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 <http://www.thetaphi.de/> http://www.thetaphi.de eMail: [email protected] From: Shai Erera [mailto:[email protected]] Sent: Tuesday, November 30, 2010 7:46 AM To: [email protected] 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
