diff --git a/src/vs/base/common/map.ts b/src/vs/base/common/map.ts
index f274d1a72d67db5ec27dd5b18c2417566e909aef..a2f048b67edf25f84d05bd330103c2a19ae5ddfa 100644
--- a/src/vs/base/common/map.ts
+++ b/src/vs/base/common/map.ts
@@ -296,3 +296,75 @@ export class LRUCache<T> extends BoundedLinkedMap<T> {
 		return null;
 	}
 }
+
+// --- trie'ish datastructure
+
+interface Node<E> {
+	element?: E;
+	children: { [key: string]: Node<E> };
+}
+
+/**
+ * A trie map that allows for fast look up when keys are substrings
+ * to the actual search keys (dir/subdir-problem).
+ */
+export class TrieMap<E> {
+
+	static PathSplitter = s => s.split(/[\\/]/);
+
+	private _splitter: (s: string) => string[];
+	private _root: Node<E> = { children: Object.create(null) };
+
+	constructor(splitter: (s: string) => string[]) {
+		this._splitter = splitter;
+	}
+
+	insert(path: string, element: E): void {
+		const parts = this._splitter(path);
+		let i = 0;
+
+		// find insertion node
+		let node = this._root;
+		for (; i < parts.length; i++) {
+			let child = node.children[parts[i]];
+			if (child) {
+				node = child;
+				continue;
+			}
+			break;
+		}
+
+		// create new nodes
+		let newNode: Node<E>;
+		for (; i < parts.length; i++) {
+			newNode = { children: Object.create(null) };
+			node.children[parts[i]] = newNode;
+			node = newNode;
+		}
+
+		node.element = element;
+	}
+
+	findSubstr(path: string): E {
+		const parts = this._splitter(path);
+
+		let lastNode: Node<E>;
+		let {children} = this._root;
+		for (const part of parts) {
+			const node = children[part];
+			if (!node) {
+				break;
+			}
+			if (node.element) {
+				lastNode = node;
+			}
+			children = node.children;
+		}
+
+		// return the last matching node
+		// that had an element
+		if (lastNode) {
+			return lastNode.element;
+		}
+	}
+}
diff --git a/src/vs/base/test/common/map.test.ts b/src/vs/base/test/common/map.test.ts
index 64d92dcf0ef38a82930084315744ccbf5a81ca5e..39545b12627f92592bd08d5afbbbb8e0e78ef9b6 100644
--- a/src/vs/base/test/common/map.test.ts
+++ b/src/vs/base/test/common/map.test.ts
@@ -5,7 +5,7 @@
 
 'use strict';
 
-import { BoundedLinkedMap, LRUCache, LinkedMap } from 'vs/base/common/map';
+import { BoundedLinkedMap, LRUCache, LinkedMap, TrieMap } from 'vs/base/common/map';
 import * as assert from 'assert';
 
 suite('Map', () => {
@@ -271,4 +271,23 @@ suite('Map', () => {
 		assert.ok(!cache.has('3'));
 		assert.ok(!cache.has('4'));
 	});
+
+
+	test('TrieMap - basics', function () {
+
+		const map = new TrieMap<number>(TrieMap.PathSplitter);
+
+		map.insert('/user/foo/bar', 1);
+		map.insert('/user/foo', 2);
+		map.insert('/user/foo/flip/flop', 3);
+
+		assert.equal(map.findSubstr('/user/bar'), undefined);
+		assert.equal(map.findSubstr('/user/foo'), 2);
+		assert.equal(map.findSubstr('\\user\\foo'), 2);
+		assert.equal(map.findSubstr('/user/foo/ba'), 2);
+		assert.equal(map.findSubstr('/user/foo/far/boo'), 2);
+		assert.equal(map.findSubstr('/user/foo/bar'), 1);
+		assert.equal(map.findSubstr('/user/foo/bar/far/boo'), 1);
+
+	});
 });
diff --git a/src/vs/workbench/api/node/extHost.api.impl.ts b/src/vs/workbench/api/node/extHost.api.impl.ts
index ff787b6ee678dcdb1685dcb337ce7dc63d902982..85097ec0ad5f3776cd612dc5af33326361ccad71 100644
--- a/src/vs/workbench/api/node/extHost.api.impl.ts
+++ b/src/vs/workbench/api/node/extHost.api.impl.ts
@@ -5,6 +5,7 @@
 'use strict';
 
 import { Emitter } from 'vs/base/common/event';
+import { TrieMap } from 'vs/base/common/map';
 import { score } from 'vs/editor/common/modes/languageSelector';
 import * as Platform from 'vs/base/common/platform';
 import { IThreadService } from 'vs/workbench/services/thread/common/threadService';
@@ -425,7 +426,7 @@ export function defineAPI(factory: IExtensionApiFactory, extensions: IExtensionD
 	let defaultApiImpl: typeof vscode;
 
 	// create trie to enable fast 'filename -> extension id' look up
-	const trie = new TrieMap<IExtensionDescription>();
+	const trie = new TrieMap<IExtensionDescription>(TrieMap.PathSplitter);
 	for (const ext of extensions) {
 		if (ext.name) {
 			const path = realpathSync(ext.extensionFolderPath);
@@ -457,68 +458,3 @@ export function defineAPI(factory: IExtensionApiFactory, extensions: IExtensionD
 		return defaultApiImpl;
 	};
 }
-
-// --- trie'ish datastructure
-
-interface Node<E> {
-	element?: E;
-	children: { [key: string]: Node<E> };
-}
-
-class TrieMap<E> {
-
-	private static _sep = /[\\/]/;
-
-	private _root: Node<E> = {
-		children: Object.create(null)
-	};
-
-	insert(path: string, element: E): void {
-		const parts = path.split(TrieMap._sep);
-		let i = 0;
-
-		// find insertion node
-		let node = this._root;
-		for (; i < parts.length; i++) {
-			let child = node.children[parts[i]];
-			if (child) {
-				node = child;
-				continue;
-			}
-			break;
-		}
-
-		// create new nodes
-		let newNode: Node<E>;
-		for (; i < parts.length; i++) {
-			newNode = { children: Object.create(null) };
-			node.children[parts[i]] = newNode;
-			node = newNode;
-		}
-
-		newNode.element = element;
-	}
-
-	findSubstr(path: string): E {
-		const parts = path.split(TrieMap._sep);
-
-		let lastNode: Node<E>;
-		let {children} = this._root;
-		for (const part of parts) {
-			const node = children[part];
-			if (!node) {
-				break;
-			}
-			if (node.element) {
-				lastNode = node;
-			}
-			children = node.children;
-		}
-
-		// return the last matching node
-		// that had an element
-		if (lastNode) {
-			return lastNode.element;
-		}
-	}
-}
\ No newline at end of file