* Please explain avoiding history simplifications when diffing merges
@ 2023-09-08 9:09 Magnus Holmgren
2023-09-15 15:10 ` Magnus Holmgren
0 siblings, 1 reply; 4+ messages in thread
From: Magnus Holmgren @ 2023-09-08 9:09 UTC (permalink / raw
To: git
Hi (and thanks for a great free tool).
QGit was bitten by
https://github.com/git/git/commit/0dec322d31db3920872f43bdd2a7ddd282a5be67
It looks like passing --simplify-merges to override the default solves the
problem, but I still want to ask here because I'm not sure I fully understand
the reasoning:
> the default history simplification would remove merge commits from
> consideration if the file "path" matched the second parent.
I guess that means that even if there was a difference relative to the first
parent, which you wanted to see, the merge commit would be omitted if there's
no diff relative to the second parent? That's fine, and history simplification
isn't trivial, but now every merge commit ever is included in the commit log
of an individual file, even if that file was only added somewhere in the
middle and never changed since. Is that really desirable? Shouldn't it be
possible to include only merge commits that are not TREESAME to *all* parents?
Thanks,
--
Magnus Holmgren
./¯\_/¯\. Milient
(also holmgren@debian.org)
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Please explain avoiding history simplifications when diffing merges
2023-09-08 9:09 Please explain avoiding history simplifications when diffing merges Magnus Holmgren
@ 2023-09-15 15:10 ` Magnus Holmgren
2023-09-17 9:58 ` Bagas Sanjaya
0 siblings, 1 reply; 4+ messages in thread
From: Magnus Holmgren @ 2023-09-15 15:10 UTC (permalink / raw
To: git
Friday, 8 September 2023 11:09:20 CEST, I wrote
> QGit was bitten by
> https://github.com/git/git/commit/0dec322d31db3920872f43bdd2a7ddd282a5be67
Maybe I should link to the QGit issue:
https://github.com/tibirna/qgit/issues/129
> It looks like passing --simplify-merges to override the default solves the
> problem, but I still want to ask here because I'm not sure I fully
> understand
> the reasoning:
> > the default history simplification would remove merge commits from
> > consideration if the file "path" matched the second parent.
As I wrote at the above URL, I realized that the old git log output without --
simplify-merges and the output with --simplify-merges aren't quite the same.
The old output indeed omits some interesting merge commits, which may explain
why the change was made, but git log --simplify-merges does include them, so
it seems a reasonable default to me.
However, QGit has a problem: git log --diff-merges=separate includes a
separate diff for each parent, but only for each parent with differences
compared to the merge commit, *and* there's no custom format placeholder for
the current parent, only for the list of parents (%P/%p). How should one go
about adding that? I figure the format_commit_context struct in pretty.c needs
another field.
--
Magnus Holmgren
./¯\_/¯\. Milient
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Please explain avoiding history simplifications when diffing merges
2023-09-15 15:10 ` Magnus Holmgren
@ 2023-09-17 9:58 ` Bagas Sanjaya
2023-09-25 16:11 ` Magnus Holmgren
0 siblings, 1 reply; 4+ messages in thread
From: Bagas Sanjaya @ 2023-09-17 9:58 UTC (permalink / raw
To: Magnus Holmgren, git
Cc: Santi Béjar, Junio C Hamano, Sergey Organov,
Christian Couder, Jeff King, René Scharfe
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On Fri, Sep 15, 2023 at 05:10:28PM +0200, Magnus Holmgren wrote:
> Friday, 8 September 2023 11:09:20 CEST, I wrote
> > QGit was bitten by
> > https://github.com/git/git/commit/0dec322d31db3920872f43bdd2a7ddd282a5be67
>
> Maybe I should link to the QGit issue:
> https://github.com/tibirna/qgit/issues/129
>
> > It looks like passing --simplify-merges to override the default solves the
> > problem, but I still want to ask here because I'm not sure I fully
> > understand
> > the reasoning:
> > > the default history simplification would remove merge commits from
> > > consideration if the file "path" matched the second parent.
>
> As I wrote at the above URL, I realized that the old git log output without --
> simplify-merges and the output with --simplify-merges aren't quite the same.
> The old output indeed omits some interesting merge commits, which may explain
> why the change was made, but git log --simplify-merges does include them, so
> it seems a reasonable default to me.
Can you provide examples?
>
> However, QGit has a problem: git log --diff-merges=separate includes a
> separate diff for each parent, but only for each parent with differences
> compared to the merge commit, *and* there's no custom format placeholder for
> the current parent, only for the list of parents (%P/%p). How should one go
> about adding that? I figure the format_commit_context struct in pretty.c needs
> another field.
What are you trying to accomplish with your proposed formatting verbs?
Confused...
--
An old man doll... just what I always wanted! - Clara
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^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: Please explain avoiding history simplifications when diffing merges
2023-09-17 9:58 ` Bagas Sanjaya
@ 2023-09-25 16:11 ` Magnus Holmgren
0 siblings, 0 replies; 4+ messages in thread
From: Magnus Holmgren @ 2023-09-25 16:11 UTC (permalink / raw
To: git, Bagas Sanjaya
Cc: Santi Béjar, Junio C Hamano, Sergey Organov,
Christian Couder, Jeff King, René Scharfe
söndag 17 september 2023 11:58:14 CEST skrev Bagas Sanjaya:
> On Fri, Sep 15, 2023 at 05:10:28PM +0200, Magnus Holmgren wrote:
> > Friday, 8 September 2023 11:09:20 CEST, I wrote
> >
> > > QGit was bitten by
> > > https://github.com/git/git/commit/0dec322d31db3920872f43bdd2a7ddd282a5be
> > > 67
> >
> > Maybe I should link to the QGit issue:
> > https://github.com/tibirna/qgit/issues/129
> >
> > > It looks like passing --simplify-merges to override the default solves
> > > the
> > > problem, but I still want to ask here because I'm not sure I fully
> > > understand
> > >
> > > the reasoning:
> > > > the default history simplification would remove merge commits from
> > > > consideration if the file "path" matched the second parent.
> >
> > As I wrote at the above URL, I realized that the old git log output
> > without -- simplify-merges and the output with --simplify-merges aren't
> > quite the same. The old output indeed omits some interesting merge
> > commits, which may explain why the change was made, but git log
> > --simplify-merges does include them, so it seems a reasonable default to
> > me.
>
> Can you provide examples?
git init git-test; cd git-test
echo foo > test; git add test; git commit -m Initial
git branch testbranch
git branch irrelevantbranch
echo foobar > test; git commit -am Change
git switch testbranch
echo barfoo > test; git commit -am Diverge
git switch irrelevantbranch
echo whatever > otherfile; git add otherfile
git commit -m "Add other file"
git switch master
git merge -m "Merge branch 'testbranch'" -s ours testbranch
git merge -m "Merge branch 'irrelevantbranch' irrelevantbranch
git log test # old git doesn't show either merge commit, new git shows both
git log --simplify-merges test # both versions show the first merge commit
git log --diff-merges=separate -p --simplify-merges test # only in new git
# note that only one diff is generated because the other would be empty,
# although the man page says "Separate log entry and diff is generated for
# each parent."
> > However, QGit has a problem: git log --diff-merges=separate includes a
> > separate diff for each parent, but only for each parent with differences
> > compared to the merge commit, *and* there's no custom format placeholder
> > for the current parent, only for the list of parents (%P/%p). How should
> > one go about adding that? I figure the format_commit_context struct in
> > pretty.c needs another field.
>
> What are you trying to accomplish with your proposed formatting verbs?
QGit builds annotated file histories by parsing git log output. To accomplish
that, it needs to use a custom, more machine-readable format, and to handle
merge commits correctly, it either needs one diff per parent in the order the
parents are listed, or it needs to know which parent each diff is relative to.
Because old git log (without --simplify-merges) only included merge commits
where the file in question is different to all parents, it didn't get confused
by missing diffs - it was all or nothing - but some merge commits were missing
in the file history view.
QGit should be rewritten to use libgit2, but regardless, I think all the
information you can get with a standard format should be available to custom
formats as well.
--
Magnus Holmgren
./¯\_/¯\. Milient
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-09-25 16:11 UTC | newest]
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2023-09-08 9:09 Please explain avoiding history simplifications when diffing merges Magnus Holmgren
2023-09-15 15:10 ` Magnus Holmgren
2023-09-17 9:58 ` Bagas Sanjaya
2023-09-25 16:11 ` Magnus Holmgren
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