perf(objects): add fastNullObject helper

package.json

@@ -2698,6 +2698,15 @@
       "types": "./dist/objects/mutate.d.ts",
       "default": "./dist/objects/mutate.js"
     },
+    "./objects/options": {
+      "source": "./src/objects/options.mts",
+      "browser": {
+        "types": "./dist/objects/options.d.ts",
+        "default": "./dist/objects/options.js"
+      },
+      "types": "./dist/objects/options.d.ts",
+      "default": "./dist/objects/options.js"
+    },
     "./objects/predicates": {
       "source": "./src/objects/predicates.mts",
       "browser": {

src/globs/matcher.mts

@@ -8,6 +8,7 @@
 import { ArrayIsArray } from '../primordials/array.mjs'
 import { JSONStringify } from '../primordials/json.mjs'
 import { ObjectKeys } from '../primordials/object.mjs'
+import { fastNullObject } from '../objects/options.mjs'
 import { arrayToSorted } from '../polyfills/array.mjs'
 import { StringPrototypeStartsWith } from '../primordials/string.mjs'
 
@@ -52,6 +53,8 @@ let matchesGlobProbed = false
  *   const isSource = getGlobMatcher(['src/**', '!**\/*.test.ts'])
  *   ```
  */
+// `fastNullObject` sets the copied object's null prototype with a primordial.
+// oxlint-disable-next-line socket/options-null-proto -- shared helper
 export function getGlobMatcher(
   glob: Pattern | Pattern[],
   options?:
@@ -62,7 +65,7 @@ export function getGlobMatcher(
       }
     | undefined,
 ): (path: string) => boolean {
-  options = { __proto__: null, ...options } as typeof options
+  options = fastNullObject(options)
   const patterns = ArrayIsArray(glob) ? glob : [glob]
   // Create stable cache key by sorting patterns and option keys.
   // Option values that are arrays (e.g. `ignore: ['a', 'b']`) get sorted

src/objects/options.mts

@@ -0,0 +1,14 @@
+/**
+ * Shallow-copy an object, then mutate the new copy's prototype to `null`.
+ *
+ * Object spread copies only own enumerable properties. Setting the prototype
+ * mutates only the newly created copy, keeping it out of Object.prototype
+ * while retaining the fast property layout of the ordinary object literal.
+ * The input object is not mutated.
+ */
+import { ObjectSetPrototypeOf } from '../primordials/object.mjs'
+
+export function fastNullObject<T extends object>(options?: T | undefined): T {
+  // oxlint-disable-next-line socket/prefer-undefined-over-null -- null creates the required null prototype.
+  return ObjectSetPrototypeOf({ ...options }, null) as T
+}

test/unit/objects/options.test.mts

@@ -0,0 +1,43 @@
+import { describe, expect, it } from 'vitest'
+
+import { fastNullObject } from '../../../src/objects/options.mjs'
+
+describe('objects/options — fastNullObject', () => {
+  it('copies own enumerable values onto a null-prototype object', () => {
+    const inherited = { inherited: 'ignored' }
+    const input = Object.assign(Object.create(inherited), {
+      dry: true,
+      verbose: false,
+    })
+
+    const options = fastNullObject(input)
+
+    expect(Object.getPrototypeOf(input)).toBe(inherited)
+    expect(Object.getPrototypeOf(options)).toBe(null)
+    expect(options).toEqual({ dry: true, verbose: false })
+    expect('inherited' in options).toBe(false)
+  })
+
+  it('preserves an own __proto__ key as data', () => {
+    const input = JSON.parse('{"__proto__":{"polluted":true}}') as Record<
+      string,
+      unknown
+    >
+
+    const options = fastNullObject(input)
+
+    expect(Object.getPrototypeOf(options)).toBe(null)
+    expect(Object.hasOwn(options, '__proto__')).toBe(true)
+    expect(
+      Object.getOwnPropertyDescriptor(options, '__proto__')?.value,
+    ).toEqual({ polluted: true })
+    expect('polluted' in options).toBe(false)
+  })
+
+  it('accepts omitted options', () => {
+    const options = fastNullObject()
+
+    expect(Object.getPrototypeOf(options)).toBe(null)
+    expect(Object.keys(options)).toEqual([])
+  })
+})