New VC mode -- review request

From: Eric S. Raymond Subject: New VC mode -- review request Date: Wed, 3 Oct 2007 06:35:02 -0400 User-agent: Mutt/1.5.15+20070412 (2007-04-11)

I am the original author of the VC mode shipped with Emacs, back in 1992-1993. Its design was well matched to the file-oriented version-control systems (VCSes) of its day, and it has proven a useful tool. But it has long been in need of a rewrite, for two reasons: (1) The code has accreted cruft over the years, and (2) the design is poorly matched to modern changeset-oriented VCSes, beginning with Subversion and including third-generation systems such as Mercurial and Bazaar. Some months ago I set out to fix these problems. The principal goal of the project was to change VC so that its primitive operations (notably checkin/commit) take sets of files as arguments rather than single files. The new VC implementation has two layers: a set of back-ends specific to each VCS, and a front end that contains VC-independent control an UI logic Over the summer I worked with Stefan Monnier and a test group (copied) on qualifying this code. The most significant event in this process was a felicitous mistake. Due to a CVS command error on my part, the new back-end code and a version of the front end with old control behavior but using the new back ends got checked into CVS HEAD rather than a branch. Fortunately, the new back-end code functioned without a hitch and Stefan decided reverting it was not necessary, Now I think it has come time for the front end to be merged. I have been using it in my everyday development work with Subversion for months. Stefan asked me to submit it to this list for final review, and I am doing so. Please find it attached. Here are the user-visible changes you should expect relative to what's in the manual: * The following commands now operate on filesets rather than files. vc-next-action = C-x v v vc-diff = C-x v = vc-print-log = C-x v l vc-revert = C-x v u vc-rollback = C-x v c vc-update = C-x v + The current fileset is either (a) one file, when you are visiting a buffer for a file under version control, or (b) marked files selected in a VC Dired buffer. If you are in a derived buffer such as a log or diff buffer, the current fileset will be that associated with the parent buffer. * In particular, C-x v v on a fileset of edited files should produce a single commit rather than a separate commit for each file. This is the big feature the mode rewrite was aimed at. * In VC Dired mode, you must explicitly mark files to put them in a fileset. The old behavior of operating on the file named on the current line has been switched off. * vc-diff works slightly differently. In the new interface you never explicitly give it a file or directory; instead it operates on the current fileset. As a special exception, if you run diff while visiting a buffer that VC knows nothing about (such as a Dired listing) and it thus cannot deduce a fileset, it will act on all version-controlled files at and below the current directory. * The prefix argument of vc-cancel-version is no longer processed. There is an equivalent command (vc-rollback) also bound to C-x v c, but it always reverts associated buffers. The old C-u vc-cancel-version behavior was all three of dangerous, hard to document, and prone to variation across back ends; we're better off without it. Changes other than these are probably bugs and you should report them. You need not restrict criticism to outright bugs; the user interface hasn't been reviewed or refreshed in a very long time before this, and it is possible we could be doing things more gracefully. -- <a href="http://www.catb.org/~esr/">Eric S. Raymond</a>

vc.el

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