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From Shai Erera <ser...@gmail.com>
Subject What are we allowed to do in 3.0?
Date Thu, 30 Apr 2009 10:25:49 GMT
Hi

Recently I was involved in several issues that required some runtime changes
to be done in 3.0 and it was not so clear what is it that we're actually
allowed to do in 3.0. So I'd like to open it for discussion, unless
everybody agree on it already.

So far I can tell that 3.0 allows us to:
1) Get rid of all the deprecated methods
2) Move to Java 1.5

But what about changes to runtime behavior, re-factoring a whole set of
classes etc? I'd like to relate to them one by one, so that we can comment
on each.

Removing deprecated methods
---------------------------------------------
As I was told, 2.9 is the last release we are allowed to mark methods as
deprecated, and remove them in 3.0. I.e., after 2.9 is out, if we feel there
is a method that should be renamed, its signature should change or be
removed altogether, we can't just do it and we'd have to deprecate it and
remove it in 4.0 (?). I personally thought that 2.9 allows us to make these
changes without letting anyone know about them in advance, which I'm ok with
since upgrading to 3.0 is not going to be as 'smooth', but I also understand
why 'letting people know in advance' (which means a release prior to the one
when they are removed) gives a "better service" to our users. I also thought
that jar drop-in-ability is not supposed to be supported from 2.9 to 3.0
(but I was corrected previously on that).
Which means upon releasing 2.9, the very first issue that's opened and
committed should be removing the current deprecated methods, or otherwise we
could open an issue that deprecates a method and accidentally remove it
later, when we handle the massive deprecation removal. We should also create
a 2.9 tag.

Changes to runtime behavior
-----------------------------------------
What is exactly the policy here? If we document in 2.9 that certain
features' runtime behavior will change in 3.0 - is that ok to make those
changes? And if we don't document them and do it (in the transition from
2.9-3.0) then it's not? Why? After all, I expect anyone who upgrades to 3.0
to run all of his unit tests to assert that everything still works (I expect
that to happen for every release, but for 3.0 in particular). Obviously the
runtime behaviors that were changed and documented in 2.9 are ones that he
might have already taken care of, but why can't he do the same reading the
CHANGES of 3.0?
I just feel that this policy forces us to think really hard and foresee
those changes in runtime behavior that we'd like to do in 3.0 so that we can
get them into 2.9, but at the end of the day we're not improving anything.
Upon upgrading to 2.9 I cannot handle the changes in runtime behaviors as
they weren't done yet. I can only do it after I upgrade to 3.0. So what's
the difference for me between fixing those that were documented in 2.9 and
the new ones that were just released?

Going forward, I don't think this community changes runtime behavior every
other Monday, and so I'd like to have the ability to make those changes
without such a strict policy. Those changes are meant to help our users (and
we are amongst them) to achieve better performance, usually, and so why
should we fear from making them, or if fear is too strong a word - why
should we refrain from doing them, while documenting the changes? If we
don't want to do it for every 'dot' release, we can do them in major
releases and I'd also vote for doing them in a mid-major release, like 3.5.

Refactoring
----------------
Today we are quite limited with refactoring. We cannot add methods to
interfaces or abstract methods to abstract classes, or even make classes
abstract. I'm perfectly fine with that as I don't want to face the need to
suddenly refactor my application just because Lucene decided to add a method
to an interface.

But recently, while working on LUCENE-1593, me and Mike spotted a need to
add some methods to Weight, but since it is an interface we can't. So I said
something "let's do it in 3.0" but then we were not sure if this can be done
in 3.0. So the alternative was "let's deprecate Weight, create an
AbstractWeight class and do it there", but we weren't sure if that's even
something we can push for in 3.0, unless we do all of it in 2.9. This also
messes up the code, introducing new classes with bad names (AbstractWeight,
AbstractSearchable) where we could have avoided it if we just changed Weight
to an abstract class in 3.0.

---------------------------

I think it all boils down to whether we MUST support jar drop-in-ability
when upgrading from 2.9 to 3.0. I think that we shouldn't as the whole
notion of 3.0 (or any future major version) is major revision to code, index
structure, JDK etc. If we're always expected to support it, then 2.9 really
becomes 3.0 in terms of our ability to make changes to the API between
2.9-3.0. I'm afraid that if that's the case, we might choose to hold on with
2.9 as much as we can so we can push as many changes as we foresee into it,
so that they can be finalized in 3.0. I'm not sure what will that give us,
because upong upgrading to 2.9 I'll have to make a major revision to my code
if I want to simply drop the 3.0 jar in.

And while back-compat of index structure is a MUST (i.e., I don't want to
rebuild my indexes every time I upgrade a major version), doing some house
cleaning to my code and taking advantage of the new classes and/or more
performing API is something I'm willing to live with.

If the answer to all my questions is "we MUST do it this way because that's
what we've decided long ago", then so be it. But if we're willing to
re-consider our back-compat policy and maybe even change it, then it's
something we can put in the CHANGES of 2.9, going forward to 3.0 :)

Shai

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