patchgit-repack doc: remove discussion of ancient caveat

The backwards compatibility caveat discussed her hasn't been a concern for anyone after Git v1.6.0. Let's simply remove it, I daresay nobody's concerned these days with having git clients running older than 2008-era git.

See b6945f570ac (git-repack: repo.usedeltabaseoffset, 2006-10-13) and 9f17688d93c (update git-repack documentation wrt repack.UseDeltaBaseOffset, 2010-02-04) for the commits that previously introduced and adjusted this documentation.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 Documentation/git-repack.txt | 10 ----------
 1 file changed, 10 deletions(-)

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

For the purpose of this message, Git 1.6.0 has no significance. Anything newer than 1.4.4 should be able to understand packfiles that use delta-base-offset, even though they may not have used delta-base-offset when writing a new one.

That's all academic. I wouldn't have written the above if the proposed log message stopped here. But with the rest of proposed log message that hints that the above statement is backed by a solid study of history, it is wrong to write a wrong version number there.

I agree that it is safe to say that anything before Git 2.0.0 is irrelevant at this point (I would actually say before Git 2.16.0, i.e. anything older than 3-4 years).

On Fri, Jul 15 2022, Junio C Hamano wrote:

1.4.4 is the version that introduced the flag, but the paragraphs I'm removing is relevant to 1.6.0, as it discusses concerns with that new-in-1.4.4 --delta-base-offset flag being turned on by default.

So this documentation matches e.g. the RelNotes update you made in e903b4095a0 (Update draft release notes for 1.6.0, 2008-07-01).

I.e. 1.4.4 was released in late 2006, 1.6.0 in mid-2008. Hence the mention of "git clients older than 2008-era git" not being a concern.

I.e. the target audience for this bit of documentatino is someone running 1.6.0. or newer that's also concerned about pre-1.4.4.

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

Step back and think why the 1.6.0 carried the mention in the release notes, and added the "use of delta-base-offset is incompatible with versions of Git that are older than 1.4.4" to the documentation.

Back in 1.6.0 days, some of the users still had to refrain from using the delta-base-offset feature by explicitly disabling it, because the version of Git running on the other side of their connection were before eb32d236 (introduce delta objects with offset to base, 2006-09-21)---1.4.4 was the first version of Git that learned how to produce packs with delta-base-offset, and how to read objects out of such packs.

If 1.4.4 were too distant in the past to matter and we were sure nobody is running such an ancient version back then, we wouldn't have written such a notice there in the document when we turned it on by default in 1.6.0.

Or, step back and think what we would have taken into account, if the patch in question were suggested during the development cycle toward Git 1.7.0, and what the reason for rejection would have been. Even if there were tons of folks who were running pre-1.6.0 versions of Git, as long as these old versions were all newer than 1.4.4, then we would have said that the warning would not matter. The reason to reject such a patch in 1.7.0 cycle would not be because of the age of 1.6.0 being too young, but because of the age of 1.4.4 being not old enough.

Both are based on how distant in the past 1.4.4 had happened. As the removed paragraph says, generated packs with delta-base-offset are "incompatible with versions of Git older than 1.4.4". If 1.4.4 and older died out, nobody needs to worry about use of d-b-o. If 1.4.4 and older are still used, we would need to. How ancient 1.6.0 does not matter.

Perhaps rein in the temptation to "attack back" in spinal reflex when somebody bothers to take time to point out where you are mistaken? They are often not attacking you, but merely offering improvements.

On Sun, Jul 17 2022, Junio C Hamano wrote:

The removed documentation covers two distinct topics:

 1. For >= 1.6.0 that the default changed to include --delta-base-offset.
 2. For < 1.4.4 that providing --delta-base-offset produces
    incompatibilties.

With "older than 2008-era git" and v1.6.0. I was referring to #1, not #2. You're pointing out that we should cover #2 more prominently, I'll re-roll to do that.

That's really not the case here. The reason I replied with a clarification was this part of your upthread <xmqqsfn21fmt.fsf@gitster.g>:

	But with the rest of proposed log message that hints that the
	above statement is backed by a solid study of history, it is
	wrong to write a wrong version number there.

Which I may have misread, but I understood as going beyond suggesting that we cover #2 over (or in addition to) #1, and into speculation that the change being suggested here was suspect because I hadn't carried out a "solid study of history".

Which I would agree with if I had mixed the two up. After all if someone proposes to remove documentation where 1.4.4 v.s. 1.6.0 is critical what else have they missed, and can the change be trusted? Perhaps there's some major caveat that the referenced older commits would reveal that the submitter didn't bother to study.

Which is why I replied rather than re-rolling. I.e. if that was the case I don't think a mere re-roll would address all of your concerns, I'd just be copy/pasting and rephrasing what you suggested, but I still wouldn't have carried out that "study of history".

But that's not the case. I was just attempting to go for brevity here. I.e. if I could establish that anything older than 1.6.0 wasn't relevant (#1) I wouldn't have to cover (#2) at all, as it follows from the chronology that if #1 isn't worth worrying about, neither is #2.

I'll re-roll with something I think addresses your comments here, and perhaps I've just dug myself deeper into the hole you've pegged my in with this reply, but hopefully this clarifies things & where I was coming from.

Thanks.

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

OK, so there was a study of history, but the resulting commit did not interpret and reflect what's significant in the history correctly. Sorry for mischaracterizing your mistake.

Lets put it this way.  Here is a statement:

    Since 1.6.0, people started to need to worry more about
    compatibility with 1.4.4 and older.

Now that statement, while it may be still correct, is irrelevant. Why?

Even if there were tons of people who still use 1.6.0 (or 1.5.3 for that matter, which happens to be one of my favorite releases in the era), as long as nobody uses 1.4.4 or older, we can safely remove such a statement from our end-user facing documentation set. Some archaeologists in us may care, but it is irrelevant to the general public, as long as 1.4.4 or older have died out. "As continued use of 1.4.4 by people stopped being an issue long time ago, remove the warning about interoperability" is the only thing we need to say about this change. We can add "that we needed to add in 1.6.0 era" at the end but that is already too verbose.

Please do not be one of those folks we had to deal with in the past who for whatever reason cannot admit that they were wrong.

Thanks.

On Mon, Jul 18 2022, Junio C Hamano wrote:

I won't, and I think on the subject of documentation & commit messages you (as in me, in this case) have already lost the "argument" if you're having to explain what was meant by the text, which clearly should be self-contained enough to resolve any such ambiguities by itself.

I was just replying to clarify what I was trying to go for in the v1, which in my mind isn't an argument *for* that version, but just an explanation. I.e. sometimes the solution is to more clearly phrase what I was going for, and sometimes it's to take another approach entirely.

In in case, I we may have crossed in E-Mails, here's a re-rolled v2:

    https://lore.kernel.org/git/patch-v2-1.1-98b6de56019-20220719T000847Z-avarab@gmail.com/

I tried to make the dates & versions involved clear, and also to work in your preference for v2.0.0 (or possibly later) as a cut-off.

It may not at all be what you had in mind, or maybe you're willing to queue it as-is, just let me know & I'll adjust it.

Thanks a lot for the review, and sorry about the misunderstanding.

As continued use of 1.4.4 by people stopped being an issue long time ago, we can safely remove the warning about interoperability that we added in 1.6.0 when the use of delta-base-offset has become default.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * Instead of outright removing, it probably is a good idea to hint
   the reason why the now seemingly useless configuration variable
   is there, perhaps.

 Documentation/git-repack.txt | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

On Tue, Jul 19 2022, Junio C Hamano wrote:

We cover that in git-config(1), I don't see a reason to continue dicsussing it in git-repack(1) as well. Just above the paragraph you're modifying we link to it.

The patch you've got here also replaces a specific reason (pre-1.4.4) with a vague reference to "hardly any reason", leaving the reader wondering what that reason is...

Ævar Arnfjörð Bjarmason <avarab@gmail.com> writes:

Yup, that is the effect I exactly wanted to have, with the "hint". If you are curious, you'd dig. If not, you can just trust the documentation and not worry about it ;-)

Remove documentation about --delta-base-offset that's only pertinent to those running versions of git older than v1.4.4 and v1.6.0. Both of those versions are too ancient to care about.

For the purposes of evaluating this change it only matters that v1.6.0 is too old at this point for anyone to care about, since the change in default behavior discussed in the removed documentation impacted pre-v1.4.4 versions of git.

Details:

A. As the documentation notes the "--delta-base-offset" switch
   introduced in 1.4.4[1] became the default in 1.6.0[2]. The "by
   default" part of the removed documentation discusses a change in what
   had been the status quo in v1.4.4..v1.6.0^.

B. When exactly "--delta-base-offset" was introduced and when it
   became the default (as noted in "A" above) is only of academic
   interest once we decide that anything older than 1.6.0 isn't worth
   caring about.

   The documentation being removed here was added in [3] and [4],
   which were first released with v1.4.4 and v1.7.0, respectively. At
   the time it was of interest to someone running v1.6.0 or later that
   they'd be creating packs incompatible with older git versions.

   But at some point the last user of v1.4.4 in the wild would have
   went away, presumably followed some time afterwards by the last
   v1.4.4..v1.6.0^ user.

   If we were turning back the clock we might have removed the
   "incompatible with" part of this documentation once v1.4.4 became
   irrelevant, but as v1.6.0 was still relevant kept the "by default"
   part.

   But as neither are relevant at this point let's remove this entire
   paragraph[5].

1. be6b19145f6 (make git-pack-objects able to create deltas with
   offset to base, 2006-09-21)
2. 22c79eab295 (repack.usedeltabaseoffset config option now defaults
   to "true", 2008-06-25)
3. b6945f570ac (git-repack: repo.usedeltabaseoffset, 2006-10-13)
4. 9f17688d93c (update git-repack documentation wrt
   repack.UseDeltaBaseOffset, 2010-02-04).
5. In <xmqqsfn21fmt.fsf@gitster.g> [6] Junio suggests that anything
   older than v2.0.0 or v2.16.0 isn't relevant at this point

   I think that's defensible, but as e.g. "gcc110" on the GCC Farm has
   a /usr/bin/git version v1.8.3.1 (which was released in mid-2013)
   that would be a different argument.

   As that case shows there are still OS's with 2013-era software in
   common use (particularly RHEL and its derivatives).

   But I don't think anyone knows about or can plausibly contrive a
   scenario where someone still is still v1.6.0 or older, and might
   therefore benefit from these docs.

   We might want to follow-up with removal of documentation that only
   benefits users of those ancient version, and tell them that they
   should consult their OS-installed documentation, newer git isn't
   going to carry those backwards compatibility notes forward.

   But as long as there are still systems in active use with those
   versions let's leave that to a future follow-up, either because
   it's far enough in the future that those versions are truly dead,
   or because we'd like to drop documentation in that category.
6. https://lore.kernel.org/git/xmqqsfn21fmt.fsf@gitster.g/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>

Changes in v2:

 * Updated commit message per
   https://lore.kernel.org/git/220718.86tu7eyhvz.gmgdl@evledraar.gmail.com/

---
Range-diff against v1:
1:  363f84a3fa7 ! 1:  98b6de56019 git-repack doc: remove discussion of ancient caveat
    @@ Metadata
     Author: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     
      ## Commit message ##
    -    git-repack doc: remove discussion of ancient caveat
    +    docs: remove pre-v1.6.0 "repack --delta-base-offset" docs
     
    -    The backwards compatibility caveat discussed her hasn't been a concern
    -    for anyone after Git v1.6.0. Let's simply remove it, I daresay
    -    nobody's concerned these days with having git clients running older
    -    than 2008-era git.
    +    Remove documentation about --delta-base-offset that's only pertinent
    +    to those running versions of git older than v1.4.4 and v1.6.0. Both of
    +    those versions are too ancient to care about.
     
    -    See b6945f570ac (git-repack: repo.usedeltabaseoffset, 2006-10-13) and
    -    9f17688d93c (update git-repack documentation wrt
    -    repack.UseDeltaBaseOffset, 2010-02-04) for the commits that previously
    -    introduced and adjusted this documentation.
    +    For the purposes of evaluating this change it only matters that v1.6.0
    +    is too old at this point for anyone to care about, since the change in
    +    default behavior discussed in the removed documentation impacted
    +    pre-v1.4.4 versions of git.
    +
    +    Details:
    +
    +    A. As the documentation notes the "--delta-base-offset" switch
    +       introduced in 1.4.4[1] became the default in 1.6.0[2]. The "by
    +       default" part of the removed documentation discusses a change in what
    +       had been the status quo in v1.4.4..v1.6.0^.
    +
    +    B. When exactly "--delta-base-offset" was introduced and when it
    +       became the default (as noted in "A" above) is only of academic
    +       interest once we decide that anything older than 1.6.0 isn't worth
    +       caring about.
    +
    +       The documentation being removed here was added in [3] and [4],
    +       which were first released with v1.4.4 and v1.7.0, respectively. At
    +       the time it was of interest to someone running v1.6.0 or later that
    +       they'd be creating packs incompatible with older git versions.
    +
    +       But at some point the last user of v1.4.4 in the wild would have
    +       went away, presumably followed some time afterwards by the last
    +       v1.4.4..v1.6.0^ user.
    +
    +       If we were turning back the clock we might have removed the
    +       "incompatible with" part of this documentation once v1.4.4 became
    +       irrelevant, but as v1.6.0 was still relevant kept the "by default"
    +       part.
    +
    +       But as neither are relevant at this point let's remove this entire
    +       paragraph[5].
    +
    +    1. be6b19145f6 (make git-pack-objects able to create deltas with
    +       offset to base, 2006-09-21)
    +    2. 22c79eab295 (repack.usedeltabaseoffset config option now defaults
    +       to "true", 2008-06-25)
    +    3. b6945f570ac (git-repack: repo.usedeltabaseoffset, 2006-10-13)
    +    4. 9f17688d93c (update git-repack documentation wrt
    +       repack.UseDeltaBaseOffset, 2010-02-04).
    +    5. In <xmqqsfn21fmt.fsf@gitster.g> [6] Junio suggests that anything
    +       older than v2.0.0 or v2.16.0 isn't relevant at this point
    +
    +       I think that's defensible, but as e.g. "gcc110" on the GCC Farm has
    +       a /usr/bin/git version v1.8.3.1 (which was released in mid-2013)
    +       that would be a different argument.
    +
    +       As that case shows there are still OS's with 2013-era software in
    +       common use (particularly RHEL and its derivatives).
    +
    +       But I don't think anyone knows about or can plausibly contrive a
    +       scenario where someone still is still v1.6.0 or older, and might
    +       therefore benefit from these docs.
    +
    +       We might want to follow-up with removal of documentation that only
    +       benefits users of those ancient version, and tell them that they
    +       should consult their OS-installed documentation, newer git isn't
    +       going to carry those backwards compatibility notes forward.
    +
    +       But as long as there are still systems in active use with those
    +       versions let's leave that to a future follow-up, either because
    +       it's far enough in the future that those versions are truly dead,
    +       or because we'd like to drop documentation in that category.
    +    6. https://lore.kernel.org/git/xmqqsfn21fmt.fsf@gitster.g/
     
         Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
     

 Documentation/git-repack.txt | 10 ----------
 1 file changed, 10 deletions(-)