Migrate to sbt 2

Now that sbt-jcheckstyle 0.3.0 publishes an sbt2 cross-build, the sbt2
migration (superseding scala-steward PR #997) is unblocked. Bumps:

- sbt: 1.12.13 -> 2.0.1
- sbt-jcheckstyle: 0.2.1 -> 0.3.0 (the actual blocker)
- sbt-osgi: 0.10.0 -> 0.11.0-RC1 (only version with an sbt2 cross-build)
- sbt-pgp, sbt-scalafmt, sbt-dynver already cross-built for sbt2 at their
  current versions

build.sbt changes required by sbt 2's new task engine:
- Wrap the jcheckStyle-dependsOn compile overrides in Def.uncached(...);
  CompileAnalysis has no JsonFormat to cache against
- Add implicitConversions import and method-call dependsOn syntax to clear
  new Scala 3.8 strictness warnings

sbt 2 itself requires JDK 17+ to run, while CI still needs to verify the
library at runtime on JDK 8/11/17/21/24. Decouple the two via
Test/fork + Test/javaHome (driven by a TEST_JAVA_HOME env var), and update
CI.yml/release.yml/snapshot.yml to install a fixed modern JDK to launch sbt
itself while forking tests onto the matrix JDK. Published bytecode is
unaffected since it's already pinned to 1.8 via javacOptions.

Author: xerial

.github/workflows/CI.yml

@@ -40,11 +40,16 @@ jobs:
     if: ${{ needs.changes.outputs.code == 'true' }}
     steps:
       - uses: actions/checkout@v6
+      # sbt 2 requires JDK 17+ to run
+      - uses: actions/setup-java@v5
+        with:
+          distribution: 'zulu'
+          java-version: '21'
       - name: jcheckstyle
         run: ./sbt jcheckStyle
       - name: scalafmtCheckAll
         run: ./sbt scalafmtCheckAll
-  
+
   test:
     name: Test JDK${{ matrix.java }}
     runs-on: ubuntu-latest
@@ -55,16 +60,29 @@ jobs:
         java: ['8', '11', '17', '21', '24']
     steps:
       - uses: actions/checkout@v6
+      # The JDK under test: msgpack-core forks its tests onto this JDK (via
+      # TEST_JAVA_HOME) so we still verify runtime behavior on each target JDK.
       - uses: actions/setup-java@v5
+        id: target-jdk
         with:
           distribution: 'zulu'
           java-version: ${{ matrix.java }}
+      # sbt 2 itself requires JDK 17+ to run, so install a fixed, newer JDK to
+      # actually launch sbt. This becomes the default JDK on PATH/JAVA_HOME.
+      - uses: actions/setup-java@v5
+        with:
+          distribution: 'zulu'
+          java-version: '21'
       - uses: actions/cache@v5
         with:
           path: ~/.cache
           key: ${{ runner.os }}-jdk${{ matrix.java }}-${{ hashFiles('**/*.sbt') }}
           restore-keys: ${{ runner.os }}-jdk${{ matrix.java }}-
       - name: Test
+        env:
+          TEST_JAVA_HOME: ${{ steps.target-jdk.outputs.path }}
         run: ./sbt test
       - name: Universal Buffer Test
+        env:
+          TEST_JAVA_HOME: ${{ steps.target-jdk.outputs.path }}
         run: ./sbt test -J-Dmsgpack.universal-buffer=true

.github/workflows/release.yml

@@ -16,11 +16,12 @@ jobs:
           fetch-depth: 10000
       # Fetch all tags so that sbt-dynver can find the previous release version
       - run: git fetch --tags -f
-      # Install OpenJDK 8
+      # sbt 2 requires JDK 17+ to run. Android compatibility (originally JDK8,
+      # see https://github.com/msgpack/msgpack-java/issues/516) is enforced
+      # independently via the -source/-target 1.8 javacOptions in build.sbt.
       - uses: actions/setup-java@v5
         with:
-          # We need to use JDK8 for Android compatibility https://github.com/msgpack/msgpack-java/issues/516
-          java-version: 8
+          java-version: 21
           distribution: adopt
       - name: Setup GPG
         env:

.github/workflows/snapshot.yml

@@ -21,9 +21,11 @@ jobs:
           fetch-depth: 10000
       # Fetch all tags so that sbt-dynver can find the previous release version
       - run: git fetch --tags
+      # sbt 2 requires JDK 17+ to run; published bytecode still targets 1.8
+      # via the javacOptions in build.sbt.
       - uses: actions/setup-java@v5
         with:
-          java-version: 11
+          java-version: 21
           distribution: adopt
       - name: Publish snapshots
         env:

build.sbt

@@ -1,3 +1,5 @@
+import scala.language.implicitConversions
+
 Global / onChangedBuildSource := ReloadOnSourceChanges
 
 // For performance testing, ensure each test run one-by-one
@@ -69,6 +71,11 @@ val buildSettings = Seq[Setting[?]](
   // JVM options for building
   scalacOptions ++= Seq("-encoding", "UTF-8", "-deprecation", "-unchecked", "-feature"),
   Test / javaOptions ++= Seq("-ea"),
+  // sbt 2 itself requires JDK 17+ to run, but CI still needs to verify the library at
+  // runtime against older JDKs (e.g. 8). Fork tests so they can run on a JDK specified
+  // via TEST_JAVA_HOME, independent of the JDK running sbt.
+  Test / fork     := true,
+  Test / javaHome := sys.env.get("TEST_JAVA_HOME").map(file),
   javacOptions ++= Seq("-source", "1.8", "-target", "1.8"),
   Compile / compile / javacOptions ++=
     Seq("-encoding", "UTF-8", "-Xlint:unchecked", "-Xlint:deprecation"),
@@ -92,8 +99,8 @@ val buildSettings = Seq[Setting[?]](
   // Style check config: (sbt-jchekcstyle)
   jcheckStyleConfig := "facebook",
   // Run jcheckstyle both for main and test codes
-  Compile / compile := ((Compile / compile) dependsOn (Compile / jcheckStyle)).value,
-  Test / compile    := ((Test / compile) dependsOn (Test / jcheckStyle)).value
+  Compile / compile := Def.uncached((Compile / compile).dependsOn(Compile / jcheckStyle).value),
+  Test / compile    := Def.uncached((Test / compile).dependsOn(Test / jcheckStyle).value)
 )
 
 val junitJupiter = "org.junit.jupiter" % "junit-jupiter"        % "5.14.4" % "test"
@@ -134,7 +141,6 @@ lazy val msgpackCore = Project(id = "msgpack-core", base = file("msgpack-core"))
         "--add-opens=java.base/java.nio=ALL-UNNAMED",
         "--add-opens=java.base/sun.nio.ch=ALL-UNNAMED"
       ),
-    Test / fork := true,
     libraryDependencies ++=
       Seq(
         // msgpack-core should have no external dependencies

project/build.properties

@@ -1,2 +1,2 @@
-sbt.version=1.12.13
+sbt.version=2.0.1
 

project/plugins.sbt

@@ -2,8 +2,8 @@ addSbtPlugin("com.github.sbt" % "sbt-pgp" % "2.3.1")
 // TODO: Fixes jacoco error:
 // java.lang.NoClassDefFoundError: Could not initialize class org.jacoco.core.internal.flow.ClassProbesAdapter
 //addSbtPlugin("com.github.sbt"   % "sbt-jacoco"      % "3.3.0")
-addSbtPlugin("org.xerial.sbt" % "sbt-jcheckstyle" % "0.2.1")
-addSbtPlugin("com.github.sbt" % "sbt-osgi"        % "0.10.0")
+addSbtPlugin("org.xerial.sbt" % "sbt-jcheckstyle" % "0.3.0")
+addSbtPlugin("com.github.sbt" % "sbt-osgi"        % "0.11.0-RC1")
 addSbtPlugin("org.scalameta"  % "sbt-scalafmt"    % "2.6.1")
 addSbtPlugin("com.github.sbt" % "sbt-dynver"      % "5.1.1")