Validate Scala 3.9.0 LTS + Scala.js 1.22.0 on Mill 1.1.8; cut 0.3.1 (TJC-2274)

.github/workflows/ci.yml

@@ -36,7 +36,7 @@ jobs:
 
       - uses: oven-sh/setup-bun@v2
         with:
-          bun-version: 1.4.0
+          bun-version: 1.4.1
 
       - name: Check formatting
         run: $MILL --no-server mill.scalalib.scalafmt.ScalafmtModule/checkFormatAll __.sources

.github/workflows/release.yml

@@ -31,7 +31,7 @@ jobs:
       - name: Set up Bun
         uses: oven-sh/setup-bun@v2
         with:
-          bun-version: 1.4.0
+          bun-version: 1.4.1
 
       - name: Cache Coursier
         uses: actions/cache@v4

.mill-version

@@ -1 +1 @@
-1.1.5
+1.1.8

CHANGELOG.md

@@ -5,6 +5,29 @@ All notable changes to `mill-bun-plugin` will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [0.3.1] - Scala 3.9.0 LTS validation, Mill 1.1.8 (2026-09-04)
+
+### Changed
+
+- Every Scala.js integration fixture, `example-scalajs`, `examples`, and the README snippets now
+  build with **Scala 3.9.0 LTS** on Scala.js 1.22.0. Scala 3.9.0 emits Scala.js 1.22 IR, which the
+  linker bundled by Mill 1.1.x's `ScalaJSConfigModule` (IR ≤ 1.20) rejects; the explicit
+  `scalaJSVersion` route introduced in 0.3.0 is the supported way to build Scala 3.9 code, and the
+  suite now proves that exact combination.
+- The plugin builds and runs its unit, integration, and example suites on **Mill 1.1.8**:
+  `.mill-version`, the launcher defaults, every fixture/example `//| mill-version` header, and —
+  the part that actually decides which Mill the fixtures run in-process — `mill-testkit` is now
+  pinned separately (`millTestkitVersion = "1.1.8"`). The compile target stays at Mill 1.1.5, so
+  the supported floor is unchanged and the jar under test is the real consumer shape.
+- The plugin's own `scalaVersion` stays at 3.8.2 on purpose and now says why in `build.mill`: it
+  must match the Scala that Mill 1.1.x compiles build files with, or consumers hit a TASTy version
+  error at build-script compile time.
+- Managed Bun default **1.4.0 → 1.4.1** (released 2026-09-04), with checksums for all twelve
+  release assets; 1.4.1 writes `lockfileVersion` 2, so committed locks stay valid. 1.4.0 stays in
+  the table for explicit `bunVersion` pins. `@types/bun` has not reached 1.4.1 on npm yet, so the
+  shipped default pairs with `DefaultBunTypesVersion = "1.4.0"` rather than tracking Bun blindly
+  (a 404 on every TypeScript frozen install); modules that override `bunVersion` keep lockstep.
+
 ## [0.3.0] - Managed toolchain, strict lockfiles, canonical vocabulary (2026-08-27)
 
 ### Added

README.md

@@ -6,18 +6,18 @@ It keeps Mill's task graph, caching, module relationships, Scala.js linker, and
 
 ## Requirements
 
-- Mill 1.1.5+
+- Mill 1.1.5+ (compiled against 1.1.5; the test suite and examples run on 1.1.8)
 - JDK 17+
 
-Bun does not need to be installed. The plugin downloads and checksum-verifies Bun 1.4.0 by default on macOS, Linux, and Windows x64/arm64. musl-based Linux (Alpine) is detected automatically; on x64 CPUs without AVX2, set `bunUseBaseline`. Set `MILL_BUN_USE_SYSTEM=true` to opt into the Bun on `PATH` instead.
+Bun does not need to be installed. The plugin downloads and checksum-verifies Bun 1.4.1 by default on macOS, Linux, and Windows x64/arm64. musl-based Linux (Alpine) is detected automatically; on x64 CPUs without AVX2, set `bunUseBaseline`. Set `MILL_BUN_USE_SYSTEM=true` to opt into the Bun on `PATH` instead.
 
 ## Scala.js quick start
 
 ```scala
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -29,7 +29,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }
@@ -57,10 +57,10 @@ Scala.js versions are explicit: choose the version your application tests agains
 ## TypeScript quick start
 
 ```scala
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -89,7 +89,7 @@ Use the paired web traits when HTML and static assets are part of the applicatio
 
 ```scala
 object frontend extends BunScalaJSWebModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.ESModule }
 }
@@ -133,7 +133,7 @@ Resolution order is:
 
 1. `bunExecutableOverride`
 2. system `PATH` when `bunUseSystem` or `MILL_BUN_USE_SYSTEM=true`
-3. checksum-verified managed Bun 1.4.0
+3. checksum-verified managed Bun 1.4.1
 
 Use `./mill app.bunDoctor` to print and validate the resolved executable, version, revision, mode, selected release asset, and linker.
 
@@ -156,7 +156,7 @@ import mill.javascriptlib.bun.*
 import mill.scalajslib.bun.*
 
 object scalaApp extends BunScalaJSModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def bunWorkspaceInstall = Task { Some(workspace.bunInstall()) }
 }
@@ -178,7 +178,7 @@ Mix `BunPublishModule` into a published Scala.js library to emit `META-INF/bun/b
 
 ```scala
 object ui extends BunScalaJSModule with BunPublishModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def npmPeerDeps = Task { Seq("react@^19.0.0") }
 }

build.mill

@@ -4,7 +4,18 @@ import mill.*, scalalib.*, publish.*
 import mill.api.BuildCtx
 
 object millbun extends ScalaModule, PublishModule {
+  // Compile target = the minimum Mill the plugin supports; Mill 1.x keeps plugin binary
+  // compatibility forwards, so the floor stays where it is while the suite below runs on
+  // the latest stable release.
   def millVersion = "1.1.5"
+  // The integration fixtures run Mill in-process via mill-testkit, so THIS is the Mill the
+  // plugin is tested against (fixture `//| mill-version` headers are only read for the
+  // mismatch warning). Kept at the latest stable Mill; the plugin jar under test is still
+  // the one compiled against millVersion above, i.e. the real consumer shape.
+  def millTestkitVersion = "1.1.8"
+  // Must match the Scala that Mill 1.1.x compiles build files with (3.8.2): a plugin built
+  // with a newer Scala emits TASTy that consumers' Mill cannot read. Fixtures and examples
+  // are free to use newer Scala (they are on 3.9.0 LTS); this pin is not.
   def scalaVersion = "3.8.2"
   def jvmVersion = "25"
   def platformSuffix = "_mill1"
@@ -24,7 +35,7 @@ object millbun extends ScalaModule, PublishModule {
 
   object integration extends ScalaTests, TestModule.Utest {
     def mvnDeps = Seq(
-      mvn"com.lihaoyi::mill-testkit:$millVersion",
+      mvn"com.lihaoyi::mill-testkit:$millTestkitVersion",
       mvn"com.lihaoyi::utest:0.8.5"
     )
     override def resources = Task.Sources()

example-scalajs/build.mill

@@ -1,7 +1,7 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -14,7 +14,7 @@ import mill.bun.bun
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.ESModule }

example-scalajs/mill

@@ -2,7 +2,7 @@
 
 set -e
 
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.5"; fi
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.8"; fi
 
 if [ -z "${GITHUB_RELEASE_CDN}" ] ; then GITHUB_RELEASE_CDN=""; fi
 

example-scalajs/mill.bat

@@ -2,7 +2,7 @@
 
 setlocal enabledelayedexpansion
 
-if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.5" )
+if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.8" )
 
 if [!MILL_GITHUB_RELEASE_CDN!]==[] ( set "MILL_GITHUB_RELEASE_CDN=" )
 

example-typescript/build.mill

@@ -1,7 +1,7 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 

example-typescript/mill

@@ -2,7 +2,7 @@
 
 set -e
 
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.5"; fi
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.8"; fi
 
 if [ -z "${GITHUB_RELEASE_CDN}" ] ; then GITHUB_RELEASE_CDN=""; fi
 

example-typescript/mill.bat

@@ -2,7 +2,7 @@
 
 setlocal enabledelayedexpansion
 
-if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.5" )
+if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.8" )
 
 if [!MILL_GITHUB_RELEASE_CDN!]==[] ( set "MILL_GITHUB_RELEASE_CDN=" )
 

examples/build.mill

@@ -1,7 +1,7 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
-//| - com.tjclp::mill-bun_mill1:0.3.0
+//| - com.tjclp::mill-bun_mill1:0.3.1
 
 package build
 
@@ -22,7 +22,7 @@ import mill.javascriptlib.bun.*
 // ./mill webServer.compileExecutable
 object webServer extends BunScalaJSModule {
   override def sources = Task.Sources(build.moduleDir / "web-server" / "src")
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.ESModule }
   override def bunBundleTarget = Task { "bun" }
@@ -32,7 +32,7 @@ object webServer extends BunScalaJSModule {
 // ./mill todoApp.bundle
 object todoApp extends BunScalaJSModule {
   override def sources = Task.Sources(build.moduleDir / "frontend" / "src")
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   def mvnDeps = Seq(mvn"org.scala-js::scalajs-dom::2.8.1")
   override def moduleKind = Task { ModuleKind.ESModule }
@@ -46,7 +46,7 @@ object todoApp extends BunScalaJSModule {
 object fullstack extends Module {
   object shared extends BunScalaJSModule {
     override def sources = Task.Sources(build.moduleDir / "fullstack" / "shared")
-    def scalaVersion = "3.8.2"
+    def scalaVersion = "3.9.0"
     def scalaJSVersion = "1.22.0"
     override def moduleKind = Task { ModuleKind.ESModule }
   }
@@ -107,7 +107,7 @@ object client extends BunTypeScriptModule {
 
 // --- Scala.js browser frontend (alternative client) ---
 object scalaClient extends BunScalaJSModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   def mvnDeps = Seq(mvn"org.scala-js::scalajs-dom::2.8.1")
   override def moduleKind = Task { ModuleKind.ESModule }
@@ -116,7 +116,7 @@ object scalaClient extends BunScalaJSModule {
 
 // --- JVM backend (Scala/Cask HTTP server, serves TS client bundle) ---
 object backend extends ScalaModule {
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def mvnDeps = Seq(
     mvn"com.lihaoyi::cask:0.10.2",
     mvn"com.lihaoyi::upickle:4.3.0"

mill

@@ -2,7 +2,7 @@
 
 set -e
 
-if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.5"; fi
+if [ -z "${DEFAULT_MILL_VERSION}" ] ; then DEFAULT_MILL_VERSION="1.1.8"; fi
 
 if [ -z "${GITHUB_RELEASE_CDN}" ] ; then GITHUB_RELEASE_CDN=""; fi
 

mill.bat

@@ -2,7 +2,7 @@
 
 setlocal enabledelayedexpansion
 
-if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.5" )
+if [!DEFAULT_MILL_VERSION!]==[] ( set "DEFAULT_MILL_VERSION=1.1.8" )
 
 if [!MILL_GITHUB_RELEASE_CDN!]==[] ( set "MILL_GITHUB_RELEASE_CDN=" )
 

millbun/integration/resources/invalid-bun-literal/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.CommonJSModule }

millbun/integration/resources/invalid-bun-specifier/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def moduleKind = Task { ModuleKind.CommonJSModule }

millbun/integration/resources/managed-bun/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY

millbun/integration/resources/mixed-workspace/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -15,7 +15,7 @@ object scalaApp extends BunScalaJSModule {
   // Renamed deliberately: the layout's directory naming, duplicate guard, AND the generated
   // member manifest must all follow this name, or bun sees a different identity than Mill.
   override def bunWorkspacePackageName = Task { "scala-app-renamed" }
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.ESModule }
   override def npmDeps = Task { Seq("is-even@1.0.0") }

millbun/integration/resources/scalajs-bundle/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -12,7 +12,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def mainClass = Some("Main")

millbun/integration/resources/scalajs-bunfig/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 object app extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
 
   override def mainClass = Some("Main")

millbun/integration/resources/scalajs-dependency-manifests/build.mill

@@ -1,4 +1,4 @@
-//| mill-version: 1.1.5
+//| mill-version: 1.1.8
 //| mill-jvm-version: system
 //| mvnDeps:
 //| - com.tjclp::mill-bun_mill1:0.0.0-NIGHTLY
@@ -13,7 +13,7 @@ import mill.scalajslib.bun.*
 
 trait StubBunModule extends BunScalaJSModule {
   override def moduleDir = build.moduleDir
-  def scalaVersion = "3.8.2"
+  def scalaVersion = "3.9.0"
   def scalaJSVersion = "1.22.0"
   override def moduleKind = Task { ModuleKind.CommonJSModule }
   override def bunExecutable = Task { "stub-bun" }