Support combining arbitrary shadows without a color with shadow color utilities (#13876)

* Support combining arbitrary shadows without a color with shadow color utilities

* Update changelog

---------

Co-authored-by: Adam Wathan <4323180+adamwathan@users.noreply.github.com>

CHANGELOG.md

@@ -14,6 +14,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Include variable in output for bare utilities like `rounded` ([#13836](https://github.com/tailwindlabs/tailwindcss/pull/13836))
 - Preserve list semantics for `ul`, `li`, and `menu` by default ([#13815](https://github.com/tailwindlabs/tailwindcss/pull/13815))
 
+### Fixed
+
+- Support combining arbitrary shadows without a color with shadow color utilities ([#13876](https://github.com/tailwindlabs/tailwindcss/pull/13876))
+
 ## [4.0.0-alpha.16] - 2024-06-07
 
 ### Fixed

packages/tailwindcss/src/utilities.test.ts

@@ -12019,7 +12019,7 @@ test('shadow', () => {
 
     .shadow-\\[10px_10px\\] {
       --tw-shadow: 10px 10px;
-      --tw-shadow-colored: 10px 10px;
+      --tw-shadow-colored: 10px 10px var(--tw-shadow-color);
       box-shadow: var(--tw-inset-shadow), var(--tw-inset-ring-shadow), var(--tw-ring-offset-shadow), var(--tw-ring-shadow), var(--tw-shadow);
     }
 
@@ -12271,7 +12271,7 @@ test('inset-shadow', () => {
 
     .inset-shadow-\\[10px_10px\\] {
       --tw-inset-shadow: inset 10px 10px;
-      --tw-inset-shadow-colored: inset 10px 10px;
+      --tw-inset-shadow-colored: inset 10px 10px var(--tw-inset-shadow-color);
       box-shadow: var(--tw-inset-shadow), var(--tw-inset-ring-shadow), var(--tw-ring-offset-shadow), var(--tw-ring-shadow), var(--tw-shadow);
     }
 

packages/tailwindcss/src/utils/replace-shadow-colors.test.ts

@@ -3,23 +3,35 @@ import { replaceShadowColors } from './replace-shadow-colors'
 
 const table = [
   {
-    input: ['var(--my-shadow)'],
+    input: 'var(--my-shadow)',
     output: 'var(--my-shadow)',
   },
   {
-    input: ['1px var(--my-shadow)'],
+    input: '1px var(--my-shadow)',
     output: '1px var(--my-shadow)',
   },
   {
-    input: ['1px 1px var(--my-color)'],
+    input: '1px 1px var(--my-color)',
     output: '1px 1px var(--tw-shadow-color)',
   },
   {
-    input: ['0 0 0 var(--my-color)'],
+    input: '0 0 0 var(--my-color)',
     output: '0 0 0 var(--tw-shadow-color)',
   },
   {
-    input: ['var(--my-shadow)', '1px 1px var(--my-color)', '0 0 1px var(--my-color)'],
+    input: '1px 2px',
+    output: '1px 2px var(--tw-shadow-color)',
+  },
+  {
+    input: '1px 2px 3px',
+    output: '1px 2px 3px var(--tw-shadow-color)',
+  },
+  {
+    input: '1px 2px 3px 4px',
+    output: '1px 2px 3px 4px var(--tw-shadow-color)',
+  },
+  {
+    input: ['var(--my-shadow)', '1px 1px var(--my-color)', '0 0 1px var(--my-color)'].join(', '),
     output: [
       'var(--my-shadow)',
       '1px 1px var(--tw-shadow-color)',
@@ -29,9 +41,9 @@ const table = [
 ]
 
 it.each(table)(
-  'should be possible to get the names for an animation: $output',
+  'should replace the color of box-shadow $input with $output',
   ({ input, output }) => {
-    let parsed = replaceShadowColors(input.join(', '), 'var(--tw-shadow-color)')
+    let parsed = replaceShadowColors(input, 'var(--tw-shadow-color)')
     expect(parsed).toEqual(output)
   },
 )

packages/tailwindcss/src/utils/replace-shadow-colors.ts

@@ -27,10 +27,18 @@ export function replaceShadowColors(input: string, replacement: string): string
       }
     }
 
-    // Only replace if we found an x-offset, y-offset, and color, otherwise we
-    // may be replacing the wrong part of the box-shadow.
-    if (offsetX !== null && offsetY !== null && color !== null) {
+    // If the x and y offsets were not detected, the shadow is either invalid or
+    // using a variable to represent more than one field in the shadow value, so
+    // we can't know what to replace.
+    if (offsetX === null || offsetY === null) continue
+
+    if (color !== null) {
+      // If a color was found, replace the color.
       input = input.replace(color, replacement)
+    } else {
+      // If no color was found, assume the shadow is relying on the browser
+      // default shadow color and append the replacement color.
+      input = `${input} ${replacement}`
     }
   }
 

packages/tailwindcss/tests/ui.spec.ts

@@ -166,6 +166,7 @@ test('shadow colors', async ({ page }) => {
     html`
       <div id="x" class="shadow shadow-red-500"></div>
       <div id="y" class="shadow-xl shadow-red-500"></div>
+      <div id="z" class="shadow-[0px_2px_4px] shadow-red-500"></div>
     `,
   )
 
@@ -187,6 +188,15 @@ test('shadow colors', async ({ page }) => {
       'rgb(239, 68, 68) 0px 20px 25px -5px, rgb(239, 68, 68) 0px 8px 10px -6px',
     ].join(', '),
   )
+  expect(await getPropertyValue('#z', 'box-shadow')).toEqual(
+    [
+      'rgba(0, 0, 0, 0) 0px 0px 0px 0px',
+      'rgba(0, 0, 0, 0) 0px 0px 0px 0px',
+      'rgba(0, 0, 0, 0) 0px 0px 0px 0px',
+      'rgba(0, 0, 0, 0) 0px 0px 0px 0px',
+      'rgb(239, 68, 68) 0px 2px 4px 0px',
+    ].join(', '),
+  )
 })
 
 test('outline style is optional', async ({ page }) => {