fix zinc binary dependencies

[jilen]

Fix #1901
Sbt use a MappedFileConverter, it will converter jdk internal classes like /module/java.base/java.lang.String associated with a dummpy rt.jar.
https://github.com/sbt/zinc/blob/57d03412abe3810be5762a8c8e8c55cbf622ed03/internal/zinc-core/src/main/scala/sbt/internal/inc/MappedVirtualFile.scala#L56

def toVirtualFile(path: Path): VirtualFile = {
    rootPaths2.find { case (_, rootPath) => path.startsWith(rootPath) } match {
      case Some((key, rootPath)) =>
        MappedVirtualFile(s"$${$key}/${rootPath.relativize(path)}".replace('\\', '/'), rootPaths)
      case _ =>
        def isCtSym =
          path.getFileSystem
            .provider()
            .getScheme == "jar" && path.getFileSystem.toString.endsWith("ct.sym")
        def isJrt = path.getFileSystem.provider().getScheme == "jrt"
        if (isJrt || path.getFileName.toString == "rt.jar" || isCtSym)
          DummyVirtualFile("rt.jar", path)
        else if (allowMachinePath) MappedVirtualFile(s"$path".replace('\\', '/'), rootPaths)
        else sys.error(s"$path cannot be mapped using the root paths $rootPaths")
    }
  }

And later the Incremental will exclude such binary dependencies.
https://github.com/sbt/zinc/blob/57d03412abe3810be5762a8c8e8c55cbf622ed03/internal/zinc-core/src/main/scala/sbt/internal/inc/Incremental.scala#L783

        // dependency is some other binary on the classpath.
        // exclude dependency tracking with rt.jar, for example java.lang.String -> rt.jar.
        if (!vf.id.endsWith("rt.jar")) {
          externalLibraryDependency(
            vf,
            onBinaryName,
            sourceFile,
            context
          )
        }

[lefou]

About the test failures. I just created

• Fixed ordering-sensitive test #1905

which fixes an ordering issue in a test, which just popped up for some days. Once it is merged, we can rebase/merge your PR to get CI green.

[lefou]

I also created

• PR Test case ensuring zinc is only re-compiling changed sources #1907

which should succeed after we apply this fix.

[lefou]

Can you please add some details to this PR description. Esp. a motivation for the solution. Also, where does the hard-coded rt.jar comes from?

[lefou]

Oh, I forgot, this PR indeed seems to fix the issue. #1907 runs successfully.

[lefou]

Thank you!