WIP: Inject buildpacks at runtime

deploy/base/task-combined.yaml

@@ -399,6 +399,27 @@ spec:
         - name: empty-dir
           mountPath: /tekton/home
 
+    - name: inject-custom-buildpacks
+      image: docker.io/library/bash:5.1.4@sha256:b208215a4655538be652b2769d82e576bc4d0a2bb132144c060efc5be8c3f5d6
+      args: []
+      script: |
+        #!/usr/bin/env bash
+        set -e
+
+        echo "--> Injecting custom buildpacks..."
+        cat >/layers/group.toml <<EOB
+        [[group]]
+          id = "heroku/python"
+          version = "0.0.0"
+          api = "0.4"
+        EOB
+
+      volumeMounts:
+        - name: layers-dir
+          mountPath: /layers
+        - name: $(params.PLATFORM_DIR)
+          mountPath: /platform
+
     - name: analyze
       image: $(params.LIFECYCLE_IMAGE)
       imagePullPolicy: Always

deploy/base/toolforge-buildpacks-phases-patch.json

@@ -16,7 +16,7 @@
   },
   {
     "op": "replace",
-    "path": "/spec/steps/8/image",
+    "path": "/spec/steps/9/image",
     "value": "docker-registry.tools.wmflabs.org/toolforge-library-bash:5.1.4"
   }
 ]