These commands filter the snapshots according to some criteria which
essentially requires loading the index before filtering the snapshots.
Thus create a copy of the snapshots list beforehand and use it later on.
The help messages suggested that the `ls` command work without
explicitly passing a snapshot ID. However, this was never the case:
without a snapshot ID the command just failed with the error
`Ignoring "", it is not a snapshot id`.
Fixes#2299
The `dump`, `find`, `forget`, `ls`, `mount`, `restore`, `snapshots`,
`stats` and `tag` commands will now take into account multiple
`--host` and `-H` flags.
This commit introduces two functions: withinDir() and
approachingMatchingTree()
Both bind the list of directories with a closure, so we don't need to
iterate over the list in the function passed to Walk(). This reduces the
indentation level and since we can just use return, we don't need the
breaks any more.
The case that len(dirs) == 0 can also be handled by the functions with a
return, which saves another indentation level.
The main function body of the function passed to Walk() was reduced to
three cases:
* Within one of the dirs: Print the node, and if recursive operation is
requested, directly return, so the walker continues recursive
traversal
* Approaching one of the dirs: don't print anything, but continue
recursive traversal.
* Nothing of the two: abort walking this branch of the tree.
Since backend.ID is always a slice of constant length, use an array
instead of a slice. Mostly, arrays behave as slices, except that an
array cannot be nil, so use `*backend.ID` insteaf of `backend.ID` in
places where the absence of an ID is possible (e.g. for the Subtree of a
Node, which may not present when the node is a file node).
This change allows to directly use backend.ID as the the key for a map,
so that arbitrary data structures (e.g. a Set implemented as a
map[backend.ID]struct{}) can easily be formed.
