This demo demonstrates how to build a native image of the Scala compiler.

1. First, make sure that the environment variables SCALA_HOME points to Scala 2.12.x. Check what scala you have on your system by running:

echo $SCALA_HOME
scala --version

2. Download GraalVM, unzip the archive, export the GraalVM home directory as the $JAVA_HOME and add $JAVA_HOME/bin to the PATH environment variable.

On Linux:

export JAVA_HOME=/home/${current_user}/path/to/graalvm
export PATH=$JAVA_HOME/bin:$PATH

On macOS:

export JAVA_HOME=/Users/${current_user}/path/to/graalvm/Contents/Home
export PATH=$JAVA_HOME/bin:$PATH

On Windows:

setx /M JAVA_HOME "C:\Progra~1\Java\<graalvm>"
setx /M PATH "C:\Progra~1\Java\<graalvm>\bin;%PATH%"

3. Download or clone the repository and navigate into the scala-examples/scalac-native directory:

git clone https://github.com/graalvm/graalvm-demos
cd graalvm-demos/scala-examples/scalac-native

4. Then enter the scalac-substitutions subfolder and build the project with sbt:

cd scalac-substitutions
sbt package
cd ..

5. Build the native image of the Scala compiler:

./scalac-image.sh

The produced native image is called scalac and has no dependencies on the JDK.

The script scalac-native calls the generated compiler and passes all the required parameters (just like scala does).

Compare to the JVM on the first run:

time $SCALA_HOME/bin/scalac HelloWorld.scala

real	0m2.315s
user	0m5.868s
sys	0m0.248s

time ./scalac-native HelloWorld.scala

real	0m0.177s
user	0m0.129s
sys	0m0.034s

When compiled with Profile-Guided Optimization (PGO) the native scalac is as fast as the one running on the JVM (with the C2 compiler).

For macros to work, the macro classes must be known to the image builder of the Scala compiler.

1. First, try a scalac image that includes macro, run:

./scalac-native macros/GreetingMacros.scala -d macros/
./scalac-image-macros.sh

2. Now you can compile a project that uses macros from GreetingMacros.scala:

./scalac-native -cp macros/ HelloMacros.scala

3. Run the compiled program with:

scala HelloMacros
Hello, World!