microsoft / microsoft/react-native-windows

Unfork MapBuffer.cpp override added during 0.85 nightly integration

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Integration Follow-up Needs: Triage :mag:
Dominant language
C++
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Description

Problem Description

During the integration of RN 0.85.0-nightly-20260128-36f07a1b2 (#16245), the upstream MapBuffer.cpp introduced signed/unsigned comparison warnings (C4018 and C4267) that our Warnings.props treats as errors (SDL-mandatory).

  • Line 27: header->bufferSize (uint32_t) compared with bytes_.size() (size_t) — C4267
  • Line 128: mapBufferLength (int32_t) compared with maxLength (size_t) — C4018

Current Fix:
A local patched copy was created at vnext/ReactCommon/TEMP_UntilReactCommonUpdate/react/renderer/mapbuffer/MapBuffer.cpp with static_cast fixes.

Link to the integration PR where the error originated

https://github.com/microsoft/react-native-windows/pull/16245

Link to react-native commit

https://github.com/facebook/react-native/compare/f15985f4f...36f07a1b2

Forked files

No response

Upstream PR in react-native

No response

Build Configuration

None

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with vnext/ReactCommon/TEMP_UntilReactCommonUpdate/react/renderer/mapbuffer/MapBuffer.cpp and compare the reported lines with the upstream MapBuffer.cpp changes linked in the issue. Check how Warnings.props treats C4018 and C4267, then run the relevant Windows build to verify both warnings are resolved and the temporary override is handled correctly.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp, react-native
Domain
build-system
Issue type
Bug
Difficulty
3/5
Estimated time
1-2 days
Activity status
Quiet
Clarity
Mostly clear
Newbie friendliness
52/100

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