Fix Gradle builds with -Werror (#670)

The warning in question is only triggered if there are annotation
processors in the build

Author: keynmol

build.sbt

@@ -357,18 +357,16 @@ lazy val minimizedSettings = List[Def.Setting[_]](
   (run / fork) := true,
   (Compile / unmanagedSourceDirectories) += minimizedSourceDirectory,
   libraryDependencies ++= List("org.projectlombok" % "lombok" % "1.18.22"),
-  javacOptions ++=
-    List[String](
-      s"-Arandomtimestamp=${System.nanoTime()}",
-      List(
-        s"-Xplugin:semanticdb",
-        s"-build-tool:sbt",
-        s"-text:on",
-        s"-verbose",
-        s"-sourceroot:${(ThisBuild / baseDirectory).value}",
-        s"-targetroot:${(Compile / semanticdbTargetRoot).value}"
-      ).mkString(" ")
-    )
+  javacOptions +=
+    List(
+      s"-Xplugin:semanticdb",
+      s"-build-tool:sbt",
+      s"-text:on",
+      s"-verbose",
+      s"-sourceroot:${(ThisBuild / baseDirectory).value}",
+      s"-targetroot:${(Compile / semanticdbTargetRoot).value}",
+      s"-randomtimestamp=${System.nanoTime()}"
+    ).mkString(" ")
 )
 
 lazy val minimized = project

semanticdb-gradle-plugin/src/main/scala/SemanticdbGradlePlugin.scala

@@ -165,8 +165,7 @@ class SemanticdbGradlePlugin extends Plugin[Project] {
                     // TODO: before this plugin is published to Maven Central,
                     // we will need to revert this change - as it can have detrimental
                     // effect on people's builds
-                    s"-Arandomtimestamp=${System.currentTimeMillis()}",
-                    s"-Xplugin:semanticdb -targetroot:$targetRoot -sourceroot:$sourceRoot"
+                    s"-Xplugin:semanticdb -targetroot:$targetRoot -sourceroot:$sourceRoot -randomtimestamp=${System.nanoTime()}"
                   ).asJava
                 )
             }

semanticdb-javac/src/main/java/com/sourcegraph/semanticdb_javac/SemanticdbJavacOptions.java

@@ -97,6 +97,7 @@ public static SemanticdbJavacOptions parse(String[] args, JavacTask task) {
         result.verboseEnabled = true;
       } else if (arg.equals("-verbose:off")) {
         result.verboseEnabled = false;
+      } else if (arg.startsWith("-randomtimestamp")) {
       } else {
         result.errors.add(String.format("unknown flag '%s'\n", arg));
       }
@@ -126,8 +127,10 @@ private static boolean isSourcerootDefined(SemanticdbJavacOptions options) {
   // warning - use of internal API
   // requires --add-exports jdk.compiler/com.sun.tools.javac.api=ALL-UNNAMED
   private static TargetPaths getJavacClassesDir(SemanticdbJavacOptions result, JavacTask task) {
-    // both Context and BasicJavacTask are internal JDK classes so not exported under >= JDK 17
-    //  com.sun.tools.javac.util.Context ctx = ((com.sun.tools.javac.api.BasicJavacTask)
+    // both Context and BasicJavacTask are internal JDK classes so not exported
+    // under >= JDK 17
+    // com.sun.tools.javac.util.Context ctx =
+    // ((com.sun.tools.javac.api.BasicJavacTask)
     // task).getContext();
     // I'm not aware of a better way to get the class output directory from javac
     Path classOutputDir = null;

tests/buildTools/src/test/scala/tests/GradleBuildToolSuite.scala

@@ -50,6 +50,38 @@ abstract class GradleBuildToolSuite(allGradle: List[String])
     gradleVersions = List(Gradle8, Gradle7, Gradle67)
   )
 
+  checkGradleBuild(
+    "build-with-Werror",
+    """|/build.gradle
+       |plugins {
+       |    id 'java-library'
+       |}
+       |repositories {
+       |    // Use Maven Central for resolving dependencies.
+       |    mavenCentral()
+       |}
+       |dependencies {
+       |  compileOnly 'org.immutables:value:2.9.2'
+       |  annotationProcessor 'org.immutables:value:2.9.2'
+       |}
+       |compileJava {
+       | options.compilerArgs << "-Werror"
+       |}
+       |/src/main/java/main/bla/ExampleClass.java
+       |package test;
+       |import org.immutables.value.Value;
+       |import java.util.Optional;
+       |@Value.Immutable
+       |public abstract class ExampleClass {
+       |    public abstract Optional<String> getWorkflowIdReusePolicy();
+       |}
+    """.stripMargin,
+    // See comment about immutable annotation processor above,
+    // it explains why we expecte 2 semanticdb files
+    expectedSemanticdbFiles = 2,
+    gradleVersions = List(Gradle8, Gradle7, Gradle67)
+  )
+
   checkGradleBuild(
     "publishing",
     """|/build.gradle