diff --git a/includes/SiteConfiguration.php b/includes/SiteConfiguration.php
index cab98a7c630..83ecee08c4c 100644
--- a/includes/SiteConfiguration.php
+++ b/includes/SiteConfiguration.php
@@ -439,8 +439,8 @@ class SiteConfiguration {
 		}
 
 		foreach ( $default as $name => $def ) {
-			if ( !isset( $ret[$name] ) || ( is_array( $default[$name] ) && !is_array( $ret[$name] ) ) ) {
-				$ret[$name] = $default[$name];
+			if ( !isset( $ret[$name] ) || ( is_array( $def ) && !is_array( $ret[$name] ) ) ) {
+				$ret[$name] = $def;
 			}
 		}
 
diff --git a/includes/changes/EnhancedChangesList.php b/includes/changes/EnhancedChangesList.php
index d2c4dd48fab..ab45356f82f 100644
--- a/includes/changes/EnhancedChangesList.php
+++ b/includes/changes/EnhancedChangesList.php
@@ -205,7 +205,7 @@ class EnhancedChangesList extends ChangesList {
 		# Default values for RC flags
 		$collectedRcFlags = [];
 		foreach ( $recentChangesFlags as $key => $value ) {
-			$flagGrouping = ( $recentChangesFlags[$key]['grouping'] ?? 'any' );
+			$flagGrouping = $value['grouping'] ?? 'any';
 			switch ( $flagGrouping ) {
 				case 'all':
 					$collectedRcFlags[$key] = true;
diff --git a/includes/deferred/LinksUpdate.php b/includes/deferred/LinksUpdate.php
index fbc01893d81..0ae1bfdb256 100644
--- a/includes/deferred/LinksUpdate.php
+++ b/includes/deferred/LinksUpdate.php
@@ -776,9 +776,9 @@ class LinksUpdate extends DataUpdate {
 		$del = [];
 		foreach ( $existing as $ns => $dbkeys ) {
 			if ( isset( $this->mLinks[$ns] ) ) {
-				$del[$ns] = array_diff_key( $existing[$ns], $this->mLinks[$ns] );
+				$del[$ns] = array_diff_key( $dbkeys, $this->mLinks[$ns] );
 			} else {
-				$del[$ns] = $existing[$ns];
+				$del[$ns] = $dbkeys;
 			}
 		}
 
@@ -795,9 +795,9 @@ class LinksUpdate extends DataUpdate {
 		$del = [];
 		foreach ( $existing as $ns => $dbkeys ) {
 			if ( isset( $this->mTemplates[$ns] ) ) {
-				$del[$ns] = array_diff_key( $existing[$ns], $this->mTemplates[$ns] );
+				$del[$ns] = array_diff_key( $dbkeys, $this->mTemplates[$ns] );
 			} else {
-				$del[$ns] = $existing[$ns];
+				$del[$ns] = $dbkeys;
 			}
 		}
 
@@ -863,9 +863,9 @@ class LinksUpdate extends DataUpdate {
 		$del = [];
 		foreach ( $existing as $prefix => $dbkeys ) {
 			if ( isset( $this->mInterwikis[$prefix] ) ) {
-				$del[$prefix] = array_diff_key( $existing[$prefix], $this->mInterwikis[$prefix] );
+				$del[$prefix] = array_diff_key( $dbkeys, $this->mInterwikis[$prefix] );
 			} else {
-				$del[$prefix] = $existing[$prefix];
+				$del[$prefix] = $dbkeys;
 			}
 		}
 
diff --git a/includes/libs/filebackend/FileOpBatch.php b/includes/libs/filebackend/FileOpBatch.php
index 58b67786624..659d6506ade 100644
--- a/includes/libs/filebackend/FileOpBatch.php
+++ b/includes/libs/filebackend/FileOpBatch.php
@@ -154,7 +154,7 @@ class FileOpBatch {
 				foreach ( $performOpsBatch as $i => $fileOp ) {
 					$status->success[$i] = false;
 					++$status->failCount;
-					$performOpsBatch[$i]->logFailure( 'attempt_aborted' );
+					$fileOp->logFailure( 'attempt_aborted' );
 				}
 				continue;
 			}
diff --git a/includes/pager/IndexPager.php b/includes/pager/IndexPager.php
index 729ef478b0f..51057f5b010 100644
--- a/includes/pager/IndexPager.php
+++ b/includes/pager/IndexPager.php
@@ -683,7 +683,7 @@ abstract class IndexPager extends ContextSource implements Pager {
 			if ( $query !== false ) {
 				$links[$type] = $this->makeLink(
 					$linkTexts[$type],
-					$queries[$type],
+					$query,
 					$type
 				);
 			} elseif ( isset( $disabledTexts[$type] ) ) {
diff --git a/includes/password/UserPasswordPolicy.php b/includes/password/UserPasswordPolicy.php
index 79a553984b1..4660ede33ba 100644
--- a/includes/password/UserPasswordPolicy.php
+++ b/includes/password/UserPasswordPolicy.php
@@ -198,7 +198,7 @@ class UserPasswordPolicy {
 			if ( in_array( $group, $userGroups ) ) {
 				$effectivePolicy = self::maxOfPolicies(
 					$effectivePolicy,
-					$policies[$group]
+					$policy
 				);
 			}
 		}
diff --git a/includes/resourceloader/ResourceLoaderOOUIImageModule.php b/includes/resourceloader/ResourceLoaderOOUIImageModule.php
index 4fcd117bbf2..5500f497d76 100644
--- a/includes/resourceloader/ResourceLoaderOOUIImageModule.php
+++ b/includes/resourceloader/ResourceLoaderOOUIImageModule.php
@@ -53,14 +53,14 @@ class ResourceLoaderOOUIImageModule extends ResourceLoaderImageModule {
 					// Images and color variants are defined per-theme, here converted to per-skin
 					case 'images':
 					case 'variants':
-						$definition[$key][$skin] = $data[$key];
+						$definition[$key][$skin] = $value;
 						break;
 
 					// Other options must be identical for each theme (or only defined in the default one)
 					default:
 						if ( !isset( $definition[$key] ) ) {
-							$definition[$key] = $data[$key];
-						} elseif ( $definition[$key] !== $data[$key] ) {
+							$definition[$key] = $value;
+						} elseif ( $definition[$key] !== $value ) {
 							throw new Exception(
 								"Mismatched OOUI theme images definition: " .
 									"key '$key' of theme '$theme' for module '$module' " .
diff --git a/includes/session/PHPSessionHandler.php b/includes/session/PHPSessionHandler.php
index a0b024e6421..36c890f342e 100644
--- a/includes/session/PHPSessionHandler.php
+++ b/includes/session/PHPSessionHandler.php
@@ -305,7 +305,7 @@ class PHPSessionHandler implements \SessionHandlerInterface {
 			if ( !array_key_exists( $key, $data ) && $session->exists( $key ) &&
 				\Wikimedia\PhpSessionSerializer::encode( [ $key => true ] )
 			) {
-				if ( $cache[$key] === $session->get( $key ) ) {
+				if ( $value === $session->get( $key ) ) {
 					// Unchanged in Session, delete it
 					$session->remove( $key );
 					$changed = true;
diff --git a/includes/specials/forms/PreferencesFormOOUI.php b/includes/specials/forms/PreferencesFormOOUI.php
index 329b32f417d..7bbecd43efd 100644
--- a/includes/specials/forms/PreferencesFormOOUI.php
+++ b/includes/specials/forms/PreferencesFormOOUI.php
@@ -178,7 +178,7 @@ class PreferencesFormOOUI extends OOUIHTMLForm {
 			$content =
 				$this->getHeaderText( $key ) .
 				$this->displaySection(
-					$this->mFieldTree[$key],
+					$val,
 					"",
 					"mw-prefsection-$key-"
 				) .