Ensure nested functions in selectors used with JavaScript plugins are not truncated (#16802)

Fixes #16799

This was caused by a wrong condition in the CSS value parser that put
child function arguments into the parent function by accident.

## Test plan

- Added a unit test to guard against regressions
- Validated against the repro:  
<img width="914" alt="Screenshot 2025-02-25 at 16 31 14"
src="https://github.com/user-attachments/assets/f5fdf2e7-9c1b-4b04-89a8-1fa78a27f0f5"
/>

Author: philipp-spiess

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fix an issue where `@reference "…"` would sometimes omit keyframe animations ([#16774](https://github.com/tailwindlabs/tailwindcss/pull/16774))
 - Ensure `z-*!` utilities are property marked as `!important` ([#16795](https://github.com/tailwindlabs/tailwindcss/pull/16795))
 - Read UTF-8 CSS files that start with a byte-order mark (BOM) ([#16796](https://github.com/tailwindlabs/tailwindcss/pull/16796))
+- Ensure nested functions in selectors used with JavaScript plugins are not truncated ([#16802](https://github.com/tailwindlabs/tailwindcss/pull/16802))
 
 ## [4.0.8] - 2025-02-21
 

packages/tailwindcss/src/compat/selector-parser.test.ts

@@ -77,6 +77,60 @@ describe('parse', () => {
       },
     ])
   })
+
+  it('parses &:has(.child:nth-child(2))', () => {
+    expect(parse('&:has(.child:nth-child(2))')).toEqual([
+      {
+        kind: 'selector',
+        value: '&',
+      },
+      {
+        kind: 'function',
+        value: ':has',
+        nodes: [
+          {
+            kind: 'selector',
+            value: '.child',
+          },
+          {
+            kind: 'function',
+            value: ':nth-child',
+            nodes: [
+              {
+                kind: 'value',
+                value: '2',
+              },
+            ],
+          },
+        ],
+      },
+    ])
+  })
+
+  it('parses &:has(:nth-child(2))', () => {
+    expect(parse('&:has(:nth-child(2))')).toEqual([
+      {
+        kind: 'selector',
+        value: '&',
+      },
+      {
+        kind: 'function',
+        value: ':has',
+        nodes: [
+          {
+            kind: 'function',
+            value: ':nth-child',
+            nodes: [
+              {
+                kind: 'value',
+                value: '2',
+              },
+            ],
+          },
+        ],
+      },
+    ])
+  })
 })
 
 describe('toCss', () => {

packages/tailwindcss/src/compat/selector-parser.ts

@@ -300,7 +300,11 @@ export function parse(input: string) {
           buffer = ''
           i = end
 
-          ast.push(node)
+          if (parent) {
+            parent.nodes.push(node)
+          } else {
+            ast.push(node)
+          }
 
           break
         }