[2.x] Support JDK 25 JEP-512/JEP-445 Main class

[eed3si9n]

Ref sbt/sbt#7384

Problem

sbt currently does not support JDK 25 Main class. JDK 25 supports:

1. non-public main method
2. doesn't need Array[String] arg
3. doesn't have to be a static method

Solution

This fixes the Main class detection for the reference compiler bridge, which is used for Scala 2.10 - 2.12, and Scala 2.13 until 2.13.11. (Luckily, 2.13.11 is compatible with JDK 25, so we can use that to test 2.13)

[lrytz]

I copied your patch to the bridge in scala/scala (2.13.x) and tried a local build. It works when setting fork := true (which seems to be the default on sbt 2.0.0-M4). Without forking I get

sbt:sbtproj> run
[info] running Test
[error] java.lang.NoSuchMethodException: Test.main([Ljava.lang.String;)
[error] 	at java.base/java.lang.Class.getMethod(Class.java:2166)
[error] stack trace is suppressed; run last Compile / run for the full output
[error] (Compile / run) java.lang.NoSuchMethodException: Test.main([Ljava.lang.String;)
[error] Total time: 0 s, completed 26 Sept 2025, 07:51:29

As mentioned by @xuwei-k, that's probably here:

https://github.com/sbt/sbt/blob/d44b2c87209364e699cce883a4891f48b25c436f/run/src/main/scala/sbt/Run.scala#L167-L169

For main methods written in Java, sbt 1.11.6 finds public static void main(String... args), but not when removing either public or static or the argument. Is that implemented here?

zinc/internal/zinc-apiinfo/src/main/scala/sbt/internal/inc/ClassToAPI.scala

Lines 172 to 181 in bcd91a1

	if (
	c.getMethods.exists(meth =>
	meth.getName == "main" &&
	Modifier.isStatic(meth.getModifiers) &&
	meth.getParameterTypes.length == 1 &&
	meth.getParameterTypes.head == classOf[Array[String]] &&
	meth.getReturnType == java.lang.Void.TYPE
	)
	) {
	cmap.mainClasses += name

[eed3si9n]

Yea, for in-process run emulation, we need to change sbt itself.

[lrytz]

I used scala.util.Properties.isJavaAtLeast(25) on scala/scala, but here it's probably safer not to rely on old (2.11) library code.

[lrytz]

I consolidated the pre / post 25 checks a bit in scala/scala#11137

[lrytz]

I also updated https://github.com/sbt/zinc/tree/develop/zinc/src/sbt-test/apiinfo/main-discovery in scala/scala#11137, that should apply here as well.

[eed3si9n]

Thanks! I've incorporated the scripted test change here.