Add MCP Root change notifications (#6502)

2 files changed, 126 insertions, 4 deletions

diff --git a/packages/core/src/utils/workspaceContext.test.ts b/packages/core/src/utils/workspaceContext.test.ts
index 5446c287..30c9ae16 100644
--- a/packages/core/src/utils/workspaceContext.test.ts
+++ b/packages/core/src/utils/workspaceContext.test.ts
@@ -4,7 +4,7 @@
  * SPDX-License-Identifier: Apache-2.0
  */
 
-import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest';
 import * as fs from 'fs';
 import * as os from 'os';
 import * as path from 'path';
@@ -294,6 +294,88 @@ describe('WorkspaceContext with real filesystem', () => {
     });
   });
 
+  describe('onDirectoriesChanged', () => {
+    it('should call listener when adding a directory', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      const listener = vi.fn();
+      workspaceContext.onDirectoriesChanged(listener);
+
+      workspaceContext.addDirectory(otherDir);
+
+      expect(listener).toHaveBeenCalledOnce();
+    });
+
+    it('should not call listener when adding a duplicate directory', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      workspaceContext.addDirectory(otherDir);
+      const listener = vi.fn();
+      workspaceContext.onDirectoriesChanged(listener);
+
+      workspaceContext.addDirectory(otherDir);
+
+      expect(listener).not.toHaveBeenCalled();
+    });
+
+    it('should call listener when setting different directories', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      const listener = vi.fn();
+      workspaceContext.onDirectoriesChanged(listener);
+
+      workspaceContext.setDirectories([otherDir]);
+
+      expect(listener).toHaveBeenCalledOnce();
+    });
+
+    it('should not call listener when setting same directories', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      const listener = vi.fn();
+      workspaceContext.onDirectoriesChanged(listener);
+
+      workspaceContext.setDirectories([cwd]);
+
+      expect(listener).not.toHaveBeenCalled();
+    });
+
+    it('should support multiple listeners', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      const listener1 = vi.fn();
+      const listener2 = vi.fn();
+      workspaceContext.onDirectoriesChanged(listener1);
+      workspaceContext.onDirectoriesChanged(listener2);
+
+      workspaceContext.addDirectory(otherDir);
+
+      expect(listener1).toHaveBeenCalledOnce();
+      expect(listener2).toHaveBeenCalledOnce();
+    });
+
+    it('should allow unsubscribing a listener', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      const listener = vi.fn();
+      const unsubscribe = workspaceContext.onDirectoriesChanged(listener);
+
+      unsubscribe();
+      workspaceContext.addDirectory(otherDir);
+
+      expect(listener).not.toHaveBeenCalled();
+    });
+
+    it('should not fail if a listener throws an error', () => {
+      const workspaceContext = new WorkspaceContext(cwd);
+      const errorListener = () => {
+        throw new Error('test error');
+      };
+      const listener = vi.fn();
+      workspaceContext.onDirectoriesChanged(errorListener);
+      workspaceContext.onDirectoriesChanged(listener);
+
+      expect(() => {
+        workspaceContext.addDirectory(otherDir);
+      }).not.toThrow();
+      expect(listener).toHaveBeenCalledOnce();
+    });
+  });
+
   describe('getDirectories', () => {
     it('should return a copy of directories array', () => {
       const workspaceContext = new WorkspaceContext(cwd);
diff --git a/packages/core/src/utils/workspaceContext.ts b/packages/core/src/utils/workspaceContext.ts
index be99a83c..924cd601 100644
--- a/packages/core/src/utils/workspaceContext.ts
+++ b/packages/core/src/utils/workspaceContext.ts
@@ -8,6 +8,8 @@ import { isNodeError } from '../utils/errors.js';
 import * as fs from 'fs';
 import * as path from 'path';
 
+export type Unsubscribe = () => void;
+
 /**
  * WorkspaceContext manages multiple workspace directories and validates paths
  * against them. This allows the CLI to operate on files from multiple directories
@@ -16,6 +18,7 @@ import * as path from 'path';
 export class WorkspaceContext {
   private directories = new Set<string>();
   private initialDirectories: Set<string>;
+  private onDirectoriesChangedListeners = new Set<() => void>();
 
   /**
    * Creates a new WorkspaceContext with the given initial directory and optional additional directories.
@@ -32,12 +35,41 @@ export class WorkspaceContext {
   }
 
   /**
+   * Registers a listener that is called when the workspace directories change.
+   * @param listener The listener to call.
+   * @returns A function to unsubscribe the listener.
+   */
+  onDirectoriesChanged(listener: () => void): Unsubscribe {
+    this.onDirectoriesChangedListeners.add(listener);
+    return () => {
+      this.onDirectoriesChangedListeners.delete(listener);
+    };
+  }
+
+  private notifyDirectoriesChanged() {
+    // Iterate over a copy of the set in case a listener unsubscribes itself or others.
+    for (const listener of [...this.onDirectoriesChangedListeners]) {
+      try {
+        listener();
+      } catch (e) {
+        // Don't let one listener break others.
+        console.error('Error in WorkspaceContext listener:', e);
+      }
+    }
+  }
+
+  /**
    * Adds a directory to the workspace.
    * @param directory The directory path to add (can be relative or absolute)
    * @param basePath Optional base path for resolving relative paths (defaults to cwd)
    */
   addDirectory(directory: string, basePath: string = process.cwd()): void {
-    this.directories.add(this.resolveAndValidateDir(directory, basePath));
+    const resolved = this.resolveAndValidateDir(directory, basePath);
+    if (this.directories.has(resolved)) {
+      return;
+    }
+    this.directories.add(resolved);
+    this.notifyDirectoriesChanged();
   }
 
   private resolveAndValidateDir(
@@ -72,9 +104,17 @@ export class WorkspaceContext {
   }
 
   setDirectories(directories: readonly string[]): void {
-    this.directories.clear();
+    const newDirectories = new Set<string>();
     for (const dir of directories) {
-      this.addDirectory(dir);
+      newDirectories.add(this.resolveAndValidateDir(dir));
+    }
+
+    if (
+      newDirectories.size !== this.directories.size ||
+      ![...newDirectories].every((d) => this.directories.has(d))
+    ) {
+      this.directories = newDirectories;
+      this.notifyDirectoriesChanged();
     }
   }