Support "deep" option in clear() & iterator() about subleveldown

[MeirionHughes]

okay, actually tested it; doesn't seem to:

  let db = levelup(encoding(memdown()));

  let dbsub = sub(db, "foo");
  let dbsubsub = sub(dbsub, "bar");

  await dbsub.put("A", "a");
  await dbsubsub.put("B", "b");

  await dumpKeys(db);

  await dbsub.clear();

  await dumpKeys(db);

DUMP:
 !foo!!bar!B
 !foo!A
DUMP:
 !foo!!bar!B

I guess I can work around it with something like: await db.clear({gte: "!foo!", lt: "!foo$"})

[vweevers]

Clearing works the same as iterating (it visits the same keys). Should we forego that symmetry?

[MeirionHughes]

probably not, but perhaps adding an option field? something like "all" to signal you want to clear everything?

[vweevers]

That might be nice for iterators too.

[vweevers]

something like "all"

Or "deep". A PR is welcome.

[MeirionHughes]

but what would be the range?
{gte: prefix, lt: prefix.substring(0, prefix.length - 1) + "$"}?.

I just guessed that lt: ...$ would be the catch all - not sure if that is valid/safe?

[vweevers]

Looking more closely at this, iterators already include the keys of nested sublevels. Maybe you were hitting a race issue in opening the db?

[vweevers]

I fail to replicate #85 (comment).

[MeirionHughes]

you're right; looks like the issue only arises when encoding-down is used - I tried to replicate in existing (subleveldown) test but couldn't, but it is only db = levelup(memdown)

if I remove encoding-down from the code above, it clears properly.

... and I've tried to test that too (var down = encoding(memdown())) in the main test file and can't replicate. no idea what is going on now...

[MeirionHughes]

dam... I think it might have been a bad version on my monorepo. I forced update to the latest versions and the issue seems to have vanished. Sorry... I thought had updated them all - but I think I had the last memdown major - sorry for wasting your time.