Scala 3 support

[mrdziuban]

Closes #76

Adds support for Scala 3.3.{0,1,2,3}, Scala 3.4.{0,1,2,3}, and Scala 3.5.0.

I aimed for as close as a 1-to-1 port as possible, especially in PluginPhase.scala and DependencyExtraction.scala where the meat of the logic lives. I'm happy to clarify/elaborate on any specific code

[mrdziuban]

I'm not too familiar with utest, but should this be wrapped in assert to prove that it's true?

[lihaoyi]

Depends what make does. If make performs the assert internally, then no need to wrap in an assert. If make returns a Boolean, then you need to wrap in an assert

[mrdziuban]

make returns a Seq[(String, String)] (and throws an exception if compilation fails), but doesn't call assert. The call to .exists here then returns a Boolean, so it looks like we do need assert. Updated to add it and to also make sure that we're matching against the uppercase string "WARNING" since the severity levels use uppercase strings

[mrdziuban]

Scala 3 diagnostics don't have a severity, instead they have a level: Int that maps to one of these 3

[lihaoyi]

I wonder how much of the logic in this file can be shared between the Scala 2 and Scala 3 implementations? Like clearly the logic for working with symbols and types and trees is all bespoke, but it seems there's a lot of stuff working with Values and DepNodes that can be shared if properly separated out from the compiler-specific logic

[mrdziuban]

Good call, I was able to share pretty much all of it by abstracting over CompilationUnit, Tree, and Symbol

[lihaoyi]

@mrdziuban sorry for the delay, just had a chance to try this out on a small test project. The cycle detection seems find, though the reporting doesn't seem to work. The Scala 2 version reports a cycle error location at each point in the cycle with More dependencies at lines... to show additional edges in a file, whereas the Scala 3 version reports all the edges

Given these files

// Foo.scala
package foo
object Foo {
  val value = Foo2.value
  def main(args: Array[String]): Unit = {}
}

// Foo2.scala
package foo
object Foo2 {
  val value = "hello"
  val value2 = Foo.value
  def main(args: Array[String]): Unit = Foo.main(args)
}

The Scala 2 version of this reports the cycle as follows:

#05 [error] Unwanted cyclic dependency
#05 [info] /Users/lihaoyi/test/foo/src/Foo2.scala:5:16:
#05 [info]   val value2 = Foo.value
#05 [info]                ^
#05 [info] symbol: object Foo
#05 [info] More dependencies at lines 6 6
#05 [info] /Users/lihaoyi/test/foo/src/Foo.scala:3:15:
#05 [info]   val value = Foo2.value
#05 [info]               ^
#05 [info] symbol: object Foo2
#05 [error] one error found

Whereas the Scala 3 version reports it as follows

#02 [error] Unwanted cyclic dependency
#02 [info] -- Info: /Users/lihaoyi/test/foo/src/Foo.scala:3:19 ----------------------------
#02 [info] 3 |  val value = Foo2.value
#02 [info]   |              ^^^^^^^^^^
#02 [info] -- Info: /Users/lihaoyi/test/foo/src/Foo2.scala:5:19 ---------------------------
#02 [info] 5 |  val value2 = Foo.value
#02 [info]   |               ^^^^^^^^^
#02 [error] Unwanted cyclic dependency
#02 [info] -- Info: /Users/lihaoyi/test/foo/src/Foo.scala:3:19 ----------------------------
#02 [info] 3 |  val value = Foo2.value
#02 [info]   |              ^^^^^^^^^^
#02 [info] -- Info: /Users/lihaoyi/test/foo/src/Foo2.scala:5:19 ---------------------------
#02 [info] 5 |  val value2 = Foo.value
#02 [info]   |               ^^^^^^^^^
#02 [error] two errors found

The Scala 3 version is missing the More dependencies at lines... indicator, and seems to duplicate the cycle being reported between val value2 = Foo.value and value value = Foo2.value

[mrdziuban]

No problem! I was able to resolve both of these issues.

the reporting doesn't seem to work

It turned out this was because the "More dependencies at..." reporting was using report.inform, which only appears if the -verbose flag is set -- https://github.com/scala/scala3/blob/3.5.0/compiler/src/dotty/tools/dotc/report.scala#L16-L17

seems to duplicate the cycle being reported

I'm pretty sure this is a nuance of how the plugin is run between Scala 2 and 3. In Scala 2 it seems like Phase#run is only called once, whereas in Scala 3 PluginPhase#run is called once per CompilationUnit. So in your case the output was duplicated, but with three files it would have been triplicated, etc.

I fixed this by adding a var alreadyRun at the Plugin level and only running the phase if it's false.

[lihaoyi]

@mrdziuban looks great! Thanks for your help. I'll wire you the bounty using the details you sent me earlier