Make error message unique

Summary: We're currently getting errors for every duplicate key and can't easily unify them, so we're adding the additional information to a warning instead.

Reviewed By: mweststrate

Differential Revision: D30337821

fbshipit-source-id: db9dc44d7d3424de169bed9b4447b482e411eb19

desktop/flipper-plugin/src/data-source/DataSource.tsx

@@ -212,7 +212,13 @@ export class DataSource<T> {
     if (this.keyAttribute) {
       const key = this.getKey(value);
       if (this._recordsById.has(key)) {
-        throw new Error(`Duplicate key: '${key}'`);
+        const existingValue = this._recordsById.get(key);
+        console.warn(
+          `Tried to append value with duplicate key: ${key} (key attribute is ${this.keyAttribute}). Old/new values:`,
+          existingValue,
+          value,
+        );
+        throw new Error(`Duplicate key`);
       }
       this._recordsById.set(key, value);
       this.storeIndexOfKey(key, this._records.length);

desktop/flipper-plugin/src/data-source/__tests__/datasource-basics.node.tsx

@@ -116,7 +116,7 @@ test('throws on invalid keys', () => {
   }).toThrow(`Invalid key value: ''`);
   expect(() => {
     ds.append({id: 'cookie', title: 'test'});
-  }).toThrow(`Duplicate key: 'cookie'`);
+  }).toThrow(`Duplicate key`);
 });
 
 test('throws on update causing duplicate key', () => {