Make error handling more robust

lib/tfw/components/snapshot_provider.py

@@ -2,7 +2,7 @@
 # All Rights Reserved. See LICENSE file for details.
 
 import re
-from subprocess import run
+from subprocess import run, CalledProcessError
 from getpass import getuser
 from os.path import isdir
 from datetime import datetime
@@ -11,7 +11,8 @@ from uuid import uuid4
 
 class SnapshotProvider:
     def __init__(self, directory, git_dir):
-        author = f'{getuser()} via TFW {self.__class__.__name__}'
+        self._classname = self.__class__.__name__
+        author = f'{getuser()} via TFW {self._classname}'
         self.gitenv = {
             'GIT_DIR': git_dir,
             'GIT_WORK_TREE': directory,
@@ -32,13 +33,16 @@ class SnapshotProvider:
             self._run(('git', 'init'))
 
         if self._number_of_commits == 0:
-            self._snapshot()
+            try:
+                self._snapshot()
+            except CalledProcessError:
+                raise EnvironmentError(f'{self._classname} cannot init on empty directories!')
 
         self._check_head_not_detached()
 
     def _check_environment(self):
         if not isdir(self.gitenv['GIT_DIR']) or not isdir(self.gitenv['GIT_WORK_TREE']):
-            raise EnvironmentError('Directories "directory" and "git_dir" must exist!')
+            raise EnvironmentError(f'{self._classname}: "directory" and "git_dir" must exist!')
 
     @property
     def _repo_is_initialized(self):
@@ -69,7 +73,7 @@ class SnapshotProvider:
 
     def _check_head_not_detached(self):
         if self._head_detached:
-            raise EnvironmentError(f'{self.__class__.__name__} cannot init from detached HEAD state!')
+            raise EnvironmentError(f'{self._classname} cannot init from detached HEAD state!')
 
     @property
     def _head_detached(self):