Ensure Event Handlers are not invoked for empty matches #454 (#456)

CHANGELOG.md

@@ -12,6 +12,8 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Changed
 
 -   Allow construction of Message without body
+-   Ensure Event Handlers are not invoked if there are no PE matches
+    https://github.com/atomist/rug/issues/454
 
 ## [0.17.1] - 2017-03-20
 

src/main/scala/com/atomist/rug/runtime/js/JavaScriptEventHandler.scala

@@ -57,7 +57,7 @@ class JavaScriptEventHandler(jsc: JavaScriptContext,
     val root = SimpleContainerGraphNode("root", targetNode)
     ctx.pathExpressionEngine.ee.evaluate(root, pathExpression, ctx.typeRegistry, None) match {
       case Right(Nil) => None
-      case Right(matches) =>
+      case Right(matches) if matches.nonEmpty =>
         val cm = jsContextMatch(
           jsSafeCommittingProxy.wrapOne(targetNode, ctx.typeRegistry),
           jsSafeCommittingProxy.wrap(matches, ctx.typeRegistry),
@@ -66,6 +66,7 @@ class JavaScriptEventHandler(jsc: JavaScriptContext,
           case plan: ScriptObjectMirror => ConstructPlan(plan)
           case other => throw new InvalidHandlerResultException(s"$name EventHandler returned an invalid response ($other) when handling $pathExpressionStr")
         }
+      case Right(matches) if matches.isEmpty => None
       case Left(failure) =>
         throw new RugRuntimeException(pathExpressionStr,
           s"Error evaluating path expression $pathExpression: [$failure]")

src/test/scala/com/atomist/rug/runtime/js/JavaScriptEventHandlerTest.scala

@@ -114,6 +114,23 @@ object JavaScriptEventHandlerTest {
        |}
        |export let handler = new SimpleHandler();
       """.stripMargin)
+
+  val eventHandlerWithEmptyMatches =  StringFileArtifact(atomistConfig.handlersRoot + "/Handler.ts",
+    s"""
+       |import {HandleEvent, Plan, Message} from '@atomist/rug/operations/Handlers'
+       |import {TreeNode, Match, PathExpression} from '@atomist/rug/tree/PathExpression'
+       |import {EventHandler, Tags} from '@atomist/rug/operations/Decorators'
+       |
+       |@EventHandler("BuildHandler", "Handles a Build event", new PathExpression<TreeNode,TreeNode>("/nomatch"))
+       |@Tags("github", "build")
+       |class SimpleHandler implements HandleEvent<TreeNode,TreeNode> {
+       |  handle(event: Match<TreeNode, TreeNode>): Message{
+       |     return new Message("woot").withCorrelationId("dude").withNode(event.root());
+       |  }
+       |}
+       |export let handler = new SimpleHandler();
+      """.stripMargin)
+
 }
 
 
@@ -221,6 +238,18 @@ class JavaScriptEventHandlerTest extends FlatSpec with Matchers with DiagrammedA
     assert(msg.treeNode.nonEmpty)
     assert(msg.correlationId.nonEmpty)
   }
+
+  it should "it should not invoke the actual handler if there matches are empty" in {
+    val rugArchive = TypeScriptBuilder.compileWithModel(SimpleFileBasedArtifactSource(JavaScriptEventHandlerTest.eventHandlerWithEmptyMatches))
+    val finder = new JavaScriptEventHandlerFinder()
+    val handlers = finder.find(new JavaScriptContext(rugArchive))
+    handlers.size should be(1)
+    val handler = handlers.head
+    handler.rootNodeName should be("nomatch")
+    handler.pathExpression should not be null
+    val actualPlan = handler.handle(LocalRugContext(TestTreeMaterializer), SysEvent)
+    assert(actualPlan.isEmpty)
+  }
 }
 
 object SysEvent extends SystemEvent ("blah", "issue", 0l)