TS plugin: warn about amp config in app (#45254)

Asked by @ijjk in
#45228 (comment):

<img width="1171" alt="CleanShot 2023-01-25 at 10 26 15@2x"
src="https://user-images.githubusercontent.com/3676859/214526847-6481e33b-060e-4e15-bf1d-4274760068f5.png">


## Bug

- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Feature

- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ]
[e2e](https://github.com/vercel/next.js/blob/canary/contributing/core/testing.md#writing-tests-for-nextjs)
tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see
[`contributing.md`](https://github.com/vercel/next.js/blob/canary/contributing.md)

## Documentation / Examples

- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)

Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>

packages/next/src/server/next-typescript.ts

@@ -28,6 +28,7 @@ const DISALLOWED_SERVER_REACT_APIS: string[] = [
   'createFactory',
 ]
 
+const LEGACY_CONFIG_EXPORT = 'config'
 const ALLOWED_EXPORTS = ['config', 'generateStaticParams']
 
 const ALLOWED_PAGE_PROPS = ['params', 'searchParams']
@@ -39,6 +40,7 @@ const NEXT_TS_ERRORS = {
   INVALID_OPTION_VALUE: 71003,
   MISPLACED_CLIENT_ENTRY: 71004,
   INVALID_PAGE_PROP: 71005,
+  INVALID_CONFIG_OPTION: 71006,
 }
 
 const API_DOCS: Record<
@@ -803,6 +805,28 @@ export function createTSPlugin(modules: {
                       })
                     }
                   }
+                } else if (name.text === LEGACY_CONFIG_EXPORT) {
+                  // export const config = { ... }
+                  // Error if using `amp: ...`
+                  const value = declarartion.initializer
+                  if (value && ts.isObjectLiteralExpression(value)) {
+                    for (const prop of value.properties) {
+                      if (
+                        ts.isPropertyAssignment(prop) &&
+                        ts.isIdentifier(prop.name) &&
+                        prop.name.text === 'amp'
+                      ) {
+                        prior.push({
+                          file: source,
+                          category: ts.DiagnosticCategory.Error,
+                          code: NEXT_TS_ERRORS.INVALID_CONFIG_OPTION,
+                          messageText: `AMP is not supported in the app directory. If you need to use AMP it will continue to be supported in the pages directory.`,
+                          start: prop.getStart(),
+                          length: prop.getWidth(),
+                        })
+                      }
+                    }
+                  }
                 }
               }
             }