filemerge: move post-merge checks into a separate function

This makes the overall filemerge function easier to follow, and makes upcoming
work simpler.

mercurial/filemerge.py

@@ -521,7 +521,9 def filemerge(repo, mynode, orig, fcd, f
             needcheck, r = func(repo, mynode, orig, fcd, fco, fca, toolconf,
                                 files, labels=labels)
 
-        if not needcheck:
+        if needcheck:
+            r = _check(r, ui, tool, fcd, files)
+
             if r:
                 if onfailure:
                     ui.warn(onfailure % fd)
@@ -532,6 +534,10 def filemerge(repo, mynode, orig, fcd, f
             util.unlink(c)
             return r
 
+def _check(r, ui, tool, fcd, files):
+    fd = fcd.path()
+    a, b, c, back = files
+
         if not r and (_toolbool(ui, tool, "checkconflicts") or
                       'conflicts' in _toollist(ui, tool, "check")):
             if re.search("^(<<<<<<< .*|=======|>>>>>>> .*)$", fcd.data(),
@@ -557,14 +563,6 def filemerge(repo, mynode, orig, fcd, f
         if _toolbool(ui, tool, "fixeol"):
             _matcheol(a, back)
 
-        if r:
-            if onfailure:
-                ui.warn(onfailure % fd)
-        else:
-            util.unlink(back)
-
-        util.unlink(b)
-        util.unlink(c)
         return r
 
 # tell hggettext to extract docstrings from these functions: