Introduction to Mill
Mill is your shiny new Java/Scala build tool! Scared of SBT? Melancholy over Maven? Grumbling about Gradle? Baffled by Bazel? Give Mill a try!
Mill aims for simplicity by reusing concepts you are already familiar with, borrowing ideas from modern tools like Bazel. It lets you build your projects in a way that’s simple, fast, and predictable.
Mill has built-in support for the Scala programming language, and can serve as a replacement for SBT. It can be extended to support any other language or platform via modules (written in Java or Scala) or through external subprocesses.
If you are using Mill, you will find the following book by the Author useful in using Mill to the fullest:
Installation
Windows
To get started, download Mill from
Github releases, and save it as mill.bat
.
If you’re using Scoop you can install Mill via
scoop install mill
Mill also works on "sh" environments on Windows (e.g., MSYS2, Cygwin, Git-Bash, WSL); to get started, follow the instructions in the Manual section below. Note that:
-
In some environments (such as WSL), Mill might have to be run without a server (using
-i
,--interactive
,--no-server
, or--repl
.) -
On Cygwin, run the following after downloading mill:
sed -i '0,/-cp "\$0"/{s/-cp "\$0"/-cp `cygpath -w "\$0"`/}; 0,/-cp "\$0"/{s/-cp "\$0"/-cp `cygpath -w "\$0"`/}' /usr/local/bin/mill
Docker
You can download and run a "Docker image containing OpenJDK, Scala and Mill" using
docker pull nightscape/scala-mill
docker run -it nightscape/scala-mill
Manual
To get started, download Mill and install it into your system via the following
curl
/chmod
command:
sudo sh -c "curl -L https://github.com/com-lihaoyi/mill/releases/download/0.10.0/0.10.0 > /usr/local/bin/mill && chmod +x /usr/local/bin/mill"
Bootstrap Scripts (Linux/OS-X Only)
If you are using Mill in a codebase, you can commit the bootstrap launcher as a
./mill
script in the project folder:
curl -L https://github.com/com-lihaoyi/mill/releases/download/0.10.0/0.10.0 > mill && chmod +x mill
Now, anyone who wants to work with the project can simply use the ./mill
script directly:
./mill version
./mill __.compile # double underscore
The mill
command will automatically use the version specified by the bootstrap script, even if you installed it via
other means. The ./mill
file has a version number embedded within it, which you can update simply by editing the
script. Note this only works for versions 0.5.0 and above.
Bootstrap scripts are also useful for running Mill in CI, ensuring that your Jenkins/Travis/etc. box has the correct version of Mill present to build/compile/test your code.
millw
Instead of installing Mill directly, you can also use lefou/millw as drop-in
replacement for mill
. It provides a small shell script and also a Windows batch file, that transparently downloads mill
and executes it on your behalf. It respects various ways to configure the preferred Mill version (MILL_VERSION
env
var, .mill-version
file, --mill-version
option) and can also be used as a bootstrap script in your project.
Updating Mill
Once installed mill is able to use newer or different versions for each project automatically. You don’t need to install multiple versions of mill yourself.
See section Overriding Mill Versions how to do it.
Getting Started
The simplest Mill build for a Java project looks as follows:
build.sc
import mill._, scalalib._
object foo extends JavaModule {}
The simplest Mill build for a Scala project looks as follows:
build.sc
import mill._, scalalib._
object foo extends ScalaModule {
def scalaVersion = "2.13.8"
}
Both of these would build a project laid out as follows:
build.sc foo/ src/ FileA.java FileB.scala resources/ ... out/ foo/ ...
You can download an example project with this layout here:
The source code for this module would live in the foo/src/
folder, matching the name you assigned to the module.
Output for this module (compiled files, resolved dependency lists, …) would live in out/foo/
.
This can be run from the Bash shell via:
$ mill foo.compile # compile sources into classfiles
$ mill foo.run # run the main method, if any
$ mill foo.runBackground # run the main method in the background
$ mill foo.launcher # prepares a foo/launcher.dest/run you can run later
$ mill foo.jar # bundle the classfiles into a jar
$ mill foo.assembly # bundle classfiles and all dependencies into a jar
$ mill -i foo.console # start a Scala console within your project (in interactive mode: "-i")
$ mill -i foo.repl # start an Ammonite REPL within your project (in interactive mode: "-i")
You can run mill resolve __
to see a full list of the different tasks that are available, mill resolve foo._
to see
the tasks within foo
, mill inspect foo.compile
to inspect a task’s doc-comment documentation or what it depends on,
or mill show foo.scalaVersion
to show the output of any task.
The most common tasks that Mill can run are cached targets, such as
compile
, and un-cached commands such as foo.run
. Targets do not re-evaluate unless one of their inputs changes,
whereas commands re-run every time.
Output
Mill puts all its output in the top-level out/
folder. The above commands would end up in:
out/
foo/
compile.dest
compile.log
compile.json
run.dest
run.log
run.json
runBackground.dest
runBackground.log
runBackground.json
launcher.dest
launcher.log
launcher.json
jar.dest
jar.log
jar.json
assembly.dest
assembly.log
assembly.json
For each task there’s a foo.json
file containing the metadata returned by that task, and
two optional paths: a foo.dest/
folder containing any files that the task generates and a foo.log
file containing the the logs of running that task. For example, out/foo/compile.dest/
contains the
compiled classfiles, while out/foo/assembly.dest/
contains the self-contained assembly with the project’s classfiles
jar-ed up with all its dependencies.
Given a task foo.bar
, all its output and results are inside its respective out/foo/bar/
folder.
Multiple Modules
Java Example
build.sc
import mill._, scalalib._
object foo extends JavaModule
object bar extends JavaModule {
def moduleDeps = Seq(foo)
}
Scala Example
build.sc
import mill._, scalalib._
object foo extends ScalaModule {
def scalaVersion = "2.13.8"
}
object bar extends ScalaModule {
def moduleDeps = Seq(foo)
def scalaVersion = "2.13.8"
}
You can define multiple modules the same way you define a single module, using
def moduleDeps
to define the relationship between them.
The above builds expect the following project layout:
build.sc foo/ src/ Main.scala resources/ ... bar/ src/ Main2.scala resources/ ... out/ foo/ ... bar/ ...
And can be built/run using:
$ mill foo.compile
$ mill bar.compile
$ mill foo.run
$ mill bar.run
$ mill foo.jar
$ mill bar.jar
$ mill foo.assembly
$ mill bar.assembly
Mill’s evaluator will ensure that the modules are compiled in the right order, and recompiled as necessary when source code in each module changes.
Modules can also be nested:
build.sc
import mill._, scalalib._
object foo extends ScalaModule {
def scalaVersion = "2.13.8"
object bar extends ScalaModule {
def moduleDeps = Seq(foo)
def scalaVersion = "2.13.8"
}
}
Which would result in a similarly nested project layout:
build.sc foo/ src/ Main.scala resources/ ... bar/ src/ Main2.scala resources/ ... out/ foo/ ... bar/ ...
Where the nested modules can be run via:
$ mill foo.compile
$ mill foo.bar.compile
$ mill foo.run
$ mill foo.bar.run
$ mill foo.jar
$ mill foo.bar.jar
$ mill foo.assembly
$ mill foo.bar.assembly
Watch and Re-evaluate
You can use the --watch
flag to make Mill watch a task’s inputs, re-evaluating the task as necessary when the inputs
change:
$ mill --watch foo.compile
$ mill --watch foo.run
$ mill -w foo.compile
$ mill -w foo.run
Mill’s --watch
flag watches both the files you are building using Mill, as well as Mill’s own build.sc
file and
anything it imports, so any changes to your build.sc
will automatically get picked up.
For long-running processes like web servers, you can use runBackground
to make sure they recompile and restart when code changes,
forcefully terminating the previous process even though it may be still alive:
$ mill -w foo.compile
$ mill -w foo.runBackground
Parallel Task Execution (Experimental)
By default, mill will evaluate all tasks in sequence. But mill also supports processing tasks in parallel. This feature is currently experimental and we encourage you to report any issues you find on our bug tracker.
To enable parallel task execution, use the --jobs
(-j
) option followed by a number of maximal parallel threads.
Example: Use up to 4 parallel threads to compile all modules:
mill -j 4 __.compile
To use as many threads as your machine has (logical) processor cores use --jobs 0
.
To disable parallel execution use --jobs 1
.
This is currently the default.
Please note that the maximal possible parallelism depends on your project. Tasks that depend on each other can’t be processed in parallel.
Command-line usage
Mill is a command-line tool and supports various options.
Run mill --help
for a complete list of options
mill --help
Mill Build Tool usage: mill [options] [[target [target-options]] [+ [target ...]]] --no-default-predef Disable the default predef and run Ammonite with the minimal predef possible -s --silent Make ivy logs go silent instead of printing though failures will still throw exception -w --watch Watch and re-run your scripts when they change --bsp Run a BSP server against the passed scripts -c --code <str> Pass in code to be run immediately in the REPL -h --home <path> The home directory of the REPL; where it looks for config and caches -p --predef <path> Lets you load your predef from a custom location, rather than the "default location in your Ammonite home --color <bool> Enable or disable colored output; by default colors are enabled in both REPL and scripts if the console is interactive, and disabled otherwise --thin Hide parts of the core of Ammonite and some of its dependencies. By default, the core of Ammonite and all of its dependencies can be seen by users from the Ammonite session. This option mitigates that via class loader isolation. --help Print this message -h --home <path> The home directory of the REPL; where it looks for config and caches --repl Run Mill in interactive mode and start a build REPL. In this mode, no mill server will be used. Must be the first argument. --no-server Run Mill in interactive mode, suitable for opening REPLs and taking user input. In this mode, no mill server will be used. Must be the first argument. -i --interactive Run Mill in interactive mode, suitable for opening REPLs and taking user input. In this mode, no mill server will be used. Must be the first argument. -v --version Show mill version and exit. -b --bell Ring the bell once if the run completes successfully, twice if it fails. --disable-ticker Disable ticker log (e.g. short-lived prints of stages and progress bars) -d --debug Show debug output on STDOUT -k --keep-going Continue build, even after build failures -D --define <k=v> Define (or overwrite) a system property -j --jobs <int> Allow processing N targets in parallel. Use 1 to disable parallel and 0 to use as much threads as available processors. rest <str>... The name of the targets you want to build, followed by any parameters you wish to pass to those targets.
All options must be given before the first target.
A target is a fully qualified task or command optionally followed by target specific arguments. You can use wildcards and brace-expansion to select multiple targets at once or to shorten the path to deeply nested targets. If you provide optional target arguments and your wildcard or brace-expansion is resolved to multiple targets, the arguments will be applied to each of the targets.
Wildcard |
Function |
|
matches a single segment of the target path |
|
matches arbitrary segments of the target path |
|
is equal to specifying two targets |
You can use the ` symbol to add another target with optional arguments.
If you need to feed a `
as argument to your target, you can mask it by preceding it with a backslash (\
).
Command-line Tools
Mill comes with a few useful command-line utilities built into it:
resolve
$ mill resolve _
[1/1] resolve
clean
foo
inspect
par
path
plan
resolve
show
shutdown
version
visualize
visualizePlan
$ mill resolve _.compile
[1/1] resolve
foo.compile
$ mill resolve foo._
[1/1] resolve
foo.allSourceFiles
foo.allSources
foo.ammoniteReplClasspath
foo.ammoniteVersion
foo.artifactId
foo.artifactName
...
resolve
lists the tasks that match a particular query, without running them.
This is useful for "dry running" an mill
command to see what would be run before you run them, or to explore what modules or tasks are available
from the command line using resolve _
, resolve foo._
, etc.
mill resolve foo.{compile,run}
mill resolve "foo.{compile,run}"
mill resolve foo.compile foo.run
mill resolve _.compile # list the compile tasks for every top-level module
mill resolve __.compile # list the compile tasks for every module
mill resolve _ # list every top level module and task
mill resolve foo._ # list every task directly within the foo module
mill resolve __ # list every module and task recursively
inspect
$ mill inspect foo.run
[1/1] inspect
foo.run(JavaModule.scala:442)
Runs this module's code in a subprocess and waits for it to finish
Inputs:
foo.finalMainClass
foo.runClasspath
foo.forkArgs
foo.forkEnv
foo.forkWorkingDir
inspect
is a more verbose version of resolve. In addition to printing out the name of one-or-more tasks,
it also displays its source location and a list of input tasks. This is very useful for debugging and interactively
exploring the structure of your build from the command line.
inspect
also works with the same _
/__
wildcard/query syntaxes that
resolve do:
mill inspect foo.compile
mill inspect foo.{compile,run}
mill inspect "foo.{compile,run}"
mill inspect foo.compile foo.run
mill inspect _.compile
mill inspect __.compile
mill inspect _
mill inspect foo._
mill inspect __
show
$ mill show foo.scalaVersion
[1/1] show
"2.13.1"
By default, Mill does not print out the metadata from evaluating a task. Most people would not be interested in e.g.
viewing the metadata related to incremental compilation: they just want to compile their code! However, if you want to
inspect the build to debug problems, you can make Mill show you the metadata output for a task using the show
command:
show
is not just for showing configuration values.
All tasks return values that can be shown with show
.
E.g. compile
returns the paths to the classes
folder and analysisFile
file produced by the compilation:
$ mill show foo.compile
[1/1] show
[10/25] foo.resources
{
"analysisFile": "/Users/lihaoyi/Dropbox/Github/test//out/foo/compile.dest/zinc",
"classes": "ref:07960649:/Users/lihaoyi/Dropbox/Github/test//out/foo/compile.dest/classes"
}
show
is generally useful as a debugging tool, to see what is going on in your build:
$ mill show foo.sources
[1/1] show
[1/1] foo.sources
[
"ref:8befb7a8:/Users/lihaoyi/Dropbox/Github/test/foo/src"
]
$ mill show foo.compileClasspath
[1/1] show
[2/11] foo.resources
[
"ref:c984eca8:/Users/lihaoyi/Dropbox/Github/test/foo/resources",
".../org/scala-lang/scala-library/2.13.1/scala-library-2.13.1.jar"
]
show
is also useful for interacting with Mill from external tools, since the JSON it outputs is structured and easily
parsed and manipulated.
path
$ mill path foo.assembly foo.sources
[1/1] path
foo.sources
foo.allSources
foo.allSourceFiles
foo.compile
foo.localClasspath
foo.assembly
mill path
prints out a dependency chain between the first task and the second.
It is very useful for exploring the build graph and trying to figure out how data gets from one task to another.
If there are multiple possible dependency chains, one of them is picked arbitrarily.
plan
$ mill plan foo.compileClasspath
[1/1] plan
foo.transitiveLocalClasspath
foo.resources
foo.unmanagedClasspath
foo.scalaVersion
foo.platformSuffix
foo.compileIvyDeps
foo.scalaOrganization
foo.scalaLibraryIvyDeps
foo.ivyDeps
foo.transitiveIvyDeps
foo.compileClasspath
mill plan foo
shows which tasks would be evaluated, and in what order, if you ran mill foo
, but without actually running them.
This is a useful tool for debugging your build: e.g. if you suspect a task foo
is running things that it
shouldn’t be running, a quick mill plan
will list out all the upstream tasks that foo
needs to run, and you can then
follow up with mill path
on any individual upstream task to see exactly how foo
depends on it.
visualize
$ mill show visualize foo._
[1/1] show
[3/3] visualize
[
".../out/visualize.dest/out.txt",
".../out/visualize.dest/out.dot",
".../out/visualize.dest/out.json",
".../out/visualize.dest/out.png",
".../out/visualize.dest/out.svg"
]
mill show visualize
takes a subset of the Mill build graph (e.g. core._
is every task directly under the core
module) and draws out their relationships in .svg
and .png
form for you to inspect. It also generates .txt
, .dot
and .json
for easy processing by downstream tools.
The above command generates the following diagram:
visualizePlan
$ mill show visualizePlan foo.compile
[1/1] show
[3/3] visualizePlan
[
".../out/visualizePlan.dest/out.txt",
".../out/visualizePlan.dest/out.dot",
".../out/visualizePlan.dest/out.json",
".../out/visualizePlan.dest/out.png",
".../out/visualizePlan.dest/out.svg"
]
mill show visualizePlan
is similar to mill show visualize
except that it shows a graph of the entire build plan,
including tasks not directly resolved by the query. Tasks directly resolved are shown with a solid border, and
dependencies are shown with a dotted border.
The above command generates the following diagram:
Another use case is to view the relationships between modules. For the following two modules:
build.sc
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"
}
mill show visualizePlan _.compile
diagrams the relationships between the compile tasks of each module, which
illustrates which module depends on which other module’s compilation output:
clean
$ mill clean
clean
deletes all the cached outputs of previously executed tasks. It can apply to the entire project, entire modules,
or specific tasks.
mill clean # clean all outputs
mill clean foo # clean all outputs for module 'foo' (including nested modules)
mill clean foo.compile # only clean outputs for task 'compile' in module 'foo'
mill clean foo.{compile,run}
mill clean "foo.{compile,run}"
mill clean foo.compile foo.run
mill clean _.compile
mill clean __.compile
Search for dependency updates
$ mill mill.scalalib.Dependency/showUpdates
Mill can search for updated versions of your project’s dependencies, if available from your project’s configured repositories. Note that it uses heuristics based on common versioning schemes, so it may not work as expected for dependencies with particularly weird version numbers.
Current limitations:
-
Only works for
JavaModule
modules (includingScalaModule
s,CrossScalaModule
s, etc.) and Maven repositories. -
Always applies to all modules in the build.
-
Doesn’t apply to
$ivy
dependencies used in the build definition itself.
mill mill.scalalib.Dependency/showUpdates
mill mill.scalalib.Dependency/showUpdates --allowPreRelease true # also show pre-release versions
IDE Support
To support various IDEs and Language Servers, Mill supports the Build Server Protocol in version 2.0.0 and has a built-in BSP server.
In addition to BSP, Mill also supports IntelliJ IDEA project configuration generation directly.
Build Server Protocol (BSP)
To install a BSP connection file .bsp/mill-bsp.json
, run:
mill mill.bsp.BSP/install
Working known clients of the BSP server are IntelliJ IDEA and Metals.
You can fine control some BSP server options by specifying command options:
Option |
Description |
|
Use |
When using Metals by default Bloop will be used as your build server unless you
explicitly choose Mill. When in a Mill workspace use the "Switch Build Server"
command from Metals which will allow you to switch to using Mill as your build
server. If no If you want to use Metals, you may also want to enable SemanticDB support. Without it, some functionality like find references may not work. We still work on a better and automatic SemanticDB support.
Until we have completed it, you can enable SemanticDB manually in your For convenience, you can mix-in the build.sc : Mix-in of ScalaMetalsSupport trait
|
IntelliJ Support
To generate IntelliJ IDEA project files into .idea/
, run:
mill mill.scalalib.GenIdea/idea
The Build REPL
$ mill --repl
Loading...
@ foo
res0: foo.type = ammonite.predef.build#foo:4
Commands:
.ideaJavaModuleFacets(ideaConfigVersion: Int)()
.ideaConfigFiles(ideaConfigVersion: Int)()
.ivyDepsTree(inverse: Boolean, withCompile: Boolean, withRuntime: Boolean)()
.runLocal(args: String*)()
.run(args: String*)()
.runBackground(args: String*)()
.runMainBackground(mainClass: String, args: String*)()
.runMainLocal(mainClass: String, args: String*)()
.runMain(mainClass: String, args: String*)()
.console()()
.repl(replOptions: String*)()
Targets:
...
@ foo.compile
res1: mill.package.T[mill.scalalib.api.CompilationResult] = foo.compile(ScalaModule.scala:143)
Compiles the current module to generate compiled classfiles/bytecode
Inputs:
foo.upstreamCompileOutput
foo.allSourceFiles
foo.compileClasspath
...
@ foo.compile()
[25/25] foo.compile
res2: mill.scalalib.api.CompilationResult = CompilationResult(
/Users/lihaoyi/Dropbox/Github/test/out/foo/compile.dest/zinc,
PathRef(/Users/lihaoyi/Dropbox/Github/test/out/foo/compile.dest/classes, false, -61934706)
)
You can run mill --repl
to open a build REPL; this is a Scala console with your build.sc
loaded, which lets you run
tasks interactively.
The task-running syntax is slightly different from the command-line, but more in line with how you
would depend on tasks from within your build file.
You can use this REPL to interactively explore your build to see what is available.
Deploying your code
The two most common things to do once your code is complete is to make an assembly (e.g. for deployment/installation) or publishing (e.g. to Maven Central). Mill comes with both capabilities built in.
Mill comes with the built-in with the ability to make assemblies. Given a simple Mill build:
build.sc
import mill._, scalalib._
object foo extends ScalaModule {
def scalaVersion = "2.13.1"
}
You can make a self-contained assembly via:
$ mill foo.assembly
$ ls -lh out/foo/assembly.dest/out.jar
-rw-r--r-- 1 lihaoyi staff 5.0M Feb 17 11:14 out/foo/assembly.dest/out.jar
You can then move the out.jar
file anywhere you would like, and run it standalone using java
:
$ java -cp out/foo/assembly.dest/out.jar foo.Example
Hello World!
To publish to Maven Central, you need to make foo
also extend Mill’s
PublishModule
trait:
build.sc
import mill._, scalalib._, publish._
object foo extends ScalaModule with PublishModule {
def scalaVersion = "2.13.1"
def publishVersion = "0.0.1"
def pomSettings = PomSettings(
description = "Hello",
organization = "com.lihaoyi",
url = "https://github.com/lihaoyi/example",
licenses = Seq(License.MIT),
versionControl = VersionControl.github("lihaoyi", "example"),
developers = Seq(
Developer("lihaoyi", "Li Haoyi", "https://github.com/lihaoyi")
)
)
}
You can change the name of the published artifact (artifactId in the Maven POM)
by overriding artifactName
in the module you want to publish.
You can download an example project with this layout here:
Which you can then publish using the mill foo.publish
command, which takes your sonatype credentials (
e.g. lihaoyi:foobarbaz
) and GPG password as inputs:
$ mill foo.publish
Missing arguments: (--sonatypeCreds: String, --release: Boolean)
Arguments provided did not match expected signature:
publish
--sonatypeCreds String (format: "username:password")
--signed Boolean (default true)
--gpgArgs Seq[String] (default Seq("--batch", "--yes", "-a", "-b"))
--readTimeout Int (default 60000)
--release Boolean (default true)
--connectTimeout Int (default 5000)
--awaitTimeout Int (default 120000)
--stagingRelease Boolean (default true)
You also need to specify release
as true
or false
, depending on whether you just want to stage your module
on oss.sonatype.org
or you want Mill to complete the release process to Maven Central.
If you are publishing multiple artifacts, you can also use mill mill.scalalib.PublishModule/publishAll
as described
Structure of the out/
folder
The out/
folder contains all the generated files & metadata for your build. It is structured with one folder
per Target
/Command
, that is run, e.g.:
-
out/core/compile/
-
out/main/test/compile/
-
out/main/test/forkTest/
-
out/scalalib/compile/
There are also top-level build-related files in the out/
folder, prefixed as
mill-*
. The most useful is mill-profile.json
, which logs the tasks run and time taken for the last Mill command you
executed. This is very useful if you want to find out exactly what tasks are being run and Mill is being slow.
Each task currently creates contains the following files:
-
foo.dest/
: optional, a path for theTask
to use either as a scratch space, or to place generated files that are returned usingPathRef
references. ATask
should only output files within its own givendest/
folder (available asT.dest
) to avoid conflicting with anotherTask
, but can name files withindest/
arbitrarily. -
foo.log
: optional, thestdout
/stderr
of theTask
. This is also streamed to the console during evaluation. -
foo.json
: the cache-key and JSON-serialized return-value of theTarget
/Command
. The return-value can also be retrieved viamill show foo.compile
. Binary blobs are typically not included infoo.json
, and instead stored as separate binary files indest/
which are then referenced byfoo.json
viaPathRef
references.
The out/
folder is intentionally kept simple and user-readable. If your build is not behaving as you would expect,
feel free to poke around the various
foo.dest/
folders to see what files are being created, or the foo.json
files to see what is being returned by a
particular task. You can also simply delete folders within out/
if you want to force portions of your project to be
rebuilt, e.g. by deleting the out/main/
or out/main/test/compile/
folders.
Overriding Mill Versions
Apart from downloading and installing new versions of Mill globally, there are a few ways of selecting/updating your Mill version:
-
Create a
.mill-version
file to specify the version of Mill you wish to use:
echo "0.5.0" > .mill-version
.mill-version
takes precedence over the version of Mill specified in the
./mill
script.
-
Pass in a
MILL_VERSION
environment variable, e.g.
MILL_VERSION=0.5.0-3-4faefb mill __.compile
or
MILL_VERSION=0.5.0-3-4faefb ./mill __.compile
to override the Mill version manually. This takes precedence over the version specified in ./mill
or .mill-version
Note that both of these overrides only work for versions 0.5.0 and above.
Automatic Mill updates
If your project is hosted on GitHub, GitLab, or Bitbucket, you can use Scala Steward to automatically open a pull request to update your Mill version (in .mill-version
file), whenever there is a newer version available.
Scala Steward can also scan your project dependencies and keep them up-to-date. |
Development Releases
In case you want to try out the latest features and improvements that are currently in the main branch, unstable versions of Mill
are
available as binaries named
#.#.#-n-hash
linked to the latest tag. Installing the latest unstable release is recommended for bootstrapping mill.
The easiest way to use a development release is by updating the Bootstrap Scripts (Linux/OS-X Only),
or
Overriding Mill Versions via an environment variable or .mill-version
file.
Running Mill with custom JVM options
It’s possible to pass JVM options to the Mill launcher. To do this you need to create a .mill-jvm-opts
file in your
project’s root. This file should contain JVM options (strings, starting with -X
), one per line. All other lines will
be ignored.
For example, if your build requires a lot of memory and bigger stack size, your .mill-jvm-opts
could look like this:
-Xss10m -Xmx10G
The file name for passing JVM options to the Mill launcher is configurable. If for some reason you don’t want to
use .mill-jvm-opts
file name, add MILL_JVM_OPTS_PATH
environment variable with any other file name.
Come by our Gitter Channel if you want to ask questions or say hi!