Add support for fallback artifact in SBT plugin

build.sbt

@@ -413,7 +413,8 @@ lazy val plugin = project
     scriptedLaunchOpts ++= Seq(
       "-Xmx1024M",
       "-XX:MaxPermSize=256M",
-      "-Dplugin.version=" + version.value
+      "-Dplugin.version=" + version.value,
+      "-Dsbttest.base=" + (sourceDirectory.value / "sbt-test").getAbsolutePath
     ),
     scriptedBufferLog := false
   )

plugin/src/main/scala-2.10/coursier/CoursierPlugin.scala

@@ -20,6 +20,7 @@ object CoursierPlugin extends AutoPlugin {
     val coursierVerbosity = Keys.coursierVerbosity
     val coursierResolvers = Keys.coursierResolvers
     val coursierSbtResolvers = Keys.coursierSbtResolvers
+    val coursierFallbackDependencies = Keys.coursierFallbackDependencies
     val coursierCache = Keys.coursierCache
     val coursierProject = Keys.coursierProject
     val coursierProjects = Keys.coursierProjects
@@ -39,6 +40,7 @@ object CoursierPlugin extends AutoPlugin {
     coursierVerbosity := Settings.defaultVerbosityLevel,
     coursierResolvers <<= Tasks.coursierResolversTask,
     coursierSbtResolvers <<= externalResolvers in updateSbtClassifiers,
+    coursierFallbackDependencies <<= Tasks.coursierFallbackDependenciesTask,
     coursierCache := Cache.default,
     update <<= Tasks.updateTask(withClassifiers = false),
     updateClassifiers <<= Tasks.updateTask(withClassifiers = true),

plugin/src/main/scala-2.10/coursier/FallbackDependenciesRepository.scala

@@ -0,0 +1,55 @@
+package coursier
+
+import java.net.URL
+
+import scalaz.{ EitherT, Monad }
+
+case class FallbackDependenciesRepository(
+  fallbacks: Map[(Module, String), (URL, Boolean)]
+) extends Repository {
+
+  private val source = new Artifact.Source {
+    def artifacts(
+      dependency: Dependency,
+      project: Project,
+      overrideClassifiers: Option[Seq[String]]
+    ) =
+      fallbacks.get(dependency.moduleVersion) match {
+        case None => Nil
+        case Some((url, changing)) =>
+          Seq(
+            Artifact(url.toString, Map.empty, Map.empty, Attributes("jar", ""), changing)
+          )
+      }
+  }
+
+  def find[F[_]](
+    module: Module,
+    version: String,
+    fetch: Fetch.Content[F]
+  )(implicit
+    F: Monad[F]
+  ): EitherT[F, String, (Artifact.Source, Project)] =
+    fallbacks.get((module, version)) match {
+      case None =>
+        EitherT.left(F.point("No fallback URL found"))
+
+      case Some((url, _)) =>
+        val proj = Project(
+          module,
+          version,
+          Nil,
+          Map.empty,
+          None,
+          Nil,
+          Nil,
+          Nil,
+          None,
+          None,
+          Nil,
+          Info.empty
+        )
+
+        EitherT.right(F.point((source, proj)))
+    }
+}

plugin/src/main/scala-2.10/coursier/FromSbt.scala

@@ -2,7 +2,7 @@ package coursier
 
 import coursier.ivy.{ IvyXml, IvyRepository }
 
-import java.net.MalformedURLException
+import java.net.{ MalformedURLException, URL }
 
 import sbt.{ Resolver, CrossVersion, ModuleID }
 import sbt.mavenint.SbtPomExtraProperties
@@ -85,6 +85,20 @@ object FromSbt {
     } yield from -> dep.copy(configuration = to, attributes = attr)
   }
 
+  def fallbackDependencies(
+    allDependencies: Seq[ModuleID],
+    scalaVersion: String,
+    scalaBinaryVersion: String
+  ): Seq[(Module, String, URL, Boolean)] =
+    for {
+      module <- allDependencies
+      artifact <- module.explicitArtifacts
+      url <- artifact.url.toSeq
+    } yield {
+      val (module0, version) = moduleVersion(module, scalaVersion, scalaBinaryVersion)
+      (module0, version, url, module.isChanging)
+    }
+
   def project(
     projectID: ModuleID,
     allDependencies: Seq[ModuleID],

plugin/src/main/scala-2.10/coursier/Keys.scala

@@ -1,6 +1,8 @@
 package coursier
 
 import java.io.File
+import java.net.URL
+
 import coursier.core.Publication
 import sbt.{ GetClassifiersModule, Resolver, SettingKey, TaskKey }
 
@@ -18,6 +20,8 @@ object Keys {
 
   val coursierCache = SettingKey[File]("coursier-cache", "")
 
+  val coursierFallbackDependencies = TaskKey[Seq[(Module, String, URL, Boolean)]]("coursier-fallback-dependencies", "")
+
   val coursierProject = TaskKey[Project]("coursier-project", "")
   val coursierProjects = TaskKey[Seq[Project]]("coursier-projects", "")
   val coursierPublications = TaskKey[Seq[(String, Publication)]]("coursier-publications", "")

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

@@ -1,6 +1,7 @@
 package coursier
 
 import java.io.{ OutputStreamWriter, File }
+import java.net.URL
 import java.nio.file.Files
 import java.util.concurrent.Executors
 
@@ -42,6 +43,26 @@ object Tasks {
       }
     }
 
+  def coursierFallbackDependenciesTask: Def.Initialize[sbt.Task[Seq[(Module, String, URL, Boolean)]]] =
+    (
+      sbt.Keys.state,
+      sbt.Keys.thisProjectRef
+    ).flatMap { (state, projectRef) =>
+
+      val allDependenciesTask = allDependencies.in(projectRef).get(state)
+
+      for {
+        allDependencies <- allDependenciesTask
+      } yield {
+
+        FromSbt.fallbackDependencies(
+          allDependencies,
+          scalaVersion.in(projectRef).get(state),
+          scalaBinaryVersion.in(projectRef).get(state)
+        )
+      }
+    }
+
   def coursierProjectTask: Def.Initialize[sbt.Task[Project]] =
     (
       sbt.Keys.state,
@@ -181,19 +202,31 @@ object Tasks {
 
       lazy val cm = coursierSbtClassifiersModule.value
 
-      val currentProject =
-        if (sbtClassifiers)
-          FromSbt.project(
+      val (currentProject, fallbackDependencies) =
+        if (sbtClassifiers) {
+          val sv = scalaVersion.value
+          val sbv = scalaBinaryVersion.value
+
+          val proj = FromSbt.project(
             cm.id,
             cm.modules,
             cm.configurations.map(cfg => cfg.name -> cfg.extendsConfigs.map(_.name)).toMap,
-            scalaVersion.value,
-            scalaBinaryVersion.value
+            sv,
+            sbv
           )
-        else {
+
+          val fallbackDeps = FromSbt.fallbackDependencies(
+            cm.modules,
+            sv,
+            sbv
+          )
+
+          (proj, fallbackDeps)
+        } else {
           val proj = coursierProject.value
           val publications = coursierPublications.value
-          proj.copy(publications = publications)
+          val fallbackDeps = coursierFallbackDependencies.value
+          (proj.copy(publications = publications), fallbackDeps)
         }
 
       val ivySbt0 = ivySbt.value
@@ -277,7 +310,25 @@ object Tasks {
         "ivy.home" -> (new File(sys.props("user.home")).toURI.getPath + ".ivy2")
       ) ++ sys.props
 
-      val repositories = Seq(globalPluginsRepo, interProjectRepo) ++ resolvers.flatMap(FromSbt.repository(_, ivyProperties))
+      val repositories = Seq(
+        globalPluginsRepo,
+        interProjectRepo
+      ) ++ resolvers.flatMap(
+        FromSbt.repository(_, ivyProperties)
+      ) ++ {
+        if (fallbackDependencies.isEmpty)
+          Nil
+        else {
+          val map = fallbackDependencies.map {
+            case (mod, ver, url, changing) =>
+              (mod, ver) -> ((url, changing))
+          }.toMap
+
+          Seq(
+            FallbackDependenciesRepository(map)
+          )
+        }
+      }
 
       def report = {
         val pool = Executors.newFixedThreadPool(parallelDownloads, Strategy.DefaultDaemonThreadFactory)

plugin/src/sbt-test/sbt-coursier/from/build.sbt

@@ -0,0 +1,31 @@
+scalaVersion := "2.11.8"
+
+libraryDependencies += "com.chuusai" %% "shapeless" % "2.3.41" from {
+  
+  val f = file(sys.props("sbttest.base")) / "sbt-coursier" / "from" / "shapeless_2.11-2.3.0.jar"
+
+  if (!f.exists()) {
+    val url0 = "https://repo1.maven.org/maven2/com/chuusai/shapeless_2.11/2.3.0/shapeless_2.11-2.3.0.jar"
+
+    scala.Console.err.println(s"Fetching $url0")
+
+    val url = new java.net.URL(url0)
+
+    val is = url.openStream()
+    val os = new java.io.FileOutputStream(f)
+
+    var read = -1
+    val b = Array.fill[Byte](16*1024)(0)
+    while ({
+      read = is.read(b)
+      read >= 0
+    }) {
+      os.write(b, 0, read)
+    }
+
+    is.close()
+    os.close()
+  }
+
+  f.toURI.toString
+}

plugin/src/sbt-test/sbt-coursier/from/project/plugins.sbt

@@ -0,0 +1,11 @@
+{
+  val pluginVersion = sys.props.getOrElse(
+    "plugin.version",
+    throw new RuntimeException(
+      """|The system property 'plugin.version' is not defined.
+         |Specify this property using the scriptedLaunchOpts -D.""".stripMargin
+    )
+  )
+
+  addSbtPlugin("io.get-coursier" % "sbt-coursier" % pluginVersion)
+}

plugin/src/sbt-test/sbt-coursier/from/src/main/scala/Main.scala

@@ -0,0 +1,13 @@
+import java.io.File
+import java.nio.file.Files
+
+import shapeless._
+
+object Main extends App {
+  case class CC(s: String)
+  val cc = CC("OK")
+  val l = Generic[CC].to(cc)
+  val msg = l.head
+
+  Files.write(new File("output").toPath, msg.getBytes("UTF-8"))
+}

plugin/src/sbt-test/sbt-coursier/from/test

@@ -0,0 +1,3 @@
+$ delete output
+> run
+$ exists output