[PATCH 4 of 7 mergedriver] filemerge._picktool: only pick from nomerge tools for change/delete conflicts

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1447652415 28800
#      Sun Nov 15 21:40:15 2015 -0800
# Node ID 6100ebf277120db2ea3efb7fb7e7deb0c2585a60
# Parent  696cd54b8958729b6b1763b19a159c3c97b7b72b
# Available At http://42.netv6.net/sid0-wip/hg/
#              hg pull http://42.netv6.net/sid0-wip/hg/ -r 6100ebf27712
filemerge._picktool: only pick from nomerge tools for change/delete conflicts

For --tool or HGMERGE, we could have either:
(a) proceeded with the particular tool, then failed the merge.
(b) chosen to prompt regardless.

We're explicitly choosing (b) here, because it's effectively what we've been
doing so far and helps maintain an easier-to-use interface.

However, in future patches we're going to change the default selection from
'pick changed version' to 'leave unresolved'. That fixes most of the brokenness
involved with choice (b).

diff --git a/mercurial/filemerge.py b/mercurial/filemerge.py
--- a/mercurial/filemerge.py
+++ b/mercurial/filemerge.py
@@ -120,8 +120,11 @@ def findexternaltool(ui, tool):
     exe = _toolstr(ui, tool, "executable", tool)
     return util.findexe(util.expandpath(exe))
 
-def _picktool(repo, ui, path, binary, symlink):
-    def check(tool, pat, symlink, binary):
+def _picktool(repo, ui, path, binary, symlink, changedelete):
+    def supportscd(tool):
+        return tool in internals and internals[tool].mergetype == nomerge
+
+    def check(tool, pat, symlink, binary, changedelete):
         tmsg = tool
         if pat:
             tmsg += " specified for " + pat
@@ -134,6 +137,10 @@ def _picktool(repo, ui, path, binary, sy
             ui.warn(_("tool %s can't handle symlinks\n") % tmsg)
         elif binary and not _toolbool(ui, tool, "binary"):
             ui.warn(_("tool %s can't handle binary\n") % tmsg)
+        elif changedelete and not supportscd(tool):
+            # the nomerge tools are the only tools that support change/delete
+            # conflicts
+            pass
         elif not util.gui() and _toolbool(ui, tool, "gui"):
             ui.warn(_("tool %s requires a GUI\n") % tmsg)
         else:
@@ -145,21 +152,27 @@ def _picktool(repo, ui, path, binary, sy
     force = ui.config('ui', 'forcemerge')
     if force:
         toolpath = _findtool(ui, force)
-        if toolpath:
-            return (force, util.shellquote(toolpath))
+        if not (changedelete and not supportscd(toolpath)):
+            if toolpath:
+                return (force, util.shellquote(toolpath))
+            else:
+                # mimic HGMERGE if given tool not found
+                return (force, force)
         else:
-            # mimic HGMERGE if given tool not found
-            return (force, force)
+            return ":prompt", None
 
     # HGMERGE takes next precedence
     hgmerge = os.environ.get("HGMERGE")
     if hgmerge:
-        return (hgmerge, hgmerge)
+        if not (changedelete and not supportscd(hgmerge)):
+            return (hgmerge, hgmerge)
+        else:
+            return ":prompt", None
 
     # then patterns
     for pat, tool in ui.configitems("merge-patterns"):
         mf = match.match(repo.root, '', [pat])
-        if mf(path) and check(tool, pat, symlink, False):
+        if mf(path) and check(tool, pat, symlink, False, changedelete):
             toolpath = _findtool(ui, tool)
             return (tool, util.shellquote(toolpath))
 
@@ -176,17 +189,19 @@ def _picktool(repo, ui, path, binary, sy
     tools = sorted([(-p, t) for t, p in tools.items() if t not in disabled])
     uimerge = ui.config("ui", "merge")
     if uimerge:
-        if uimerge not in names:
+        # external tools defined in uimerge won't be able to handle
+        # change/delete conflicts
+        if uimerge not in names and not changedelete:
             return (uimerge, uimerge)
         tools.insert(0, (None, uimerge)) # highest priority
     tools.append((None, "hgmerge")) # the old default, if found
     for p, t in tools:
-        if check(t, None, symlink, binary):
+        if check(t, None, symlink, binary, changedelete):
             toolpath = _findtool(ui, t)
             return (t, util.shellquote(toolpath))
 
     # internal merge or prompt as last resort
-    if symlink or binary:
+    if symlink or binary or changedelete:
         return ":prompt", None
     return ":merge", None
 
@@ -535,7 +550,8 @@ def _filemerge(premerge, repo, mynode, o
     fd = fcd.path()
     binary = fcd.isbinary() or fco.isbinary() or fca.isbinary()
     symlink = 'l' in fcd.flags() + fco.flags()
-    tool, toolpath = _picktool(repo, ui, fd, binary, symlink)
+    changedelete = fcd.isabsent() or fco.isabsent()
+    tool, toolpath = _picktool(repo, ui, fd, binary, symlink, changedelete)
     if tool in internals and tool.startswith('internal:'):
         # normalize to new-style names (':merge' etc)
         tool = tool[len('internal'):]