The 'decode' call fails in what is already a unicode string. I'm not
sure under what circumstances the string is or isn't unicode (apparently
it varies), so I added a check. The test passes with the patch, at
least.
This allows matches to indicate both missing and unmatched tracks in their
candidates and solves some of the spaghetti tuples that were passed around
during autotagging.
In an attempt to finally address the longstanding SQLite locking issues, I'm
introducing a way to explicitly, lexically scope transactions. The Transaction
class is a context manager that always fully fetches after SELECTs and
automatically commits on exit. No direct access to the library is allowed, so
all changes will eventually be committed and all queries will be completed. This
will also provide a debugging mechanism to show where concurrent transactions
are beginning and ending.
To support composition (transaction reentrancy), an internal, per-Library stack
of transactions is maintained. Commits only happen when the outermost
transaction exits. This means that, while it's possible to introduce atomicity
bugs by invoking Library methods outside of a transaction, you can conveniently
call them *without* a currently-active transaction to get a single atomic
action.
Note that this "transaction stack" concepts assumes a single Library object per
thread. Because we need to duplicate Library objects for concurrent access due
to sqlite3 limitation already, this is fine for now. Later, the interface should
provide one transaction stack per thread for shared Library objects.
Instead of parsing the template at each call to destination(), it's now possible
to parse them *once*, a priori, and re-use the resulting template object. This
is analogous to the re module's compiled expressions.
There's no longer a distinction between Unix and Windows substitutions. Enough
users reported problems with Windows-forbidden characters on Samba shares that
it seems appropriate to make all filenames Windows-safe, even on Unix. Users who
really want those additional characters (<>:"?*|\) can re-enable them via the
"replace" option. Nobody has complained about beets being *too* conservative.
This also adds sanitization of control characters, which is an all-around good
idea, and the substitution now runs in the Unicode (rather than byte) domain.
