[PATCH] repair: use context manager for lock management

[Matt Harbison]

# HG changeset patch
# User Matt Harbison <matt_harbison at yahoo.com>
# Date 1490327243 14400
#      Thu Mar 23 23:47:23 2017 -0400
# Node ID c053dc8a24afad24872397e5cd3f57411fc7d172
# Parent  d0c2db2d9f13dca534c598de050eb1919ef79059
repair: use context manager for lock management

If repo.lock() raised inside of the try block, 'tr' would have been None in the
finally block where it tries to release().  Modernize the syntax instead of just
winching the lock out of the try block.

I found several other instances of acquiring the lock inside of the 'try', but
those finally blocks handle None references.  I also started switching some
trivial try/finally blocks to context managers, but didn't get them all because
indenting over 3x for lock, wlock and transaction would have spilled over 80
characters.  That got me wondering if there should be a repo.rwlock(), to handle
locking and unlocking in the proper order.

It also looks like py27 supports supports multiple context managers for a single
'with' statement.  Should I hold off on the rest until py26 is dropped?

diff --git a/mercurial/repair.py b/mercurial/repair.py
--- a/mercurial/repair.py
+++ b/mercurial/repair.py
@@ -214,15 +214,10 @@
 
         for m in updatebm:
             bm[m] = repo[newbmtarget].node()
-        lock = tr = None
-        try:
-            lock = repo.lock()
-            tr = repo.transaction('repair')
-            bm.recordchange(tr)
-            tr.close()
-        finally:
-            tr.release()
-            lock.release()
+
+        with repo.lock():
+            with repo.transaction('repair') as tr:
+                bm.recordchange(tr)
 
         # remove undo files
         for undovfs, undofile in repo.undofiles():