Add support for INFORMATION_SCHEMA.SCHEMATA table

This also moves database name handling from a global variable
to the INFORMATION_SCHEMA.SCHEMATA table.

Author: JanJakes

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

@@ -105,7 +105,7 @@ public function configure_database(): void {
 			$this->schema_builder->ensure_information_schema_tables();
 			$this->schema_reconstructor->ensure_correct_information_schema();
 			$this->save_current_driver_version();
-			$this->save_current_database_name();
+			$this->ensure_schemata_data();
 		} catch ( Throwable $e ) {
 			$this->driver->execute_sqlite_query( 'ROLLBACK' );
 			throw $e;
@@ -131,15 +131,43 @@ private function ensure_global_variables_table(): void {
 	}
 
 	/**
-	 * Save the current database name.
+	 * Ensure that the "SCHEMATA" table data is correctly populated.
 	 *
-	 * This method saves the current database name to the database.
+	 * This method ensures that the "INFORMATION_SCHEMA.SCHEMATA" table contains
+	 * records for both the "INFORMATION_SCHEMA" database and the user database.
+	 * At the moment, only a single user database is supported.
 	 */
-	public function save_current_database_name(): void {
+	public function ensure_schemata_data(): void {
+		$schemata_table = $this->schema_builder->get_table_name( false, 'schemata' );
+
+		// 1. Ensure that the "INFORMATION_SCHEMA" database record exists.
+		$this->driver->execute_sqlite_query(
+			sprintf(
+				'INSERT INTO %s (SCHEMA_NAME, DEFAULT_CHARACTER_SET_NAME, DEFAULT_COLLATION_NAME)
+				VALUES (?, ?, ?) ON CONFLICT(SCHEMA_NAME) DO NOTHING',
+				$this->driver->get_connection()->quote_identifier( $schemata_table )
+			),
+			array( 'information_schema', 'utf8mb3', 'utf8mb3_general_ci' )
+		);
+
+		// 2. Check if a user database record exists.
+		$user_db_record_exists = $this->driver->execute_sqlite_query(
+			sprintf(
+				"SELECT COUNT(*) FROM %s WHERE SCHEMA_NAME != 'information_schema'",
+				$this->driver->get_connection()->quote_identifier( $schemata_table )
+			),
+		)->fetchColumn() > 0;
+
+		if ( $user_db_record_exists ) {
+			return;
+		}
+
 		/*
+		 * 3. Migrate from older driver versions without the "SCHEMATA" table.
+		 *
 		 * If a record with an existing database name value is already stored in
-		 * the information schema, we need to use that value. This ensures correct
-		 * migration from older driver versions without the database name variable.
+		 * "INFORMATION_SCHEMA.TABLES", we need to use that value. This ensures
+		 * migration from older driver versions without the "SCHEMATA" table.
 		 */
 		$information_schema_db_name = $this->driver->execute_sqlite_query(
 			sprintf(
@@ -156,14 +184,13 @@ public function save_current_database_name(): void {
 			$db_name = $this->db_name;
 		}
 
+		// 4. Create a user database record.
 		$this->driver->execute_sqlite_query(
 			sprintf(
-				'INSERT INTO %s (name, value) VALUES (?, ?) ON CONFLICT(name) DO UPDATE SET value = ?',
-				$this->driver->get_connection()->quote_identifier(
-					WP_SQLite_Driver::GLOBAL_VARIABLES_TABLE_NAME
-				)
+				'INSERT INTO %s (SCHEMA_NAME, DEFAULT_CHARACTER_SET_NAME, DEFAULT_COLLATION_NAME) VALUES (?, ?, ?)',
+				$this->driver->get_connection()->quote_identifier( $schemata_table )
 			),
-			array( WP_SQLite_Driver::DATABASE_NAME_VARIABLE_NAME, $db_name )
+			array( $db_name, 'utf8mb4', 'utf8mb4_0900_ai_ci' )
 		);
 	}
 

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

@@ -51,13 +51,6 @@ class WP_SQLite_Driver {
 	 */
 	const DRIVER_VERSION_VARIABLE_NAME = self::RESERVED_PREFIX . 'driver_version';
 
-	/**
-	 * The name of the SQLite database name variable.
-	 *
-	 * This internal variable is used to store the name of the SQLite database.
-	 */
-	const DATABASE_NAME_VARIABLE_NAME = self::RESERVED_PREFIX . 'database_name';
-
 	/**
 	 * A map of MySQL tokens to SQLite data types.
 	 *
@@ -556,12 +549,12 @@ public function get_saved_driver_version(): string {
 	 */
 	public function get_saved_database_name(): string {
 		try {
+			$schemata_table = $this->information_schema_builder->get_table_name( false, 'schemata' );
 			return $this->execute_sqlite_query(
 				sprintf(
-					'SELECT value FROM %s WHERE name = ?',
-					$this->quote_sqlite_identifier( self::GLOBAL_VARIABLES_TABLE_NAME )
-				),
-				array( self::DATABASE_NAME_VARIABLE_NAME )
+					'SELECT SCHEMA_NAME FROM %s WHERE SCHEMA_NAME != "information_schema" LIMIT 1',
+					$this->quote_sqlite_identifier( $schemata_table )
+				)
 			)->fetchColumn() ?? '';
 		} catch ( PDOException $e ) {
 			if ( str_contains( $e->getMessage(), 'no such table' ) ) {

wp-includes/sqlite-ast/class-wp-sqlite-information-schema-builder.php

@@ -17,6 +17,7 @@ class WP_SQLite_Information_Schema_Builder {
 	 * We only implement a limited subset that is necessary for a database schema
 	 * introspection and representation, currently covering the following tables:
 	 *
+	 *  - SCHEMATA
 	 *  - TABLES
 	 *  - COLUMNS
 	 *  - STATISTICS (indexes)
@@ -30,6 +31,17 @@ class WP_SQLite_Information_Schema_Builder {
 	 *  - TRIGGERS
 	 */
 	const INFORMATION_SCHEMA_TABLE_DEFINITIONS = array(
+		// INFORMATION_SCHEMA.SCHEMATA
+		'schemata'          => "
+			CATALOG_NAME TEXT NOT NULL DEFAULT 'def' COLLATE NOCASE,      -- always 'def'
+			SCHEMA_NAME TEXT NOT NULL COLLATE NOCASE,                     -- database name
+			DEFAULT_CHARACTER_SET_NAME TEXT NOT NULL COLLATE NOCASE,      -- default character set
+			DEFAULT_COLLATION_NAME TEXT NOT NULL COLLATE NOCASE,          -- default collation
+			SQL_PATH TEXT NULL COLLATE NOCASE,                            -- always NULL
+			DEFAULT_ENCRYPTION TEXT NOT NULL DEFAULT 'NO' COLLATE NOCASE, -- not implemented
+			PRIMARY KEY (SCHEMA_NAME)
+		",
+
 		// INFORMATION_SCHEMA.TABLES
 		'tables'            => "
 			TABLE_CATALOG TEXT NOT NULL DEFAULT 'def' COLLATE NOCASE, -- always 'def'