[PATCH RFC] commit: add --amend option to amend the parent changeset

[Idan Kamara]

# HG changeset patch
# User Idan Kamara <idankk86 at gmail.com>
# Date 1328185747 -7200
# Branch stable
# Node ID cc7dec00d5016f03acf789c35ce6ef50b204f0cb
# Parent  0620421044a2bcaafd054a6ee454614888699de8
commit: add --amend option to amend the parent changeset

Commits a new changeset incorporating both the changes to the given files
and all the changes from the current parent changeset into the repository.

You cannot amend public changesets. Amending a changeset with children
results in a warning (we might want to forbid this).

Behind the scenes, first commit the update as a regular child of the current
parent. Then create a new commit on the parent's parents with the updated
contents. Then change the working copy parent to this new combined changeset.
Finally, strip the intermediate commit created in the beginning (might
want to also strip the amended commit if it has no children).

This is an RFC, which last discussed one year ago: http://markmail.org/message/skalggb4typm27um

I think this attempt is less intrusive and more contained than the previous one
(it was done quickly to see if there's interest, so still unfinished), with a
much cleaner implementation (largely due to parren's work on evolution, thanks ;).

It doesn't try to be too smart, and now that we have phases it should be safe.

This is arguably one of the most common history editing operations. I don't
think referring people to mq (or rollback, which is worse) for this is particularly good.
It requires activating a 'heavy' extension and use new commands that the user
isn't familiar with. This way the user is in familiar territory, knowing all the flags etc.

diff --git a/mercurial/commands.py b/mercurial/commands.py
--- a/mercurial/commands.py
+++ b/mercurial/commands.py
@@ -9,7 +9,7 @@
 from lock import release
 from i18n import _, gettext
 import os, re, difflib, time, tempfile, errno
-import hg, scmutil, util, revlog, extensions, copies, error, bookmarks
+import hg, scmutil, util, revlog, extensions, copies, error, bookmarks, repair
 import patch, help, url, encoding, templatekw, discovery
 import archival, changegroup, cmdutil, hbisect
 import sshserver, hgweb, hgweb.server, commandserver
@@ -1163,6 +1163,7 @@
      _('mark new/missing files as added/removed before committing')),
     ('', 'close-branch', None,
      _('mark a branch as closed, hiding it from the branch list')),
+    ('', 'amend', None, _('amend a commit')),
     ] + walkopts + commitopts + commitopts2 + subrepoopts,
     _('[OPTION]... [FILE]...'))
 def commit(ui, repo, *pats, **opts):
@@ -1209,6 +1210,15 @@
     branch = repo[None].branch()
     bheads = repo.branchheads(branch)
 
+    if opts.get('amend'):
+        curr = repo['.']
+        if len(curr.parents()) > 1:
+            raise util.Abort(_('cannot amend merge changesets'))
+        if curr.phase() == phases.public:
+            raise util.Abort(_('cannot amend public changesets'))
+        if len(curr.children()):
+            ui.warn(_('warning: amending changeset with children'))
+
     node = cmdutil.commit(ui, repo, commitfunc, pats, opts)
     if not node:
         stat = repo.status(match=scmutil.match(repo[None], pats, opts))
@@ -1222,6 +1232,68 @@
     ctx = repo[node]
     parents = ctx.parents()
 
+    if opts.get('amend'):
+        old = repo['.'].p1()
+        base = old.p1()
+        bm = bookmarks.readcurrent(repo)
+
+        # commit a new version of the old changeset, including the update
+        # collect all files which might be affected
+        files = set(old.files())
+        files.update(ctx.files())
+        # prune files which were reverted by the updates
+        def samefile(f):
+            if f in ctx.manifest():
+                a = ctx.filectx(f)
+                if f in base.manifest():
+                    b = base.filectx(f)
+                    return (a.data() == b.data()
+                            and a.flags() == b.flags()
+                            and a.renamed() == b.renamed())
+                else:
+                    return False
+            else:
+                return f not in base.manifest()
+        files = [f for f in files if not samefile(f)]
+        # commit version of these files as defined by head
+        headmf = ctx.manifest()
+        def filectxfn(repo, ctx_, path):
+            if path in headmf:
+                return ctx.filectx(path)
+            raise IOError()
+        new = context.memctx(repo,
+                             parents=[old.p1().node(), old.p2().node()],
+                             text=opts.get('message') or old.description(),
+                             files=files,
+                             filectxfn=filectxfn,
+                             user=opts.get('user'),
+                             date=opts.get('date'),
+                             extra=extra)
+        newid = repo.commitctx(new)
+
+        wlock = repo.wlock()
+        try:
+            # reroute the working copy parent to the new changeset
+            repo.dirstate.setparents(newid, nullid)
+
+            # update the bookmark
+            if bm:
+                repo._bookmarks[bm] = newid
+                bookmarks.write(repo)
+        finally:
+            wlock.release()
+
+        ui.note('stripping intermediate commit %s\n' % ctx)
+        lock = repo.lock()
+        try:
+            # no backup
+            repair.strip(ui, repo, node, '')
+        finally:
+            lock.release()
+
+        ctx = repo[newid]
+        parents = ctx.parents()
+
     if (bheads and node not in bheads and not
         [x for x in parents if x.node() in bheads and x.branch() == branch]):
         ui.status(_('created new head\n'))
diff --git a/tests/test-commit.t b/tests/test-commit.t
--- a/tests/test-commit.t
+++ b/tests/test-commit.t
@@ -88,6 +88,36 @@
   dir/file
   committed changeset 4:49176991390e
 
+commit --amend
+
+  $ echo foo >> foo
+  $ hg commit -m 'base'
+  $ hg diff --nodates -c . foo
+  diff -r 49176991390e -r 1846759e3d5f foo
+  --- a/foo
+  +++ b/foo
+  @@ -1,2 +1,3 @@
+   foo
+   foo
+  +foo
+  $ echo bar >> foo
+  $ hg phase -r . -p
+  $ hg commit --amend
+  abort: cannot amend public changesets
+  [255]
+  $ hg phase -f -r . -d
+  $ hg commit --amend -m 'base amend'
+  created new head
+  $ hg diff --nodates -c . foo
+  diff -r 49176991390e -r 013d43f99c45 foo
+  --- a/foo
+  +++ b/foo
+  @@ -1,2 +1,4 @@
+   foo
+   foo
+  +foo
+  +bar
+
 An empty date was interpreted as epoch origin
 
   $ echo foo >> foo