set @tailwind utilities nodes

Instead of replacing the node that represents the `@tailwind utilities`
with the generated AST nodes from the rawCandidates, we will set the
nodes of the `@tailwind utilities` rule to the AST nodes instead.

This way we dont' have to remove and replace the `@tailwind utilities`
rule with `n` new nodes. This will later allow us to track the
`@tailwindcss utilities` rule itself and update its `nodes` for
incremental rebuilds.

This also requires a small change to the printer where we now need to
print the children of the `@tailwind utilities` rule. Note: we keep the
same `depth` as-if the `@tailwindcss utilities` rule was not there.
Otherwise additional indentation would be present.

packages/tailwindcss/src/ast.ts

@@ -105,6 +105,13 @@ export function toCss(ast: AstNode[]) {
         return css
       }
 
+      if (node.selector === '@tailwind utilities') {
+        for (let child of node.nodes) {
+          css += stringify(child, depth)
+        }
+        return css
+      }
+
       // Print at-rules without nodes with a `;` instead of an empty block.
       //
       // E.g.:

packages/tailwindcss/src/index.test.ts

@@ -93,9 +93,7 @@ describe('compiling CSS', () => {
 
       .grid {
         display: grid;
-      }
-
-      @tailwind utilities;"
+      }"
     `)
   })
 

packages/tailwindcss/src/index.ts

@@ -105,9 +105,11 @@ export function compile(
 
   // Find `@tailwind utilities` and replace it with the actual generated utility
   // class CSS.
-  walk(ast, (node, { replaceWith }) => {
+  walk(ast, (node) => {
     if (node.kind === 'rule' && node.selector === '@tailwind utilities') {
-      replaceWith(compileCandidates(rawCandidates, designSystem).astNodes)
+      // Set the `@tailwind utilities` nodes, to the actual generated CSS
+      node.nodes = compileCandidates(rawCandidates, designSystem).astNodes
+
       // 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.