mq: backup local changes in qpush --force

qpush help says the following about --force:
1- When -f/--force is applied, all local changes in patched files will
   be lost.
2- Apply on top of local changes

In practice, qpush --force will attempt to apply the patch on top of
local changes, and on success will merge them in the pushed patch. On
failure, patched files will contain a mix of local changes (where the
patch could not apply) and a mix of patch changes (were it applied). So,
local changes are less lost than entangled with a mass of other changes.

This patch makes qpush --force backup all locally modified files touched
by the next patch being applied. When multiple patches are being pushed,
this logic is repeated for each patch. Note that modified but
successfully patched files are preserved as well.

hgext/mq.py

@@ -554,14 +554,17 b' class queue(object):'
         except OSError, inst:
             self.ui.warn(_('error removing undo: %s\n') % str(inst))
 
-    def backup(self, repo, files):
+    def backup(self, repo, files, copy=False):
         # backup local changes in --force case
         for f in sorted(files):
             absf = repo.wjoin(f)
             if os.path.lexists(absf):
                 self.ui.note(_('saving current version of %s as %s\n') %
                              (f, f + '.orig'))
-                util.rename(absf, absf + '.orig')
+                if copy:
+                    util.copyfile(absf, absf + '.orig')
+                else:
+                    util.rename(absf, absf + '.orig')
 
     def printdiff(self, repo, diffopts, node1, node2=None, files=None,
                   fp=None, changes=None, opts={}):
@@ -677,7 +680,8 b' class queue(object):'
             return (False, list(files), False)
 
     def apply(self, repo, series, list=False, update_status=True,
-              strict=False, patchdir=None, merge=None, all_files=None):
+              strict=False, patchdir=None, merge=None, all_files=None,
+              tobackup=None):
         wlock = lock = tr = None
         try:
             wlock = repo.wlock()
@@ -685,7 +689,8 b' class queue(object):'
             tr = repo.transaction("qpush")
             try:
                 ret = self._apply(repo, series, list, update_status,
-                                  strict, patchdir, merge, all_files=all_files)
+                                  strict, patchdir, merge, all_files=all_files,
+                                  tobackup=tobackup)
                 tr.close()
                 self.savedirty()
                 return ret
@@ -702,9 +707,14 b' class queue(object):'
             self.removeundo(repo)
 
     def _apply(self, repo, series, list=False, update_status=True,
-               strict=False, patchdir=None, merge=None, all_files=None):
-        '''returns (error, hash)
-        error = 1 for unable to read, 2 for patch failed, 3 for patch fuzz'''
+               strict=False, patchdir=None, merge=None, all_files=None,
+               tobackup=None):
+        """returns (error, hash)
+
+        error = 1 for unable to read, 2 for patch failed, 3 for patch
+        fuzz. tobackup is None or a set of files to backup before they
+        are modified by a patch.
+        """
         # TODO unify with commands.py
         if not patchdir:
             patchdir = self.path
@@ -736,6 +746,11 b' class queue(object):'
                 message = '\n'.join(message)
 
             if ph.haspatch:
+                if tobackup:
+                    touched = patchmod.changedfiles(self.ui, repo, pf)
+                    touched = set(touched) & tobackup
+                    self.backup(repo, touched, copy=True)
+                    tobackup = tobackup - touched
                 (patcherr, files, fuzz) = self.patch(repo, pf)
                 if all_files is not None:
                     all_files.update(files)
@@ -1241,13 +1256,19 b' class queue(object):'
             else:
                 end = self.series.index(patch, start) + 1
 
+            tobackup = set()
+            if force:
+                m, a, r, d = self.checklocalchanges(repo, force=True)
+                tobackup.update(m + a)
+
             s = self.series[start:end]
             all_files = set()
             try:
                 if mergeq:
                     ret = self.mergepatch(repo, mergeq, s, diffopts)
                 else:
-                    ret = self.apply(repo, s, list, all_files=all_files)
+                    ret = self.apply(repo, s, list, all_files=all_files,
+                                     tobackup=tobackup)
             except:
                 self.ui.warn(_('cleaning up working directory...'))
                 node = repo.dirstate.p1()

tests/test-mq-qpush-fail.t

@@ -188,3 +188,52 b' test qpop --force and backup files'
   bb
   $ cat c.orig
   cc
+
+test qpush --force and backup files
+
+  $ echo a >> a
+  $ hg qnew p2
+  $ echo b >> b
+  $ echo d > d
+  $ echo e > e
+  $ hg add d e
+  $ hg rm c
+  $ hg qnew p3
+  $ hg qpop -a
+  popping p3
+  popping p2
+  patch queue now empty
+  $ echo a >> a
+  $ echo b1 >> b
+  $ echo d1 > d
+  $ hg add d
+  $ echo e1 > e
+  $ hg qpush -a --force --verbose
+  applying p2
+  saving current version of a as a.orig
+  patching file a
+  a
+  applying p3
+  saving current version of b as b.orig
+  saving current version of d as d.orig
+  patching file b
+  patching file c
+  patching file d
+  file d already exists
+  1 out of 1 hunks FAILED -- saving rejects to file d.rej
+  patching file e
+  file e already exists
+  1 out of 1 hunks FAILED -- saving rejects to file e.rej
+  patch failed to apply
+  b
+  patch failed, rejects left in working dir
+  errors during apply, please fix and refresh p3
+  [2]
+  $ cat a.orig
+  a
+  a
+  $ cat b.orig
+  b
+  b1
+  $ cat d.orig
+  d1

tests/test-mq.t

@@ -1356,11 +1356,15 b' qpush should fail, local changes'
 
 apply force, should discard changes in hello, but not bye
 
-  $ hg qpush -f
+  $ hg qpush -f --verbose
   applying empty
+  saving current version of hello.txt as hello.txt.orig
+  patching file hello.txt
+  hello.txt
   now at: empty
   $ hg st
   M bye.txt
+  ? hello.txt.orig
   $ hg diff --config diff.nodates=True
   diff -r ba252371dbc1 bye.txt
   --- a/bye.txt