enso/docs/infrastructure/sbt.md

layout	title	category	tags	order
developer-doc	Build Tools	infrastructure	infrastructure build	1

Build Tools

The project is built using the Scala Build Tool which manages dependencies between the projects as well as external dependencies and allows for incremental compilation. The build configuration is defined in build.sbt.

• Incremental Compilation
• Compile Hooks
• Helper Tasks
  • Graal and Flatc Version Check
  • Benchmarks
  • Build Information
  • Instruments Generation
  • Flatbuffers Generation
  • Ensuring JARs Were Loaded
  • Debugging Command
  • Recompile Parser
• Native Image

Incremental Compilation

To help wit build times, we do not want to rebuild the whole project with every change, but to only recompile the files that have been affected by the change. This is handled by sbt which under the hood uses zinc (the incremental compiler for Scala). zinc analyses the compiled files and detects dependencies between them to determine which files have to be recompiled when something has been changed.

Compile Hooks

There are some invariants that are specific to our project, so they are not tracked by sbt, but we want to ensure that they hold to avoid cryptic errors at compilation or runtime.

To check some state before compilation, we add our tasks as dependencies of Compile / compile / compileInputs by adding the following to the settings of a particular project.

Compile / compile / compileInputs := (Compile / compile / compileInputs)
        .dependsOn(preCompileHookTask)
        .value

Tasks that should be run before compilation, should be attached to the compileInputs task. That is because the actual compilation process is ran in the task compileIncremental. Compile / compile depends on compileIncremental but if we add our dependency to Compile / compile, it is considered as independent with compileIncremental, so sbt may schedule it to run in parallel with the actual compilation process. To guarantee that our pre-flight checks complete before the actual compilation, we add them as a dependency of compileInputs which runs strictly before actual compilation.

To check some invariants after compilation, we can replace the original Compile / compile task with a custom one which does its post-compile checks and returns the result of (Compile / compile).value.

Helper Tasks

There are additional tasks defined in the project directory. They are used by build.sbt to provide some additional functionality.

Graal and Flatc Version Check

EnvironmentCheck defines a helper function that can be attached to the default Global / onLoad state transition to run a version check when loading the sbt project. This helper function compares the version of JVM running sbt with GraalVM version defined in build.sbt and the version of flatc installed in the system with the Flatbuffers library version defined in build.sbt. If the versions do not match it reports an error telling the user to change to the correct version.

Benchmarks

BenchTasks defines configuration keys for benchmarking.

Build Information

BenchTasks records version information including what git commit has been used for compiling the project. This information is used by enso --version.

Instruments Generation

Truffle annotation processor generates a file that registers instruments provided by the runtime. Unfortunately, with incremental compilation, only the changed instruments are recompiled and the annotation processor does not detect this, so un-changed instruments get overwritten.

In the past we had a pre-compile task (see FixInstrumentsGeneration) that detected changes to instruments and if only one of them was to be recompiled, it forced recompilation of all of them, to ensure consistency. This workaround helped to avoid later runtime issues but sometimes triggered a cascade of recompilations, which weren't clear to the end user. Instead, to avoid overwriting entries in META-INF files, individual services were moved to separate subprojects and during assembly of uber jar we concatenate meta files with the same service name.

Flatbuffers Generation

GenerateFlatbuffers defines the task that runs the Flatbuffer compiler flatc whenever the flatbuffer definitions have been changed. It also makes sure that flatc is available on PATH and that its version matches the version of the library. It reports any errors.

Debugging Command

WithDebugCommand defines a command that allows to run a task with additional JVM-level flags.

Recompile Parser

RecompileParser defines a task that can be attached to the compile task in configurations of the syntax project. This task ensures that the syntax project is recompiled whenever syntax-definition changes.

Native Image

NativeImage task is described at Native Image.