Diff for "PartialClone"

Problem: on large repos, it would be useful to be able to do a partial clone and/or checkout

Proposal: add a new file like .hgignore to the .hg/ directory that specifies which files should be ignored for clone/checkout.

[http://www.selenic.com/mercurial/bts/issue105 Issue105 in the BTS] covers partial checkouts and suggests using -X/-I on clone or checkout.

To implement:

• pick a sensible name for this file (BryanOSullivan suggests ignoremissing)
• teach localrepo to use this filtering where appropriate (checkout, pull)
• teach changegroup to choke if someone attempts to pull a changeset from us with a file we don't have

Not to be confused with TrimmingHistory, which trims in the history tree, not the directory tree.

Comments from Matt Mackall:

> > How hard would this be to implement?

On a scale of 1 to 10, I'd rate it about a 7.

The simplest approach is probably "allow cloning of subdirectories". Here's how that would work:

• add a file called "subdir" to .hg/store containing the subdirectory we're cloning
• do a clone as usual, but don't write out revlogs that aren't in subdir
• adjust the functions dealing with paths (localrepo.wjoin, etc.) appropriately
• teach various things (checkout, status, etc.) to skip files outside the subdirectory
• teach merge not allow merging when files outside the subdirectory conflict

Merging is the tricky part, and I expect there's a gotcha or two buried in there.

CategoryNewFeatures