merge: make in-memory changes visible to external update hooks 51844b8b5017 (while 3.4 code-freeze) made all 'update' hooks run after releasing wlock for visibility of in-memory dirstate changes. But this breaks paired invocation of 'preupdate' and 'update' hooks. For example, 'hg backout --merge' for TARGET revision, which isn't parent of CURRENT, consists of steps below: 1. update from CURRENT to TARGET 2. commit BACKOUT revision, which backs TARGET out 3. update from BACKOUT to CURRENT 4. merge TARGET into CURRENT Then, we expects hooks to run in the order below: - 'preupdate' on CURRENT for (1) - 'update' on TARGET for (1) - 'preupdate' on BACKOUT for (3) - 'update' on CURRENT for (3) - 'preupdate' on TARGET for (4) - 'update' on CURRENT/TARGET for (4) But hooks actually run in the order below: - 'preupdate' on CURRENT for (1) - 'preupdate' on BACKOUT for (3) - 'preupdate' on TARGET for (4) - 'update' on TARGET for (1), but actually on CURRENT/TARGET - 'update' on CURRENT for (3), but actually on CURRENT/TARGET - 'update' on CURRENT for (4), but actually on CURRENT/TARGET Root cause of the issue focused by 51844b8b5017 is that external 'update' hook process can't view in-memory changes (especially, of dirstate), because they aren't written out until the end of transaction (or wlock). Now, hooks can be invoked just after updating, because previous patches made in-memory changes visible to external process. This patch may break backward compatibility from the point of view of "scheduling hook execution", but should be reasonable because 'update' hooks had been executed in this order before 3.4. This patch tests "hg backout" and "hg unshelve", because the former activates the transaction before 'update' hook invocation, but the former doesn't.

--- a/tests/test-hook.t	Sat Oct 17 01:15:34 2015 +0900
+++ b/tests/test-hook.t	Sat Oct 17 01:15:34 2015 +0900
@@ -223,8 +223,8 @@
   $ echo "update = printenv.py update" >> .hg/hgrc
   $ hg update
   preupdate hook: HG_PARENT1=539e4b31b6dc
+  update hook: HG_ERROR=0 HG_PARENT1=539e4b31b6dc
   2 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  update hook: HG_ERROR=0 HG_PARENT1=539e4b31b6dc
 
 pushkey hook
 
@@ -644,8 +644,8 @@
   $ hg ci -ma
   223eafe2750c tip
   $ hg up 0 --config extensions.largefiles=
+  cb9a9f314b8b
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
-  cb9a9f314b8b
 
 make sure --verbose (and --quiet/--debug etc.) are propagated to the local ui
 that is passed to pre/post hooks