/* @flow */
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/**
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* In SSR, the vdom tree is generated only once and never patched, so
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* we can optimize most element / trees into plain string render functions.
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* The SSR optimizer walks the AST tree to detect optimizable elements and trees.
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*
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* The criteria for SSR optimizability is quite a bit looser than static tree
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* detection (which is designed for client re-render). In SSR we bail only for
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* components/slots/custom directives.
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*/
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import { no, makeMap, isBuiltInTag } from 'shared/util'
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// optimizability constants
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export const optimizability = {
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FALSE: 0, // whole sub tree un-optimizable
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FULL: 1, // whole sub tree optimizable
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SELF: 2, // self optimizable but has some un-optimizable children
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CHILDREN: 3, // self un-optimizable but have fully optimizable children
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PARTIAL: 4 // self un-optimizable with some un-optimizable children
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}
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let isPlatformReservedTag
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export function optimize (root: ?ASTElement, options: CompilerOptions) {
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if (!root) return
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isPlatformReservedTag = options.isReservedTag || no
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walk(root, true)
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}
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function walk (node: ASTNode, isRoot?: boolean) {
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if (isUnOptimizableTree(node)) {
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node.ssrOptimizability = optimizability.FALSE
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return
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}
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// root node or nodes with custom directives should always be a VNode
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const selfUnoptimizable = isRoot || hasCustomDirective(node)
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const check = child => {
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if (child.ssrOptimizability !== optimizability.FULL) {
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node.ssrOptimizability = selfUnoptimizable
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? optimizability.PARTIAL
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: optimizability.SELF
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}
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}
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if (selfUnoptimizable) {
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node.ssrOptimizability = optimizability.CHILDREN
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}
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if (node.type === 1) {
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for (let i = 0, l = node.children.length; i < l; i++) {
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const child = node.children[i]
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walk(child)
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check(child)
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}
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if (node.ifConditions) {
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for (let i = 1, l = node.ifConditions.length; i < l; i++) {
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const block = node.ifConditions[i].block
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walk(block, isRoot)
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check(block)
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}
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}
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if (node.ssrOptimizability == null ||
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(!isRoot && (node.attrsMap['v-html'] || node.attrsMap['v-text']))
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) {
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node.ssrOptimizability = optimizability.FULL
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} else {
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node.children = optimizeSiblings(node)
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}
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} else {
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node.ssrOptimizability = optimizability.FULL
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}
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}
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function optimizeSiblings (el) {
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const children = el.children
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const optimizedChildren = []
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let currentOptimizableGroup = []
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const pushGroup = () => {
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if (currentOptimizableGroup.length) {
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optimizedChildren.push({
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type: 1,
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parent: el,
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tag: 'template',
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attrsList: [],
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attrsMap: {},
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rawAttrsMap: {},
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children: currentOptimizableGroup,
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ssrOptimizability: optimizability.FULL
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})
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}
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currentOptimizableGroup = []
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}
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for (let i = 0; i < children.length; i++) {
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const c = children[i]
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if (c.ssrOptimizability === optimizability.FULL) {
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currentOptimizableGroup.push(c)
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} else {
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// wrap fully-optimizable adjacent siblings inside a template tag
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// so that they can be optimized into a single ssrNode by codegen
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pushGroup()
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optimizedChildren.push(c)
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}
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}
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pushGroup()
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return optimizedChildren
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}
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function isUnOptimizableTree (node: ASTNode): boolean {
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if (node.type === 2 || node.type === 3) { // text or expression
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return false
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}
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return (
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isBuiltInTag(node.tag) || // built-in (slot, component)
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!isPlatformReservedTag(node.tag) || // custom component
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!!node.component || // "is" component
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isSelectWithModel(node) // <select v-model> requires runtime inspection
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)
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}
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const isBuiltInDir = makeMap('text,html,show,on,bind,model,pre,cloak,once')
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function hasCustomDirective (node: ASTNode): ?boolean {
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return (
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node.type === 1 &&
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node.directives &&
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node.directives.some(d => !isBuiltInDir(d.name))
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)
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}
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// <select v-model> cannot be optimized because it requires a runtime check
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// to determine proper selected option
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function isSelectWithModel (node: ASTNode): boolean {
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return (
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node.type === 1 &&
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node.tag === 'select' &&
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node.directives != null &&
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node.directives.some(d => d.name === 'model')
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)
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}
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