Fix purging in 1.8 (#2320)

* re-add missing `@layer`'s for responsive rules

* use toMatchCss for better diffing

* do not wrap user `@responsive` rules in an `@layer`

__tests__/purgeUnusedStyles.test.js

@@ -430,7 +430,7 @@ test(
           'utf8'
         )
 
-        expect(result.css).toBe(expected)
+        expect(result.css).toMatchCss(expected)
       })
   })
 )
@@ -457,7 +457,7 @@ test('does not purge if the array is empty', () => {
             'utf8'
           )
 
-          expect(result.css).toBe(expected)
+          expect(result.css).toMatchCss(expected)
         })
     })
   )
@@ -482,7 +482,7 @@ test('does not purge if explicitly disabled', () => {
             'utf8'
           )
 
-          expect(result.css).toBe(expected)
+          expect(result.css).toMatchCss(expected)
         })
     })
   )
@@ -507,7 +507,7 @@ test('does not purge if purge is simply false', () => {
             'utf8'
           )
 
-          expect(result.css).toBe(expected)
+          expect(result.css).toMatchCss(expected)
         })
     })
   )

src/lib/substituteResponsiveAtRules.js

@@ -4,16 +4,31 @@ import cloneNodes from '../util/cloneNodes'
 import buildMediaQuery from '../util/buildMediaQuery'
 import buildSelectorVariant from '../util/buildSelectorVariant'
 
+function isLayer(node) {
+  if (Array.isArray(node)) {
+    return node.length === 1 && isLayer(node[0])
+  }
+  return node.type === 'atrule' && node.name === 'layer'
+}
+
+function layerNodes(nodes) {
+  return isLayer(nodes) ? nodes[0].nodes : nodes
+}
+
 export default function(config) {
   return function(css) {
-    // Store the `layer` for each responsive at-rule directly on the at-rule for later reference.
+    // Wrap any `responsive` rules with a copy of their parent `layer` to
+    // ensure the layer isn't lost when copying to the `screens` location.
     css.walkAtRules('layer', layerAtRule => {
       const layer = layerAtRule.params
       layerAtRule.walkAtRules('responsive', responsiveAtRule => {
-        responsiveAtRule.__tailwind = {
-          ...responsiveAtRule.__tailwind,
-          layer,
-        }
+        const nestedlayerAtRule = postcss.atRule({
+          name: 'layer',
+          params: layer,
+        })
+        nestedlayerAtRule.prepend(responsiveAtRule.nodes)
+        responsiveAtRule.removeAll()
+        responsiveAtRule.prepend(nestedlayerAtRule)
       })
     })
 
@@ -27,7 +42,16 @@ export default function(config) {
     css.walkAtRules('responsive', atRule => {
       const nodes = atRule.nodes
       responsiveRules.append(...cloneNodes(nodes))
-      atRule.before(nodes)
+
+      // If the parent is already a `layer` (this is true for anything coming from
+      // a plugin, including core plugins) we don't want to create a double nested
+      // layer, so only insert the layer children. If there is no parent layer,
+      // preserve the layer information when inserting the nodes.
+      if (isLayer(atRule.parent)) {
+        atRule.before(layerNodes(nodes))
+      } else {
+        atRule.before(nodes)
+      }
       atRule.remove()
     })