[TEP-0059] Scope when expressions to Task only

In [TEP-0007: Conditions Beta][tep-0007], we introduced `when`
expressions to guard execution of `Tasks` in `Pipelines`.
To align with `Conditions`, we set scope of `when` expressions
to the guarded `Task` and its dependent `Tasks`.

In [TEP-0059: Skipping Strategies][tep-0059], we proposed changing
the scope of `when` expressions to the guarded `Task` only. This
was implemented in tektoncd#4085.
We provided a feature flag, `scope-when-expressions-to-task`, to
support migration. It defaulted to `false` for 9 months per our
[Beta API compatibility policy][policy], meaning that we continued
to guard the `Task` and its dependent `Tasks`. In this change, we
flip the flag to `true` to guard the `Task` only by default.

[tep-0007]: https://github.com/tektoncd/community/blob/main/teps/0007-conditions-beta.md
[tep-0059]: https://github.com/tektoncd/community/blob/main/teps/0059-skipping-strategies.md
[policy]: https://github.com/tektoncd/pipeline/blob/main/api_compatibility_policy.md

config/config-feature-flags.yaml

@@ -84,4 +84,4 @@ data:
   enable-api-fields: "stable"
   # Setting this flag to "true" scopes when expressions to guard a Task only
   # instead of a Task and its dependent Tasks.
-  scope-when-expressions-to-task: "false"
+  scope-when-expressions-to-task: "true"

docs/deprecations.md

@@ -25,6 +25,5 @@ being deprecated.
 | [`Conditions` CRD is deprecated and will be removed. Use `when` expressions instead.](https://github.com/tektoncd/community/blob/main/teps/0007-conditions-beta.md) | [v0.16.0](https://github.com/tektoncd/pipeline/releases/tag/v0.16.0) | Alpha                                                                                                  | Nov 02 2020                         |
 | [The `disable-home-env-overwrite` flag will be removed](https://github.com/tektoncd/pipeline/issues/2013)                                                           | [v0.24.0](https://github.com/tektoncd/pipeline/releases/tag/v0.24.0) | Beta                                                                                                   | February 10 2022                    |
 | [The `disable-working-dir-overwrite` flag will be removed](https://github.com/tektoncd/pipeline/issues/1836)                                                        | [v0.24.0](https://github.com/tektoncd/pipeline/releases/tag/v0.24.0) | Beta                                                                                                   | February 10 2022                    |
-| [The `scope-when-expressions-to-task` flag will be flipped from "false" to "true"](https://github.com/tektoncd/pipeline/issues/4461)                                | [v0.27.0](https://github.com/tektoncd/pipeline/releases/tag/v0.27.0) | Beta                                                                                                   | February 10 2022                    |
 | [The `scope-when-expressions-to-task` flag will be removed](https://github.com/tektoncd/pipeline/issues/4461)                                                       | [v0.27.0](https://github.com/tektoncd/pipeline/releases/tag/v0.27.0) | Beta                                                                                                   | March 10 2022                       |
 | [`PipelineResources` are deprecated.](https://github.com/tektoncd/community/blob/main/teps/0074-deprecate-pipelineresources.md)                                     | [v0.30.0](https://github.com/tektoncd/pipeline/releases/tag/v0.30.0) | Alpha                                                                                                  | Dec 20 2021                         |

docs/install.md

@@ -378,7 +378,7 @@ most stable features to be used. Set it to "alpha" to allow [alpha
 features](#alpha-features) to be used.
 
 - `scope-when-expressions-to-task`: set this flag to "true" to scope `when` expressions to guard a `Task` only. Set it
-  to "false" to guard a `Task` and its dependent `Tasks`. It defaults to "false". For more information, see [guarding
+  to "false" to guard a `Task` and its dependent `Tasks`. It defaults to "true". For more information, see [guarding
   `Task` execution using `when` expressions](pipelines.md#guard-task-execution-using-whenexpressions).
 
 For example:

docs/pipelines.md

@@ -496,14 +496,24 @@ There are a lot of scenarios where `when` expressions can be really useful. Some
 
 #### Guarding a `Task` and its dependent `Tasks`
 
-When  `when` expressions evaluate to `False`, the `Task` and its dependent `Tasks` will be skipped by default while the
-rest of the `Pipeline` will execute. Dependencies between `Tasks` can be either ordering ([`runAfter`](https://github.com/tektoncd/pipeline/blob/main/docs/pipelines.md#using-the-runafter-parameter))
+> :warning: **Scoping `when` expressions to a `Task` and its dependent `Tasks` is deprecated.**
+>
+> Consider migrating to scoping `when` expressions to the guarded `Task` only instead.
+> Read more in the [documentation](#guarding-a-task-only) and [TEP-0059: Skipping Strategies][tep-0059].
+> 
+[tep-0059]: https://github.com/tektoncd/community/blob/main/teps/0059-skipping-strategies.md
+
+To guard a `Task` and its dependent `Tasks`, set the global default scope of `when` expressions to `Task` using the
+`scope-when-expressions-to-task` field in [`config/config-feature-flags.yaml`](install.md#customizing-the-pipelines-controller-behavior)
+by changing it to "false".
+
+When  `when` expressions evaluate to `False`, and `scope-when-expressions-to-task` is set to "false", the `Task` and 
+its dependent `Tasks` will be skipped while the rest of the `Pipeline` will execute. Dependencies between `Tasks` can
+be either ordering ([`runAfter`](https://github.com/tektoncd/pipeline/blob/main/docs/pipelines.md#using-the-runafter-parameter))
 or resource (e.g. [`Results`](https://github.com/tektoncd/pipeline/blob/main/docs/pipelines.md#using-results))
 dependencies, as further described in [configuring execution order](#configuring-the-task-execution-order). The global
-default scope of `when` expressions is set to a `Task` and its dependent`Tasks`; `scope-when-expressions-to-task` field
-in [`config/config-feature-flags.yaml`](install.md#customizing-the-pipelines-controller-behavior) defaults to "false".
-
-**Note:** Scoping `when` expressions to a `Task` and its dependent `Tasks` is deprecated
+default scope of `when` expressions is set to a `Task` only; `scope-when-expressions-to-task` field in 
+[`config/config-feature-flags.yaml`](install.md#customizing-the-pipelines-controller-behavior) defaults to "true".
 
 To guard a `Task` and its dependent Tasks:
 - cascade the `when` expressions to the specific dependent `Tasks` to be guarded as well
@@ -646,9 +656,7 @@ tasks:
 
 #### Guarding a `Task` only
 
-To guard a `Task` only and unblock execution of its dependent `Tasks`, set the global default scope of `when` expressions
-to `Task` using the `scope-when-expressions-to-task` field in [`config/config-feature-flags.yaml`](install.md#customizing-the-pipelines-controller-behavior)
-by changing it to "true"
+When `when` expressions evaluate to `False`, the `Task` will be skipped and:
 - The ordering-dependent `Tasks` will be executed
 - The resource-dependent `Tasks` (and their dependencies) will be skipped because of missing `Results` from the skipped 
   parent `Task`. When we add support for [default `Results`](https://github.com/tektoncd/community/pull/240), then the 
@@ -657,6 +665,8 @@ by changing it to "true"
   to handle the execution of the child `Task` in case the expected file is missing from the `Workspace` because the 
   guarded parent `Task` is skipped. 
 
+On the other hand, the rest of the `Pipeline` will continue executing.
+
 ```
                                      tests
                                        |
@@ -706,7 +716,7 @@ tasks:
     name: slack-msg
 ```
 
-With `when` expressions scoped to `Task`, if `manual-approval` is skipped, execution of it's dependent `Tasks` 
+With `when` expressions scoped to `Task`, if `manual-approval` is skipped, execution of its dependent `Tasks` 
 (`slack-msg`, `build-image` and `deploy-image`) would be unblocked regardless:
 - `build-image` and `deploy-image` should be executed successfully
 - `slack-msg` will be skipped because it is missing the `approver` `Result` from `manual-approval`

pkg/apis/config/feature_flags.go

@@ -47,7 +47,7 @@ const (
 	// DefaultEnableCustomTasks is the default value for "enable-custom-tasks".
 	DefaultEnableCustomTasks = false
 	// DefaultScopeWhenExpressionsToTask is the default value for "scope-when-expressions-to-task".
-	DefaultScopeWhenExpressionsToTask = false
+	DefaultScopeWhenExpressionsToTask = true
 	// DefaultEnableAPIFields is the default value for "enable-api-fields".
 	DefaultEnableAPIFields = StableAPIFields
 

pkg/reconciler/pipelinerun/pipelinerun_test.go

@@ -5153,7 +5153,7 @@ func TestReconcileWithWhenExpressionsWithTaskResults(t *testing.T) {
 
 	wantEvents := []string{
 		"Normal Started",
-		"Normal Running Tasks Completed: 1 \\(Failed: 0, Cancelled 0\\), Incomplete: 1, Skipped: 2",
+		"Normal Running Tasks Completed: 1 \\(Failed: 0, Cancelled 0\\), Incomplete: 2, Skipped: 1",
 	}
 	pipelineRun, clients := prt.reconcileRun("foo", "test-pipeline-run-different-service-accs", wantEvents, false)
 
@@ -5206,14 +5206,12 @@ func TestReconcileWithWhenExpressionsWithTaskResults(t *testing.T) {
 			Operator: "in",
 			Values:   []string{"missing"},
 		}},
-	}, {
-		Name: "d-task",
 	}}
 	if d := cmp.Diff(actualSkippedTasks, expectedSkippedTasks); d != "" {
 		t.Errorf("expected to find Skipped Tasks %v. Diff %s", expectedSkippedTasks, diff.PrintWantGot(d))
 	}
 
-	skippedTasks := []string{"c-task", "d-task"}
+	skippedTasks := []string{"c-task"}
 	for _, skippedTask := range skippedTasks {
 		labelSelector := fmt.Sprintf("tekton.dev/pipelineTask=%s,tekton.dev/pipelineRun=test-pipeline-run-different-service-accs", skippedTask)
 		actualSkippedTask, err := clients.Pipeline.TektonV1beta1().TaskRuns("foo").List(prt.TestAssets.Ctx, metav1.ListOptions{