On Thu, Feb 16, 2017 at 11:17 PM, Jeff King <peff@xxxxxxxx> wrote:
> This isn't difflame's fault; that's what "git blame" tells you about
> that line. But since I already told difflame "v2.6.5..HEAD", it would
> probably make sense to similarly limit the blame to that range. That
> turns up a boundary commit for the line. Which is _also_ not helpful,
> but at least the tool is telling me that the line came from before
> v2.6.5, and I don't really need to care much about it.
I'm running my own tests on difflame and I have a theory about "when"
it breaks.... at least one of the cases when it breaks:
Analysis for deleted lines is being driven by git blame --reverse.
What I have noticed is that it "breaks" when blame --reverse drives
the analysis into revisions where "treeish1" is not part of their
history (like, bringing analysis "to the sides" of treeish1 instead of
keeping analysis in revisions in the history of treeish2 that have
treeish1 as one of their ancestors.... which is definitely a valid
case for analysis, anyway). In this case, blame --reverse stops being
helpful.
Take this example (I just pushed a debug-deletion branch into gh...
probably more debugging messages will be needed):
$ difflame.py HEAD~100 HEAD -- Documentation/git-commit.txt
diff --git a/Documentation/git-commit.txt b/Documentation/git-commit.txt
index f2ab0ee2e..4f8f20a36 100644
--- a/Documentation/git-commit.txt
+++ b/Documentation/git-commit.txt
@@ -265,7 +265,8 @@ FROM UPSTREAM REBASE" section in linkgit:git-rebase[1].)
bcf9626a71 (Matthieu Moy 2016-06-28 13:40:11 +0200 265) If this
option is specified together with `--amend`, then
04c8ce9c1c (Markus Heidelberg 2008-12-19 13:14:18 +0100 266) no
paths need to be specified, which can be used to amend
d4ba07cac5 (Johannes Sixt 2008-04-10 13:33:09 +0200 267) the
last commit without committing changes that have
Range of revisions: 02db2d..066fb04
Treeish1 02db2d04: 02db2d042 Merge branch 'ah/grammos'
Treeish2 066fb0494: 066fb0494 blame: draft of line format
Blamed Revision afe0e2a39: afe0e2a39 Merge branch
'da/difftool-dir-diff-fix'
Original Filename a/Documentation/git-commit.txt Deleted Line 268
Children revisions:
3aead1cad7a: 3aead1cad Merge branch 'ak/commit-only-allow-empty'
There's only one child revision.... on that revision the line
we are tracking is gone
Parents of this child revision:
afe0e2a39166: afe0e2a39 Merge branch 'da/difftool-dir-diff-fix'
beb635ca9ce: beb635ca9 commit: remove 'Clever' message
for --only --amend
Finding parent where the line has been deleted:
beb635ca9: beb635ca9 commit: remove 'Clever' message
for --only --amend
Range of revisions: 02db2d042..beb635c
Treeish1 02db2d0: 02db2d042 Merge branch 'ah/grammos'
Treeish2 beb635c: beb635ca9 commit: remove 'Clever'
message for --only --amend
Blamed Revision 02db2d0: 02db2d042 Merge branch 'ah/grammos'
Original Filename a/Documentation/git-commit.txt Deleted Line 268
Children revisions:
Found no children... will return the original blamed revision
(02db2d0) saying that the deleting revision could not be found
beb635ca9 commit: remove 'Clever' message for --only --amend
-beb635ca9 (Andreas Krey 2016-12-09 05:10:21 +0100 268)
already been staged.
319d83524 commit: make --only --allow-empty work without paths
+319d835240 (Andreas Krey 2016-12-02 23:15:13 +0100 268)
already been staged. ...
+319d835240 (Andreas Krey 2016-12-02 23:15:13 +0100 269) paths
are also not requi...
d4ba07cac5 (Johannes Sixt 2008-04-10 13:33:09 +0200 270)
1947bdbc31 (Junio C Hamano 2008-06-22 14:32:27 -0700 271) -u[<mode>]::
1947bdbc31 (Junio C Hamano 2008-06-22 14:32:27 -0700 272)
--untracked-files[=<mode>]::
I know that line 268 was deleted on 319d835240.
So.... on the first round of merge analysis it says "let's go into
beb635ca9". That's fine. That's exactly the path that is required to
reach 319d835240. But then when using this new "range of revisions"
for git blame --reverse, we get that line 268 is not telling us
anything useful:
$ git blame --reverse -L268,268 02db2d042..beb635c --
Documentation/git-commit.txt
^02db2d042 (Junio C Hamano 2016-12-19 14:45:30 -0800 268)
already been staged.
So, instead of pointing to 319d835240 (the parent of beb635c), it's
basically saying something like "I give up". My hunch (haven't sat
down to digest all the details about the output of git blame
--reverse... YET) is that, given that 02db2d042 is _not_ part of the
history of beb635c, git blame reverse is trying to tell me just
that... and that means I'll have to "script around this scenario".
$ git merge-base 02db2d042 beb635c
0202c411edc25940cc381bf317badcdf67670be4
Thanks in advance.