Re: Branches & directories

[Jeff King <peff@peff.net>]

On Mon, Oct 03, 2011 at 12:15:33AM -0700, Hilco Wijbenga wrote:

> On 2 October 2011 20:07, Jeff King <peff@peff.net> wrote:
> <snip/>
> > Or did you really mean your example literally, as in you run two
> > checkouts back to back, without running anything in between, and the
> > second checkout restores the state before the first one. In that case,
> > yes, it would be correct to keep the old timestamps. But this is an
> > optimization that can only apply in a few very specific cases. And
> > moreoever, how can git know when it is OK to apply that optimization? It
> > has no idea what commands you might have run since the last time we were
> > at "master".
> 
> Yes, I meant it literally. And, no, Git could not possibly know so it
> would have to be optional behaviour. But it's probably a lot of work
> for (for most people) little gain.

If you really want the human to trigger it, then you can do something
like this:

  cat >git-checkout-timestamp <<\EOF
  #!/bin/sh

  old=`git rev-parse HEAD`
  git checkout "$@" || exit 1
  time=`git log -1 --format=%at`
  git diff-tree --name-only -z "$old" HEAD |
    perl -0ne "utime($time, $time, \$_)";
  EOF

Drop that somewhere in your $PATH, and use it instead of regular
checkout. It restores the timestamps on any changed files, but not on
those that were not touched. So your:

  git checkout branch
  git checkout master

example would end up with timestamps set for "master" on the changed
files. Two caveats:

  1. This can still break makefiles! For example, like this:

       make foo.o ;# now foo.o is recent
       vi foo.c   ;# but foo.c is _more_ recent
       git checkout branch ;# now it's even newer
       git checkout-timestamp master ;# now we've restored it to some
                                     ;# old timestamp, and make will
                                     ;# think it's older than foo.o

  2. In general, I'm not sure it makes any sense if there are local
     worktree modifications to the files in question. But I didn't think
     about it too hard. That ways madness lies.

-Peff