Fix wildcard duplication issue (#7478)

This would be better as a symbol but the stringy-ness of class candidates is fairly well baked into assumptions across the codebase. Using `new String` with a well placed check seems to solve the problem.

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Remove opacity variables from `:visited` pseudo class ([#7458](https://github.com/tailwindlabs/tailwindcss/pull/7458))
 - Support arbitrary values + calc + theme with quotes ([#7462](https://github.com/tailwindlabs/tailwindcss/pull/7462))
+- Don't duplicate layer output when scanning content with variants + wildcards ([#7478](https://github.com/tailwindlabs/tailwindcss/pull/7478))
 
 ## [3.0.22] - 2022-02-11
 

src/lib/expandTailwindAtRules.js

@@ -158,7 +158,7 @@ export default function expandTailwindAtRules(context) {
     // ---
 
     // Find potential rules in changed files
-    let candidates = new Set(['*'])
+    let candidates = new Set([sharedState.NOT_ON_DEMAND])
     let seen = new Set()
 
     env.DEBUG && console.time('Reading changed files')

src/lib/generateRules.js

@@ -5,6 +5,7 @@ import isPlainObject from '../util/isPlainObject'
 import prefixSelector from '../util/prefixSelector'
 import { updateAllClasses } from '../util/pluginUtils'
 import log from '../util/log'
+import * as sharedState from './sharedState'
 import { formatVariantSelector, finalizeSelector } from '../util/formatVariantSelector'
 import { asClass } from '../util/nameClass'
 import { normalize } from '../util/dataTypes'
@@ -382,6 +383,10 @@ function* resolveMatchedPlugins(classCandidate, context) {
 }
 
 function splitWithSeparator(input, separator) {
+  if (input === sharedState.NOT_ON_DEMAND) {
+    return [sharedState.NOT_ON_DEMAND]
+  }
+
   return input.split(new RegExp(`\\${separator}(?![^[]*\\])`, 'g'))
 }
 

src/lib/setupContextUtils.js

@@ -138,7 +138,7 @@ function withIdentifiers(styles) {
 
     // If this isn't "on-demandable", assign it a universal candidate to always include it.
     if (containsNonOnDemandableSelectors) {
-      candidates.unshift('*')
+      candidates.unshift(sharedState.NOT_ON_DEMAND)
     }
 
     // However, it could be that it also contains "on-demandable" candidates.
@@ -163,8 +163,8 @@ function buildPluginApi(tailwindConfig, context, { variantList, variantMap, offs
   }
 
   function prefixIdentifier(identifier, options) {
-    if (identifier === '*') {
-      return '*'
+    if (identifier === sharedState.NOT_ON_DEMAND) {
+      return sharedState.NOT_ON_DEMAND
     }
 
     if (!options.respectPrefix) {

src/lib/sharedState.js

@@ -5,6 +5,7 @@ export const env = {
 export const contextMap = new Map()
 export const configContextMap = new Map()
 export const contextSourcesMap = new Map()
+export const NOT_ON_DEMAND = new String('*')
 
 export function resolveDebug(debug) {
   if (debug === undefined) {

tests/basic-usage.test.js

@@ -1,7 +1,7 @@
 import fs from 'fs'
 import path from 'path'
 
-import { html, run, css } from './util/run'
+import { html, run, css, defaults } from './util/run'
 
 test('basic usage', () => {
   let config = {
@@ -188,3 +188,64 @@ it('can scan extremely long classes without crashing', () => {
     expect(result.css).toMatchFormattedCss(css``)
   })
 })
+
+it('does not produce duplicate output when seeing variants preceding a wildcard (*)', () => {
+  let config = {
+    content: [{ raw: html`underline focus:*` }],
+    corePlugins: { preflight: false },
+  }
+
+  let input = css`
+    @tailwind base;
+    @tailwind components;
+    @tailwind utilities;
+
+    * {
+      color: red;
+    }
+
+    .combined,
+    * {
+      text-align: center;
+    }
+
+    @layer base {
+      * {
+        color: blue;
+      }
+
+      .combined,
+      * {
+        color: red;
+      }
+    }
+  `
+
+  return run(input, config).then((result) => {
+    expect(result.css).toMatchFormattedCss(css`
+      * {
+        color: blue;
+      }
+
+      .combined,
+      * {
+        color: red;
+      }
+
+      ${defaults}
+
+      .underline {
+        text-decoration-line: underline;
+      }
+
+      * {
+        color: red;
+      }
+
+      .combined,
+      * {
+        text-align: center;
+      }
+    `)
+  })
+})