Re: [RFC] git blame-tree

[Will Palmer <wmpalmer@gmail.com>]

On Wed, 2011-03-02 at 11:40 -0500, Jeff King wrote:
> [I know, I know, another RFC. I'll get to actually cleaning up and
> submitting some of these patches soon.]
> 
> It's sometimes useful to get a list of files in a tree along with the
> last commit that touched them. This is the default tree view shown on
> github.com, but it can also be handy from the command line (there has
> been talk lately of having a "git ls"), or as plumbing for a local
> fancier tree view. E.g., something like:
> 
>      add.c 6e7293e git-add: make -A description clearer vs. -u
>    apply.c fd03881 add description parameter to OPT__VERBOSE
>    blame.c 9ca1169 parse-options: Don't call parse_options_check() so much
>   branch.c 62270f6 branch_merged: fix grammar in warning
>   bundle.c 62b4698 Use angles for placeholders consistently
> 
> The obvious naive way to do this is something like:
> 
>   for i in `git ls-tree --name-only HEAD`; do
>     echo "`git rev-list -1 --no-merges HEAD -- $i` $i";
>   done
> 
> which is really slow, because we end up traversing the same commits many
> times (plus the startup overhead for each rev-list).  It takes about 35
> seconds to run on git.git.
> 
> So the next obvious thing is to do one traversal, output the changed
> files for each commit, and then mark each file as you see it. The perl
> script below does this (though the careful reader will note it is
> actually buggy with sub-trees; I didn't bother fixing it since it was
> just a stage in the evolution):
> 
[code snipped]
> 
> This runs in about 3 seconds. And besides the above-mentioned bug,
> also doesn't properly handle things like filenames that need quoting.
> 
> So I wrote it in C, which drops the time down to about 1.5 seconds, and
> of course doesn't have any parsing issues.  The patch is below.
> 
> I wasn't sure at first what to call it or what the calling conventions
> should be. The initial thought was to make it part of "ls-tree". But
> that feels wrong, as ls-tree otherwise never cares about traversal. The
> combination of traversal and diff made me think of blame, and indeed, I
> think this is really just about blaming a whole tree at the file-level,
> rather than at the content-level. Thus I called it blame-tree, and I
> used the same calling conventions as blame: "git blame-tree <path>
> <rev opts>". See the test script for examples.
> 
> I have many thoughts on the patch already, but rather than put them
> here, I'll include the patch without further ado, and put them inline in
> a reply.
> 
[patch snipped]

Coincidentally, I'm doing a similar thing in a shell script at the
moment. Unfortunately, no tree-object is involved: I'm instead using the
output from "git diff" on two different branches to generate a list of
files I care about. How hard would it be to accept a nul-delimited list
of filenames via stdin, rather than from a tree? If I'm reading this
right, it looks like a pretty trivial change. (I couldn't get the
existing patch to apply, myself.. I assume I'm just doing something
wrong as I don't need to use "git am" very often.)