Fix brace expansion with range going down (#17591)

Author: RobinMalfait

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Ensure `color-mix(…)` polyfills do not cause used CSS variables to be removed ([#17555](https://github.com/tailwindlabs/tailwindcss/pull/17555))
 - Ensure the `color-mix(…)` polyfill creates fallbacks for theme variables that reference other theme variables ([#17562](https://github.com/tailwindlabs/tailwindcss/pull/17562))
+- Fix brace expansion in `@source inline('z-{10..0}')` with range going down ([#17591](https://github.com/tailwindlabs/tailwindcss/pull/17591))
 
 ## [4.1.3] - 2025-04-04
 

packages/tailwindcss/src/utils/brace-expansion.test.ts

@@ -14,11 +14,10 @@ describe('expand(…)', () => {
     ['a/{0..5}/b', ['a/0/b', 'a/1/b', 'a/2/b', 'a/3/b', 'a/4/b', 'a/5/b']],
     ['a/{-5..0}/b', ['a/-5/b', 'a/-4/b', 'a/-3/b', 'a/-2/b', 'a/-1/b', 'a/0/b']],
     ['a/{0..-5}/b', ['a/0/b', 'a/-1/b', 'a/-2/b', 'a/-3/b', 'a/-4/b', 'a/-5/b']],
-    [
-      'a/{0..10..5}/b',
-      ['a/0/b', 'a/5/b', 'a/10/b'],
-      ['a/{10..0..5}/b', ['a/10/b', 'a/5/b', 'a/0/b']],
-    ],
+    ['a/{0..10..5}/b', ['a/0/b', 'a/5/b', 'a/10/b']],
+    ['a/{0..10..-5}/b', ['a/10/b', 'a/5/b', 'a/0/b']],
+    ['a/{10..0..5}/b', ['a/10/b', 'a/5/b', 'a/0/b']],
+    ['a/{10..0..-5}/b', ['a/0/b', 'a/5/b', 'a/10/b']],
 
     // Numeric range with padding (we do not support padding)
     ['a/{00..05}/b', ['a/0/b', 'a/1/b', 'a/2/b', 'a/3/b', 'a/4/b', 'a/5/b']],
@@ -64,7 +63,7 @@ describe('expand(…)', () => {
 
     // Should not try to expand ranges with decimals
     ['{1.1..2.2}', ['1.1..2.2']],
-  ])('should expand %s', (input, expected) => {
+  ])('should expand %s (%#)', (input, expected) => {
     expect(expand(input).sort()).toEqual(expected.sort())
   })
 

packages/tailwindcss/src/utils/brace-expansion.ts

@@ -78,16 +78,13 @@ function expandSequence(seq: string): string[] {
     if (step === 0) {
       throw new Error('Step cannot be zero in sequence expansion.')
     }
-    if (step > 0) {
-      for (let i = startNum; i <= endNum; i += step) {
-        let numStr = i.toString()
-        result.push(numStr)
-      }
-    } else {
-      for (let i = startNum; i >= endNum; i += step) {
-        let numStr = i.toString()
-        result.push(numStr)
-      }
+
+    let increasing = startNum < endNum
+    if (increasing && step < 0) step = -step
+    if (!increasing && step > 0) step = -step
+
+    for (let i = startNum; increasing ? i <= endNum : i >= endNum; i += step) {
+      result.push(i.toString())
     }
   }
   return result