[PATCH stable] patch: allow empty patches on existing files (issue2135)

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1351103179 25200
# Node ID e010bb5b0ee2f9e9241a3dddb7faf0fe2f22a71f
# Parent  917a37b76845811aaea1dc9b1ad0a8110e8b7439
patch: allow empty patches on existing files (issue2135)

When applying a patch that added an empty file,
the patch would fail if the file already existed at the destination.
This changes patch.py to succeed in that scenario, and emits a
warning message notifying the user of this case. Example:

file foo.py not changed: file already exists and patch file is empty

Adds a test for this in the transplant test suite, since that's
where the issue was originally encountered.

diff -r 917a37b76845 -r e010bb5b0ee2 mercurial/patch.py
--- a/mercurial/patch.py	Tue Oct 23 09:28:42 2012 +0200
+++ b/mercurial/patch.py	Wed Oct 24 11:26:19 2012 -0700
@@ -1328,10 +1328,14 @@
                         # must be created
                         data = ''
                 if data or mode:
-                    if (gp.op in ('ADD', 'RENAME', 'COPY')
+                    if (gp.op in ('RENAME', 'COPY')
                         and backend.exists(gp.path)):
                         raise PatchError(_("cannot create %s: destination "
                                            "already exists") % gp.path)
+                    if (gp.op == 'ADD' and backend.exists(gp.path)):
+                        ui.warn(_('file %s not changed: file already exists '
+                                  'and file patch is empty\n') % gp.path)
+                        continue
                     backend.setfile(gp.path, data, mode, gp.oldpath)
                 continue
             try:
diff -r 917a37b76845 -r e010bb5b0ee2 tests/test-transplant.t
--- a/tests/test-transplant.t	Tue Oct 23 09:28:42 2012 +0200
+++ b/tests/test-transplant.t	Wed Oct 24 11:26:19 2012 -0700
@@ -632,6 +632,22 @@
   skipping emptied changeset 7a7d57e15850
   $ cd ..
 
+Issue2135: test transplanting an added empty file onto an existing file
+
+  $ hg init emptyfilerepo
+  $ cd emptyfilerepo
+  $ touch b3
+  $ hg ci -Am addb3
+  adding b3
+  $ cd ../t
+  $ hg transplant -s ../emptyfilerepo 0
+  searching for changes
+  warning: repository is unrelated
+  applying 74c381100194
+  file b3 not changed: file already exists and file patch is empty
+  skipping emptied changeset 74c381100194
+  $ cd ..
+
 Explicitly kill daemons to let the test exit on Windows
 
   $ "$TESTDIR/killdaemons.py" $DAEMON_PIDS