Use local user css cache for apply (#7524)

* Fix context reuse test

* Don't update files with at-apply when content changes

* Prevent at-apply directives from creating new contexts

* Rework apply to use local postcss root

We were storing user CSS in the context so we could use it with apply. The problem is that this CSS does not get updated on save unless it has a tailwind directive in it resulting in stale apply caches. This could result in either stale generation or errors about missing classes.

* Don’t build local cache unless `@apply` is used

* Update changelog

CHANGELOG.md

@@ -12,6 +12,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Allow default ring color to be a function ([#7587](https://github.com/tailwindlabs/tailwindcss/pull/7587))
 - Preserve source maps for generated CSS ([#7588](https://github.com/tailwindlabs/tailwindcss/pull/7588))
 - Split box shadows on top-level commas only ([#7479](https://github.com/tailwindlabs/tailwindcss/pull/7479))
+- Use local user css cache for `@apply` ([#7524](https://github.com/tailwindlabs/tailwindcss/pull/7524))
 
 ### Changed
 

src/lib/expandApplyAtRules.js

@@ -5,6 +5,8 @@ import { resolveMatches } from './generateRules'
 import bigSign from '../util/bigSign'
 import escapeClassName from '../util/escapeClassName'
 
+/** @typedef {Map<string, [any, import('postcss').Rule[]]>} ApplyCache */
+
 function extractClasses(node) {
   let classes = new Set()
   let container = postcss.root({ nodes: [node.clone()] })
@@ -35,6 +37,131 @@ function prefix(context, selector) {
   return typeof prefix === 'function' ? prefix(selector) : prefix + selector
 }
 
+function* pathToRoot(node) {
+  yield node
+  while (node.parent) {
+    yield node.parent
+    node = node.parent
+  }
+}
+
+/**
+ * Only clone the node itself and not its children
+ *
+ * @param {*} node
+ * @param {*} overrides
+ * @returns
+ */
+function shallowClone(node, overrides = {}) {
+  let children = node.nodes
+  node.nodes = []
+
+  let tmp = node.clone(overrides)
+
+  node.nodes = children
+
+  return tmp
+}
+
+/**
+ * Clone just the nodes all the way to the top that are required to represent
+ * this singular rule in the tree.
+ *
+ * For example, if we have CSS like this:
+ * ```css
+ * @media (min-width: 768px) {
+ *   @supports (display: grid) {
+ *     .foo {
+ *       display: grid;
+ *       grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
+ *     }
+ *   }
+ *
+ *   @supports (backdrop-filter: blur(1px)) {
+ *     .bar {
+ *       backdrop-filter: blur(1px);
+ *     }
+ *   }
+ *
+ *   .baz {
+ *     color: orange;
+ *   }
+ * }
+ * ```
+ *
+ * And we're cloning `.bar` it'll return a cloned version of what's required for just that single node:
+ *
+ * ```css
+ * @media (min-width: 768px) {
+ *   @supports (backdrop-filter: blur(1px)) {
+ *     .bar {
+ *       backdrop-filter: blur(1px);
+ *     }
+ *   }
+ * }
+ * ```
+ *
+ * @param {import('postcss').Node} node
+ */
+function nestedClone(node) {
+  for (let parent of pathToRoot(node)) {
+    if (node === parent) {
+      continue
+    }
+
+    if (parent.type === 'root') {
+      break
+    }
+
+    node = shallowClone(parent, {
+      nodes: [node],
+    })
+  }
+
+  return node
+}
+
+/**
+ * @param {import('postcss').Root} root
+ */
+function buildLocalApplyCache(root, context) {
+  /** @type {ApplyCache} */
+  let cache = new Map()
+
+  let highestOffset = context.layerOrder.user >> 4n
+
+  root.walkRules((rule, idx) => {
+    // Ignore rules generated by Tailwind
+    for (let node of pathToRoot(rule)) {
+      if (node.raws.tailwind?.layer !== undefined) {
+        return
+      }
+    }
+
+    // Clone what's required to represent this singular rule in the tree
+    let container = nestedClone(rule)
+
+    for (let className of extractClasses(rule)) {
+      let list = cache.get(className) || []
+      cache.set(className, list)
+
+      list.push([
+        {
+          layer: 'user',
+          sort: BigInt(idx) + highestOffset,
+          important: false,
+        },
+        container,
+      ])
+    }
+  })
+
+  return cache
+}
+
+/**
+ * @returns {ApplyCache}
+ */
 function buildApplyCache(applyCandidates, context) {
   for (let candidate of applyCandidates) {
     if (context.notClassCache.has(candidate) || context.applyClassCache.has(candidate)) {
@@ -62,6 +189,43 @@ function buildApplyCache(applyCandidates, context) {
   return context.applyClassCache
 }
 
+/**
+ * Build a cache only when it's first used
+ *
+ * @param {() => ApplyCache} buildCacheFn
+ * @returns {ApplyCache}
+ */
+function lazyCache(buildCacheFn) {
+  let cache = null
+
+  return {
+    get: (name) => {
+      cache = cache || buildCacheFn()
+
+      return cache.get(name)
+    },
+    has: (name) => {
+      cache = cache || buildCacheFn()
+
+      return cache.has(name)
+    },
+  }
+}
+
+/**
+ * Take a series of multiple caches and merge
+ * them so they act like one large cache
+ *
+ * @param {ApplyCache[]} caches
+ * @returns {ApplyCache}
+ */
+function combineCaches(caches) {
+  return {
+    get: (name) => caches.flatMap((cache) => cache.get(name) || []),
+    has: (name) => caches.some((cache) => cache.has(name)),
+  }
+}
+
 function extractApplyCandidates(params) {
   let candidates = params.split(/[\s\t\n]+/g)
 
@@ -72,7 +236,7 @@ function extractApplyCandidates(params) {
   return [candidates, false]
 }
 
-function processApply(root, context) {
+function processApply(root, context, localCache) {
   let applyCandidates = new Set()
 
   // Collect all @apply rules and candidates
@@ -90,7 +254,7 @@ function processApply(root, context) {
   // Start the @apply process if we have rules with @apply in them
   if (applies.length > 0) {
     // Fill up some caches!
-    let applyClassCache = buildApplyCache(applyCandidates, context)
+    let applyClassCache = combineCaches([localCache, buildApplyCache(applyCandidates, context)])
 
     /**
      * When we have an apply like this:
@@ -302,12 +466,15 @@ function processApply(root, context) {
     }
 
     // Do it again, in case we have other `@apply` rules
-    processApply(root, context)
+    processApply(root, context, localCache)
   }
 }
 
 export default function expandApplyAtRules(context) {
   return (root) => {
-    processApply(root, context)
+    // Build a cache of the user's CSS so we can use it to resolve classes used by @apply
+    let localCache = lazyCache(() => buildLocalApplyCache(root, context))
+
+    processApply(root, context, localCache)
   }
 }

src/lib/expandTailwindAtRules.js

@@ -204,17 +204,29 @@ export default function expandTailwindAtRules(context) {
     // Replace any Tailwind directives with generated CSS
 
     if (layerNodes.base) {
-      layerNodes.base.before(cloneNodes([...baseNodes, ...defaultNodes], layerNodes.base.source))
+      layerNodes.base.before(
+        cloneNodes([...baseNodes, ...defaultNodes], layerNodes.base.source, {
+          layer: 'base',
+        })
+      )
       layerNodes.base.remove()
     }
 
     if (layerNodes.components) {
-      layerNodes.components.before(cloneNodes([...componentNodes], layerNodes.components.source))
+      layerNodes.components.before(
+        cloneNodes([...componentNodes], layerNodes.components.source, {
+          layer: 'components',
+        })
+      )
       layerNodes.components.remove()
     }
 
     if (layerNodes.utilities) {
-      layerNodes.utilities.before(cloneNodes([...utilityNodes], layerNodes.utilities.source))
+      layerNodes.utilities.before(
+        cloneNodes([...utilityNodes], layerNodes.utilities.source, {
+          layer: 'utilities',
+        })
+      )
       layerNodes.utilities.remove()
     }
 
@@ -234,10 +246,18 @@ export default function expandTailwindAtRules(context) {
     })
 
     if (layerNodes.variants) {
-      layerNodes.variants.before(cloneNodes(variantNodes, layerNodes.variants.source))
+      layerNodes.variants.before(
+        cloneNodes(variantNodes, layerNodes.variants.source, {
+          layer: 'variants',
+        })
+      )
       layerNodes.variants.remove()
     } else if (variantNodes.length > 0) {
-      root.append(cloneNodes(variantNodes, root.source))
+      root.append(
+        cloneNodes(variantNodes, root.source, {
+          layer: 'variants',
+        })
+      )
     }
 
     // If we've got a utility layer and no utilities are generated there's likely something wrong

src/lib/setupContextUtils.js

@@ -230,17 +230,6 @@ function buildPluginApi(tailwindConfig, context, { variantList, variantMap, offs
       // Preserved for backwards compatibility but not used in v3.0+
       return []
     },
-    addUserCss(userCss) {
-      for (let [identifier, rule] of withIdentifiers(userCss)) {
-        let offset = offsets.user++
-
-        if (!context.candidateRuleMap.has(identifier)) {
-          context.candidateRuleMap.set(identifier, [])
-        }
-
-        context.candidateRuleMap.get(identifier).push([{ sort: offset, layer: 'user' }, rule])
-      }
-    },
     addBase(base) {
       for (let [identifier, rule] of withIdentifiers(base)) {
         let prefixedIdentifier = prefixIdentifier(identifier, {})
@@ -521,15 +510,6 @@ function collectLayerPlugins(root) {
     }
   })
 
-  root.walkRules((rule) => {
-    // At this point it is safe to include all the left-over css from the
-    // user's css file. This is because the `@tailwind` and `@layer` directives
-    // will already be handled and will be removed from the css tree.
-    layerPlugins.push(function ({ addUserCss }) {
-      addUserCss(rule, { respectPrefix: false })
-    })
-  })
-
   return layerPlugins
 }
 

src/lib/setupTrackingContext.js

@@ -112,7 +112,7 @@ function resolveChangedFiles(candidateFiles, fileModifiedMap) {
 // source path), or set up a new one (including setting up watchers and registering
 // plugins) then return it
 export default function setupTrackingContext(configOrPath) {
-  return ({ tailwindDirectives, registerDependency, applyDirectives }) => {
+  return ({ tailwindDirectives, registerDependency }) => {
     return (root, result) => {
       let [tailwindConfig, userConfigPath, tailwindConfigHash, configDependencies] =
         getTailwindConfig(configOrPath)
@@ -125,7 +125,7 @@ export default function setupTrackingContext(configOrPath) {
       // being part of this trigger too, but it's tough because it's impossible
       // for a layer in one file to end up in the actual @tailwind rule in
       // another file since independent sources are effectively isolated.
-      if (tailwindDirectives.size > 0 || applyDirectives.size > 0) {
+      if (tailwindDirectives.size > 0) {
         // Add current css file as a context dependencies.
         contextDependencies.add(result.opts.from)
 
@@ -153,7 +153,7 @@ export default function setupTrackingContext(configOrPath) {
       // We may want to think about `@layer` being part of this trigger too, but it's tough
       // because it's impossible for a layer in one file to end up in the actual @tailwind rule
       // in another file since independent sources are effectively isolated.
-      if (tailwindDirectives.size > 0 || applyDirectives.size > 0) {
+      if (tailwindDirectives.size > 0) {
         let fileModifiedMap = getFileModifiedMap(context)
 
         // Add template paths as postcss dependencies.

src/util/cloneNodes.js

@@ -1,4 +1,4 @@
-export default function cloneNodes(nodes, source) {
+export default function cloneNodes(nodes, source = undefined, raws = undefined) {
   return nodes.map((node) => {
     let cloned = node.clone()
 
@@ -12,6 +12,13 @@ export default function cloneNodes(nodes, source) {
       }
     }
 
+    if (raws !== undefined) {
+      cloned.raws.tailwind = {
+        ...cloned.raws.tailwind,
+        ...raws,
+      }
+    }
+
     return cloned
   })
 }