revert: option to choose what to keep, not what to discard

I know the you (the reader) are probably tired of discussing how `hg
revert -i -r .` should behave and so am I. And I know I'm one of the
people who argued that showing the diff from the working copy to the
parent was confusing. I think it is less confusing now that we show
the diff from the parent to the working copy, but I still find it
confusing. I think showing the diff of hunks to keep might make it
easier to understand. So that's what this patch provides an option
for.

One argument doing it this way is that most people seem to find `hg
split` natural. I suspect that is because it shows the forward diff
(from parent commit to the commit) and asks you what to put in the
first commit. I think the new "keep" mode for revert (this patch)
matches that.

In "keep" mode, all the changes are still selected by default. That
means that `hg revert -i` followed by 'A' (keep all) (or 'c' in
curses) will be different from `hg revert -a`. That's mostly because
that was simplest. It can also be argued that it's safest. But it can
also be argued that it should be consistent with `hg revert -a`.

Note that in this mode, you can edit the hunks and it will do what you
expect (e.g. add new lines to your file if you added a new lines when
editing). The test case shows that that works.

Differential Revision: https://phab.mercurial-scm.org/D6125

mercurial/cmdutil.py

@@ -3176,22 +3176,25 b' def _performrevert(repo, parents, ctx, n'
                                          configprefix='revert.interactive.')
         diffopts.nodates = True
         diffopts.git = True
-        operation = 'discard'
-        reversehunks = True
-        if node != parent:
-            operation = 'apply'
-            reversehunks = False
-        if reversehunks:
+        operation = 'apply'
+        if node == parent:
+            if repo.ui.configbool('experimental',
+                                  'revert.interactive.select-to-keep'):
+                operation = 'keep'
+            else:
+                operation = 'discard'
+
+        if operation == 'apply':
+            diff = patch.diff(repo, None, ctx.node(), m, opts=diffopts)
+        else:
             diff = patch.diff(repo, ctx.node(), None, m, opts=diffopts)
-        else:
-            diff = patch.diff(repo, None, ctx.node(), m, opts=diffopts)
         originalchunks = patch.parsepatch(diff)
 
         try:
 
             chunks, opts = recordfilter(repo.ui, originalchunks,
                                         operation=operation)
-            if reversehunks:
+            if operation == 'discard':
                 chunks = patch.reversehunks(chunks)
 
         except error.PatchError as err:
@@ -3205,6 +3208,7 b' def _performrevert(repo, parents, ctx, n'
         # chunks are serialized per file, but files aren't sorted
         for f in sorted(set(c.header.filename() for c in chunks if ishunk(c))):
             prntstatusmsg('revert', f)
+        files = set()
         for c in chunks:
             if ishunk(c):
                 abs = c.header.filename()
@@ -3214,6 +3218,10 b' def _performrevert(repo, parents, ctx, n'
                     bakname = scmutil.backuppath(repo.ui, repo, abs)
                     util.copyfile(target, bakname)
                     tobackup.remove(abs)
+                if abs not in files:
+                    files.add(abs)
+                    if operation == 'keep':
+                        checkout(abs)
             c.write(fp)
         dopatch = fp.tell()
         fp.seek(0)

mercurial/configitems.py

@@ -595,6 +595,9 b" coreconfigitem('experimental', 'remotena"
 coreconfigitem('experimental', 'removeemptydirs',
     default=True,
 )
+coreconfigitem('experimental', 'revert.interactive.select-to-keep',
+    default=False,
+)
 coreconfigitem('experimental', 'revisions.prefixhexnode',
     default=False,
 )

mercurial/crecord.py

@@ -566,6 +566,7 b' def testchunkselector(testfn, ui, header'
 _headermessages = { # {operation: text}
     'apply': _('Select hunks to apply'),
     'discard': _('Select hunks to discard'),
+    'keep': _('Select hunks to keep'),
     None: _('Select hunks to record'),
 }
 

mercurial/patch.py

@@ -1012,11 +1012,13 b' def getmessages():'
         'multiple': {
             'apply': _("apply change %d/%d to '%s'?"),
             'discard': _("discard change %d/%d to '%s'?"),
+            'keep': _("keep change %d/%d to '%s'?"),
             'record': _("record change %d/%d to '%s'?"),
         },
         'single': {
             'apply': _("apply this change to '%s'?"),
             'discard': _("discard this change to '%s'?"),
+            'keep': _("keep this change to '%s'?"),
             'record': _("record this change to '%s'?"),
         },
         'help': {
@@ -1040,6 +1042,16 b' def getmessages():'
                          '$$ Discard &all changes to all remaining files'
                          '$$ &Quit, discarding no changes'
                          '$$ &? (display help)'),
+            'keep': _('[Ynesfdaq?]'
+                         '$$ &Yes, keep this change'
+                         '$$ &No, skip this change'
+                         '$$ &Edit this change manually'
+                         '$$ &Skip remaining changes to this file'
+                         '$$ Keep remaining changes to this &file'
+                         '$$ &Done, skip remaining changes and files'
+                         '$$ Keep &all changes to all remaining files'
+                         '$$ &Quit, keeping all changes'
+                         '$$ &? (display help)'),
             'record': _('[Ynesfdaq?]'
                         '$$ &Yes, record this change'
                         '$$ &No, skip this change'

tests/test-revert-interactive.t

@@ -444,4 +444,52 b' Prompt before undeleting file(issue6008)'
   > EOF
   add back removed file a (Yn)? n
   $ ls
+  $ hg revert -a
+  undeleting a
   $ cd ..
+
+Test "keep" mode
+
+  $ cat <<EOF >> $HGRCPATH
+  > [experimental]
+  > revert.interactive.select-to-keep = true
+  > EOF
+
+  $ cd repo
+  $ printf "x\na\ny\n" > a
+  $ hg diff
+  diff -r cb9a9f314b8b a
+  --- a/a	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/a	Thu Jan 01 00:00:00 1970 +0000
+  @@ -1,1 +1,3 @@
+  +x
+   a
+  +y
+  $ cat > $TESTTMP/editor.sh << '__EOF__'
+  > echo "+new line" >> "$1"
+  > __EOF__
+
+  $ HGEDITOR="\"sh\" \"${TESTTMP}/editor.sh\"" hg revert -i  <<EOF
+  > y
+  > n
+  > e
+  > EOF
+  diff --git a/a b/a
+  2 hunks, 2 lines changed
+  examine changes to 'a'? [Ynesfdaq?] y
+  
+  @@ -1,1 +1,2 @@
+  +x
+   a
+  keep change 1/2 to 'a'? [Ynesfdaq?] n
+  
+  @@ -1,1 +2,2 @@
+   a
+  +y
+  keep change 2/2 to 'a'? [Ynesfdaq?] e
+  
+  reverting a
+  $ cat a
+  a
+  y
+  new line