In v0.14 Tekton introduced the so called finally Tasks, which run at the end of every Pipeline - regardless which Task failed or succeeded. As the docs state:

finally tasks are guaranteed to be executed in parallel after all PipelineTasks under tasks have completed regardless of success or error.

In general finally tasks look like this:

spec:
  tasks:
    - name: tests
      taskRef:
        name: integration-test
  finally:
    - name: cleanup-test
      taskRef:
        name: cleanup

But how do we create the corresponding STATE in our gitlab-set-status Task? With using when expressions inside our finally tasks we can run our gitlab-set-status Task based on the overall Pipeline status (or Aggregate Pipeline status):

finally:
  - name: notify-any-failure # executed only when one or more tasks fail
    when:
      - input: $(tasks.status)
        operator: in
        values: ["Failed"]
    taskRef:
      name: notify-failure

We grab the Aggregate Execution Status by simply using $(tasks.status). This variable is stated to have those 4 possible status:

• Succeeded ("all tasks have succeeded")
• Completed ("all tasks completed successfully including one or more skipped tasks")

-> which could be translated into the gitlab-set-status Tasks STATE value success.

• Failed ("one ore more tasks failed")
• None ("no aggregate execution status available (i.e. none of the above), one or more tasks could be pending/running/cancelled/timedout")

-> which could both be translated into the gitlab-set-status Tasks STATE value failed. For None this is only valid, since we're in a finally task, since pending/running could otherwise also mean that a Pipeline is in a good state.

Having 4 states we need to check in our when expressions, do we need to implement a separate finally Task for each of them? No, since luckily the when expressions "values is an array of string values.". So we're able to do

  when:
    - input: $(tasks.status)
      operator: in
      values: [ "Failed", "None" ]

and

  when:
    - input: $(tasks.status)
      operator: in
      values: [ "Succeeded", "Completed" ]

Finally this results in our Tekton Pipeline's locking like this (and implementing 2 finally tasks report-pipeline-failed-to-gitlab and report-pipeline-success-to-gitlab):

...
  finally:
    - name: report-pipeline-failed-to-gitlab
      when:
        - input: $(tasks.status)
          operator: in
          values: [ "Failed", "None" ] # see aggregated status https://tekton.dev/docs/pipelines/pipelines/#using-aggregate-execution-status-of-all-tasks
      taskRef:
        name: "gitlab-set-status"
      params:
        - name: "STATE"
          value: "failed"
        - name: "GITLAB_HOST_URL"
          value: "$(params.GITLAB_HOST)"
        - name: "REPO_FULL_NAME"
          value: "$(params.REPO_PATH_ONLY)"
        - name: "GITLAB_TOKEN_SECRET_NAME"
          value: "gitlab-api-secret"
        - name: "GITLAB_TOKEN_SECRET_KEY"
          value: "token"
        - name: "SHA"
          value: "$(params.SOURCE_REVISION)"
        - name: "TARGET_URL"
          value: "$(params.TEKTON_DASHBOARD_HOST)/#/namespaces/default/pipelineruns/$(context.pipelineRun.name)"
        - name: "CONTEXT"
          value: "tekton-pipeline"
        - name: "DESCRIPTION"
          value: "An error occurred building your commit in Tekton"
    - name: report-pipeline-success-to-gitlab
      when:
          - input: $(tasks.status)
            operator: in
            values: [ "Succeeded", "Completed" ] # see aggregated status https://tekton.dev/docs/pipelines/pipelines/#using-aggregate-execution-status-of-all-tasks
      taskRef:
        name: "gitlab-set-status"
      params:
        - name: "STATE"
          value: "success"
        - name: "GITLAB_HOST_URL"
          value: "$(params.GITLAB_HOST)"
        - name: "REPO_FULL_NAME"
          value: "$(params.REPO_PATH_ONLY)"
        - name: "GITLAB_TOKEN_SECRET_NAME"
          value: "gitlab-api-secret"
        - name: "GITLAB_TOKEN_SECRET_KEY"
          value: "token"
        - name: "SHA"
          value: "$(params.SOURCE_REVISION)"
        - name: "TARGET_URL"
          value: "$(params.TEKTON_DASHBOARD_HOST)/#/namespaces/default/pipelineruns/$(context.pipelineRun.name)"
        - name: "CONTEXT"
          value: "tekton-pipeline"
        - name: "DESCRIPTION"
          value: "Finished building your commit in Tekton"

Executing our Tekton Pipeline should now be reported correctly to our GitLab. Failures look like this:

Succeeded Pipelines look like this: