Fixed merging task libraries from targets (#868)

## Changes
Previous we (erroneously) kept the reference and merged into the
original tasks and not the copies which we later used to replace
existing tasks. Thus the merging of slices and references was incorrect.

Fixes #864 

## Tests
Added a regression test

bundle/config/resources/job.go

@@ -41,7 +41,7 @@ func (j *Job) MergeJobClusters() error {
 		ref, ok := keys[key]
 		if !ok {
 			output = append(output, j.JobClusters[i])
-			keys[key] = &j.JobClusters[i]
+			keys[key] = &output[len(output)-1]
 			continue
 		}
 
@@ -74,7 +74,7 @@ func (j *Job) MergeTasks() error {
 		ref, ok := keys[key]
 		if !ok {
 			tasks = append(tasks, j.Tasks[i])
-			keys[key] = &j.Tasks[i]
+			keys[key] = &tasks[len(tasks)-1]
 			continue
 		}
 

bundle/config/resources/job_test.go

@@ -67,6 +67,9 @@ func TestJobMergeTasks(t *testing.T) {
 						NodeTypeId:   "i3.xlarge",
 						NumWorkers:   2,
 					},
+					Libraries: []compute.Library{
+						{Whl: "package1"},
+					},
 				},
 				{
 					TaskKey: "bar",
@@ -80,6 +83,11 @@ func TestJobMergeTasks(t *testing.T) {
 						NodeTypeId: "i3.2xlarge",
 						NumWorkers: 4,
 					},
+					Libraries: []compute.Library{
+						{Pypi: &compute.PythonPyPiLibrary{
+							Package: "package2",
+						}},
+					},
 				},
 			},
 		},
@@ -93,10 +101,14 @@ func TestJobMergeTasks(t *testing.T) {
 	assert.Equal(t, "bar", j.Tasks[1].TaskKey)
 
 	// This task was merged with a subsequent one.
-	task0 := j.Tasks[0].NewCluster
-	assert.Equal(t, "13.3.x-scala2.12", task0.SparkVersion)
-	assert.Equal(t, "i3.2xlarge", task0.NodeTypeId)
-	assert.Equal(t, 4, task0.NumWorkers)
+	task0 := j.Tasks[0]
+	cluster := task0.NewCluster
+	assert.Equal(t, "13.3.x-scala2.12", cluster.SparkVersion)
+	assert.Equal(t, "i3.2xlarge", cluster.NodeTypeId)
+	assert.Equal(t, 4, cluster.NumWorkers)
+	assert.Len(t, task0.Libraries, 2)
+	assert.Equal(t, task0.Libraries[0].Whl, "package1")
+	assert.Equal(t, task0.Libraries[1].Pypi.Package, "package2")
 
 	// This task was left untouched.
 	task1 := j.Tasks[1].NewCluster