Support JEP-261 Module System

[retronym]

(Part of the epic, #139)

• Expose new command line options to scalac (and later to the scala script runner) (--module-path, etc)
• Build atop StandardJavaFileManager and java.lang.module._, to process these options and create a ClassPath implementation and resolved module graph
• Update Context.isAccessible to check for reads/exports edges between the call site and referenced symbol.
• To support mixed compilation, add a parser for module-info.java, and feed a descriptor of the module descriptor to the module graph configuration.

WIP: https://github.com/retronym/scala/tree/topic/jpms

% qscalac  -nobootcp -modulepath ""  $(f "class C { def foo = javax.xml.bind.DatatypeConverter.printBase64Binary _ }")
/tmp/a.scala:1: error: object DatatypeConverter is not a member of package javax.xml.bind
class C { def foo = javax.xml.bind.DatatypeConverter.printBase64Binary _ }
                                   ^
one error found

% qscalac  -nobootcp -modulepath "" -addmodules:java.xml.bind  $(f "class C { def foo = javax.xml.bind.DatatypeConverter.printBase64Binary _ }")

% qscalac  -nobootcp -modulepath "" $(f "class C { sun.reflect.misc.ConstructorUtil.getConstructors(null) }")
/tmp/a.scala:1: error: class ConstructorUtil in package misc cannot be accessed in package sun.reflect.misc
class C { sun.reflect.misc.ConstructorUtil.getConstructors(null) }
                           ^
one error found

% qscalac  -nobootcp -modulepath "" -addexports:java.base/sun.reflect.misc=ALL-UNNAMED  $(f "class C { sun.reflect.misc.ConstructorUtil.getConstructors(null) }")

Non Goals

Support for --module-source-path. A batch of source files will be associated with at most one module.

Open Issues

How should we structure our build to allow us to call Java 9 APIs from this code path? I'm thinking we do this from a small pure-Java project and incorporate the results into scala-reflect.jar, similar to how we've dealt with scala-asm.

[Knut-Fjellheim]

Is there a target date, or target version, for this feature?

[retronym]

I hope its ready for Scala 2.13.0 later this year. If not, then we'll make sure we at least have the plumbing installed to add it for 2.13.1.

[retronym]

This test in my WIP branch shows what I've got working so far.

[rgoldberg]

Are there any updates for this issue? Thanks.

[som-snytt]

JDK 16 is stricter, like the sign that says last exit before toll as you head toward the bridge.

[pelamfi]

Any news on this?

[SethTisue]

Nobody is currently working on this (to my knowledge, but I'm pretty sure).

It's unlikely to progress without an external contributor or sponsor. Any planning around this would need to include Scala 3, since as a rule as we don't add new features to Scala 2 unless the path is clear for adding the feature to Scala 3 as well. (Targeting only Scala 3 would be acceptable.)

[sgammon]

Hello from 2024. It has been 6 years, 6 months, and 23 days since Java 9's release.