`margin: var(--v)` with `--v: 1px 2px` reaches native as `margin: [1, 2]`, which React Native drops

Start with src/compiler/declarations.ts and src/native/styles/resolve.ts, then inspect the shorthand handlers under src/native/styles/shorthands/ to see how variable values reach native styles. Run the reproducer test src/__tests__/native/shorthand-through-variable.test.tsx. Done means kept variables containing two-value margin and padding resolve to the same four side properties as the written declarations.

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

margin: 1px 2px written in a rule compiles into its four sides. The same value read through a custom property the compiler keeps reaches the element as margin: [1, 2], and React Native's margin takes one length, so the margin is lost. padding does the same. A variable is kept when it is declared more than once (a theme with a dark override), listed in inlineVariables.exclude, or compiled with inlineVariables: false.

The first two fail; the element gets { margin: [1, 2] } and { padding: [1, 2] }. The third passes.

An unparsed declaration whose property is not in unparsedRuntimeParsing (src/compiler/declarations.ts) compiles to a plain runtime read, and resolveValue (src/native/styles/resolve.ts) hands the property whatever list the variable resolves to: border, box-shadow, text-shadow and transform resolve through handlers in src/native/styles/shorthands/, and the per-side shorthands have none.

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/shorthand-through-variable.test.tsx, and install:

   git clone --branch repro/518-shorthand-variable-reaches-native-as-a-list https://github.com/YevheniiKotyrlo/react-native-css
   cd react-native-css
   yarn install
   

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

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

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

test.each([
  ["margin", { marginTop: 1, marginBottom: 1, marginLeft: 2, marginRight: 2 }],
  [
    "padding",
    { paddingTop: 1, paddingBottom: 1, paddingLeft: 2, paddingRight: 2 },
  ],
])(
  "%s: 1px 2px read through a kept variable reaches native as its sides",
  (property, sides) => {
    registerCSS(`.a { --v: 1px 2px; ${property}: var(--v); }`, {
      inlineVariables: false,
    });
    render(<View testID={testID} className="a" />);
    expect(screen.getByTestId(testID).props.style).toStrictEqual(sides);
  },
);

test("margin: 1px 2px written out reaches native as its sides", () => {
  registerCSS(`.a { margin: 1px 2px; }`);
  render(<View testID={testID} className="a" />);
  expect(screen.getByTestId(testID).props.style).toStrictEqual({
    marginTop: 1,
    marginBottom: 1,
    marginLeft: 2,
    marginRight: 2,
  });
});

Expected: margin: var(--v) over --v: 1px 2px sets the four sides, as the written margin: 1px 2px does, and padding likewise.

Actual: it reaches native as margin: [1, 2], which React Native drops.

FAIL src/__tests__/native/shorthand-through-variable.test.tsx
  × margin: 1px 2px read through a kept variable reaches native as its sides (21 ms)
  × padding: 1px 2px read through a kept variable reaches native as its sides (5 ms)
  √ margin: 1px 2px written out reaches native as its sides (3 ms)
  ● margin: 1px 2px read through a kept variable reaches native as its sides
    expect(received).toStrictEqual(expected) // deep equality
    - Expected  - 4
    + Received  + 4
      Object {
    -   "marginBottom": 1,
    -   "marginLeft": 2,
    -   "marginRight": 2,
    -   "marginTop": 1,
    +   "margin": Array [
    +     1,
    +     2,
    +   ],
      }
      16 |     });
      17 |     render(<View testID={testID} className="a" />);
    > 18 |     expect(screen.getByTestId(testID).props.style).toStrictEqual(sides);
         |                                                    ^
      19 |   },
      20 | );
      21 |
      at toStrictEqual (src/__tests__/native/shorthand-through-variable.test.tsx:18:52)
  ● padding: 1px 2px read through a kept variable reaches native as its sides
    expect(received).toStrictEqual(expected) // deep equality
    - Expected  - 4
    + Received  + 4
      Object {
    -   "paddingBottom": 1,
    -   "paddingLeft": 2,
    -   "paddingRight": 2,
    -   "paddingTop": 1,
    +   "padding": Array [
    +     1,
    +     2,
    +   ],
      }
      16 |     });
      17 |     render(<View testID={testID} className="a" />);
    > 18 |     expect(screen.getByTestId(testID).props.style).toStrictEqual(sides);
         |                                                    ^
      19 |   },
      20 | );
      21 |
      at toStrictEqual (src/__tests__/native/shorthand-through-variable.test.tsx:18:52)
Test Suites: 1 failed, 1 total
Tests:       2 failed, 1 passed, 3 total
Snapshots:   0 total
Time:        1.107 s, estimated 2 s
Ran all test suites matching /src\\__tests__\\native\\shorthand-through-variable.test.tsx/i.

Reproducible example repository

https://github.com/YevheniiKotyrlo/react-native-css/tree/repro/518-shorthand-variable-reaches-native-as-a-list