Fixes sbt#1634. Adds inconsistent duplicate warning

sbt#1634 is about a library getting wiped out of deps graph when it’s
included twice in ascending order of version.
I’d say that’s a logically inconsistent state, and we should just issue
warning instead of trying to fix it.

ivy/src/main/scala/sbt/Ivy.scala

@@ -527,6 +527,29 @@ private[sbt] object IvySbt {
       parser
     }
 
+  def inconsistentDuplicateWarning(moduleID: DefaultModuleDescriptor): List[String] =
+    {
+      import IvyRetrieve.toModuleID
+      val dds = moduleID.getDependencies
+      inconsistentDuplicateWarning(dds map { dd => toModuleID(dd.getDependencyRevisionId) })
+    }
+
+  def inconsistentDuplicateWarning(dependencies: Seq[ModuleID]): List[String] =
+    {
+      val warningHeader = "Multiple dependencies with the same organization/name but different versions. To avoid conflict, pick one version:"
+      val out: mutable.ListBuffer[String] = mutable.ListBuffer()
+      (dependencies groupBy { dep => (dep.organization, dep.name) }) foreach {
+        case (k, vs) if vs.size > 1 =>
+          val v0 = vs.head
+          (vs find { _.revision != v0.revision }) foreach { v =>
+            out += s" * ${v0.organization}:${v0.name}:(" + (vs map { _.revision }).mkString(", ") + ")"
+          }
+        case _ => ()
+      }
+      if (out.isEmpty) Nil
+      else warningHeader :: out.toList
+    }
+
   /** This method is used to add inline dependencies to the provided module. */
   def addDependencies(moduleID: DefaultModuleDescriptor, dependencies: Seq[ModuleID], parser: CustomXmlParser.CustomParser) {
     val converted = dependencies map { dependency => convertDependency(moduleID, dependency, parser) }

ivy/src/main/scala/sbt/IvyActions.scala

@@ -166,6 +166,8 @@ object IvyActions {
       case (ivy, md, default) if module.owner.configuration.updateOptions.cachedResolution && depDir.isDefined =>
         ivy.getResolveEngine match {
           case x: CachedResolutionResolveEngine =>
+            val iw = IvySbt.inconsistentDuplicateWarning(md)
+            iw foreach { log.warn(_) }
             val resolveOptions = new ResolveOptions
             val resolveId = ResolveOptions.getDefaultResolveId(md)
             resolveOptions.setResolveId(resolveId)
@@ -181,6 +183,8 @@ object IvyActions {
             }
         }
       case (ivy, md, default) =>
+        val iw = IvySbt.inconsistentDuplicateWarning(md)
+        iw foreach { log.warn(_) }
         val (report, err) = resolve(configuration.logging)(ivy, md, default)
         err match {
           case Some(x) if !configuration.missingOk =>

ivy/src/test/scala/InconsistentDuplicateSpec.scala

@@ -0,0 +1,28 @@
+package sbt
+
+import org.specs2._
+
+class InconsistentDuplicateSpec extends Specification {
+  def is = s2"""
+
+  This is a specification to check the inconsistent duplicate warnings
+
+  Duplicate with different version should
+    be warned                                                   $warn1
+
+  Duplicate with same version should
+    not be warned                                               $nodupe1
+                                                                """
+
+  def akkaActor214 = ModuleID("com.typesafe.akka", "akka-actor", "2.1.4", Some("compile")) cross CrossVersion.binary
+  def akkaActor230 = ModuleID("com.typesafe.akka", "akka-actor", "2.3.0", Some("compile")) cross CrossVersion.binary
+  def akkaActor230Test = ModuleID("com.typesafe.akka", "akka-actor", "2.3.0", Some("test")) cross CrossVersion.binary
+
+  def warn1 =
+    IvySbt.inconsistentDuplicateWarning(Seq(akkaActor214, akkaActor230)) must_==
+      List("Multiple dependencies with the same organization/name but different versions. To avoid conflict, pick one version:",
+        " * com.typesafe.akka:akka-actor:(2.1.4, 2.3.0)")
+
+  def nodupe1 =
+    IvySbt.inconsistentDuplicateWarning(Seq(akkaActor230Test, akkaActor230)) must_== Nil
+}

notes/0.13.8/inconsistent-duplicates.markdown

@@ -0,0 +1,13 @@
+  [@cunei]: https://github.com/cunei
+  [@eed3si9n]: https://github.com/eed3si9n
+  [@gkossakowski]: https://github.com/gkossakowski
+  [@jsuereth]: https://github.com/jsuereth
+  [1634]: https://github.com/sbt/sbt/pull/1634
+
+### Fixes with compatibility implications
+
+### Improvements
+
+### Bug fixes
+
+- Issues warning if multiple dependencies to a same library is found with different version. [#1634][1634] by [@eed3si9n][@eed3si9n]