text: /* @flow */
  
  import { genHandlers } from './events'
  import baseDirectives from '../directives/index'
  import { camelize, no, extend } from 'shared/util'
  import { baseWarn, pluckModuleFunction } from '../helpers'
  import { emptySlotScopeToken } from '../parser/index'
  
  type TransformFunction = (el: ASTElement, code: string) => string;
  type DataGenFunction = (el: ASTElement) => string;
  type DirectiveFunction = (el: ASTElement, dir: ASTDirective, warn: Function) => boolean;
  
  export class CodegenState {
    options: CompilerOptions;
    warn: Function;
    transforms: Array<TransformFunction>;
    dataGenFns: Array<DataGenFunction>;
    directives: { [key: string]: DirectiveFunction };
    maybeComponent: (el: ASTElement) => boolean;
    onceId: number;
    staticRenderFns: Array<string>;
    pre: boolean;
  
    constructor (options: CompilerOptions) {
      this.options = options
      this.warn = options.warn || baseWarn
      this.transforms = pluckModuleFunction(options.modules, 'transformCode')
      this.dataGenFns = pluckModuleFunction(options.modules, 'genData')
      this.directives = extend(extend({}, baseDirectives), options.directives)
      const isReservedTag = options.isReservedTag || no
      this.maybeComponent = (el: ASTElement) => !!el.component || !isReservedTag(el.tag)
      this.onceId = 0
      this.staticRenderFns = []
      this.pre = false
    }
  }
  
  export type CodegenResult = {
    render: string,
    staticRenderFns: Array<string>
  };
  
  export function generate (
    ast: ASTElement | void,
    options: CompilerOptions
  ): CodegenResult {
    const state = new CodegenState(options)
    const code = ast ? genElement(ast, state) : '_c("div")'
    return {
      render: `with(this){return ${code}}`,
      staticRenderFns: state.staticRenderFns
    }
  }
  
  export function genElement (el: ASTElement, state: CodegenState): string {
    if (el.parent) {
      el.pre = el.pre || el.parent.pre
    }
  
    if (el.staticRoot && !el.staticProcessed) {
      return genStatic(el, state)
    } else if (el.once && !el.onceProcessed) {
      return genOnce(el, state)
    } else if (el.for && !el.forProcessed) {
      return genFor(el, state)
    } else if (el.if && !el.ifProcessed) {
      return genIf(el, state)
    } else if (el.tag === 'template' && !el.slotTarget && !state.pre) {
      return genChildren(el, state) || 'void 0'
    } else if (el.tag === 'slot') {
      return genSlot(el, state)
    } else {
      // component or element
      let code
      if (el.component) {
        code = genComponent(el.component, el, state)
      } else {
        let data
        if (!el.plain || (el.pre && state.maybeComponent(el))) {
          data = genData(el, state)
        }
  
        const children = el.inlineTemplate ? null : genChildren(el, state, true)
        code = `_c('${el.tag}'${
          data ? `,${data}` : '' // data
        }${
          children ? `,${children}` : '' // children
        })`
      }
      // module transforms
      for (let i = 0; i < state.transforms.length; i++) {
        code = state.transforms[i](el, code)
      }
      return code
    }
  }
  
  // hoist static sub-trees out
  function genStatic (el: ASTElement, state: CodegenState): string {
    el.staticProcessed = true
    // Some elements (templates) need to behave differently inside of a v-pre
    // node.  All pre nodes are static roots, so we can use this as a location to
    // wrap a state change and reset it upon exiting the pre node.
    const originalPreState = state.pre
    if (el.pre) {
      state.pre = el.pre
    }
    state.staticRenderFns.push(`with(this){return ${genElement(el, state)}}`)
    state.pre = originalPreState
    return `_m(${
      state.staticRenderFns.length - 1
    }${
      el.staticInFor ? ',true' : ''
    })`
  }
  
  // v-once
  function genOnce (el: ASTElement, state: CodegenState): string {
    el.onceProcessed = true
    if (el.if && !el.ifProcessed) {
      return genIf(el, state)
    } else if (el.staticInFor) {
      let key = ''
      let parent = el.parent
      while (parent) {
        if (parent.for) {
          key = parent.key
          break
        }
        parent = parent.parent
      }
      if (!key) {
        process.env.NODE_ENV !== 'production' && state.warn(
          `v-once can only be used inside v-for that is keyed. `,
          el.rawAttrsMap['v-once']
        )
        return genElement(el, state)
      }
      return `_o(${genElement(el, state)},${state.onceId++},${key})`
    } else {
      return genStatic(el, state)
    }
  }
  
  export function genIf (
    el: any,
    state: CodegenState,
    altGen?: Function,
    altEmpty?: string
  ): string {
    el.ifProcessed = true // avoid recursion
    return genIfConditions(el.ifConditions.slice(), state, altGen, altEmpty)
  }
  
  function genIfConditions (
    conditions: ASTIfConditions,
    state: CodegenState,
    altGen?: Function,
    altEmpty?: string
  ): string {
    if (!conditions.length) {
      return altEmpty || '_e()'
    }
  
    const condition = conditions.shift()
    if (condition.exp) {
      return `(${condition.exp})?${
        genTernaryExp(condition.block)
      }:${
        genIfConditions(conditions, state, altGen, altEmpty)
      }`
    } else {
      return `${genTernaryExp(condition.block)}`
    }
  
    // v-if with v-once should generate code like (a)?_m(0):_m(1)
    function genTernaryExp (el) {
      return altGen
        ? altGen(el, state)
        : el.once
          ? genOnce(el, state)
          : genElement(el, state)
    }
  }
  
  export function genFor (
    el: any,
    state: CodegenState,
    altGen?: Function,
    altHelper?: string
  ): string {
    const exp = el.for
    const alias = el.alias
    const iterator1 = el.iterator1 ? `,${el.iterator1}` : ''
    const iterator2 = el.iterator2 ? `,${el.iterator2}` : ''
  
    if (process.env.NODE_ENV !== 'production' &&
      state.maybeComponent(el) &&
      el.tag !== 'slot' &&
      el.tag !== 'template' &&
      !el.key
    ) {
      state.warn(
        `<${el.tag} v-for="${alias} in ${exp}">: component lists rendered with ` +
        `v-for should have explicit keys. ` +
        `See https://vuejs.org/guide/list.html#key for more info.`,
        el.rawAttrsMap['v-for'],
        true /* tip */
      )
    }
  
    el.forProcessed = true // avoid recursion
    return `${altHelper || '_l'}((${exp}),` +
      `function(${alias}${iterator1}${iterator2}){` +
        `return ${(altGen || genElement)(el, state)}` +
      '})'
  }
  
  export function genData (el: ASTElement, state: CodegenState): string {
    let data = '{'
  
    // directives first.
    // directives may mutate the el's other properties before they are generated.
    const dirs = genDirectives(el, state)
    if (dirs) data += dirs + ','
  
    // key
    if (el.key) {
      data += `key:${el.key},`
    }
    // ref
    if (el.ref) {
      data += `ref:${el.ref},`
    }
    if (el.refInFor) {
      data += `refInFor:true,`
    }
    // pre
    if (el.pre) {
      data += `pre:true,`
    }
    // record original tag name for components using "is" attribute
    if (el.component) {
      data += `tag:"${el.tag}",`
    }
    // module data generation functions
    for (let i = 0; i < state.dataGenFns.length; i++) {
      data += state.dataGenFns[i](el)
    }
    // attributes
    if (el.attrs) {
      data += `attrs:${genProps(el.attrs)},`
    }
    // DOM props
    if (el.props) {
      data += `domProps:${genProps(el.props)},`
    }
    // event handlers
    if (el.events) {
      data += `${genHandlers(el.events, false)},`
    }
    if (el.nativeEvents) {
      data += `${genHandlers(el.nativeEvents, true)},`
    }
    // slot target
    // only for non-scoped slots
    if (el.slotTarget && !el.slotScope) {
      data += `slot:${el.slotTarget},`
    }
    // scoped slots
    if (el.scopedSlots) {
      data += `${genScopedSlots(el, el.scopedSlots, state)},`
    }
    // component v-model
    if (el.model) {
      data += `model:{value:${
        el.model.value
      },callback:${
        el.model.callback
      },expression:${
        el.model.expression
      }},`
    }
    // inline-template
    if (el.inlineTemplate) {
      const inlineTemplate = genInlineTemplate(el, state)
      if (inlineTemplate) {
        data += `${inlineTemplate},`
      }
    }
    data = data.replace(/,$/, '') + '}'
    // v-bind dynamic argument wrap
    // v-bind with dynamic arguments must be applied using the same v-bind object
    // merge helper so that class/style/mustUseProp attrs are handled correctly.
    if (el.dynamicAttrs) {
      data = `_b(${data},"${el.tag}",${genProps(el.dynamicAttrs)})`
    }
    // v-bind data wrap
    if (el.wrapData) {
      data = el.wrapData(data)
    }
    // v-on data wrap
    if (el.wrapListeners) {
      data = el.wrapListeners(data)
    }
    return data
  }
  
  function genDirectives (el: ASTElement, state: CodegenState): string | void {
    const dirs = el.directives
    if (!dirs) return
    let res = 'directives:['
    let hasRuntime = false
    let i, l, dir, needRuntime
    for (i = 0, l = dirs.length; i < l; i++) {
      dir = dirs[i]
      needRuntime = true
      const gen: DirectiveFunction = state.directives[dir.name]
      if (gen) {
        // compile-time directive that manipulates AST.
        // returns true if it also needs a runtime counterpart.
        needRuntime = !!gen(el, dir, state.warn)
      }
      if (needRuntime) {
        hasRuntime = true
        res += `{name:"${dir.name}",rawName:"${dir.rawName}"${
          dir.value ? `,value:(${dir.value}),expression:${JSON.stringify(dir.value)}` : ''
        }${
          dir.arg ? `,arg:${dir.isDynamicArg ? dir.arg : `"${dir.arg}"`}` : ''
        }${
          dir.modifiers ? `,modifiers:${JSON.stringify(dir.modifiers)}` : ''
        }},`
      }
    }
    if (hasRuntime) {
      return res.slice(0, -1) + ']'
    }
  }
  
  function genInlineTemplate (el: ASTElement, state: CodegenState): ?string {
    const ast = el.children[0]
    if (process.env.NODE_ENV !== 'production' && (
      el.children.length !== 1 || ast.type !== 1
    )) {
      state.warn(
        'Inline-template components must have exactly one child element.',
        { start: el.start }
      )
    }
    if (ast && ast.type === 1) {
      const inlineRenderFns = generate(ast, state.options)
      return `inlineTemplate:{render:function(){${
        inlineRenderFns.render
      }},staticRenderFns:[${
        inlineRenderFns.staticRenderFns.map(code => `function(){${code}}`).join(',')
      }]}`
    }
  }
  
  function genScopedSlots (
    el: ASTElement,
    slots: { [key: string]: ASTElement },
    state: CodegenState
  ): string {
    // by default scoped slots are considered "stable", this allows child
    // components with only scoped slots to skip forced updates from parent.
    // but in some cases we have to bail-out of this optimization
    // for example if the slot contains dynamic names, has v-if or v-for on them...
    let needsForceUpdate = Object.keys(slots).some(key => {
      const slot = slots[key]
      return slot.slotTargetDynamic || slot.if || slot.for
    })
    // OR when it is inside another scoped slot (the reactivity is disconnected)
    // #9438
    if (!needsForceUpdate) {
      let parent = el.parent
      while (parent) {
        if (parent.slotScope && parent.slotScope !== emptySlotScopeToken) {
          needsForceUpdate = true
          break
        }
        parent = parent.parent
      }
    }
  
    return `scopedSlots:_u([${
      Object.keys(slots).map(key => {
        return genScopedSlot(slots[key], state)
      }).join(',')
    }]${needsForceUpdate ? `,true` : ``})`
  }
  
  function genScopedSlot (
    el: ASTElement,
    state: CodegenState
  ): string {
    const isLegacySyntax = el.attrsMap['slot-scope']
    if (el.if && !el.ifProcessed && !isLegacySyntax) {
      return genIf(el, state, genScopedSlot, `null`)
    }
    if (el.for && !el.forProcessed) {
      return genFor(el, state, genScopedSlot)
    }
    const slotScope = el.slotScope === emptySlotScopeToken
      ? ``
      : String(el.slotScope)
    const fn = `function(${slotScope}){` +
      `return ${el.tag === 'template'
        ? el.if && isLegacySyntax
          ? `(${el.if})?${genChildren(el, state) || 'undefined'}:undefined`
          : genChildren(el, state) || 'undefined'
        : genElement(el, state)
      }}`
    // reverse proxy v-slot without scope on this.$slots
    const reverseProxy = slotScope ? `` : `,proxy:true`
    return `{key:${el.slotTarget || `"default"`},fn:${fn}${reverseProxy}}`
  }
  
  export function genChildren (
    el: ASTElement,
    state: CodegenState,
    checkSkip?: boolean,
    altGenElement?: Function,
    altGenNode?: Function
  ): string | void {
    const children = el.children
    if (children.length) {
      const el: any = children[0]
      // optimize single v-for
      if (children.length === 1 &&
        el.for &&
        el.tag !== 'template' &&
        el.tag !== 'slot'
      ) {
        const normalizationType = checkSkip
          ? state.maybeComponent(el) ? `,1` : `,0`
          : ``
        return `${(altGenElement || genElement)(el, state)}${normalizationType}`
      }
      const normalizationType = checkSkip
        ? getNormalizationType(children, state.maybeComponent)
        : 0
      const gen = altGenNode || genNode
      return `[${children.map(c => gen(c, state)).join(',')}]${
        normalizationType ? `,${normalizationType}` : ''
      }`
    }
  }
  
  // determine the normalization needed for the children array.
  // 0: no normalization needed
  // 1: simple normalization needed (possible 1-level deep nested array)
  // 2: full normalization needed
  function getNormalizationType (
    children: Array<ASTNode>,
    maybeComponent: (el: ASTElement) => boolean
  ): number {
    let res = 0
    for (let i = 0; i < children.length; i++) {
      const el: ASTNode = children[i]
      if (el.type !== 1) {
        continue
      }
      if (needsNormalization(el) ||
          (el.ifConditions && el.ifConditions.some(c => needsNormalization(c.block)))) {
        res = 2
        break
      }
      if (maybeComponent(el) ||
          (el.ifConditions && el.ifConditions.some(c => maybeComponent(c.block)))) {
        res = 1
      }
    }
    return res
  }
  
  function needsNormalization (el: ASTElement): boolean {
    return el.for !== undefined || el.tag === 'template' || el.tag === 'slot'
  }
  
  function genNode (node: ASTNode, state: CodegenState): string {
    if (node.type === 1) {
      return genElement(node, state)
    } else if (node.type === 3 && node.isComment) {
      return genComment(node)
    } else {
      return genText(node)
    }
  }
  
  export function genText (text: ASTText | ASTExpression): string {
    return `_v(${text.type === 2
      ? text.expression // no need for () because already wrapped in _s()
      : transformSpecialNewlines(JSON.stringify(text.text))
    })`
  }
  
  export function genComment (comment: ASTText): string {
    return `_e(${JSON.stringify(comment.text)})`
  }
  
  function genSlot (el: ASTElement, state: CodegenState): string {
    const slotName = el.slotName || '"default"'
    const children = genChildren(el, state)
    let res = `_t(${slotName}${children ? `,${children}` : ''}`
    const attrs = el.attrs || el.dynamicAttrs
      ? genProps((el.attrs || []).concat(el.dynamicAttrs || []).map(attr => ({
          // slot props are camelized
          name: camelize(attr.name),
          value: attr.value,
          dynamic: attr.dynamic
        })))
      : null
    const bind = el.attrsMap['v-bind']
    if ((attrs || bind) && !children) {
      res += `,null`
    }
    if (attrs) {
      res += `,${attrs}`
    }
    if (bind) {
      res += `${attrs ? '' : ',null'},${bind}`
    }
    return res + ')'
  }
  
  // componentName is el.component, take it as argument to shun flow's pessimistic refinement
  function genComponent (
    componentName: string,
    el: ASTElement,
    state: CodegenState
  ): string {
    const children = el.inlineTemplate ? null : genChildren(el, state, true)
    return `_c(${componentName},${genData(el, state)}${
      children ? `,${children}` : ''
    })`
  }
  
  function genProps (props: Array<ASTAttr>): string {
    let staticProps = ``
    let dynamicProps = ``
    for (let i = 0; i < props.length; i++) {
      const prop = props[i]
      const value = __WEEX__
        ? generateValue(prop.value)
        : transformSpecialNewlines(prop.value)
      if (prop.dynamic) {
        dynamicProps += `${prop.name},${value},`
      } else {
        staticProps += `"${prop.name}":${value},`
      }
    }
    staticProps = `{${staticProps.slice(0, -1)}}`
    if (dynamicProps) {
      return `_d(${staticProps},[${dynamicProps.slice(0, -1)}])`
    } else {
      return staticProps
    }
  }
  
  /* istanbul ignore next */
  function generateValue (value) {
    if (typeof value === 'string') {
      return transformSpecialNewlines(value)
    }
    return JSON.stringify(value)
  }
  
  // #3895, #4268
  function transformSpecialNewlines (text: string): string {
    return text
      .replace(/\u2028/g, '\\u2028')
      .replace(/\u2029/g, '\\u2029')
  }
  