Warn in case of source dependencies where sbt-coursier isn't enabled

modules/sbt-coursier-shared/src/main/scala/coursier/sbtcoursiershared/InputsTasks.scala

@@ -102,10 +102,17 @@ object InputsTasks {
 
       val projectRefs = Structure.allRecursiveInterDependencies(state, projectRef)
 
-      val t = coursierProject.forAllProjects(state, projectRefs).map(_.values.toVector)
+      val t = coursierProject.forAllProjectsOpt(state, projectRefs)
 
       Def.task {
-        val projects = t.value
+        val projects = t.value.toVector.flatMap {
+          case (ref, None) =>
+            if (ref.build != projectRef.build)
+              state.log.warn(s"Cannot get coursier info for project under ${ref.build}, is sbt-coursier also added to it?")
+            Nil
+          case (_, Some(p)) =>
+            Seq(p)
+        }
         val projectModules = projects.map(_.module).toSet
 
         // this includes org.scala-sbt:global-plugins referenced from meta-builds in particular

modules/sbt-coursier-shared/src/main/scala/coursier/sbtcoursiershared/Structure.scala

@@ -54,5 +54,21 @@ object Structure {
       val tasks = projects.flatMap(p => key.in(p).get(structure(state).data).map(_.map(it => (p, it))))
       std.TaskExtra.joinTasks(tasks).join.map(_.toMap)
     }
+
+    // ^^ things from sbt-structure ^^
+
+    def forAllProjectsOpt(state: State, projects: Seq[ProjectRef]): sbt.Task[Map[ProjectRef, Option[T]]] = {
+      val settings = structure(state).data
+      val tasks = projects.map { p =>
+        val taskOpt = key.in(p).get(settings)
+        taskOpt match {
+          case None =>
+            Def.task(p -> Option.empty[T]).evaluate(settings)
+          case Some(t) =>
+            t.map(p -> Option(_))
+        }
+      }
+      std.TaskExtra.joinTasks(tasks).join.map(_.toMap)
+    }
   }
 }