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:
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:
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.
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
To run test suites:
./mill main.test
./mill scalalib.test
./mill scalajslib.test
./mill integration.test
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)
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.
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/
The Mill project is organized roughly as follows:
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.
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/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.
For details refer to milestone after 0.7.3 and the list of commits.
For details refer to milestone 0.7.3 and the list of commits.
For details refer to milestone 0.7.2 and the list of commits.
For details refer to milestone 0.7.1 and the list of commits.
- Greatly improved parallel builds via
-j <n>
/--jobs <n>
, with better scheduling and utilization of multiple cores build.sc
files now uses Scala 2.13.2- Avoid duplicate target resolution with
mill resolve __
- Add ability to pass GPG arguments to publish via
--gpgArgs
-w
/--watch
now works forT.source
targets
For details refer to milestone 0.7.0 and the list of commits.
- 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.
- Mill can now execute targets in parallel.
This is experimental and need to be enabled with
--jobs <n>
option. PublishModule
: newpublishM2Local
to publish into local Maven repositoriesPublishModule
: enhancedpublishLocal
to 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.
- Bugfix: Mill now no longer leaks open files (version bump to uPickle 1.0.0)
- New
--version
option - Added Support for Scala.js 1.0.0+
- Added Support for Scala Native 0.4.0-M2
JavaModule
: EnhancedivyDepsTree
to optionally include compile-time and runtime-time dependenciesJavaModule
:allSourceFiles
no 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.dir
when generating bloop config)
For details refer to milestone 0.6.1 and the list of commits.
- Support for METALS 0.8.0 in VSCode
For details refer to milestone 0.6.0 and the list of commits.
- 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.
- 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.
(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
-i
option 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.
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
CoursierModule
to 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.
TestModule
: newtestCached
target, 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.
- 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_VERSION
in 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.
-
Mill now supports a
./mill
bootstrap 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-version
file orMILL_VERSION
environment variable for Overriding Mill Versions -
Fix scoverage: inherit repositories from outer project #645
-
Fixes for scala native test suites without test frameworks #627
-
Fix publication of artifacts by increasing sonatype timeouts
-
Bug fixes for Scoverage integration #623
-
Publish
compileIvyDeps
as 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
-
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-going
commandline option to disable fail fast behaviour and continue build as long as possible in case of a failure
- Bump uPickle to 0.7.1
- Mill is now bundled with OS-Lib, providing a simpler way of dealing with filesystem APIs and subprocesses
-
Added new
debug
method to context logger, to log additional debug info into the task specific output dir (out/<task>/log
) -
Added
--debug
option to enable debug output to STDERR -
Fix
ScalaModule#docJar
task when Scala minor versions differ 475
- Automatically detect main class to make
ScalaModule#assembly
self-executable
-
Bump Ammonite to 1.3.2, Fastparse to 2.0.4
-
Sped up
ScalaModule#docJar
task by about 10x, greatly speeding up publishing -
Add a flag
JavaModule#skipIdea
you can override to disable Intellij project generation #458 -
Allow sub-domains when publishing #441
-
mill inspect
now 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
-
Add
visualizePlan
command -
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
/runBackground
working directory viaforkWorkingDir
-
Reduced executable size, improved incremental compilation in #414
-
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.sc
files by removing duplicate macro generated routing code
-
Add
.runBackground
and.runMainBackground
commands, 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.runBackground
command is run a second time to spawn a new version of the process. Can be used with-w
for auto-reloading of long-running servers. -
Scala-Native support. Try it out!
-
Add
--disable-ticker
to reduce spam in CI -
Fix propagation of
--color
flag
-
Fix resolution of
scala-{library,compiler,reflect}
in case of conflict -
Allow configuration of
JavaModule
andScalafmtModule
scala workers -
Allow hyphens in module and task names
-
Fix publishing of ScalaJS modules to properly handle upstream ScalaJS dependencies
-
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 $ivy
in 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)
-
Preserve caches when transitioning between
-i
/--interactive
and the fast client/server mode (329) -
Keep Mill daemon running if you Ctrl-C during
-w
/--watch
mode (327) -
Allow
mill version
to 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.repl
command (333) -
Add
mill clean
(315) to easily delete the Mill build caches for specific targets -
Improve IntelliJ integration of
MavenModule
s/SbtModule
s' test folders (298) -
Avoid showing useless stack traces when
foo.test
result-reporting fails orfoo.run
fails -
ScalaFmt support (308)
-
Allow
ScalaModule#generatedSources
to allow single files (previous you could only pass in directories)
-
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
publishAll
using--interactive
when on OSX and your GPG key has a passphrase -
First-class support for
JavaModule
s -
Properly pass compiler plugins to Scaladoc (#282)
-
Support for ivy version-pinning via
ivy"...".forceVersion()
-
Support for ivy excludes via
ivy"...".exclude()
(#254) -
Make
ivyDepsTree
properly 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)
-
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
ScalaJSModule
tests -
Passing command-line arguments with spaces in them to tests no longer parses wrongly
-
ScalaModule#repositories
,scalacPluginIvyDeps
,scalacOptions
,javacOptions
are now automatically propagated toTests
modules -
ScalaJSModule
linking errors no longer show a useless stack trace -
ScalaModule#docJar
now properly uses the compileClasspath rather than runClasspath -
Bumped underlying Ammonite version to 1.1.0, which provides the improved Windows and Java 9 support
-
Fixes for non-interactive (client/server) mode on Java 9
-
Windows batch (.bat) generation for launcher, assembly, and release
-
Introduced the
mill plan foo.bar
command, which shows you what the execution plan of running thefoo.bar
task looks like without actually evaluating it. -
Mill now generates an
out/mill-profile.json
file containing task-timings, to make it easier to see where your mill evaluation time is going -
Introduced
ScalaModule#ivyDepsTree
command to show dependencies tree -
Rename
describe
toinspect
for consistency with SBT -
mill resolve
now prints results sorted alphabetically -
Node.js configuration can be customised with
ScalaJSModule#nodeJSConfig
-
Scala.js
fullOpt
now uses Google Closure Compiler after generating the optimized Javascript output -
Scala.js now supports
NoModule
andCommonJSModule
module kinds -
Include
compileIvyDeps
when 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
-
Speed up Mill client initialization by another 50-100ms
-
Speed up incremental
assembly
s in the common case where upstream dependencies do not change. -
Make
ScalaJSModule#run
work with main-method discovery -
Make
ScalaWorkerModule
user-defineable, so you can use your own custom coursier resolvers when resolving Mill's own jars -
Simplify definitions of
SCM
strings -
Make the build REPL explicitly require
-i
/--interactive
to run -
Log a message when Mill is initializing the Zinc compiler interface
-
Greatly reduced the overhead of evaluating Mill tasks, with a warm already-cached
mill dev.launcher
now taking ~450ms instead of ~1000ms -
Mill now saves compiled build files in
~/.mill/ammonite
, which is configurable via the--home
CLI arg. -
Fixed linking of multi-module Scala.js projects
-
Mill now keeps a long-lived work-daemon around in between commands; this should improve performance of things like
compile
which benefit from the warm JVM. You can use-i
/--interactive
for interactive consoles/REPLs and for running commands without the daemon -
Implemented the
ScalaModule#launcher
target for easily creating command-line launchers you can run outside of Mill -
ScalaModule#docJar
no longer fails if you don't havescala-compiler
on classpath -
Support for multiple
testFrameworks
in a test module.
- Fixes for
foo.console
- Enable Ammonite REPL integration via
foo.repl
- First public release