Rewrite timestamp formatting using Java 8 Instant

Author: jchadwick-buf

build.gradle.kts

@@ -264,7 +264,6 @@ mavenPublishing {
 dependencies {
     annotationProcessor(libs.nullaway)
     api(libs.protobuf.java)
-    implementation(libs.protobuf.java.util)
     implementation(enforcedPlatform(libs.cel))
     implementation(libs.cel.core)
     implementation(libs.guava)

gradle/libs.versions.toml

@@ -25,7 +25,6 @@ junit-bom = { module = "org.junit:junit-bom", version.ref = "junit" }
 maven-plugin = { module = "com.vanniktech:gradle-maven-publish-plugin", version.ref = "maven-publish" }
 nullaway = { module = "com.uber.nullaway:nullaway", version = "0.12.1" }
 protobuf-java = { module = "com.google.protobuf:protobuf-java", version.ref = "protobuf" }
-protobuf-java-util = { module = "com.google.protobuf:protobuf-java-util", version.ref = "protobuf" }
 spotless = { module = "com.diffplug.spotless:spotless-plugin-gradle", version = "6.25.0" }
 
 [plugins]

src/main/java/build/buf/protovalidate/internal/celext/Format.java

@@ -14,11 +14,13 @@
 
 package build.buf.protovalidate.internal.celext;
 
+import static java.time.format.DateTimeFormatter.ISO_INSTANT;
+
 import com.google.protobuf.Duration;
 import com.google.protobuf.Timestamp;
-import com.google.protobuf.util.Timestamps;
 import java.nio.charset.StandardCharsets;
 import java.text.DecimalFormat;
+import java.time.Instant;
 import java.util.List;
 import org.projectnessie.cel.common.types.Err.ErrException;
 import org.projectnessie.cel.common.types.IntT;
@@ -214,7 +216,8 @@ private static void formatList(StringBuilder builder, Val val) {
    */
   private static void formatTimestamp(StringBuilder builder, Val val) {
     Timestamp timestamp = val.convertToNative(Timestamp.class);
-    builder.append(Timestamps.toString(timestamp));
+    Instant instant = Instant.ofEpochSecond(timestamp.getSeconds(), timestamp.getNanos());
+    builder.append(ISO_INSTANT.format(instant));
   }
 
   /**