🏁 Use PowerShell to get User path

in Windows when installing via Squirrel, replacing reg.exe
that fails to execute if registry editing is disabled in the group policy.

This was causing the user Path to get deleted if registry editing is
disabled.  The workaround that was in place kept the existing path, but
failed to add Atom to it.

src/browser/squirrel-update.coffee

@@ -11,9 +11,11 @@ exeName = path.basename(process.execPath)
 if process.env.SystemRoot
   system32Path = path.join(process.env.SystemRoot, 'System32')
   regPath = path.join(system32Path, 'reg.exe')
+  powershellPath = path.join(system32Path, 'WindowsPowerShell', 'v1.0', 'powershell.exe')
   setxPath = path.join(system32Path, 'setx.exe')
 else
   regPath = 'reg.exe'
+  powershellPath = 'powershell.exe'
   setxPath = 'setx.exe'
 
 # Registry keys used for context menu
@@ -43,11 +45,23 @@ spawn = (command, args, callback) ->
     error?.code ?= code
     error?.stdout ?= stdout
     callback?(error, stdout)
+  # This is necessary if using Powershell 2 on Windows 7 to get the events to raise
+  # http://stackoverflow.com/questions/9155289/calling-powershell-from-nodejs
+  spawnedProcess.stdin.end()
+
 
 # Spawn reg.exe and callback when it completes
 spawnReg = (args, callback) ->
   spawn(regPath, args, callback)
 
+# Spawn powershell.exe and callback when it completes
+spawnPowershell = (args, callback) ->
+  args.unshift('-command')
+  args.unshift('RemoteSigned')
+  args.unshift('-ExecutionPolicy')
+  args.unshift('-noprofile')
+  spawn(powershellPath, args, callback)
+
 # Spawn setx.exe and callback when it completes
 spawnSetx = (args, callback) ->
   spawn(setxPath, args, callback)
@@ -85,37 +99,17 @@ isAscii = (text) ->
 
 # Get the user's PATH environment variable registry value.
 getPath = (callback) ->
-  spawnReg ['query', environmentKeyPath, '/v', 'Path'], (error, stdout) ->
+  spawnPowershell ['[environment]::GetEnvironmentVariable(\'Path\',\'User\')'], (error, stdout) ->
     if error?
-      if error.code is 1
-        # FIXME Don't overwrite path when reading value is disabled
-        # https://github.com/atom/atom/issues/5092
-        if stdout.indexOf('ERROR: Registry editing has been disabled by your administrator.') isnt -1
-          return callback(error)
+      return callback(error)
 
-        # The query failed so the Path does not exist yet in the registry
-        return callback(null, '')
-      else
-        return callback(error)
-
-    # Registry query output is in the form:
-    #
-    # HKEY_CURRENT_USER\Environment
-    #     Path    REG_SZ    C:\a\folder\on\the\path;C\another\folder
-    #
-
-    lines = stdout.split(/[\r\n]+/).filter (line) -> line
-    segments = lines[lines.length - 1]?.split('    ')
-    if segments[1] is 'Path' and segments.length >= 3
-      pathEnv = segments?[3..].join('    ')
-      if isAscii(pathEnv)
-        callback(null, pathEnv)
-      else
-        # FIXME Don't corrupt non-ASCII PATH values
-        # https://github.com/atom/atom/issues/5063
-        callback(new Error('PATH contains non-ASCII values'))
+    pathOutput = stdout.replace(/^\s+|\s+$/g, '')
+    if isAscii(pathOutput)
+      callback(null, pathOutput)
     else
-      callback(new Error('Registry query for PATH failed'))
+      # FIXME Don't corrupt non-ASCII PATH values
+      # https://github.com/atom/atom/issues/5063
+      callback(new Error('PATH contains non-ASCII values'))
 
 # Uninstall the Open with Atom explorer context menu items via the registry.
 uninstallContextMenu = (callback) ->