EDEV-20: Catch model deletions in CI/CD

.github/scripts/check_migrations.py

@@ -0,0 +1,73 @@
+import subprocess
+import sys
+
+DEV_BRANCH = "develop"
+LIVE_BRANCH = "main"
+
+
+def get_diff():
+    """
+    Gets the file diff between the current branch (your branch) and the
+    develop branch. If there are no changes, it gets the diff between
+    the current branch and the main branch - this will be the case for
+    merging develop into the main branch.
+    """
+    subprocess.run(
+        ["git", "fetch", "origin"], stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL
+    )
+    output = [
+        f"./{file_path}"
+        for file_path in subprocess.check_output(
+            ["git", "diff", "--name-only", f"origin/{DEV_BRANCH}"]
+        )
+        .decode()
+        .splitlines()
+    ]
+    if not output:
+        output = [
+            f"./{file_path}"
+            for file_path in subprocess.check_output(
+                ["git", "diff", "--name-only", f"origin/{LIVE_BRANCH}"]
+            )
+            .decode()
+            .splitlines()
+        ]
+    return output
+
+
+def check_migration_file(file):
+    """
+    Checks if a migration file contains any of the keywords listed
+    in the `keywords` list that may be potentially harmful to our
+    data.
+
+    While AlterField is generally safe, it can be harmful if the
+    field is being changed to a type that does not support the
+    current data type. For example, changing a CharField to an
+    IntegerField will result in a loss of data.
+    """
+    with open(file) as f:
+        contents = f.read()
+
+    keywords = ["DeleteModel", "RenameModel", "RemoveField", "AlterField"]
+    for keyword in keywords:
+        if keyword in contents and f"# etna:allow{keyword}" not in contents:
+            print(f"Warning: {file} contains a migration that may cause data loss.")
+            return True
+
+
+def main():
+    file_diff = get_diff()
+
+    migration_alert = False
+    for file in file_diff:
+        if "/migrations/" in file and file.endswith(".py"):
+            if check_migration_file(file):
+                migration_alert = True
+    if migration_alert:
+        print("Please review the migrations before pushing, to ensure no loss of data.")
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()

.github/workflows/check-migrations.yml

@@ -0,0 +1,23 @@
+name: Check Migrations
+
+on:
+  pull_request:
+    paths:
+      - 'etna/*/migrations/**'
+
+jobs:
+  check-migrations:
+    name: Check Migrations
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout code
+        uses: actions/checkout@v2
+
+      - name: Set up Python
+        uses: actions/setup-python@v2
+        with:
+          python-version: '3.10'
+
+      - name: Check migrations
+        run: python .github/scripts/check_migrations.py

docs/developer-guide/project-conventions.md

@@ -71,6 +71,24 @@ $ fab test --lint
 
 This will be checked by CI on every commit, so it's a good idea to run this locally before pushing your changes.
 
+### Migrations
+
+We also have CI to check Django migrations, in order to help prevent any potential data issues. The CI will only run on a pull request, if any `/migrations` folders have been changed.
+
+If a migration contains a potentially dangerous operation, the developer should check that the migration is safe to run, and verify they have checked this by adding a comment to the migration file,
+in the following format:
+
+```python
+# etna:allowDeleteModel
+```
+
+The operations that require a comment are `DeleteModel`, `RenameModel`, `RemoveField`, and `AlterField`.
+
+If the comment isn't added, the Github Action will flag that the migration is potentially dangerous, and the pull request will fail. The Github Action's log will tell you which file(s) are failing. The developer will then need to add the comment/check the migration, and push the changes to the pull request.
+
+While this won't entirely stop potential data issues, it will help to catch any potential issues by forcing the developer to check that their migrations are sound, before they
+are deployed.
+
 ### SASS/CSS and Javascript
 
 The Etna project uses a few tools to improve the consistency and quality of SASS/CSS and JavaScript code: