Add additional bullet for proxy

Co-authored-by: Joseph <[email protected]>

Author: devjiwonchoi

crates/next-core/src/middleware.rs

@@ -184,10 +184,18 @@ impl Issue for MiddlewareMissingExportIssue {
         let relative_path_str = self.get_relative_path();
         let type_description = self.get_type_description();
 
+        let migration_bullet = if self.file_type.as_str() == "Proxy" {
+            "- You are migrating from `middleware` to `proxy`, but haven't updated the exported \
+             function.\n"
+        } else {
+            ""
+        };
+
         // Rest of the message goes in description to avoid formatIssue indentation
         let description_text = format!(
             "This function is what Next.js runs for every request handled by this {}.\n\n\
              Why this happens:\n\
+             {}\
              - The file exists but doesn't export a function.\n\
              - The export is not a function (e.g., an object or constant).\n\
              - There's a syntax error preventing the export from being recognized.\n\n\
@@ -197,6 +205,7 @@ impl Issue for MiddlewareMissingExportIssue {
              - Restart the dev server if the error persists.\n\n\
              Learn more: https://nextjs.org/docs/messages/middleware-to-proxy",
             type_description,
+            migration_bullet,
             relative_path_str,
             self.function_name
         );

packages/next/src/build/analysis/get-page-static-info.ts

@@ -403,6 +403,9 @@ function validateMiddlewareProxyExports({
       `The file "${relativeFilePath}" must export a function, either as a default export or as a named "${fileName}" export.\n` +
         `This function is what Next.js runs for every request handled by this ${fileName === 'proxy' ? 'proxy (previously called middleware)' : 'middleware'}.\n\n` +
         `Why this happens:\n` +
+        (isProxy
+          ? "- You are migrating from `middleware` to `proxy`, but haven't updated the exported function.\n"
+          : '') +
         `- The file exists but doesn't export a function.\n` +
         `- The export is not a function (e.g., an object or constant).\n` +
         `- There's a syntax error preventing the export from being recognized.\n\n` +

packages/next/src/build/templates/middleware.ts

@@ -29,6 +29,9 @@ if (typeof handler !== 'function') {
     `The file "${resolvedRelativeFilePath}" must export a function, either as a default export or as a named "${fileName}" export.\n` +
       `This function is what Next.js runs for every request handled by this ${fileName === 'proxy' ? 'proxy (previously called middleware)' : 'middleware'}.\n\n` +
       `Why this happens:\n` +
+      (isProxy
+        ? "- You are migrating from `middleware` to `proxy`, but haven't updated the exported function.\n"
+        : '') +
       `- The file exists but doesn't export a function.\n` +
       `- The export is not a function (e.g., an object or constant).\n` +
       `- There's a syntax error preventing the export from being recognized.\n\n` +

test/e2e/app-dir/proxy-missing-export/proxy-missing-export.test.ts

@@ -6,6 +6,7 @@ const errorMessage = `The file "./proxy.ts" must export a function, either as a
 This function is what Next.js runs for every request handled by this proxy (previously called middleware).
 
 Why this happens:
+- You are migrating from \`middleware\` to \`proxy\`, but haven't updated the exported function.
 - The file exists but doesn't export a function.
 - The export is not a function (e.g., an object or constant).
 - There's a syntax error preventing the export from being recognized.