Make handler optional in object plugins

__tests__/processPlugins.test.js

@@ -1244,3 +1244,46 @@ test('plugins can be provided as an object with a handler function', () => {
     }
   `)
 })
+
+test('plugins can provide a config but no handler', () => {
+  const { components, utilities } = processPlugins(
+    [
+      {
+        config: {
+          prefix: 'tw-',
+        },
+      },
+      {
+        handler({ addUtilities }) {
+          addUtilities({
+            '.object-fill': {
+              'object-fit': 'fill',
+            },
+            '.object-contain': {
+              'object-fit': 'contain',
+            },
+            '.object-cover': {
+              'object-fit': 'cover',
+            },
+          })
+        },
+      },
+    ],
+    makeConfig()
+  )
+
+  expect(components.length).toBe(0)
+  expect(css(utilities)).toMatchCss(`
+    @variants {
+      .object-fill {
+        object-fit: fill
+      }
+      .object-contain {
+        object-fit: contain
+      }
+      .object-cover {
+        object-fit: cover
+      }
+    }
+  `)
+})

__tests__/resolveConfig.test.js

@@ -1367,7 +1367,6 @@ test('plugin config modifications are applied', () => {
         config: {
           prefix: 'tw-',
         },
-        handler() {},
       },
     ],
   }
@@ -1416,7 +1415,6 @@ test('user config takes precedence over plugin config modifications', () => {
         config: {
           prefix: 'tw-',
         },
-        handler() {},
       },
     ],
   }
@@ -1468,13 +1466,11 @@ test('plugin config can register plugins that also have config', () => {
               config: {
                 important: true,
               },
-              handler() {},
             },
             {
               config: {
                 separator: '__',
               },
-              handler() {},
             },
           ],
         },
@@ -1530,7 +1526,6 @@ test('plugin configs take precedence over plugin configs registered by that plug
               config: {
                 prefix: 'inner-',
               },
-              handler() {},
             },
           ],
         },

src/util/processPlugins.js

@@ -29,7 +29,7 @@ export default function(plugins, config) {
   const getConfigValue = (path, defaultValue) => _.get(config, path, defaultValue)
 
   plugins.forEach(plugin => {
-    const handler = isFunction(plugin) ? plugin : plugin.handler
+    const handler = isFunction(plugin) ? plugin : _.get(plugin, 'handler', () => {})
 
     handler({
       postcss,