Force upper case drive names in external terminal

This change needs to be made at this layer since a change to URI.fsPath
(the root cause) is too risky as lower case drives are relied upon.

Part of #9448

src/vs/workbench/parts/execution/electron-browser/terminalService.ts

@@ -2,6 +2,7 @@
  *  Copyright (c) Microsoft Corporation. All rights reserved.
  *  Licensed under the MIT License. See License.txt in the project root for license information.
  *--------------------------------------------------------------------------------------------*/
+
 'use strict';
 
 import cp = require('child_process');
@@ -71,6 +72,11 @@ export class WinTerminalService implements ITerminalService {
 		// contains spaces
 		let cmdArgs = ['/c', 'start', '/wait', '""', exec];
 
+		// Make the drive letter uppercase on Windows (see #9448)
+		if (path && path[1] === ':') {
+			path = path[0].toUpperCase() + path.substr(1);
+		}
+
 		return new TPromise<void>((c, e) => {
 			let env = path ? { cwd: path } : void 0;
 			let child = spawner.spawn(command, cmdArgs, env);

src/vs/workbench/parts/execution/test/electron-browser/terminalService.test.ts

@@ -79,6 +79,30 @@ suite('Execution - TerminalService', () => {
 		);
 	});
 
+	test("WinTerminalService - uses default terminal when configuration.terminal.external.windowsExec is undefined", done => {
+		let testShell = 'cmd';
+		let testCwd = 'c:/foo';
+		let mockSpawner = {
+			spawn: (command, args, opts) => {
+				// assert
+				equal(opts.cwd, 'C:/foo', 'cwd should be uppercase regardless of the case that\'s passed in');
+				done();
+				return {
+					on: (evt) => evt
+				}
+			}
+		};
+		let testService = new WinTerminalService(mockConfig);
+		(<any>testService).spawnTerminal(
+			mockSpawner,
+			mockConfig,
+			testShell,
+			testCwd,
+			mockOnExit,
+			mockOnError
+		);
+	});
+
 	test("MacTerminalService - uses terminal from configuration", done => {
 		let testCwd = 'path/to/workspace';
 		let mockSpawner = {