Add a slack notification to remind the Android team about the merge day

Author: DonalMe

.github/workflows/fenix-beta-cut-slack.yml

@@ -0,0 +1,45 @@
+name: Fenix beta cut Slack announcement
+
+on:
+  schedule:
+    # Runs once a day at 12:00 UTC, which is 8am Eastern for the eight months
+    # of the year Eastern is on daylight saving, and 7am for the rest: cron has
+    # no time zone, so one of the two has to drift.
+    #
+    # Ahead of the 16:00 UTC merge on purpose: the version bump lands during
+    # merge day, and after that the API's "nightly" is the next major, not the
+    # one merging today.
+    - cron: '0 12 * * *'
+  workflow_dispatch:
+    inputs:
+      dry_run:
+        description: 'Print the message instead of posting it to Slack'
+        required: false
+        type: boolean
+        default: true
+      test_date:
+        description: 'Pretend today is this date (YYYY-MM-DD), e.g. 2026-08-27'
+        required: false
+        type: string
+
+jobs:
+  announce:
+    runs-on: ubuntu-latest
+    timeout-minutes: 30
+    permissions:
+      contents: read
+    steps:
+      - uses: actions/checkout@v5
+        with:
+          persist-credentials: false
+
+      - uses: actions/setup-python@v5
+        with:
+          python-version: '3.12'
+
+      - name: Announce the Fenix beta cut if today is the Nightly merge day
+        env:
+          SLACK_WEBHOOK_URL: ${{ secrets.MOBILE_ANDROID_TEAM_SLACK_WEBHOOK }}
+          DRY_RUN: ${{ inputs.dry_run }}
+          TEST_DATE: ${{ inputs.test_date }}
+        run: python3 app/scripts/fenix_beta_cut_slack_notifier.py

app/scripts/fenix_beta_cut_slack_notifier.py

@@ -0,0 +1,82 @@
+#!/usr/bin/env python3
+"""
+Announces the Fenix beta cut in #mobile-android-team on desktop merge day.
+
+Run daily by .github/workflows/fenix-beta-cut-slack.yml. It reads the current
+Nightly's schedule and posts only when today is that version's merge day, so it is
+safe to run every day of the year.
+
+The run is deliberately scheduled ahead of the merge. The version bump
+lands during merge day itself, and once it has, "nightly" answers with the next
+major, whose merge day is a fortnight away. Asking before the merge gets the version
+that is merging today.
+
+Requires the SLACK_WEBHOOK_URL environment variable (set from the
+MOBILE_ANDROID_TEAM_SLACK_WEBHOOK repo secret in the workflow, named for the
+#mobile-android-team channel it posts to).
+
+Env vars for testing:
+  DRY_RUN=1           print the message instead of posting it. Accepts
+                      1/true/yes/on to enable and 0/false/no/off or empty to
+                      disable; anything else is an error rather than a guess.
+  TEST_DATE=Y-m-d     pretend today is this date, to exercise a merge day that
+                      isn't today (e.g. 2026-08-27)
+"""
+import os
+import sys
+from datetime import datetime
+
+from lib.env import env_flag
+from lib.schedule import fetch_schedule, parse_date, today as utc_today
+from lib.slack import post_to_slack
+
+# Slack has no list markdown — a literal bullet character is how you get a list.
+MESSAGE = (
+    "*Fenix Beta Cut Time*\n"
+    "Today is the <https://whattrainisitnow.com/release/?version={version}|FX{version}> "
+    "merge day. Later today, release management will merge main to beta, and then bump main to "
+    "{next_version}.\n"
+    "• Who's responsible? Check <https://www.whoisdoingwhat.dev/|here> to see which "
+    "squad is assigned.\n"
+    "• Taking on the starting the nightly Fx{next_version} development cycle? Please "
+    "leave a message here to let others know.\n"
+    "• Need instructions? Find them <https://firefox-source-docs.mozilla.org/mobile/"
+    "android/fenix/release-checklist.html|here>."
+)
+
+
+def main() -> int:
+    dry_run = env_flag("DRY_RUN")
+    webhook_url = os.environ.get("SLACK_WEBHOOK_URL")
+    if not webhook_url and not dry_run:
+        print("SLACK_WEBHOOK_URL is not set — nothing to do.", file=sys.stderr)
+        return 1
+
+    test_date = os.environ.get("TEST_DATE")
+    if test_date:
+        today = datetime.strptime(test_date, "%Y-%m-%d").date()
+        print(f"TEST MODE: pretending today is {today}")
+    else:
+        today = utc_today()
+
+    schedule = fetch_schedule("nightly")
+    merge_day = parse_date(schedule["merge_day"])
+    if today != merge_day:
+        print(f"{today}: not merge day (next one is {merge_day}). Nothing to post.")
+        return 0
+
+    # "156.0" -> 156: the message talks about the major, not the build.
+    version = int(schedule["version"].split(".")[0])
+    text = MESSAGE.format(version=version, next_version=version + 1)
+
+    if dry_run:
+        print(f"DRY RUN — would post:\n{text}")
+        return 0
+
+    post_to_slack(webhook_url, text)
+    print(f"{today}: posted the Fenix beta cut announcement for Firefox {version}.")
+    return 0
+
+
+if __name__ == "__main__":
+    raise SystemExit(main())