Restore support for SOURCE_DATE_EPOCH env var

Author: marcphilipp

gradle/plugins/build-parameters/build.gradle.kts

@@ -70,7 +70,8 @@ buildParameters {
 	}
 	group("manifest") {
 		string("buildTimestamp") {
-			description = "Overrides the value of the 'Build-Date' and 'Build-Time' jar manifest entries (e.g. '2023-11-05 17:49:13.996+0100')."
+			description = "Overrides the value of the 'Build-Date' and 'Build-Time' jar manifest entries. Can be set as a String (e.g. '2023-11-05 17:49:13.996+0100') or as seconds since the epoch."
+			fromEnvironment("SOURCE_DATE_EPOCH") // see https://reproducible-builds.org/docs/source-date-epoch/
 		}
 		string("builtBy") {
 			description = "Overrides the value of the 'Built-By' jar manifest entry"

gradle/plugins/common/src/main/kotlin/junitbuild.build-metadata.gradle.kts

@@ -1,4 +1,6 @@
+import java.time.Instant
 import java.time.OffsetDateTime
+import java.time.ZoneOffset
 import java.time.format.DateTimeFormatter
 import java.time.format.DateTimeFormatterBuilder
 
@@ -11,12 +13,14 @@ val timeFormatter = DateTimeFormatter.ofPattern("HH:mm:ss.SSSZ")
 
 val buildTimeAndDate = buildParameters.manifest.buildTimestamp
 	.map {
-		DateTimeFormatterBuilder()
-			.append(dateFormatter)
-			.appendLiteral(' ')
-			.append(timeFormatter)
-			.toFormatter()
-			.parse(it)
+		it.toLongOrNull()
+			?.let { s -> Instant.ofEpochSecond(s).atOffset(ZoneOffset.UTC) }
+			?: DateTimeFormatterBuilder()
+				.append(dateFormatter)
+				.appendLiteral(' ')
+				.append(timeFormatter)
+				.toFormatter()
+				.parse(it)
 	}
 	.orNull
 	?: OffsetDateTime.now()

gradle/scripts/checkBuildReproducibility.sh

@@ -2,16 +2,16 @@
 
 rm -rf checksums*
 
-BUILD_TIMESTAMP=$(date -Iseconds)
+export SOURCE_DATE_EPOCH=$(date +%s)
 
 function calculate_checksums() {
     OUTPUT=$1
 
     ./gradlew \
+        --configuration-cache \
         --no-build-cache \
         -Porg.gradle.java.installations.auto-download=false \
         -Dscan.tag.Reproducibility \
-        -Pmanifest.buildTimestamp="${BUILD_TIMESTAMP}" \
         clean \
         assemble