We've had the public_heads for as long as we've had the View object,
IIRC (I didn't check), but we still don't use it for anything. I don't
have any concrete plans for using it either. Maybe our config for
immutable commits is good enough, or maybe we'll want something more
generic (like Mercurial's phases). For now, I think we should simplify
by removing it the storage for public heads.
If indexing failed due to missing commit objects, the repo won't be loadable
without --ignore-working-copy (at least in colocated environment.) In that
case, we can use "op abandon" to recover, but we had to work around the failed
index loading by --ignore-working-copy. Since "op abandon" isn't a repo-level
command, it's better to bypass working-copy snapshot and import of git refs at
all.
--at-op is rejected because it's useless and we'll need extra care for "@"
expression resolution and working-copy updates.
In order to implement GC (#12), we'll need to somehow prune old operations.
Perhaps the easiest implementation is to just remove unwanted operation files
and put tombstone file instead (like git shallow.) However, the removed
operations might be referenced by another jj process running in parallel. Since
the parallel operation thinks all the historical head commits are reachable, the
removed operations would have to be resurrected (or fix up index data, etc.)
when the op heads get merged.
The idea behind this patch is to split the "op log" GC into two steps:
1. recreate operations to be retained and make the old history unreachable,
2. delete unreachable operations if the head was created e.g. 3 days ago.
The latter will be run by "jj util gc". I don't think GC can be implemented
100% safe against lock-less append-only storage, and we'll probably need some
timestamp-based mechanism to not remove objects that might be referenced by
uncommitted operation.
FWIW, another nice thing about this implementation is that the index is
automatically invalidated as the op id changes. The bad thing is that the
"undo" description would contain an old op id. It seems the performance is
pretty okay.
This removes CommandError dependency from these resolution functions. We might
want to refactor the error types again if we introduce a real "opset" evaluator.
The error message for unresolved op heads now includes "@" instead of the whole
expression.
There's a subtle behavior change. Unlike the original remove_remote_branch(),
remote_views entry is not discarded when the branches map becomes empty. The
reasoning here is that the remote view can be added/removed when the remote
is added/removed respectively, though that's not implemented yet. Since the
serialized data cannot represent an empty remote, such view may generate
non-unique content hash.
I think this is less surprising than falling back to the default length.
i64-to-usize conversion can also overflow on 32 bit environment, but I'm not
bothered to handle overflow scenario.
