Fix source maps of variant utilities that come from an @layer rule (#12508)

* Refactor

* Keep traversing sibling nodes

* Make sure the root node has a source location for the end

* Add source map test for at-rule variants

* Update changelog

CHANGELOG.md

@@ -16,6 +16,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Improve candidate detection in minified JS arrays (without spaces) ([#12396](https://github.com/tailwindlabs/tailwindcss/pull/12396))
 - Don't crash when given applying a variant to a negated version of a simple utility ([#12514](https://github.com/tailwindlabs/tailwindcss/pull/12514))
 - Fix support for slashes in arbitrary modifiers ([#12515](https://github.com/tailwindlabs/tailwindcss/pull/12515))
+- Fix source maps of variant utilities that come from an `@layer` rule ([#12508](https://github.com/tailwindlabs/tailwindcss/pull/12508))
 - [Oxide] Remove `autoprefixer` dependency ([#11315](https://github.com/tailwindlabs/tailwindcss/pull/11315))
 - [Oxide] Fix source maps issue resulting in a crash ([#11319](https://github.com/tailwindlabs/tailwindcss/pull/11319))
 - [Oxide] Fallback to RegEx based parser when using custom transformers or extractors ([#11335](https://github.com/tailwindlabs/tailwindcss/pull/11335))

src/lib/expandTailwindAtRules.js

@@ -291,6 +291,9 @@ export default function expandTailwindAtRules(context) {
       root.append(cloned)
     }
 
+    // TODO: Why is the root node having no source location for `end` possible?
+    root.source.end = root.source.end ?? root.source.start
+
     // If we've got a utility layer and no utilities are generated there's likely something wrong
     const hasUtilityVariants = variantNodes.some(
       (node) => node.raws.tailwind?.parentLayer === 'utilities'

src/util/cloneNodes.js

@@ -1,21 +1,13 @@
+/**
+ * @param {import('postcss').Container[]} nodes
+ * @param {any} source
+ * @param {any} raws
+ * @returns {import('postcss').Container[]}
+ */
 export default function cloneNodes(nodes, source = undefined, raws = undefined) {
   return nodes.map((node) => {
     let cloned = node.clone()
 
-    // We always want override the source map
-    // except when explicitly told not to
-    let shouldOverwriteSource = node.raws.tailwind?.preserveSource !== true || !cloned.source
-
-    if (source !== undefined && shouldOverwriteSource) {
-      cloned.source = source
-
-      if ('walk' in cloned) {
-        cloned.walk((child) => {
-          child.source = source
-        })
-      }
-    }
-
     if (raws !== undefined) {
       cloned.raws.tailwind = {
         ...cloned.raws.tailwind,
@@ -23,6 +15,35 @@ export default function cloneNodes(nodes, source = undefined, raws = undefined)
       }
     }
 
+    if (source !== undefined) {
+      traverse(cloned, (node) => {
+        // Do not traverse nodes that have opted
+        // to preserve their original source
+        let shouldPreserveSource = node.raws.tailwind?.preserveSource === true && node.source
+        if (shouldPreserveSource) {
+          return false
+        }
+
+        // Otherwise we can safely replace the source
+        // And continue traversing
+        node.source = source
+      })
+    }
+
     return cloned
   })
 }
+
+/**
+ * Traverse a tree of nodes and don't traverse children if the callback
+ * returns false. Ideally we'd use Container#walk instead of this
+ * function but it stops traversing siblings too.
+ *
+ * @param {import('postcss').Container} node
+ * @param {(node: import('postcss').Container) => boolean} onNode
+ */
+function traverse(node, onNode) {
+  if (onNode(node) !== false) {
+    node.each?.((child) => traverse(child, onNode))
+  }
+}

tests/source-maps.test.js

@@ -427,7 +427,7 @@ test('components have source maps', async () => {
 
 test('source maps for layer rules are not rewritten to point to @tailwind directives', async () => {
   let config = {
-    content: [{ raw: `font-normal foo hover:foo` }],
+    content: [{ raw: `font-normal foo hover:foo lg:foo` }],
   }
 
   let utilitiesFile = postcss.parse(
@@ -481,6 +481,11 @@ test('source maps for layer rules are not rewritten to point to @tailwind direct
       "6:0 -> 6:0",
       "7:2-23 -> 7:2-23",
       "8:0 -> 8:0",
+      "10:0 -> 10:0",
+      "11:2 -> 11:2",
+      "12:4-25 -> 12:4-25",
+      "13:2 -> 13:2",
+      "14:0 -> 14:0",
     ]
   `)
 })