Fix empty XDG_* environment variables.

Use fallback, if an enviroment variable is unset *or* empty.

Bug:
- XDG_CONFIG_HOME='' alot

Problem:
Does not find the configuration file (among others), because
os.environ.get('XDG_CONFIG_HOME', '~/.config') returns '', instead of
'~/.config'.

5 files changed, 42 insertions, 9 deletions

diff --git a/alot/__main__.py b/alot/__main__.py
index ee5e442a..207c8b92 100644
--- a/alot/__main__.py
+++ b/alot/__main__.py
@@ -11,6 +11,7 @@ import sys
 import alot
 from alot.settings.const import settings
 from alot.settings.errors import ConfigError
+from alot.helper import get_env
 from alot.db.manager import DBManager
 from alot.ui import UI
 from alot.commands import *
@@ -92,9 +93,8 @@ def main():
 
     # locate alot config files
     if options.config is None:
-        alotconfig = os.path.join(
-            os.environ.get('XDG_CONFIG_HOME', os.path.expanduser('~/.config')),
-            'alot', 'config')
+        xdg_dir = get_env('XDG_CONFIG_HOME', os.path.expanduser('~/.config'))
+        alotconfig = os.path.join(xdg_dir, 'alot', 'config')
         if os.path.exists(alotconfig):
             settings.alot_rc_path = alotconfig
     else:
diff --git a/alot/helper.py b/alot/helper.py
index be5191d8..06362e06 100644
--- a/alot/helper.py
+++ b/alot/helper.py
@@ -625,3 +625,9 @@ def email_as_string(mail):
                            as_string, flags=re.MULTILINE)
 
     return as_string
+
+
+def get_env(env_name, fallback):
+    """ Gets environment variable and returns fallback if unset or empty """
+    env = os.environ.get(env_name)
+    return env if env else fallback
diff --git a/alot/settings/manager.py b/alot/settings/manager.py
index 296ef22b..99954639 100644
--- a/alot/settings/manager.py
+++ b/alot/settings/manager.py
@@ -15,7 +15,7 @@ from configobj import ConfigObj, Section
 from ..account import SendmailAccount
 from ..addressbook.abook import AbookAddressBook
 from ..addressbook.external import ExternalAddressbook
-from ..helper import pretty_datetime, string_decode
+from ..helper import pretty_datetime, string_decode, get_env
 from ..utils import configobj as checks
 
 from .errors import ConfigError, NoMatchingAccount
@@ -25,8 +25,8 @@ from .theme import Theme
 
 
 DEFAULTSPATH = os.path.join(os.path.dirname(__file__), '..', 'defaults')
-DATA_DIRS = os.environ.get('XDG_DATA_DIRS',
-                           '/usr/local/share:/usr/share').split(':')
+DATA_DIRS = get_env('XDG_DATA_DIRS',
+                    '/usr/local/share:/usr/share').split(':')
 
 
 class SettingsManager(object):
@@ -157,8 +157,8 @@ class SettingsManager(object):
         if path:
             path = os.path.expanduser(path)
         else:
-            xdgdir = os.environ.get('XDG_CONFIG_HOME',
-                                    os.path.expanduser('~/.config'))
+            xdgdir = get_env('XDG_CONFIG_HOME',
+                             os.path.expanduser('~/.config'))
             path = os.path.join(xdgdir, fallback)
 
         self._config[setting_name] = path
diff --git a/alot/ui.py b/alot/ui.py
index c97f2fc1..6c0dea6e 100644
--- a/alot/ui.py
+++ b/alot/ui.py
@@ -18,6 +18,7 @@ from .commands import CommandCanceled
 from .commands import CommandParseError
 from .helper import split_commandline
 from .helper import string_decode
+from .helper import get_env
 from .widgets.globals import CompleteEdit
 from .widgets.globals import ChoiceWidget
 
@@ -83,7 +84,7 @@ class UI(object):
 
         # load histories
         self._cache = os.path.join(
-            os.environ.get('XDG_CACHE_HOME', os.path.expanduser('~/.cache')),
+            get_env('XDG_CACHE_HOME', os.path.expanduser('~/.cache')),
             'alot', 'history')
         self._cmd_hist_file = os.path.join(self._cache, 'commands')
         self._sender_hist_file = os.path.join(self._cache, 'senders')
diff --git a/tests/helper_test.py b/tests/helper_test.py
index c2927725..02105a29 100644
--- a/tests/helper_test.py
+++ b/tests/helper_test.py
@@ -464,3 +464,29 @@ class TestCallCmdAsync(unittest.TestCase):
             yield helper.call_cmd_async(['_____better_not_exist'])
         self.assertEqual(cm.exception.exitCode, 1)
         self.assertTrue(cm.exception.stderr)
+
+
+class TestGetEnv(unittest.TestCase):
+    env_name = 'XDG_CONFIG_HOME'
+    default = '~/.config'
+
+    def test_env_not_set(self):
+        with mock.patch.dict('os.environ'):
+            if self.env_name in os.environ:
+                del os.environ[self.env_name]
+            self.assertEqual(helper.get_env(self.env_name, self.default),
+                             self.default)
+
+    def test_env_empty(self):
+        with mock.patch.dict('os.environ'):
+            os.environ[self.env_name] = ''
+            self.assertEqual(helper.get_env(self.env_name, self.default),
+                             self.default)
+
+    def test_env_not_empty(self):
+        custom_path = '/my/personal/config/home'
+
+        with mock.patch.dict('os.environ'):
+            os.environ[self.env_name] = custom_path
+            self.assertEqual(helper.get_env(self.env_name, self.default),
+                             custom_path)