API · Coursier

This page describes the new high level API of coursier, being added since 1.1.0-M10. It's still subject to source / binary compatibility breakages, even though its general outline shouldn't change much. See low level API for the former API, less subject to change.

The high level API of coursier aims at being as simple to use as its CLI, with sensible defaults in particular, while retaining the purity of the low-level API.

It exposes a few objects under the coursier namespace, most notably coursier.Resolve and coursier.Fetch, allowing to resolve dependencies and fetch their artifacts.

To get started with the high level API, add the settings below to build.sbt

// build.sbt
//
libraryDependencies ++= Seq(
  "io.get-coursier" %% "coursier" % "2.1.25-M23",
)

Resolve API

coursier.Resolve allows to run resolutions, that is finding all the transitive dependencies of some initial dependencies (while reconciling their versions at the same time).

This entirely relies on metadata, that is POM or maven-metadata.xml files for Maven repositories, and ivy.xml files for Ivy repositories.

If you're fine with all the defaults (cache location, resolution parameters, …), you can just resolve some dependencies with

import coursier._

val resolution = Resolve()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .run()

This runs the resolution synchronously. To run resolutions in the background, the future and io methods can be called instead of run, to start resolution eagerly via scala.concurrent.Future, or lazily via an IO monad.

resolution is a coursier.core.Resolution, which represents the (final) state of the resolution. It has various methods allowing to process dependencies, most notably minDependencies, returning a set of dependencies (with redundant dependencies stripped).

The object returned by Resolve() allows to optionally change a number of parameters, discussed below.

Dependencies

Pass some extra dependencies with addDependencies. addDependencies accepts multiple dependencies, and can be called several times. If you prefer, you can also call withDependencies, that accepts a Seq[Dependency], and wipes any previously passed dependency.

import coursier._

val resolution = Resolve()
  .addDependencies(
    dep"org.http4s:http4s-dsl_2.12:0.18.22",
    dep"org.tpolecat:doobie-core_2.12:0.6.0"
  )
  .run()

Repositories

The default repositories are the Ivy2 local repository (only on the JVM) and Maven Central. More details here. One can add some extra repositories with addRepositories, that accepts multiple arguments, and can be called several times. Optionally, one can call withRepositories to set all the repositories at once, wiping the default ones and any previously passed one.

import coursier._

val resolution = Resolve()
  .addDependencies(dep"sh.almond:scala-kernel-api_2.12.8:0.2.2")
  .addRepositories(
    Repositories.sonatype("releases"),
    Repositories.jitpack
  )
  .run()

Cache

One can override the default cache, and adjust its parameters, with withCache:

import coursier._
import coursier.cache._
import coursier.cache.loggers._

import scala.concurrent.duration._

val pool = java.util.concurrent.Executors.newFixedThreadPool(3)

val cache = FileCache()
  .withLocation("./path/to/custom-cache")
  .withLogger(RefreshLogger.create(System.out))
  .withPool(pool)
  .withTtl(1.hour)

val resolution = Resolve()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .withCache(cache)
  .run()

pool.shutdown()

Resolution parameters

A number of resolution parameters can be adjusted by passing a custom ResolutionParams to withResolutionParameters,

import coursier._
import coursier.params._
import coursier.params.rule._
import coursier.version.VersionConstraint

val params = ResolutionParams()
  .withMaxIterations(50)
  .withScalaVersion("2.12.8")
  .addForceVersion0(
    mod"joda-time:joda-time" -> VersionConstraint("2.10.1")
  )
  .addRule(
    SameVersion(mod"com.fasterxml.jackson.*:jackson-*")
  )

val resolution = Resolve()
  .addDependencies(dep"org.apache.spark:spark-sql_2.12:2.4.0")
  .withResolutionParams(params)
  .run()

Fetch API

coursier.Fetch resolves dependencies, then fetches their artifacts.

Use it like

import coursier._

val files = Fetch()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .run()

// files: Seq[java.io.File]

One can

add dependencies,
adjust repositories,
adjust the cache, or
change the resolution parameters,

with the same methods as coursier.Resolve.

Classifiers

Call addClassifiers to adjust the classifiers you're interested in, like

import coursier._

val files = Fetch()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .addClassifiers(Classifier.javadoc, Classifier.sources)
  .run()

To keep default artifacts while also fetching classifiers, call withMainArtifacts, like

import coursier._

val files = Fetch()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .addClassifiers(Classifier.javadoc, Classifier.sources)
  .withMainArtifacts()
  .run()

Artifact types

If you know what you're doing and want to fetch all or some specific artifact types, call allArtifactTypes or addArtifactType, like

import coursier._

val files = Fetch()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .allArtifactTypes()
  .run()

import coursier._

val files = Fetch()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .addArtifactTypes(Type.pom, Type.testJar)
  .run()

If none of these methods are called, artifact types are automatically adjusted depending on classifiers.

Versions API

coursier.Versions resolves available artifact versions.

Use it like

import coursier._
import coursier.version.Version

val versions = Versions()
  .withModule(mod"org.typelevel:cats-kernel_2.12")
  .run()

versions.latest0
// res13: Version = Version(repr = "2.13.0")

One can

adjust repositories,
adjust the cache

with the same methods as coursier.Resolve.

Asynchronous / synchronous evaluation

With the .run() methods, the API methods perform network calls on the calling thread, which may or may not fit with your needs. Coursier also provides ways to use its API asynchronously with your effect of choice.

Future

If you prefer to eagerly run calls in the background via a Future, call future instead of run, like

import coursier._

// You can do this for other APIs too, like Fetch
val futureResolution = Resolve()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .future()

IO

If you prefer resolutions to be run lazily in the background via an IO monad, call io instead of run or future, like

import coursier._

val ioResolution = Resolve()
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .io

The default IO monad is the rather basic coursier.util.Task, that ships with coursier. This monad can be changed by changing the cache upfront, like

import coursier._
import coursier.cache._
import coursier.interop.cats._

import cats.effect.IO
import cats.effect.unsafe.implicits.global
import scala.concurrent.ExecutionContext

val cache = FileCache[IO]()

val ioResolution = Resolve(cache) // note the cache passed here
  .addDependencies(dep"org.tpolecat:doobie-core_2.12:0.6.0")
  .io

Note that this example requires the coursier-cats-interop module (io.get-coursier::coursier-cats-interop:2.1.25-M23).