Add a disableable watcher wrapper.

Author: ericsnowcurrently

src/client/pythonEnvironments/base/watchers.ts

@@ -1,7 +1,8 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
-import { Event } from 'vscode';
+import { Disposable, Event } from 'vscode';
+import { Disableable } from '../../common/utils/misc';
 import { IPythonEnvsWatcher, PythonEnvsChangedEvent, PythonEnvsWatcher } from './watcher';
 
 /**
@@ -21,3 +22,33 @@ export class PythonEnvsWatchers {
         });
     }
 }
+
+// tslint:disable-next-line:no-any
+type EnvsEventListener = (e: PythonEnvsChangedEvent) => any;
+
+/**
+ * A watcher wrapper that can be disabled.
+ *
+ * If disabled, events emitted by the wrapped watcher are discarded.
+ */
+export class DisableableEnvsWatcher extends Disableable {
+    constructor(
+        // To wrap more than one use `PythonEnvWatchers`.
+        private readonly wrapped: IPythonEnvsWatcher
+    ) {
+        super();
+    }
+
+    // tslint:disable-next-line:no-any
+    public onChanged(listener: EnvsEventListener, thisArgs?: any, disposables?: Disposable[]): Disposable {
+        return this.wrapped.onChanged(
+            (e: PythonEnvsChangedEvent) => {
+                if (this.isEnabled) {
+                    listener(e);
+                }
+            },
+            thisArgs,
+            disposables
+        );
+    }
+}