`@container (width > 10em)` never matches: a container query's `em` is never resolved

Offen

#512 erstellt am 29.10.2026 0 Kommentare 0 Reaktionen 0 zugewiesene Personen Auf GitHub ansehen

Maintainer antworten meist innerhalb von 3 Tagen

Dieses Issue hat noch niemand übernommen.

Bewertung

Schwierigkeit: 4/5
Geschätzter Aufwand: 3-5 Tage
Anfängerfreundlichkeit: 59/100

Issue-Typ: Bug
Klarheit: Klar beschrieben
Aktivitätsstatus: Aktiv
Tech-Stack: react-native, typescript
Bereich: frontend, testing

Rechercherichtung

Start with src/native/conditions/container-query.ts and the named container width and height families in src/native/reactivity.ts; compare how src/native/styles/units.ts reads an element's em value. Run the reproducer with yarn jest src/__tests__/native/container-em-bound.test.tsx (the test file is on the reproducer branch). Done means all three reported conditions match the expected results using the container's computed font size.

Vom Indexierungsmodell aus dem Issue-Text verfasst.

Beschreibung

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

In a container query condition, em is relative to the query container's computed font size (CSS Conditional 5 §6.1): in a 400px container that sets none, 10em is 160px, and Chromium 156, Firefox 157 and WebKit 27.2 match @container (width > 10em). The compiler emits the bound as [{}, "em", 10, 1], and testContainerMediaCondition (src/native/conditions/container-query.ts) compares the container's width only with a number, so the condition is false at every size.

condition	Chromium, Firefox, WebKit	`main` (2421ea7)	#426 (40bfda2)
`(width > 10em)`	match	no match	no match
`(width > 30em)`	no match	no match	no match
`not (width > 30em)`	match	match	no match

not (width > 30em) matches on main only because the bound reads as false; #426 answers it unknown (MQ5 §3.1) and lists this among its known limits. #494 resolves a media query's em, which is the root font size rather than a container's.

Resolving it means measuring each container's computed fontSize beside its width and height (containerWidthFamily and containerHeightFamily in src/native/reactivity.ts), as the style resolver reads an element's em from __rn-css-em (src/native/styles/units.ts).

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

Clone the reproducer branch, which is main at 2421ea7 with one file added, src/__tests__/native/container-em-bound.test.tsx, and install:

git clone --branch repro/512-container-em-bound https://github.com/YevheniiKotyrlo/react-native-css
cd react-native-css
yarn install

Run yarn jest src/__tests__/native/container-em-bound.test.tsx.

src/__tests__/native/container-em-bound.test.tsx:

// A container query's em is the container's font size (CSS Conditional 5 §6.1), so 10em is 160px in a container that sets none
import { fireEvent, render, screen } from "@testing-library/react-native";
import { View } from "react-native-css/components/View";
import { registerCSS } from "react-native-css/jest";

test.each([
  ["(width > 10em)", true],
  ["(width > 30em)", false],
  ["not (width > 30em)", true],
])("@container %s in a 400px container matches: %s", (condition, expected) => {
  registerCSS(`
    .parent { container-type: size; }
    .child { width: 10px; }
    @container ${condition} { .child { width: 37px; } }
  `);
  render(
    <View testID="parent" className="parent">
      <View testID="child" className="child" />
    </View>,
  );
  fireEvent(screen.getByTestId("parent"), "layout", {
    nativeEvent: { layout: { x: 0, y: 0, width: 400, height: 200 } },
  });
  expect(screen.getByTestId("child").props.style.width === 37).toBe(expected);
});

Expected: @container (width > 10em) matches in the 400px container, where 10em is 160px, and not (width > 30em) matches too, so the test's three cases pass.

Actual: the bound never compares, so (width > 10em) is false at every size and its case fails.

The run's output on main at 2421ea7, Windows 11, Node 26.12.1

FAIL src/__tests__/native/container-em-bound.test.tsx
  × @container (width > 10em) in a 400px container matches: true (42 ms)
  √ @container (width > 30em) in a 400px container matches: false (5 ms)
  √ @container not (width > 30em) in a 400px container matches: true (2 ms)
  ● @container (width > 10em) in a 400px container matches: true
    expect(received).toBe(expected) // Object.is equality
    Expected: true
    Received: false
      22 |     nativeEvent: { layout: { x: 0, y: 0, width: 400, height: 200 } },
      23 |   });
    > 24 |   expect(screen.getByTestId("child").props.style.width === 37).toBe(expected);
         |                                                                ^
      25 | });
      26 |
      at toBe (src/__tests__/native/container-em-bound.test.tsx:24:64)
Test Suites: 1 failed, 1 total
Tests:       1 failed, 2 passed, 3 total
Snapshots:   0 total
Time:        1.533 s, estimated 3 s
Ran all test suites matching /src\\__tests__\\native\\container-em-bound.test.tsx/i.

Reproducible example repository

https://github.com/YevheniiKotyrlo/react-native-css/tree/repro/512-container-em-bound

Vorherrschende Sprache: TypeScript
Sterne: 166
Forks: 45
Ø Merge: 13 T. 14 Std.
Gemergte PRs (30 T.): 1

Entwicklungsumgebung

Kein Dockerfile und keine Docker-Compose-Datei
Keine Pull-Request-Vorlage
Beitragsleitfaden lesen

Erste Schritte

Lesen Sie das ganze Issue und danach den Beitragsleitfaden des Projekts.
Schreiben Sie ins Issue, dass Sie es übernehmen — das erspart doppelte Arbeit.
Forken Sie das Repository und arbeiten Sie in einem Branch.
Öffnen Sie einen Pull Request, der die Issue-Nummer nennt.

Mehr aus nativewind/react-native-css

The Tailwind test harness's `render` throws on an element whose child is text
Offen
- Stimmt etwas nicht?
Schwierigkeit 2/5 1-3 Stunden Anfängerfreundlichkeit 78/100

nativewind/react-native-css#545 · Erstellt am 29.10.2026

Maintainer antworten meist innerhalb von 3 Tagen
A media `resolution` in `dpi` or `dpcm` converts to dppx at 160 dpi, so `(min-resolution: 300dpi)` matches a 2x screen
Offen
- Stimmt etwas nicht?
Schwierigkeit 2/5 1-3 Stunden Anfängerfreundlichkeit 78/100

nativewind/react-native-css#544 · Erstellt am 29.10.2026

Maintainer antworten meist innerhalb von 3 Tagen
`useNativeVariable("--x")` fails to type-check in a React Native app: the package types it `() => never`
Offen
- Stimmt etwas nicht?
Schwierigkeit 2/5 1-3 Stunden Anfängerfreundlichkeit 78/100

nativewind/react-native-css#543 · Erstellt am 29.10.2026

Maintainer antworten meist innerhalb von 3 Tagen
`overflow: scroll` is refused, though React Native's `overflow` takes it
Offen
- Stimmt etwas nicht?
Schwierigkeit 2/5 1-3 Stunden Anfängerfreundlichkeit 84/100

nativewind/react-native-css#540 · Erstellt am 29.10.2026

Maintainer antworten meist innerhalb von 3 Tagen
A runtime `calc()` drops `infinity`: `width: var(--r)` over `--r: calc(infinity * 1px)` renders nothing
Offen
- Stimmt etwas nicht?
Schwierigkeit 2/5 1-3 Stunden Anfängerfreundlichkeit 78/100

nativewind/react-native-css#538 · Erstellt am 29.10.2026

Maintainer antworten meist innerhalb von 3 Tagen

Alle Issues in nativewind/react-native-css

`@container (width > 10em)` never matches: a container query's `em` is never resolved

Stimmt etwas nicht?

Bewertung

Rechercherichtung

Beschreibung

Before submitting a new issue

Bug summary

Library version

Environment info

Steps to reproduce

Reproducible example repository

Entwicklungsumgebung

Erste Schritte

Mehr aus nativewind/react-native-css

Stimmt etwas nicht?

Stimmt etwas nicht?

Stimmt etwas nicht?

Stimmt etwas nicht?

Stimmt etwas nicht?

Ähnliche Issues

Stimmt etwas nicht?

Stimmt etwas nicht?

Stimmt etwas nicht?

Stimmt etwas nicht?

Stimmt etwas nicht?

Neue Issues direkt in Ihr Postfach