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[Compiler Bug]: NaN in dependency list of useMemo always causes re-evaluation | GoodFirstPicks

[Compiler Bug]: NaN in dependency list of useMemo always causes re-evaluation

facebook/react 3 comments 1mo ago
View on GitHub
mediumopenScope: somewhat clearSkill match: maybeTest focusedReactJavaScriptTypeScript

Why this is a good first issue

Compiler incorrectly handles NaN in dependency lists causing unnecessary re-evaluations.

AI Summary

The issue reports that the React compiler mishandles NaN values in useMemo dependency lists, causing unnecessary re-evaluations. This requires understanding compiler internals around dependency comparison logic. While the reproduction case is clear, the fix may involve non-trivial changes to dependency tracking.

Issue Description

What kind of issue is this?

  • React Compiler core (the JS output is incorrect, or your app works incorrectly after optimization)
  • babel-plugin-react-compiler (build issue installing or using the Babel plugin)
  • eslint-plugin-react-hooks (build issue installing or using the eslint plugin)
  • react-compiler-healthcheck (build issue installing or using the healthcheck script)

Link to repro

https://playground.react.dev/#N4Igzg9grgTgxgUxALhASwLYAcIwC4AEASggIZx4A0BwBUYCJAZtfQgMp6l4IEC+BJjAgYCAchhkKYgDoA7eUyhyKaCHIIZSAawQB9GKTkATEQAoAlDXkFbBSXlgaAstwAWAOkMnzF+X3l5BAAPHHwCYwQmUigAG0IlFTw1FwBPAEEsLEtrDTsAenyCMEwsWN4wLh4CPAgCOBiGewQAWkkTBBgbOzh1SoIAbUruBGoGPE4RgF0CAF5iKTwPNkmeMwAGPwU820KagjQwAlJYgHdSVKOAOVIr4rQVCqreE-PLggA+efXu2165fqEebDapfAjrAgAfgINzuyHBgR2BD26liqUEaEkR3UiAIpzQeDc0EIvWwaHKXSR-36ADc5gtyEs2M4EBgIGYcrMPrk7LzkUVXhcjgBzBByTojI7i072IymURyKAYABGnQIvz5DicBzAsLMeCs0K0ugMct8BHhPyRfGoAzwUy2iN5e3xhPqIiw5LVYtIyvKxmodMOdCwxhGxgI6gIUjc9ViaDg2g1WpgGgAPMY0HT1ABheOJ2bATnc8arBBmOBzblwADUAEYLHwPgAJBCxWJ1ADquFixnhwBpAiKwBBCD4afymZpHwA3P55CBKCB-kw0MKUOhsLhCHhUlheLQAAqxKDCh4AeSwyT6-EEwlEYmVvrbLTKp4ebUWLVJnopk8OeBiHO2xmMA3SFD+5LcCkzgQJE8IyCAJyxIh-jFNBYCrggRzHu+ciXteAIWDOi7gESpwAJJyDwqYnGAKDRLEDB8EAA

Repro steps

See playground link. Click on the div to increment the counter and see that the memoised value changes even though the single dependency is always NaN.

The example is obviously contrived and perhaps you consider having NaN in a dependency list not valid/supported. However useMemo without the compiler handles this case and does not re-evaluate. This caused a subtle bug in my app when enabling the compiler.

Apologies if this is a duplicate, I looked but could not find similar.

How often does this bug happen?

Every time

What version of React are you using?

19.2.4

What version of React Compiler are you using?

1.0.0

GitHub Labels

Type: BugStatus: Unconfirmed

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Risk Flags

  • NaN handling
  • dependency comparison
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Details

Points15 pts
Difficultymedium
Scopesomewhat clear
Skill Matchmaybe
Test Focusedyes