Use the pre-release check task from plumbing

Add the pre-release check task to the release pipeline, to ensure
we don't override an existing release by mistake.

Also fix the README to specify the correct setup for the nightly
release pipeline and the manual release pipeline.

Closes #983

tekton/README.md

@@ -144,18 +144,23 @@ The nightly release Pipeline is currently missing Tasks which we want to add onc
 
 ## Install Tekton
 
-The Pipelines and Tasks in this repo work with v0.3.1 due to
+Some of the Pipelines and Tasks in this repo work with v0.3.1 due to
 [Prow #13948](https://github.com/kubernetes/test-infra/issues/13948), so that
 they can be used [with Prow](https://github.com/tektoncd/plumbing/tree/master/prow).
 
+Specifically, nightly releases are triggered by Prow, so they are compatible with
+v0.3.1, while full releases are triggered manually and require Tekton >= v0.7.0.
 
 ```bash
 # If this is your first time installing Tekton in the cluster you might need to give yourself permission to do so
 kubectl create clusterrolebinding cluster-admin-binding-someusername \
   --clusterrole=cluster-admin \
   --user=$(gcloud config get-value core/account)
 
-# Apply version v0.3.1 of Tekton
+# For Tekton v0.3.1 - apply version v0.3.1
+kubectl apply --filename  https://storage.googleapis.com/tekton-releases/previous/v0.3.1/release.yaml
+
+# For Tekton v0.7.0 - apply version v0.7.0 - Do not apply both versions in the same cluster!
 kubectl apply --filename  https://storage.googleapis.com/tekton-releases/previous/v0.3.1/release.yaml
 ```
 
@@ -164,15 +169,34 @@ kubectl apply --filename  https://storage.googleapis.com/tekton-releases/previou
 Add all the `Tasks` to the cluster, including the
 [`golang`](https://github.com/tektoncd/catalog/tree/master/golang)
 Tasks from the
-[`tektoncd/catalog`](https://github.com/tektoncd/catalog) (pinned to a version that
-works [with v0.3.1](#install-tekton))
+[`tektoncd/catalog`](https://github.com/tektoncd/catalog), and the
+[release pre-check](https://github.com/tektoncd/plumbing/tree/master/tekton/) Task from
+[`tektoncd/plumbing`](https://github.com/tektoncd/plumbing).
+
+For nightly releases, use a version of the [`tektoncdcatalog`](https://github.com/tektoncd/catalog)
+tasks that is compatible with Tekton v0.3.1:
 
 ```bash
 # Apply the Tasks we are using from the catalog
 kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/14d38f2041312b0ad17bc079cfa9c0d66895cc7a/golang/lint.yaml
 kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/14d38f2041312b0ad17bc079cfa9c0d66895cc7a/golang/build.yaml
 kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/14d38f2041312b0ad17bc079cfa9c0d66895cc7a/golang/tests.yaml
+```
+
+For full releases, use a version of the [`tektoncdcatalog`](https://github.com/tektoncd/catalog)
+tasks that is compatible with Tekton v0.7.0 (`master`) and install the pre-release
+check Task from plumbing too:
 
+```bash
+# Apply the Tasks we are using from the catalog
+kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/master/golang/lint.yaml
+kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/master/golang/build.yaml
+kubectl apply -f https://raw.githubusercontent.com/tektoncd/catalog/master/golang/tests.yaml
+kubectl apply -f https://raw.githubusercontent.com/tektoncd/plumbing/master/tekton/prerelease_checks.yaml
+```
+
+Apply the tasks from the `pipeline` repo:
+```bash
 # Apply the Tasks and Pipelines we use from this repo
 kubectl apply -f tekton/ci-images.yaml
 kubectl apply -f tekton/publish.yaml

tekton/release-pipeline.yaml

@@ -44,7 +44,22 @@ spec:
   - name: builtGcsFetcherImage
     type: image
   tasks:
+    - name: precheck
+      taskRef:
+        name: prerelease-check
+      params:
+        - name: package
+          value: $(params.package)
+        - name: versionTag
+          value: $(params.versionTag)
+      resources:
+        inputs:
+          - name: release-bucket
+            resource: bucket
+          - name: source-to-release
+            resource: source-repo
     - name: lint
+      runAfter: [precheck]
       taskRef:
         name: golangci-lint
       params: