Add explorer check using SystemRoot path

Closes #4551

spec/buffered-process-spec.coffee

@@ -1,4 +1,5 @@
 BufferedProcess  = require '../src/buffered-process'
+ChildProcess = require 'child_process'
 
 describe "BufferedProcess", ->
   describe "when a bad command is specified", ->
@@ -40,3 +41,26 @@ describe "BufferedProcess", ->
           expect(window.onerror).toHaveBeenCalled()
           expect(window.onerror.mostRecentCall.args[0]).toContain 'Failed to spawn command `bad-command-nope`'
           expect(window.onerror.mostRecentCall.args[4].name).toBe 'BufferedProcessError'
+
+  describe "when the explorer command is spawned on Windows", ->
+    originalPlatform = null
+
+    beforeEach ->
+      # Prevent any commands from actually running and affecting the host
+      originalSpawn = ChildProcess.spawn
+      spyOn(ChildProcess, 'spawn').andCallFake ->
+        # Just spawn something that won't actually modify the host
+        if originalPlatform is 'win32'
+          originalSpawn('dir')
+        else
+          originalSpawn('ls')
+
+      originalPlatform = process.platform
+      Object.defineProperty process, 'platform', value: 'win32'
+
+    afterEach ->
+      Object.defineProperty process, 'platform', value: originalPlatform
+
+    it "doesn't quote arguments of the form /root,C...", ->
+      new BufferedProcess({command: 'explorer.exe', args: ['/root,C:\\foo']})
+      expect(ChildProcess.spawn.argsForCall[0][1][2]).toBe '"explorer.exe /root,C:\\foo"'

src/buffered-process.coffee

@@ -47,12 +47,12 @@ class BufferedProcess
     @emitter = new Emitter
     options ?= {}
     # Related to joyent/node#2318
-    if process.platform is "win32"
+    if process.platform is 'win32'
       # Quote all arguments and escapes inner quotes
       if args?
         cmdArgs = args.filter (arg) -> arg?
-        cmdArgs = cmdArgs.map (arg) ->
-          if command in ['explorer.exe', 'explorer'] and /^\/[a-zA-Z]+,.*$/.test(arg)
+        cmdArgs = cmdArgs.map (arg) =>
+          if @isExplorerCommand(command) and /^\/[a-zA-Z]+,.*$/.test(arg)
             # Don't wrap /root,C:\folder style arguments to explorer calls in
             # quotes since they will not be interpreted correctly if they are
             arg
@@ -191,6 +191,14 @@ class BufferedProcess
     @process?.kill()
     @process = null
 
+  isExplorerCommand: (command) ->
+    if command is 'explorer.exe' or command is 'explorer'
+      true
+    else if process.env.SystemRoot
+      command is path.join(process.env.SystemRoot, 'explorer.exe') or command is path.join(process.env.SystemRoot, 'explorer')
+    else
+      false
+
   # Public: Terminate the process.
   kill: ->
     return if @killed