Codegen using `generateOptionalProperties` generates no optional for e.g. `Float`

[hannojg]

Description

In this PR:

• Add optional props generation support #54724

support was added in codegen for specifying generateOptionalProperties: true which should generate optional props as std::optional in the c++ binding.
I tested it and it works well for e.g. string.

However, when tested with Float it never generates the optional condition. The reason seems to be that for Float we pick a default value like 0.0.

E.g. for this prop:

export interface NativeProps extends ViewProps {
  animatedHeight?: Float;

and adding a comment here:
https://github.com/facebook/react-native/blob/ca520ee4c19dd921f9225c71a9ad872c4bbd7cb9/packages/react-native-codegen/src/generators/components/GeneratePropsCpp.js#L112-L120

We can see that the float comes with a default value:

{
  name: 'animatedHeight',
  optional: true,
  typeAnnotation: { type: 'FloatTypeAnnotation', default: 0 }

I feel like when specifying generateOptionalProperties: true this is unexpected behaviour.
If i were to specify:

export interface NativeProps extends ViewProps {
  animatedHeight?: WithDefault<Float, 0>;

i agree that the default would be correct.

This can actually be worked around by specifying:

export interface NativeProps extends ViewProps {
  animatedHeight?: WithDefault<Float, null>;

I wanted to open this issue to open a discussion whether we should:
a) Add a check in codegen if generateOptionalProperties: true and .default == defaultTypeForType (e.g. 0), so to check for the default value
b) if a property is optional and using generateOptionalProperties never put down a default value, if not explicitly specified (ie. this is a bug in the ts parser) (ie change the change to if (!prop.typeAnnotation.default))
c) Call this fine and do nothing?

Steps to reproduce

Create a simple typescript spec as above and run codegen.

React Native Version

0.83.1

Affected Platforms

Runtime - Android

Output of npx @react-native-community/cli info

System:
  OS: macOS 15.7.3
  CPU: (14) arm64 Apple M4 Pro
  Memory: 159.64 MB / 48.00 GB
  Shell:
    version: "5.9"
    path: /bin/zsh
Binaries:
  Node:
    version: 22.14.0
    path: /nix/store/04fc23dsflkxl4s9p6lkigia1hq3vjp2-nodejs-22.14.0/bin/node
  Yarn:
    version: 4.9.2
    path: /nix/store/04fc23dsflkxl4s9p6lkigia1hq3vjp2-nodejs-22.14.0/bin/yarn
  npm:
    version: 10.9.2
    path: /nix/store/04fc23dsflkxl4s9p6lkigia1hq3vjp2-nodejs-22.14.0/bin/npm
  Watchman:
    version: 2024.03.11.00
    path: /Users/hannogodecke/Documents/discord/.local/bin/watchman
Managers:
  CocoaPods:
    version: 1.16.2
    path: /Users/hannogodecke/.rbenv/shims/pod
SDKs:
  iOS SDK:
    Platforms:
      - DriverKit 25.2
      - iOS 26.2
      - macOS 26.2
      - tvOS 26.2
      - visionOS 26.2
      - watchOS 26.2
  Android SDK:
    API Levels:
      - "31"
      - "34"
      - "35"
      - "36"
    Build Tools:
      - 34.0.0
      - 35.0.0
      - 35.0.1
      - 36.0.0
    System Images:
      - android-35 | Google APIs ARM 64 v8a
      - android-35 | Google Play ARM 64 v8a
      - android-35 | Pre-Release 16 KB Page Size Google Play ARM 64 v8a
      - android-35 | Pre-Release 16 KB Page Size Google APIs ARM 64 v8a
      - android-35 | Google APIs ATD ARM 64
      - android-36 | Google Play ARM 64 v8a
    Android NDK: Not Found
IDEs:
  Android Studio: 2025.2 AI-252.25557.131.2521.14432022
  Xcode:
    version: 26.2/17C52
    path: /usr/bin/xcodebuild
Languages:
  Java:
    version: 17.0.15
    path: /Users/hannogodecke/.jenv/shims/javac
  Ruby:
    version: 3.4.4
    path: /Users/hannogodecke/.rbenv/shims/ruby
npmPackages:
  "@react-native-community/cli": Not Found
  react: Not Found
  react-native:
    installed: 0.83.1
    wanted: "*"
  react-native-macos: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Stacktrace or Logs

No logs, this is more of a discussion item

MANDATORY Reproducer

https://github.com/hannojg/react-native/blob/main/packages/rn-tester/js/examples/Playground/RNTesterPlayground.js

Screenshots and Videos

No response

[react-native-bot]

Warning

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[hannojg]

only for string (of the primitive types) this seems to work fine.
For Int32 the <WithDefault, null>` workaround doesn't seem to really work

[hannojg]

For Int32 the bug seems to be in the typescript parser code where we don't check for nullability:

https://github.com/facebook/react-native/blob/36f07a1b29277a788cf8ee31626b31a014248bd1/packages/react-native-codegen/src/parsers/typescript/components/componentsUtils.js#L343-L351

But given that this is the same in the flow parser, i am wondering if this is intended behaviour?
(however, with generateOptionalProperties i feel like its reasonable to assume it would behave differently?)

[react-native-bot]

This issue is stale because it has been open for 180 days with no activity. It will be closed in 7 days unless you comment on it or remove the "Stale" label.

[react-native-bot]

This issue was closed because it has been stalled for 7 days with no activity.