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Different projects have different policies for managing the "main development path" as distinguished from various kinds of release (such as candidate releases, experimental releases, and stable releases).
arch
is flexible enough to allow many such policies to be
implemented in a direct way. Here are some examples and hints about
using arch
.
One development policy is based on milestones . The team works on one milestone goal at a time. When they have just about reached that milestone, they make candidate releases of the milestone for people to test. After fixing bugs, a milestone release is made.
After several milestones, the milestone release gets a version number, and becomes a version release .
Beginning from scratch on the first milestone, the developers create the first development path -- in which to work on reaching the first milestone:
mozilla--devo--1.0 ------------------ base-0 patch-1 patch-2 patch-3 patch-4
After some time, they are ready to make some candidate releases
and enter a bug-fixing cycle. They'll use tags for that -- making the
bug fixes in the devo
branch:
mozilla--devo--1.0 ------------------ base-0 patch-1 patch-2 mozilla--milestone--1.0 patch-3 ----------------------- patch-4 --------------------->base-0 (tag -- 1st release candidate) patch-5 .------>patch-1 (tag -- 2nd candidate) patch-6 -------------- ---->patch-3 (tag -- 3rd candidate) patch-7 | patch-8 ----------------
In the diagram, patches 5..8
in the devo
branch are fixes made
based on reports from candidate releases. We'll suppose that after
patch-8
, the first milestone appears to be stable. The developers
want to make the milestone release, and begin work on milestone 2
:
mozilla--devo--1.0 ------------------ base-0 patch-1 patch-2 mozilla--milestone--1.0 patch-3 ----------------------- patch-4 --------------------->base-0 (tag -- 1st release candidate) patch-5 .------>patch-1 (tag -- 2nd candidate) patch-6 -------------- ---->patch-3 (tag -- 2rd candidate) patch-7 | version-0 (milestone release) --patch-8 ---------------- | | mozilla--devo--2.0 (development path for the second milestone) | ------------------ ->base-0 (continuation)
That pattern can continue indefinately, eventually resulting in a versioned release, (again using tags):
mozilla--devo--1.0 mozilla-milestone--1.0 ------------------ ---------------------- ... --patch-N---------------------->... | version-0 (milestone 1 release) | | | mozilla--devo--2.0 mozilla-milestone--2.0 | ------------------ ---------------------- | ... ->patch-N---------------------->... | version-0 (milestone 2 release) | | | mozilla--devo--3.0 mozilla-milestone--3.0 | ------------------ ---------------------- | ... ->patch-N---------------------->... | version-0 (milestone 3 release) | ... | | mozilla--devo--10.0 mozilla-milestone--10.0 | ------------------- ----------------------- | ... ->patch-N---------------------->... --version-0 (milestone 10 release) | | mozilla-1.0 | ----------- ->base-0 (tag) version-0 (versioned release)
That pattern of arch
usage is very simple because the developers
stay in sync, following a strict cycle of working on a milestone,
making candidate releases and bug-fixing, making a milestone releases
and starting on the next milestone. Less synchronized development
can be much more complicated, as illustrated in the next example:
Another, more intricate policy is based on version numbers. Odd numbered versions are the "leading-edge" of development -- often unstable, but having the very latest sources. Even numbered versions are "stable" -- lagging behind the leading-edge, but containing only code known to work reasonably well.
The arch
concept of a "continuation version" is ideal for this,
because there is no requirement that a continuation version be a
continuation of the immediately preceeding version.
A series of diagrams can help to illustrate this usage of arch
and
some of the subtleties that can arise. We'll start with just
the initial leading-edge development path
linux--0.1 ---------- base-0 patch-1 patch-2 patch-3 patch-4 version-0
At that point, the developers decide to make the first stable release:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | patch-4 | version-0 ------
We can suppose that patch-1
of linux--0.2
is just a quick change
to the top level README
file, and that after that -- the new stable
version is sealed (creating version-0
) and released. We never
particularly want to merge patch-1
of linux-0.2
back on to the
odd-numbered versions.
Naturally, some bugs are detected in the stable release -- three in rapid succession. The developers fix these on the leading edge branch, planning to merge them with the stable tree later:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | patch-4 | version-0 ------ versionfix-1 versionfix-2 versionfix-3
They wait a week for some testing to occur. The bug fixes are looking ok, so the developers decide to start work on the next leading-edge version:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | patch-4 | version-0 ------ versionfix-1 versionfix-2 --versionfix-3 | | | linux--0.3 | --------- ->base-0 (continuation) patch-1
Just as the developers are about to merge the bug fixes with the stable version, one more bug report trickles in. Fortunately, it's a trivial bug -- so the developers are confident about making the fix in the leading edge, but immediately releasing it in the stable version.
Here's a catch, though -- the latest leading edge version
(linux--0.3
) has already diverged from the stable version because of
patch-1
. The developers definately don't want patch-1
of 0.3
in
the the stable 0.2
yet, so they fix the newly reported bug in 0.1
,
then merge all four bug fixes with the stable tree in the usual way.
Meanwhile, separate work also continues on 0.3
:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | ->versionfix-1 (merge) patch-4 | | version-0 ------ | versionfix-1\ | versionfix-2 |------- --versionfix-3 | | versionfix-4/ | | | | linux--0.3 | --------- ->base-0 (continuation) patch-1 patch-2 patch-3
It's worth noting at that point that linux--0.3
is missing a bug-fix
(versionfix-4
) from linux--0.1
:
% cd ~/wd/linux--0.3
% larch whats-missing linux--0.1 versionfix-4
We'll eventually do an update to pick up that bug fix, but first, let's make the situation more complicated.
Suppose, some mailing lists get wind of patch-3
in linux--0.3
.
Soon Slashdot
and Newsforge
pick up the story. It turns out that
patch-3
is a very desirable feature and the implementation appears
to be clean and stable. People are clammering for its appearence in a
stable release, and the developers happen to think it is a good idea.
So, they start the next stable revision:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | ->versionfix-1 (merge) patch-4 | | | version-0 ------ | | versionfix-1\ | | versionfix-2 |------- | linux--0.4 --versionfix-3 | | ---------- | versionfix-4/ --->base-0 (continuation) | | | | linux--0.3 | --------- ->base-0 (continuation) patch-1 patch-2 patch-3
They only want patch-3
of 0.3
for 0.4
-- not anything else.
That's a job for replay --exact
:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | ->versionfix-1 (merge) patch-4 | | | version-0 ------ | | versionfix-1\ | | versionfix-2 |------- | linux--0.4 --versionfix-3 | | ---------- | versionfix-4/ --->base-0 (continuation) | =->patch-1 (replay --exact merge) | | version-0 | . | linux--0.3 | | --------- . ->base-0 (continuation) | patch-1 . patch-2 | patch-3-=--=--=--=--=--=--=- ...
After merging the much-desired patch-3
of 0.3
into 0.4
, the
developers seal 0.4
and make the stable release.
Let's suppose that development on 0.3
continues for a while.
After some time, the developers decide that 0.3
has aquired enough
new features. They want to do two things: start 0.5
, and start
getting the stable 0.6
release ready:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | ->versionfix-1 (merge) patch-4 | | | version-0 ------ | | versionfix-1\ | | versionfix-2 |------- | linux--0.4 --versionfix-3 | | ---------- | versionfix-4/ --->base-0 (continuation) | =->patch-1 (replay --exact merge) | | version-0 | . | linux--0.3 | | --------- . ->base-0 (continuation) | patch-1 . patch-2 | patch-3-=--=--=--=--=--=--=- ... linux--0.6 -version-0 ---------- | | | | linux--0.5 | ---------- ->base-0
Notice that they haven't created the base revision for 0.6
yet.
There's a choice here. They could make 0.6
a continuation of 0.4
,
then merge in all the patches they're missing from 0.3
. On the
other hand, they could make 0.6
a continuation of some 0.3
and
pick up all those missing patches "the easy way".
But, oops, when someone checks out version-0
from 0.3
and runs
whats-missing
, they find out that the 0.3
branch never picked up
versionfix-4
from 0.1
. That's easily fixed by updating a 0.3
tree against 0.1
, and checking in the resulting merge to 0.3
.
The resulting merge is also the revision that will become the base
revision for 0.6
:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | ->versionfix-1 (merge) patch-4 | | | version-0 ------ | | versionfix-1\ | | versionfix-2 |------- | linux--0.4 --versionfix-3 | | ---------- | versionfix-4/ --->base-0 (continuation) | | =->patch-1 (replay --exact merge) | ----- | version-0 | | . | linux--0.3 | | | --------- | . ->base-0 (continuation) | patch-1 | . patch-2 | | patch-3-=--=--=--=--=--=--=- ... | linux--0.6 -version-0 V ---------- | versionfix-1 (0.1 update)------>base-0 (continuation) | version-0 | | linux--0.5 | ---------- ->base-0 patch-1 patch-2
Meanwhile, new work continues on 0.5
.
But now, the 0.5
tree is in an interesting state. If a developer
checks out the latest 0.5
and asks:
% larch whats-missing linux--0.1 linux--0.1--versionfix-4
If the developer asks whats-missing
from 0.3
, the answer is:
% larch whats-missing linux--0.3 linux--0.3--versionfix-1
If those two patches were unrelated -- there would be no problem:
simply update from both branches and check the result into 0.5
.
In fact, though, versionfix-1
from 0.3
is really the same change
as versionfix-4
from 0.1
(look back at how versionfix-1
was
created). Let's also suppose that when the fix was merged into 0.3
,
a slight change had to be made -- to resolve a merge conflict.
So if the developer just blindly updates from 0.1
, then from 0.3
,
the second update will result in new conflicts. That might not be so
bad if we're only talking about two patches -- but if we were talking
about 20
or 200
, a lot of needless work would be called for.
Fortunately, arch
can help. First, the developer gets the latest
0.5
revision:
% larch get linux--0.5 ~/wd/linux--0.5
Then gets a list of all patches missing from 0.1
and 0.3
:
% cd ~/wd/linux--0.5
% larch whats-missing --full linux--0.1 linux--0.3 archive@kernel.org--primary/linux--0.1--versionfix-4 archive@kernel.org--primary/linux--0.3--versionfix-1
That list can be piped into the reconcile
tool:
% ... | larch reconcile archive@kernel.org--primary/linux--0.3--versionfix-1
What happened? reconcile
figured out that versionfix-1
from
0.3
already includes versionfix-4
from 0.1
-- there's no need to
apply both patches. So patch-plan
reported the list of patches
that do need to be applied, and in this case, there's only one.
In a more complicated situation, patch-plan
would print a list of
patches in the order they should be applied. In general, it will be a
subset of the patches in its input, but applying that subset will have
the same effect as applying all of the patches (but hopefully with
fewer conflicts).
The developer uses larch replay --list
to process that list, finally
winding up with:
linux--0.1 linux--0.2 ---------- ---------- base-0 ----> base-0 (continuation) patch-1 | patch-1 patch-2 | version-0 patch-3 | ->versionfix-1 (merge) patch-4 | | | version-0 ------ | | versionfix-1\ | | versionfix-2 |------- | linux--0.4 --versionfix-3 | | ---------- | versionfix-4/ --->base-0 (continuation) | | =->patch-1 (replay --exact merge) | ----- | version-0 | | . | linux--0.3 | | | --------- | . ->base-0 (continuation) | patch-1 | . patch-2 | | patch-3-=--=--=--=--=--=--=- ... | linux--0.6 -version-0 V ---------- | versionfix-1 (0.1 update)------>base-0 (continuation) | | version-0 | | | linux--0.5 | | ---------- | ->base-0 | patch-1 | patch-2 V patch-3 (0.1/0.3 reconciliation)
Now if someone gets the latest revision of 0.5
and asks:
% larch whats-missing --full linux--0.1 linux--0.3 [no output]
Isn't reconcile
handy?
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