Support for named slots in type checking

packages/next/build/webpack/plugins/flight-types-plugin.ts

@@ -1,4 +1,5 @@
 import path from 'path'
+import { promises as fs } from 'fs'
 
 import { webpack, sources } from 'next/dist/compiled/webpack/webpack'
 import { WEBPACK_LAYERS } from '../../../lib/constants'
@@ -17,6 +18,7 @@ function createTypeGuardFile(
   relativePath: string,
   options: {
     type: 'layout' | 'page'
+    slots?: string[]
   }
 ) {
   return `// File: ${fullPath}
@@ -32,6 +34,11 @@ interface PageProps {
 }
 interface LayoutProps {
   children: React.ReactNode
+${
+  options.slots
+    ? options.slots.map((slot) => `  ${slot}: React.ReactNode`).join('\n')
+    : ''
+}
   params: any
 }
 
@@ -68,6 +75,18 @@ type NonNegative<T extends Numeric> = T extends Zero ? T : Negative<T> extends n
 `
 }
 
+async function collectNamedSlots(layoutPath: string) {
+  const layoutDir = path.dirname(layoutPath)
+  const items = await fs.readdir(layoutDir, { withFileTypes: true })
+  const slots = []
+  for (const item of items) {
+    if (item.isDirectory() && item.name.startsWith('@')) {
+      slots.push(item.name.slice(1))
+    }
+  }
+  return slots
+}
+
 export class FlightTypesPlugin {
   dir: string
   appDir: string
@@ -84,7 +103,7 @@ export class FlightTypesPlugin {
   apply(compiler: webpack.Compiler) {
     const assetPrefix = this.dev ? '..' : this.isEdgeServer ? '..' : '../..'
 
-    const handleModule = (_mod: webpack.Module, assets: any) => {
+    const handleModule = async (_mod: webpack.Module, assets: any) => {
       if (_mod.layer !== WEBPACK_LAYERS.server) return
       const mod: webpack.NormalModule = _mod as any
 
@@ -111,9 +130,11 @@ export class FlightTypesPlugin {
       const assetPath = assetPrefix + '/' + typePath.replace(/\\/g, '/')
 
       if (IS_LAYOUT) {
+        const slots = await collectNamedSlots(mod.resource)
         assets[assetPath] = new sources.RawSource(
           createTypeGuardFile(mod.resource, relativeImportPath, {
             type: 'layout',
+            slots,
           })
         ) as unknown as webpack.sources.RawSource
       } else if (IS_PAGE) {
@@ -126,19 +147,22 @@ export class FlightTypesPlugin {
     }
 
     compiler.hooks.compilation.tap(PLUGIN_NAME, (compilation) => {
-      compilation.hooks.processAssets.tap(
+      compilation.hooks.processAssets.tapAsync(
         {
           name: PLUGIN_NAME,
           stage: webpack.Compilation.PROCESS_ASSETS_STAGE_OPTIMIZE_HASH,
         },
-        (assets) => {
+        async (assets, callback) => {
+          const promises: Promise<any>[] = []
           for (const entrypoint of compilation.entrypoints.values()) {
             for (const chunk of entrypoint.chunks) {
               compilation.chunkGraph.getChunkModules(chunk).forEach((mod) => {
-                handleModule(mod, assets)
+                promises.push(handleModule(mod, assets))
               })
             }
           }
+          await Promise.all(promises)
+          callback()
         }
       )
     })

packages/next/lib/typescript/diagnosticFormatter.ts

@@ -103,14 +103,24 @@ function getFormattedLayoutAndPageDiagnosticMessageText(
                   }
                   break
                 case 2741:
-                  const incompatProp = item.messageText.match(
+                  const incompatPageProp = item.messageText.match(
                     /Property '(.+)' is missing in type 'PageProps'/
                   )
-                  if (incompatProp) {
+                  if (incompatPageProp) {
                     main += '\n' + ' '.repeat(indent * 2)
                     main += `Prop "${chalk.bold(
-                      incompatProp[1]
+                      incompatPageProp[1]
                     )}" will never be passed. Remove it from the component's props.`
+                  } else {
+                    const extraLayoutProp = item.messageText.match(
+                      /Property '(.+)' is missing in type 'LayoutProps' but required in type '(.+)'/
+                    )
+                    if (extraLayoutProp) {
+                      main += '\n' + ' '.repeat(indent * 2)
+                      main += `Prop "${chalk.bold(
+                        extraLayoutProp[1]
+                      )}" is not valid for this Layout, remove it to fix.`
+                    }
                   }
                   break
                 default: