Use the same Deps logic in v1alpha1 and v1beta1

Sometimes the PipelineTask that Deps is being executed on is actually
v1beta1 instead of v1alpha1 and the old Deps function, which doesn't
account for Results, is being called.

This PR duplicates the logics so the Deps function is the same.
After #2410 we'll be able to assume we're always using the v1beta1 types
and will not need the logic in both places and can avoid bugs like this.

It also duplicates the DAG test logic which is the closest thing Deps()
currently has to a set of unit tests.

Part of #2463

(cherry picked from commit 893dde2)

pkg/apis/pipeline/v1beta1/pipeline_types.go

@@ -136,6 +136,27 @@ func (pt PipelineTask) Deps() []string {
 		for _, rd := range cond.Resources {
 			deps = append(deps, rd.From...)
 		}
+		for _, param := range cond.Params {
+			expressions, ok := GetVarSubstitutionExpressionsForParam(param)
+			if ok {
+				if resultRefs, err := NewResultRefs(expressions); err == nil {
+					for _, resultRef := range resultRefs {
+						deps = append(deps, resultRef.PipelineTask)
+					}
+				}
+			}
+		}
+	}
+	// Add any dependents from task results
+	for _, param := range pt.Params {
+		expressions, ok := GetVarSubstitutionExpressionsForParam(param)
+		if ok {
+			if resultRefs, err := NewResultRefs(expressions); err == nil {
+				for _, resultRef := range resultRefs {
+					deps = append(deps, resultRef.PipelineTask)
+				}
+			}
+		}
 	}
 	return deps
 }

pkg/reconciler/pipeline/dag/dag_test.go

@@ -42,8 +42,15 @@ func testGraph(t *testing.T) *dag.Graph {
 	}, {
 		Name: "b",
 	}, {
-		Name:     "w",
-		RunAfter: []string{"b", "y"},
+		Name: "w",
+		Params: []v1alpha1.Param{{
+			Name: "foo",
+			Value: v1alpha1.ArrayOrString{
+				Type:      v1alpha1.ParamTypeString,
+				StringVal: "$(tasks.y.results.bar)",
+			},
+		}},
+		RunAfter: []string{"b"},
 	}, {
 		Name:     "x",
 		RunAfter: []string{"a"},