--- a/hgmerge	Fri Mar 10 23:25:50 2006 -0800
+++ b/hgmerge	Fri Mar 10 23:34:36 2006 -0800
@@ -4,6 +4,12 @@
 #
 # This tries to find a way to do three-way merge on the current system.
 # The result ought to end up in $1.
+#
+# Environment variables set by Mercurial:
+# HG_ROOT            repo root
+# HG_FILE            name of file within repo
+# HG_MY_NODE         revision being merged
+# HG_OTHER_NODE      revision being merged
 
 set -e # bail out quickly on failure
 

--- a/mercurial/localrepo.py	Fri Mar 10 23:25:50 2006 -0800
+++ b/mercurial/localrepo.py	Fri Mar 10 23:34:36 2006 -0800
@@ -55,7 +55,7 @@
         def runhook(name, cmd):
             self.ui.note(_("running hook %s: %s\n") % (name, cmd))
             env = dict([('HG_' + k.upper(), v) for k, v in args.iteritems()])
-            r = util.esystem(cmd, environ=env, cwd=self.root)
+            r = util.system(cmd, environ=env, cwd=self.root)
             if r:
                 desc, r = util.explain_exit(r)
                 if throw:
@@ -1636,10 +1636,12 @@
         # merge the tricky bits
         files = merge.keys()
         files.sort()
+        xp1 = hex(p1)
+        xp2 = hex(p2)
         for f in files:
             self.ui.status(_("merging %s\n") % f)
             my, other, flag = merge[f]
-            ret = self.merge3(f, my, other)
+            ret = self.merge3(f, my, other, xp1, xp2)
             if ret:
                 err = True
             util.set_exec(self.wjoin(f), flag)
@@ -1677,7 +1679,7 @@
             self.dirstate.setparents(p1, p2)
         return err
 
-    def merge3(self, fn, my, other):
+    def merge3(self, fn, my, other, p1, p2):
         """perform a 3-way merge in the working directory"""
 
         def temp(prefix, node):
@@ -1700,7 +1702,14 @@
 
         cmd = (os.environ.get("HGMERGE") or self.ui.config("ui", "merge")
                or "hgmerge")
-        r = os.system('%s "%s" "%s" "%s"' % (cmd, a, b, c))
+        r = util.system('%s "%s" "%s" "%s"' % (cmd, a, b, c),
+                        environ={'HG_ROOT': self.root,
+                                 'HG_FILE': fn,
+                                 'HG_MY_NODE': p1,
+                                 'HG_OTHER_NODE': p2,
+                                 'HG_FILE_MY_NODE': hex(my),
+                                 'HG_FILE_OTHER_NODE': hex(other),
+                                 'HG_FILE_BASE_NODE': hex(base)})
         if r:
             self.ui.warn(_("merging %s failed!\n") % fn)
 

--- a/mercurial/ui.py	Fri Mar 10 23:25:50 2006 -0800
+++ b/mercurial/ui.py	Fri Mar 10 23:34:36 2006 -0800
@@ -209,7 +209,9 @@
                   os.environ.get("EDITOR", "vi"))
 
         os.environ["HGUSER"] = self.username()
-        util.system("%s \"%s\"" % (editor, name), errprefix=_("edit failed"))
+        util.system("%s \"%s\"" % (editor, name),
+                    environ={'HGUSER': self.username()},
+                    onerr=util.Abort, errprefix=_("edit failed"))
 
         t = open(name).read()
         t = re.sub("(?m)^HG:.*\n", "", t)

--- a/mercurial/util.py	Fri Mar 10 23:25:50 2006 -0800
+++ b/mercurial/util.py	Fri Mar 10 23:34:36 2006 -0800
@@ -315,19 +315,13 @@
                          (files and filematch(fn)))),
             (inc or exc or (pats and pats != [('glob', '**')])) and True)
 
-def system(cmd, errprefix=None):
-    """execute a shell command that must succeed"""
-    rc = os.system(cmd)
-    if rc:
-        errmsg = "%s %s" % (os.path.basename(cmd.split(None, 1)[0]),
-                            explain_exit(rc)[0])
-        if errprefix:
-            errmsg = "%s: %s" % (errprefix, errmsg)
-        raise Abort(errmsg)
+def system(cmd, environ={}, cwd=None, onerr=None, errprefix=None):
+    '''enhanced shell command execution.
+    run with environment maybe modified, maybe in different dir.
 
-def esystem(cmd, environ={}, cwd=None):
-    '''enhanced shell command execution.
-    run with environment maybe modified, maybe in different dir.'''
+    if command fails and onerr is None, return status.  if ui object,
+    print error message and return status, else raise onerr object as
+    exception.'''
     oldenv = {}
     for k in environ:
         oldenv[k] = os.environ.get(k)
@@ -338,7 +332,17 @@
             os.environ[k] = str(v)
         if cwd is not None and oldcwd != cwd:
             os.chdir(cwd)
-        return os.system(cmd)
+        rc = os.system(cmd)
+        if rc and onerr:
+            errmsg = '%s %s' % (os.path.basename(cmd.split(None, 1)[0]),
+                                explain_exit(rc)[0])
+            if errprefix:
+                errmsg = '%s: %s' % (errprefix, errmsg)
+            try:
+                onerr.warn(errmsg + '\n')
+            except AttributeError:
+                raise onerr(errmsg)
+        return rc
     finally:
         for k, v in oldenv.iteritems():
             if v is None: