Re: [Feature Request] git blame showing only revisions from git rev-list --first-parent

[Jeff King <peff@peff.net>]

On Fri, Sep 11, 2015 at 11:47:30AM +0100, Stephen Connolly wrote:

> A command line option to `git blame HEAD -- path` that instructs that
> the revisions of blame be the revisions where the change was applied
> to the current branch not the revision where the change first
> originated (i.e. limit commits to `git rev-list --first-parent HEAD`)
> 
> I can get what I want with the following:
> 
> git rev-list --first-parent HEAD | awk '{print p " " $0}{p=$0}' >
> tmpfile && git blame -b -S tmpfile HEAD -- path && rm tmpfile
> 
> But that is a rather ugly command. Could we have something built in to
> git blame to make this much easier for users?

I agree this would be a useful feature. Though blame takes rev-list
options, it doesn't use the stock rev-list traversal internally, so it
has to handle first-parent itself.

I'm not too familiar with the code, but this _seems_ to work for me:

diff --git a/builtin/blame.c b/builtin/blame.c
index 21321be..2e03d47 100644
--- a/builtin/blame.c
+++ b/builtin/blame.c
@@ -1375,6 +1375,10 @@ static struct commit_list *first_scapegoat(struct rev_info *revs, struct commit
 static int num_scapegoats(struct rev_info *revs, struct commit *commit)
 {
 	struct commit_list *l = first_scapegoat(revs, commit);
+	if (!l)
+		return 0;
+	if (revs->first_parent_only)
+		return 1;
 	return commit_list_count(l);
 }
 

I suspect it doesn't work at all with `--reverse`. I also have the
nagging feeling that this could be handled inside revision.c with
parent-rewriting, but I don't really know.

But "git blame --first-parent <file>" seems to behave sanely in git.git
with this.

-Peff