Catch build issue by comparing release artifacts with jardiff after build job

.gitlab-ci.yml

@@ -495,6 +495,33 @@ test_published_artifacts:
     paths:
       - ./check_reports
 
+validate_build:
+  extends: .gradle_build
+  stage: tests
+  needs: [ build ]
+  variables:
+    CACHE_TYPE: "lib"
+  script:
+    # Preserve the `build` job artifacts before Gradle rebuilds and overwrites them under
+    # workspace/**/build/libs, so jardiff can compare the rebuilt jars against them.
+    - mkdir -p reference-artifacts
+    - cp workspace/dd-java-agent/build/libs/*.jar reference-artifacts/
+    - cp workspace/dd-trace-api/build/libs/*.jar reference-artifacts/
+    - cp workspace/dd-trace-ot/build/libs/*.jar reference-artifacts/
+    - ./gradlew --version
+    # This will run the shadowJar task and exercise the build cache, allowing to identify build-cache issues
+    - ./gradlew compareToReferenceJar -PjardiffReferenceDir="$CI_PROJECT_DIR/reference-artifacts" -PskipTests $GRADLE_ARGS
+  after_script:
+    - source .gitlab/gitlab-utils.sh
+    - gitlab_section_start "collect-reports" "Collecting reports"
+    - .gitlab/collect_reports.sh --destination ./check_reports
+    - gitlab_section_end "collect-reports"
+  artifacts:
+    when: always
+    paths:
+      - ./check_reports
+      - '.gradle/daemon/*/*.out.log'
+
 .check_job:
   extends: .gradle_build
   needs: [ build ]

buildSrc/build.gradle.kts

@@ -73,6 +73,11 @@ gradlePlugin {
       id = "dd-trace-java.sca-enrichments"
       implementationClass = "datadog.gradle.plugin.sca.ScaEnrichmentsPlugin"
     }
+
+    create("jardiff-plugin") {
+      id = "dd-trace-java.jardiff"
+      implementationClass = "datadog.gradle.plugin.jardiff.JardiffPlugin"
+    }
   }
 }
 

buildSrc/src/main/kotlin/datadog/gradle/plugin/jardiff/JardiffComparison.kt

@@ -0,0 +1,84 @@
+package datadog.gradle.plugin.jardiff
+
+import java.io.File
+
+/**
+ * Pure, Gradle-free helpers for driving the [jardiff](https://github.com/bric3/jardiff) CLI.
+ *
+ * Kept separate from [JardiffTask] so the argument construction and exit-code interpretation can
+ * be unit-tested without spinning up a Gradle build or resolving the jardiff jar.
+ */
+object JardiffComparison {
+  /** Outcome of a jardiff run, derived from its process exit value. */
+  enum class Outcome {
+    /** Exit 0 — the two jars are identical (for the selected include/exclude set). */
+    IDENTICAL,
+
+    /** Exit 1 — jardiff reported differences (behaves like `diff(1)` under `--exit-code`). */
+    DIFFERENT,
+
+    /** Any other exit value — jardiff itself failed (bad arguments, unreadable jar, ...). */
+    ERROR,
+  }
+
+  /**
+   * Builds the jardiff argument list comparing [reference] (left) against [candidate] (right).
+   *
+   * [mode] selects the output mode (e.g. `--stat` for a `git diff --stat`-like summary, `--status`,
+   * or blank for the default full diff). `--exit-code` is always added.
+   * The [JardiffTask] relies on the process exit value.
+   * [includes]/[excludes] are comma-joined glob patterns (empty means comparing every entry), and
+   * [additionalOptions] are passed through verbatim, right before the two jars.
+   */
+  fun buildArguments(
+    reference: File,
+    candidate: File,
+    mode: String,
+    includes: List<String> = emptyList(),
+    excludes: List<String> = emptyList(),
+    additionalOptions: List<String> = emptyList(),
+  ): List<String> = buildList {
+    if (mode.isNotBlank()) {
+      add(mode)
+    }
+    add("--exit-code")
+    add("--color=never")
+    if (includes.isNotEmpty()) {
+      add("--include=" + includes.joinToString(","))
+    }
+    if (excludes.isNotEmpty()) {
+      add("--exclude=" + excludes.joinToString(","))
+    }
+    addAll(additionalOptions)
+    // jardiff positional arguments: <left> <right>.
+    // The reference (the artifact validated by the build job) is the left/baseline side,
+    // the freshly built candidate is the right side.
+    add(reference.absolutePath)
+    add(candidate.absolutePath)
+  }
+
+  /** Maps a jardiff process exit value to an [Outcome]. */
+  fun outcomeOf(exitValue: Int): Outcome = when (exitValue) {
+    0 -> Outcome.IDENTICAL
+    1 -> Outcome.DIFFERENT
+    else -> Outcome.ERROR
+  }
+
+  /**
+   * Renders the equivalent `java -cp … <mainClass> <arguments>` shell command, so the comparison
+   * can be copy-pasted and reproduced outside Gradle. Tokens containing shell-significant
+   * characters (spaces, globs, commas, ...) are single-quoted.
+   */
+  fun shellCommandLine(classpath: Iterable<File>, mainClass: String, arguments: List<String>): String {
+    val classpathValue = classpath.joinToString(File.pathSeparator) { it.absolutePath }
+    return (listOf("java", "-cp", classpathValue, mainClass) + arguments)
+      .joinToString(" ", transform = ::shellQuote)
+  }
+
+  private fun shellQuote(token: String): String =
+    if (token.isNotEmpty() && token.all { it.isLetterOrDigit() || it in "/._-=:" }) {
+      token
+    } else {
+      "'" + token.replace("'", "'\\''") + "'"
+    }
+}

buildSrc/src/main/kotlin/datadog/gradle/plugin/jardiff/JardiffExtension.kt

@@ -0,0 +1,43 @@
+package datadog.gradle.plugin.jardiff
+
+import org.gradle.api.file.DirectoryProperty
+import org.gradle.api.provider.ListProperty
+import org.gradle.api.provider.Property
+
+/** Configuration for the [JardiffPlugin]. */
+interface JardiffExtension {
+  /**
+   * Maven coordinate of the jardiff CLI resolved to run the comparison.
+   * Defaults to [JardiffPlugin.DEFAULT_TOOL_COORDINATE].
+   */
+  val toolCoordinate: Property<String>
+
+  /**
+   * Fully qualified main class of the jardiff CLI.
+   * Defaults to [JardiffPlugin.DEFAULT_MAIN_CLASS].
+   */
+  val mainClass: Property<String>
+
+  /**
+   * jardiff output mode flag, e.g. `--stat` or `--status`; blank selects the default full diff.
+   * Defaults to [JardiffPlugin.DEFAULT_MODE].
+   */
+  val mode: Property<String>
+
+  /**
+   * Extra jardiff options passed verbatim, right before the two jars (e.g. `--ignore-member-order`
+   * or `--class-text-producer=javap`). Empty by default.
+   */
+  val additionalOptions: ListProperty<String>
+
+  /**
+   * Directory receiving jardiff reports. Defaults to `build/reports/jardiff` in the target project.
+   */
+  val reportDir: DirectoryProperty
+
+  /**
+   * When true, tolerate mismatching candidate and reference jar hashes if jardiff reports no
+   * differences. Defaults to false.
+   */
+  val ignoreHashCheck: Property<Boolean>
+}

buildSrc/src/main/kotlin/datadog/gradle/plugin/jardiff/JardiffPlugin.kt

@@ -0,0 +1,100 @@
+package datadog.gradle.plugin.jardiff
+
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+import org.gradle.api.tasks.bundling.AbstractArchiveTask
+import org.gradle.kotlin.dsl.create
+import org.gradle.kotlin.dsl.named
+import org.gradle.kotlin.dsl.register
+
+/**
+ * Registers the `compareToReferenceJar` task ([JardiffTask]) and wires its reusable inputs:
+ * - the jardiff CLI classpath (resolved from [JardiffExtension.toolCoordinate]),
+ * - the candidate archive — the module's main publishable jar (the shadow jar when the shadow
+ *   plugin is applied, otherwise the plain jar),
+ * - the reference jar, resolved from the `-PjardiffReferenceDir` project property by matching the
+ *   candidate's file name inside that directory.
+ *
+ * Apply it with `id("dd-trace-java.jardiff")`.
+ */
+class JardiffPlugin : Plugin<Project> {
+  override fun apply(project: Project) {
+    val extension = project.extensions.create<JardiffExtension>("jardiff")
+    extension.toolCoordinate.convention(DEFAULT_TOOL_COORDINATE)
+    extension.mainClass.convention(DEFAULT_MAIN_CLASS)
+    extension.mode.convention(DEFAULT_MODE)
+    extension.additionalOptions.convention(emptyList())
+    extension.reportDir.convention(project.layout.buildDirectory.dir("reports/jardiff"))
+    extension.ignoreHashCheck.convention(false)
+
+    // Use a detached configuration (created here, resolved only when the task runs)
+    // 
+    // This keeps the jardiff artifact out of `lockAllConfigurations()` dependency locking.
+    // The dependency is added lazily, so overriding `jardiff.toolCoordinate` still takes effect.
+    // The `@jar` requests the artifact only, because jardiff ships a self-contained "fat" CLI jar
+    // under a non-default Gradle Module Metadata variant, the default resolution misses it.
+    // Appending `@jar` ignores metadata and fetches that jar.
+    val toolClasspath = project.configurations.detachedConfiguration().apply {
+      dependencies.addLater(
+        extension.toolCoordinate.map { coordinate ->
+          val artifactOnly = if ('@' in coordinate) coordinate else "$coordinate@jar"
+          project.dependencies.create(artifactOnly)
+        },
+      )
+    }
+
+    val projectDirectory = project.layout.projectDirectory
+    val referenceDirProperty =
+      project.providers.gradleProperty("jardiffReferenceDir").filter { it.isNotBlank() }
+
+    val compare = project.tasks.register<JardiffTask>(COMPARE_TASK_NAME) {
+      group = "verification"
+      description = "Compares the built jar against a reference jar (typically the CI `build` " +
+          "job artifact) using jardiff, failing if they differ. Set the reference with " +
+          "--reference-jar=<path> or -PjardiffReferenceDir=<dir>."
+      jardiffClasspath.convention(toolClasspath)
+      mainClass.convention(extension.mainClass)
+      mode.convention(extension.mode)
+      additionalOptions.convention(extension.additionalOptions)
+      reportDir.convention(extension.reportDir)
+      ignoreHashCheck.convention(extension.ignoreHashCheck)
+      // Ignore **/*.version by default, except under CI where the build and deploy
+      // jobs share the same commit.
+      ignoreVersionFiles.convention(
+        project.providers.environmentVariable("CI").map { false }.orElse(true),
+      )
+      referenceJar.convention(
+        // Use the same name as the candidate jar
+        referenceDirProperty.flatMap { dir ->
+          candidateJar.map { candidate -> projectDirectory.dir(dir).file(candidate.asFile.name) }
+        },
+      )
+    }
+
+    // candidateJar = the module's main publishable archive
+    project.pluginManager.withPlugin("java") {
+      compare.configure {
+        candidateJar.convention(
+          project.tasks.named<AbstractArchiveTask>("jar").flatMap { it.archiveFile },
+        )
+      }
+    }
+    project.pluginManager.withPlugin("com.gradleup.shadow") {
+      compare.configure {
+        candidateJar.set(
+          project.tasks.named<AbstractArchiveTask>("shadowJar").flatMap { it.archiveFile },
+        )
+      }
+    }
+  }
+
+  companion object {
+    const val DEFAULT_TOOL_COORDINATE = "io.github.bric3.jardiff:jardiff-cli:0.2.0"
+
+    const val DEFAULT_MAIN_CLASS = "io.github.bric3.jardiff.app.Main"
+
+    const val DEFAULT_MODE = "--stat"
+
+    const val COMPARE_TASK_NAME = "compareToReferenceJar"
+  }
+}