`:root { font-size: 12pt }` leaves `1rem` at 14: the compile-time root size is read with a px-only regex

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評估

難度
2/5
預估耗時
1-3 小時
新手友好度
80/100
Issue 類型
缺陷
描述清晰度
描述清楚
活躍度
活躍
技術堆疊
react-native, typescript
領域
frontend, testing

研究方向

先從 compiler.ts 中編譯時的根字型大小解析開始，接著閱讀原生字型大小測試。執行重現測試 src/__tests__/native/root-font-size-absolute-unit.test.tsx，確認失敗的 12pt 案例。完成條件是：根字型大小為 12pt 時，1rem 解析為 16，且現有的 16px 案例仍然通過。

由索引模型根據 Issue 內容生成。

描述

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

rem is the root element's computed font size (css-values-4). The compile-time rem comes from a regex over the raw CSS (compiler.ts, /:root\s*\{[^}]*font-size:\s*([\d.]+)px/), so a root size in an absolute unit other than px — :root { font-size: 12pt }, 16px — is never read, and 1rem stays at the default 14, while the root em comes from the parsed :root declaration.

The 16px case passes; the 12pt case fails, the element receiving { fontSize: 14 }.

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/root-font-size-absolute-unit.test.tsx, and install: 
    git clone --branch repro/536-root-font-size-two-resolutions https://github.com/YevheniiKotyrlo/react-native-css
cd react-native-css
yarn install
  2. Run yarn jest src/__tests__/native/root-font-size-absolute-unit.test.tsx.

src/__tests__/native/root-font-size-absolute-unit.test.tsx:

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

test.each([
  ["16px", 16],
  ["12pt", 16],
])(":root { font-size: %s } makes 1rem %p", (rootSize, expected) => {
  registerCSS(`:root { font-size: ${rootSize}; } .a { font-size: 1rem; }`);
  render(<Text testID={testID} className="a" />);
  expect(screen.getByTestId(testID).props.style).toStrictEqual({ fontSize: expected });
});

Expected: :root { font-size: 12pt } makes 1rem 16px.

Actual: 1rem stays at the default 14.

The run's output on main at 2421ea7, Windows 11, Node 26.12.1 
FAIL src/__tests__/native/root-font-size-absolute-unit.test.tsx
  √ :root { font-size: 16px } makes 1rem 16 (18 ms)
  × :root { font-size: 12pt } makes 1rem 16 (7 ms)
  ● :root { font-size: 12pt } makes 1rem 16
    expect(received).toStrictEqual(expected) // deep equality
    - Expected  - 1
    + Received  + 1
      Object {
    -   "fontSize": 16,
    +   "fontSize": 14,
      }
       9 |   registerCSS(`:root { font-size: ${rootSize}; } .a { font-size: 1rem; }`);
      10 |   render(<Text testID={testID} className="a" />);
    > 11 |   expect(screen.getByTestId(testID).props.style).toStrictEqual({ fontSize: expected });
         |                                                  ^
      12 | });
      13 |
      at toStrictEqual (src/__tests__/native/root-font-size-absolute-unit.test.tsx:11:50)
Test Suites: 1 failed, 1 total
Tests:       1 failed, 1 passed, 2 total
Snapshots:   0 total
Time:        1.067 s, estimated 2 s
Ran all test suites matching /src\\__tests__\\native\\root-font-size-absolute-unit.test.tsx/i.
Reproducible example repository

https://github.com/YevheniiKotyrlo/react-native-css/tree/repro/536-root-font-size-two-resolutions

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