Support defining variants as functions for easier extending

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - New `layers` mode for `purge` ([#2288](https://github.com/tailwindlabs/tailwindcss/pull/2288))
 - New `font-variant-numeric` utilities ([#2305](https://github.com/tailwindlabs/tailwindcss/pull/2305))
 - New `place-items`, `place-content`, `place-self`, `justify-items`, and `justify-self` utilities ([#2306](https://github.com/tailwindlabs/tailwindcss/pull/2306))
+- Support configuring variants as functions ([#2309](https://github.com/tailwindlabs/tailwindcss/pull/2309))
 
 ### Deprecated
 

__tests__/resolveConfig.test.js

@@ -1736,3 +1736,65 @@ test('user theme extensions take precedence over plugin theme extensions with th
     plugins: userConfig.plugins,
   })
 })
+
+test('variants can be defined as a function', () => {
+  const userConfig = {
+    variants: {
+      backgroundColor: ({ variants }) => [...variants('backgroundColor'), 'disabled'],
+      padding: ({ before }) => before(['active']),
+      float: ({ before }) => before(['disabled'], 'focus'),
+      margin: ({ before }) => before(['hover'], 'focus'),
+      borderWidth: ({ after }) => after(['active']),
+      backgroundImage: ({ after }) => after(['disabled'], 'hover'),
+      opacity: ({ after }) => after(['hover'], 'focus'),
+      rotate: ({ without }) => without(['hover']),
+      cursor: ({ before, after, without }) =>
+        without(['responsive'], before(['checked'], 'hover', after(['hover'], 'focus'))),
+    },
+  }
+
+  const otherConfig = {
+    variants: {
+      backgroundColor: ({ variants }) => [...variants('backgroundColor'), 'active'],
+    },
+  }
+
+  const defaultConfig = {
+    prefix: '',
+    important: false,
+    separator: ':',
+    theme: {},
+    variants: {
+      backgroundColor: ['responsive', 'hover', 'focus'],
+      padding: ['responsive', 'focus'],
+      float: ['responsive', 'hover', 'focus'],
+      margin: ['responsive'],
+      borderWidth: ['responsive', 'focus'],
+      backgroundImage: ['responsive', 'hover', 'focus'],
+      opacity: ['responsive'],
+      rotate: ['responsive', 'hover', 'focus'],
+      cursor: ['responsive', 'focus'],
+    },
+  }
+
+  const result = resolveConfig([userConfig, otherConfig, defaultConfig])
+
+  expect(result).toEqual({
+    prefix: '',
+    important: false,
+    separator: ':',
+    theme: {},
+    variants: {
+      backgroundColor: ['responsive', 'hover', 'focus', 'active', 'disabled'],
+      padding: ['active', 'responsive', 'focus'],
+      float: ['responsive', 'hover', 'disabled', 'focus'],
+      margin: ['responsive', 'hover'],
+      borderWidth: ['responsive', 'focus', 'active'],
+      backgroundImage: ['responsive', 'hover', 'disabled', 'focus'],
+      opacity: ['hover', 'responsive'],
+      rotate: ['responsive', 'focus'],
+      cursor: ['focus', 'checked', 'hover'],
+    },
+    plugins: userConfig.plugins,
+  })
+})

src/util/resolveConfig.js

@@ -83,15 +83,15 @@ function mergeExtensions({ extend, ...theme }) {
 }
 
 function resolveFunctionKeys(object) {
-  const resolveThemePath = (key, defaultValue) => {
+  const resolvePath = (key, defaultValue) => {
     const path = toPath(key)
 
     let index = 0
     let val = object
 
     while (val !== undefined && val !== null && index < path.length) {
       val = val[path[index++]]
-      val = isFunction(val) ? val(resolveThemePath, configUtils) : val
+      val = isFunction(val) ? val(resolvePath, configUtils) : val
     }
 
     return val === undefined ? defaultValue : val
@@ -100,7 +100,7 @@ function resolveFunctionKeys(object) {
   return Object.keys(object).reduce((resolved, key) => {
     return {
       ...resolved,
-      [key]: isFunction(object[key]) ? object[key](resolveThemePath, configUtils) : object[key],
+      [key]: isFunction(object[key]) ? object[key](resolvePath, configUtils) : object[key],
     }
   }, {})
 }
@@ -128,6 +128,65 @@ function extractPluginConfigs(configs) {
   return allConfigs
 }
 
+function resolveVariants([firstConfig, ...variantConfigs]) {
+  if (Array.isArray(firstConfig)) {
+    return firstConfig
+  }
+
+  return [firstConfig, ...variantConfigs].reverse().reduce((resolved, variants) => {
+    Object.entries(variants || {}).forEach(([plugin, pluginVariants]) => {
+      if (isFunction(pluginVariants)) {
+        resolved[plugin] = pluginVariants({
+          variants(path) {
+            return get(resolved, path, [])
+          },
+          before(toInsert, variant, existingPluginVariants = get(resolved, plugin, [])) {
+            if (variant === undefined) {
+              return [...toInsert, ...existingPluginVariants]
+            }
+
+            const index = existingPluginVariants.indexOf(variant)
+
+            if (index === -1) {
+              return [...existingPluginVariants, ...toInsert]
+            }
+
+            return [
+              ...existingPluginVariants.slice(0, index),
+              ...toInsert,
+              ...existingPluginVariants.slice(index),
+            ]
+          },
+          after(toInsert, variant, existingPluginVariants = get(resolved, plugin, [])) {
+            if (variant === undefined) {
+              return [...existingPluginVariants, ...toInsert]
+            }
+
+            const index = existingPluginVariants.indexOf(variant)
+
+            if (index === -1) {
+              return [...toInsert, ...existingPluginVariants]
+            }
+
+            return [
+              ...existingPluginVariants.slice(0, index + 1),
+              ...toInsert,
+              ...existingPluginVariants.slice(index + 1),
+            ]
+          },
+          without(toRemove, existingPluginVariants = get(resolved, plugin, [])) {
+            return existingPluginVariants.filter(v => !toRemove.includes(v))
+          },
+        })
+      } else {
+        resolved[plugin] = pluginVariants
+      }
+    })
+
+    return resolved
+  }, {})
+}
+
 export default function resolveConfig(configs) {
   const allConfigs = extractPluginConfigs(configs)
 
@@ -136,11 +195,7 @@ export default function resolveConfig(configs) {
       theme: resolveFunctionKeys(
         mergeExtensions(mergeThemes(map(allConfigs, t => get(t, 'theme', {}))))
       ),
-      variants: (firstVariants => {
-        return Array.isArray(firstVariants)
-          ? firstVariants
-          : defaults({}, ...map(allConfigs, 'variants'))
-      })(defaults({}, ...map(allConfigs)).variants),
+      variants: resolveVariants(allConfigs.map(c => c.variants)),
     },
     ...allConfigs
   )