Add support for unquoted identifiers for system variable values

Author: JanJakes

tests/WP_SQLite_Driver_Tests.php

@@ -6070,6 +6070,36 @@ public function testSessionSystemVariables(): void {
 		$this->assertSame( 'utf8mb4', $result[0]->{'@@session.character_set_client'} );
 	}
 
+	public function testSystemVariablesWithKeywords(): void {
+		$this->assertQuery( 'SET default_storage_engine = InnoDB' );
+		$result = $this->assertQuery( 'SELECT @@default_storage_engine' );
+		$this->assertSame( 'InnoDB', $result[0]->{'@@default_storage_engine'} );
+
+		$this->assertQuery( 'SET default_collation_for_utf8mb4 = utf8mb4_0900_ai_ci' );
+		$result = $this->assertQuery( 'SELECT @@default_collation_for_utf8mb4' );
+		$this->assertSame( 'utf8mb4_0900_ai_ci', $result[0]->{'@@default_collation_for_utf8mb4'} );
+
+		$this->assertQuery( 'SET resultset_metadata = FULL' );
+		$result = $this->assertQuery( 'SELECT @@resultset_metadata' );
+		$this->assertSame( 'FULL', $result[0]->{'@@resultset_metadata'} );
+
+		$this->assertQuery( 'SET session_track_gtids = OWN_GTID' );
+		$result = $this->assertQuery( 'SELECT @@session_track_gtids' );
+		$this->assertSame( 'OWN_GTID', $result[0]->{'@@session_track_gtids'} );
+
+		$this->assertQuery( 'SET session_track_transaction_info = STATE' );
+		$result = $this->assertQuery( 'SELECT @@session_track_transaction_info' );
+		$this->assertSame( 'STATE', $result[0]->{'@@session_track_transaction_info'} );
+
+		$this->assertQuery( 'SET transaction_isolation = SERIALIZABLE' );
+		$result = $this->assertQuery( 'SELECT @@transaction_isolation' );
+		$this->assertSame( 'SERIALIZABLE', $result[0]->{'@@transaction_isolation'} );
+
+		$this->assertQuery( 'SET use_secondary_engine = FORCED' );
+		$result = $this->assertQuery( 'SELECT @@use_secondary_engine' );
+		$this->assertSame( 'FORCED', $result[0]->{'@@use_secondary_engine'} );
+	}
+
 	public function testUserVariables(): void {
 		$this->assertQuery( 'SET @my_var = 1' );
 		$result = $this->assertQuery( 'SELECT @my_var' );

wp-includes/sqlite-ast/class-wp-sqlite-driver.php

@@ -2188,7 +2188,31 @@ private function execute_set_system_variable_statement(
 			$type           = $var_ident_type->get_first_child_token()->id;
 		}
 
-		$value = $this->evaluate_expression( $value_node );
+		/*
+		 * Some MySQL system variables values can be set using an unquoted pure
+		 * identifier rather than a string literal. This includes non-reserved
+		 * keywords. This is equivalent to using a corresponding string literal.
+		 *
+		 * For example, the following statement pairs are equivalent:
+		 *
+		 *   SET default_storage_engine = InnoDB
+		 *   SET default_storage_engine = 'InnoDB'
+		 *
+		 *   SET default_collation_for_utf8mb4 = utf8mb4_0900_ai_ci
+		 *   SET default_collation_for_utf8mb4 = 'utf8mb4_0900_ai_ci'
+		 *
+		 * In this cases, we need to use the value directly without attempting
+		 * to evaluate the expression, as that would result in a query error.
+		 * In the grammar, unquoted identifiers are captured by "columnRef".
+		 */
+		$identifier = $this->translate( $value_node->get_first_descendant_node( 'columnRef' ) );
+		if ( $identifier && $identifier === $this->translate( $value_node ) ) {
+			$value = $this->unquote_sqlite_identifier( $identifier );
+		} elseif ( ! $value_node->has_child_node( 'expr' ) ) {
+			$value = $this->unquote_sqlite_identifier( $this->translate( $value_node ) );
+		} else {
+			$value = $this->evaluate_expression( $value_node );
+		}
 
 		if ( WP_MySQL_Lexer::SESSION_SYMBOL === $type ) {
 			if ( 'sql_mode' === $name ) {