feat(context): null-prototype scope frames via createScope (#899)

- Add createScope() building Object.create(null) with optional own props

- Initialize context stack bottom with createScope() for assign/capture

- Push null-proto scopes from for, tablerow, block, layout, include (incl. Jekyll)

Co-authored-by: Cursor <cursoragent@cursor.com>

Author: harttle

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 { createScope, Scope } from './scope'
 import { hasOwnProperty, isArray, isNil, isUndefined, isString, isFunction, toLiquid, InternalUndefinedVariableError, toValueSync, isObject, Limiter, toValue } from '../util'
 
 type PropertyKey = string | number;
@@ -12,7 +12,7 @@ export class Context {
    * insert a Context-level empty scope,
    * for tags like `{% capture %}` `{% assign %}` to operate
    */
-  private scopes: Scope[] = [{}]
+  private scopes: Scope[] = [createScope()]
   private registers = {}
   /**
    * user passed in scope

src/context/scope.ts

@@ -1,7 +1,13 @@
 import { Drop } from '../drop/drop'
 
-interface ScopeObject extends Record<string | number | symbol, any> {
+export interface ScopeObject extends Record<string | number | symbol, any> {
   toLiquid?: () => any;
 }
 
 export type Scope = ScopeObject | Drop
+
+export function createScope (from?: ScopeObject): ScopeObject {
+  const scope = Object.create(null)
+  if (from) Object.assign(scope, from)
+  return scope
+}

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 '..'
@@ -38,7 +38,7 @@ export default class extends Tag {
       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/for.ts

@@ -1,5 +1,6 @@
 import { Hash, ValueToken, Liquid, Tag, evalToken, Emitter, TagToken, TopLevelToken, Context, Template, ParseStream } from '..'
 import { assertEmpty, isValueToken, toEnumerable } from '../util'
+import { createScope } from '../context/scope'
 import { ForloopDrop } from '../drop/forloop-drop'
 import { Parser } from '../parser'
 import { Arguments } from '../template'
@@ -50,7 +51,7 @@ 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, {}) }))
     const hash = yield this.hash.render(ctx)
     ctx.pop()
 
@@ -65,7 +66,7 @@ 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

@@ -1,5 +1,5 @@
 import { Template, ValueToken, TopLevelToken, Liquid, Tag, assert, evalToken, Hash, Emitter, TagToken, Context } from '..'
-import { BlockMode, Scope } from '../context'
+import { BlockMode, createScope, Scope } from '../context'
 import { Parser } from '../parser'
 import { Argument, Arguments, PartialScope } from '../template'
 import { isString, isValueToken } from '../util'
@@ -34,10 +34,10 @@ export default class extends Tag {
     const saved = ctx.saveRegister('blocks', 'blockMode')
     ctx.setRegister('blocks', {})
     ctx.setRegister('blockMode', BlockMode.OUTPUT)
-    const scope = (yield hash.render(ctx)) as Scope
+    const scope = createScope((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 }) : scope)
     yield renderer.renderTemplates(templates, ctx, emitter)
     ctx.pop()
     ctx.restoreRegister(saved)

src/tags/layout.ts

@@ -1,5 +1,5 @@
 import { Scope, Template, Liquid, Tag, assert, Emitter, Hash, TagToken, TopLevelToken, Context } from '..'
-import { BlockMode } from '../context'
+import { BlockMode, createScope } from '../context'
 import { parseFilePath, renderFilePath, ParsedFileName } from './render'
 import { BlankDrop } from '../drop'
 import { Parser } from '../parser'
@@ -39,7 +39,7 @@ export default class extends Tag {
     ctx.setRegister('blockMode', BlockMode.OUTPUT)
 
     // render the layout file use stored blocks
-    ctx.push((yield args.render(ctx)) as Scope)
+    ctx.push(createScope((yield args.render(ctx)) as Scope))
     yield renderer.renderTemplates(templates, ctx, emitter)
     ctx.pop()
   }

src/tags/tablerow.ts

@@ -1,4 +1,5 @@
 import { isValueToken, toEnumerable } from '../util'
+import { createScope } from '../context/scope'
 import { ValueToken, Liquid, Tag, evalToken, Emitter, Hash, TagToken, TopLevelToken, Context, Template, ParseStream } from '..'
 import { TablerowloopDrop } from '../drop/tablerowloop-drop'
 import { Parser } from '../parser'
@@ -48,7 +49,7 @@ 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()) {