make isUNC more spec compliant

src/vs/base/common/paths.ts

@@ -233,14 +233,48 @@ export const join: (...parts: string[]) => string = function () {
 };
 
 
+/**
+ * Check if the path follows this pattern: `\\hostname\sharename`.
+ *
+ * @see https://msdn.microsoft.com/en-us/library/gg465305.aspx
+ * @return A boolean indication if the path is a UNC path, on none-windows
+ * always false.
+ */
 export function isUNC(path: string): boolean {
-	if (!isWindows || !path) {
-		return false; // UNC is a windows concept
+	if (!isWindows) {
+		// UNC is a windows concept
+		return false;
 	}
 
-	path = this.normalize(path, true);
+	if (!path || path.length < 5) {
+		// at least \\a\b
+		return false;
+	}
 
-	return path[0] === nativeSep && path[1] === nativeSep;
+	let code = path.charCodeAt(0);
+	if (code !== _backslash) {
+		return false;
+	}
+	code = path.charCodeAt(1);
+	if (code !== _backslash) {
+		return false;
+	}
+	let pos = 2;
+	let start = pos;
+	for (; pos < path.length; pos++) {
+		code = path.charCodeAt(pos);
+		if (code === _backslash) {
+			break;
+		}
+	}
+	if (start === pos) {
+		return false;
+	}
+	code = path.charCodeAt(pos + 1);
+	if (isNaN(code) || code === _backslash) {
+		return false;
+	}
+	return true;
 }
 
 function isPosixAbsolute(path: string): boolean {

src/vs/base/test/common/paths.test.ts

@@ -174,14 +174,16 @@ suite('Paths', () => {
 	});
 
 	test('isUNC', () => {
-		assert(!paths.isUNC('foo'));
-		assert(!paths.isUNC('/foo'));
-		assert(!paths.isUNC('\\foo'));
-
 		if (platform.isWindows) {
-			assert(paths.isUNC('\\\\foo'));
-		} else {
-			assert(!paths.isUNC('\\\\foo'));
+			assert.ok(!paths.isUNC('foo'));
+			assert.ok(!paths.isUNC('/foo'));
+			assert.ok(!paths.isUNC('\\foo'));
+			assert.ok(!paths.isUNC('\\\\foo'));
+			assert.ok(paths.isUNC('\\\\a\\b'));
+			assert.ok(!paths.isUNC('//a/b'));
+			assert.ok(paths.isUNC('\\\\server\\share'));
+			assert.ok(paths.isUNC('\\\\server\\share\\'));
+			assert.ok(paths.isUNC('\\\\server\\share\\path'));
 		}
 	});