生成预设代码

由于 mode 的值是 modules 所以会执行 genModulePreamble 生成预设代码

genModulePreamble

function genModulePreamble(
  ast: RootNode,
  context: CodegenContext,
  genScopeId: boolean,
  inline?: boolean
) {
  const {
    push,
    newline,
    optimizeImports,
    runtimeModuleName,
    ssrRuntimeModuleName
  } = context

  if (genScopeId && ast.hoists.length) {
    ast.helpers.push(PUSH_SCOPE_ID, POP_SCOPE_ID)
  }

  // generate import statements for helpers
  if (ast.helpers.length) {
    if (optimizeImports) {
      // when bundled with webpack with code-split, calling an import binding
      // as a function leads to it being wrapped with `Object(a.b)` or `(0,a.b)`,
      // incurring both payload size increase and potential perf overhead.
      // therefore we assign the imports to variables (which is a constant ~50b
      // cost per-component instead of scaling with template size)
      push(
        `import { ${ast.helpers
          .map(s => helperNameMap[s])
          .join(', ')} } from ${JSON.stringify(runtimeModuleName)}\n`
      )
      push(
        `\n// Binding optimization for webpack code-split\nconst ${ast.helpers
          .map(s => `_${helperNameMap[s]} = ${helperNameMap[s]}`)
          .join(', ')}\n`
      )
    } else {
      push(
        `import { ${ast.helpers
          .map(s => `${helperNameMap[s]} as _${helperNameMap[s]}`)
          .join(', ')} } from ${JSON.stringify(runtimeModuleName)}\n`
      )
    }
  }

  if (ast.ssrHelpers && ast.ssrHelpers.length) {
    push(
      `import { ${ast.ssrHelpers
        .map(s => `${helperNameMap[s]} as _${helperNameMap[s]}`)
        .join(', ')} } from "${ssrRuntimeModuleName}"\n`
    )
  }

  if (ast.imports.length) {
    genImports(ast.imports, context)
    newline()
  }

  genHoists(ast.hoists, context)
  newline()

  if (!inline) {
    push(`export `)
  }
}

helperNameMap

• 每个属性对应的值是一个字符串 就是需要引用的模块或者函数的名称
• 创建 vnode 函数 createVnode 是直接通过模块的方式导出的 其他函数都是类似

// Name mapping for runtime helpers that need to be imported from 'vue' in
// generated code. Make sure these are correctly exported in the runtime!
export const helperNameMap: Record<symbol, string> = {
  [FRAGMENT]: `Fragment`,
  [TELEPORT]: `Teleport`,
  [SUSPENSE]: `Suspense`,
  [KEEP_ALIVE]: `KeepAlive`,
  [BASE_TRANSITION]: `BaseTransition`,
  [OPEN_BLOCK]: `openBlock`,
  [CREATE_BLOCK]: `createBlock`,
  [CREATE_ELEMENT_BLOCK]: `createElementBlock`,
  [CREATE_VNODE]: `createVNode`,
  [CREATE_ELEMENT_VNODE]: `createElementVNode`,
  [CREATE_COMMENT]: `createCommentVNode`,
  [CREATE_TEXT]: `createTextVNode`,
  [CREATE_STATIC]: `createStaticVNode`,
  [RESOLVE_COMPONENT]: `resolveComponent`,
  [RESOLVE_DYNAMIC_COMPONENT]: `resolveDynamicComponent`,
  [RESOLVE_DIRECTIVE]: `resolveDirective`,
  [RESOLVE_FILTER]: `resolveFilter`,
  [WITH_DIRECTIVES]: `withDirectives`,
  [RENDER_LIST]: `renderList`,
  [RENDER_SLOT]: `renderSlot`,
  [CREATE_SLOTS]: `createSlots`,
  [TO_DISPLAY_STRING]: `toDisplayString`,
  [MERGE_PROPS]: `mergeProps`,
  [NORMALIZE_CLASS]: `normalizeClass`,
  [NORMALIZE_STYLE]: `normalizeStyle`,
  [NORMALIZE_PROPS]: `normalizeProps`,
  [GUARD_REACTIVE_PROPS]: `guardReactiveProps`,
  [TO_HANDLERS]: `toHandlers`,
  [CAMELIZE]: `camelize`,
  [CAPITALIZE]: `capitalize`,
  [TO_HANDLER_KEY]: `toHandlerKey`,
  [SET_BLOCK_TRACKING]: `setBlockTracking`,
  [PUSH_SCOPE_ID]: `pushScopeId`,
  [POP_SCOPE_ID]: `popScopeId`,
  [WITH_CTX]: `withCtx`,
  [UNREF]: `unref`,
  [IS_REF]: `isRef`,
  [WITH_MEMO]: `withMemo`,
  [IS_MEMO_SAME]: `isMemoSame`
}

genHoists

• 内部先执行 newline 生成一个空行 然后遍历 hoists 数组 生成静态提升遍历定义的函数

function genHoists(hoists: (JSChildNode | null)[], context: CodegenContext) {
  if (!hoists.length) {
    return
  }
  context.pure = true
  const { push, newline, helper, scopeId, mode } = context
  const genScopeId = !__BROWSER__ && scopeId != null && mode !== 'function'
  newline()

  // generate inlined withScopeId helper
  if (genScopeId) {
    push(
      `const _withScopeId = n => (${helper(
        PUSH_SCOPE_ID
      )}("${scopeId}"),n=n(),${helper(POP_SCOPE_ID)}(),n)`
    )
    newline()
  }

  for (let i = 0; i < hoists.length; i++) {
    const exp = hoists[i]
    if (exp) {
      const needScopeIdWrapper = genScopeId && exp.type === NodeTypes.VNODE_CALL
      push(
        `const _hoisted_${i + 1} = ${
          needScopeIdWrapper ? `${PURE_ANNOTATION} _withScopeId(() => ` : ``
        }`
      )
      genNode(exp, context)
      if (needScopeIdWrapper) {
        push(`)`)
      }
      newline()
    }
  }

  context.pure = false
}