A keyword read through a variable keeps its case: `--v: ABSOLUTE; position: var(--v)` reaches React Native as `"ABSOLUTE"`

Start with parseUnparsed in src/compiler/declarations.ts, then trace how a resolved var() reaches the React Native style. Run the reproducer from src/__tests__/native/keyword-case.test.tsx on the linked branch; its output compares written keywords with variable values. Done when those routes produce the same lowercase keyword values for the reported properties.

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

CSS keywords are ASCII case-insensitive, and lightningcss lowercases a written one: position: ABSOLUTE renders position: "absolute". The same keyword held in a variable the runtime keeps reaches React Native as written, position: "ABSOLUTE", which React Native does not read, and so do flex-direction, transition-timing-function and animation-direction.

position: ABSOLUTE
written: {"position":"absolute"}
kept:    {"position":"ABSOLUTE"}
flex-direction: Row
written: {"flexDirection":"row"}
kept:    {"flexDirection":"Row"}
transition-timing-function: EASE-IN
written: {"transitionTimingFunction":"ease-in"}
kept:    {"transitionTimingFunction":"EASE-IN"}
animation-direction: ALTERNATE
written: {"animationDirection":["alternate"]}
kept:    {"animationDirection":"ALTERNATE"}

Expected: the kept route renders the written route's lowercase keyword. parseUnparsed (src/compiler/declarations.ts) stores an ident token's value as written, and the runtime hands a resolved var() to the style as it is; only the typed route, through lightningcss, folds a keyword's case.

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/keyword-case.test.tsx, and install:

   git clone --branch repro/529-keyword-through-a-variable-keeps-its-case https://github.com/YevheniiKotyrlo/react-native-css
   cd react-native-css
   yarn install
   

2. Run yarn jest src/__tests__/native/keyword-case.test.tsx.

src/__tests__/native/keyword-case.test.tsx:

// Run from a react-native-css checkout: copy to src/__tests__/native/keyword-case.test.tsx, then `yarn jest` it.
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 styleOf = (css: string, inlineVariables: boolean) => {
  registerCSS(css, inlineVariables ? {} : { inlineVariables: false });
  render(<View testID={testID} className="a" />);
  const style = StyleSheet.flatten(screen.getByTestId(testID).props.style);
  screen.unmount();
  return JSON.stringify(style);
};

test.each([
  ["position", "ABSOLUTE"],
  ["display", "NONE"],
  ["flex-direction", "Row"],
  ["transition-timing-function", "EASE-IN"],
  ["animation-direction", "ALTERNATE"],
])("%s: %s written and through a variable", (property, value) => {
  console.log(
    `${property}: ${value}\n  written: ${styleOf(`.a { ${property}: ${value}; }`, true)}\n  kept:    ${styleOf(`.a { --v: ${value}; ${property}: var(--v); }`, false)}`,
  );
});

Expected: a keyword read through a variable is lowercased as a written one is: position: "absolute".

Actual: it reaches React Native as written, position: "ABSOLUTE", which React Native does not read, and so do the other keywords the test reads.

  console.log
    position: ABSOLUTE
      written: {"position":"absolute"}
      kept:    {"position":"ABSOLUTE"}
      at log (src/__tests__/native/keyword-case.test.tsx:27:11)
  console.log
    flex-direction: Row
      written: {"flexDirection":"row"}
      kept:    {"flexDirection":"Row"}
      at log (src/__tests__/native/keyword-case.test.tsx:27:11)
  console.log
    transition-timing-function: EASE-IN
      written: {"transitionTimingFunction":"ease-in"}
      kept:    {"transitionTimingFunction":"EASE-IN"}
      at log (src/__tests__/native/keyword-case.test.tsx:27:11)
  console.log
    animation-direction: ALTERNATE
      written: {"animationDirection":["alternate"]}
      kept:    {"animationDirection":"ALTERNATE"}
      at log (src/__tests__/native/keyword-case.test.tsx:27:11)
FAIL src/__tests__/native/keyword-case.test.tsx
  √ position: ABSOLUTE written and through a variable (30 ms)
  × display: NONE written and through a variable (4 ms)
  √ flex-direction: Row written and through a variable (4 ms)
  √ transition-timing-function: EASE-IN written and through a variable (2 ms)
  √ animation-direction: ALTERNATE written and through a variable (2 ms)
  ● display: NONE written and through a variable
    Unable to find an element with testID: react-native-css
    <View
      style={
        {
          "display": "none",
        }
      }
      testID="react-native-css"
    />
      13 |   registerCSS(css, inlineVariables ? {} : { inlineVariables: false });
      14 |   render(<View testID={testID} className="a" />);
    > 15 |   const style = StyleSheet.flatten(screen.getByTestId(testID).props.style);
         |                                           ^
      16 |   screen.unmount();
      17 |   return JSON.stringify(style);
      18 | };
      at getByTestId (src/__tests__/native/keyword-case.test.tsx:15:43)
      at styleOf (src/__tests__/native/keyword-case.test.tsx:28:42)
Test Suites: 1 failed, 1 total
Tests:       1 failed, 4 passed, 5 total
Snapshots:   0 total
Time:        1.124 s, estimated 3 s
Ran all test suites matching /src\\__tests__\\native\\keyword-case.test.tsx/i.

Reproducible example repository

https://github.com/YevheniiKotyrlo/react-native-css/tree/repro/529-keyword-through-a-variable-keeps-its-case