Prevent append of trailing slash in cases where path ends with a file extension

packages/next/src/lib/metadata/resolvers/resolve-url.test.ts

@@ -110,6 +110,17 @@ describe('resolveAbsoluteUrlWithPathname', () => {
         'https://example.com/foo?bar'
       )
     })
+
+    it('should not add trailing slash to relative url that matches file pattern', () => {
+      expect(resolver('/foo.html')).toBe('https://example.com/foo.html')
+      expect(resolver('/foo.html?q=v')).toBe('https://example.com/foo.html?q=v')
+      expect(resolver(new URL('/.well-known/bar.jpg', metadataBase))).toBe(
+        'https://example.com/.well-known/bar.jpg/'
+      )
+      expect(resolver(new URL('/foo.html', metadataBase))).toBe(
+        'https://example.com/foo.html'
+      )
+    })
   })
 })
 

packages/next/src/lib/metadata/resolvers/resolve-url.ts

@@ -86,6 +86,13 @@ function resolveRelativeUrl(url: string | URL, pathname: string): string | URL {
   return url
 }
 
+// The regex is matching logic from packages/next/src/lib/load-custom-routes.ts
+const FILE_REGEX =
+  /^(?:\/((?!\.well-known(?:\/.*)?)(?:[^/]+\/)*[^/]+\.\w+))(\/?|$)/i
+function isFilePattern(pathname: string): boolean {
+  return FILE_REGEX.test(pathname)
+}
+
 // Resolve `pathname` if `url` is a relative path the compose with `metadataBase`.
 function resolveAbsoluteUrlWithPathname(
   url: string | URL,
@@ -110,18 +117,27 @@ function resolveAbsoluteUrlWithPathname(
   // - Doesn't have query
   if (trailingSlash && !resolvedUrl.endsWith('/')) {
     let isRelative = resolvedUrl.startsWith('/')
-    let isExternal = false
     let hasQuery = resolvedUrl.includes('?')
+    let isExternal = false
+    let isFileUrl = false
+
     if (!isRelative) {
       try {
         const parsedUrl = new URL(resolvedUrl)
         isExternal =
           metadataBase != null && parsedUrl.origin !== metadataBase.origin
+        isFileUrl = isFilePattern(parsedUrl.pathname)
       } catch {
         // If it's not a valid URL, treat it as external
         isExternal = true
       }
-      if (!isExternal && !hasQuery) return `${resolvedUrl}/`
+      if (
+        // Do not apply trailing slash for file like urls, aligning with the behavior with `trailingSlash`
+        !isFileUrl &&
+        !isExternal &&
+        !hasQuery
+      )
+        return `${resolvedUrl}/`
     }
   }