Allow plugins to register new config variables

__tests__/configFunction.test.js

@@ -1,8 +1,15 @@
+import _ from 'lodash'
 import postcss from 'postcss'
+import config from '../defaultConfig.stub.js'
 import plugin from '../src/lib/evaluateTailwindFunctions'
+import processPlugins from '../src/util/processPlugins'
 
-function run(input, opts = {}) {
-  return postcss([plugin(opts)]).process(input, { from: undefined })
+function run(input, opts = config) {
+  return postcss([
+    plugin(opts, processPlugins(_.get(opts, 'plugins', []), opts).configValues),
+  ]).process(input, {
+    from: undefined,
+  })
 }
 
 test('it looks up values in the config using dot notation', () => {
@@ -80,3 +87,48 @@ test('quotes are preserved around default values', () => {
     expect(result.warnings().length).toBe(0)
   })
 })
+
+test('plugins can register values that should be available to the config function', () => {
+  const input = `
+    .banana { color: config('banana.sandwich'); }
+  `
+
+  const output = `
+    .banana { color: blue; }
+  `
+
+  return run(input, {
+    plugins: [
+      function({ addConfig }) {
+        addConfig('banana', {
+          sandwich: 'blue',
+        })
+      },
+    ],
+  }).then(result => {
+    expect(result.css).toMatchCss(output)
+    expect(result.warnings().length).toBe(0)
+  })
+})
+
+test('plugin config values do not override first-class config values', () => {
+  const input = `
+    .banana { color: config('separator'); }
+  `
+
+  const output = `
+    .banana { color: _; }
+  `
+
+  return run(input, {
+    separator: '_',
+    plugins: [
+      function({ addConfig }) {
+        addConfig('separator', '+')
+      },
+    ],
+  }).then(result => {
+    expect(result.css).toMatchCss(output)
+    expect(result.warnings().length).toBe(0)
+  })
+})

src/lib/evaluateTailwindFunctions.js

@@ -1,11 +1,12 @@
 import _ from 'lodash'
 import functions from 'postcss-functions'
 
-export default function(config) {
+export default function(config, pluginConfigValues) {
   return functions({
     functions: {
       config: (path, defaultValue) => {
-        return _.get(config, _.trim(path, `'"`), defaultValue)
+        const trimmedPath = _.trim(path, `'"`)
+        return _.get(config, trimmedPath, _.get(pluginConfigValues, trimmedPath, defaultValue))
       },
     },
   })

src/processTailwindFeatures.js

@@ -18,7 +18,7 @@ export default function(getConfig) {
 
     return postcss([
       substituteTailwindAtRules(config, processedPlugins),
-      evaluateTailwindFunctions(config),
+      evaluateTailwindFunctions(config, processedPlugins.configValues),
       substituteVariantsAtRules(config, processedPlugins),
       substituteResponsiveAtRules(config),
       substituteScreenAtRules(config),

src/util/processPlugins.js

@@ -19,6 +19,7 @@ export default function(plugins, config) {
   const pluginComponents = []
   const pluginUtilities = []
   const pluginVariantGenerators = {}
+  const pluginConfigValues = {}
 
   plugins.forEach(plugin => {
     plugin({
@@ -64,6 +65,9 @@ export default function(plugins, config) {
       addVariant: (name, generator) => {
         pluginVariantGenerators[name] = generateVariantFunction(generator)
       },
+      addConfig: (namespace, value) => {
+        pluginConfigValues[namespace] = value
+      },
     })
   })
 
@@ -71,5 +75,6 @@ export default function(plugins, config) {
     components: pluginComponents,
     utilities: pluginUtilities,
     variantGenerators: pluginVariantGenerators,
+    configValues: pluginConfigValues,
   }
 }