Re: Re: git log -M -- filename is not working?

From: Eli Barzilay <eli@barzilay.org>
Date: May 8, 2010, 07:08 UTC
Message-ID: <19429.3589.823244.270582@winooski.ccs.neu.edu>
In-Reply-To: <7v39y3c5p1.fsf@alter.siamese.dyndns.org>

On May  7, Junio C Hamano wrote:

Show 9 quoted lines

> Eli Barzilay <eli@barzilay.org> writes:
> 
> > So if there was some single
> >
> >   --do-whatever-you-can-as-much-as-you-can-to-find-all-renames
> 
> If I am not mistaken, that is exactly the point of Bo's patch:
> 
>     Message-Id: <1273207949-18500-4-git-send-email-struggleyb.nku@gmail.com>

(Actually, I was talking about some meta option that always turns on whatever can be done to track copies; but given the clarification from Jeff below, it's not as important as I first thought.)

On May  8, Jeff King wrote:

Show 15 quoted lines

> On Sat, May 08, 2010 at 01:12:58AM -0400, Eli Barzilay wrote:
> 
> > > > BTW, I've had at least 4 people now who got confused by this.  Is
> > > > there any use for -M/-C without --follow?  In any case, it will be
> > > > very helpful if the -M/-C descriptions said "see also --follow".
> > > 
> > > Yes, it detects renames when doing diffs.
> > 
> > OK, so just to clear this up: -C and -M (and --find-copies-harder)
> > are for `diff', and --follow is for `log' with a single file (and
> > each will pass it on to the other)?
> 
> Yes (well, diff can never pass --follow to log, since diff never
> invokes log, but yes, the per-commit diff shown by log uses the -C
> and -M given to log).

Aha -- I now see what makes most of this confusion, and an easy way to improve it considerably: looking at the `git-log' man page, I have to wade through 11 pages of general diff options (well, 11 is so high because I like big fonts in my emacs...) before I get to the log options, and even worse, there is no clear indication that those options are only relevant if I want to get patches, which is (at least in my interactive use cases) far from being something I do often. (Googling around, I see more than a few examples of confused uses of `git log -M', even the git faq says "'git log -M' will give the commit history with rename information" -- no mention of it not making any sense with a file that went through a rename.)

So I think that it would really help if (1) the diff options in the git-log man page move to after its own options, and (2) they appeared after a title saying that these are the diff options, (3) `--follow' moves up before the few preceding options that seem to me less important. To clarify, I added a simple patch to the end of this message. (`git-format-patch' has the same thing, but there it looks more sensible to leave it as is.)

Show 6 quoted lines

> > So if there was some single
> > 
> >   --do-whatever-you-can-as-much-as-you-can-to-find-all-renames
> 
> But I think all you really wanted was "--follow". I'd have to check the
> code, but I'm not even sure whether "-C" will impact --follow at all.

If -C/-M are really only affecting the patches, then yes, I'd probably be happy with only `--follow' (or a way to have --follow on by default when possible).

Show 6 quoted lines

> No, copy detection can be _really_ slow. There is a reason it isn't
> on by default. Try "git log -1000 -p" versus "git log -1000 -p -C -M
> --find-copies-harder" in some repository. In a simple git.git test,
> it is almost 5x slower (about 1 second versus 5 seconds on my
> machine). For large repositories, it can be much worse, because now
> each diff is O(size of repository) instead of O(size of changes).

Yes, I see that. I was talking about interactive uses, where I'd never want to see a 1000 diffs, or even 2. But given that -C/-M are only for patches, then I agree with that.

> Still, I see your point that you might want it on all the time, if you
> have a sufficiently small repo. There is "diff.renames" to turn on
> rename detection all the time.

(Ah, I missed that...)

Show 11 quoted lines

> But I think a log.follow option doesn't make sense at this
> point. For example:
> 
>   $ git config log.follow true
>   $ git log foo.c ;# ok, follow foo.c
>   $ git log foo.c bar.c ;# uh oh, now what?
> 
> Does the last one just barf, and make you say "git log --no-follow
> foo.c bar.c"? Does it quietly turn off --follow, making the user
> guess why "git log foo.c" finds some history that "git log foo.c
> bar.c" doesn't?

How about these options:

  git config log.follow if-single-file
    makes it use --follow only when there's a single file path given,
    ignoring it otherwise (with no confusion about it now)

  git config log.follow if-possible
    makes it do the same, but might also do it for more cases if/when
    they become available (so this is the "do the best you can"
    option)

  git config log.follow true
    invalid until it is always possible to use --follow

[this is the patch that I mentioned above]

-------------------------------------------------------------------------------

diff --git a/Documentation/git-log.txt b/Documentation/git-log.txt
index fb184ba..6bc7064 100644
--- a/Documentation/git-log.txt
+++ b/Documentation/git-log.txt
@@ -24,7 +24,6 @@ OPTIONS
 -------
 
 :git-log: 1
-include::diff-options.txt[]
 
 -<n>::
 	Limits the number of commits to show.
@@ -37,6 +36,10 @@ include::diff-options.txt[]
 	and <until>, see "SPECIFYING REVISIONS" section in
 	linkgit:git-rev-parse[1].
 
+--follow::
+	Continue listing the history of a file beyond renames
+	(works only for a single file).
+
 --decorate[=short|full]::
 	Print out the ref names of any commits that are shown. If 'short' is
 	specified, the ref name prefixes 'refs/heads/', 'refs/tags/' and
@@ -55,9 +58,6 @@ include::diff-options.txt[]
 	the specified paths; this means that "<path>..." limits only
 	commits, and doesn't limit diff for those commits.
 
---follow::
-	Continue listing the history of a file beyond renames.
-
 --log-size::
 	Before the log message print out its size in bytes. Intended
 	mainly for porcelain tools consumption. If git is unable to
@@ -71,6 +71,10 @@ include::diff-options.txt[]
 	to be prefixed with "\-- " to separate them from options or
 	refnames.
 
+Common diff options
+~~~~~~~~~~~~~~~~~~~
+
+include::diff-options.txt[]
 
 include::rev-list-options.txt[]
 
-------------------------------------------------------------------------------

-- 
          ((lambda (x) (x x)) (lambda (x) (x x)))          Eli Barzilay:
                    http://barzilay.org/                   Maze is Life!