# HG changeset patch
# User Bryan O'Sullivan <bryano@fb.com>
# Date 1452892487 28800
# Node ID b2145c195f24a545a2f7051e5830c7ebb40734da
# Parent  3315a9c2019c6eaef0b010b276e932d4ef74d7ec
transaction: turn a transaction into a Python context manager

This lets us greatly simply acquire/release cycles.

If the block completes without raising an exception, the transaction
is closed.

Code pattern before:

  try:
    tr = repo.transaction('x')
    # zillions of lines of code
    tr.close()
  finally:
    tr.release()

And after:

  with tr.transaction('x'):
    # ...

diff --git a/mercurial/transaction.py b/mercurial/transaction.py
--- a/mercurial/transaction.py
+++ b/mercurial/transaction.py
@@ -333,6 +333,14 @@
         if self.count > 0 and self.usages == 0:
             self._abort()
 
+    def __enter__(self):
+        return self
+
+    def __exit__(self, exc_type, exc_val, exc_tb):
+        if exc_type is None:
+            self.close()
+        self.release()
+
     def running(self):
         return self.count > 0