merge-tools: when calling external merge tool, describe the resolve inputs It is a common complaint that a user will be running some operation (histedit, rebase, evolve, etc.), get into a merge-conflict situation, and not understand what they are seeing - it is possible that the merge tool is configured to display the hash, but it's difficult for most merge tools to display a good snippet of the description. In the worst case, configuring this template will lead to output that is immediately covered by a terminal application, maybe the user can hit ctrl-z to see it. In the common case, the output will be in a terminal window and a GUI program will start, and it should be possible to view both the terminal and the GUI program at the same time. Differential Revision: https://phab.mercurial-scm.org/D5094

--- a/mercurial/configitems.py	Fri Oct 26 21:46:37 2018 +0900
+++ b/mercurial/configitems.py	Sat Oct 13 07:49:20 2018 -0700
@@ -1193,6 +1193,9 @@
 coreconfigitem('ui', 'patch',
     default=None,
 )
+coreconfigitem('ui', 'pre-merge-tool-output-template',
+    default=None,
+)
 coreconfigitem('ui', 'portablefilenames',
     default='warn',
 )