From 30dc2990c300cf3446ff5d795d47be146b8ee413 Mon Sep 17 00:00:00 2001
From: Adam Wathan <adam.wathan@gmail.com>
Date: Wed, 12 May 2021 16:58:03 -0400
Subject: [PATCH] Error when `@layer` used without matching `@tailwind`
 directive (#4335)

Also refactor to only detect `@tailwind` directives once per build to improve performance.
---
 src/jit/index.js                           |   8 +-
 src/jit/lib/expandTailwindAtRules.js       |  13 +--
 src/jit/lib/removeLayerAtRules.js          |  19 +++-
 src/jit/lib/rewriteTailwindImports.js      |   8 ++
 src/jit/lib/setupContext.js                |  11 +--
 tests/jit/layer-without-tailwind.test.css  |   5 +
 tests/jit/layer-without-tailwind.test.html |   1 +
 tests/jit/layer-without-tailwind.test.js   | 101 +++++++++++++++++++++
 tests/jit/prefix.test.js                   |   2 +-
 9 files changed, 145 insertions(+), 23 deletions(-)
 create mode 100644 tests/jit/layer-without-tailwind.test.css
 create mode 100644 tests/jit/layer-without-tailwind.test.html
 create mode 100644 tests/jit/layer-without-tailwind.test.js

diff --git a/src/jit/index.js b/src/jit/index.js
index 0c8f63c2f..d155f1ee4 100644
--- a/src/jit/index.js
+++ b/src/jit/index.js
@@ -30,9 +30,9 @@ export default function (configOrPath = {}) {
         })
       }
 
-      rewriteTailwindImports(root)
+      let tailwindDirectives = rewriteTailwindImports(root)
 
-      let context = setupContext(configOrPath)(result, root)
+      let context = setupContext(configOrPath, tailwindDirectives)(result, root)
 
       if (!env.TAILWIND_DISABLE_TOUCH) {
         if (context.configPath !== null) {
@@ -41,8 +41,8 @@ export default function (configOrPath = {}) {
       }
 
       return postcss([
-        removeLayerAtRules(context),
-        expandTailwindAtRules(context, registerDependency),
+        removeLayerAtRules(context, tailwindDirectives),
+        expandTailwindAtRules(context, registerDependency, tailwindDirectives),
         expandApplyAtRules(context),
         evaluateTailwindFunctions(context.tailwindConfig),
         substituteScreenAtRules(context.tailwindConfig),
diff --git a/src/jit/lib/expandTailwindAtRules.js b/src/jit/lib/expandTailwindAtRules.js
index cd528f1c0..6b421d8ac 100644
--- a/src/jit/lib/expandTailwindAtRules.js
+++ b/src/jit/lib/expandTailwindAtRules.js
@@ -111,9 +111,12 @@ function buildStylesheet(rules, context) {
   return returnValue
 }
 
-export default function expandTailwindAtRules(context, registerDependency) {
+export default function expandTailwindAtRules(context, registerDependency, tailwindDirectives) {
   return (root) => {
-    let foundTailwind = false
+    if (tailwindDirectives.size === 0) {
+      return root
+    }
+
     let layerNodes = {
       base: null,
       components: null,
@@ -126,8 +129,6 @@ export default function expandTailwindAtRules(context, registerDependency) {
     // file as a dependency since the output of this CSS does not depend on
     // the source of any templates. Think Vue <style> blocks for example.
     root.walkAtRules('tailwind', (rule) => {
-      foundTailwind = true
-
       if (rule.params === 'base') {
         layerNodes.base = rule
       }
@@ -145,10 +146,6 @@ export default function expandTailwindAtRules(context, registerDependency) {
       }
     })
 
-    if (!foundTailwind) {
-      return root
-    }
-
     // ---
 
     if (sharedState.env.TAILWIND_DISABLE_TOUCH) {
diff --git a/src/jit/lib/removeLayerAtRules.js b/src/jit/lib/removeLayerAtRules.js
index 009ae2004..77ca8441e 100644
--- a/src/jit/lib/removeLayerAtRules.js
+++ b/src/jit/lib/removeLayerAtRules.js
@@ -1,7 +1,22 @@
-export default function removeLayerAtRules() {
+export default function removeLayerAtRules(_context, tailwindDirectives) {
   return (root) => {
     root.walkAtRules((rule) => {
-      if (['layer', 'responsive', 'variants'].includes(rule.name)) {
+      if (rule.name === 'layer' && ['base', 'components', 'utilities'].includes(rule.params)) {
+        if (!tailwindDirectives.has(rule.params)) {
+          throw rule.error(
+            `\`@layer ${rule.params}\` is used but no matching \`@tailwind ${rule.params}\` directive is present.`
+          )
+        }
+        rule.remove()
+      } else if (rule.name === 'responsive') {
+        if (!tailwindDirectives.has('utilities')) {
+          throw rule.error('`@responsive` is used but `@tailwind utilities` is missing.')
+        }
+        rule.remove()
+      } else if (rule.name === 'variants') {
+        if (!tailwindDirectives.has('utilities')) {
+          throw rule.error('`@variants` is used but `@tailwind utilities` is missing.')
+        }
         rule.remove()
       }
     })
diff --git a/src/jit/lib/rewriteTailwindImports.js b/src/jit/lib/rewriteTailwindImports.js
index b022ebd64..51cf06aa9 100644
--- a/src/jit/lib/rewriteTailwindImports.js
+++ b/src/jit/lib/rewriteTailwindImports.js
@@ -23,4 +23,12 @@ export default function rewriteTailwindImports(root) {
       atRule.params = 'screens'
     }
   })
+
+  let tailwindDirectives = new Set()
+
+  root.walkAtRules('tailwind', (rule) => {
+    tailwindDirectives.add(rule.params)
+  })
+
+  return tailwindDirectives
 }
diff --git a/src/jit/lib/setupContext.js b/src/jit/lib/setupContext.js
index 99534988e..2fa79d63f 100644
--- a/src/jit/lib/setupContext.js
+++ b/src/jit/lib/setupContext.js
@@ -314,6 +314,7 @@ function rebootWatcher(context) {
           touch(context.configPath)
         } else {
           context.changedFiles.add(path.resolve('.', file))
+          console.log(context.touchFile)
           touch(context.touchFile)
         }
       })
@@ -686,14 +687,8 @@ function cleanupContext(context) {
 // Retrieve an existing context from cache if possible (since contexts are unique per
 // source path), or set up a new one (including setting up watchers and registering
 // plugins) then return it
-export default function setupContext(configOrPath) {
+export default function setupContext(configOrPath, tailwindDirectives) {
   return (result, root) => {
-    let foundTailwind = false
-
-    root.walkAtRules('tailwind', () => {
-      foundTailwind = true
-    })
-
     let sourcePath = result.opts.from
     let [
       tailwindConfig,
@@ -712,7 +707,7 @@ export default function setupContext(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 (foundTailwind) {
+    if (tailwindDirectives.size > 0) {
       contextDependencies.add(sourcePath)
       for (let message of result.messages) {
         if (message.type === 'dependency') {
diff --git a/tests/jit/layer-without-tailwind.test.css b/tests/jit/layer-without-tailwind.test.css
new file mode 100644
index 000000000..28dfe0bb5
--- /dev/null
+++ b/tests/jit/layer-without-tailwind.test.css
@@ -0,0 +1,5 @@
+@layer components {
+  .foo {
+    color: black;
+  }
+}
diff --git a/tests/jit/layer-without-tailwind.test.html b/tests/jit/layer-without-tailwind.test.html
new file mode 100644
index 000000000..a6d7176e1
--- /dev/null
+++ b/tests/jit/layer-without-tailwind.test.html
@@ -0,0 +1 @@
+<div class="foo"></div>
diff --git a/tests/jit/layer-without-tailwind.test.js b/tests/jit/layer-without-tailwind.test.js
new file mode 100644
index 000000000..07d2d9f68
--- /dev/null
+++ b/tests/jit/layer-without-tailwind.test.js
@@ -0,0 +1,101 @@
+import postcss from 'postcss'
+import path from 'path'
+import tailwind from '../../src/jit/index.js'
+
+function run(input, config = {}) {
+  const { currentTestName } = expect.getState()
+
+  return postcss(tailwind(config)).process(input, {
+    from: `${path.resolve(__filename)}?test=${currentTestName}`,
+  })
+}
+
+test('using @layer without @tailwind', async () => {
+  let config = {
+    purge: [path.resolve(__dirname, './layer-without-tailwind.test.html')],
+    mode: 'jit',
+    theme: {},
+    plugins: [],
+  }
+
+  let css = `
+    @layer components {
+      .foo {
+        color: black;
+      }
+    }
+  `
+
+  await expect(run(css, config)).rejects.toThrowError(
+    '`@layer components` is used but no matching `@tailwind components` directive is present.'
+  )
+})
+
+test('using @responsive without @tailwind', async () => {
+  let config = {
+    purge: [path.resolve(__dirname, './layer-without-tailwind.test.html')],
+    mode: 'jit',
+    theme: {},
+    plugins: [],
+  }
+
+  let css = `
+    @responsive {
+      .foo {
+        color: black;
+      }
+    }
+  `
+
+  await expect(run(css, config)).rejects.toThrowError(
+    '`@responsive` is used but `@tailwind utilities` is missing.'
+  )
+})
+
+test('using @variants without @tailwind', async () => {
+  let config = {
+    purge: [path.resolve(__dirname, './layer-without-tailwind.test.html')],
+    mode: 'jit',
+    theme: {},
+    plugins: [],
+  }
+
+  let css = `
+    @variants hover {
+      .foo {
+        color: black;
+      }
+    }
+  `
+
+  await expect(run(css, config)).rejects.toThrowError(
+    '`@variants` is used but `@tailwind utilities` is missing.'
+  )
+})
+
+test('non-Tailwind @layer rules are okay', async () => {
+  let config = {
+    purge: [path.resolve(__dirname, './layer-without-tailwind.test.html')],
+    mode: 'jit',
+    theme: {},
+    plugins: [],
+  }
+
+  let css = `
+    @layer custom {
+      .foo {
+        color: black;
+      }
+    }
+  `
+
+  return run(css, config).then((result) => {
+    expect(result.css).toMatchFormattedCss(`
+      @layer custom {
+        .foo {
+          color: black;
+        }
+      }
+    `)
+  })
+})
diff --git a/tests/jit/prefix.test.js b/tests/jit/prefix.test.js
index 553a1ce7b..3d21bfa24 100644
--- a/tests/jit/prefix.test.js
+++ b/tests/jit/prefix.test.js
@@ -66,7 +66,7 @@ test('prefix', () => {
       }
     }
     @tailwind utilities;
-    @layer utilites {
+    @layer utilities {
       .custom-utility {
         foo: bar;
       }