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Oxygen.1a brought initial support to configure new options as defined in JEP 261 (beware, we have been told that the JEP contains outdated information).

The new UI extending the Java Build Path configuration does not yet cover all possible & desirable use cases. This page collects the open issues and discusses how we can support everything in a maximally consistent way.

When discussing integration in the Java Build Path configuration, will this be picked up by launch configurations automatically, or is more needed also in JDT/Debug?

[SH]: I have created a first UI proposal for discussion


What's missing?

  • bug 526831
  • --add-reads my.mod=XXX
    • special case --add-reads my.mod=ALL_UNNAMED

So far, --add-reads can only be applied to a module on which the current project depends, but not on the current module itself.

Use cases

Why is this relevant / what is the user trying to achieve by this option?

  • Does it make a difference whether reading named or unnamed modules?
    • Yes, module-info cannot say "reads ALL_UNNAMED".
  • Do we still need to support named modules?
    • Yes, for test code. See bug 526963.
      • [SH]: Let me check if I can construct a user story for this (correct me if I'm wrong):
        • A project defines a module M1
        • Additionally, it has a test source folder, that depends on module M2
        • M1 should not require M2, ergo "reads" is not a property of the project but of the test folder
        • The test folder cannot define its own module-info, so it cannot easily declare test-specific requires (files in this folders will be associated to the 'main' module of the project and can only use dependencies declared there).
        • Hence we need a way to express that M1 comes in two variants, with / without test source & test dependencies.
          • [NL]: This is a possibility, or at least a way to think about it.
        • Question: Is this issue limited to "reads" or would the test variant possibly need other directives, too?
          • Export packages to test folders of downstream projects? My guess: yes!
          • Declare service consumption? My guess: yes!
          • [NL]: It could also need --add-exports from the module it reads to itself if the module being read does not export the needed packages by itself. This is already possible in the UI.
            • [SH]: (minor:) If module-info already requires M1 and tests need M1 to export p1, that package would then be accessible also from main code of the project. This might be undesirable.
      • [SH]: If the above bullet is a true rendition of the issue at hand, could the same be expressed in syntax, rather than as directives on the build path? Reason for asking: I see explicitly tweaking "Modularity Details" mainly as a tool during migration towards modules - in a perfect modular world none of this would be needed - whereas different main / test dependencies is a part of good software engineering, designed to stay.
        • [NL]: You can add the readability edges in module-info directly, but this means that you will need Eclipse-specific module-info files because it's the only IDE that treats test folders this way. As things stand, whether the case is a full modular world or a migration world, the problem of test folders still needs to be solved.
      • [SS] My vote will be to use for all named modular dependencies.
      • [SH]: How close does "require static" come to expressing test dependencies?
        • [NL]: I *think* this is exactly the alternative mentioned above with "could the same be expressed in syntax".
      • [NL]: I think that ideally Eclipse should do what other IDEs do (do they treat test sources as "real non-modules", which adds reads for everything?). Maybe have every source folder its own module - I think this is best. If not, allow to specify in the UI read edges (can be done directly in the classpath).
        • [SH]: Have "other IDEs" converged on a single solution that is both intuitive and powerful? Otherwise I'd prioritize consistency within our approach over copying other IDEs' concepts.
  • How does the request interact with the distinction main/test sources?
    • [NL]: main sources are can do everything in module-info so they are fine. Test sources are restricted by module-info, but cannot change it, so they need a way to express their special needs.

Solution discussion

  • Specifically for test code we seem to have two conflicting mental models, which should be sorted out before discussing details of a solution:
    • Test code is not part of the project's module, it has all the privileges of an unnamed module.
    • Test code is part of the project's module, but two different views of that module exist: main and main-and-test
    (I believe this is the appropriate description for our current implementation).
    • [TB] Currently, test code reads the unnamed module (as maven does). For the use case where test code should read additional named modules, maven-compiler-plugin 3.8.0 now seems to support a secondary in the test source folder (but I haven't checked how it is compiled or executed. Maybe we should try to support that, too?
  • Where in the UI should this option be represented?
    • [TB] In that context: should we have a "test-only" flag for add-reads configurations or in general extra test-module-options?
    • Is it a property of a source folder?
      • How do we handle multiple source folders per project?
    • Is it a property of the project?
      • If so, which part of the Build Path dialogs best represents "the project"?
  • What should be the gestures / dialogs etc. to define this?


What's missing?

So far, --patch-module can only declare that the current project patches an existing module on which it declares a dependency.

In bug 529923 it is argued that we should also support the case where one dependency (a non-modular(?) jar, project ...) patches another module on the build path.

Use cases

Why is this relevant / what is the user trying to achieve by this option?

  • What kind of locations can be declared as patching another module?
    • JEP 261 speaks of a "filesystem path name of a module definition", but then if a module-info is found there, a warning is raised and the file ignored.
    • [TB] This is the way to run with a test-specific (actually main code needs to be configured to patch the test code). I think Remi Forax's pro build tool does that.
  • Would we even need the option to declare some external code to patch the current module?

[SS] If we want to test with different implementations before adopting, it might help but I feel it is good to have but not a blocker.

  • How does the request interact with the distinction main/test sources?
    • Automatically added --patch-module for test execution would need to be merged with user-configured --patch-module directives.

Solution discussion

  • Where in the UI should this option be represented?
  • What should be the gestures / dialogs etc. to define this?


Use case

Replace a module with a custom variant of the same name, where the original module could either be

  • a system module, or
  • an application module on the module path
([SH]: why would one put a module on the module path, if later you want to replace that module with another one??).

Solution discussion

  • User's intention could already be expressed like this:
    • exclude the given module from the "Contents" of the JRE node on the Java Build Path
      • [NL]: Isn't this how limit-module is expressed? If so, there will be a runtime issue as mentioned in the bug.
        • [SH]: As mentioned below I was thinking of using that UI while generating a specific upgrade-module-path for launching - if exclusion and addition match.
    • add the replacement to the module path
  • If that is too implicit, a warning could be given requiring the user to add a flag "yes I mean to replace a system module"
  • Alternatively, Upgrade Modulepath could be added as a third node below Classpath & Modulepath

Even if the user doesn't explicitly say "upgrade-module-path" this option could be synthesized behind the scenes (for launching).


  • not a build time concept but bug 531127 argues that the Java Build Path might still be an intuitive location

Solution discussion

  • Build Path > Modular Options
  • Not in Build Path.

Defining the main class

Solution discussion

  • Build Path > Source
  • Build Path > Modular Options

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