add WalkAction to indicate how the walk function should behave

You can `Continue` its execution (the default behaviour), `Skip` walking
the current node, or `Stop` walking entirely.

packages/tailwindcss/src/ast.ts

@@ -42,28 +42,44 @@ export function comment(value: string): Comment {
   }
 }
 
+export enum WalkAction {
+  /** Continue walking, which is the default */
+  Continue,
+
+  /** Skip visiting the children of this node */
+  Skip,
+
+  /** Stop the walk entirely */
+  Stop,
+}
+
 export function walk(
   ast: AstNode[],
   visit: (
     node: AstNode,
     utils: {
       replaceWith(newNode: AstNode | AstNode[]): void
     },
-  ) => void | false,
+  ) => void | WalkAction,
 ) {
   for (let i = 0; i < ast.length; i++) {
     let node = ast[i]
-    let shouldContinue = visit(node, {
-      replaceWith(newNode) {
-        ast.splice(i, 1, ...(Array.isArray(newNode) ? newNode : [newNode]))
-        // We want to visit the newly replaced node(s), which start at the current
-        // index (i). By decrementing the index here, the next loop will process
-        // this position (containing the replaced node) again.
-        i--
-      },
-    })
-
-    if (shouldContinue === false) return
+    let status =
+      visit(node, {
+        replaceWith(newNode) {
+          ast.splice(i, 1, ...(Array.isArray(newNode) ? newNode : [newNode]))
+          // We want to visit the newly replaced node(s), which start at the
+          // current index (i). By decrementing the index here, the next loop
+          // will process this position (containing the replaced node) again.
+          i--
+        },
+      }) ?? WalkAction.Continue
+
+    // Stop the walk entirely
+    if (status === WalkAction.Stop) return
+
+    // Skip visiting the children of this node
+    if (status === WalkAction.Skip) continue
 
     if (node.kind === 'rule') {
       walk(node.nodes, visit)

packages/tailwindcss/src/index.ts

@@ -1,6 +1,6 @@
 import { Features, transform } from 'lightningcss'
 import { version } from '../package.json'
-import { comment, decl, rule, toCss, walk, type AstNode, type Rule } from './ast'
+import { WalkAction, comment, decl, rule, toCss, walk, type AstNode, type Rule } from './ast'
 import { compileCandidates } from './compile'
 import * as CSS from './css-parser'
 import { buildDesignSystem } from './design-system'
@@ -29,7 +29,7 @@ export function compile(css: string, rawCandidates: string[]) {
       if (node.kind === 'rule' && node.selector.startsWith('@keyframes ')) {
         keyframesRules.push(node)
         replaceWith([])
-        return
+        return WalkAction.Skip
       }
 
       if (node.kind !== 'declaration') return
@@ -94,7 +94,7 @@ export function compile(css: string, rawCandidates: string[]) {
       // Stop walking after finding `@tailwind utilities` to avoid walking all
       // of the generated CSS. This means `@tailwind utilities` can only appear
       // once per file but that's the intended usage at this point in time.
-      return false
+      return WalkAction.Stop
     }
   })