friendly error message in Item.write (GC-437)

beets/library.py

@@ -23,6 +23,7 @@ import shlex
 import unicodedata
 import threading
 import contextlib
+import traceback
 from collections import defaultdict
 from unidecode import unidecode
 from beets.mediafile import MediaFile
@@ -283,7 +284,12 @@ class Item(object):
         f = MediaFile(syspath(self.path))
         for key in ITEM_KEYS_WRITABLE:
             setattr(f, key, getattr(self, key))
-        f.save()
+
+        try:
+            f.save()
+        except (OSError, IOError) as exc:
+            raise util.FilesystemError(exc, 'write', (self.path,),
+                                       traceback.format_exc())
 
         # The file has a new mtime.
         self.mtime = self.current_mtime()

beets/util/__init__.py

@@ -93,7 +93,7 @@ class FilesystemError(HumanReadableException):
             clause = 'while {0} {1} to {2}'.format(
                 self._gerund(), repr(self.paths[0]), repr(self.paths[1])
             )
-        elif self.verb in ('delete',):
+        elif self.verb in ('delete', 'write'):
             clause = 'while {0} {1}'.format(
                 self._gerund(), repr(self.paths[0])
             )

docs/changelog.rst

@@ -29,6 +29,7 @@ Changelog
   modify files' tags even when they successfully change the database.
 * Fix a VFS bug leading to a crash in the :doc:`/plugins/bpd` when files had
   non-ASCII extensions.
+* Add a human-readable error message when writing files' tags fails.
 
 .. _Tomahawk resolver: http://beets.radbox.org/blog/tomahawk-resolver.html