fix(index): improve LockedFD handling

Relying on the destructor will not work, even though
the code used to rely on it.

Now we handle failures more explicitly. Far from perfect,
but a good start for a fix.

Fixes gitpython-developers#514

Author: Byron

git/index/base.py

@@ -118,13 +118,17 @@ def _set_cache_(self, attr):
             # read the current index
             # try memory map for speed
             lfd = LockedFD(self._file_path)
+            ok = False
             try:
                 fd = lfd.open(write=False, stream=False)
+                ok = True
             except OSError:
-                lfd.rollback()
                 # in new repositories, there may be no index, which means we are empty
                 self.entries = dict()
                 return
+            finally:
+                if not ok:
+                    lfd.rollback()
             # END exception handling
 
             # Here it comes: on windows in python 2.5, memory maps aren't closed properly
@@ -209,8 +213,14 @@ def write(self, file_path=None, ignore_extension_data=False):
         self.entries
         lfd = LockedFD(file_path or self._file_path)
         stream = lfd.open(write=True, stream=True)
+        ok = False
 
-        self._serialize(stream, ignore_extension_data)
+        try:
+            self._serialize(stream, ignore_extension_data)
+            ok = True
+        finally:
+            if not ok:
+                lfd.rollback()
 
         lfd.commit()
 

git/test/test_index.py

@@ -135,6 +135,23 @@ def _cmp_tree_index(self, tree, index):
             raise AssertionError("CMP Failed: Missing entries in index: %s, missing in tree: %s" %
                                  (bset - iset, iset - bset))
         # END assertion message
+        
+    @with_rw_repo('0.1.6')
+    def test_index_lock_handling(self, rw_repo):
+        def add_bad_blob():
+            rw_repo.index.add([Blob(rw_repo, b'f' * 20, 'bad-permissions', 'foo')])
+
+        try:
+            ## 1st fail on purpose adding into index.
+            add_bad_blob()
+        except Exception as ex:
+            assert "cannot convert argument to integer" in str(ex)
+
+        ## 2nd time should not fail due to stray lock file
+        try:
+            add_bad_blob()
+        except Exception as ex:
+            assert "index.lock' could not be obtained" not in str(ex)
 
     @with_rw_repo('0.1.6')
     def test_index_file_from_tree(self, rw_repo):