fix: tie proto key blocking to ownPropertyOnly policy

Block __proto__, constructor, and prototype only when ownPropertyOnly
is true or when access would traverse the prototype chain. Allow own
properties with those names when ownPropertyOnly is false.

Co-authored-by: Cursor <[email protected]>

src/context/context.spec.ts

@@ -198,8 +198,20 @@ describe('Context', function () {
         delete (Array.prototype as any)[0]
       }
     })
-    it('should block __proto__ access', function () {
-      ctx.push({ foo: { __proto__: { bar: 'BAR' } } })
+    it('should allow own blocked keys when ownPropertyOnly=false', function () {
+      ctx = new Context({
+        foo: {
+          ...JSON.parse('{"__proto__": {"bar": "BAR"}}'),
+          constructor: { name: 'Custom' },
+          prototype: { x: 1 }
+        }
+      }, { ownPropertyOnly: false } as any)
+      expect(ctx.getSync(['foo', '__proto__', 'bar'])).toEqual('BAR')
+      expect(ctx.getSync(['foo', 'constructor', 'name'])).toEqual('Custom')
+      expect(ctx.getSync(['foo', 'prototype', 'x'])).toEqual(1)
+    })
+    it('should still block inherited blocked keys when ownPropertyOnly=false', function () {
+      ctx = new Context({ foo: Object.create({ __proto__: { bar: 'BAR' } }) }, { ownPropertyOnly: false } as any)
       expect(ctx.getSync(['foo', '__proto__'])).toEqual(undefined)
     })
     it('should block constructor access', function () {

src/context/context.ts

@@ -1,7 +1,7 @@
 import { Drop } from '../drop/drop'
 import { __assign } from 'tslib'
 import { NormalizedFullOptions, defaultOptions, RenderOptions } from '../liquid-options'
-import { createScope, isBlockedScopeKey, Scope } from './scope'
+import { createScope, isBlockedScopeKey, Scope, shouldBlockScopeKeyRead } from './scope'
 import { hasOwnProperty, isArray, isNil, isUndefined, isString, isFunction, isNumber, toLiquid, InternalUndefinedVariableError, toValueSync, isObject, Limiter, toValue, readArrayElement } from '../util'
 
 type PropertyKey = string | number;
@@ -116,7 +116,7 @@ export class Context {
     })
   }
   private findScope (key: string | number) {
-    if (isBlockedScopeKey(key)) return createScope()
+    if (isBlockedScopeKey(key) && this.ownPropertyOnly) return createScope()
     const hasKey = (obj: Scope) => {
       if (obj == null) return false
       return this.ownPropertyOnly
@@ -147,7 +147,7 @@ export class Context {
 }
 
 export function readJSProperty (obj: Scope, key: PropertyKey, ownPropertyOnly: boolean) {
-  if (isBlockedScopeKey(key)) return undefined
+  if (shouldBlockScopeKeyRead(obj, key, ownPropertyOnly)) return undefined
   if (ownPropertyOnly && !hasOwnProperty.call(obj, key) && !(obj instanceof Drop)) return undefined
   return obj[key]
 }

src/context/scope.ts

@@ -13,6 +13,16 @@ export function isBlockedScopeKey (key: PropertyKey): boolean {
   return typeof key === 'string' && BLOCKED_SCOPE_KEYS.has(key)
 }
 
+export function shouldBlockScopeKeyRead (obj: Scope, key: PropertyKey, ownPropertyOnly: boolean): boolean {
+  if (!isBlockedScopeKey(key)) return false
+  if (ownPropertyOnly) return true
+  return !hasOwnProperty.call(obj, key)
+}
+
+export function shouldBlockScopeKeyWrite (key: PropertyKey, ownPropertyOnly: boolean): boolean {
+  return ownPropertyOnly && isBlockedScopeKey(key)
+}
+
 export function createScope (from?: ScopeObject): ScopeObject {
   return from ? sanitizeScope(from) : Object.create(null)
 }
@@ -20,7 +30,7 @@ export function createScope (from?: ScopeObject): ScopeObject {
 export function sanitizeScope (obj: ScopeObject): ScopeObject {
   const scope = Object.create(null)
   for (const key of Object.keys(obj)) {
-    if (!isBlockedScopeKey(key) && hasOwnProperty.call(obj, key)) {
+    if (hasOwnProperty.call(obj, key)) {
       scope[key] = obj[key]
     }
   }