A value the compiler can only partly convert is kept in part: `--t: 10px 1cap` renders `translate: var(--t)` as `{ translate: true }`

Start with src/compiler/declarations.ts, especially reduceParseUnparsed and parseUnparsed, then run the supplied reproducer at src/__tests__/native/custom-property-partial-value.test.tsx. Trace how declarations and custom property values are parsed, and check whether each full value is accepted or only partially converted. Done means all four reproductions leave the affected style unset.

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 declaration whose value does not match its property's grammar is invalid and ignored, and a var() that substitutes such a value makes the declaration invalid at computed-value time, so the property is unset. The compiler keeps the tokens it can convert and drops the rest: translate: 10px 1cap moves the element 10px, and the same value through a variable renders { translate: true }; font-family: Inter, Helvetica,, a stack with an empty entry, sets the array ["Inter", "Helvetica"] either way.

All four fail, the element receiving:

translate:                    {"transform": [{"translateX": 10}, {"translateY": undefined}]}
translate through a variable: {"transform": [{"translate": true}]}
font-family:                  {"fontFamily": ["Inter", "Helvetica"]}
font-family through a variable: {"fontFamily": ["Inter", "Helvetica"]}

reduceParseUnparsed (src/compiler/declarations.ts) maps every token through parseUnparsed and keeps what is not undefined; parseUnparsed returns undefined, with a warning, for a length whose unit it cannot convert, for inherit and initial, and for a token it does not read, and an empty entry between commas leaves no group. #389 and #417 ignore the written translate and font stack; a custom property's value goes through reduceParseUnparsed and keeps what it can convert.

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/custom-property-partial-value.test.tsx, and install:

   git clone --branch repro/523-custom-property-drops-what-it-cannot-take https://github.com/YevheniiKotyrlo/react-native-css
   cd react-native-css
   yarn install
   

2. Run yarn jest src/__tests__/native/custom-property-partial-value.test.tsx.

src/__tests__/native/custom-property-partial-value.test.tsx:

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

test.each([
  ["translate", ".a { translate: 10px 1cap; }"],
  [
    "translate through a variable",
    ":root { --t: 10px 1cap; } .a { translate: var(--t); }",
  ],
])("%s holding 10px 1cap leaves the element untranslated", (_, css) => {
  registerCSS(css, { inlineVariables: false });
  render(<View testID={testID} className="a" />);
  expect(screen.getByTestId(testID).props.style).toBeUndefined();
});

test.each([
  ["font-family", ".a { font-family: Inter, Helvetica,; }"],
  [
    "font-family through a variable",
    ":root { --t: Inter, Helvetica,; } .a { font-family: var(--t); }",
  ],
])("%s holding Inter, Helvetica, sets no font", (_, css) => {
  registerCSS(css, { inlineVariables: false });
  render(<Text testID={testID} className="a" />);
  expect(screen.getByTestId(testID).props.style).toBeUndefined();
});

Expected: a value the compiler cannot convert whole leaves its property unset, written or read through a variable.

Actual: the parts it can convert are kept: translate: var(--t) over 10px 1cap renders { translate: true }, and font-family: Inter, Helvetica, sets ["Inter", "Helvetica"].

FAIL src/__tests__/native/custom-property-partial-value.test.tsx
  × translate holding 10px 1cap leaves the element untranslated (20 ms)
  × translate through a variable holding 10px 1cap leaves the element untranslated (5 ms)
  × font-family holding Inter, Helvetica, sets no font (2 ms)
  × font-family through a variable holding Inter, Helvetica, sets no font (1 ms)
  ● translate holding 10px 1cap leaves the element untranslated
    expect(received).toBeUndefined()
    Received: {"transform": [{"translateX": 10}, {"translateY": undefined}]}
      13 |   registerCSS(css, { inlineVariables: false });
      14 |   render(<View testID={testID} className="a" />);
    > 15 |   expect(screen.getByTestId(testID).props.style).toBeUndefined();
         |                                                  ^
      16 | });
      17 |
      18 | test.each([
      at toBeUndefined (src/__tests__/native/custom-property-partial-value.test.tsx:15:50)
  ● translate through a variable holding 10px 1cap leaves the element untranslated
    expect(received).toBeUndefined()
    Received: {"transform": [{"translate": true}]}
      13 |   registerCSS(css, { inlineVariables: false });
      14 |   render(<View testID={testID} className="a" />);
    > 15 |   expect(screen.getByTestId(testID).props.style).toBeUndefined();
         |                                                  ^
      16 | });
      17 |
      18 | test.each([
      at toBeUndefined (src/__tests__/native/custom-property-partial-value.test.tsx:15:50)
  ● font-family holding Inter, Helvetica, sets no font
    expect(received).toBeUndefined()
    Received: {"fontFamily": ["Inter", "Helvetica"]}
      25 |   registerCSS(css, { inlineVariables: false });
      26 |   render(<Text testID={testID} className="a" />);
    > 27 |   expect(screen.getByTestId(testID).props.style).toBeUndefined();
         |                                                  ^
      28 | });
      29 |
      at toBeUndefined (src/__tests__/native/custom-property-partial-value.test.tsx:27:50)
  ● font-family through a variable holding Inter, Helvetica, sets no font
    expect(received).toBeUndefined()
    Received: {"fontFamily": ["Inter", "Helvetica"]}
      25 |   registerCSS(css, { inlineVariables: false });
      26 |   render(<Text testID={testID} className="a" />);
    > 27 |   expect(screen.getByTestId(testID).props.style).toBeUndefined();
         |                                                  ^
      28 | });
      29 |
      at toBeUndefined (src/__tests__/native/custom-property-partial-value.test.tsx:27:50)
Test Suites: 1 failed, 1 total
Tests:       4 failed, 4 total
Snapshots:   0 total
Time:        1.107 s, estimated 2 s
Ran all test suites matching /src\\__tests__\\native\\custom-property-partial-value.test.tsx/i.

Reproducible example repository

https://github.com/YevheniiKotyrlo/react-native-css/tree/repro/523-custom-property-drops-what-it-cannot-take