feat(rule): safe-migration detection (closes #6)

__tests__/database/safe-migration.test.js

@@ -0,0 +1,63 @@
+const rule = require('../../src/rules/database/safe-migration');
+
+describe('Safe Migration Rule', () => {
+  it('labels for additive migrations without risky ops', () => {
+    const files = [{ filename: 'migrations/001_add_users.sql', patch: '+ ALTER TABLE users ADD COLUMN age INT;' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toContain('safe-migration');
+  });
+
+  it('labels for CREATE INDEX operations', () => {
+    const files = [{ filename: 'db/migrations/002_add_index.sql', patch: '+ CREATE INDEX idx_email ON users(email);' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toContain('safe-migration');
+  });
+
+  it('labels for CREATE TABLE operations', () => {
+    const files = [{ filename: 'database/migrations/003_create.sql', patch: '+ CREATE TABLE posts (id INT);' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toContain('safe-migration');
+  });
+
+  it('does not label when risky ops are present', () => {
+    const files = [{ filename: 'migrations/002_drop_table.sql', patch: '+ DROP TABLE users;' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toEqual([]);
+  });
+
+  it('does not label when ALTER DROP is present', () => {
+    const files = [{ filename: 'migrations/003_alter.sql', patch: '+ ALTER TABLE users DROP COLUMN age;' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toEqual([]);
+  });
+
+  it('does not label when no migrations found', () => {
+    const files = [{ filename: 'src/app.ts', patch: '+ const x = 1;' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toEqual([]);
+  });
+
+  it('does not label when migration has no patch', () => {
+    const files = [{ filename: 'migrations/004_test.sql' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toEqual([]);
+  });
+
+  it('does not label when only risky ops without additive', () => {
+    const files = [{ filename: 'migrations/005_truncate.sql', patch: '+ TRUNCATE TABLE users;' }];
+    const labels = rule({ files, pr: {}, enableDebug: false });
+    expect(labels).toEqual([]);
+  });
+
+  it('handles empty files array', () => {
+    const labels = rule({ files: [], pr: {}, enableDebug: false });
+    expect(labels).toEqual([]);
+  });
+
+  it('handles debug mode', () => {
+    const files = [{ filename: 'migrations/006_add.sql', patch: '+ ADD COLUMN name VARCHAR(255);' }];
+    expect(() => rule({ files, pr: {}, enableDebug: true })).not.toThrow();
+  });
+});
+
+

src/rules/database/safe-migration.js

@@ -0,0 +1,52 @@
+/**
+ * Safe Migration Detection Rule
+ *
+ * Adds `safe-migration` when migration files are present and no risky/schema
+ * keywords are detected (i.e., only additive changes like ADD COLUMN/INDEX).
+ */
+
+module.exports = function safeMigrationRule({ files, pr, enableDebug }) {
+  const labels = [];
+
+  const isMigration = (name) => /(^|\/)(migrations|db\/migrations|database\/migrations)\//i.test(name) || /\.sql$/i.test(name);
+  const risky = /(DROP\s+TABLE|TRUNCATE\s+TABLE|ALTER\s+TABLE\s+[^;]*\s+DROP\b|RENAME\s+COLUMN|MODIFY\s+COLUMN)/i;
+  const additive = /(CREATE\s+INDEX|ADD\s+COLUMN|CREATE\s+TABLE|ADD\s+CONSTRAINT)/i;
+
+  let hasMigration = false;
+  let hasRisky = false;
+  let hasAdditive = false;
+
+  for (const file of files || []) {
+    const name = (file && file.filename ? String(file.filename) : '').toLowerCase();
+    if (!name || !isMigration(name)) continue;
+    hasMigration = true;
+    const patch = file && file.patch ? String(file.patch) : '';
+    if (patch) {
+      if (risky.test(patch)) hasRisky = true;
+      if (additive.test(patch)) hasAdditive = true;
+    }
+  }
+
+  if (hasMigration && !hasRisky && hasAdditive) {
+    labels.push('safe-migration');
+  }
+
+  if (enableDebug) {
+    console.log(`[Safe Migration Rule] hasMigration=${hasMigration} risky=${hasRisky} additive=${hasAdditive} → ${labels.join(', ') || 'none'}`);
+  }
+
+  return labels;
+};
+
+module.exports.metadata = {
+  name: 'Safe Migration Detection',
+  description: 'Detects additive-only DB migrations (safe to apply)',
+  labels: [
+    { name: 'safe-migration', color: '0E8A16', description: 'Additive database migration detected' }
+  ],
+  author: 'pr-auto-labeler',
+  version: '1.0.0',
+  category: 'database'
+};
+
+