implement purge safelist (#4580)

* fix --help output in tests

* add tests to ensure we can use `purge.safelist`

* implement the `purge.safelist` for strings

* proxy `purge.safelist` to `purge.options.safelist`

This allows us to have a similar API in `AOT` and `JIT` mode.

* only proxy `purge.safelist` to `purge.options.safelist` if
`purge.options.safelist` doesn't exists yet.

integrations/tailwindcss-cli/tests/cli.test.js

@@ -172,7 +172,7 @@ describe('Build command', () => {
          -o, --output             Output file
          -w, --watch              Watch for changes and rebuild as needed
              --jit                Build using JIT mode
-             --files              Template files to scan for class names
+             --purge              Content paths to use for removing unused classes
              --postcss            Load custom PostCSS configuration
          -m, --minify             Minify the output
          -c, --config             Path to a custom config file

integrations/tailwindcss-cli/tests/integration.test.js

@@ -25,6 +25,58 @@ describe('static build', () => {
       `
     )
   })
+
+  it('should safelist a list of classes to always include', async () => {
+    await writeInputFile('index.html', html`<div class="font-bold"></div>`)
+    await writeInputFile(
+      '../tailwind.config.js',
+      javascript`
+        module.exports = {
+          purge: {
+            content: ['./src/index.html'],
+            safelist: ['bg-red-500','bg-red-600']
+          },
+          mode: 'jit',
+          darkMode: false, // or 'media' or 'class'
+          theme: {
+            extend: {
+            },
+          },
+          variants: {
+            extend: {},
+          },
+          corePlugins: {
+            preflight: false,
+          },
+          plugins: [],
+        }
+      `
+    )
+
+    $('node ../../lib/cli.js -i ./src/index.css -o ./dist/main.css', {
+      env: { NODE_ENV: 'production' },
+    })
+
+    await waitForOutputFileCreation('main.css')
+
+    expect(await readOutputFile('main.css')).toIncludeCss(
+      css`
+        .bg-red-500 {
+          --tw-bg-opacity: 1;
+          background-color: rgba(239, 68, 68, var(--tw-bg-opacity));
+        }
+
+        .bg-red-600 {
+          --tw-bg-opacity: 1;
+          background-color: rgba(220, 38, 38, var(--tw-bg-opacity));
+        }
+
+        .font-bold {
+          font-weight: 700;
+        }
+      `
+    )
+  })
 })
 
 describe('watcher', () => {

integrations/webpack-5/tests/integration.test.js

@@ -227,4 +227,56 @@ describe.each([{ TAILWIND_MODE: 'watch' }, { TAILWIND_MODE: undefined }])('watch
 
     return runningProcess.stop()
   })
+
+  it('should safelist a list of classes to always include', async () => {
+    await writeInputFile('index.html', html`<div class="font-bold"></div>`)
+    await writeInputFile(
+      '../tailwind.config.js',
+      javascript`
+        module.exports = {
+          purge: {
+            content: ['./src/index.html'],
+            safelist: ['bg-red-500','bg-red-600']
+          },
+          mode: 'jit',
+          darkMode: false, // or 'media' or 'class'
+          theme: {
+            extend: {
+            },
+          },
+          variants: {
+            extend: {},
+          },
+          corePlugins: {
+            preflight: false,
+          },
+          plugins: [],
+        }
+      `
+    )
+
+    let runningProcess = $('webpack --mode=development --watch', { env })
+
+    await waitForOutputFileCreation('main.css')
+
+    expect(await readOutputFile('main.css')).toIncludeCss(
+      css`
+        .bg-red-500 {
+          --tw-bg-opacity: 1;
+          background-color: rgba(239, 68, 68, var(--tw-bg-opacity));
+        }
+
+        .bg-red-600 {
+          --tw-bg-opacity: 1;
+          background-color: rgba(220, 38, 38, var(--tw-bg-opacity));
+        }
+
+        .font-bold {
+          font-weight: 700;
+        }
+      `
+    )
+
+    return runningProcess.stop()
+  })
 })

src/cli.js

@@ -356,7 +356,25 @@ async function build() {
   }
 
   function extractContent(config) {
-    return Array.isArray(config.purge) ? config.purge : config.purge.content
+    let content = Array.isArray(config.purge) ? config.purge : config.purge.content
+
+    return content.concat(
+      (config.purge?.safelist ?? []).map((content) => {
+        if (typeof content === 'string') {
+          return { raw: content, extension: 'html' }
+        }
+
+        if (content instanceof RegExp) {
+          throw new Error(
+            "Values inside 'purge.safelist' can only be of type 'string', found 'regex'."
+          )
+        }
+
+        throw new Error(
+          `Values inside 'purge.safelist' can only be of type 'string', found '${typeof content}'.`
+        )
+      })
+    )
   }
 
   function extractFileGlobs(config) {

src/jit/lib/setupTrackingContext.js

@@ -88,6 +88,23 @@ function resolvedChangedContent(context, candidateFiles, fileModifiedMap) {
       : context.tailwindConfig.purge.content
   )
     .filter((item) => typeof item.raw === 'string')
+    .concat(
+      (context.tailwindConfig.purge?.safelist ?? []).map((content) => {
+        if (typeof content === 'string') {
+          return { raw: content, extension: 'html' }
+        }
+
+        if (content instanceof RegExp) {
+          throw new Error(
+            "Values inside 'purge.safelist' can only be of type 'string', found 'regex'."
+          )
+        }
+
+        throw new Error(
+          `Values inside 'purge.safelist' can only be of type 'string', found '${typeof content}'.`
+        )
+      })
+    )
     .map(({ raw, extension }) => ({ content: raw, extension }))
 
   for (let changedFile of resolveChangedFiles(candidateFiles, fileModifiedMap)) {

src/jit/lib/setupWatchingContext.js

@@ -235,6 +235,23 @@ function resolvedChangedContent(context, candidateFiles) {
       : context.tailwindConfig.purge.content
   )
     .filter((item) => typeof item.raw === 'string')
+    .concat(
+      (context.tailwindConfig.purge?.safelist ?? []).map((content) => {
+        if (typeof content === 'string') {
+          return { raw: content, extension: 'html' }
+        }
+
+        if (content instanceof RegExp) {
+          throw new Error(
+            "Values inside 'purge.safelist' can only be of type 'string', found 'regex'."
+          )
+        }
+
+        throw new Error(
+          `Values inside 'purge.safelist' can only be of type 'string', found '${typeof content}'.`
+        )
+      })
+    )
     .map(({ raw, extension }) => ({ content: raw, extension }))
 
   for (let changedFile of resolveChangedFiles(context, candidateFiles)) {

src/lib/purgeUnusedStyles.js

@@ -81,6 +81,10 @@ export default function purgeUnusedUtilities(
   const transformers = config.purge.transform || {}
   let { defaultExtractor: originalDefaultExtractor, ...purgeOptions } = config.purge.options || {}
 
+  if (config.purge?.safelist && !purgeOptions.hasOwnProperty('safelist')) {
+    purgeOptions.safelist = config.purge.safelist
+  }
+
   if (!originalDefaultExtractor) {
     originalDefaultExtractor =
       typeof extractors === 'function' ? extractors : extractors.DEFAULT || tailwindExtractor

tests/purgeUnusedStyles.test.js

@@ -579,6 +579,32 @@ test(
   })
 )
 
+test(
+  'proxying purge.safelist to purge.options.safelist works',
+  suppressConsoleLogs(() => {
+    const inputPath = path.resolve(`${__dirname}/fixtures/tailwind-input.css`)
+    const input = fs.readFileSync(inputPath, 'utf8')
+
+    return postcss([
+      tailwind({
+        ...config,
+        purge: {
+          enabled: true,
+          safelist: ['md:bg-green-500'],
+          options: {
+            content: [path.resolve(`${__dirname}/fixtures/**/*.html`)],
+          },
+        },
+      }),
+    ])
+      .process(input, { from: withTestName(inputPath) })
+      .then((result) => {
+        expect(result.css).toContain('.md\\:bg-green-500')
+        assertPurged(result)
+      })
+  })
+)
+
 test(
   'can purge all CSS, not just Tailwind classes',
   suppressConsoleLogs(() => {