make build reproducable

Author: infeo

.github/workflows/build.yml

@@ -222,8 +222,10 @@ jobs:
           distribution: 'temurin'
           java-version: ${{ env.JAVA_VERSION }}
           cache: 'maven'
-      - name: Ensure to use tagged version
-        run: ./mvnw versions:set --file ./pom.xml -DnewVersion=${GITHUB_REF##*/}
+      - name: Ensure to use tagged version and update build timestamp
+        run: |
+          ./mvnw versions:set --file ./pom.xml -DnewVersion=${GITHUB_REF##*/}
+          ./mvnw versions:set-property --file ./pom.xml -Dproperty=project.build.outputTimestamp -DnewVersion="$(date --iso-8601=seconds)"
       - name: Build
         run: >
           ./mvnw -B install -DskipTests

pom.xml

@@ -40,6 +40,8 @@
 		<java.version>25</java.version>
 		<jextract.path>${user.home}/.sdkman/candidates/jextract/current/bin/jextract</jextract.path>
 		<project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
+		<!-- TODO: for reproducible builds, can be removed with Maven 4 -->
+		<project.build.outputTimestamp>2026-01-26T00:00:00Z</project.build.outputTimestamp>
 
 		<jb-annotations.version>26.0.2-1</jb-annotations.version>