Add support for the JVM release option for scalac and javac #170

vasilmkd · 2022-02-18T22:15:23Z

No description provided.

armanbilge · 2022-02-18T22:17:42Z

I think this closes #79 :)

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

armanbilge · 2022-02-18T22:42:42Z

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

@@ -29,13 +29,17 @@ object TypelevelSettingsPlugin extends AutoPlugin {
  object autoImport {
    lazy val tlFatalWarnings =
      settingKey[Boolean]("Convert compiler warnings into errors (default: false)")
+    lazy val tlJvmRelease =


Sorry, bikeshed: why "jvm" vs "jdk"?

JDK seems to be what everyone else is saying e.g. in scala/scala#6362.

Oh, interesting, javac uses JVM.

--release <release> Compile for a specific VM version. Supported targets: 6, 7, 8, 9, 10, 11 -target <release> Generate class files for specific VM version

Renamed to jdk.

armanbilge

Yay! Thank you :)

armanbilge · 2022-02-20T23:41:11Z

I've been thinking about how we can get this PR in to the 0.4.x series. Since CI is running on JDK 8 anyway, I guess the point of this PR is to support projects that are published manually, from possibly newer JDKs?

If that's the case, I propose we actually don't set a default value for this setting. If this setting is not set, then no flags are added; but if it is set, it works exactly like you've got it here. So for the projects release manually this can be set to 8 as needed.

We can create a follow-up issue to default it to 8 when we break compat in the next minor bump.

WDYT?

armanbilge · 2022-02-21T16:00:21Z

@vasilmkd sorry I have another question about this.

IIUC fs2 will have to set tlJdkRelease := 16 or something (at least for the fs2-io module). After it does that, will the generated jars still be consumable from older JVMs?

vasilmkd · 2022-02-21T19:37:14Z

Nothing that's added here works for fs2 and essentially breaks it. We should put this on ice.

armanbilge · 2022-02-21T19:56:14Z

Right, by ice you mean until the next breaking release, yes?

Fast-forwarding to then, I'm still concerned whether this works for fs2 at all.

vasilmkd · 2022-02-21T19:57:49Z

It doesn't, if this ships, fs2 would have to disable all of it.

armanbilge · 2022-02-21T19:58:26Z

So then maybe the setting should be an Option[Int]? Where None disables it?

armanbilge · 2022-02-21T20:33:58Z

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

  }

  import autoImport._
  import TypelevelKernelPlugin.autoImport._

  override def globalSettings = Seq(
    tlFatalWarnings := false,
+    tlJdkRelease := Some(8),


Not to be too annoying, but we can make this None and get this into series/0.4 :)

vasilmkd · 2022-02-21T20:34:47Z

Yeah, sorry, I got distracted.

armanbilge · 2022-02-21T20:39:34Z

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

+    scalacOptions ++= {
+      val releaseOption = tlJdkRelease
+        .value
+        .map { release => if (isJava8) Seq.empty else Seq("-release", release.toString) }


Why do we need the isJava8 check for scalacOptions?

Also, what is the failure mode if tlJdkRelease > 8 but java.version == 1.8?

If java.version == 1.8 it means we're running javac 1.8 which doesn't understand the --release flag. scalac somehow makes use of this and also fails compilation with

[error] '8' is not a valid choice for '-target' [21](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:21) [error] '8' is not a valid choice for '-target' [22](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:22) [error] bad option: '-target:8' [23](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:23) [error] bad option: '-target:8' [24](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:24) [error] (kernelJVM / Compile / compileIncremental) Compilation failed [25](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:25) [error] (kernelJS / Compile / compileIncremental) Compilation failed [26](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:26) [error] Total time: 13 s, completed Feb 16, 2022 11:57:41 AM [27](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:27) [28](https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true#step:12:28) Error: Process completed with exit code 1.

from https://github.com/typelevel/cats-effect/runs/5215692131?check_suite_focus=true

Oh, cool, that seems good. But if we don't add the flag, it won't protect us from a target JDK newer than the compile-time JDK since it basically ignores that setting, so it seems we need another check?

JDK 8 cannot target a newer JDK. Am I understanding your question correctly?

If you don't specify anything, javac 1.8 compiles JVM 8 bytecode, 17 compiles JVM 17 bytecode, while scalac compiles JVM 8 bytecode.

Apologies if I'm not reading your code correctly. Here's my hypothetical situation:

tlJdkRelease := Some(17)

I load my project in sbt on Java 8

No release flags are added to scalacOptions, b/c java.version == 1.8

My project compiles, even though I asked to target JDK 17.

If a project is specifically targetting 17 and the code is compilable by JDK 8, I don't know why they're targetting 17 in the first place. 😆

That's a fair point :)

scalac can generate more optimized bytecode in certain situations when targeting newer JDKs.

Also, the fact that your project would fail to compile if you load it in Java 9 (but 8 would work!) is a bit odd imo :)

e.g.

Use StringConcatFactory for string concatenation on JDK 9+ scala/scala3#12929

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

wip

armanbilge · 2022-02-22T15:59:28Z

settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala

+        }
+      case n =>
+        sys.error(
+          s"You're using JDK $n, which is not supported by `sbt-typelevel`. Please switch to a newer JDK.")


n is the target JDK right, not the user's runtime JDK?

Suggested change

s"You're using JDK $n, which is not supported by `sbt-typelevel`. Please switch to a newer JDK.")

s"Target JDK is $n, which is not supported by `sbt-typelevel`. Please select a JDK >= 8.")

armanbilge · 2022-02-23T16:13:01Z

@vasilmkd looks like they are discussing renaming these flags in Scala 3.
https://contributors.scala-lang.org/t/improving-scala-3-forward-compatibility/5298/22

armanbilge linked an issue Feb 18, 2022 that may be closed by this pull request

Add JDK target setting #79

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vasilmkd marked this pull request as ready for review February 18, 2022 22:19

armanbilge reviewed Feb 18, 2022

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armanbilge reviewed Feb 18, 2022

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vasilmkd changed the base branch from series/0.4 to main February 18, 2022 23:01

vasilmkd closed this Feb 18, 2022

vasilmkd reopened this Feb 18, 2022

armanbilge reviewed Feb 21, 2022

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vasilmkd added 6 commits February 21, 2022 21:40

Add support for the JVM release option for scalac and javac

b3a6b68

Adjust target option syntax for older compilers

efb01f0

Rename jvm to jdk

deb7f68

Use an optional value for the key

a081678

Use Seq.empty instead of Seq.apply

b837ff2

Switch the default value to None

e36f991

vasilmkd changed the base branch from main to series/0.4 February 21, 2022 20:41

vasilmkd closed this Feb 21, 2022

vasilmkd reopened this Feb 21, 2022

Be more consistent across failure modes

e58b9f7

armanbilge reviewed Feb 22, 2022

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settings/src/main/scala/org/typelevel/sbt/TypelevelSettingsPlugin.scala Outdated Show resolved Hide resolved

Better error messages and DRY

69daaf4

armanbilge reviewed Feb 22, 2022

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Correct error message

523d408

armanbilge merged commit 43dc219 into typelevel:series/0.4 Feb 28, 2022

armanbilge mentioned this pull request Mar 9, 2022

-release and friends renamed in Scala 3.1.2 #205

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Add support for the JVM release option for scalac and javac #170

Add support for the JVM release option for scalac and javac #170

vasilmkd commented Feb 18, 2022

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armanbilge commented Feb 23, 2022

	s"You're using JDK $n, which is not supported by `sbt-typelevel`. Please switch to a newer JDK.")
	s"Target JDK is $n, which is not supported by `sbt-typelevel`. Please select a JDK >= 8.")

Add support for the JVM release option for scalac and javac #170

Add support for the JVM release option for scalac and javac #170

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