reproducible builds: SOURCE_DATE_EPOCH support - Remove some non-determinism - closes #2547, by @gsantner

Author: gsantner

build.gradle

@@ -104,5 +104,10 @@ ext.getGitLastCommitMessage = providers.exec {
 static String getBuildDate() {
     final SimpleDateFormat RFC3339_LIKE = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm'Z'")
     RFC3339_LIKE.setTimeZone(TimeZone.getTimeZone("UTC"))
-    return RFC3339_LIKE.format(new Date())
+    Date buildDate = new Date()
+
+    // https://reproducible-builds.org/docs/source-date-epoch/
+    try { buildDate = new Date(Long.parseLong(System.getenv('SOURCE_DATE_EPOCH')) * 1000) } catch(Exception ignore) {}
+
+    return RFC3339_LIKE.format(buildDate)
 }