add warining in case no JDK is found

2 files changed, 17 insertions, 5 deletions

diff --git a/project/Build.scala b/project/Build.scala
index bfadd37..bd31c1b 100644
--- a/project/Build.scala
+++ b/project/Build.scala
@@ -118,7 +118,7 @@ object FlowBuild extends Build {
     settings (unixNativeSettings: _*)
     settings (
       target := baseDirectory.value / "target" / "linux",
-      includeDirectories in Native += jdkHome.value / "include" / "linux",
+      includeDirectories in Native ++= jdkHome.value.map(jdk => jdk / "include" / "linux").toSeq,
       linkFlags in Native ++= Seq("-shared", s"-Wl,-soname,libflow.so.${BinaryMajorVersion}"),
       binaryName in Native := s"libflow.so.${BinaryMajorVersion}.${UnixBinaryMinorVersion}"
     )
diff --git a/project/jni.scala b/project/jni.scala
index 7cde93b..5e248f2 100644
--- a/project/jni.scala
+++ b/project/jni.scala
@@ -1,9 +1,11 @@
 import sbt._
 import Keys._
 import NativeKeys._
+import scala.util.Try
 
 object JniKeys {
-  val jdkHome = settingKey[File]("Home of JDK.")
+  val jdkHome = settingKey[Option[File]]("Home of JDK.")
+  val jdkHomeNotFound = taskKey[Unit]("Utility task that informs user that no JDK was found.")
   val javahHeaderDirectory = settingKey[File]("Directory where generated javah header files are placed.")
   val javahClasses = settingKey[Seq[String]]("Fully qualified names of classes containing native declarations.")
   val javahClasspath = taskKey[Seq[File]]("Classpath to use in javah.")
@@ -14,12 +16,22 @@ object JniDefaults {
   import JniKeys._
 
   val defaultSettings: Seq[Setting[_]] = Seq(
-    jdkHome := file(sys.env("JAVA_HOME")),
+    jdkHome := Try(file(sys.env("JAVA_HOME"))).toOption,
+    jdkHomeNotFound := jdkHomeNotFoundImpl.value,
+    nativeCompile in Native := ((nativeCompile in Native) dependsOn jdkHomeNotFound).value,
     javahHeaderDirectory := (sourceManaged in Native).value / "javah",
-    javah := javahImpl.value, 
+    javah := javahImpl.value,
     sourceGenerators in Native <+= javah map { headers => headers},
     includeDirectories in Native += javahHeaderDirectory.value,
-    includeDirectories in Native += jdkHome.value / "include")
+    includeDirectories in Native ++= jdkHome.value.map( jdk => jdk / "include").toSeq)
+    
+  def jdkHomeNotFoundImpl = Def.task {
+    if (jdkHome.value == None) {
+      streams.value.log.warn(
+        "No JDK home directory found, any native code using JNI may not compile. Please set JAVA_HOME environment variable.")
+    }
+    ()
+  } 
 
   def javahImpl = Def.task {
     val cps = javahClasspath.value