PR workflow: add mergify

This config should always follow our worklof and other way around. They should both be in sync.

What can mergify do? Almost everything we need. First step would be to not merge anything, just use labels
and help us to keep PRs up to date with labels.

If this works, we can get CI to check specific labels to trigger CI (or use commands) and other things, this needs more work.

Author: 0xc0170

.mergify.yml

@@ -0,0 +1,140 @@
+#
+# Copyright (c) 2029, Arm Limited and affiliates.
+# SPDX-License-Identifier: Apache-2.0
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+# Mergify follow our workflow: https://os.mbed.com/docs/mbed-os/latest/contributing/workflow.html
+
+pull_request_rules:
+  - name: "label needs: work when changes were requested"
+    conditions:
+      # Labels
+      - "label!=needs: work"
+      - "label!=needs: preceding PR"
+
+      # Reviewers
+      - "#changes-requested-reviews-by>0"
+    actions:
+      label:
+        add: 
+          - "needs: work"
+        remove: 
+          - "needs: review"
+
+  - name: "label needs: work when travis-ci failed"
+    conditions:
+      # Labels
+      - "label!=needs: work"
+      - "label!=needs: preceding PR"
+
+      # Travis failing
+      - status-failure~=continuous-integration/travis-ci/pr
+    actions:
+      label:
+        add: 
+          - "needs: work"
+        remove: 
+          - "needs: review"
+
+  - name: "label needs: work when Jenkins CI failed"
+    conditions:
+      # Jenkins CI failing
+      - status-failure~=continuous-integration/jenkins/pr-head
+    actions:
+      label:
+        add: 
+          - "needs: work"
+
+  - name: "label needs: CI when at least one reviewers approval"
+    conditions:
+      # Labels
+      - "label!=needs: work"
+      - "label!=needs: preceding PR"
+
+      # Reviewers
+      - "#changes-requested-reviews-by=0"
+      - "#approved-reviews-by>=1"
+
+      # CI green policy, at least Travis should be green
+      - status-success~=continuous-integration/travis-ci/pr
+      # new CI needs to be done
+      - status-neutral~=continuous-integration/jenkins/pr-head
+    actions:
+      label:
+        add: 
+          - "needs: CI"
+        remove: 
+          - "needs: review"
+
+  - name: remove ready for merge when merged
+    conditions:
+      - merged
+      - label=ready for merge
+    actions:
+      label:
+        remove:
+          - ready for merge
+
+  - name: add "do not merge" label when WIP is in title
+    conditions:
+       - title~=^(\[wip\]( |:) |\[WIP\]( |:) |wip( |:) |WIP( |:)).*
+    actions:
+      label:
+        add:
+          - do not merge
+
+  - name: "label needs: work when there is a conflict"
+    conditions:
+      - conflict
+    actions:
+      label:
+        add:
+          - "needs: work"
+        remove: 
+          - "needs: review"
+      comment:
+        message: This PR cannot be merged due to conflicts. Please rebase to resolve them.
+
+  - name: "add label feature branch for feature branch additions"
+    conditions:
+      - base~=^feature
+    actions:
+      label:
+        add:
+          - "release-version: feature branch"
+
+  - name: label "ready for merge" when ready
+    conditions:
+      # Labels
+      - label!=do not merge
+      - "label!=needs: work"
+      - "label!=needs: preceding PR"
+      - "label!=needs: review"
+      - "label=needs: CI"
+
+      # Reviewers
+      - "#approved-reviews-by>=1"
+      - "#changes-requested-reviews-by=0"
+
+      # CI green policy
+      - status-success~=continuous-integration/travis-ci/pr
+      # Internal Jenkins - we rely on PR head to provide status - all passed 
+      - status-success~=continuous-integration/jenkins/pr-head
+    actions:
+      label:
+        add: 
+          - ready for merge
+        remove: 
+          - "needs: CI"
+