add patched version of sbt.util.Changed (see discussion in sbt#57)

godenji · Aug 10, 2017 · 71a91b0 · 71a91b0
1 parent 703c585
commit 71a91b0
Showing 1 changed file with 24 additions and 3 deletions.
diff --git a/src/main/scala-sbt-1.0/com/typesafe/sbt/SbtCompat.scala b/src/main/scala-sbt-1.0/com/typesafe/sbt/SbtCompat.scala
@@ -1,8 +1,8 @@
 package com.typesafe.sbt
 
 import java.io.File
-import sbt.{Changed, FileInfo}
-import sbt.util.{CacheStore, CacheStoreFactory}
+import sbt.FileInfo
+import sbt.util.{CacheStore, CacheStoreFactory, Tracked}
 import sjsonnew.JsonFormat
 
 object SbtCompat {
@@ -14,5 +14,26 @@ object SbtCompat {
       sbt.FileFunction.cached(CacheStoreFactory(cacheBaseDirectory), inStyle, outStyle)(action)
   }
 
-  def changed[O: Equiv: JsonFormat](store: File): Changed[O] = new Changed[O](CacheStore(store))
+  def changed[O: Equiv: JsonFormat](store: File) = {
+    new Changed[O](CacheStore(store))
+  }
+
+  private[sbt] class Changed[O: Equiv: JsonFormat](val store: CacheStore) extends Tracked {
+    def clean() = store.delete()
+
+    def apply[O2](ifChanged: O => O2, ifUnchanged: O => O2): O => O2 = value => {
+      if (uptodate(value)) ifUnchanged(value)
+      else {
+        update(value)
+        ifChanged(value)
+      }
+    }
+
+    def update(value: O): Unit = store.write(value)
+    def uptodate(value: O): Boolean = {
+      val equiv: Equiv[O] = implicitly
+      try { equiv.equiv(value, store.read[O]) }
+      catch { case _: Exception => false }
+    }
+  }
 }