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From Shai Erera <>
Subject Re: API Semantics and Backwards
Date Tue, 30 Nov 2010 09:47:11 GMT
I realize the benefits of not storing the backwards source -- I don't care
too much about the size of the checkout, but more about it making
introducing bw breaks easier.

And that that it happened w/ MockRAMDir only so far, doesn't mean it won't
bite us somewhere else too. But it's not a good enough reason to create a
bw/src/java either.

It would be great if we can remove all the unrelated tests from backwards.
As I see it, we should have two types of tests - those that check that
*public* API hasn't changed, and this can be in the form of reflection or
simply creating classes that call/extend the public API. Also, we want to
have tests that assert *runtime* backwards support, such as for Tokenizers,
QueryParser etc. For those we can have special test cases that assert
exactly that.

Like you said, the rest of the tests just increase the test running time.


On Tue, Nov 30, 2010 at 9:50 AM, Uwe Schindler <> wrote:

> Hi Shai,
> there are few comments:
> You are right with „we should not check backwards” for internal or **
> experimental** apis, the problem is that some tests use these internal
> APIs to check some internals. But as the idea behind backwards tests say: we
> test only drop in replacements. The functionality behind the tests is just
> nonsense, as the functionality is already tested by the main tests. So we
> just run the tests two times. Because of this, we can simply disable all
> tests that **explicitely** check internal APIs. An example would be a test
> that checks the exact class names of some returned objects (e.g. in
> MultiTermQuery rewrites).
> The problem are Mock classes in the backwards tests, that check internal
> apis (the famous example is MockRAMDirectory) as it is used by almost every
> test. If we would disable all these tests, we would not have the possibility
> to test any of them. For the current problem (and another one with this
> exact same class), we have a solution, I attached it to the issue. It’s a 10
> lines patch, it’s a hack, but its better than living with the cruft of
> having a modifiable backwards branch. If you really have to change these
> mock classes, you can do it like in the patch – but then you know you are
> doing something special and you can **mark** it as such (like I did in my
> patch).
> I am against reinserting the previous version’s classes for several
> reasons:
> -          The checkout gets big
> -          When we release a bugfix release of the previous version, we
> should be able to replace the old jar file by the bugfix one. I will sonn
> replace lucene-core-3.0.2.jar with 3.0.3.
> -          We should really don’t ever change the core test, because it
> contradicts the sense of backwards tests. If we really need to fix it (like
> for mock classes that are used by every test), it can be done in various
> ways: Remove the extra check code from the mock classes (this is often
> easiest) or use a reflection hack (we only have two of them now – but you
> changed the backwards branch much more often before I reverted it when
> adding the previous jar file).
> -          For tests that simply test some internal apis and nothing else
> important (for plugin compatibility): lets comment out the test. In the bw
> folder we did this with a special comment to leave the code intact.
> Uwe
> -----
> Uwe Schindler
> H.-H.-Meier-Allee 63, D-28213 Bremen
> eMail:
> *From:* Shai Erera []
> *Sent:* Tuesday, November 30, 2010 7:46 AM
> *To:*
> *Subject:* API Semantics and Backwards
> Hi
> I'd like to discuss the semantics of our API and how backwards tests relate
> to it. First, I'd like to confirm my understanding - currently it relates to
> 3x, but it will apply to 4x after 4.0 will be released:
> Public/Protected -- this API is 'public' and we should maintain
> back-compat, in the form of jar drop-in. That is, we cannot rename or modify
> it, w/o deprecating first (I leave *exceptions* deliberately outside the
> discussion).
> Package-private -- this is not public API and while users can use it if
> they declare their classes under the relevant package, they should not
> expect jar drop-in support.
> Public @internal -- this is public API following Java language, however not
> public to the users. We need to make this API public so that Lucene can
> access it, but it's used for internal purposes only. Users can still use it,
> however cannot expect jar drop-in support.
> Public @experimental -- this API is intended to be made 'public' one day,
> however we're still working on it, and even though it's checked-in or even
> released, it may change unexpectedly. Not sure we want to say that jar
> drop-in support cannot be expected, though according to the definition we
> are allowed to change it ... so perhaps it's like @internal, only w/ the
> intention to make it public one day.
> Both @internal and @experimental tags should be removed if they do not
> apply anymore.
> Now comes the question about backwards tests -- our tests touch all the API
> types above, however they are not resilient to changes in 3 out of 4 of
> them. In the past this wasn't a problem - the backwards layer had both
> src/java and src/test, tests we compiled against src/java and then executed
> against core.jar. This allowed changing the source code of the "non public"
> API and make the same changes to backwards/src/java, and tests would still
> run. This had a disadvantage too - it was 'easier' to break back-compat on
> the first API type (the *true* public API) because you could still change
> bw/src/java and be done w/ it.
> Today though bw tests are compiled against the previous release source. But
> if you make changes to the non public API, they break while they shouldn't.
> So the question is what can we do about the backwards tests so that we can
> still make allowed changes to the API w/o them breaking?
> * We can say that unit tests should not test package-private / @internal /
> @experimental classes, but I don't believe in it.
> * We can re-introduce bw/src/java and ask all committers to make careful
> changes to it. If we're careful, we won't introduce any *true* public API
> break.
> The second is the more realistic solution IMO, but since this was the
> situation in the past and changed to how it is today, I don't know if it's
> acceptable.
> Whatever we do though, we cannot have backwards tests dictate what is
> public API and what isn't, because bw tests are compiled following Java
> semantics, that have nothing to do w/ Lucene's 'public' notion.
> Shai

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