Handle utilities with 1 keys in a JS config

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Substitute `@variant` inside legacy JS APIs ([#19263](https://github.com/tailwindlabs/tailwindcss/pull/19263))
+- Handle utilities with `1` keys in a JS config  ([#19254](https://github.com/tailwindlabs/tailwindcss/pull/19254))
 
 ### Added
 

packages/tailwindcss/src/compat/apply-config-to-theme.test.ts

@@ -1,7 +1,11 @@
 import { describe, expect, test } from 'vitest'
 import { buildDesignSystem } from '../design-system'
 import { Theme, ThemeOptions } from '../theme'
-import { applyConfigToTheme, keyPathToCssProperty } from './apply-config-to-theme'
+import {
+  applyConfigToTheme,
+  keyPathToCssProperty,
+  keyPathsToCssProperty,
+} from './apply-config-to-theme'
 import { resolveConfig } from './config/resolve-config'
 
 test('config values can be merged into the theme', () => {
@@ -213,6 +217,48 @@ describe('keyPathToCssProperty', () => {
   })
 })
 
+describe('keyPathsToCssProperty', () => {
+  test.each([
+    // No "1" entries - should return single result
+    [['width', '40', '2/5'], ['width-40-2/5']],
+    [['spacing', '0.5'], ['spacing-0_5']],
+
+    // Single "1" entry before the end - should return two variants
+    [
+      ['fontSize', 'xs', '1', 'lineHeight'],
+      ['text-xs--line-height', 'text-xs-1-line-height'],
+    ],
+
+    // Multiple "1" entries before the end - should only split the last "1"
+    [
+      ['test', '1', 'middle', '1', 'end'],
+      ['test-1-middle--end', 'test-1-middle-1-end'],
+    ],
+
+    // A "1" at the end means everything should be kept as-is
+    [['spacing', '1'], ['spacing-1']],
+
+    // Even when there are other 1s in the path
+    [['test', '1', 'middle', '1'], ['test-1-middle-1']],
+
+    [['colors', 'a', '1', 'DEFAULT'], ['color-a-1']],
+    [
+      ['colors', 'a', '1', 'foo'],
+      ['color-a--foo', 'color-a-1-foo'],
+    ],
+  ])('converts %s to %s', (keyPath, expected) => {
+    expect(keyPathsToCssProperty(keyPath)).toEqual(expected)
+  })
+
+  test('returns empty array for container path', () => {
+    expect(keyPathsToCssProperty(['container', 'sm'])).toEqual([])
+  })
+
+  test('returns empty array for invalid keys', () => {
+    expect(keyPathsToCssProperty(['test', 'invalid@key'])).toEqual([])
+  })
+})
+
 test('converts opacity modifiers from decimal to percentage values', () => {
   let theme = new Theme()
   let design = buildDesignSystem(theme)

packages/tailwindcss/src/compat/apply-config-to-theme.ts

@@ -25,10 +25,9 @@ export function applyConfigToTheme(
   replacedThemeKeys: Set<string>,
 ) {
   for (let replacedThemeKey of replacedThemeKeys) {
-    let name = keyPathToCssProperty([replacedThemeKey])
-    if (!name) continue
-
-    designSystem.theme.clearNamespace(`--${name}`, ThemeOptions.DEFAULT)
+    for (let name of keyPathsToCssProperty([replacedThemeKey])) {
+      designSystem.theme.clearNamespace(`--${name}`, ThemeOptions.DEFAULT)
+    }
   }
 
   for (let [path, value] of themeableValues(theme)) {
@@ -50,14 +49,13 @@ export function applyConfigToTheme(
       }
     }
 
-    let name = keyPathToCssProperty(path)
-    if (!name) continue
-
-    designSystem.theme.add(
-      `--${name}`,
-      '' + value,
-      ThemeOptions.INLINE | ThemeOptions.REFERENCE | ThemeOptions.DEFAULT,
-    )
+    for (let name of keyPathsToCssProperty(path)) {
+      designSystem.theme.add(
+        `--${name}`,
+        '' + value,
+        ThemeOptions.INLINE | ThemeOptions.REFERENCE | ThemeOptions.DEFAULT,
+      )
+    }
   }
 
   // If someone has updated `fontFamily.sans` or `fontFamily.mono` in a JS
@@ -150,8 +148,12 @@ export function themeableValues(config: ResolvedConfig['theme']): [string[], unk
 const IS_VALID_KEY = /^[a-zA-Z0-9-_%/\.]+$/
 
 export function keyPathToCssProperty(path: string[]) {
+  return keyPathsToCssProperty(path)[0] ?? null
+}
+
+export function keyPathsToCssProperty(path: string[]): string[] {
   // The legacy container component config should not be included in the Theme
-  if (path[0] === 'container') return null
+  if (path[0] === 'container') return []
 
   path = path.slice()
 
@@ -170,32 +172,43 @@ export function keyPathToCssProperty(path: string[]) {
   if (path[0] === 'transitionTimingFunction') path[0] = 'ease'
 
   for (let part of path) {
-    if (!IS_VALID_KEY.test(part)) return null
+    if (!IS_VALID_KEY.test(part)) return []
   }
 
-  return (
-    path
-      // [1] should move into the nested object tuple. To create the CSS variable
-      // name for this, we replace it with an empty string that will result in two
-      // subsequent dashes when joined.
-      //
-      // E.g.:
-      // - `fontSize.xs.1.lineHeight` -> `font-size-xs--line-height`
-      // - `spacing.1` -> `--spacing-1`
-      .map((path, idx, all) => (path === '1' && idx !== all.length - 1 ? '' : path))
-
-      // Resolve the key path to a CSS variable segment
+  // Find the position of the last `1` as long as it's not at the end
+  let lastOnePosition = path.lastIndexOf('1')
+  if (lastOnePosition === path.length - 1) lastOnePosition = -1
+
+  // Generate two combinations based on tuple access:
+  let paths: string[][] = []
+
+  // Option 1: Replace the last "1" with empty string if it exists
+  //
+  // We place this first as we "prefer" treating this as a tuple access. The exception to this is if
+  // the keypath ends in `DEFAULT` otherwise we'd see a key that ends in a dash like `--color-a-`
+  if (lastOnePosition !== -1 && path.at(-1) !== 'DEFAULT') {
+    let modified = path.slice()
+    modified[lastOnePosition] = ''
+    paths.push(modified)
+  }
+
+  // Option 2: The path as is
+  paths.push(path)
+
+  return paths.map((path) => {
+    // Remove the `DEFAULT` key at the end of a path
+    // We're reading from CSS anyway so it'll be a string
+    if (path.at(-1) === 'DEFAULT') path = path.slice(0, -1)
+
+    // Resolve the key path to a CSS variable segment
+    return path
       .map((part) =>
         part
           .replaceAll('.', '_')
           .replace(/([a-z])([A-Z])/g, (_, a, b) => `${a}-${b.toLowerCase()}`),
       )
-
-      // Remove the `DEFAULT` key at the end of a path
-      // We're reading from CSS anyway so it'll be a string
-      .filter((part, index) => part !== 'DEFAULT' || index !== path.length - 1)
       .join('-')
-  )
+  })
 }
 
 function isValidThemePrimitive(value: unknown) {

packages/tailwindcss/src/compat/config.test.ts

@@ -297,6 +297,74 @@ test('Variants in CSS overwrite variants from plugins', async () => {
   `)
 })
 
+test('A `1` key is treated like a nested theme key *and* a normal theme key', async () => {
+  let input = css`
+    @tailwind utilities;
+    @config "./config.js";
+  `
+
+  let compiler = await compile(input, {
+    loadModule: async () => ({
+      module: {
+        theme: {
+          fontSize: {
+            xs: ['0.5rem', { lineHeight: '0.25rem' }],
+          },
+          colors: {
+            a: {
+              1: { DEFAULT: '#ffffff', hovered: '#000000' },
+              2: { DEFAULT: '#000000', hovered: '#c0ffee' },
+            },
+            b: {
+              1: '#ffffff',
+              2: '#000000',
+            },
+          },
+        },
+      },
+      base: '/root',
+      path: '',
+    }),
+  })
+
+  expect(
+    compiler.build([
+      'text-xs',
+
+      'text-a-1',
+      'text-a-2',
+      'text-a-1-hovered',
+      'text-a-2-hovered',
+      'text-b-1',
+      'text-b-2',
+    ]),
+  ).toMatchInlineSnapshot(`
+    ".text-xs {
+      font-size: 0.5rem;
+      line-height: var(--tw-leading, 0.25rem);
+    }
+    .text-a-1 {
+      color: #ffffff;
+    }
+    .text-a-1-hovered {
+      color: #000000;
+    }
+    .text-a-2 {
+      color: #000000;
+    }
+    .text-a-2-hovered {
+      color: #c0ffee;
+    }
+    .text-b-1 {
+      color: #ffffff;
+    }
+    .text-b-2 {
+      color: #000000;
+    }
+    "
+  `)
+})
+
 describe('theme callbacks', () => {
   test('tuple values from the config overwrite `@theme default` tuple-ish values from the CSS theme', async ({
     expect,