Warn user when on-cel-expression is used alongside on-target-branch and on-event

[chmouel]

Description:
When using both on-event and on-target-branch annotations, it's important to note that if an on-cel-expression annotation is also present, the on-cel-expression will take precedence. This means that the conditions specified in on-event and on-target-branch will be ignored.

To avoid confusion, we should warn users in both the user events namespace and the controller logs when they define a PipelineRun that includes both on-cel-expression and either on-event or on-target-branch.

Example Scenario:

metadata:
  name: example-pipeline
  annotations:
    pipelinesascode.tekton.dev/on-event: "[pull_request]"
    pipelinesascode.tekton.dev/on-target-branch: "[main]"
    pipelinesascode.tekton.dev/on-cel-expression: |
      event == "pull_request" && target_branch == "main" && source_branch == "feature"

In this example, even though on-event and on-target-branch are specified, the on-cel-expression will take precedence. The PipelineRun will only be triggered if the event is a pull request targeting the main branch and the source branch is feature.

Proposed Solution:

1. User Events Namespace Warning:

   • When a PipelineRun is created with both on-cel-expression and on-event/on-target-branch, a warning event should be emitted in the user's namespace. This warning should clearly state that on-cel-expression will override the other annotations.

   Example warning message:

   Warning: The PipelineRun "example-pipeline" has both `on-cel-expression` and `on-event`/`on-target-branch` annotations. The `on-cel-expression` will take precedence, and the other annotations will be ignored.
   

2. Controller Logs Warning:

   • Similarly, a warning should be logged in the Pipelines-as-Code controller logs to indicate that the user has defined conflicting annotations. This will help administrators and developers debug issues related to PipelineRun matching.

   Example log message:

   WARN: PipelineRun "example-pipeline" in namespace "user-namespace" has conflicting annotations (`on-cel-expression` and `on-event`/`on-target-branch`). `on-cel-expression` will take precedence.
   

Why This Matters:

• User Awareness: Users may not realize that on-cel-expression overrides other annotations, leading to unexpected behavior in their CI pipelines. A clear warning in their namespace will help them understand why their PipelineRun is not being triggered as expected.
• Debugging: Logging this warning in the controller logs will assist administrators in identifying and resolving issues related to PipelineRun configurations.

Next Steps:

• Implement the warning mechanism in the Pipelines-as-Code controller to emit events in the user's namespace and log warnings when conflicting annotations are detected.
• Update the documentation to explicitly mention this behavior and the warnings that users can expect.

[chmouel]

JIRA: https://issues.redhat.com/browse/SRVKP-7234