Migrate to sbt 2 (#998)

- Bump sbt 1.12.13 -> 2.0.1, sbt-jcheckstyle 0.2.1 -> 0.3.0 (now sbt2 cross-built, the previous blocker), sbt-osgi 0.10.0 -> 0.11.0-RC1 (only version with an sbt2 cross-build so far)
- Fix build.sbt for sbt 2's new task engine (Def.uncached for the checkstyle-dependsOn override, Scala 3.8 strictness warnings)
- sbt 2 requires JDK 17+ to run, so decouple "JDK running sbt" from "JDK under test/compile": fork both compilation and tests onto a target JDK via javaHome/TEST_JAVA_HOME, with -release 8 added to scalacOptions since scalac compiles in-process and doesn't fork like javac
- Update CI.yml/release.yml/snapshot.yml accordingly so the JDK 8/11/17/21/24 test matrix and publish workflows keep working
- Fix an unrelated flaky MessageBufferInputTest (mkdirs() ordering) surfaced while validating the migration

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

@@ -16,19 +16,27 @@ 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
+      # We need to compile with JDK8 for Android compatibility
+      # https://github.com/msgpack/msgpack-java/issues/516
       - uses: actions/setup-java@v5
+        id: jdk8
         with:
-          # We need to use JDK8 for Android compatibility https://github.com/msgpack/msgpack-java/issues/516
           java-version: 8
           distribution: adopt
+      # sbt 2 itself requires JDK 17+ to run; build.sbt forks the compiler (and tests)
+      # onto JDK8 via TEST_JAVA_HOME, so this becomes the default JDK on PATH/JAVA_HOME.
+      - uses: actions/setup-java@v5
+        with:
+          java-version: 21
+          distribution: adopt
       - name: Setup GPG
         env:
           PGP_SECRET: ${{ secrets.PGP_SECRET }}
         run: echo $PGP_SECRET | base64 --decode | gpg --import --batch --yes
       - name: Build bundle
         env:
           PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
+          TEST_JAVA_HOME: ${{ steps.jdk8.outputs.path }}
         run: |
           ./sbt publishSigned
       - name: Release to Sonatype

.github/workflows/snapshot.yml

@@ -22,11 +22,19 @@ jobs:
       # Fetch all tags so that sbt-dynver can find the previous release version
       - run: git fetch --tags
       - uses: actions/setup-java@v5
+        id: jdk11
         with:
           java-version: 11
           distribution: adopt
+      # sbt 2 itself requires JDK 17+ to run; build.sbt forks the compiler onto JDK11
+      # via TEST_JAVA_HOME, so this becomes the default JDK on PATH/JAVA_HOME.
+      - uses: actions/setup-java@v5
+        with:
+          java-version: 21
+          distribution: adopt
       - name: Publish snapshots
         env:
           SONATYPE_USERNAME: '${{ secrets.SONATYPE_USERNAME }}'
           SONATYPE_PASSWORD: '${{ secrets.SONATYPE_PASSWORD }}'
+          TEST_JAVA_HOME: ${{ steps.jdk11.outputs.path }}
         run: ./sbt publish

build.sbt

@@ -1,3 +1,5 @@
+import scala.language.implicitConversions
+
 Global / onChangedBuildSource := ReloadOnSourceChanges
 
 // For performance testing, ensure each test run one-by-one
@@ -67,8 +69,25 @@ val buildSettings = Seq[Setting[?]](
   crossPaths        := false,
   publishMavenStyle := true,
   // JVM options for building
-  scalacOptions ++= Seq("-encoding", "UTF-8", "-deprecation", "-unchecked", "-feature"),
+  // -release 8 pins scalac's resolution of JDK API calls to the JDK8 surface (e.g.
+  // test code calling ByteBuffer.flip() resolves to the inherited Buffer.flip():Buffer
+  // rather than JDK9's covariant ByteBuffer.flip():ByteBuffer override, which doesn't
+  // exist on a real JDK8 at runtime -> NoSuchMethodError). Unlike javac's --release,
+  // this doesn't need an ignore-symbol-file escape hatch since test code never touches
+  // JDK-internal APIs the way the main sources' Unsafe usage does.
+  scalacOptions ++=
+    Seq("-encoding", "UTF-8", "-deprecation", "-unchecked", "-feature", "-release", "8"),
   Test / javaOptions ++= Seq("-ea"),
+  // sbt 2 itself requires JDK 17+ to run, but each CI lane still needs to compile and
+  // test against its own target JDK (e.g. 8) to faithfully reproduce runtime behavior:
+  // javac resolves API calls against whichever JDK actually runs it (-source/-target
+  // only constrain language level and bytecode version, not API resolution), so e.g.
+  // compiling on JDK9+ can bind to covariant overloads like ByteBuffer.flip():
+  // ByteBuffer that don't exist on a real JDK8 at runtime. When TEST_JAVA_HOME is set,
+  // fork both compilation and test execution onto that JDK; otherwise use the JDK
+  // running sbt, as before.
+  javaHome    := sys.env.get("TEST_JAVA_HOME").map(file),
+  Test / fork := true,
   javacOptions ++= Seq("-source", "1.8", "-target", "1.8"),
   Compile / compile / javacOptions ++=
     Seq("-encoding", "UTF-8", "-Xlint:unchecked", "-Xlint:deprecation"),
@@ -92,8 +111,8 @@ 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 +153,6 @@ 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

msgpack-core/src/test/scala/org/msgpack/core/buffer/MessageBufferInputTest.scala

@@ -58,8 +58,9 @@ class MessageBufferInputTest extends AirSpec:
     def toByteBuffer = ByteBuffer.wrap(b)
 
     def saveToTmpFile: File =
-      val tmp = File.createTempFile("testbuf", ".dat", new File("target"))
-      tmp.getParentFile.mkdirs()
+      val dir = new File("target")
+      dir.mkdirs()
+      val tmp = File.createTempFile("testbuf", ".dat", dir)
       tmp.deleteOnExit()
       withResource(new FileOutputStream(tmp)) { out =>
         out.write(b)

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")