feat: prerender hint based on ssrContext access

playground/pages/hydration.vue

@@ -4,7 +4,10 @@ const isServer = import.meta.server ? 1 : 0
 
 <template>
   <div>
-    <p :data-test="isServer ? 'server' : 'client'" class="fzejkebkzjefbjkzebfkjzebfkjzebfzebfkjzebkfjbzekjjjjjjjjjjjjjjjjjjjjkfzebjkfbzkjebfjkjk">
+    <p
+      :data-test="isServer ? 'server' : 'client'"
+      class="fzejkebkzjefbjkzebfkjzebfkjzebfzebfkjzebkfjbzekjjjjjjjjjjjjjjjjjjjjkfzebjkfbzkjebfjkjk"
+    >
       isServer: {{ isServer }} <span v-if="!isServer">test</span>
     </p>
 

playground/pages/prerender/index.vue

@@ -0,0 +1,25 @@
+<template>
+  <div class="test">
+    Hello. Could this page be prerendered ? {{ shouldPrerender }}
+  </div>
+</template>
+
+<script setup lang="ts">
+import { useNuxtApp, useState } from '#app'
+import { onMounted } from 'vue'
+
+const shouldPrerender = useState('shouldPrerender', () => true)
+
+if (import.meta.server) {
+  // ssr context access will be detected by the prerender plugin
+  console.log(useNuxtApp().ssrContext?.event.context.shouldPrerender)
+}
+
+onMounted(() => {
+  // @ts-expect-error for demo purposes
+  if (typeof window.__NUXT_HINTS_SHOULD_PRERENDER__ !== 'undefined') {
+  // @ts-expect-error for demo purposes
+    shouldPrerender.value = window.__NUXT_HINTS_SHOULD_PRERENDER__
+  }
+})
+</script>

src/module.ts

@@ -53,6 +53,10 @@ export default defineNuxtModule<ModuleOptions>({
     addPlugin(resolver.resolve('./runtime/third-party-scripts/plugin.client'))
     addServerPlugin(resolver.resolve('./runtime/third-party-scripts/nitro.plugin'))
 
+    // prerender
+    addServerPlugin(resolver.resolve('./runtime/prerender/nitro.plugin'))
+    addPlugin(resolver.resolve('./runtime/prerender/plugin.server'))
+
     nuxt.hook('prepare:types', ({ references }) => {
       references.push({
         types: resolver.resolve('./runtime/types.d.ts'),

src/runtime/prerender/nitro.plugin.ts

@@ -0,0 +1,20 @@
+import type { NitroAppPlugin } from 'nitropack'
+
+export default <NitroAppPlugin> function nitroHintsPlugin(nitroApp) {
+  nitroApp.hooks.hook('render:before', ({ event }) => {
+    event.context.shouldPrerender = true
+  })
+
+  nitroApp.hooks.hook('render:html', (htmlContext, { event }) => {
+    if (event.context.shouldPrerender === false) {
+      htmlContext.bodyAppend.push(
+        `<script>window.__NUXT_HINTS_SHOULD_PRERENDER__ = false</script>`,
+      )
+    }
+    else {
+      htmlContext.bodyAppend.push(
+        `<script>window.__NUXT_HINTS_SHOULD_PRERENDER__ = true</script>`,
+      )
+    }
+  })
+}

src/runtime/prerender/plugin.server.ts

@@ -0,0 +1,44 @@
+import { defineNuxtPlugin } from '#imports'
+import { getStackTraceLines } from './utils'
+
+export default defineNuxtPlugin({
+  name: 'hints:prerender-detection',
+  setup(nuxtApp) {
+    const event = nuxtApp.ssrContext!.event
+
+    let watching = true
+
+    const ssrContext = nuxtApp.ssrContext
+    // Access to any property on ssrContext will mark the page as non-prerenderable
+    Object.defineProperty(nuxtApp, 'ssrContext', {
+      get() {
+        if (watching && isUserLandCode()) {
+          // Mark as non-prerenderable
+          // we only want to do this when user-land code is being executed
+          // to avoid false positives from internal framework code
+          // it's better to be slightly overzealous here than miss actual user code
+          event.context.shouldPrerender = false
+        }
+        return ssrContext
+      },
+    })
+
+    nuxtApp.hook('app:rendered', () => {
+      watching = false
+    })
+  },
+  order: -100000,
+})
+
+/**
+ * Determine if the current execution context is user-land code
+ * by analyzing the stack trace.
+ * Should ignore the first line as the fn call is this function itself.
+ */
+function isUserLandCode(offset: number = 1): boolean {
+  const stack = getStackTraceLines()
+  const lines = stack.slice(2)
+  const line = lines[offset]
+  const isUserLand = !line?.includes('node_modules') && !line?.includes('node:internal')
+  return isUserLand
+}

src/runtime/prerender/utils.ts

@@ -0,0 +1,13 @@
+/**
+ * Get all stacktrace lines without the current file
+ * Don't use in build files if we ever goes into build mode nuxt hiints. Thank you.
+ */
+export function getStackTraceLines(): string[] {
+  const stackObject: { stack: string } = {} as { stack: string }
+  Error.captureStackTrace(stackObject)
+
+  return stackObject.stack
+    .split('\n')
+    .slice(1)
+    .map(line => line.trim())
+}