[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 #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:/tektoncd/community/blob/main/teps/0007-conditions-beta.md
[tep-0059]: https:/tektoncd/community/blob/main/teps/0059-skipping-strategies.md
[policy]: https:/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:/tektoncd/community/blob/main/teps/0007-conditions-beta.md) | [v0.16.0](https:/tektoncd/pipeline/releases/tag/v0.16.0) | Alpha | Nov 02 2020 |
 | [The `disable-home-env-overwrite` flag will be removed](https:/tektoncd/pipeline/issues/2013) | [v0.24.0](https:/tektoncd/pipeline/releases/tag/v0.24.0) | Beta | February 10 2022 |
 | [The `disable-working-dir-overwrite` flag will be removed](https:/tektoncd/pipeline/issues/1836) | [v0.24.0](https:/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:/tektoncd/pipeline/issues/4461) | [v0.27.0](https:/tektoncd/pipeline/releases/tag/v0.27.0) | Beta | February 10 2022 |
 | [The `scope-when-expressions-to-task` flag will be removed](https:/tektoncd/pipeline/issues/4461) | [v0.27.0](https:/tektoncd/pipeline/releases/tag/v0.27.0) | Beta | March 10 2022 |
 | [`PipelineResources` are deprecated.](https:/tektoncd/community/blob/main/teps/0074-deprecate-pipelineresources.md) | [v0.30.0](https:/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:/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:/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:/tektoncd/pipeline/blob/main/docs/pipelines.md#using-the-runafter-parameter))
 or resource (e.g. [`Results`](https:/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:/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

@@ -5036,7 +5036,7 @@ 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)
 
@@ -5089,14 +5089,12 @@ 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{