Try to automatically fix temp folder permissions on windows

manual/faq.rst

@@ -790,7 +790,9 @@ folder.
 Some users have reported that running the following command in an Administrator
 Command Prompt fixed their permissions.  To get an Administrator Command Prompt
 search for cmd.exe in the start menu, then right click on the command prompt
-entry and select Run as Administrator::
+entry and select Run as Administrator. At the command prompt type the following
+command and press Enter::
+
     icacls "%appdata%\..\Local\Temp" /reset /T
 
 Alternately, you can run calibre as Administrator, but doing so will cause

src/calibre/__init__.py

@@ -436,13 +436,21 @@ def fit_image(width, height, pwidth, pheight):
 
 class CurrentDir(object):
 
-    def __init__(self, path):
+    def __init__(self, path, workaround_temp_folder_permissions=False):
         self.path = path
         self.cwd = None
+        self.workaround_temp_folder_permissions = workaround_temp_folder_permissions
 
     def __enter__(self, *args):
         self.cwd = os.getcwdu()
-        os.chdir(self.path)
+        try:
+            os.chdir(self.path)
+        except OSError:
+            if not self.workaround_temp_folder_permissions:
+                raise
+            from calibre.ptempfile import reset_temp_folder_permissions
+            reset_temp_folder_permissions()
+            os.chdir(self.path)
         return self.cwd
 
     def __exit__(self, *args):

src/calibre/customize/conversion.py

@@ -233,7 +233,7 @@ class InputFormatPlugin(Plugin):
             # In case stdout is broken
             pass
 
-        with CurrentDir(output_dir):
+        with CurrentDir(output_dir, workaround_temp_folder_permissions=True):
             for x in os.listdir('.'):
                 shutil.rmtree(x) if os.path.isdir(x) else os.remove(x)
 

src/calibre/ptempfile.py

@@ -34,6 +34,19 @@ def app_prefix(prefix):
         return '%s_'%__appname__
     return '%s_%s_%s'%(__appname__, __version__, prefix)
 
+def reset_temp_folder_permissions():
+    # There are some broken windows installs where the permissions for the temp
+    # folder are set to not be executable, which means chdir() into temp
+    # folders fails. Try to fix that by resetting the permissions on the temp
+    # folder.
+    global _base_dir
+    if iswindows and _base_dir:
+        import subprocess
+        from calibre import prints
+        parent = os.path.dirname(_base_dir)
+        retcode = subprocess.Popen(['icacls.exe', parent, '/reset', '/Q', '/T']).wait()
+        prints('Trying to reset permissions of temp folder', parent, 'return code:', retcode)
+
 def base_dir():
     global _base_dir
     if _base_dir is not None and not os.path.exists(_base_dir):