ci: add task to check changed files

.tekton/tasks/check-git-files-changed.yaml

@@ -0,0 +1,46 @@
+apiVersion: tekton.dev/v1alpha1
+kind: Task
+metadata:
+  name: check-git-files-changed
+  annotations:
+    description: |
+      Returns "passed" in the "check" result if any of the files changed
+      in the source on the workspace matches the regular expression.
+      Returns a "files" result as a list of files modified by the PR that
+      match the regex in the parameters.
+    ci.tekton.dev/condition: |
+      The result of this task is used to evaluate a condition.
+      Events from this task are ignored downstream, when it comes to update the CI job status.
+spec:
+  params:
+    - name: gitCloneDepth
+      description: Number of commits + 1
+    - name: regex
+      description: Regular expression to match files changed
+  workspaces:
+    - name: input
+  results:
+    - name: check
+      description: passed or failed
+    - name: files
+      description: list of files modified that match
+  steps:
+    - name: check-files-changed
+      image: alpine/git
+      env:
+      - name: GIT_CLONE_DEPTH
+        value: $(params.gitCloneDepth)
+      - name: REGEX
+        value: $(params.regex)
+      script: |
+        #!/bin/sh
+        set -ex
+        set -o pipefail
+        BACK="HEAD~$(( ${GIT_CLONE_DEPTH} - 1 ))"
+        CHECK="failed"
+        cd $(workspaces.input.path)
+        git diff-tree --no-commit-id --name-only -r HEAD $BACK | \
+            grep -E "${REGEX}" > $(results.files.path) || true
+        git diff-tree --no-commit-id --name-only -r HEAD $BACK | \
+            grep -E "${REGEX}" && CHECK="passed"
+        printf $CHECK > $(results.check.path)

.tekton/tasks/kustomization.yaml

@@ -4,3 +4,4 @@ kind: Kustomization
 resources:
   - external.yaml
   - lint.yaml
+  - check-git-files-changed.yaml