merge: add a config to specify merge tool in interactive mode

Summary:
Add a way to specify different merge tools for interactive and non-interactive
mode.

This will be used for the default `editmerge` merge tool, which pops up the
`EDITOR` (vim) regardless of interactive mode, causing various user complains
and hangs, including `arc pull` running rebase triggering editor, or VS Code
running rebase triggering editor, and some other rebase hangs or vim errors.

Reviewed By: DurhamG

Differential Revision: D24069105

fbshipit-source-id: ec16fdc704cab6daeedb0c23d4028b4309d96d3f

eden/scm/edenscm/mercurial/filemerge.py

@@ -220,7 +220,12 @@ def _picktool(repo, ui, path, binary, symlink, changedelete):
             disabled.add(t)
     names = tools.keys()
     tools = sorted([(-p, tool) for tool, p in tools.items() if tool not in disabled])
-    uimerge = ui.config("ui", "merge")
+    interactive = ui.interactive() and ui.formatted
+    uimerge = None
+    if interactive:
+        uimerge = ui.config("ui", "merge:interactive")
+    if not uimerge:
+        uimerge = ui.config("ui", "merge")
     if uimerge:
         # external tools defined in uimerge won't be able to handle
         # change/delete conflicts

eden/scm/edenscm/mercurial/helptext.py

@@ -2492,6 +2492,10 @@ User interface controls.
     For more information on merge tools see :hg:`help merge-tools`.
     For configuring merge tools see the ``[merge-tools]`` section.
 
+``merge:interactive``
+    If set, override ``ui.merge`` in interactive mode (usually when both
+    stdin and stdout are ttys).
+
 ``mergemarkers``
     Sets the merge conflict marker label styling. The ``detailed``
     style uses the ``mergemarkertemplate`` setting to style the labels.

eden/scm/tests/test-merge-tools.t

@@ -1379,3 +1379,15 @@ specified file as expected
   couldn't find merge tool true (for pattern f)
   couldn't find merge tool true
   f = false
+
+test ui.merge:interactive
+
+  $ hg debugpickmergetool --config ui.formatted=false --config ui.interactive=false --config ui.merge=nonint --config ui.merge:interactive=int f
+  f = nonint
+  $ hg debugpickmergetool --config ui.formatted=false --config ui.interactive=true  --config ui.merge=nonint --config ui.merge:interactive=int f
+  f = nonint
+  $ hg debugpickmergetool --config ui.formatted=true  --config ui.interactive=false --config ui.merge=nonint --config ui.merge:interactive=int f
+  f = nonint
+  $ hg debugpickmergetool --config ui.formatted=true  --config ui.interactive=true  --config ui.merge=nonint --config ui.merge:interactive=int f
+  f = int
+