Allow users to block generation of certain utilities (#9812)

* Add blocklist tests

* Build initial implementation of blocklist

* wip

* wip

* wip

* Update changelog

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Added
+
+- Allow users to block generation of certain utilities ([#9812](https://github.com/tailwindlabs/tailwindcss/pull/9812))
+
 ### Fixed
 
 - Fix watching of files on Linux when renames are involved ([#9796](https://github.com/tailwindlabs/tailwindcss/pull/9796))

src/lib/setupContextUtils.js

@@ -1165,7 +1165,8 @@ export function createContext(tailwindConfig, changedContent = [], root = postcs
     candidateRuleCache: new Map(),
     classCache: new Map(),
     applyClassCache: new Map(),
-    notClassCache: new Set(),
+    // Seed the not class cache with the blocklist (which is only strings)
+    notClassCache: new Set(tailwindConfig.blocklist ?? []),
     postCssNodeCache: new Map(),
     candidateRuleMap: new Map(),
     tailwindConfig,

src/util/normalizeConfig.js

@@ -150,6 +150,24 @@ export function normalizeConfig(config) {
     return []
   })()
 
+  // Normalize the `blocklist`
+  config.blocklist = (() => {
+    let { blocklist } = config
+
+    if (Array.isArray(blocklist)) {
+      if (blocklist.every((item) => typeof item === 'string')) {
+        return blocklist
+      }
+
+      log.warn('blocklist-invalid', [
+        'The `blocklist` option must be an array of strings.',
+        'https://tailwindcss.com/docs/content-configuration#discarding-classes',
+      ])
+    }
+
+    return []
+  })()
+
   // Normalize prefix option
   if (typeof config.prefix === 'function') {
     log.warn('prefix-function', [

tests/blocklist.test.js

@@ -0,0 +1,116 @@
+import { run, html, css } from './util/run'
+
+let warn
+
+beforeEach(() => {
+  warn = jest.spyOn(require('../src/util/log').default, 'warn')
+})
+
+afterEach(() => warn.mockClear())
+
+it('can block classes matched literally', () => {
+  let config = {
+    content: [
+      {
+        raw: html`<div
+          class="font-bold uppercase sm:hover:text-sm hover:text-sm bg-red-500/50 my-custom-class"
+        ></div>`,
+      },
+    ],
+    blocklist: ['font', 'uppercase', 'hover:text-sm', 'bg-red-500/50', 'my-custom-class'],
+  }
+
+  let input = css`
+    @tailwind utilities;
+    .my-custom-class {
+      color: red;
+    }
+  `
+
+  return run(input, config).then((result) => {
+    return expect(result.css).toMatchCss(css`
+      .font-bold {
+        font-weight: 700;
+      }
+      .my-custom-class {
+        color: red;
+      }
+      @media (min-width: 640px) {
+        .sm\:hover\:text-sm:hover {
+          font-size: 0.875rem;
+          line-height: 1.25rem;
+        }
+      }
+    `)
+  })
+})
+
+it('can block classes inside @layer', () => {
+  let config = {
+    content: [
+      {
+        raw: html`<div class="font-bold my-custom-class"></div>`,
+      },
+    ],
+    blocklist: ['my-custom-class'],
+  }
+
+  let input = css`
+    @tailwind utilities;
+    @layer utilities {
+      .my-custom-class {
+        color: red;
+      }
+    }
+  `
+
+  return run(input, config).then((result) => {
+    return expect(result.css).toMatchCss(css`
+      .font-bold {
+        font-weight: 700;
+      }
+    `)
+  })
+})
+
+it('blocklists do NOT support regexes', async () => {
+  let config = {
+    content: [{ raw: html`<div class="font-bold bg-[#f00d1e]"></div>` }],
+    blocklist: [/^bg-\[[^]+\]$/],
+  }
+
+  let result = await run('@tailwind utilities', config)
+
+  expect(result.css).toMatchCss(css`
+    .bg-\[\#f00d1e\] {
+      --tw-bg-opacity: 1;
+      background-color: rgb(240 13 30 / var(--tw-bg-opacity));
+    }
+    .font-bold {
+      font-weight: 700;
+    }
+  `)
+
+  expect(warn).toHaveBeenCalledTimes(1)
+  expect(warn.mock.calls.map((x) => x[0])).toEqual(['blocklist-invalid'])
+})
+
+it('can block classes generated by the safelist', () => {
+  let config = {
+    content: [{ raw: html`<div class="font-bold"></div>` }],
+    safelist: [{ pattern: /^bg-red-(400|500)$/ }],
+    blocklist: ['bg-red-500'],
+  }
+
+  return run('@tailwind utilities', config).then((result) => {
+    return expect(result.css).toMatchCss(css`
+      .bg-red-400 {
+        --tw-bg-opacity: 1;
+        background-color: rgb(248 113 113 / var(--tw-bg-opacity));
+      }
+      .font-bold {
+        font-weight: 700;
+      }
+    `)
+  })
+})