Support alpha values for theme() function (#8416)

* Fix typo

* Support alpha modifier for theme color values

* Eliminate redundant object creation in resolveFunctionKeys

Building an object of N keys incrementally using Object.reduce + splat results in N intermediate objects. We should just create one object and assign each key.

* Switch to inline theme values in theme fn in config

* Add test case

And fix typos that were definitely not there

* Update changelog

CHANGELOG.md

@@ -49,6 +49,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Add `matchVariant` API ([#8310](https://github.com/tailwindlabs/tailwindcss/pull/8310))
 - Add `prefers-contrast` media query variants ([#8410](https://github.com/tailwindlabs/tailwindcss/pull/8410))
 - Experimental support for variant grouping ([#8405](https://github.com/tailwindlabs/tailwindcss/pull/8405))
+- Add opacity support when referencing colors with `theme` function ([#8416](https://github.com/tailwindlabs/tailwindcss/pull/8416))
 
 ## [3.0.24] - 2022-04-12
 

src/lib/evaluateTailwindFunctions.js

@@ -5,6 +5,7 @@ import parseValue from 'postcss-value-parser'
 import { normalizeScreens } from '../util/normalizeScreens'
 import buildMediaQuery from '../util/buildMediaQuery'
 import { toPath } from '../util/toPath'
+import { withAlphaValue } from '../util/withAlphaVariable'
 
 function isObject(input) {
   return typeof input === 'object' && input !== null
@@ -37,7 +38,7 @@ function listKeys(obj) {
   return list(Object.keys(obj))
 }
 
-function validatePath(config, path, defaultValue) {
+function validatePath(config, path, defaultValue, themeOpts = {}) {
   const pathString = Array.isArray(path)
     ? pathToString(path)
     : path.replace(/^['"]+/g, '').replace(/['"]+$/g, '')
@@ -114,7 +115,7 @@ function validatePath(config, path, defaultValue) {
 
   return {
     isValid: true,
-    value: transformThemeValue(themeSection)(value),
+    value: transformThemeValue(themeSection)(value, themeOpts),
   }
 }
 
@@ -160,16 +161,29 @@ let nodeTypePropertyMap = {
 export default function ({ tailwindConfig: config }) {
   let functions = {
     theme: (node, path, ...defaultValue) => {
-      const { isValid, value, error } = validatePath(
+      let matches = path.match(/^([^\/\s]+)(?:\s*\/\s*([^\/\s]+))$/)
+      let alpha = undefined
+
+      if (matches) {
+        path = matches[1]
+        alpha = matches[2]
+      }
+
+      let { isValid, value, error } = validatePath(
         config,
         path,
-        defaultValue.length ? defaultValue : undefined
+        defaultValue.length ? defaultValue : undefined,
+        { opacityValue: alpha }
       )
 
       if (!isValid) {
         throw node.error(error)
       }
 
+      if (alpha !== undefined) {
+        value = withAlphaValue(value, alpha, value)
+      }
+
       return value
     },
     screen: (node, screen) => {

src/lib/setupContextUtils.js

@@ -221,16 +221,25 @@ function buildPluginApi(tailwindConfig, context, { variantList, variantMap, offs
     return context.tailwindConfig.prefix + identifier
   }
 
+  function resolveThemeValue(path, defaultValue, opts = {}) {
+    const [pathRoot, ...subPaths] = toPath(path)
+    const value = getConfigValue(['theme', pathRoot, ...subPaths], defaultValue)
+    return transformThemeValue(pathRoot)(value, opts)
+  }
+
+  const theme = Object.assign(
+    (path, defaultValue = undefined) => resolveThemeValue(path, defaultValue),
+    {
+      withAlpha: (path, opacityValue) => resolveThemeValue(path, undefined, { opacityValue }),
+    }
+  )
+
   let api = {
     postcss,
     prefix: applyConfiguredPrefix,
     e: escapeClassName,
     config: getConfigValue,
-    theme(path, defaultValue) {
-      const [pathRoot, ...subPaths] = toPath(path)
-      const value = getConfigValue(['theme', pathRoot, ...subPaths], defaultValue)
-      return transformThemeValue(pathRoot)(value)
-    },
+    theme,
     corePlugins: (path) => {
       if (Array.isArray(tailwindConfig.corePlugins)) {
         return tailwindConfig.corePlugins.includes(path)

src/util/resolveConfig.js

@@ -8,6 +8,7 @@ import { toPath } from './toPath'
 import { normalizeConfig } from './normalizeConfig'
 import isPlainObject from './isPlainObject'
 import { cloneDeep } from './cloneDeep'
+import { withAlphaValue } from './withAlphaVariable'
 
 function isFunction(input) {
   return typeof input === 'function'
@@ -164,40 +165,81 @@ function mergeExtensions({ extend, ...theme }) {
   })
 }
 
+/**
+ *
+ * @param {string} key
+ * @return {Iterable<string[] & {alpha: string | undefined}>}
+ */
+function* toPaths(key) {
+  let path = toPath(key)
+
+  if (path.length === 0) {
+    return
+  }
+
+  yield path
+
+  if (Array.isArray(key)) {
+    return
+  }
+
+  let pattern = /^(.*?)\s*\/\s*([^/]+)$/
+  let matches = key.match(pattern)
+
+  if (matches !== null) {
+    let [, prefix, alpha] = matches
+
+    let newPath = toPath(prefix)
+    newPath.alpha = alpha
+
+    yield newPath
+  }
+}
+
 function resolveFunctionKeys(object) {
+  // theme('colors.red.500 / 0.5') -> ['colors', 'red', '500 / 0', '5]
+
   const resolvePath = (key, defaultValue) => {
-    const path = toPath(key)
+    for (const path of toPaths(key)) {
+      let index = 0
+      let val = object
 
-    let index = 0
-    let val = object
+      while (val !== undefined && val !== null && index < path.length) {
+        val = val[path[index++]]
 
-    while (val !== undefined && val !== null && index < path.length) {
-      val = val[path[index++]]
-      val = isFunction(val) ? val(resolvePath, configUtils) : val
-    }
+        let shouldResolveAsFn =
+          isFunction(val) && (path.alpha === undefined || index < path.length - 1)
 
-    if (val === undefined) {
-      return defaultValue
-    }
+        val = shouldResolveAsFn ? val(resolvePath, configUtils) : val
+      }
+
+      if (val !== undefined) {
+        if (path.alpha !== undefined) {
+          return withAlphaValue(val, path.alpha)
+        }
+
+        if (isPlainObject(val)) {
+          return cloneDeep(val)
+        }
 
-    if (isPlainObject(val)) {
-      return cloneDeep(val)
+        return val
+      }
     }
 
-    return val
+    return defaultValue
   }
 
-  resolvePath.theme = resolvePath
+  // colors.red.500/50
 
-  for (let key in configUtils) {
-    resolvePath[key] = configUtils[key]
-  }
+  Object.assign(resolvePath, {
+    theme: resolvePath,
+    ...configUtils,
+  })
 
   return Object.keys(object).reduce((resolved, key) => {
-    return {
-      ...resolved,
-      [key]: isFunction(object[key]) ? object[key](resolvePath, configUtils) : object[key],
-    }
+    resolved[key] = isFunction(object[key]) ? object[key](resolvePath, configUtils) : object[key]
+
+    return resolved
   }, {})
 }
 

src/util/toPath.js

@@ -4,7 +4,7 @@
  * Square bracket notation `a[b]` may be used to "escape" dots that would otherwise be interpreted as path separators.
  *
  * Example:
- * a -> ['a]
+ * a -> ['a']
  * a.b.c -> ['a', 'b', 'c']
  * a[b].c -> ['a', 'b', 'c']
  * a[b.c].e.f -> ['a', 'b.c', 'e', 'f']

src/util/transformThemeValue.js

@@ -44,8 +44,10 @@ export default function transformThemeValue(themeSection) {
     }
   }
 
-  return (value) => {
-    if (typeof value === 'function') value = value({})
+  return (value, opts = {}) => {
+    if (typeof value === 'function') {
+      value = value(opts)
+    }
 
     return value
   }