fix: show better error for missing widgets (#3377)

packages/netlify-cms-core/src/lib/__tests__/registry.spec.js

@@ -147,4 +147,26 @@ describe('registry', () => {
       });
     });
   });
+
+  describe('getWidget', () => {
+    it('should throw on missing widget', () => {
+      const { getWidget } = require('../registry');
+
+      expect(() => getWidget('Unknown')).toThrow(
+        new Error(
+          `Could not find widget 'Unknown'. Please make sure the widget name is configured correctly or register it via 'registerwidget'.`,
+        ),
+      );
+    });
+
+    it('should throw on missing widget and suggest lowercase name', () => {
+      const { getWidget, registerWidget } = require('../registry');
+
+      registerWidget('string', {});
+
+      expect(() => getWidget('String')).toThrow(
+        new Error(`Could not find widget 'String'. Did you mean 'string'?`),
+      );
+    });
+  });
 });

packages/netlify-cms-core/src/lib/registry.js

@@ -113,7 +113,16 @@ export function registerWidget(name, control, preview) {
   }
 }
 export function getWidget(name) {
-  return registry.widgets[name];
+  const widget = registry.widgets[name];
+  if (!widget) {
+    const nameLowerCase = name.toLowerCase();
+    const hasLowerCase = !!registry.widgets[nameLowerCase];
+    const message = hasLowerCase
+      ? `Could not find widget '${name}'. Did you mean '${nameLowerCase}'?`
+      : `Could not find widget '${name}'. Please make sure the widget name is configured correctly or register it via 'registerwidget'.`;
+    throw new Error(message);
+  }
+  return widget;
 }
 export function getWidgets() {
   return produce(Object.entries(registry.widgets), draft => {