Okay, sounds good, I think these are compatible goals. Restating here to make 
sure I understood clearly, then I'll make a few notes on the existing tickets, 
new tickets to track this:
 * ant test (more or less) should correctly filter out java9+ jre emulation 
tests when run from Java 8. All tests will be run in Java 11 (or Java.latest, 
when we add tests that require a newer JDK)
 * ant dist-dev should run correctly in Java 8, Java 11, and Java.latest
 * Based on the current status of javadoc, ant dist will for now run on Java8 
only, then later only on any Java9+. (elemental hasnt actually been removed 
yet, but I have a patch for it...)

Steps to achieve this, roughly in order:
 * Remove Java 7/8 filters in ant wiring, make everything run cleanly/simply on 
Java 8 alone
 * Finish making the distribution part of the code run cleanly on Java >=9 
(https://gwt-review.googlesource.com/c/gwt/+/22640 is the last step until this 
is finished)
 * Update build to skip any doc tasks when on Java >8
 * Add Java <11 filters to ant wiring, allowing specific tests to be excluded 
when running on something older than Java 11 in anticipation of this emulation 
to be finished, landed.
 * Update Javadoc to support >8 only, update build to skip any doc tasks when 
on Java 8



On Wed, Jul 1, 2020, at 11:34 AM, Thomas Broyer wrote:
> 
> 
> On Wednesday, July 1, 2020 at 3:32:34 AM UTC+2, Colin Alworth wrote:
>> Thanks Goktug for clarifying - I am personally in favor of a more coarse 
>> approach, more future proofed approach that will end up with making changes 
>> now rather than later. And to your followup, agreed, all else equal, let's 
>> avoid supersource.
>> 
>> Thomas - While I made a Java8-first option was the first bullet at the end 
>> of my email, I deliberately skipped the option of "we can either produce 
>> build artifacts, or test the output, but not both in the same build", but it 
>> may be worth considering, even if it means each release has to be built 
>> twice.
>> 
>> My thinking on the javadoc wiring is that it is better done once, and better 
>> done sooner than later. There are other advantages to modernizing the 
>> javadoc: dropping the deprecated API, search, etc. If the concern is only 
>> saving the effort of this work, then I'm happy to own this task, if we think 
>> it would be preferred to only produce output artifacts using Java8 then it 
>> seems it wouldn't make sense to try it at all, at least until we get closer 
>> to something resembling a Java 8 EOL, or find ourselves needing a baseline 
>> higher than Java 8 for other reasons. That is, optimizing for 
>> minimum-effort-today has its advantages, but my current mindset was to seek 
>> to future proof a bit, as long as I'm excising Java7-specific things and 
>> ensuring other code builds on Java9+.
>> 
>> With the assumption that Javadoc is handled, is there any objection to 
>> requiring Java 11+ to run tests, Java 9+ to produce a complete build? It 
>> sounds like this is the direction everyone is moving, only supporting tests 
>> in a limited range of versions, only supporting releases in a limited range 
>> of versions (or, just one), or is the objection specifically to dropping 
>> Java 8 as the build version of choice?
> 
> I'm concerned with dropping JDK 8 testing. If we want to make sure it works 
> with JDK 8, we have to test with JDK 8. If we want to make sure it works with 
> JDK 11, we have to test with JDK 11. (IMO, supporting JDK14, then 15, etc. 
> would only be a bonus)
> Given how Ant works, this probably does not mean *building* (the non-test 
> code) with either, i.e. we could probably build and test with JDK8 
> (JAVA_HOME=… ant build) and then run tests with JDK 11 (JAVA_HOME=… ant test, 
> in the same directory, reusing the classes already compiled by the previous 
> build with the other JDK), or the reverse.
> Of course, it also depends what we want to test!
> Unfortunately, JDK 8 and JDK 9+ are different enough (at runtime) that we'd 
> really want to test both (AFAIK, we(you) only did smoke tests with JDK 11 for 
> GWT 2.9.0, and smoke tests might actually be enough)
> 
> So, what do we want to achieve?
>  * Make it possible to "ant dist-dev" and "ant test" with JDK 11 (or even 
> 14)? to run JDK9+ specific tests (and make it easier for anyone to contribute)
>  * Make it possible to "ant clean elemental dist" with JDK 11 (or even 14)? 
> (this could/would mean dropping support for JDK 8 for "ant doc", but keep 
> "ant dist-dev" and "ant test" working)
> In any case, I believe we should keep "ant dist-dev" and "ant test" working 
> with both JDK 8 and JDK 11 (or even 14), and ideally actually run with both 
> JDKs nightly (possibly one after the other in the same directory, or even 
> have the Ant build call the other JDK during a single build, whatever; it's 
> probably easier currently to just run the build twice).
> This is easier said than done though ;-)
> 
>> 
>> 
>> --
>> 
>> "--release 8" - this is actually required (and implicit?) when running 
>> j2cl_library at the moment. All of the Java 9, 10, 11 emulation I have 
>> working now uses only java 8 language features, but still seem to compile 
>> correctly even when building Java9+ features, as long as it is internally 
>> consistent. This makes sense, since we were doing this before too, targeting 
>> and running on java7, but with java8 classes available to gwt projects. 
>> Tests are a different story, as discussed.
>> 
>> 
>> 
>> On Tuesday, June 30, 2020 at 4:40:29 PM UTC-5, Goktug Gokdogan wrote:
>>> (which you already pointed but what matters me the most :))
>>> 
>>> On Tue, Jun 30, 2020 at 11:39 AM Goktug Gokdogan <[email protected]> wrote:
>>>> Super sourcing with tests is errorprone; it is easy to get one method 
>>>> added in one version but note the other and basically you end up testing 
>>>> nothing.
>>>> 
>>>> On Tue, Jun 30, 2020 at 1:36 AM Thomas Broyer <[email protected]> wrote:
>>>>> So, IIUC, there are 2 distinct issues, but both related to JDK versions.
>>>>> 
>>>>> First, the doclet/taglet where JDK8 has com.sun.javadoc and JDK9+ have 
>>>>> jdk.javadoc.doclet. This is an internal tool, so it would be wasted 
>>>>> effort to maintain 2 versions. Either we keep the current code and 
>>>>> require JDK8, or we migrate to the new API and require JDK.lts or 
>>>>> JDK.latest. Those requirements only apply to building the javadoc though, 
>>>>> i.e. to actually cut the releases.
>>>>> 
>>>>> Next, the tests. If we want to be able to test JDK9+ syntax and/or APIs, 
>>>>> then we either have to require such a JDK (for those tests at least), or 
>>>>> supersource the code so it can run with JDK8.
>>>>> So what are the pros and cons?
>>>>>  * Require a specific JDK:
>>>>>    * do we require JDK.lts? or JDK.latest? (currently, JDK.lts would be 
>>>>> enough, but as soon as we add newer language syntax and/or APIs, we'd 
>>>>> have to use JDK.latest to test those)
>>>>>    * do we require it only for those specific tests (aka "use ant 
>>>>> filters") or for the whole build? (and using "--release 8" for non-test 
>>>>> code to target JDK 8; BTW, can we use "--release 8" at all? not all JDK8 
>>>>> APIs are available that way, specifically "internal" APIs)
>>>>> requiring recent JDKs for the whole build means we no longer test with 
>>>>> JDK8, and we *have* to migrate the doclets to the new API. Those are 
>>>>> rather big cons if you ask me.
>>>>>    * Assuming ant filters then:
>>>>>      * pro: tests are easy to write/maintain, you only have to follow a 
>>>>> naming convention for the test class
>>>>>      * con: testing everything requires the JDK.lts/JDK.latest; running 
>>>>> the tests with JDK8 only covers JDK8-compatible code. If we keep the 
>>>>> doclets on JDK8, this means we have to run the build twice when cutting a 
>>>>> release: once with JDK.lts/JDK.latest to make sure the tests pass, and 
>>>>> then once with JDK8 to actually build the artifacts.
>>>>>      * con: requires setting up the new JDKs, and new jobs, on the CI 
>>>>> server. If we keep using the current build.gwtproject.org, this puts the 
>>>>> burden on Google; that'd likely precipitate the replacement of the server.
>>>>>      * con: requires 2 builds to make sure things still build/run with 
>>>>> JDK8
>>>>>  * Supersourcing
>>>>>    * pro: tests can run with JDK8, so the whole build is JDK8-compatible 
>>>>> and still covers all tests
>>>>>    * con: requires somehow maintaining the tests twice, keeping the 
>>>>> javac'd and supersourced versions in sync (AFAIK, the javac'd version has 
>>>>> to have the test methods so they're detected by JUnit, even if their body 
>>>>> is empty; so it would be rather easy to add a test to the supersourced 
>>>>> version and never actually run it because the method is missing from the 
>>>>> javac'd version)
>>>>> The situation requiring the minimum effort in the short term would be 
>>>>> keeping the doclets as they are and using supersourcing for the tests.
>>>>> In the long run, as JDK9+ tests grow, supersourcing might become 
>>>>> unsustainable, but the impact on the CI server et al. is non-negligible. 
>>>>> We could still possibly, at least temporarily, build only with JDK8, and 
>>>>> only run the JDK9+ tests once in a while (at release time?), manually on 
>>>>> a developer's machine as a smoke test.
>>>>> 
>>>>> So, my vote would be: "require JDK8 for javadoc, supersource tests", with 
>>>>> a fallback to an option you didn't list: "Allow any JDK 8+, use ant 
>>>>> filters, only actually produce javadoc on JDK8 builds", and if/when 
>>>>> someone wants to put the effort then migrate the doclets and move on to 
>>>>> your third option: "allow any JDK8+, use ant filters, only actually 
>>>>> produce javadoc on JDK9+ builds"
>>>>> 
>>>>> On Tuesday, June 30, 2020 at 3:45:36 AM UTC+2, Colin Alworth wrote:
>>>>>> As of somewhere in the time leading up to the GWT 2.9.0 release, it is 
>>>>>> no longer possible to build GWT with Java7, and similarly the decision 
>>>>>> was made to no longer officially support running on Java7 
>>>>>> (jsinterop-annotations use of "TYPE_USE", newer jetty version too I 
>>>>>> believe). 
>>>>>> 
>>>>>> There is still some defunct wiring in the build to handle Java 7 vs Java 
>>>>>> 8 though, mostly with regards to running tests - since we first javac 
>>>>>> our java classes, and then run gwtc on them, we need to make sure that 
>>>>>> the java version being use can correctly compile those tests.
>>>>>> 
>>>>>> The issue https://github.com/gwtproject/gwt/issues/9683 is tracking some 
>>>>>> of the existing work on this: the main remaining piece is to decide how 
>>>>>> to handle javadoc. GWT has its own custom doclet to handle a few custom 
>>>>>> tags, "example", "gwt.include", and "tip". None of this compiles after 
>>>>>> Java 8, since Java 9 came with a new, incompatible API to build custom 
>>>>>> tags, so either we drop Java 8 support for building the toolkit, require 
>>>>>> _only_ Java 8 to build, support two parallel copies of the custom doc 
>>>>>> wiring, or drop the doc wiring entirely and remove these custom tags 
>>>>>> throughout the codebase.
>>>>>> 
>>>>>> Since the release of GWT 2.9 and my own work on the above ticket, I've 
>>>>>> been picking back up some Java 9/10/11 JRE emulation work that I had 
>>>>>> previously paused, and I'm running into the issue described at the top - 
>>>>>> if you write a test that calls Map.of() and run it on Java8 as a 
>>>>>> GWTTestCase, you'll get a compile error.
>>>>>> 
>>>>>> Two basic ways I can easily see to fix this: we can make two copies of 
>>>>>> each test, one as an empty "real" java type and one as supersource, or 
>>>>>> we can guard those tests behind java version args in the build glue like 
>>>>>> we did for Java7 vs Java8. The first option is clunky, and while I see 
>>>>>> this was done for `com.google.gwt.dev.jjs.test.Java8Test`, it clearly 
>>>>>> wasn't done for JRE emulation tests, and I assume there was a reason for 
>>>>>> that. The second option requires changing our CI to build+test on some 
>>>>>> new JRE...
>>>>>> 
>>>>>> ...and given the constraints of the Java LTS system, and the java 8/9 
>>>>>> divide for custom doclet stuff, it seems like the clearest win is to 
>>>>>> move all the way to Java11, though continue to target java 8 releases, 
>>>>>> and test on all JREs up until current.
>>>>>> 
>>>>>> So that's my pitch. For completeness, some other options that seem 
>>>>>> workable, keeping in mind that at present there are about 3 important 
>>>>>> JRE versions to support well: Java 8, Java 11, and the current stable 
>>>>>> release.
>>>>>>  * Require Java8 for javadoc, supersource tests
>>>>>>  * Allow any JRE 8+, use ant filters for tests for each version, 
>>>>>> maintain two javadoc builds
>>>>>>  * Allow any JRE 8+, use ant filters, only actually produce javadoc on 
>>>>>> java9+ builds
>>>>>> 
>>>>>> Other technical ways to deal with this, or have a missed an easier 
>>>>>> solution to one of these problems?
>>>>> 

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