[modules/arch-update] Gracefully handle exit code 2

fixes #624

bumblebee_status/modules/contrib/arch-update.py

@@ -33,13 +33,16 @@ class Module(core.module.Module):
         return self.__packages == 0 and not self.__error
 
     def update(self):
-        try:
-            result = util.cli.execute("checkupdates")
-            self.__packages = len(result.split("\n")) - 1
         self.__error = False
-        except Exception as e:
-            logging.exception(e)
+        code, result = util.cli.execute("checkupdates", ignore_errors=True, return_exitcode=True)
+
+        if code == 0:
+            self.__packages = len(result.split("\n"))
+        elif code == 2:
+            self.__packages = 0
+        else:
             self.__error = True
+            log.error("checkupdates exited with {}: {}".format(code, result))
 
     def state(self, widget):
         if self.__error:

bumblebee_status/util/cli.py

@@ -4,7 +4,7 @@ import subprocess
 import logging
 
 
-def execute(cmd, wait=True, ignore_errors=False, include_stderr=False, env=None):
+def execute(cmd, wait=True, ignore_errors=False, include_stderr=False, env=None, return_exitcode=False):
     """Executes a commandline utility and returns its output
 
     :param cmd: the command (as string) to execute, returns the program's output
@@ -12,11 +12,12 @@ def execute(cmd, wait=True, ignore_errors=False, include_stderr=False, env=None)
     :param ignore_errors: set to True to return a string when an exception is thrown, otherwise might throw, defaults to False
     :param include_stderr: set to True to include stderr output in the return value, defaults to False
     :param env: provide a dict here to specify a custom execution environment, defaults to None
+    :param return_exitcode: set to True to return a pair, where the first member is the exit code and the message the second, defaults to False
 
     :raises RuntimeError: the command either didn't exist or didn't exit cleanly, and ignore_errors was set to False
 
-    :return: output of cmd, or stderr, if ignore_errors is True and the command failed
-    :rtype: string
+    :return: output of cmd, or stderr, if ignore_errors is True and the command failed; or a tuple of exitcode and the previous, if return_exitcode is set to True
+    :rtype: string or tuple (if return_exitcode is set to True)
     """
     args = shlex.split(cmd)
     logging.debug(cmd)
@@ -35,10 +36,11 @@ def execute(cmd, wait=True, ignore_errors=False, include_stderr=False, env=None)
         if proc.returncode != 0:
             err = "{} exited with code {}".format(cmd, proc.returncode)
             if ignore_errors:
-                return err
+                return (proc.returncode, err) if return_exitcode else err
             raise RuntimeError(err)
-        return out.decode("utf-8")
-    return ""
+        res = out.decode("utf-8")
+        return (proc.returncode, res) if return_exitcode else res
+    return (0, "") if return_exitcode else ""
 
 
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