JarCasting
Mill 
Your shiny new Scala build tool! Confused by SBT? Frustrated by Maven? Perplexed by Gradle? Give Mill a try!
If you want to use Mill in your own projects, check out our documentation:
Here is some quick example, so that you can imagine how it looks:
import mill._, scalalib._
object foo extends ScalaModule {
def scalaVersion = "2.13.1"
}
object bar extends ScalaModule {
def moduleDeps = Seq(foo)
def scalaVersion = "2.13.1"
}
If you use Mill and like it, you will probably enjoy the following book by the Author:
Hands-on Scala has a Chapter 10: Static Build Pipelines dedicated to Mill, but rest of the book introduces other libraries and tools in a similar style. Hands-on Scala is a great way to level up your skills in Scala in general and Mill in particular
The remainder of this readme is developer-documentation targeted at people who wish to work on Mill's own codebase. The developer docs assume you have read through the user-facing documentation linked above. It's also worth spending a few minutes reading the following blog posts to get a sense of Mill's design & motivation:
How to build and test
Mill is built using Mill. To begin, first download & install Mill as described in the documentation above. As Mill is under active development, stable releases may not be able to build the current development branch of Mill. It is recommended to install the latest unstable release manually.
IntelliJ Setup
If you are using IntelliJ IDEA to edit Mill's Scala code, you can create the IntelliJ project files via:
./mill mill.scalalib.GenIdea/idea
Automated Tests
To run test suites:
./mill main.test
./mill scalalib.test
./mill scalajslib.test
./mill integration.test
Manual Testing
To manually test Mill on a small build, you can use the scratch folder:
./mill -i dev.run scratch -w resolve _
This runs the task resolve _ with your current checkout of Mill on the trivial build defined in scratch/build.sc. You can modify that build file to add additional modules, files, etc. and see how it behaves.
More generally, you can use:
./mill -i dev.run [target-dir] [...args]
To create run your current checkout of Mill in the given target-dir with the given args. This is useful e.g. to test a modified version of Mill on some other project's Mill build.
You can also create a launcher-script to let you run the current checkout of Mill without the bootstrap Mill process present:
./mill dev.launcher
This creates the out/dev/launcher/dest/run launcher script, which you can then use to run your current checkout of Mill where-ever you'd like. Note that this script relies on the compiled code already present in the Mill out/ folder, and thus isn't suitable for testing on Mill's own Mill build since you would be over-writing the compiled code at the same time as the launcher script is using it.
You can also run your current checkout of Mill on the build in your scratch/ folder without the bootstrap Mill process being present via:
./mill dev.launcher && (cd scratch && ../out/dev/launcher/dest/run -w show thingy)
Bootstrapping: Building Mill with your current checkout of Mill
To test bootstrapping of Mill's own Mill build using a version of Mill built from your checkout, you can run
ci/publish-local.sh
This creates a standalone assembly at ~/mill-release you can use, which references jars published locally in your ~/.ivy2/local cache. You can then use this standalone assembly to build & re-build your current Mill checkout without worrying about stomping over compiled code that the assembly is using.
This assemby is design to work on bash, bash-like shells and Windows Cmd. If you have another default shell like zsh or fish, you probably need to invoke it with sh ~/mill-release or prepend the file with a proper shebang.
Troubleshooting
In case of troubles with caching and/or incremental compilation, you can always restart from scratch removing the out directory:
os.remove.all -rf out/
Project Layout
The Mill project is organized roughly as follows:
Core modules that are included in the main assembly
core,main,main.client,scalalib,scalajslib.
These are general lightweight and dependency-free: mostly configuration & wiring of a Mill build and without the heavy lifting.
Heavy lifting is delegated to the worker modules (described below), which the core modules resolve from Maven Central (or from the local filesystem in dev) and load into isolated classloaders.
Worker modules that are resolved from Maven Central
scalalib.worker,scalajslib.worker[0.6],scalajslib.worker[1.0]
These modules are where the heavy-lifting happens, and include heavy dependencies like the Scala compiler, Scala.js optimizer, etc.. Rather than being bundled in the main assembly & classpath, these are resolved separately from Maven Central (or from the local filesystem in dev) and kept in isolated classloaders.
This allows a single Mill build to use multiple versions of e.g. the Scala.js optimizer without classpath conflicts.
Contrib modules
contrib/bloop/,contrib/flyway/,contrib/scoverage/, etc.
These are modules that help integrate Mill with the wide variety of different tools and utilities available in the JVM ecosystem.
These modules are not as stringently reviewed as the main Mill core/worker codebase, and are primarily maintained by their individual contributors. These are maintained as part of the primary Mill Github repo for easy testing/updating as the core Mill APIs evolve, ensuring that they are always tested and passing against the corresponding version of Mill.
Changelog
master
For details refer to milestone after 0.9.5 and the list of commits.
0.9.5 - 2021-01-26
- Updated zinc to 1.4.4
- Support for Scala Native 0.4.0
- Support for Scala.js ESModule (including Bloop support)
- Inner
Teststraits in modules likeJavaModule,ScalaModuleand others now have unique names (JavaModuleTests,ScalaModuleTests, etc), to allow for easier customization - Various version bumps of dependencies
- CI now runs all tests, it did miss some before
For details refer to milestone 0.9.5 and the list of commits.
0.9.4 - 2020-12-21
- Implemented more BSP protocol commands and fixed some glitches with IntelliJ
- Stabilized CI builds
- Various fixes and improvements
- Various version bumps
For details refer to milestone 0.9.4 and the list of commits.
0.9.3 - 2020-11-26
(We also tagged 0.9.0, 0.9.1, and 0.9.2, but due to release difficulties, we ask you not to use them.)
- Replace the built in
@mainmethod functionality with the MainArgs library - Note that the MainArgs replacement has some backwards incompatibilities: Short flags like
-ican no longer be passed via--i, the@doc("")is now@arg(doc = ""),Seq[T]parameters are now passed via repeated--fooflags rather than comma-separated. - Add the ability to relocate/shade files in
.assembly#947 - Twirl enhancements #952
- Add
scalacPluginClasspathto Tests #956 - Add
toMapmethods toBuildInfo#958 - Bump coursier to version 2.0.0 #973
- Make BSP support a first-class citizen #969
- Omit the suffix in
artifactNamein cross modules #953 - Allow test classes with constructor parameters #982
- Proguard contrib module #972
- Support Scala.js useECMAScript2015 option and ModuleKind.ESModule #1004
- Support Scala.js incremental linking #1007
For details refer to milestone 0.9.3 and the list of commits.
0.8.0 - 2020-07-20
- Bump external dependencies: uPickle 1.2.0, Ammonite 2.2.0, etc.
- Use default coursier repos (#931)
- Work around relative paths issue on windows (#936)
- Support Scala.js versions >1.0.0 (#934)
For details refer to milestone 0.8.0 and the list of commits.
0.7.4 - 2020-07-03
- new command line options
--repland--no-server, deprecated--interactiveoption - Support for Scala.js 1.1
- Fixed missing source maps for Scala.js 1.0 and 1.1
- Improved BSP contrib module
For details refer to milestone 0.7.4 and the list of commits.
0.7.3
For details refer to milestone 0.7.3 and the list of commits.
0.7.2 - 2020-05-19
For details refer to milestone 0.7.2 and the list of commits.
0.7.1 - 2020-05-17
For details refer to milestone 0.7.1 and the list of commits.
0.7.0 - 2020-05-15
- Greatly improved parallel builds via
-j <n>/--jobs <n>, with better scheduling and utilization of multiple cores build.scfiles now uses Scala 2.13.2- Avoid duplicate target resolution with
mill resolve __ - Add ability to pass GPG arguments to publish via
--gpgArgs -w/--watchnow works forT.sourcetargets
For details refer to milestone 0.7.0 and the list of commits.
0.6.3 - 2020-05-10
- Finished incomplete support to publish extra artifacts to IVY repositories (
publishLocal) - Improved Sonatype uploads
GenIdea: improvements for shared source dirs and skipped modulesScoverageModule: Some refactorings to allow better customization- More robust classpath handling under Windows
For details refer to milestone 0.6.3 and the list of commits.
0.6.2 - 2020-04-22
- Mill can now execute targets in parallel. This is experimental and need to be enabled with
--jobs <n>option. PublishModule: newpublishM2Localto publish into local Maven repositoriesPublishModule: enhancedpublishLocalto specify to ivy repository location- Windows: Fixed windows launcher and more robust classpath handling
ScalaNativeModule: improved compiling and linking support- new contrib module
VersionFile Dependency: improved dependency update checker and expose results for programmatic use- ǹew contrib module
Bintray - ǹew contrib module
Artifactory - fixed testCached support in various modules
GenIdea: improvements, esp. related to source jars
For details refer to milestone 0.6.2 and the list of commits.
0.6.1 - 2020-02-24
- Bugfix: Mill now no longer leaks open files (version bump to uPickle 1.0.0)
- New
--versionoption - Added Support for Scala.js 1.0.0+
- Added Support for Scala Native 0.4.0-M2
JavaModule: EnhancedivyDepsTreeto optionally include compile-time and runtime-time dependenciesJavaModule:allSourceFilesno longer include Scala sourcesJavaModule: assembly supports configurable separator when merging resourcesScoverageModule: respectunmanagedClasspath, added console reporterScalaPBModule: added more configuration options- Bloop: Fixed inconsistent working directory when executing tests via bloop (forces
-Duser.dirwhen generating bloop config)
For details refer to milestone 0.6.1 and the list of commits.
0.6.0 - 2020-01-20
- Support for METALS 0.8.0 in VSCode
For details refer to milestone 0.6.0 and the list of commits.
0.5.9 - 2020-01-14
- Bump library versions again
- Alias
T.ctx.*functions toT.*:T.dest,T.log, etc. - Bump Mill's client-connect-to-server timeout, to reduce flakiness when the server is taking a moment to start up
For details refer to the list of commits.
Verison 0.5.8 has some binary compatibility issues in requests-scala/geny and should not be used.
0.5.7 - 2019-12-28
- Bump library versions: Ammonite 2.0.1, uPickle 0.9.6, Scalatags 0.8.3, OS-Lib 0.6.2, Requests 0.4.7, Geny 0.4.2
For details refer to milestone 0.5.7 and the list of commits.
0.5.5 / 0.5.6 - 2019-12-20
(we skipped version 0.5.4 as we had some publishing issues)
- Bump library versions: Ammonite 1.9.2, uPickle 0.9.0, Scalatags 0.8.2, OS-Lib 0.5.0, Requests 0.3.0, Geny 0.2.0, uTest 0.7.1
- Fixed a long standing issue that output of sub-processes are only shown when
-ioption was used. Now, you will always seen output of sub-process. - Mill now properly restarts it's server after it's version has changed
PublishModule: added ability to publish into non-staging repositoriesScalaPBModule: added extra include path option
For details refer to milestone 0.5.5 and the list of commits.
0.5.3 - 2019-12-07
GenIdea/idea: improved support for generated sources and use/download sources in more cases- ScalaJS: improvements and support for ScalaJS 0.6.29+ and 1.0.1.RC1
- Introduced new
CoursierModuleto use dependency management independent from a compiler ScoverageModule: better handling of report directoriesScalaPBModule: more configuration options- various other fixes and improvements
For details refer to milestone 0.5.3 and the list of commits.
0.5.2 - 2019-10-17
TestModule: newtestCachedtarget, which only re-runs tests after relevant changesTestModule.test: fixed issue when stacktraces have no filename infoDependency/updates: fixed issue with reading stale dependenciesGenIdea/idea: no longer shared output directories between mill and IntelliJ IDEA- support for Dotty >= 0.18.1
- Fixed backwards compatibility of mill wrapper script
- Mill now support the Build Server Protocol 2.0 (BSP) and can act as a build server
- bloop: removed semanticDB dependency
- Documentation updates
For details refer to milestone 0.5.2 and the list of commits.
0.5.1 - 2019-09-05
- GenIdea: Bug fixes
- GenIdea: Support for module specific extensions (Facets) and additional config files
- Add ability to define JAR manifests
- Dotty support: Updates and support for binary compiler bridges
- Ivy: improved API to create optional dependendies
- Interpolate
$MILL_VERSIONin ivy imports - Zinc: Fixed logger output
- Scoverage: Upgrade to Scoverage 1.4.0
- Flyway: Upgrade to Flyway 6.0.1
- Bloop: Updated semanticDB version to 4.2.2
- Documentation updates
- Improved robustness in release/deployment process
For details refer to milestone 0.5.1 and the list of commits.
0.5.0
-
Mill now supports a
./millbootstrap script, allowing a project to pin the version of Mill it requires, as well as letting contributors use./mill ...to begin development without needing to install Mill beforehand. -
Support for a
.mill-versionfile orMILL_VERSIONenvironment variable for Overriding Mill Versions -
Fix scoverage: inherit repositories from outer project #645
0.4.2
0.4.1
-
Fixes for scala native test suites without test frameworks #627
-
Fix publication of artifacts by increasing sonatype timeouts
-
Bug fixes for Scoverage integration #623
0.4.0
-
Publish
compileIvyDepsas provided scope (535) -
Added contrib modules to integrate Bloop, Flyway, Play Framework, Scoverage
-
Allow configuration of GPG key names when publishing (530)
-
Bump Ammonite version to 1.6.7, making Requests-Scala available to use in your
build.sc -
Support for Scala 2.13.0-RC2
-
ScalaFmt support now uses the version specified in
.scalafmt.conf
0.3.6
-
Started to splitting out mill.api from mill.core
-
Avoid unnecessary dependency downloading by providing fetches per cache policy
-
Added detailed dependency download progress to the progress ticker
-
Fixed internal code generator to support large projects
-
Zinc worker: compiler bridge can be either pre-compiled or on-demand-compiled
-
Zinc worker: configurable scala library/compiler jar discovery
-
Zinc worker: configurable compiler cache supporting parallelism
-
Version bumps: ammonite 1.6.0, scala 2.12.8, zinc 1.2.5
-
Mill now by default fails fast, so in case a build tasks fails, it exits immediately
-
Added new
-k/--keep-goingcommandline option to disable fail fast behaviour and continue build as long as possible in case of a failure
0.3.5
- Bump uPickle to 0.7.1
0.3.4
- Mill is now bundled with OS-Lib, providing a simpler way of dealing with filesystem APIs and subprocesses
0.3.3
-
Added new
debugmethod to context logger, to log additional debug info into the task specific output dir (out/<task>/log) -
Added
--debugoption to enable debug output to STDERR -
Fix
ScalaModule#docJartask when Scala minor versions differ 475
0.3.2
- Automatically detect main class to make
ScalaModule#assemblyself-executable
0.3.0
-
Bump Ammonite to 1.3.2, Fastparse to 2.0.4
-
Sped up
ScalaModule#docJartask by about 10x, greatly speeding up publishing -
Add a flag
JavaModule#skipIdeayou can override to disable Intellij project generation #458 -
Allow sub-domains when publishing #441
0.2.8
-
mill inspectnow displays out the doc-comment documentation for a task. -
Avoid shutdown hook failures in tests #422
-
Ignore unreadable output files rather than crashing #423
-
Don't compile hidden files #428
0.2.7
-
Add
visualizePlancommand -
Basic build-info plugin in
mill-contrib-buildinfo -
ScalaPB integration in
mill-contrib-scalapblib -
Fixes for Twirl support, now in
mill-contrib-twirllib -
Support for building Dotty projects #397
-
Allow customization of
run/runBackgroundworking directory viaforkWorkingDir -
Reduced executable size, improved incremental compilation in #414
0.2.6
-
Improve incremental compilation to work with transitive module dependencies
-
Speed up hot compilation performance by properly re-using classloaders
-
Speed up compilation time of
build.scfiles by removing duplicate macro generated routing code
0.2.5
-
Add
.runBackgroundand.runMainBackgroundcommands, to run something in the background without waiting for it to return. The process will keep running until it exits normally, or until the same.runBackgroundcommand is run a second time to spawn a new version of the process. Can be used with-wfor auto-reloading of long-running servers. -
Scala-Native support. Try it out!
-
Add
--disable-tickerto reduce spam in CI -
Fix propagation of
--colorflag
0.2.4
-
Fix resolution of
scala-{library,compiler,reflect}in case of conflict -
Allow configuration of
JavaModuleandScalafmtModulescala workers -
Allow hyphens in module and task names
-
Fix publishing of ScalaJS modules to properly handle upstream ScalaJS dependencies
0.2.3
-
Added the mill show visualize command, making it easy to visualize the relationships between various tasks and modules in your Mill build.
-
Improve Intellij support (351): better jump-to-definition for third-party libraries, no longer stomping over manual configuration, and better handling of
import $ivyin your build file. -
Support for un-signed publishing and cases where your GPG key has no passphrase (346)
-
Basic support for Twirl, Play Framework's templating language (271)
-
Better performance for streaming large amounts of stdout from Mill's daemon process.
-
Allow configuration of append/exclude rules in
ScalaModule#assembly(309)
0.2.2
-
Preserve caches when transitioning between
-i/--interactiveand the fast client/server mode (329) -
Keep Mill daemon running if you Ctrl-C during
-w/--watchmode (327) -
Allow
mill versionto run without a build file (328) -
Make
docJar(and thus publishing) robust against scratch files in the source directories (334) and work with Scala compiler options (336) -
Allow passing Ammonite command-line options to the
foo.replcommand (333) -
Add
mill clean(315) to easily delete the Mill build caches for specific targets -
Improve IntelliJ integration of
MavenModules/SbtModules' test folders (298) -
Avoid showing useless stack traces when
foo.testresult-reporting fails orfoo.runfails -
ScalaFmt support (308)
-
Allow
ScalaModule#generatedSourcesto allow single files (previous you could only pass in directories)
0.2.0
-
Universal (combined batch/sh) script generation for launcher, assembly, and release (#264)
-
Windows client/server improvements (#262)
-
Windows repl support (note: MSYS2 subsystem/shell will be supported when jline3 v3.6.3 is released)
-
Fixed Java 9 support
-
Remove need for running
publishAllusing--interactivewhen on OSX and your GPG key has a passphrase -
First-class support for
JavaModules -
Properly pass compiler plugins to Scaladoc (#282)
-
Support for ivy version-pinning via
ivy"...".forceVersion() -
Support for ivy excludes via
ivy"...".exclude()(#254) -
Make
ivyDepsTreeproperly handle transitive dependencies (#226) -
Fix handling of
runtime-scoped ivy dependencies (#173) -
Make environment variables available to Mill builds (#257)
-
Support ScalaCheck test runner (#286)
-
Support for using Typelevel Scala (#275)
-
If a module depends on multiple submodules with different versions of an ivy dependency, only one version is resolved (#273)
0.1.7
-
Support for non-interactive (client/server) mode on Windows.
-
More fixes for Java 9
-
Bumped the Mill daemon timeout from 1 minute to 5 minutes of inactivity before it shuts down.
-
Avoid leaking Node.js subprocesses when running
ScalaJSModuletests -
Passing command-line arguments with spaces in them to tests no longer parses wrongly
-
ScalaModule#repositories,scalacPluginIvyDeps,scalacOptions,javacOptionsare now automatically propagated toTestsmodules -
ScalaJSModulelinking errors no longer show a useless stack trace -
ScalaModule#docJarnow properly uses the compileClasspath rather than runClasspath -
Bumped underlying Ammonite version to 1.1.0, which provides the improved Windows and Java 9 support
0.1.6
-
Fixes for non-interactive (client/server) mode on Java 9
-
Windows batch (.bat) generation for launcher, assembly, and release
0.1.5
-
Introduced the
mill plan foo.barcommand, which shows you what the execution plan of running thefoo.bartask looks like without actually evaluating it. -
Mill now generates an
out/mill-profile.jsonfile containing task-timings, to make it easier to see where your mill evaluation time is going -
Introduced
ScalaModule#ivyDepsTreecommand to show dependencies tree -
Rename
describetoinspectfor consistency with SBT -
mill resolvenow prints results sorted alphabetically -
Node.js configuration can be customised with
ScalaJSModule#nodeJSConfig -
Scala.js
fullOptnow uses Google Closure Compiler after generating the optimized Javascript output -
Scala.js now supports
NoModuleandCommonJSModulemodule kinds -
Include
compileIvyDepswhen generating IntelliJ projects -
Fixed invalid POM generation
-
Support for Java 9 (and 10)
-
Fixes for Windows support
-
Fixed test classes discovery by skipping interfaces
-
Include "optional" artifacts in dependency resolution if they exist
-
out/{module_name}now added as a content root in generated IntelliJ project
0.1.4
-
Speed up Mill client initialization by another 50-100ms
-
Speed up incremental
assemblys in the common case where upstream dependencies do not change. -
Make
ScalaJSModule#runwork with main-method discovery -
Make
ScalaWorkerModuleuser-defineable, so you can use your own custom coursier resolvers when resolving Mill's own jars -
Simplify definitions of
SCMstrings -
Make the build REPL explicitly require
-i/--interactiveto run -
Log a message when Mill is initializing the Zinc compiler interface
0.1.3
-
Greatly reduced the overhead of evaluating Mill tasks, with a warm already-cached
mill dev.launchernow taking ~450ms instead of ~1000ms -
Mill now saves compiled build files in
~/.mill/ammonite, which is configurable via the--homeCLI arg. -
Fixed linking of multi-module Scala.js projects
0.1.2
-
Mill now keeps a long-lived work-daemon around in between commands; this should improve performance of things like
compilewhich benefit from the warm JVM. You can use-i/--interactivefor interactive consoles/REPLs and for running commands without the daemon -
Implemented the
ScalaModule#launchertarget for easily creating command-line launchers you can run outside of Mill -
ScalaModule#docJarno longer fails if you don't havescala-compileron classpath -
Support for multiple
testFrameworksin a test module.
0.1.1
- Fixes for
foo.console - Enable Ammonite REPL integration via
foo.repl
0.1.0
- First public release