[mathiasrw]

Closes #2948

Problem

ROLLBACK TRANSACTION on a FILESTORAGE database with AUTOCOMMIT OFF throws, restores nothing, and never calls the callback.

Query (after INSERT INTO t VALUES (1); COMMIT TRANSACTION; INSERT INTO t VALUES (2))	Before	After
alasql('ROLLBACK TRANSACTION')	TypeError: alasql.loadFile is not a function	1
alasql('SELECT * FROM t') afterwards	[{a: 1}, {a: 2}]	[{a: 1}]
alasql('ROLLBACK TRANSACTION', [], cb)	throws, cb never called	cb(1) after the rows are restored

Cause

FS.rollback in src/94filestorage.js called alasql.loadFile, which does not exist (the loader is alasql.utils.loadFile, loadFile in the bundle). Behind that, the file content was assigned to db.data without JSON.parse, and the function never returned its result.

What changed

• FS.rollback loads the file with loadFile, parses it, and rebuilds db.data and db.tables the way FS.attachDatabase does, so a rolled back database looks like a freshly attached one.
• The schema version is bumped after the restore, so cached statements are compiled again.
• Without a callback the file is read synchronously and 1 is returned. With a callback the existing wait for a save in progress is kept, and the callback runs once the rows are restored.
• An error from the loader is thrown instead of calling an undefined error handler.

Test

test/test2948.js:

• A) sync ROLLBACK TRANSACTION returns 1 and restores the rows of the last COMMIT
• B) ROLLBACK TRANSACTION with a callback calls it with 1 after the rows are restored
• C) the database keeps working afterwards: insert, commit, detach, attach, same rows

Without the change in src/ (restored from develop and rebuilt), A and B fail with TypeError: alasql.loadFile is not a function. With the change, all 3 pass.

Full suite: 2543 pass, 213 skip, 0 fail.

Reported by email from a Perch Scan run.

Related: #2625 (rollback on in-memory databases).