clone the inputs

Signed-off-by: Matteo Collina <[email protected]>

package.json

@@ -37,6 +37,8 @@
     "borp": "^0.10.0",
     "desm": "^1.3.1",
     "prettier": "^3.2.5",
+    "@types/rfdc": "^1.2.0",
+    "@types/semver": "^7.5.8",
     "typescript": "^5.3.3"
   },
   "prettier": {
@@ -57,7 +59,7 @@
   "main": "./dist/semgrator.js",
   "types": "./dist/semgrator.d.ts",
   "dependencies": {
-    "@types/semver": "^7.5.8",
+    "rfdc": "^1.3.1",
     "semver": "^7.6.0"
   }
 }

src/lib/semgrator.ts

@@ -2,6 +2,9 @@ import semver from 'semver'
 import { join } from 'node:path'
 import { pathToFileURL } from 'node:url'
 import { readdir } from 'node:fs/promises'
+import rfdc from 'rfdc'
+
+const clone = rfdc()
 
 export type Migration<Input, Output = Input> = {
   version: string
@@ -87,7 +90,7 @@ async function* processMigrations<Input, Output>(
   for await (const migration of migrations) {
     if (semver.gt(migration.version, lastVersion)) {
       // @ts-expect-error
-      result = await migration.up(result)
+      result = await migration.up(clone(result))
       lastVersion = migration.toVersion || migration.version
       changed = true
     }

src/test/semgrator.test.ts

@@ -2,13 +2,17 @@ import { test } from 'node:test'
 import { semgrator, Migration } from '../lib/semgrator.js'
 import { tspl } from '@matteo.collina/tspl'
 import { throws } from 'node:assert/strict'
+import { equal, deepEqual } from 'node:assert/strict'
 
 type SeenBy = {
   foo: string
   seenBy?: string
+  deep?: {
+    seenBy?: string
+  }
 }
 
-test('apply all  migrations', async t => {
+test('apply all migrations', async t => {
   const plan = tspl(t, { plan: 4 })
   const m1: Migration<SeenBy> = {
     version: '2.0.0',
@@ -207,3 +211,44 @@ test('throws if version is missing', async t => {
     },
   )
 })
+
+test('clones at each step', async t => {
+  const m1: Migration<SeenBy> = {
+    version: '2.0.0',
+    async up(input) {
+      input.seenBy = '2.0.0'
+      input.deep ||= {}
+      input.deep.seenBy = '2.0.0'
+      return input
+    },
+  }
+
+  const input = {
+    foo: 'bar',
+    deep: {
+      seenBy: '1.0.0',
+    },
+  }
+
+  const res = await semgrator<SeenBy, SeenBy>({
+    version: '1.0.0',
+    migrations: [m1],
+    input,
+  })
+
+  equal(res.version, '2.0.0')
+  equal(res.changed, true)
+  deepEqual(res.result, {
+    foo: 'bar',
+    seenBy: '2.0.0',
+    deep: {
+      seenBy: '2.0.0',
+    },
+  })
+  deepEqual(input, {
+    foo: 'bar',
+    deep: {
+      seenBy: '1.0.0',
+    },
+  })
+})