From 01be96399ae6cd84ce49525568bd6418bf52e26f Mon Sep 17 00:00:00 2001
From: Jakob Odersky <jakob@odersky.com>
Date: Mon, 3 Jul 2017 16:51:54 -0700
Subject: Add example of reproducible builds

---
 examples/package-example/Main.scala        |  6 +++++
 examples/package-example/build/build.scala | 42 ++++++++++++++++++++++++++++++
 test/test.scala                            |  5 ++++
 3 files changed, 53 insertions(+)
 create mode 100644 examples/package-example/Main.scala
 create mode 100644 examples/package-example/build/build.scala

diff --git a/examples/package-example/Main.scala b/examples/package-example/Main.scala
new file mode 100644
index 0000000..61e6b63
--- /dev/null
+++ b/examples/package-example/Main.scala
@@ -0,0 +1,6 @@
+package package_example
+object Main{
+  def main( args: Array[String] ): Unit = {
+    println( Console.GREEN ++ "Hello World" ++ Console.RESET )
+  }
+}
diff --git a/examples/package-example/build/build.scala b/examples/package-example/build/build.scala
new file mode 100644
index 0000000..3874507
--- /dev/null
+++ b/examples/package-example/build/build.scala
@@ -0,0 +1,42 @@
+package package_example_build
+import java.nio.file._
+import java.security.MessageDigest
+import cbt._
+class Build(val context: Context) extends BaseBuild with PackageJars {
+  override def groupId = "org.example"
+  override def version = "1.0.0"
+
+  def hash(file: Path): String = {
+    val digest = MessageDigest.getInstance("SHA-256");
+    val in = Files.newInputStream(file)
+    try {
+      val chunk = new Array[Byte](4096)
+      while(in.read(chunk) > 0) {
+        digest.update(chunk)
+      }
+    } finally {
+      in.close
+    }
+    val bytes = digest.digest()
+    val builder = new StringBuilder(bytes.length * 2);
+    for(b <- bytes) {
+      builder.append(f"$b%02x")
+    }
+    builder.toString
+  }
+
+  override def run = {
+    val pass1 = super.`package`.map(f => hash(f.toPath))
+    lib.clean(cleanFiles, true, false, false, false)
+    transientCache.clear()
+    val pass2 = super.`package`.map(f => hash(f.toPath))
+
+    assert(
+      pass1 == pass2,
+      "The checksums of jars generated during two separate builds did not match. " +
+        "The build is not reproducible."
+    )
+    ExitCode.Success
+  }
+
+}
diff --git a/test/test.scala b/test/test.scala
index 9cb7fd9..63bcabc 100644
--- a/test/test.scala
+++ b/test/test.scala
@@ -506,6 +506,11 @@ object Main{
       assert(res.exit0)
     }
 
+    {
+      val res = runCbt("../examples/package-example", Seq("run"))
+      assert(res.exit0)
+    }
+
     /*
     // currently fails with
     // java.lang.UnsupportedOperationException: scalafix.rewrite.ScalafixMirror.fromMirror $anon#typeSignature requires the semantic api
-- 
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