Bugfix: make compile() non-mutating (fix bcherny#370, fix bcherny#443)

Author: Boris Cherny

src/index.ts

@@ -1,7 +1,7 @@
 import {readFileSync} from 'fs'
 import {JSONSchema4} from 'json-schema'
 import {Options as $RefOptions} from 'json-schema-ref-parser'
-import {endsWith, merge} from 'lodash'
+import {cloneDeep, endsWith, merge} from 'lodash'
 import {dirname} from 'path'
 import {Options as PrettierOptions} from 'prettier'
 import {format} from './formatter'
@@ -138,9 +138,12 @@ export async function compile(schema: JSONSchema4, name: string, options: Partia
     _options.cwd += '/'
   }
 
-  const dereferenced = await dereference(schema, _options)
+  // Initial clone to avoid mutating the input
+  const _schema = cloneDeep(schema)
+
+  const dereferenced = await dereference(_schema, _options)
   if (process.env.VERBOSE) {
-    if (isDeepStrictEqual(schema, dereferenced)) {
+    if (isDeepStrictEqual(_schema, dereferenced)) {
       log('green', 'dereferencer', time(), '✅ No change')
     } else {
       log('green', 'dereferencer', time(), '✅ Result:', dereferenced)

test/test.ts

@@ -1,6 +1,7 @@
 import {run as runCLITests} from './testCLI'
 import {run as runCompileFromFileTests} from './testCompileFromFile'
 import {hasOnly, run as runE2ETests} from './testE2E'
+import {run as runIdempotenceTests} from './testIdempotence'
 import {run as runLinkerTests} from './testLinker'
 import {run as runNormalizerTests} from './testNormalizer'
 import {run as runUtilsTests} from './testUtils'
@@ -10,6 +11,7 @@ runE2ETests()
 if (!hasOnly()) {
   runCompileFromFileTests()
   runCLITests()
+  runIdempotenceTests()
   runLinkerTests()
   runNormalizerTests()
   runUtilsTests()

test/testIdempotence.ts

@@ -0,0 +1,28 @@
+import test from 'ava'
+import {JSONSchema4} from 'json-schema'
+import {cloneDeep} from 'lodash'
+import {compile} from '../src'
+
+export function run() {
+  const SCHEMA: JSONSchema4 = {
+    type: 'object',
+    properties: {
+      firstName: {
+        type: 'string'
+      }
+    },
+    required: ['firstName']
+  }
+
+  test('compile() should not mutate its input', async t => {
+    const before = cloneDeep(SCHEMA)
+    await compile(SCHEMA, 'A')
+    t.deepEqual(before, SCHEMA)
+  })
+
+  test('compile() should be idempotent', async t => {
+    const a = await compile(SCHEMA, 'A')
+    const b = await compile(SCHEMA, 'A')
+    t.deepEqual(a, b)
+  })
+}