✨ NextJS- addNextjsError component

[BeltranBulbarellaDD]

Motivation

This PR adds error reporting support to @datadog/browser-rum-nextjs for the App Router.

Changes

packages/rum-nextjs

• Added addNextjsError(error, errorInfo?) — a new public API, mirroring addReactError from rum-react, for reporting errors from Next.js App Router error boundaries (error.tsx, global-error.tsx) and from createRoot's onUncaughtError / onRecoverableError hooks
• Refactored nextjsPlugin to use addError instead of addEvent, aligning with how reactPlugin works
• Exported addNextjsError from the package entry point

packages/core

• Added 'nextjs error' as a valid createHandlingStack type

test/apps/nextjs

• Added App Router test pages: /error-test, /error-test/server-error, /global-error-test, and global-error.tsx to exercise client, server digest, and global error scenarios

test/e2e

• Added E2E scenarios covering:
  • Client-side error reported via addNextjsError
  • Server error with digest reported via addNextjsError
  • Global error via global-error.tsx
• Error scenarios scoped to App Router only

Test instructions

You can build the test app:
yarn install && yarn build && yarn build:apps cd test/apps/nextjs/ yarn dev

Checklist

• Tested locally
• Tested on staging
• Added unit tests for this change.
• Added e2e/integration tests for this change.
• Updated documentation and/or relevant AGENTS.md file

[datadog-prod-us1-6]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage (details)
• Patch Coverage: 90.91%
• Overall Coverage: 77.25% (+0.01%)

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[amortemousque]

❓ question: ‏Any reason to use dev mode?

[BeltranBulbarellaDD]

In local we use dev and in the CI we use the prod one. I thought it would cover all cases but we could just do prod. WDYT?

[amortemousque]

Shouldn’t this double fire also happen with the React plugin? How do we handle it there?

[BeltranBulbarellaDD]

Yeah we do the same "optimistic check" this is what React does:
toBeGreaterThan(0)

[amortemousque]

Okay so you can keep it like this :)

[amortemousque]

❓ question: ‏Should nextjs.digest part of the rum-evens-format

[cit-pr-commenter-54b7da]

Bundles Sizes Evolution

📦 Bundle Name	Base Size	Local Size	𝚫	𝚫%	Status
Rum	175.02 KiB	175.02 KiB	0 B	0.00%	✅
Rum Profiler	6.16 KiB	6.16 KiB	0 B	0.00%	✅
Rum Recorder	27.46 KiB	27.46 KiB	0 B	0.00%	✅
Logs	56.80 KiB	56.80 KiB	0 B	0.00%	✅
Flagging	944 B	944 B	0 B	0.00%	✅
Rum Slim	130.66 KiB	130.66 KiB	0 B	0.00%	✅
Worker	23.63 KiB	23.63 KiB	0 B	0.00%	✅

🚀 CPU Performance

Action Name	Base CPU Time (ms)	Local CPU Time (ms)	𝚫%
RUM - add global context	0.0038	0.0046	+21.05%
RUM - add action	0.0124	0.0129	+4.03%
RUM - add error	0.0126	0.0147	+16.67%
RUM - add timing	0.0025	0.0027	+8.00%
RUM - start view	0.0121	0.0122	+0.83%
RUM - start/stop session replay recording	0.0007	0.0007	0.00%
Logs - log message	0.0138	0.0168	+21.74%

🧠 Memory Performance

Action Name	Base Memory Consumption	Local Memory Consumption	𝚫
RUM - add global context	27.56 KiB	26.67 KiB	-907 B
RUM - add action	51.79 KiB	51.72 KiB	-63 B
RUM - add timing	25.59 KiB	26.26 KiB	+679 B
RUM - add error	56.29 KiB	54.82 KiB	-1.47 KiB
RUM - start/stop session replay recording	25.04 KiB	25.81 KiB	+792 B
RUM - start view	461.57 KiB	465.17 KiB	+3.60 KiB
Logs - log message	43.71 KiB	43.99 KiB	+287 B

🔗 RealWorld

[amortemousque]

Okay so you can keep it like this :)