Allow overriding JAR manifest entries for reproducibility

With these changes, the `Build-Date`, `Build-Time`, and `Created-By`
manifest entries can be taken from the released JARs and passed to the
build in order to check for reproducibility:

    ./gradlew assemble \
        -Pmanifest.buildTimestamp='2024-01-07 14:00:54.292+0100' \
        -Pmanifest.createdBy='21.0.1 (BellSoft 21.0.1+12-LTS)'

Closes #3559.

gradle.properties

@@ -9,8 +9,6 @@ platformVersion = 1.11.0-SNAPSHOT
 vintageGroup    = org.junit.vintage
 vintageVersion  = 5.11.0-SNAPSHOT
 
-defaultBuiltBy  = JUnit Team
-
 # We need more metaspace due to apparent memory leak in Asciidoctor/JRuby
 # The exports are needed due to https://github.com/diffplug/spotless/issues/834
 org.gradle.jvmargs=-Xmx1g -XX:MaxMetaspaceSize=512m -XX:+HeapDumpOnOutOfMemoryError \

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

@@ -68,4 +68,15 @@ buildParameters {
 			description = "Sign artifacts before publishing them to Maven repos"
 		}
 	}
+	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')."
+		}
+		string("builtBy") {
+			description = "Overrides the value of the 'Built-By' jar manifest entry"
+		}
+		string("createdBy") {
+			description = "Overrides the value of the 'Created-By' jar manifest entry"
+		}
+	}
 }

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

@@ -1,28 +1,30 @@
-import java.time.Instant
 import java.time.OffsetDateTime
-import java.time.ZoneOffset
 import java.time.format.DateTimeFormatter
+import java.time.format.DateTimeFormatterBuilder
 
-val buildTimeAndDate =
-	if (System.getenv().containsKey("SOURCE_DATE_EPOCH")) {
-
-		// SOURCE_DATE_EPOCH is a UNIX timestamp for pinning build metadata against
-		// in order to achieve reproducible builds
-		//
-		// More details - https://reproducible-builds.org/docs/source-date-epoch/
-		val sourceDateEpoch = System.getenv("SOURCE_DATE_EPOCH").toLong()
+plugins {
+	id("junitbuild.build-parameters")
+}
 
-		Instant.ofEpochSecond(sourceDateEpoch).atOffset(ZoneOffset.UTC)
+val dateFormatter = DateTimeFormatter.ISO_LOCAL_DATE
+val timeFormatter = DateTimeFormatter.ofPattern("HH:mm:ss.SSSZ")
 
-	} else {
-		OffsetDateTime.now()
+val buildTimeAndDate = buildParameters.manifest.buildTimestamp
+	.map {
+		DateTimeFormatterBuilder()
+			.append(dateFormatter)
+			.appendLiteral(' ')
+			.append(timeFormatter)
+			.toFormatter()
+			.parse(it)
 	}
+	.orNull
+	?: OffsetDateTime.now()
 
-val buildDate: String by extra { DateTimeFormatter.ISO_LOCAL_DATE.format(buildTimeAndDate) }
-val buildTime: String by extra { DateTimeFormatter.ofPattern("HH:mm:ss.SSSZ").format(buildTimeAndDate) }
+val buildDate: String by extra { dateFormatter.format(buildTimeAndDate) }
+val buildTime: String by extra { timeFormatter.format(buildTimeAndDate) }
 val buildRevision: String by extra {
 	providers.exec {
 		commandLine("git", "rev-parse", "--verify", "HEAD")
 	}.standardOutput.asText.get()
 }
-val builtByValue by extra { project.findProperty("builtBy") ?: project.property("defaultBuiltBy") }

gradle/plugins/common/src/main/kotlin/junitbuild.java-library-conventions.gradle.kts

@@ -11,6 +11,7 @@ plugins {
 	idea
 	checkstyle
 	id("junitbuild.base-conventions")
+	id("junitbuild.build-parameters")
 	id("junitbuild.jacoco-java-conventions")
 }
 
@@ -19,7 +20,6 @@ val modularProjects: List<Project> by rootProject.extra
 val buildDate: String by rootProject.extra
 val buildTime: String by rootProject.extra
 val buildRevision: Any by rootProject.extra
-val builtByValue: String by rootProject.extra
 
 val extension = extensions.create<JavaLibraryExtension>("javaLibrary")
 
@@ -211,8 +211,9 @@ tasks.withType<Jar>().configureEach {
 tasks.jar {
 	manifest {
 		attributes(
-				"Created-By" to "${System.getProperty("java.version")} (${System.getProperty("java.vendor")} ${System.getProperty("java.vm.version")})",
-				"Built-By" to builtByValue,
+				"Created-By" to (buildParameters.manifest.createdBy.orNull
+					?: "${System.getProperty("java.version")} (${System.getProperty("java.vendor")} ${System.getProperty("java.vm.version")})"),
+				"Built-By" to buildParameters.manifest.builtBy.orElse("JUnit Team"),
 				"Build-Date" to buildDate,
 				"Build-Time" to buildTime,
 				"Build-Revision" to buildRevision,

gradle/scripts/checkBuildReproducibility.sh

@@ -2,18 +2,24 @@
 
 rm -rf checksums*
 
-export SOURCE_DATE_EPOCH=$(date +%s)
+BUILD_TIMESTAMP=$(date -Iseconds)
 
 function calculate_checksums() {
     OUTPUT=$1
 
-    ./gradlew --no-build-cache clean assemble --parallel -Porg.gradle.java.installations.auto-download=false -Dscan.tag.Reproducibility
+    ./gradlew \
+        --no-build-cache \
+        -Porg.gradle.java.installations.auto-download=false \
+        -Dscan.tag.Reproducibility \
+        -Pmanifest.buildTimestamp="${BUILD_TIMESTAMP}" \
+        clean \
+        assemble
 
     find . -name '*.jar' \
         | grep '/build/libs/' \
         | grep --invert-match 'javadoc' \
         | sort \
-        | xargs sha256sum > ${OUTPUT}
+        | xargs sha256sum > "${OUTPUT}"
 }