Implement reading session SQL modes

Author: JanJakes

tests/WP_SQLite_Driver_Tests.php

@@ -4297,4 +4297,31 @@ public function testNonStrictSqlModeNotNullWithDefault(): void {
 		$this->assertCount( 1, $result );
 		$this->assertSame( '', $result[0]->value );
 	}
+
+	public function testSessionSqlModes(): void {
+		// Syntax: "sql_mode" ("@@sql_mode" for SELECT)
+		$this->assertQuery( 'SET sql_mode = "ERROR_FOR_DIVISION_BY_ZERO"' );
+		$result = $this->assertQuery( 'SELECT @@sql_mode' );
+		$this->assertSame( 'ERROR_FOR_DIVISION_BY_ZERO', $result[0]->{'@@sql_mode'} );
+
+		// Syntax: "@@sql_mode"
+		$this->assertQuery( 'SET @@sql_mode = "NO_ENGINE_SUBSTITUTION"' );
+		$result = $this->assertQuery( 'SELECT @@sql_mode' );
+		$this->assertSame( 'NO_ENGINE_SUBSTITUTION', $result[0]->{'@@sql_mode'} );
+
+		// Syntax: "SESSION sql_mode" ("@@sql_mode" for SELECT)
+		$this->assertQuery( 'SET SESSION sql_mode = "NO_ZERO_DATE"' );
+		$result = $this->assertQuery( 'SELECT @@sql_mode' );
+		$this->assertSame( 'NO_ZERO_DATE', $result[0]->{'@@sql_mode'} );
+
+		// Syntax: "@@SESSION.sql_mode"
+		$this->assertQuery( 'SET @@SESSION.sql_mode = "NO_ZERO_IN_DATE"' );
+		$result = $this->assertQuery( 'SELECT @@SESSION.sql_mode' );
+		$this->assertSame( 'NO_ZERO_IN_DATE', $result[0]->{'@@SESSION.sql_mode'} );
+
+		// Mixed case
+		$this->assertQuery( 'SET @@session.SQL_mode = "only_full_group_by"' );
+		$result = $this->assertQuery( 'SELECT @@session.SQL_mode' );
+		$this->assertSame( 'ONLY_FULL_GROUP_BY', $result[0]->{'@@session.SQL_mode'} );
+	}
 }

tests/WP_SQLite_Driver_Translation_Tests.php

@@ -1220,17 +1220,17 @@ public function testSerialDataTypes(): void {
 
 	public function testSystemVariables(): void {
 		$this->assertQuery(
-			'SELECT NULL',
+			"SELECT 'ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE,ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES' AS `@@sql_mode`",
 			'SELECT @@sql_mode'
 		);
 
 		$this->assertQuery(
-			'SELECT NULL',
+			"SELECT 'ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE,ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES' AS `@@SESSION.sql_mode`",
 			'SELECT @@SESSION.sql_mode'
 		);
 
 		$this->assertQuery(
-			'SELECT NULL',
+			"SELECT 'ERROR_FOR_DIVISION_BY_ZERO,NO_ENGINE_SUBSTITUTION,NO_ZERO_DATE,NO_ZERO_IN_DATE,ONLY_FULL_GROUP_BY,STRICT_TRANS_TABLES' AS `@@GLOBAL.sql_mode`",
 			'SELECT @@GLOBAL.sql_mode'
 		);
 	}

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

@@ -2094,9 +2094,9 @@ private function translate( $node ): ?string {
 					throw $this->new_invalid_input_exception();
 				}
 
-				$type = self::DATA_TYPE_MAP[ $child->id ] ?? null;
-				if ( null !== $type ) {
-					return $type;
+				$type_token = self::DATA_TYPE_MAP[ $child->id ] ?? null;
+				if ( null !== $type_token ) {
+					return $type_token;
 				}
 
 				// SERIAL is an alias for BIGINT UNSIGNED NOT NULL AUTO_INCREMENT UNIQUE.
@@ -2136,12 +2136,37 @@ private function translate( $node ): ?string {
 			case 'functionCall':
 				return $this->translate_function_call( $node );
 			case 'systemVariable':
-				// @TODO: Emulate some system variables, or use reasonable defaults.
+				$var_ident_type = $node->get_first_child_node( 'varIdentType' );
+				$type_token     = $var_ident_type ? $var_ident_type->get_first_child_token() : null;
+				$original_name  = $this->unquote_sqlite_identifier(
+					$this->translate( $node->get_first_child_node( 'textOrIdentifier' ) )
+				);
+
+				$name = strtolower( $original_name );
+				$type = $type_token ? $type_token->id : WP_MySQL_Lexer::SESSION_SYMBOL;
+				if ( 'sql_mode' === $name ) {
+					$value = $this->pdo->quote( implode( ',', $this->active_sql_modes ) );
+				} else {
+					// When we have no value, it's reasonable to use NULL.
+					$value = 'NULL';
+				}
+
+				// @TODO: Emulate more system variables, or use reasonable defaults.
 				//        See: https://dev.mysql.com/doc/refman/8.4/en/server-system-variable-reference.html
 				//        See: https://dev.mysql.com/doc/refman/8.4/en/server-system-variables.html
 
-				// When we have no value, it's reasonable to use NULL.
-				return 'NULL';
+				// TODO: Original name should come from the original MySQL input,
+				//       exactly as it was written by the user, and not translated.
+
+				// TODO: The '% AS %' syntax is compatible with SELECT lists only.
+				//       We need to translate it differently when used as a value.
+				return sprintf(
+					'%s AS %s',
+					$value,
+					$this->quote_sqlite_identifier(
+						'@@' . ( $type_token ? "$type_token->value." : '' ) . $original_name
+					)
+				);
 			case 'castType':
 				// Translate "CAST(... AS BINARY)" to "CAST(... AS BLOB)".
 				if ( $node->has_child_token( WP_MySQL_Lexer::BINARY_SYMBOL ) ) {