truncate path components to 30 characters on Windows (work around #120)

NEWS

@@ -20,6 +20,7 @@
   completely wrong association of track names to files. The order
   applied was always just alphabetical by filename, which is frequently
   but not always what you want.
+* Filenames are now truncated to 30 characters on Windows.
 * Fix crash in lastid when the artist name is not available.
 * Fixed a spurious crash when LANG or a related environment variable is
   set to an invalid value (such as 'UTF-8' on some installations of Mac

beets/library.py

@@ -24,6 +24,7 @@ from beets.mediafile import MediaFile, UnreadableFileError, FileTypeError
 from beets import plugins
 
 MAX_FILENAME_LENGTH = 200
+MAX_WINDOWS_FILENAME_LENGTH = 30
 
 # Fields in the "items" database table; all the metadata available for
 # items in the library. These are used directly in SQL; they are
@@ -203,8 +204,9 @@ def _sanitize_path(path, pathmod=None):
             comp = regex.sub(repl, comp)
         
         # Truncate each component.
-        if len(comp) > MAX_FILENAME_LENGTH:
-            comp = comp[:MAX_FILENAME_LENGTH]
+        maxlen = MAX_WINDOWS_FILENAME_LENGTH if windows else MAX_FILENAME_LENGTH
+        if len(comp) > maxlen:
+            comp = comp[:maxlen]
                 
         comps[i] = comp
     return pathmod.join(*comps)

test/test_db.py

@@ -259,6 +259,14 @@ class DestinationTest(unittest.TestCase):
         p = beets.library._sanitize_path(u':', posixpath)
         self.assertEqual(p, u'-')
     
+    def test_sanitize_windows_uses_very_short_names(self):
+        p = beets.library._sanitize_path('X'*300 + '/' + 'Y'*200, ntpath)
+        self.assertLessEqual(len(p), 100)
+
+    def test_sanitize_unix_uses_longer_names(self):
+        p = beets.library._sanitize_path('X'*300 + '/' + 'Y'*200, posixpath)
+        self.assertGreaterEqual(len(p), 100)
+
     def test_path_with_format(self):
         self.lib.path_format = '$artist/$album ($format)'
         p = self.lib.destination(self.i)