Invalidate context when CSS changes

src/lib/cacheInvalidation.js

@@ -0,0 +1,36 @@
+import crypto from 'crypto'
+import * as sharedState from './sharedState'
+
+/**
+ *
+ * @param {string} str
+ */
+function getHash(str) {
+  try {
+    return crypto.createHash('md5').update(str, 'utf-8').digest('binary')
+  } catch (err) {
+    return ''
+  }
+}
+
+/**
+ * @param {string} sourcePath
+ * @param {import('postcss').Node} root
+ */
+export function hasContentChanged(sourcePath, root) {
+  let css = root.toString()
+
+  // We only care about files with @tailwind directives
+  // Other files use an existing context
+  if (!css.includes('@tailwind')) {
+    return false
+  }
+
+  let existingHash = sharedState.sourceHashMap.get(sourcePath)
+  let rootHash = getHash(css)
+  let didChange = existingHash !== rootHash
+
+  sharedState.sourceHashMap.set(sourcePath, rootHash)
+
+  return didChange
+}

src/lib/setupContextUtils.js

@@ -20,6 +20,7 @@ import log from '../util/log'
 import negateValue from '../util/negateValue'
 import isValidArbitraryValue from '../util/isValidArbitraryValue'
 import { generateRules } from './generateRules'
+import { hasContentChanged } from './cacheInvalidation.js'
 
 function prefix(context, selector) {
   let prefix = context.tailwindConfig.prefix
@@ -790,6 +791,8 @@ export function createContext(tailwindConfig, changedContent = [], root = postcs
   let resolvedPlugins = resolvePlugins(context, root)
   registerPlugins(resolvedPlugins, context)
 
+  sharedState.contextInvalidationCount++
+
   return context
 }
 
@@ -822,14 +825,16 @@ export function getContext(
     existingContext = context
   }
 
+  let cssDidChange = hasContentChanged(sourcePath, root)
+
   // If there's already a context in the cache and we don't need to
   // reset the context, return the cached context.
   if (existingContext) {
     let contextDependenciesChanged = trackModified(
       [...contextDependencies],
       getFileModifiedMap(existingContext)
     )
-    if (!contextDependenciesChanged) {
+    if (!contextDependenciesChanged && !cssDidChange) {
       return [existingContext, false]
     }
   }

src/lib/sharedState.js

@@ -5,6 +5,13 @@ export const env = {
 export const contextMap = new Map()
 export const configContextMap = new Map()
 export const contextSourcesMap = new Map()
+/**
+ * A map of source files to their sizes / hashes
+ *
+ * @type {Map<string, string>}
+ */
+export const sourceHashMap = new Map()
+export const contextInvalidationCount = 0
 export const NOT_ON_DEMAND = new String('*')
 
 export function resolveDebug(debug) {

tests/context-reuse.test.js

@@ -85,3 +85,39 @@ it('re-uses the context across multiple files with the same config', async () =>
   // And none of this should have resulted in multiple contexts being created
   expect(sharedState.contextSourcesMap.size).toBe(1)
 })
+
+it('passing in different css invalidates the context if it contains @tailwind directives', async () => {
+  sharedState.contextInvalidationCount = 0
+
+  let from = path.resolve(__filename)
+
+  // Save the file a handful of times with no changes
+  // This builds the context at most once
+  for (let n = 0; n < 5; n++) {
+    await run(`@tailwind utilities;`, configPath, `${from}?id=1`)
+  }
+
+  expect(sharedState.contextInvalidationCount).toBe(1)
+
+  // Save the file twice with a change
+  // This should rebuild the context again but only once
+  await run(`@tailwind utilities; .foo {}`, configPath, `${from}?id=1`)
+  await run(`@tailwind utilities; .foo {}`, configPath, `${from}?id=1`)
+
+  expect(sharedState.contextInvalidationCount).toBe(2)
+
+  // Save the file twice with a content but not length change
+  // This should rebuild the context two more times
+  await run(`@tailwind utilities; .bar {}`, configPath, `${from}?id=1`)
+  await run(`@tailwind utilities; .baz {}`, configPath, `${from}?id=1`)
+
+  expect(sharedState.contextInvalidationCount).toBe(4)
+
+  // Save a file with a change that does not affect the context
+  // No invalidation should occur
+  await run(`.foo { @apply mb-1; }`, configPath, `${from}?id=2`)
+  await run(`.foo { @apply mb-1; }`, configPath, `${from}?id=2`)
+  await run(`.foo { @apply mb-1; }`, configPath, `${from}?id=2`)
+
+  expect(sharedState.contextInvalidationCount).toBe(4)
+})