fix(context): use null-prototype scope and register objects

Add createScope(); use for bottom scope, spawn default, getAll merge, ctx.push frames, filter loops, include/layout blocks registers, and cycle groups. registers uses Object.create(null) and getRegister uses ??.

For-loop continue register defaults to 0 (not {}): Array.slice coerces plain {} but not null-prototype objects.

Export createScope from the package entry.

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

src/context/context.spec.ts

@@ -216,4 +216,12 @@ describe('Context', function () {
       expect(ctx.getSync(['foo'])).toEqual('zoo')
     })
   })
+  describe('scope storage', function () {
+    it('should use null prototype for bottom scope', function () {
+      expect(Object.getPrototypeOf(new Context().bottom())).toBeNull()
+    })
+    it('should use null prototype for getAll() merge result', function () {
+      expect(Object.getPrototypeOf(new Context({ a: 1 }).getAll())).toBeNull()
+    })
+  })
 })

src/context/context.ts

@@ -2,7 +2,7 @@ import { getPerformance } from '../util/performance'
 import { Drop } from '../drop/drop'
 import { __assign } from 'tslib'
 import { NormalizedFullOptions, defaultOptions, RenderOptions } from '../liquid-options'
-import { Scope } from './scope'
+import { Scope, createScope } from './scope'
 import { hasOwnProperty, isArray, isNil, isUndefined, isString, isFunction, toLiquid, InternalUndefinedVariableError, toValueSync, isObject, Limiter, toValue } from '../util'
 
 type PropertyKey = string | number;
@@ -12,8 +12,8 @@ export class Context {
    * insert a Context-level empty scope,
    * for tags like `{% capture %}` `{% assign %}` to operate
    */
-  private scopes: Scope[] = [{}]
-  private registers = {}
+  private scopes: Scope[] = [createScope()]
+  private registers: Record<string, any> = Object.create(null)
   /**
    * user passed in scope
    * `{% increment %}`, `{% decrement %}` changes this scope,
@@ -49,7 +49,7 @@ export class Context {
     this.renderLimit = renderLimit ?? new Limiter('template render', getPerformance().now() + (renderOptions.renderLimit ?? opts.renderLimit))
   }
   public getRegister<T> (key: string, defaultValue: T = undefined as T): T {
-    return (this.registers[key] = this.registers[key] || defaultValue)
+    return (this.registers[key] = this.registers[key] ?? defaultValue)
   }
   public setRegister (key: string, value: any) {
     return (this.registers[key] = value)
@@ -62,7 +62,7 @@ export class Context {
   }
   public getAll () {
     return [this.globals, this.environments, ...this.scopes]
-      .reduce((ctx, val) => __assign(ctx, val), {})
+      .reduce((ctx, val) => __assign(ctx, val), createScope())
   }
   /**
    * @deprecated use `_get()` or `getSync()` instead
@@ -102,7 +102,7 @@ export class Context {
   public bottom () {
     return this.scopes[0]
   }
-  public spawn (scope = {}) {
+  public spawn (scope: object = createScope()) {
     return new Context(scope, this.opts, {
       sync: this.sync,
       globals: this.globals,

src/context/scope.ts

@@ -5,3 +5,13 @@ interface ScopeObject extends Record<string | number | symbol, any> {
 }
 
 export type Scope = ScopeObject | Drop
+
+/**
+ * Plain scope bag with a null prototype so lookups like `__proto__` are not the
+ * Object.prototype accessor unless explicitly assigned as an own property.
+ */
+export function createScope (props?: Record<PropertyKey, any>): ScopeObject {
+  return props == null
+    ? Object.create(null)
+    : Object.assign(Object.create(null), props)
+}

src/filters/array.ts

@@ -2,7 +2,7 @@ import { toArray, argumentsToValue, toValue, stringify, caseInsensitiveCompare,
 import { arrayIncludes, equals, evalToken, isTruthy } from '../render'
 import { Value, FilterImpl } from '../template'
 import { Tokenizer } from '../parser'
-import type { Scope } from '../context'
+import { createScope, type Scope } from '../context'
 import { EmptyDrop } from '../drop'
 
 export const join = argumentsToValue(function (this: FilterImpl, v: any[], arg: string) {
@@ -139,7 +139,7 @@ function * filter_exp<T extends object> (this: FilterImpl, include: boolean, arr
   const array = toArray(arr)
   this.context.memoryLimit.use(array.length)
   for (const item of array) {
-    this.context.push({ [itemName]: item })
+    this.context.push(createScope({ [itemName]: item }))
     const value = yield keyTemplate.value(this.context)
     this.context.pop()
     if (value === include) filtered.push(item)
@@ -182,7 +182,7 @@ export function * group_by_exp<T extends object> (this: FilterImpl, arr: T[], it
   arr = toEnumerable(arr)
   this.context.memoryLimit.use(arr.length)
   for (const item of arr) {
-    this.context.push({ [itemName]: item })
+    this.context.push(createScope({ [itemName]: item }))
     const key = yield keyTemplate.value(this.context)
     this.context.pop()
     if (!map.has(key)) map.set(key, [])
@@ -205,7 +205,7 @@ function * search_exp<T extends object> (this: FilterImpl, arr: T[], itemName: s
   const predicate = new Value(stringify(exp), this.liquid)
   const array = toArray(arr)
   for (let index = 0; index < array.length; index++) {
-    this.context.push({ [itemName]: array[index] })
+    this.context.push(createScope({ [itemName]: array[index] }))
     const value = yield predicate.value(this.context)
     this.context.pop()
     if (value) return [index, array[index]]

src/index.ts

@@ -7,7 +7,7 @@ export { Drop } from './drop'
 export type { Comparable } from './drop'
 export { Emitter } from './emitters'
 export { defaultOperators, Operators, evalToken, evalQuotedToken, Expression, isFalsy, isTruthy } from './render'
-export { Context, Scope } from './context'
+export { Context, Scope, createScope } from './context'
 export { Value, Hash, Template, FilterImplOptions, Tag, Filter, Output, Variable, VariableLocation, VariableSegments, Variables, StaticAnalysis, StaticAnalysisOptions, analyze, analyzeSync, Arguments, PartialScope } from './template'
 export type { TagRenderReturn } from './template'
 export { Token, TopLevelToken, TagToken, ValueToken } from './tokens'

src/tags/block.ts

@@ -1,4 +1,4 @@
-import { BlockMode } from '../context'
+import { BlockMode, createScope } from '../context'
 import { isTagToken } from '../util'
 import { BlockDrop } from '../drop'
 import { Liquid, TagToken, TopLevelToken, Template, Context, Emitter, Tag } from '..'
@@ -23,7 +23,7 @@ export default class extends Tag {
   * render (ctx: Context, emitter: Emitter) {
     const blockRender = this.getBlockRender(ctx)
     if (ctx.getRegister('blockMode') === BlockMode.STORE) {
-      ctx.getRegister('blocks', {} as Record<string, any>)[this.block] = blockRender
+      ctx.getRegister('blocks', createScope() as Record<string, any>)[this.block] = blockRender
     } else {
       yield blockRender(new BlockDrop(), emitter)
     }
@@ -32,13 +32,13 @@ export default class extends Tag {
   private getBlockRender (ctx: Context) {
     const self = this as Tag
     const { liquid, templates } = this
-    const renderChild = ctx.getRegister('blocks', {} as Record<string, any>)[this.block]
+    const renderChild = ctx.getRegister('blocks', createScope() as Record<string, any>)[this.block]
     const renderCurrent = function * (superBlock: BlockDrop, emitter: Emitter) {
       const stack: Tag[] = ctx.getRegister('blockStack', [])
       if (stack.includes(self)) throw new Error('block tag cannot be nested')
 
       stack.push(self)
-      ctx.push({ block: superBlock })
+      ctx.push(createScope({ block: superBlock }))
       yield liquid.renderer.renderTemplates(templates, ctx, emitter)
       ctx.pop()
       stack.pop()

src/tags/cycle.ts

@@ -1,4 +1,4 @@
-import { TopLevelToken, Liquid, ValueToken, evalToken, Emitter, TagToken, Context, Tag } from '..'
+import { TopLevelToken, Liquid, ValueToken, evalToken, Emitter, TagToken, Context, Tag, createScope } from '..'
 import { Arguments } from '../template'
 
 export default class extends Tag {
@@ -27,7 +27,7 @@ export default class extends Tag {
   * render (ctx: Context, emitter: Emitter): Generator<unknown, unknown, unknown> {
     const group = (yield evalToken(this.group, ctx)) as ValueToken
     const fingerprint = `cycle:${group}:` + this.candidates.join(',')
-    const groups = ctx.getRegister('cycle', {} as Record<string, number>)
+    const groups = ctx.getRegister('cycle', createScope() as Record<string, number>)
     let idx = groups[fingerprint]
 
     if (idx === undefined) {

src/tags/for.ts

@@ -1,4 +1,4 @@
-import { Hash, ValueToken, Liquid, Tag, evalToken, Emitter, TagToken, TopLevelToken, Context, Template, ParseStream } from '..'
+import { Hash, ValueToken, Liquid, Tag, evalToken, Emitter, TagToken, TopLevelToken, Context, Template, ParseStream, createScope } from '..'
 import { assertEmpty, isValueToken, toEnumerable } from '../util'
 import { ForloopDrop } from '../drop/forloop-drop'
 import { Parser } from '../parser'
@@ -50,7 +50,7 @@ export default class extends Tag {
     }
 
     const continueKey = 'continue-' + this.variable + '-' + this.collection.getText()
-    ctx.push({ continue: ctx.getRegister(continueKey, {}) })
+    ctx.push(createScope({ continue: ctx.getRegister(continueKey, 0) }))
     const hash = yield this.hash.render(ctx)
     ctx.pop()
 
@@ -65,7 +65,7 @@ export default class extends Tag {
     }, collection)
 
     ctx.setRegister(continueKey, (hash['offset'] || 0) + collection.length)
-    const scope = { forloop: new ForloopDrop(collection.length, this.collection.getText(), this.variable) }
+    const scope = createScope({ forloop: new ForloopDrop(collection.length, this.collection.getText(), this.variable) })
     ctx.push(scope)
     for (const item of collection) {
       scope[this.variable] = item

src/tags/include.ts

@@ -1,4 +1,4 @@
-import { Template, ValueToken, TopLevelToken, Liquid, Tag, assert, evalToken, Hash, Emitter, TagToken, Context } from '..'
+import { Template, ValueToken, TopLevelToken, Liquid, Tag, assert, evalToken, Hash, Emitter, TagToken, Context, createScope } from '..'
 import { BlockMode, Scope } from '../context'
 import { Parser } from '../parser'
 import { Argument, Arguments, PartialScope } from '../template'
@@ -32,12 +32,12 @@ export default class extends Tag {
     assert(filepath, () => `illegal file path "${filepath}"`)
 
     const saved = ctx.saveRegister('blocks', 'blockMode')
-    ctx.setRegister('blocks', {})
+    ctx.setRegister('blocks', createScope())
     ctx.setRegister('blockMode', BlockMode.OUTPUT)
     const scope = (yield hash.render(ctx)) as Scope
     if (withVar) scope[filepath] = yield evalToken(withVar, ctx)
     const templates = (yield liquid._parsePartialFile(filepath, ctx.sync, this['currentFile'])) as Template[]
-    ctx.push(ctx.opts.jekyllInclude ? { include: scope } : scope)
+    ctx.push(ctx.opts.jekyllInclude ? createScope({ include: scope }) : Object.assign(createScope(), scope))
     yield renderer.renderTemplates(templates, ctx, emitter)
     ctx.pop()
     ctx.restoreRegister(saved)

src/tags/layout.ts

@@ -1,4 +1,4 @@
-import { Scope, Template, Liquid, Tag, assert, Emitter, Hash, TagToken, TopLevelToken, Context } from '..'
+import { Scope, Template, Liquid, Tag, assert, Emitter, Hash, TagToken, TopLevelToken, Context, createScope } from '..'
 import { BlockMode } from '../context'
 import { parseFilePath, renderFilePath, ParsedFileName } from './render'
 import { BlankDrop } from '../drop'
@@ -32,14 +32,14 @@ export default class extends Tag {
     // render remaining contents and store rendered results
     ctx.setRegister('blockMode', BlockMode.STORE)
     const html = yield renderer.renderTemplates(this.templates, ctx)
-    const blocks = ctx.getRegister('blocks', {} as Record<string, any>)
+    const blocks = ctx.getRegister('blocks', createScope() as Record<string, any>)
 
     // set whole content to anonymous block if anonymous doesn't specified
     if (blocks[''] === undefined) blocks[''] = (parent: BlankDrop, emitter: Emitter) => emitter.write(html)
     ctx.setRegister('blockMode', BlockMode.OUTPUT)
 
     // render the layout file use stored blocks
-    ctx.push((yield args.render(ctx)) as Scope)
+    ctx.push(Object.assign(createScope(), (yield args.render(ctx)) as Scope))
     yield renderer.renderTemplates(templates, ctx, emitter)
     ctx.pop()
   }

src/tags/tablerow.ts

@@ -1,5 +1,5 @@
 import { isValueToken, toEnumerable } from '../util'
-import { ValueToken, Liquid, Tag, evalToken, Emitter, Hash, TagToken, TopLevelToken, Context, Template, ParseStream } from '..'
+import { ValueToken, Liquid, Tag, evalToken, Emitter, Hash, TagToken, TopLevelToken, Context, Template, ParseStream, createScope } from '..'
 import { TablerowloopDrop } from '../drop/tablerowloop-drop'
 import { Parser } from '../parser'
 import { Arguments } from '../template'
@@ -48,7 +48,7 @@ export default class extends Tag {
 
     const r = this.liquid.renderer
     const tablerowloop = new TablerowloopDrop(collection.length, cols, this.collection.getText(), this.variable)
-    const scope = { tablerowloop }
+    const scope = createScope({ tablerowloop })
     ctx.push(scope)
 
     for (let idx = 0; idx < collection.length; idx++, tablerowloop.next()) {