Throw more helpful error if kanela-agent jar is undiscoverable (#1393)

* throw more helpful error if kanela-agent jar is undiscoverable; log errors in case of weird build surprises

* revert ci version bump (???)

* dedup

Author: hughsimpson

build.sbt

@@ -1007,7 +1007,6 @@ lazy val bundle = (project in file("bundle"))
     `kamon-runtime-attacher`
   )
 
-import com.lightbend.sbt.javaagent.Modules
 import BundleKeys._
 
 lazy val commonBundleSettings = Seq(
@@ -1045,8 +1044,8 @@ lazy val `kamon-runtime-attacher` = (project in file("bundle/kamon-runtime-attac
     moduleName := "kamon-runtime-attacher",
     buildInfoPackage := "kamon.runtime.attacher",
     buildInfoKeys := Seq[BuildInfoKey](kanelaAgentJarName),
-    kanelaAgentJar := update.value.matching(Modules.exactFilter(kanelaAgent)).head,
-    kanelaAgentJarName := kanelaAgentJar.value.getName,
+    kanelaAgentJar := BaseProject.findKanelaAgentJar.value,
+    kanelaAgentJarName := BaseProject.findKanelaAgentJar.value.getName,
     Compile / resourceGenerators += Def.task(Seq(kanelaAgentJar.value)).taskValue,
     assembly / assemblyShadeRules := Seq(
       ShadeRule.zap("**module-info").inAll,

bundle/kamon-runtime-attacher/src/main/scala/kamon/runtime/Attacher.scala

@@ -29,7 +29,9 @@ object Attacher {
 
     } else {
 
-      val embeddedAgentFile = Attacher.getClass.getClassLoader.getResourceAsStream(BuildInfo.kanelaAgentJarName)
+      val embeddedAgentFile =
+        Option(Attacher.getClass.getClassLoader.getResourceAsStream(BuildInfo.kanelaAgentJarName))
+          .getOrElse(throw new RuntimeException(s"Couldn't find kanela jar resource '${BuildInfo.kanelaAgentJarName}'"))
       val temporaryAgentFile = Files.createTempFile(BuildInfo.kanelaAgentJarName, ".jar")
       Files.copy(embeddedAgentFile, temporaryAgentFile, StandardCopyOption.REPLACE_EXISTING)
 

project/Build.scala

@@ -220,10 +220,28 @@ object BaseProject extends AutoPlugin {
   }
 
   def findKanelaAgentJar = Def.task {
+    val hasSemver = """.*[0-9]+\.[0-9]+\.[0-9]+.*"""
     update.value.matching {
       moduleFilter(organization = "io.kamon", name = "kanela-agent") &&
       artifactFilter(`type` = "jar")
-    }.head
+    }.toList match {
+      case s @ Nil => throw new NoClassDefFoundError("No kanela agent jar found")
+      case h +: Nil =>
+        if (h.getName.matches(hasSemver)) println("Single matching kanela-agent jar found")
+        else System.err.println("kanela-agent jar name did not contain version")
+        h
+      case s =>
+        System.err.println(s"Multiple matching jars - ${s.map(f => f.getName)}")
+        s.filter(_.getName.matches(hasSemver)) match {
+          case Nil =>
+            System.err.println("No jars matching semver ")
+            s.head
+          case v +: Nil => v
+          case more =>
+            System.err.println("Multiple jars matching semver ")
+            more.head
+        }
+    }
   }
 
   private def defaultPomExtra() = {