ref(nextjs): Remove compensation for workaround in _error.js (#5378)

For a long time, the `_error.js` page we provide `@sentry/nextjs` users contained a workaround for vercel/next.js#8592. When most of the code in `_error.js` was moved into `captureUnderscoreErrorException`, parts of the workaround came along for the ride. Now that that issue has been fixed, the workaround is no longer necessary.

This removes as many of the workaround's vestiges in `captureUnderscoreErrorException` as possible. (We can't remove them all, because the workaround existed in user code rather than ours, and we can't stop people from continuing to use it. This fixes things so that if they do that, it'll just bail gracefully.)

Author: lobsterkatie

packages/nextjs/src/utils/_error.ts

@@ -1,6 +1,6 @@
 import { captureException, withScope } from '@sentry/core';
 import { getCurrentHub } from '@sentry/hub';
-import { addExceptionMechanism, addRequestDataToEvent, objectify } from '@sentry/utils';
+import { addExceptionMechanism, addRequestDataToEvent } from '@sentry/utils';
 import { NextPageContext } from 'next';
 
 type ContextOrProps = {
@@ -31,15 +31,14 @@ export async function captureUnderscoreErrorException(contextOrProps: ContextOrP
     return Promise.resolve();
   }
 
-  // Nextjs only passes the pathname in the context data given to `getInitialProps`, not the main render function, but
-  // unlike `req` and `res`, for which that also applies, it passes it on both server and client.
-  //
-  // TODO: This check is only necessary because of the workaround for https://github.com/vercel/next.js/issues/8592
-  // explained below. Once that's fixed, we'll have to keep the `inGetInitialProps` check, because lots of people will
-  // still call this function in their custom error component's `render` function, but we can get rid of the check for
-  // `err` and just always bail if we're not in `getInitialProps`.
-  const inGetInitialProps = contextOrProps.pathname !== undefined;
-  if (!inGetInitialProps && !err) {
+  // In previous versions of the suggested `_error.js` page in which this function is meant to be used, there was a
+  // workaround for https://github.com/vercel/next.js/issues/8592 which involved an extra call to this function, in the
+  // custom error component's `render` method, just in case it hadn't been called by `getInitialProps`. Now that that
+  // issue has been fixed, the second call is unnecessary, but since it lives in user code rather than our code, users
+  // have to be the ones to get rid of it, and guaraneteedly, not all of them will. So, rather than capture the error
+  // twice, we just bail if we sense we're in that now-extraneous second call. (We can tell which function we're in
+  // because Nextjs passes `pathname` to `getInitialProps` but not to `render`.)
+  if (!contextOrProps.pathname) {
     return Promise.resolve();
   }
 
@@ -49,8 +48,7 @@ export async function captureUnderscoreErrorException(contextOrProps: ContextOrP
         type: 'instrument',
         handled: true,
         data: {
-          // TODO: Get rid of second half of ternary once https://github.com/vercel/next.js/issues/8592 is fixed.
-          function: inGetInitialProps ? '_error.getInitialProps' : '_error.customErrorComponent',
+          function: '_error.getInitialProps',
         },
       });
       return event;
@@ -62,14 +60,7 @@ export async function captureUnderscoreErrorException(contextOrProps: ContextOrP
 
     // If third-party libraries (or users themselves) throw something falsy, we want to capture it as a message (which
     // is what passing a string to `captureException` will wind up doing)
-    const finalError = err || `_error.js called with falsy error (${err})`;
-
-    // In case we have a primitive, wrap it in the equivalent wrapper class (string -> String, etc.) so that we can
-    // store a seen flag on it. (Because of https://github.com/vercel/next.js/issues/8592, it can happen that the custom
-    // error component's `getInitialProps` won't have run, so we have people call this function in their error
-    // component's main render function in addition to in its `getInitialProps`, just in case. By forcing it to be an
-    // object, we can flag it as seen, so that if we hit this a second time, we can no-op.)
-    captureException(objectify(finalError));
+    captureException(err || `_error.js called with falsy error (${err})`);
   });
 
   // In case this is being run as part of a serverless function (as is the case with the server half of nextjs apps