Fix '~' for dependent projects with a broken parent

In #4446, @japgolly reported that in some projects, if a parent project
was broken, then '~' would immediately exit upon startup. I tracked it
down to this managed sources filter. The idea of this filter is to avoid
getting stuck in a build loop if managedSources writes into an unmanaged
source directory. If the (managedSources in ThisScope).value line
failed, however, it would cause the watchSources, and by delegation,
watchTransitiveSources task to fail. The fix is to only create this
filter if the managedSources task succeeds.

I'm not 100% sure if we shouldn't just get rid of this filter entirely
and just document that '~' will probably loop if a build writes the
result of managedSources into an unmanaged source directory.

.travis.yml

@@ -41,7 +41,7 @@ env:
     - SBT_CMD="scripted source-dependencies/*1of3"
     - SBT_CMD="scripted source-dependencies/*2of3"
     - SBT_CMD="scripted source-dependencies/*3of3"
-    - SBT_CMD="scripted tests/*"
+    - SBT_CMD="scripted tests/* watch/*"
     - SBT_CMD="repoOverrideTest:scripted dependency-management/*"
 
 notifications:

main/src/main/scala/sbt/Defaults.scala

@@ -361,8 +361,10 @@ object Defaults extends BuildCommon {
       val include = (includeFilter in unmanagedSources).value
       val exclude = (excludeFilter in unmanagedSources).value match {
         case e =>
-          (managedSources in ThisScope).value match {
+          val s = state.value
-            case l if l.nonEmpty =>
+          try {
+            Project.extract(s).runTask(managedSources in Compile in ThisScope, s) match {
+              case (_, l) if l.nonEmpty =>
                 e || new FileFilter {
                   private val files = l.toSet
                   override def accept(pathname: File): Boolean = files.contains(pathname)
@@ -370,6 +372,9 @@ object Defaults extends BuildCommon {
                 }
               case _ => e
             }
+          } catch {
+            case NonFatal(_) => e
+          }
       }
       val baseSources =
         if (sourcesInBase.value) Seq(new Source(baseDir, include, exclude, recursive = false))

sbt/src/sbt-test/watch/watch-sources/build.sbt

@@ -0,0 +1,3 @@
+lazy val root = (project in file(".")).aggregate(parent, child)
+lazy val parent = project
+lazy val child = project.enablePlugins(JmhPlugin).dependsOn(parent)

sbt/src/sbt-test/watch/watch-sources/changes/Foo.scala

@@ -0,0 +1 @@
+class Foo

sbt/src/sbt-test/watch/watch-sources/child/src/main/scala/Bar.scala

@@ -0,0 +1 @@
+class Bar

sbt/src/sbt-test/watch/watch-sources/parent/src/main/scala/Foo.scala

@@ -0,0 +1 @@
+class Foo {

sbt/src/sbt-test/watch/watch-sources/project/plugin.sbt

@@ -0,0 +1 @@
+addSbtPlugin("pl.project13.scala" % "sbt-jmh" % "0.3.4")

sbt/src/sbt-test/watch/watch-sources/test

@@ -0,0 +1,9 @@
+> watchTransitiveSources
+
+-> compile
+
+$ copy-file changes/Foo.scala parent/src/main/scala/Foo.scala
+
+> watchTransitiveSources
+
+> compile