Suppress console flash on Windows

elm_format.py

@@ -12,11 +12,8 @@
 
 class ElmFormatCommand(sublime_plugin.TextCommand):
     def run(self, edit):
-        # Hide the console window on Windows
-        shell = False
         path_separator = ':'
         if os.name == "nt":
-            shell = True
             path_separator = ';'
 
         binary = self.get_setting('elm_format_binary') or 'elm-format'
@@ -28,7 +25,13 @@ def run(self, edit):
 
         working_dir = self.working_dir()
         command = binary.split() + [self.view.file_name(), '--yes'] + options.split()
-        p = subprocess.Popen(command, cwd=working_dir, stdout=subprocess.PIPE, stderr=subprocess.PIPE, shell=shell)
+        p = subprocess.Popen(
+            command,
+            cwd=working_dir,
+            stdout=subprocess.PIPE,
+            stderr=subprocess.PIPE,
+            startupinfo=get_popen_startupinfo()
+        )
 
         if path:
             os.environ['PATH'] = old_path

elm_make.py

@@ -54,7 +54,8 @@ def run(self, cmd=[], kill=False):
             self.format_cmd(cmd),
             stdout=subprocess.PIPE,
             stderr=subprocess.STDOUT,
-            cwd=working_dir
+            cwd=working_dir,
+            startupinfo=get_popen_startupinfo()
         )
         self.killed = False
 

elm_plugin.py

@@ -1,6 +1,8 @@
 import sublime
 import sublime_plugin
+import os
 import os.path as fs
+import subprocess
 
 def is_ST2():
     return sublime.version().startswith('2')
@@ -66,3 +68,19 @@ def new(cls, *args, **kwargs):
         return target_cls
 
     return decorator
+
+# Construct STARTUPINFO value that can be passed to Popen constructor on
+# Windows to suppress the console window that otherwise gets flashed when
+# elm.exe or elm-format.exe is run; this is more secure than passing
+# 'shell=True'.
+#
+# https://stackoverflow.com/questions/1765078/how-to-avoid-console-window-with-pyw-file-containing-os-system-call/12964900#12964900
+# https://docs.python.org/3.3/library/subprocess.html#subprocess.STARTUPINFO
+def get_popen_startupinfo():
+    if os.name == 'nt':
+        startupinfo = subprocess.STARTUPINFO()
+        startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW
+        startupinfo.wShowWindow = subprocess.SW_HIDE
+        return startupinfo
+    else:
+        return None