transplant: properly skip empty changeset (issue4423)

If resolving a merge conflict result in an empty changesets, we now properly
skip the changeset instead of crashing.

Original patch from Robert Collins <[e-mail]>.

hgext/transplant.py

@@ -301,8 +301,12 b' class transplanter(object):'
         '''recover last transaction and apply remaining changesets'''
         if os.path.exists(os.path.join(self.path, 'journal')):
             n, node = self.recover(repo, source, opts)
-            self.ui.status(_('%s transplanted as %s\n') % (short(node),
-                                                           short(n)))
+            if n:
+                self.ui.status(_('%s transplanted as %s\n') % (short(node),
+                                                               short(n)))
+            else:
+                self.ui.status(_('%s skipped due to empty diff\n')
+                               % (short(node),))
         seriespath = os.path.join(self.path, 'series')
         if not os.path.exists(seriespath):
             self.transplants.write()
@@ -343,12 +347,16 b' class transplanter(object):'
                                  revlog.hex(parent))
             if merge:
                 repo.setparents(p1, parents[1])
-            n = repo.commit(message, user, date, extra=extra,
-                            editor=self.getcommiteditor())
-            if not n:
-                raise util.Abort(_('commit failed'))
-            if not merge:
-                self.transplants.set(n, node)
+            modified, added, removed, deleted = repo.status()[:4]
+            if merge or modified or added or removed or deleted:
+                n = repo.commit(message, user, date, extra=extra,
+                                editor=self.getcommiteditor())
+                if not n:
+                    raise util.Abort(_('commit failed'))
+                if not merge:
+                    self.transplants.set(n, node)
+            else:
+                n = None
             self.unlog()
 
             return n, node

tests/test-transplant.t

@@ -768,6 +768,22 b' test transplanting a patch turning into '
   searching for changes
   applying 7a7d57e15850
   skipping emptied changeset 7a7d57e15850
+
+Test empty result in --continue
+
+  $ hg transplant -s ../binarysource 1
+  searching for changes
+  applying 645035761929
+  file b already exists
+  1 out of 1 hunks FAILED -- saving rejects to file b.rej
+  patch failed to apply
+  abort: fix up the merge and run hg transplant --continue
+  [255]
+  $ hg status
+  ? b.rej
+  $ hg transplant --continue
+  645035761929 skipped due to empty diff
+
   $ cd ..
 
 Explicitly kill daemons to let the test exit on Windows