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 +71,11 @@ $ 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.
 
+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.
+
+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: