feat: add empty instrumentation stub detector Gradle plugin

Author: bm1549

buildSrc/build.gradle.kts

@@ -59,6 +59,11 @@ gradlePlugin {
       id = "dd-trace-java.instrumentation-naming"
       implementationClass = "datadog.gradle.plugin.naming.InstrumentationNamingPlugin"
     }
+
+    create("empty-instrumentation-linter") {
+      id = "dd-trace-java.empty-instrumentation-linter"
+      implementationClass = "datadog.gradle.plugin.lint.EmptyInstrumentationLinter"
+    }
   }
 }
 

buildSrc/src/main/kotlin/datadog/gradle/plugin/lint/EmptyInstrumentationLinter.kt

@@ -0,0 +1,92 @@
+package datadog.gradle.plugin.lint
+
+import org.gradle.api.GradleException
+import org.gradle.api.Plugin
+import org.gradle.api.Project
+
+class EmptyInstrumentationLinter : Plugin<Project> {
+  override fun apply(target: Project) {
+    target.tasks.register("checkEmptyInstrumentations") {
+      group = "verification"
+      description = "Detects empty instrumentation stub classes with no transform() calls in methodAdvice()"
+
+      doLast {
+        val instrumentationsDir = target.rootProject.file("dd-java-agent/instrumentation")
+
+        if (!instrumentationsDir.exists() || !instrumentationsDir.isDirectory) {
+          throw GradleException(
+            "Instrumentations directory not found: ${instrumentationsDir.absolutePath}"
+          )
+        }
+
+        val violations = mutableListOf<String>()
+        val hasAdvicePattern = Regex("""implements\s+[^{]*\b(?:HasMethodAdvice|HasAdvice)\b""")
+        val methodAdviceStartPattern = Regex("""(?:public\s+)?(?:\S+\s+)?methodAdvice\s*\(""")
+        val transformCallPattern = Regex("""\btransform\s*\(""")
+
+        instrumentationsDir.walk()
+          .filter { it.isFile && it.name.endsWith(".java") }
+          .forEach { file ->
+            val lines = file.readLines()
+            val content = lines.joinToString("\n")
+
+            if (!hasAdvicePattern.containsMatchIn(content)) return@forEach
+
+            // Find methodAdvice( method and check its body for transform( calls
+            var methodAdviceLineIndex = -1
+            for (i in lines.indices) {
+              if (methodAdviceStartPattern.containsMatchIn(lines[i])) {
+                methodAdviceLineIndex = i
+                break
+              }
+            }
+
+            if (methodAdviceLineIndex < 0) return@forEach
+
+            // Extract method body by tracking brace depth
+            var braceDepth = 0
+            var methodBodyStart = -1
+            val methodBodyLines = mutableListOf<String>()
+
+            for (i in methodAdviceLineIndex until lines.size) {
+              val line = lines[i]
+              for (ch in line) {
+                when (ch) {
+                  '{' -> {
+                    braceDepth++
+                    if (braceDepth == 1) methodBodyStart = i
+                  }
+                  '}' -> {
+                    braceDepth--
+                    if (braceDepth == 0 && methodBodyStart >= 0) {
+                      methodBodyLines.add(line)
+                      break
+                    }
+                  }
+                }
+              }
+              if (methodBodyStart >= 0) {
+                methodBodyLines.add(line)
+              }
+              if (braceDepth == 0 && methodBodyStart >= 0) break
+            }
+
+            val methodBody = methodBodyLines.joinToString("\n")
+            if (!transformCallPattern.containsMatchIn(methodBody)) {
+              val classNamePattern = Regex("""class\s+(\w+)""")
+              val className = classNamePattern.find(content)?.groupValues?.get(1) ?: "<unknown>"
+              val relPath = file.relativeTo(target.rootProject.projectDir).path
+              violations.add("EMPTY STUB: $relPath:${methodAdviceLineIndex + 1} — $className.methodAdvice() contains no transform() calls")
+            }
+          }
+
+        if (violations.isNotEmpty()) {
+          violations.forEach { target.logger.error(it) }
+          throw GradleException("Empty instrumentation stubs found! See errors above.")
+        } else {
+          target.logger.lifecycle("✓ No empty instrumentation stubs found")
+        }
+      }
+    }
+  }
+}