fix(turbopack): respect basePath when generating metadata icons

[Jeevankumar-s]

What?

Fix metadata icon URLs generated with Turbopack to correctly respect basePath.

Why?

When using Turbopack with a configured basePath, metadata icons (favicon, apple icons, etc.)
are generated without the basePath prefix, resulting in broken icon URLs.
This works correctly with Webpack but fails with Turbopack.

How?

• Apply basePath to root-relative metadata icon URLs during metadata resolution
• Skip absolute URLs and prevent double-prefixing
• Match Webpack behavior without changing public APIs

Fixes #87422

[nextjs-bot]

Allow CI Workflow Run

• approve CI run for commit: 28dc767

Note: this should only be enabled once the PR is ready to go and can only be enabled by a maintainer

[vercel]

Additional Suggestion:

The createMetadataContext function doesn't include the basePath property that the metadata icon resolution code expects, causing the basePath to never be applied to icon URLs.

View Details

📝 Patch Details

diff --git a/packages/next/src/lib/metadata/metadata-context.tsx b/packages/next/src/lib/metadata/metadata-context.tsx
index 7f65e6ac8c..9d7c347eb3 100644
--- a/packages/next/src/lib/metadata/metadata-context.tsx
+++ b/packages/next/src/lib/metadata/metadata-context.tsx
@@ -1,11 +1,12 @@
 import type { AppRenderContext } from '../../server/app-render/app-render'
-import type { MetadataContext } from './types/resolvers'
+import type { MetadataContext, MetadataContextWithBasePath } from './types/resolvers'
 
 export function createMetadataContext(
   renderOpts: AppRenderContext['renderOpts']
-): MetadataContext {
+): MetadataContextWithBasePath {
   return {
     trailingSlash: renderOpts.trailingSlash,
     isStaticMetadataRouteFile: false,
+    basePath: renderOpts.basePath,
   }
 }

Analysis

Missing basePath property in createMetadataContext causes icon basePath to never be applied

What fails: The createMetadataContext() function does not include the basePath property from renderOpts, causing ctx.basePath to be undefined in applyBasePathToIcons(), which prevents icon URLs from being prefixed with the configured basePath.

How to reproduce:

// In resolve-metadata.ts, when processing metadata with icons and a configured basePath:
const metadataContext = createMetadataContext(ctx.renderOpts)  // ctx.renderOpts.basePath = '/my-app'
// ...later in mergeMetadata()
const ctx = metadataContext as MetadataContextWithBasePath
applyBasePathToIcons(resolvedIcons, ctx.basePath)  // ctx.basePath is undefined

Result: Icon URLs are not prefixed with the basePath. For example, /favicon.ico remains /favicon.ico instead of becoming /my-app/favicon.ico.

Expected: The createMetadataContext() function should include the basePath from renderOpts in the returned context object, allowing applyBasePathToIcons() to correctly apply the basePath prefix to icon URLs.

Files affected: packages/next/src/lib/metadata/metadata-context.tsx