`animation: var(--a)` with a full shorthand in `--a` renders no animation

Start with the provided reproducer test, src/__tests__/native/animation-shorthand-through-variable.test.tsx, and compare how the written shorthand and custom property cases reach the flattened style. Then trace custom property resolution and animation shorthand handling from the test’s registerCSS setup. Done means both cases produce the expected animation longhands and the focused Jest test passes.

Before submitting a new issue

• I tested using the latest version of the library, as the bug might be already fixed.
• I tested using a supported version of react native.
• I checked for possible duplicate issues, with possible answers.

Bug summary

A written animation: slide-in 1s linear 250ms 2 alternate both reaches Reanimated as its longhands. The same value read through a custom property the runtime keeps renders no animation at all; animation: slide-in 1s through a variable still animates.

The written shorthand passes; through a variable the style is {}.

Library version

main at 2421ea7 (0.0.0-nightly.2421ea7)

Environment info

System:
  OS: Windows 11 10.0.26300
  CPU: "(32) x64 AMD Ryzen 9 9950X3D 16-Core Processor          "
  Memory: 155.26 GB / 255.67 GB
Binaries:
  Node:
    version: 26.12.1
    path: C:\Program Files\nodejs\node.EXE
  Yarn:
    version: 4.9.2
    path: C:\Users\<user>\AppData\Roaming\npm\yarn.CMD
  npm:
    version: 12.2.1
    path: C:\Program Files\nodejs\npm.CMD
  Watchman: Not Found
SDKs:
  Android SDK:
    API Levels:
      - "33"
      - "35"
      - "35"
      - "35"
      - "36"
      - "37"
    Build Tools:
      - 35.0.0
      - 36.0.0
      - 36.1.0
      - 37.0.0
    System Images:
      - android-26 | Google APIs Intel x86_64 Atom
      - android-28 | Google APIs Intel x86_64 Atom
      - android-29 | Google APIs Intel x86_64 Atom
      - android-30 | Google APIs Intel x86_64 Atom
      - android-31 | Google APIs Intel x86_64 Atom
      - android-32 | Google APIs Intel x86_64 Atom
      - android-33 | Google APIs Intel x86_64 Atom
      - android-34 | Google APIs Intel x86_64 Atom
      - android-35 | Google APIs Intel x86_64 Atom
      - android-36.1 | Google Play Intel x86_64 Atom
      - android-36.1 | Pre-Release 16 KB Page Size Google Play Intel x86_64 Atom
      - android-37.0 | Google APIs Intel x86_64 Atom
    Android NDK: Not Found
  Windows SDK: Not Found
IDEs:
  Android Studio: AI-262.9437.185.2621.16467767
  Visual Studio: Not Found
Languages:
  Java:
    version: 17.0.20.1
    path: C:\Program Files\Microsoft\jdk-17.0.20.101-hotspot\bin\javac.EXE
  Ruby: Not Found
npmPackages:
  "@react-native-community/cli": Not Found
  react:
    installed: 19.2.3
    wanted: 19.2.3
  react-native:
    installed: 0.86.3
    wanted: 0.86.3
  react-native-windows: Not Found
npmGlobalPackages:
  "*react-native*": Not Found
Android:
  hermesEnabled: Not found
  newArchEnabled: Not found
iOS:
  hermesEnabled: Not found
  newArchEnabled: Not found

Steps to reproduce

1. Clone the reproducer branch, which is main at 2421ea7 with one file added, src/__tests__/native/animation-shorthand-through-variable.test.tsx, and install:

   git clone --branch repro/525-animation-shorthand-through-a-variable-renders-none https://github.com/YevheniiKotyrlo/react-native-css
   cd react-native-css
   yarn install
   

2. Run yarn jest src/__tests__/native/animation-shorthand-through-variable.test.tsx.

src/__tests__/native/animation-shorthand-through-variable.test.tsx:

import { StyleSheet } from "react-native";

import { render, screen } from "@testing-library/react-native";
import { View } from "react-native-css/components/View";
import { registerCSS, testID } from "react-native-css/jest";

jest.mock("../../native/reanimated", () => ({
  animatedComponentFamily: (component: unknown) => component,
}));

const keyframes =
  "@keyframes slide-in { from { margin-left: 100%; } to { margin-left: 0%; } }";

test.each([
  [
    "written",
    ".motion { animation: slide-in 1s linear 250ms 2 alternate both; }",
  ],
  [
    "through a variable",
    ":root { --a: slide-in 1s linear 250ms 2 alternate both; } .motion { animation: var(--a); }",
  ],
])(
  "animation: slide-in 1s linear 250ms 2 alternate both %s reaches Reanimated as its longhands",
  (_, css) => {
    registerCSS(`${keyframes} ${css}`, { inlineVariables: false });
    render(<View testID={testID} className="motion" />);
    expect(
      StyleSheet.flatten(screen.getByTestId(testID).props.style),
    ).toMatchObject({
      animationDuration: [1000],
      animationDelay: [250],
      animationIterationCount: [2],
      animationDirection: ["alternate"],
      animationFillMode: ["both"],
    });
  },
);

Expected: animation: var(--a) over a full shorthand reaches Reanimated as its longhands, as the written shorthand does.

Actual: it renders no animation.

FAIL src/__tests__/native/animation-shorthand-through-variable.test.tsx
  √ animation: slide-in 1s linear 250ms 2 alternate both written reaches Reanimated as its longhands (20 ms)
  × animation: slide-in 1s linear 250ms 2 alternate both through a variable reaches Reanimated as its longhands (8 ms)
  ● animation: slide-in 1s linear 250ms 2 alternate both through a variable reaches Reanimated as its longhands
    expect(received).toMatchObject(expected)
    - Expected  - 17
    + Received  +  1
    - Object {
    -   "animationDelay": Array [
    -     250,
    -   ],
    -   "animationDirection": Array [
    -     "alternate",
    -   ],
    -   "animationDuration": Array [
    -     1000,
    -   ],
    -   "animationFillMode": Array [
    -     "both",
    -   ],
    -   "animationIterationCount": Array [
    -     2,
    -   ],
    - }
    + Object {}
      28 |     expect(
      29 |       StyleSheet.flatten(screen.getByTestId(testID).props.style),
    > 30 |     ).toMatchObject({
         |       ^
      31 |       animationDuration: [1000],
      32 |       animationDelay: [250],
      33 |       animationIterationCount: [2],
      at toMatchObject (src/__tests__/native/animation-shorthand-through-variable.test.tsx:30:7)
Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 passed, 2 total
Snapshots:   0 total
Time:        1.038 s, estimated 2 s
Ran all test suites matching /src\\__tests__\\native\\animation-shorthand-through-variable.test.tsx/i.

Reproducible example repository

https://github.com/YevheniiKotyrlo/react-native-css/tree/repro/525-animation-shorthand-through-a-variable-renders-none