Make notmuch db location logic match upstream

alot/__main__.py

@@ -15,6 +15,7 @@
 from alot.commands import *
 from alot.commands import CommandParseError, COMMANDS
 from alot.utils import argparse as cargparse
+from alot.utils.notmuch import find_db
 
 from twisted.internet import asyncioreactor
 asyncioreactor.install()
@@ -120,8 +121,7 @@ def main():
         settings.set('colourmode', options.colour_mode)
 
     # get ourselves a database manager
-    indexpath = settings.get_notmuch_setting('database', 'path')
-    indexpath = options.mailindex_path or indexpath
+    indexpath = options.mailindex_path or find_db(settings)
     dbman = DBManager(path=indexpath, ro=options.read_only)
 
     # determine what to do

alot/utils/notmuch.py

@@ -0,0 +1,26 @@
+# encoding=utf-8
+
+# SPDX-FileCopyrightText: 2020 Kirill Elagin <https://kir.elagin.me/>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+from os import environ
+import os.path
+
+
+# Replicate the logic for locating the notmuch database:
+#
+# * Can be absolute or relative to $HOME.
+# * Default: $MAILDIR variable if set, otherwise $HOME/mail.
+def find_db(settings):
+    path_from_settings = settings.get_notmuch_setting('database', 'path')
+    if path_from_settings is None:
+        maildir = environ.get('MAILDIR')
+        if maildir is not None:
+            return maildir
+        else:
+            return os.path.join(environ.get('HOME'), 'mail')
+    else:
+        if not os.path.isabs(path_from_settings):
+            return os.path.join(environ.get('HOME'), path_from_settings)
+        else:
+            return path_from_settings

tests/utils/test_notmuch.py

@@ -0,0 +1,66 @@
+# encoding=utf-8
+
+# SPDX-FileCopyrightText: 2020 Kirill Elagin <https://kir.elagin.me/>
+# SPDX-License-Identifier: GPL-3.0-or-later
+
+"""Tests for alot.utils.notmuch"""
+
+import unittest
+from unittest import mock
+
+import os.path
+
+from alot.utils import notmuch
+
+# Good descriptive test names often don't fit PEP8, which is meant to cover
+# functions meant to be called by humans.
+# pylint: disable=invalid-name
+
+
+class MockSettings:
+    def __init__(self, database_path):
+        self._database_path = database_path
+
+    def get_notmuch_setting(self, section, key):
+        if section == 'database' and key == 'path':
+            return self._database_path
+        else:
+            return None
+
+db_path_rel = os.path.join('path', 'to', 'db')
+home = os.path.abspath(os.path.join(os.path.sep, 'home', 'someuser'))
+maildir = os.path.abspath(os.path.join(os.path.sep, 'var', 'mail'))
+
+class TestFindDb(unittest.TestCase):
+    """Tests for the find_db function."""
+
+    @mock.patch.dict(os.environ, {}, clear=True)
+    def test_absolute_path(self):
+        db_path_abs = os.path.abspath(os.path.join(os.path.sep, db_path_rel))
+        settings = MockSettings(db_path_abs)
+        self.assertEqual(notmuch.find_db(settings), db_path_abs)
+
+    @mock.patch.dict(os.environ, {'HOME': home}, clear=True)
+    def test_relative_path(self):
+        settings = MockSettings(db_path_rel)
+        self.assertEqual(notmuch.find_db(settings), os.path.join(home, db_path_rel))
+
+    @mock.patch.dict(os.environ, {'MAILDIR': maildir}, clear=True)
+    def test_maildir(self):
+        settings = MockSettings(None)
+        self.assertEqual(notmuch.find_db(settings), maildir)
+
+    @mock.patch.dict(os.environ, {'HOME': home}, clear=True)
+    def test_home_mail(self):
+        settings = MockSettings(None)
+        self.assertEqual(notmuch.find_db(settings), os.path.join(home, 'mail'))
+
+
+    # Additional tests to make sure we closely replicate the behaviour
+    # of notmuch even if the user’s environment is weird/wrong.
+
+    @mock.patch.dict(os.environ, {'HOME': home, 'MAILDIR': ''}, clear=True)
+    def test_empty_maildir(self):
+        """Empty maildir should not be treated as unset."""
+        settings = MockSettings(None)
+        self.assertEqual(notmuch.find_db(settings), '')