Better handling of optional dependencies

core/shared/src/main/scala/coursier/core/Resolution.scala

@@ -351,6 +351,7 @@ object Resolution {
   private val mavenScopes = {
     val base = Map[String, Set[String]](
       "compile" -> Set("compile"),
+      "optional" -> Set("compile", "optional"),
       "provided" -> Set(),
       "runtime" -> Set("compile", "runtime"),
       "test" -> Set()
@@ -463,10 +464,16 @@ object Resolution {
           default
         else
           keepOpt.fold(default) { keep =>
-            if (keep(config))
-              // really keeping the  from.configuration, with its fallback config part
-              Seq(dep.copy(configuration = from.configuration))
-            else
+            if (keep(config)) {
+              val depConfig =
+                if (actualConfig == "optional")
+                  defaultConfiguration
+                else
+                  // really keeping the  from.configuration, with its fallback config part
+                  from.configuration
+
+              Seq(dep.copy(configuration = depConfig))
+            } else
               Nil
           }
     }

core/shared/src/main/scala/coursier/maven/MavenRepository.scala

@@ -287,12 +287,12 @@ final case class MavenRepository(
     for {
       str <- fetch(projectArtifact(module, version, versioningValue))
       rawListFilesPage <- fetch(artifactFor(listFilesUrl))
-      proj <- EitherT(F.point[String \/ Project](parseRawPom(str)))
+      proj0 <- EitherT(F.point[String \/ Project](parseRawPom(str)))
     } yield {
 
       val files = WebPage.listFiles(listFilesUrl, rawListFilesPage)
 
-      val versioning = proj
+      val versioning = proj0
         .snapshotVersioning
         .flatMap(versioning =>
           mavenVersioning(versioning, "", "")
@@ -300,7 +300,7 @@ final case class MavenRepository(
 
       val prefix = s"${module.name}-${versioning.getOrElse(version)}"
 
-      val packagingTpeMap = proj.packagingOpt
+      val packagingTpeMap = proj0.packagingOpt
         .map { packaging =>
           (MavenSource.typeDefaultClassifier(packaging), MavenSource.typeExtension(packaging)) -> packaging
         }
@@ -323,9 +323,14 @@ final case class MavenRepository(
             )
         }
 
+      val proj = Pom.addOptionalDependenciesInConfig(
+        proj0.copy(configurations = defaultConfigurations),
+        Set("", "compile"),
+        "optional"
+      )
+
       proj.copy(
         actualVersionOpt = Some(version),
-        configurations = defaultConfigurations,
         publications = foundPublications
       )
     }

core/shared/src/main/scala/coursier/maven/Pom.scala

@@ -451,4 +451,24 @@ object Pom {
         } yield modVers :+ modVer
     }
   }
+
+  def addOptionalDependenciesInConfig(
+    proj: Project,
+    fromConfigs: Set[String],
+    optionalConfig: String
+  ): Project = {
+
+    val optionalDeps = proj.dependencies.collect {
+      case (conf, dep) if dep.optional && fromConfigs(conf) =>
+        optionalConfig -> dep.copy(optional = false)
+    }
+
+    val configurations = proj.configurations +
+      (optionalConfig -> (proj.configurations.getOrElse(optionalConfig, Nil) ++ fromConfigs.filter(_.nonEmpty)).distinct)
+
+    proj.copy(
+      configurations = configurations,
+      dependencies = proj.dependencies ++ optionalDeps
+    )
+  }
 }

sbt-coursier/src/main/scala-2.10/coursier/Tasks.scala

@@ -1,6 +1,6 @@
 package coursier
 
-import java.io.{ OutputStreamWriter, File }
+import java.io.{ File, InputStream, OutputStreamWriter }
 import java.net.URL
 import java.util.concurrent.{ ExecutorService, Executors }
 
@@ -123,10 +123,14 @@ object Tasks {
         allDependencies <- allDependenciesTask
       } yield {
 
+        val configMap = configurations
+          .map { cfg => cfg.name -> cfg.extendsConfigs.map(_.name) }
+          .toMap
+
         FromSbt.project(
           projId,
           allDependencies,
-          configurations.map { cfg => cfg.name -> cfg.extendsConfigs.map(_.name) }.toMap,
+          configMap,
           sv,
           sbv
         )

tests/shared/src/test/resources/resolutions/org.scala-lang/scala-compiler/2.11.8

@@ -0,0 +1,5 @@
+org.scala-lang:scala-compiler:2.11.8:compile
+org.scala-lang:scala-library:2.11.8:compile
+org.scala-lang:scala-reflect:2.11.8:compile
+org.scala-lang.modules:scala-parser-combinators_2.11:1.0.4:compile
+org.scala-lang.modules:scala-xml_2.11:1.0.4:compile

tests/shared/src/test/resources/resolutions/org.scala-lang/scala-compiler/2.11.8_optional

@@ -0,0 +1,6 @@
+jline:jline:2.12.1:compile
+org.scala-lang:scala-compiler:2.11.8:optional
+org.scala-lang:scala-library:2.11.8:compile
+org.scala-lang:scala-reflect:2.11.8:compile
+org.scala-lang.modules:scala-parser-combinators_2.11:1.0.4:compile
+org.scala-lang.modules:scala-xml_2.11:1.0.4:compile

tests/shared/src/test/scala/coursier/test/CentralTests.scala

@@ -465,6 +465,22 @@ object CentralTests extends TestSuite {
         "0.5.0"
       )
     }
+
+    'scalaCompilerJLine - {
+
+      // optional should bring jline
+
+      * - resolutionCheck(
+        Module("org.scala-lang", "scala-compiler"),
+        "2.11.8"
+      )
+
+      * - resolutionCheck(
+        Module("org.scala-lang", "scala-compiler"),
+        "2.11.8",
+        configuration = "optional"
+      )
+    }
   }
 
 }