commit 870b9a7a2645f11ec461063d94222eb96a7a6fc1
Author: david_wobrock <dw@3yourmind.com>
Date:   Sat Apr 1 20:18:56 2017 +0200

    Very first version of the migration checker and its tests

diff --git a/migration_checker.py b/migration_checker.py
new file mode 100644
index 0000000..2a2af15
--- /dev/null
+++ b/migration_checker.py
@@ -0,0 +1,132 @@
+from __future__ import print_function
+import os
+import re
+from subprocess import Popen, PIPE
+import sys
+
+
+class MigrationChecker:
+    MIGRATION_FOLDER_NAME = 'migrations'
+
+    migration_tests = ({
+            'fn': lambda sql: re.search('NOT NULL', sql),
+            'err_msg': 'NOT NULL constraint on columns'
+        }, {
+            'fn': lambda sql: re.search('DROP COLUMN', sql),
+            'err_msg': 'DROPPING columns'
+        }, {
+            'fn': lambda sql: re.search('ADD COLUMN .* DEFAULT', sql),
+            'err_msg': 'ADD columns with default'
+        }
+    )
+
+    def __init__(self, django_folder, commit_id=None):
+        self.location = django_folder
+        self.commit_id = commit_id
+        self.changed_migration_files = []
+        self._gather_migrations()
+        
+    def _gather_migrations(self):
+        # Find (one of) the initial commits
+        if not self.commit_id:
+            git_init_cmd = 'cd {0} && git rev-list HEAD | tail -n 1'.format(self.location)
+            process = Popen(git_init_cmd, shell=True, stdout=PIPE, stderr=PIPE)
+            for line in process.stdout.readlines():
+                self.commit_id = line.strip()
+                break
+            process.wait()
+
+        # Get changes since specified commit
+        git_diff_command = 'cd {0} && git diff --name-only {1}'.format(self.location, self.commit_id)
+        diff_process = Popen(git_diff_command, shell=True, stdout=PIPE, stderr=PIPE)
+        for line in diff_process.stdout.readlines():
+            # Only gather lines that include migrations
+            if self.MIGRATION_FOLDER_NAME in line:
+                self.changed_migration_files.append(line.strip())
+        diff_process.wait()
+
+    def check_migrations(self):
+        nb_valid = 0
+        nb_erroneous = 0
+        for migration in self.changed_migration_files:
+            app_name, migration_name = self._split_migration_path(migration)
+            sql_statements = self.django_sqlmigrate(app_name, migration_name)
+            print('{0}... '.format(migration), end='')
+
+            errors = set()
+            for statement in sql_statements:
+                is_valid, err_msg = self._test_sql_statement_for_backward_incompatibility(statement)
+                if not is_valid:
+                    errors.add(err_msg)
+            if not errors:
+                print('OK')
+                nb_valid += 1
+            else:
+                print('ERR')
+                nb_erroneous += 1
+                for err in errors:
+                    print(err)
+        print('*** Summary:')
+        print('Valid migrations: {0}/{1} - erroneous migrations: {2}/{1}'.format(nb_valid, len(self.changed_migration_files), nb_erroneous))
+
+    def _split_migration_path(self, migration_path):
+        decomposed_path = split_path(migration_path)
+        for i, p in enumerate(decomposed_path):
+            if p == self.MIGRATION_FOLDER_NAME:
+                return decomposed_path[i-1], os.path.splitext(decomposed_path[i+1])[0]
+
+    def django_sqlmigrate(self, app_name, migration_name):
+        git_diff_command = 'cd {0} && python manage.py sqlmigrate {1} {2}'.format(self.location, app_name, migration_name)
+        diff_process = Popen(git_diff_command, shell=True, stdout=PIPE, stderr=PIPE)
+        sql_statements = []
+        for line in diff_process.stdout.readlines():
+            if not line.startswith('--'):  # Do not take sql comments into account
+                sql_statements.append(line.strip())
+        diff_process.wait()
+        return sql_statements
+
+    def _test_sql_statement_for_backward_incompatibility(self, sql_statement):
+        for test in self.migration_tests:
+            if test['fn'](sql_statement):
+                return False, test['err_msg']
+        return True, None
+
+
+def valid_folder(folder):
+    """Verify folder exists,
+    folder is a django project
+    and folder is git versioned
+    """
+    if not os.path.isdir(folder):
+        print("The passed argument doesn't seem to be a folder.")
+        return False
+    django_manage_file = os.path.join(folder, 'manage.py')
+    if not os.path.isfile(django_manage_file):
+        print("The passed folder doesn't seem to be a django project (no manage.py found).")
+        return False
+    git_folder = os.path.join(folder, '.git')
+    if not os.path.isdir(git_folder):
+        print("The passed folder doesn't seem to versioned by git (no .git/ folder found).")
+        return False
+    return True
+
+
+def split_path(path):
+    a, b = os.path.split(path)
+    return (split_path(a) if len(a) > 0 else []) + [b]
+
+
+def print_usage():
+    print('Usage')
+
+
+if __name__ == '__main__':
+    if len(sys.argv) < 1:
+        print_usage()
+        sys.exit(1)
+
+    folder_name = sys.argv[1]
+    if valid_folder(folder_name):
+        commit_id = sys.argv[2] if len(sys.argv) > 2 else None
+        checker = MigrationChecker(folder_name, commit_id)
+        checker.check_migrations()
diff --git a/test_migration_checker.py b/test_migration_checker.py
new file mode 100644
index 0000000..b52acef
--- /dev/null
+++ b/test_migration_checker.py
@@ -0,0 +1,17 @@
+import unittest
+
+import checker
+
+
+class CheckerTest(unittest.TestCase):
+    def test_split_migration_path(self):
+        input_path = 'apps/the_app/migrations/0001_stuff.py'
+        app, mig = checker.split_migration_path(input_path)
+        self.assertEqual(app, 'the_app')
+        self.assertEqual(mig, '0001_stuff')
+
+    def test_split_migration_path_2(self):
+        input_path = 'the_app/migrations/0001_stuff.py'
+        app, mig = checker.split_migration_path(input_path)
+        self.assertEqual(app, 'the_app')
+        self.assertEqual(mig, '0001_stuff')