Show notification when there's a conflict with an extensions command (#17890)

packages/cli/src/services/SlashCommandConflictHandler.ts

@@ -0,0 +1,54 @@
+/**
+ * @license
+ * Copyright 2025 Google LLC
+ * SPDX-License-Identifier: Apache-2.0
+ */
+
+import {
+  coreEvents,
+  CoreEvent,
+  type SlashCommandConflictsPayload,
+} from '@google/gemini-cli-core';
+
+export class SlashCommandConflictHandler {
+  private notifiedConflicts = new Set<string>();
+
+  constructor() {
+    this.handleConflicts = this.handleConflicts.bind(this);
+  }
+
+  start() {
+    coreEvents.on(CoreEvent.SlashCommandConflicts, this.handleConflicts);
+  }
+
+  stop() {
+    coreEvents.off(CoreEvent.SlashCommandConflicts, this.handleConflicts);
+  }
+
+  private handleConflicts(payload: SlashCommandConflictsPayload) {
+    const newConflicts = payload.conflicts.filter((c) => {
+      const key = `${c.name}:${c.loserExtensionName}`;
+      if (this.notifiedConflicts.has(key)) {
+        return false;
+      }
+      this.notifiedConflicts.add(key);
+      return true;
+    });
+
+    if (newConflicts.length > 0) {
+      const conflictMessages = newConflicts
+        .map((c) => {
+          const winnerSource = c.winnerExtensionName
+            ? `extension '${c.winnerExtensionName}'`
+            : 'an existing command';
+          return `- Command '/${c.name}' from extension '${c.loserExtensionName}' was renamed to '/${c.renamedTo}' because it conflicts with ${winnerSource}.`;
+        })
+        .join('\n');
+
+      coreEvents.emitFeedback(
+        'info',
+        `Command conflicts detected:\n${conflictMessages}`,
+      );
+    }
+  }
+}