danny712
+ */
+class StubGlobalUser extends StubObject {
+
+	/** @var bool */
+	public static $destructorDeprecationDisarmed = false;
+
+	/** @var User */
+	public $realUser;
+
+	/**
+	 * @param User $realUser
+	 */
+	public function __construct( User $realUser ) {
+		parent::__construct( 'wgUser' );
+		$this->realUser = $realUser;
+	}
+
+	/**
+	 * @return User
+	 */
+	public function _newObject() {
+		// Based on DeprecatedGlobal::_newObject
+		/*
+		 * Put the caller offset for wfDeprecated as 6, as
+		 * that gives the function that uses this object, since:
+		 *
+		 * 1 = this function ( _newObject )
+		 * 2 = StubGlobalUser::_unstub
+		 * 3 = StubObject::_call
+		 * 4 = StubObject::__call
+		 * 5 = StubGlobalUser::<method of global called>
+		 * 6 = Actual function using the global.
+		 * (the same applies to _get/__get or _set/__set instead of _call/__call)
+		 *
+		 * Of course its theoretically possible to have other call
+		 * sequences for this method, but that seems to be
+		 * rather unlikely.
+		 */
+		// Officially deprecated since 1.35
+		wfDeprecated( '$wgUser', '1.35', false, 6 );
+		return $this->realUser;
+	}
+
+	/**
+	 * Reset the stub global user to a different "real" user object, while ensuring that
+	 * any method calls on that object will still trigger deprecation notices.
+	 *
+	 * @param StubGlobalUser|User $user
+	 */
+	public static function setUser( $user ) {
+		// This is intended to be interacting with the deprecated global
+		// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
+		global $wgUser;
+
+		self::$destructorDeprecationDisarmed = true;
+		// Supports StubGlobalUser parameter in case something fetched the existing value of
+		// $wgUser, set it to something else, and now is trying to restore it
+		$realUser = self::getRealUser( $user );
+		$wgUser = new self( $realUser );
+		self::$destructorDeprecationDisarmed = false;
+	}
+
+	/**
+	 * Get the relevant "real" user object based on either a User object or a StubGlobalUser
+	 * wrapper. Bypasses deprecation notices from converting a StubGlobalUser to an actual
+	 * user, and does not change $wgUser.
+	 *
+	 * @param StubGlobalUser|User $globalUser
+	 * @return User
+	 */
+	public static function getRealUser( $globalUser ): User {
+		if ( $globalUser instanceof StubGlobalUser ) {
+			return $globalUser->realUser;
+		} elseif ( $globalUser instanceof User ) {
+			return $globalUser;
+		} else {
+			throw new InvalidArgumentException(
+				'$globalUser must be a User (or StubGlobalUser), got ' .
+					( is_object( $globalUser ) ? get_class( $globalUser ) : gettype( $globalUser ) )
+			);
+		}
+	}
+
+	/**
+	 * This function creates a new object of the real class and replace it in
+	 * the global variable.
+	 * This is public, for the convenience of external callers wishing to access
+	 * properties, e.g. eval.php
+	 *
+	 * Overriding StubObject::_unstub because for some reason that thinks there is
+	 * an unstub loop when trying to use the magic __set() logic, but there isn't
+	 * any loop because _newObject() returns a specific instance of User rather
+	 * than calling any methods that could then try to use $wgUser. The main difference
+	 * between this and the parent method is that we don't try to check for
+	 * recursion loops.
+	 *
+	 * @param string $name Name of the method called in this object.
+	 * @param int $level Level to go in the stack trace to get the function
+	 *   who called this function.
+	 * @return User The unstubbed version
+	 */
+	public function _unstub( $name = '_unstub', $level = 2 ) {
+		if ( !$GLOBALS[$this->global] instanceof self ) {
+			return $GLOBALS[$this->global]; // already unstubbed.
+		}
+
+		$caller = wfGetCaller( $level );
+		wfDebug( "Unstubbing \${$this->global} on call of "
+			. "\${$this->global}::$name from $caller" );
+		$GLOBALS[$this->global] = $this->_newObject();
+		return $GLOBALS[$this->global];
+	}
+
+	public function __destruct() {
+		if ( !self::$destructorDeprecationDisarmed ) {
+			wfDeprecatedMsg( '$wgUser reassignment detected', '1.37', false, 3 );
+		}
+	}
+}

includes/api/ApiMain.php

@@ -528,10 +528,9 @@ class ApiMain extends ApiBase {
 			// If we're in a mode that breaks the same-origin policy, strip
 			// user credentials for security.
 			if ( $this->lacksSameOriginSecurity() ) {
-				global $wgUser;
 				wfDebug( "API: stripping user credentials when the same-origin policy is not applied" );
 				$user = new User();
-				$wgUser = $user;
+				StubGlobalUser::setUser( $user );
 				$derivativeContext->setUser( $user );
 				$request->response()->header( 'MediaWiki-Login-Suppressed: true' );
 			}

includes/context/RequestContext.php

@@ -579,7 +579,7 @@ class RequestContext implements IContextSource, MutableContext {
 		}
 
 		$importSessionFunc = static function ( User $user, array $params ) {
-			global $wgRequest, $wgUser;
+			global $wgRequest;
 
 			$context = RequestContext::getMain();
 
@@ -608,7 +608,7 @@ class RequestContext implements IContextSource, MutableContext {
 			// and caught (leaving the main context in a mixed state), there is no risk
 			// of the User object being attached to the wrong IP, headers, or session.
 			$context->setUser( $user );
-			$wgUser = $context->getUser(); // b/c
+			StubGlobalUser::setUser( $context->getUser() ); // b/c
 			if ( $session && MediaWiki\Session\PHPSessionHandler::isEnabled() ) {
 				session_id( $session->getId() );
 				AtEase::quietCall( 'session_start' );

includes/installer/Installer.php

@@ -446,7 +446,7 @@ abstract class Installer {
 	 * @throws MWException
 	 */
 	public function resetMediaWikiServices( Config $installerConfig = null, $serviceOverrides = [] ) {
-		global $wgUser, $wgObjectCaches, $wgLang;
+		global $wgObjectCaches, $wgLang;
 
 		$serviceOverrides += [
 			// Disable interwiki lookup, to avoid database access during parses
@@ -482,7 +482,7 @@ abstract class Installer {
 		// Note that this will reset the context's language,
 		// so set the user before setting the language.
 		$user = User::newFromId( 0 );
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		RequestContext::getMain()->setUser( $user );
 

includes/jobqueue/jobs/DoubleRedirectJob.php

@@ -169,6 +169,7 @@ class DoubleRedirectJob extends Job {
 		}
 
 		// Save it
+		// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
 		global $wgUser;
 		$oldUser = $wgUser;
 		$wgUser = $user;

includes/page/WikiPage.php

@@ -1841,8 +1841,9 @@ class WikiPage implements Page, IDBAccessObject, PageRecord {
 
 		if ( !$performer ) {
 			// Its okay to fallback to $wgUser because this whole method is deprecated
+			// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
 			global $wgUser;
-			$performer = $wgUser;
+			$performer = StubGlobalUser::getRealUser( $wgUser );
 		}
 
 		return $this->doUserEditContent(
@@ -2060,8 +2061,9 @@ class WikiPage implements Page, IDBAccessObject, PageRecord {
 	) {
 		if ( !$user ) {
 			wfDeprecated( __METHOD__ . ' without a UserIdentity', '1.37' );
+			// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
 			global $wgUser;
-			$user = $wgUser;
+			$user = StubGlobalUser::getRealUser( $wgUser );
 		}
 
 		$slots = RevisionSlotsUpdate::newFromContent( [ SlotRecord::MAIN => $content ] );

includes/specialpage/LoginSignupSpecialPage.php

@@ -484,7 +484,7 @@ abstract class LoginSignupSpecialPage extends AuthManagerSpecialPage {
 	 * reflected in the current request.
 	 */
 	protected function setSessionUserForCurrentRequest() {
-		global $wgUser, $wgLang;
+		global $wgLang;
 
 		$context = RequestContext::getMain();
 		$localContext = $this->getContext();
@@ -495,7 +495,7 @@ abstract class LoginSignupSpecialPage extends AuthManagerSpecialPage {
 
 		$user = $context->getRequest()->getSession()->getUser();
 
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 		$context->setUser( $user );
 
 		$wgLang = $context->getLanguage();

includes/specialpage/SpecialPageFactory.php

@@ -1386,6 +1386,7 @@ class SpecialPageFactory {
 	public function capturePath(
 		PageReference $page, IContextSource $context, LinkRenderer $linkRenderer = null
 	) {
+		// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
 		global $wgTitle, $wgOut, $wgRequest, $wgUser, $wgLang;
 		$main = RequestContext::getMain();
 

maintenance/cleanupSpam.php

@@ -47,7 +47,7 @@ class CleanupSpam extends Maintenance {
 	}
 
 	public function execute() {
-		global $IP, $wgLocalDatabases, $wgUser;
+		global $IP, $wgLocalDatabases;
 
 		$username = wfMessage( 'spambot_username' )->text();
 		$user = User::newSystemUser( $username );
@@ -56,7 +56,7 @@ class CleanupSpam extends Maintenance {
 		}
 		// Hack: Grant bot rights so we don't flood RecentChanges
 		MediaWikiServices::getInstance()->getUserGroupManager()->addUserToGroup( $user, 'bot' );
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		$spec = $this->getArg( 0 );
 

maintenance/deleteBatch.php

@@ -50,8 +50,6 @@ class DeleteBatch extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgUser;
-
 		# Change to current working directory
 		$oldCwd = getcwd();
 		chdir( $oldCwd );
@@ -69,7 +67,7 @@ class DeleteBatch extends Maintenance {
 		if ( !$user ) {
 			$this->fatalError( "Invalid username" );
 		}
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		if ( $this->hasArg( 0 ) ) {
 			$file = fopen( $this->getArg( 0 ), 'r' );

maintenance/deleteDefaultMessages.php

@@ -41,7 +41,6 @@ class DeleteDefaultMessages extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgUser;
 		$services = MediaWikiServices::getInstance();
 
 		$this->output( "Checking existence of old default messages..." );
@@ -86,7 +85,7 @@ class DeleteDefaultMessages extends Maintenance {
 		}
 		$userGroupManager = $services->getUserGroupManager();
 		$userGroupManager->addUserToGroup( $user, 'bot' );
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		// Handle deletion
 		$this->output( "\n...deleting old default messages (this may take a long time!)...", 'msg' );

maintenance/deleteEqualMessages.php

@@ -174,8 +174,7 @@ class DeleteEqualMessages extends Maintenance {
 		if ( !$user ) {
 			$this->fatalError( "Invalid username" );
 		}
-		global $wgUser;
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		// Hide deletions from RecentChanges
 		$userGroupManager = $services->getUserGroupManager();

maintenance/edit.php

@@ -49,8 +49,6 @@ class EditCLI extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgUser;
-
 		$userName = $this->getOption( 'user', false );
 		$summary = $this->getOption( 'summary', '' );
 		$remove = $this->hasOption( 'remove' );
@@ -71,7 +69,7 @@ class EditCLI extends Maintenance {
 		if ( $user->isAnon() ) {
 			$user->addToDatabase();
 		}
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		$title = Title::newFromText( $this->getArg( 0 ) );
 		if ( !$title ) {

maintenance/importImages.php

@@ -125,7 +125,7 @@ class ImportImages extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgFileExtensions, $wgUser, $wgRestrictionLevels;
+		global $wgFileExtensions, $wgRestrictionLevels;
 
 		$services = MediaWikiServices::getInstance();
 		$permissionManager = $services->getPermissionManager();
@@ -160,7 +160,7 @@ class ImportImages extends Maintenance {
 		if ( !$user instanceof User ) {
 			$user = User::newSystemUser( User::MAINTENANCE_SCRIPT_USER, [ 'steal' => true ] );
 		}
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		# Get block check. If a value is given, this specified how often the check is performed
 		$checkUserBlock = (int)$this->getOption( 'check-userblock' );
@@ -286,7 +286,7 @@ class ImportImages extends Maintenance {
 							);
 							continue;
 						}
-						$wgUser = $realUser;
+						StubGlobalUser::setUser( $realUser );
 						$user = $realUser;
 					}
 				} else {

maintenance/importSiteScripts.php

@@ -41,15 +41,13 @@ class ImportSiteScripts extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgUser;
-
 		$username = $this->getOption( 'username', false );
 		if ( $username === false ) {
 			$user = User::newSystemUser( 'ScriptImporter', [ 'steal' => true ] );
 		} else {
 			$user = User::newFromName( $username );
 		}
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		$baseUrl = $this->getArg( 1 );
 		$pageList = $this->fetchScriptList();

maintenance/moveBatch.php

@@ -47,8 +47,6 @@ class MoveBatch extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgUser;
-
 		# Change to current working directory
 		$oldCwd = getcwd();
 		chdir( $oldCwd );
@@ -76,7 +74,7 @@ class MoveBatch extends Maintenance {
 		if ( !$user ) {
 			$this->fatalError( "Invalid username" );
 		}
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		# Setup complete, now start
 		$dbw = $this->getDB( DB_PRIMARY );

maintenance/preprocessorFuzzTest.php

@@ -214,14 +214,12 @@ class PPFuzzTest {
 	}
 
 	public function execute() {
-		global $wgUser;
-
 		$user = new PPFuzzUser;
 		$user->mName = 'Fuzz';
 		$user->mFrom = 'name';
 		$user->ppfz_test = $this;
 
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		$options = ParserOptions::newFromUser( $user );
 		$options->setTemplateCallback( [ $this, 'templateHook' ] );

maintenance/undelete.php

@@ -33,8 +33,6 @@ class Undelete extends Maintenance {
 	}
 
 	public function execute() {
-		global $wgUser;
-
 		$username = $this->getOption( 'user', false );
 		$reason = $this->getOption( 'reason', '' );
 		$pageName = $this->getArg( 0 );
@@ -51,7 +49,7 @@ class Undelete extends Maintenance {
 		if ( !$user ) {
 			$this->fatalError( "Invalid username" );
 		}
-		$wgUser = $user;
+		StubGlobalUser::setUser( $user );
 
 		$archive = new PageArchive( $title, RequestContext::getMain()->getConfig() );
 		$this->output( "Undeleting " . $title->getPrefixedDBkey() . '...' );

tests/parser/ParserTestRunner.php

@@ -1316,7 +1316,7 @@ class ParserTestRunner {
 			Wikimedia\restoreWarnings();
 
 			// Reset context to the restored globals
-			$context->setUser( $GLOBALS['wgUser'] );
+			$context->setUser( StubGlobalUser::getRealUser( $GLOBALS['wgUser'] ) );
 			$context->setSkin( $oldSkin );
 			$context->setOutput( $GLOBALS['wgOut'] );
 		};

tests/phpunit/MediaWikiIntegrationTestCase.php

@@ -1863,11 +1863,14 @@ abstract class MediaWikiIntegrationTestCase extends PHPUnit\Framework\TestCase {
 			if ( in_array( 'user', $tablesUsed ) ) {
 				TestUserRegistry::clear();
 
-				// Reset $wgUser, which is probably 127.0.0.1, as its loaded data is probably not valid
-				// @todo Should we start setting $wgUser to something nondeterministic
+				// Reset context user, which is probably 127.0.0.1, as its loaded
+				// data is probably not valid. This used to manipulate $wgUser but
+				// since that is deprecated tests are more likely to be relying on
+				// RequestContext::getMain() instead.
+				// @todo Should we start setting the user to something nondeterministic
 				//  to encourage tests to be updated to not depend on it?
-				global $wgUser;
-				$wgUser->clearInstanceCache( $wgUser->mFrom );
+				$user = RequestContext::getMain()->getUser();
+				$user->clearInstanceCache( $user->mFrom );
 			}
 
 			$this->truncateTables( $tablesUsed, $db );

tests/phpunit/includes/api/ApiMainTest.php

@@ -101,8 +101,15 @@ class ApiMainTest extends ApiTestCase {
 	}
 
 	public function testSuppressedLogin() {
+		// Testing some logic that changes the global $wgUser
+		// ApiMain will be setting it to a StubGlobalUser object, it should already
+		// be one but in case its a full User object we will wrap the comparisons
+		// in StubGlobalUser::getRealUser() which will return the inner User object
+		// for a StubGlobalUser, or the actual User object if given a user.
+
+		// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
 		global $wgUser;
-		$origUser = $wgUser;
+		$origUser = StubGlobalUser::getRealUser( $wgUser );
 
 		$api = $this->getNonInternalApiMain( [
 			'action' => 'query',
@@ -114,7 +121,7 @@ class ApiMainTest extends ApiTestCase {
 		$api->execute();
 		ob_end_clean();
 
-		$this->assertNotSame( $origUser, $wgUser );
+		$this->assertNotSame( $origUser, StubGlobalUser::getRealUser( $wgUser ) );
 		$this->assertSame( 'true', $api->getContext()->getRequest()->response()
 			->getHeader( 'MediaWiki-Login-Suppressed' ) );
 	}

tests/phpunit/includes/page/WikiPageDbTest.php

@@ -266,7 +266,14 @@ class WikiPageDbTest extends MediaWikiLangTestCase {
 	public function testDoEditContent() {
 		$this->hideDeprecated( 'WikiPage::doEditContent' );
 
+		// We set $wgUser to a User we create to avoid dealing with StubGlobalUser
+		// deprecation, etc. The entire method is deprecated anyway.
+		$user = $this->getTestSysop()->getUser();
+
+		// phpcs:ignore MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
 		global $wgUser;
+		$originalUser = $wgUser;
+		$wgUser = $user;
 
 		// NOTE: Test that Editing also works with a fragment title!
 		$page = $this->newPage( __METHOD__ . '#Fragment' );
@@ -332,8 +339,11 @@ class WikiPageDbTest extends MediaWikiLangTestCase {
 		$this->assertStringContainsString( '[[gubergren]]', $newText, 'New text must replace old text.' );
 		$this->assertStringNotContainsString( '[[Lorem ipsum]]', $newText, 'New text must replace old text.' );
 		$this->assertStringNotContainsString( '~~~~', $newText, 'PST must substitute signature.' );
-		$this->assertStringContainsString( $wgUser->getName(), $newText,
+		$this->assertStringContainsString( $user->getName(), $newText,
 			'Must fall back to $wgUser when no user has been specified.' );
+
+		// Reset so that other tests would still fail if interacting with $wgUser
+		$wgUser = $originalUser;
 	}
 
 	/**

tests/phpunit/integration/includes/StubGlobalUserTest.php

@@ -0,0 +1,169 @@
+<?php
+
+/**
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ * http://www.gnu.org/copyleft/gpl.html
+ *
+ * @file
+ */
+
+// phpcs:disable MediaWiki.Usage.DeprecatedGlobalVariables.Deprecated$wgUser
+
+/**
+ * Tests the StubGlobalUser, including magic support for __get() and __set()
+ *
+ * @author DannyS712
+ *
+ * @covers \StubGlobalUser
+ */
+class StubGlobalUserTest extends MediaWikiIntegrationTestCase {
+
+	/** @var int */
+	private $oldErrorLevel;
+
+	protected function setUp(): void {
+		parent::setUp();
+
+		// Make sure deprecation notices are seen
+		$this->oldErrorLevel = error_reporting( -1 );
+
+		// Using User::newFromRow() to avoid needing any integration
+		$userFields = [
+			'user_id' => 12345,
+		];
+		$realUser = User::newFromRow( (object)$userFields );
+		StubGlobalUser::setUser( $realUser );
+	}
+
+	protected function tearDown(): void {
+		error_reporting( $this->oldErrorLevel );
+		parent::tearDown();
+	}
+
+	public function testRealUser() {
+		// Should not be emitting deprecation warnings
+		global $wgUser;
+
+		$this->assertInstanceOf( StubGlobalUser::class, $wgUser );
+
+		$real = StubGlobalUser::getRealUser( $wgUser );
+		$this->assertInstanceOf( User::class, $real );
+
+		$real2 = StubGlobalUser::getRealUser( $real );
+		$this->assertSame( $real, $real2 );
+	}
+
+	public function testRealUser_exception() {
+		$this->expectException( InvalidArgumentException::class );
+		$this->expectExceptionMessage(
+			'$globalUser must be a User (or StubGlobalUser), got integer'
+		);
+		StubGlobalUser::getRealUser( 12345 );
+	}
+
+	public function testMagicCall() {
+		$this->expectDeprecation();
+		$this->expectDeprecationMessage( 'Use of $wgUser was deprecated in MediaWiki 1.35' );
+
+		global $wgUser;
+		$this->assertInstanceOf(
+			StubGlobalUser::class,
+			$wgUser,
+			'Sanity check: $wgUser should be a StubGlobalUser at the start of the test'
+		);
+		$this->assertSame(
+			12345,
+			$wgUser->getId(),
+			'__call() based on id set in ::setUp()'
+		);
+		$this->assertInstanceOf(
+			User::class,
+			$wgUser,
+			'__call() resulted in unstubbing'
+		);
+	}
+
+	public function testGetMagic() {
+		$this->expectDeprecation();
+		$this->expectDeprecationMessage( 'Use of $wgUser was deprecated in MediaWiki 1.35' );
+
+		global $wgUser;
+		$this->assertInstanceOf(
+			StubGlobalUser::class,
+			$wgUser,
+			'Sanity check: $wgUser should be a StubGlobalUser at the start of the test'
+		);
+		$this->assertSame(
+			12345,
+			$wgUser->mId,
+			'__get() based on id set in ::setUp()'
+		);
+		$this->assertInstanceOf(
+			User::class,
+			$wgUser,
+			'__get() resulted in unstubbing'
+		);
+	}
+
+	public function testSetMagic() {
+		// This test is why we need StubGlobalUser::_unstub to override StubObject::_unstub
+		// and not try to detect and throw exceptions in unstub loops - for some reason it
+		// thinks this creates a loop.
+
+		$this->expectDeprecation();
+		$this->expectDeprecationMessage( 'Use of $wgUser was deprecated in MediaWiki 1.35' );
+
+		global $wgUser;
+		$this->assertInstanceOf(
+			StubGlobalUser::class,
+			$wgUser,
+			'Sanity check: $wgUser should be a StubGlobalUser at the start of the test'
+		);
+		$wgUser->mId = 2000;
+		$this->assertInstanceOf(
+			User::class,
+			$wgUser,
+			'__set() resulted in unstubbing'
+		);
+		$this->assertSame(
+			2000,
+			$wgUser->mId,
+			'__set() call worked'
+		);
+	}
+
+	public function testDeprecationEmittedWhenReassigned() {
+		$this->expectDeprecation();
+		global $wgUser;
+		$wgUser = new User;
+	}
+
+	/**
+	 * @doesNotPerformAssertions
+	 */
+	public function testReassignmentWithRestoring() {
+		global $wgUser;
+		$oldUser = $wgUser;
+		$wgUser = new User;
+		$wgUser = $oldUser;
+	}
+
+	/**
+	 * @doesNotPerformAssertions
+	 */
+	public function testSetUserNoDeprecation() {
+		StubGlobalUser::setUser( new User );
+	}
+}