histedit: extract InterventionRequired transaction handling to utils

rebase will have similar logic, so let's extract it. Besides, it makes
the histedit code more readable.

We may want to parametrize acceptintervention() by the exception(s)
that should result in transaction close.

Differential Revision: https://phab.mercurial-scm.org/D66

hgext/histedit.py

@@ -1122,7 +1122,7 b' def _continuehistedit(ui, repo, state):'
         # and reopen a transaction. For example, if the action executes an
         # external process it may choose to commit the transaction first.
         tr = repo.transaction('histedit')
-    try:
+    with util.acceptintervention(tr):
         while state.actions:
             state.write(tr=tr)
             actobj = state.actions[0]
@@ -1136,17 +1136,6 b' def _continuehistedit(ui, repo, state):'
             state.replacements.extend(replacement_)
             state.actions.pop(0)
 
-        if tr is not None:
-            tr.close()
-    except error.InterventionRequired:
-        if tr is not None:
-            tr.close()
-        raise
-    except Exception:
-        if tr is not None:
-            tr.abort()
-        raise
-
     state.write()
     ui.progress(_("editing"), None)
 

mercurial/util.py

@@ -19,6 +19,7 b' import bz2'
 import calendar
 import codecs
 import collections
+import contextlib
 import datetime
 import errno
 import gc
@@ -589,6 +590,24 b' class sortdict(collections.OrderedDict):'
             del self[key]
         super(sortdict, self).__setitem__(key, value)
 
[e-mail]
+def acceptintervention(tr=None):
+    """A context manager that closes the transaction on InterventionRequired
+
+    If no transaction was provided, this simply runs the body and returns
+    """
+    if not tr:
+        yield
+        return
+    try:
+        yield
+        tr.close()
+    except error.InterventionRequired:
+        tr.close()
+        raise
+    finally:
+        tr.release()
+
 class _lrucachenode(object):
     """A node in a doubly linked list.