Migrate build to mill

.github/actions/setup-mill/action.yml

@@ -0,0 +1,42 @@
+name: Set up Mill
+description: Set up the JDK and dependency cache, optionally restoring compiled Mill output.
+inputs:
+  artifact-id:
+    description: Compiled output artifact to restore; omit when compiling from source.
+    required: false
+    default: ""
+runs:
+  using: composite
+  steps:
+    - name: Fetch git tags
+      shell: bash
+      run: git fetch -f --depth=1 origin '+refs/tags/*:refs/tags/*'
+
+    - name: Set up JDK 21
+      uses: actions/setup-java@v5
+      with:
+        distribution: "zulu"
+        java-version: "21"
+
+    - name: Cache Mill and Coursier
+      uses: actions/cache@v5
+      with:
+        path: |
+          ~/.cache/mill
+          ~/.cache/coursier
+        key: ${{ runner.os }}-mill-${{ hashFiles('build.mill', '**/*.mill') }}
+        restore-keys: |
+          ${{ runner.os }}-mill-
+
+    - name: Download compiled output
+      if: inputs.artifact-id != ''
+      uses: actions/download-artifact@v8.0.2
+      with:
+        artifact-ids: ${{ inputs.artifact-id }}
+        path: ${{ runner.temp }}/mill-compiled
+
+    - name: Restore compiled output
+      if: inputs.artifact-id != ''
+      shell: bash
+      run: tar -xzf "$RUNNER_TEMP/mill-compiled/mill-compiled.tar.gz"
+

.github/actions/test-instrumentation/action.yml

@@ -0,0 +1,14 @@
+name: Test instrumentation
+description: Run one instrumentation test group using the prepared Mill environment.
+inputs:
+  group:
+    description: Instrumentation group to run (akka, pekko, play, or other).
+    required: true
+runs:
+  using: composite
+  steps:
+    - name: Run instrumentation tests
+      shell: bash
+      env:
+        INSTRUMENTATION_GROUP: ${{ inputs.group }}
+      run: python3 "$GITHUB_ACTION_PATH/test-instrumentation.py" "$INSTRUMENTATION_GROUP"

.github/actions/test-instrumentation/test-instrumentation.py

@@ -0,0 +1,54 @@
+#!/usr/bin/env python3
+"""Resolve and run a disjoint group of instrumentation tests."""
+
+import argparse
+import subprocess
+
+
+MODULE_GROUPS = {
+    "akka": {"akka", "akkaHttp", "akkaGrpc", "alpakkaKafka", "lagom"},
+    "pekko": {"pekko", "pekkoHttp", "pekkoGrpc", "pekkoConnectorsKafka"},
+    "play": {"play"},
+}
+
+
+def task_group(task):
+    module = task.removeprefix("instrumentation.").split("[", 1)[0].split(".", 1)[0]
+    for group, modules in MODULE_GROUPS.items():
+        if module in modules:
+            return group
+    return "other"
+
+
+def main():
+    parser = argparse.ArgumentParser(description=__doc__)
+    parser.add_argument("group", choices=[*MODULE_GROUPS, "other"])
+    parser.add_argument("--list", action="store_true", help="List tasks without running tests")
+    args = parser.parse_args()
+
+    resolved = subprocess.check_output(
+        ["./mill", "--no-daemon", "resolve", "instrumentation.__.testForked"],
+        text=True,
+    )
+    tasks = [
+        line.strip()
+        for line in resolved.splitlines()
+        if line.strip().startswith("instrumentation.")
+        and line.strip().endswith(".testForked")
+    ]
+    selected = [task for task in tasks if task_group(task) == args.group]
+    if not selected:
+        parser.exit(1, f"No instrumentation tests resolved for group {args.group!r}\n")
+
+    print("\n".join(selected), flush=True)
+    if not args.list:
+        selectors = []
+        for task in selected:
+            if selectors:
+                selectors.append("+")
+            selectors.append(task)
+        subprocess.run(["./mill", "--no-daemon", "-j", "1", *selectors], check=True)
+
+
+if __name__ == "__main__":
+    main()

.github/workflows/ci.yml

@@ -1,6 +1,6 @@
-name: Test all the things
+name: CI
 
-on:
+"on":
   pull_request:
   push:
     branches:
@@ -11,26 +11,184 @@ env:
   JVM_OPTS: -Xms5120M -Xmx5120M -Xss6M -XX:ReservedCodeCacheSize=256M -Dfile.encoding=UTF-8
 
 jobs:
-  ci:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - run: git fetch -f --depth=1 origin '+refs/tags/*:refs/tags/*'
-      - uses: coursier/cache-action@v6
-      - uses: coursier/setup-action@v1
-        with:
-          jvm: zulu:17
-          apps: sbt
-      - name: Test
-        run: sbt -v ";+core/test;+instrumentation/test;+reporters/test"
-  lint:
-    runs-on: ubuntu-latest
-    steps:
-      - uses: actions/checkout@v4
-      - uses: coursier/cache-action@v6
-      - uses: coursier/setup-action@v1
-        with:
-          jvm: zulu:17
-          apps: sbt
-      - name: Test
-        run: sbt -v "+scalafmtCheckAll;scalafmtSbtCheck"
+  compile:
+    name: Compile everything
+    runs-on: ubuntu-26.04
+    outputs:
+      artifact-id: ${{ steps.compiled.outputs.artifact-id }}
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+
+      - name: Verify build loading
+        run: ./mill --no-daemon version
+
+      - name: Check Scala formatting
+        run: ./mill --no-daemon mill.scalalib.scalafmt.ScalafmtModule/checkFormatAll
+
+      - name: Compile all modules
+        run: ./mill --no-daemon '__.compile'
+
+      - name: Archive compiled output
+        run: |
+          tar -czf "$RUNNER_TEMP/mill-compiled.tar.gz" \
+            --exclude='out/mill-daemon' \
+            --exclude='out/mill-no-daemon' \
+            --exclude='out/mill-out-lock' \
+            --exclude='out/mill-worker-*' \
+            out
+
+      - name: Get short commit SHA
+        id: commit
+        run: echo "short-sha=${GITHUB_SHA:0:7}" >> "$GITHUB_OUTPUT"
+
+      - name: Upload compiled output
+        id: compiled
+        uses: actions/upload-artifact@v7.0.2
+        with:
+          name: mill-compiled-${{ steps.commit.outputs.short-sha }}-${{ github.run_attempt }}
+          path: ${{ runner.temp }}/mill-compiled.tar.gz
+          if-no-files-found: error
+          compression-level: 0
+
+  core:
+    name: Run core tests
+    needs: compile
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Test core modules
+        run: ./mill --no-daemon 'core.__.testForked'
+
+  instrumentation-akka:
+    name: Run Akka tests
+    needs: [compile, core]
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Test Akka instrumentation
+        uses: ./.github/actions/test-instrumentation
+        with:
+          group: akka
+
+  instrumentation-pekko:
+    name: Run Pekko tests
+    needs: [compile, core]
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Test Pekko instrumentation
+        uses: ./.github/actions/test-instrumentation
+        with:
+          group: pekko
+
+  instrumentation-play:
+    name: Run Play tests
+    needs: [compile, core]
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Test Play instrumentation
+        uses: ./.github/actions/test-instrumentation
+        with:
+          group: play
+
+  instrumentation-other:
+    name: Run all other tests
+    needs: [compile, core]
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Test other instrumentation
+        uses: ./.github/actions/test-instrumentation
+        with:
+          group: other
+
+  exporters:
+    name: Run reporter tests
+    needs: [compile, core]
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Test reporters
+        run: ./mill --no-daemon -j 1 'reporters.__.testForked'
+
+  bundle:
+    name: Verify release packaging
+    needs: [compile, core]
+    runs-on: ubuntu-26.04
+    steps:
+      - name: Checkout repository
+        uses: actions/checkout@v5
+        with:
+          fetch-depth: 0
+
+      - name: Set up Mill
+        uses: ./.github/actions/setup-mill
+        with:
+          artifact-id: ${{ needs.compile.outputs.artifact-id }}
+
+      - name: Verify published bundles
+        run: ./mill --no-daemon 'bundle.bundle.__.verifyJar'
+
+      - name: Generate release artifacts
+        run: ./mill --no-daemon '__.publishArtifacts'

.github/workflows/release.yml

@@ -6,23 +6,54 @@ on:
 
 jobs:
   release:
-    runs-on: ubuntu-latest
+    runs-on: ubuntu-26.04
     env:
       JAVA_OPTS: -Xms5120M -Xmx5120M -Xss6M -XX:ReservedCodeCacheSize=256M -Dfile.encoding=UTF-8
       JVM_OPTS: -Xms5120M -Xmx5120M -Xss6M -XX:ReservedCodeCacheSize=256M -Dfile.encoding=UTF-8
     steps:
-      - uses: actions/checkout@v4
-      - run: git fetch -f --depth=1 origin '+refs/tags/*:refs/tags/*'
-      - uses: coursier/cache-action@v6
-      - uses: coursier/setup-action@v1
+      - name: Checkout repository
+        uses: actions/checkout@v5
         with:
-          jvm: zulu:17
-          apps: sbt
-      - name: Release
-        run: sbt ";+instrumentation/publishLocal; release"
+          fetch-depth: 0
+          ref: ${{ github.event.release.tag_name }}
+
+      - name: Fetch git tags
+        run: git fetch -f --depth=1 origin '+refs/tags/*:refs/tags/*'
+
+      - name: Set up JDK 21
+        uses: actions/setup-java@v5
+        with:
+          distribution: 'zulu'
+          java-version: '21'
+
+      - name: Cache Mill and Coursier
+        uses: actions/cache@v5
+        with:
+          path: |
+            ~/.cache/mill
+            ~/.cache/coursier
+          key: ${{ runner.os }}-mill-${{ hashFiles('build.mill', '**/*.mill') }}
+          restore-keys: |
+            ${{ runner.os }}-mill-
+
+      - name: Verify published bundles
+        run: ./mill --no-daemon 'bundle.bundle.__.verifyJar'
+
+      - name: Publish to Maven Central
+        run: |
+          if [ -n "$MILL_PGP_SECRET_BASE64" ]; then
+            if ! echo "$MILL_PGP_SECRET_BASE64" | base64 -d > /dev/null 2>&1; then
+              export MILL_PGP_SECRET_BASE64="$(echo "$MILL_PGP_SECRET_BASE64" | base64 -w 0)"
+            fi
+          fi
+          ./mill --no-daemon mill.javalib.SonatypeCentralPublishModule/publishAll
         shell: bash
         env:
-          PGP_SECRET: ${{ secrets.PGP_SECRET }}
-          PGP_PASSPHRASE: ${{ secrets.PGP_PASSPHRASE }}
-          SONATYPE_PASSWORD: ${{ secrets.SONATYPE_PASSWORD }}
-          SONATYPE_USERNAME: ${{ secrets.SONATYPE_USERNAME }}
+          MILL_SONATYPE_USERNAME: ${{ secrets.MILL_SONATYPE_USERNAME || secrets.SONATYPE_USERNAME }}
+          MILL_SONATYPE_PASSWORD: ${{ secrets.MILL_SONATYPE_PASSWORD || secrets.SONATYPE_PASSWORD }}
+          MILL_PGP_SECRET_BASE64: ${{ secrets.MILL_PGP_SECRET_BASE64 || secrets.MILL_PGP_SECRET || secrets.PGP_SECRET }}
+          MILL_PGP_PASSPHRASE: ${{ secrets.MILL_PGP_PASSPHRASE || secrets.PGP_PASSPHRASE }}
+          SONATYPE_USERNAME: ${{ secrets.MILL_SONATYPE_USERNAME || secrets.SONATYPE_USERNAME }}
+          SONATYPE_PASSWORD: ${{ secrets.MILL_SONATYPE_PASSWORD || secrets.SONATYPE_PASSWORD }}
+          PGP_SECRET: ${{ secrets.MILL_PGP_SECRET_BASE64 || secrets.MILL_PGP_SECRET || secrets.PGP_SECRET }}
+          PGP_PASSPHRASE: ${{ secrets.MILL_PGP_PASSPHRASE || secrets.PGP_PASSPHRASE }}