amend: new extension providing the amend command

Various third parties have implemented the `amend` command, which is in high
demand. This patch adds it as an experimental extension so its interface
could be formalized in core directly.

Since `commit --amend` is basically what `amend` should do. The command is
just a thin wrapper around `commit --amend` and just prevent the editor from
popping up by passing `--message`.

hgext/amend.py

@@ -0,0 +1,51
+# amend.py - provide the amend command
+#
+# Copyright 2017 Facebook, Inc.
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+"""provide the amend command (EXPERIMENTAL)
+
+This extension provides an ``amend`` command that is similar to
+``commit --amend`` but does not prompt an editor.
+"""
+
+from __future__ import absolute_import
+
+from mercurial.i18n import _
+from mercurial import (
+    cmdutil,
+    commands,
+    registrar,
+)
+
+# Note for extension authors: ONLY specify testedwith = 'ships-with-hg-core' for
+# extensions which SHIP WITH MERCURIAL. Non-mainline extensions should
+# be specifying the version(s) of Mercurial they are tested with, or
+# leave the attribute unspecified.
+testedwith = 'ships-with-hg-core'
+
+cmdtable = {}
+command = registrar.command(cmdtable)
+
+@command('amend',
+    [('A', 'addremove', None,
+      _('mark new/missing files as added/removed before committing')),
+     ('e', 'edit', None, _('invoke editor on commit messages')),
+     ('i', 'interactive', None, _('use interactive mode')),
+    ] + cmdutil.walkopts + cmdutil.commitopts + cmdutil.commitopts2,
+    _('[OPTION]... [FILE]...'),
+    inferrepo=True)
+def amend(ui, repo, *pats, **opts):
+    """amend the working copy parent with all or specified outstanding changes
+
+    Similar to :hg:`commit --amend`, but reuse the commit message without
+    invoking editor, unless ``--edit`` was set.
+
+    See :hg:`help commit` for more details.
+    """
+    with repo.wlock(), repo.lock():
+        if not opts.get('logfile'):
+            opts['message'] = opts.get('message') or repo['.'].description()
+        opts['amend'] = True
+        return commands._docommit(ui, repo, *pats, **opts)

tests/test-amend.t

@@ -0,0 +1,220
+#testcases obsstore-off obsstore-on
+
+  $ cat << EOF >> $HGRCPATH
+  > [extensions]
+  > amend=
+  > debugdrawdag=$TESTDIR/drawdag.py
+  > [diff]
+  > git=1
+  > EOF
+
+#if obsstore-on
+  $ cat << EOF >> $HGRCPATH
+  > [experimental]
+  > evolution=createmarkers
+  > EOF
+#endif
+
+Basic amend
+
+  $ hg init repo1
+  $ cd repo1
+  $ hg debugdrawdag <<'EOS'
+  > B
+  > |
+  > A
+  > EOS
+
+  $ hg update B -q
+  $ echo 2 >> B
+
+#if obsstore-off
+  $ hg amend
+  saved backup bundle to $TESTTMP/repo1/.hg/strip-backup/112478962961-af2c0941-amend.hg (glob)
+  $ hg log -p -G --hidden -T '{rev} {node|short} {desc}\n'
+  @  1 be169c7e8dbe B
+  |  diff --git a/B b/B
+  |  new file mode 100644
+  |  --- /dev/null
+  |  +++ b/B
+  |  @@ -0,0 +1,1 @@
+  |  +B2
+  |
+  o  0 426bada5c675 A
+     diff --git a/A b/A
+     new file mode 100644
+     --- /dev/null
+     +++ b/A
+     @@ -0,0 +1,1 @@
+     +A
+     \ No newline at end of file
+  
+#else
+  $ hg amend
+  $ hg log -p -G --hidden -T '{rev} {node|short} {desc}\n'
+  @  3 be169c7e8dbe B
+  |  diff --git a/B b/B
+  |  new file mode 100644
+  |  --- /dev/null
+  |  +++ b/B
+  |  @@ -0,0 +1,1 @@
+  |  +B2
+  |
+  | x  2 edf08988b141 temporary amend commit for 112478962961
+  | |  diff --git a/B b/B
+  | |  --- a/B
+  | |  +++ b/B
+  | |  @@ -1,1 +1,1 @@
+  | |  -B
+  | |  \ No newline at end of file
+  | |  +B2
+  | |
+  | x  1 112478962961 B
+  |/   diff --git a/B b/B
+  |    new file mode 100644
+  |    --- /dev/null
+  |    +++ b/B
+  |    @@ -0,0 +1,1 @@
+  |    +B
+  |    \ No newline at end of file
+  |
+  o  0 426bada5c675 A
+     diff --git a/A b/A
+     new file mode 100644
+     --- /dev/null
+     +++ b/A
+     @@ -0,0 +1,1 @@
+     +A
+     \ No newline at end of file
+  
+#endif
+
+Nothing changed
+
+  $ hg amend
+  nothing changed
+  [1]
+
+Matcher and metadata options
+
+  $ echo 3 > C
+  $ echo 4 > D
+  $ hg add C D
+  $ hg amend -m NEWMESSAGE -I C -q
+  $ hg log -r . -T '{node|short} {desc} {files}\n'
+  c7ba14d9075b NEWMESSAGE B C
+  $ echo 5 > E
+  $ rm C
+  $ hg amend -d '2000 1000' -u 'Foo <[e-mail]>' -A C D -q
+  $ hg log -r . -T '{node|short} {desc} {files} {author} {date}\n'
+  14f6c4bcc865 NEWMESSAGE B D Foo <[e-mail]> 2000.01000
+
+Amend with editor
+
+  $ cat > $TESTTMP/prefix.sh <<'EOF'
+  > printf 'EDITED: ' > $TESTTMP/msg
+  > cat "$1" >> $TESTTMP/msg
+  > mv $TESTTMP/msg "$1"
+  > EOF
+  $ chmod +x $TESTTMP/prefix.sh
+
+  $ HGEDITOR="$TESTTMP/prefix.sh" hg amend --edit -q
+  $ hg log -r . -T '{node|short} {desc}\n'
+  298f085230c3 EDITED: NEWMESSAGE
+  $ HGEDITOR="$TESTTMP/prefix.sh" hg amend -e -m MSG -q
+  $ hg log -r . -T '{node|short} {desc}\n'
+  974f07f28537 EDITED: MSG
+
+  $ echo FOO > $TESTTMP/msg
+  $ hg amend -l $TESTTMP/msg -m BAR
+  abort: options --message and --logfile are mutually exclusive
+  [255]
+  $ hg amend -l $TESTTMP/msg -q
+  $ hg log -r . -T '{node|short} {desc}\n'
+  507be9bdac71 FOO
+
+Interactive mode
+
+  $ touch F G
+  $ hg add F G
+  $ cat <<EOS | hg amend -i --config ui.interactive=1 -q
+  > y
+  > n
+  > EOS
+  diff --git a/F b/F
+  new file mode 100644
+  examine changes to 'F'? [Ynesfdaq?] y
+  
+  diff --git a/G b/G
+  new file mode 100644
+  examine changes to 'G'? [Ynesfdaq?] n
+  
+  $ hg log -r . -T '{files}\n'
+  B D F
+
+Amend in the middle of a stack
+
+  $ hg init $TESTTMP/repo2
+  $ cd $TESTTMP/repo2
+  $ hg debugdrawdag <<'EOS'
+  > C
+  > |
+  > B
+  > |
+  > A
+  > EOS
+
+  $ hg update -q B
+  $ echo 2 >> B
+  $ hg amend
+  abort: cannot amend changeset with children
+  [255]
+
+#if obsstore-on
+
+With allowunstable, amend could work in the middle of a stack
+
+  $ cat >> $HGRCPATH <<EOF
+  > [experimental]
+  > evolution=createmarkers, allowunstable
+  > EOF
+
+  $ hg amend
+  $ hg log -T '{rev} {node|short} {desc}\n' -G
+  @  4 be169c7e8dbe B
+  |
+  | o  2 26805aba1e60 C
+  | |
+  | x  1 112478962961 B
+  |/
+  o  0 426bada5c675 A
+  
+#endif
+
+Cannot amend public changeset
+
+  $ hg phase -r A --public
+  $ hg update -C -q A
+  $ hg amend -m AMEND -q
+  abort: cannot amend public changesets
+  [255]
+
+Amend a merge changeset
+
+  $ hg init $TESTTMP/repo3
+  $ cd $TESTTMP/repo3
+  $ hg debugdrawdag <<'EOS'
+  >   C
+  >  /|
+  > A B
+  > EOS
+  $ hg update -q C
+  $ hg amend -m FOO -q
+  $ rm .hg/localtags
+  $ hg log -G -T '{desc}\n'
+  @    FOO
+  |\
+  | o  B
+  |
+  o  A
+