Support DROP INDEX edge case, improve the tests

Author: JanJakes

tests/WP_SQLite_Driver_Tests.php

@@ -5665,12 +5665,57 @@ public function testDropIndex(): void {
 		$this->assertQuery( 'CREATE TABLE t (id INT PRIMARY KEY, val_unique INT UNIQUE, val_index INT)' );
 		$this->assertQuery( 'CREATE INDEX idx_val_index ON t (val_index)' );
 
+		// Verify that the indexes were saved in the information schema.
 		$result = $this->assertQuery( 'SHOW INDEX FROM t' );
 		$this->assertCount( 3, $result );
 		$this->assertEquals( 'PRIMARY', $result[0]->Key_name );
 		$this->assertEquals( 'val_unique', $result[1]->Key_name );
 		$this->assertEquals( 'idx_val_index', $result[2]->Key_name );
 
+		// Verify that the indexes exist in the SQLite database.
+		$result = $this->engine->execute_sqlite_query( "PRAGMA index_list('t')" )->fetchAll( PDO::FETCH_ASSOC );
+		$this->assertCount( 3, $result );
+		$this->assertEquals( 't__idx_val_index', $result[0]['name'] );
+		$this->assertEquals( 't__val_unique', $result[1]['name'] );
+		$this->assertEquals( 'sqlite_autoindex_t_1', $result[2]['name'] );
+
+		// DROP the explicitly named index.
 		$this->assertQuery( 'DROP INDEX idx_val_index ON t' );
+
+		// Verify that the index was removed from the information schema.
+		$result = $this->assertQuery( 'SHOW INDEX FROM t' );
+		$this->assertCount( 2, $result );
+		$this->assertEquals( 'PRIMARY', $result[0]->Key_name );
+		$this->assertEquals( 'val_unique', $result[1]->Key_name );
+
+		// Verify that the index was removed from the SQLite database.
+		$result = $this->engine->execute_sqlite_query( "PRAGMA index_list('t')" )->fetchAll( PDO::FETCH_ASSOC );
+		$this->assertCount( 2, $result );
+		$this->assertEquals( 't__val_unique', $result[0]['name'] );
+		$this->assertEquals( 'sqlite_autoindex_t_1', $result[1]['name'] );
+
+		// DROP the UNIQUE index.
+		$this->assertQuery( 'DROP INDEX val_unique ON t' );
+
+		// Verify that the index was removed from the information schema.
+		$result = $this->assertQuery( 'SHOW INDEX FROM t' );
+		$this->assertCount( 1, $result );
+		$this->assertEquals( 'PRIMARY', $result[0]->Key_name );
+
+		// Verify that the index was removed from the SQLite database.
+		$result = $this->engine->execute_sqlite_query( "PRAGMA index_list('t')" )->fetchAll( PDO::FETCH_ASSOC );
+		$this->assertCount( 1, $result );
+		$this->assertEquals( 'sqlite_autoindex_t_1', $result[0]['name'] );
+
+		// DROP the PRIMARY KEY index.
+		$this->assertQuery( 'DROP INDEX `PRIMARY` ON t' );
+
+		// Verify that the index was removed from the information schema.
+		$result = $this->assertQuery( 'SHOW INDEX FROM t' );
+		$this->assertCount( 0, $result );
+
+		// Verify that the index was removed from the SQLite database.
+		$result = $this->engine->execute_sqlite_query( "PRAGMA index_list('t')" )->fetchAll( PDO::FETCH_ASSOC );
+		$this->assertCount( 0, $result );
 	}
 }

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

@@ -1531,6 +1531,17 @@ private function execute_drop_index_statement( WP_Parser_Node $node ): void {
 			$this->translate( $drop_index->get_first_child_node( 'indexRef' ) )
 		);
 
+		/*
+		 * In MySQL, "DROP INDEX `PRIMARY` ON <table>" removes the PRIMARY KEY.
+		 * This is not supported in SQLite, so in such cases, we need to recreate
+		 * the table without the PRIMARY KEY using the updated information schema.
+		 */
+		if ( 'PRIMARY' === strtoupper( $index_name ) ) {
+			$table_is_temporary = $this->information_schema_builder->temporary_table_exists( $table_name );
+			$this->recreate_table_from_information_schema( $table_is_temporary, $table_name );
+			return;
+		}
+
 		$sqlite_index_name = $this->get_sqlite_index_name( $table_name, $index_name );
 		$this->execute_sqlite_query(
 			sprintf(