X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=dgit.git;a=blobdiff_plain;f=git-debrebase;h=5e8a8bb2dc81b979e1e15f95cc5ad744a67da31a;hp=37982499351e8365da2ef022c71f9abff5873b29;hb=0c244082ddb4b2443ccfbc1c438ead4fda1c33ca;hpb=a7e1b2feb9013251c5d1c763394170acc95eef65

diff --git a/git-debrebase b/git-debrebase
index 37982499..5e8a8bb2 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -21,6 +21,7 @@
 END { $? = $Debian::Dgit::ExitStatus::desired // -1; };
 use Debian::Dgit::GDR;
 use Debian::Dgit::ExitStatus;
+use Debian::Dgit::I18n;
 
 use strict;
 
@@ -30,6 +31,7 @@ setup_sigwarn();
 use Memoize;
 use Carp;
 use POSIX;
+use Locale::gettext;
 use Data::Dumper;
 use Getopt::Long qw(:config posix_default gnu_compat bundling);
 use Dpkg::Version;
@@ -38,7 +40,7 @@ use File::Copy;
 
 $debugcmd_when_debuglevel = 2;
 
-our ($usage_message) = <<'END';
+our ($usage_message) = i_ <<'END';
 usages:
   git-debrebase [<options>] [--|-i <git rebase options...>]
   git-debrebase [<options>] status
@@ -50,16 +52,19 @@ usages:
 See git-debrebase(1), git-debrebase(5), dgit-maint-debrebase(7) (in dgit).
 END
 
-our ($opt_force, $opt_noop_ok, @opt_anchors);
+our ($opt_force, $opt_noop_ok, $opt_merges, @opt_anchors);
 our ($opt_defaultcmd_interactive);
 
 our $us = qw(git-debrebase);
 
+our $wrecknoteprefix = 'refs/debrebase/wreckage';
+our $merge_cache_ref = 'refs/debrebase/merge-resolutions';
+
 $|=1;
 
 sub badusage ($) {
     my ($m) = @_;
-    print STDERR "$us: bad usage: $m\n";
+    print STDERR f_ "%s: bad usage: %s\n", $us, $m;
     finish 8;
 }
 
@@ -70,7 +75,7 @@ sub getoptions_main {
 }
 sub getoptions {
     my $sc = shift;
-    getoptions_main "bad options follow \`git-debrebase $sc'", @_;
+    getoptions_main +(f_ "bad options follow \`git-debrebase %s'", $sc), @_;
 }
 
 sub cfg ($;$) {
@@ -81,7 +86,7 @@ sub cfg ($;$) {
     push @cmd, $k;
     my $out = cmdoutput_errok @cmd;
     if (!defined $out) {
-	fail "missing required git config $k" unless $optional;
+	fail f_ "missing required git config %s", $k unless $optional;
 	return ();
     }
     my @l = split /\0/, $out;
@@ -100,15 +105,15 @@ sub dd ($) {
 sub get_commit ($) {
     my ($objid) = @_;
     my $data = (git_cat_file $objid, 'commit');
-    $data =~ m/(?<=\n)\n/ or die "$objid ($data) ?";
+    $data =~ m/(?<=\n)\n/ or confess "$objid ($data) ?";
     return ($`,$');
 }
 
 sub D_UPS ()      { 0x02; } # upstream files
 sub D_PAT_ADD ()  { 0x04; } # debian/patches/ extra patches at end
 sub D_PAT_OTH ()  { 0x08; } # debian/patches other changes
-sub D_DEB_CLOG () { 0x10; } # debian/ (not patches/ or changelog)
-sub D_DEB_OTH ()  { 0x20; } # debian/changelog
+sub D_DEB_CLOG () { 0x10; } # debian/changelog
+sub D_DEB_OTH ()  { 0x20; } # debian/ (not patches/ or changelog)
 sub DS_DEB ()     { D_DEB_CLOG | D_DEB_OTH; } # debian/ (not patches/)
 
 our $playprefix = 'debrebase';
@@ -126,8 +131,10 @@ sub in_workarea ($) {
     die $@ if $@;
 }
 
-sub fresh_workarea () {
-    $workarea = fresh_playground "$playprefix/work";
+sub fresh_workarea (;$) {
+    my ($subdir) = @_;
+    $subdir //= 'work';
+    $workarea = fresh_playground "$playprefix/$subdir";
     in_workarea sub { playtree_setup };
 }
 
@@ -137,10 +144,10 @@ sub run_ref_updates_now ($$) {
 
     my @upd_cmd = (git_update_ref_cmd "debrebase: $mrest", qw(--stdin));
     debugcmd '>|', @upd_cmd;
-    open U, "|-", @upd_cmd or die $!;
+    open U, "|-", @upd_cmd or confess $!;
     foreach (@$updates) {
 	printdebug ">= ", $_, "\n";
-	print U $_, "\n" or die $!;
+	print U $_, "\n" or confess $!;
     }
     printdebug ">\$\n";
     close U or failedcmd @upd_cmd;
@@ -152,14 +159,24 @@ our $snags_summarised = 0;
 our @deferred_updates;
 our @deferred_update_messages;
 
+sub merge_wreckage_cleaning ($) {
+    my ($updates) = @_;
+    git_for_each_ref("$wrecknoteprefix/*", sub {
+	my ($objid,$objtype,$fullrefname,$reftail) = @_;
+	push @$updates, "delete $fullrefname";
+    });
+}
+
 sub all_snags_summarised () {
     $snags_forced + $snags_tripped == $snags_summarised;
 }
 sub run_deferred_updates ($) {
     my ($mrest) = @_;
 
-    confess 'dangerous internal error' unless all_snags_summarised();
+    my $m = 'dangerous internal error';
+    confess $m.' - '.__ $m unless all_snags_summarised();
 
+    merge_wreckage_cleaning \@deferred_updates;
     run_ref_updates_now $mrest, \@deferred_updates;
     print $_, "\n" foreach @deferred_update_messages;
 
@@ -167,72 +184,158 @@ sub run_deferred_updates ($) {
     @deferred_update_messages = ();
 }
 
+sub get_tree ($;$$) {
+    # tree object name => ([ $name, $info ], ...)
+    # where $name is the sort key, ie has / at end for subtrees
+    # $info is the LHS from git-ls-tree (<mode> <type> <hash>)
+    # without $precheck, will crash if $x does not exist, so don't do that;
+    # instead pass '' to get ().
+    my ($x, $precheck, $recurse) = @_;
+
+    return () if !length $x;
+
+    if ($precheck) {
+	my ($type, $dummy) = git_cat_file $x, [qw(tree missing)];
+	return () if $type eq 'missing';
+    }
+
+    $recurse = !!$recurse;
+
+    confess "get_tree needs object not $x ?" unless $x =~ m{^[0-9a-f]+\:};
+
+    our (@get_tree_memo, %get_tree_memo);
+    my $memo = $get_tree_memo{$recurse,$x};
+    return @$memo if $memo;
+
+    local $Debian::Dgit::debugcmd_when_debuglevel = 3;
+    my @l;
+    my @cmd = (qw(git ls-tree -z --full-tree));
+    push @cmd, qw(-r) if $recurse;
+    push @cmd, qw(--), $x;
+    my $o = cmdoutput @cmd;
+    $o =~ s/\0$//s;
+    my $last = '';
+    foreach my $l (split /\0/, $o) {
+	my ($i, $n) = split /\t/, $l, 2;
+	$n .= '/' if $i =~ m/^\d+ tree /;
+	push @l, [ $n, $i ];
+	confess "$x need $last < $n ?" unless $last lt $n;
+    }
+    $get_tree_memo{$recurse,$x} = \@l;
+    push @get_tree_memo, $x;
+    if (@get_tree_memo > 10) {
+	delete $get_tree_memo{ shift @get_tree_memo };
+    }
+    return @l;
+}
+
+sub trees_diff_walk ($$$;$) {
+    # trees_diff_walk [{..opts...},] $x, $y, sub {... }
+    # calls sub->($name, $ix, $iy) for each difference
+    # $x and $y are as for get_tree
+    # where $name, $ix, $iy are $name and $info from get_tree
+    # opts are   all       call even for names same in both
+    #            recurse   call even for names same in both
+    my $opts = shift @_ if @_>=4;
+    my ($x,$y,$call) = @_;
+    my $all = $opts->{all};
+    return if !$all and $x eq $y;
+    my @x = get_tree $x, 0, $opts->{recurse};
+    my @y = get_tree $y, 0, $opts->{recurse};
+    printdebug "trees_diff_walk(..$x,$y..) ".Dumper(\@x,\@y)
+	if $debuglevel >= 3;
+    while (@x || @y) {
+	my $cmp = !@x       <=> !@y          # eg @y empty? $cmp=-1, use x
+ 	     ||    $x[0][0] cmp  $y[0][0];   # eg, x lt y ? $cmp=-1, use x
+	my ($n, $ix, $iy);                   # all same? $cmp=0, use both
+	$ix=$iy='';
+	printdebug "trees_diff_walk $cmp : @{ $x[0]//[] } | @{ $y[0]//[] }\n"
+	    if $debuglevel >= 3;
+	($n, $ix) = @{ shift @x } if $cmp <= 0;
+	($n, $iy) = @{ shift @y } if $cmp >= 0;
+	next if !$all and $ix eq $iy;
+	printdebug sprintf
+	    "trees_diff_walk(%d,'%s','%s') call('%s','%s','%s')\n",
+	    !!$all,$x,$y, $n,$ix,$iy
+	    if $debuglevel >= 2;
+	$call->($n, $ix, $iy);
+    }
+}
+
 sub get_differs ($$) {
     my ($x,$y) = @_;
-    # This resembles quiltify_trees_differ, in dgit, a bit.
+    # This does a similar job to quiltify_trees_differ, in dgit, a bit.
     # But we don't care about modes, or dpkg-source-unrepresentable
     # changes, and we don't need the plethora of different modes.
     # Conversely we need to distinguish different kinds of changes to
     # debian/ and debian/patches/.
+    # Also, here we have, and want to use, trees_diff_walk, because
+    # we may be calling this an awful lot and we want it to be fast.
 
     my $differs = 0;
+    my @debian_info;
 
-    my $rundiff = sub {
-	my ($opts, $limits, $fn) = @_;
-	my @cmd = (@git, qw(diff-tree -z --no-renames));
-	push @cmd, @$opts;
-	push @cmd, "$_:" foreach $x, $y;
-	push @cmd, '--', @$limits;
-	my $diffs = cmdoutput @cmd;
-	foreach (split /\0/, $diffs) { $fn->(); }
-    };
+    no warnings qw(exiting);
 
-    $rundiff->([qw(--name-only)], [], sub {
-        $differs |= $_ eq 'debian' ? DS_DEB : D_UPS;
-    });
+    my $plain = sub { $_[0] =~ m{^(100|0*)644 blob }s; };
 
-    if ($differs & DS_DEB) {
-	$differs &= ~DS_DEB;
-	$rundiff->([qw(--name-only -r)], [qw(debian)], sub {
-            $differs |=
-		m{^debian/patches/}      ? D_PAT_OTH  :
-		$_ eq 'debian/changelog' ? D_DEB_CLOG :
-		                           D_DEB_OTH;
-	});
-	die "mysterious debian changes $x..$y"
-	    unless $differs & (D_PAT_OTH|DS_DEB);
-    }
-
-    if ($differs & D_PAT_OTH) {
-	my $mode;
-	$differs &= ~D_PAT_OTH;
-	my $pat_oth = sub {
-	    $differs |= D_PAT_OTH;
-	    no warnings qw(exiting);  last;
-	};
-	$rundiff->([qw(--name-status -r)], [qw(debian/patches/)], sub {
-            no warnings qw(exiting);
-            if (!defined $mode) {
-		$mode = $_;  next;
+    trees_diff_walk "$x:", "$y:", sub {
+	my ($n,$ix,$iy) = @_;
+
+	# analyse difference at the toplevel
+
+	if ($n ne 'debian/') {
+	    $differs |= D_UPS;
+	    next;
+	}
+	if ($n eq 'debian') {
+	    # one side has a non-tree for ./debian !
+	    $differs |= D_DEB_OTH;
+	    next;
+	}
+
+	my $xd = $ix && "$x:debian";
+	my $yd = $iy && "$y:debian";
+	trees_diff_walk $xd, $yd, sub {
+	    my ($n,$ix,$iy) = @_;
+	    
+	    # analyse difference in debian/
+
+	    if ($n eq 'changelog' && (!$ix || $plain->($ix))
+                                  &&          $plain->($iy) ) {
+		$differs |= D_DEB_CLOG;
+		next;
 	    }
-	    die unless s{^debian/patches/}{};
-	    my $ok;
-	    if ($mode eq 'A' && !m/\.series$/s) {
-		$ok = 1;
-	    } elsif ($mode eq 'M' && $_ eq 'series') {
-		my $x_s = (git_cat_file "$x:debian/patches/series", 'blob');
-		my $y_s = (git_cat_file "$y:debian/patches/series", 'blob');
-		chomp $x_s;  $x_s .= "\n";
-		$ok = $x_s eq substr($y_s, 0, length $x_s);
-	    } else {
-		# nope
+	    if ($n ne 'patches/') {
+		$differs |= D_DEB_OTH;
+		next;
 	    }
-	    $mode = undef;
-	    $differs |= $ok ? D_PAT_ADD : D_PAT_OTH;
-        });
-	die "mysterious debian/patches changes $x..$y"
-	    unless $differs & (D_PAT_ADD|D_PAT_OTH);
-    }
+
+	    my $xp = $ix && "$xd/patches";
+	    my $yp = $iy && "$yd/patches";
+	    trees_diff_walk { recurse=>1 }, $xp, $yp, sub {
+		my ($n,$ix,$iy) = @_;
+
+		# analyse difference in debian/patches
+
+		my $ok;
+		if ($n =~ m{/$}s) {
+		    # we are recursing; directories may appear and disappear
+		    $ok = 1;
+		} elsif ($n !~ m/\.series$/s && !$ix && $plain->($iy)) {
+		    $ok = 1;
+		} elsif ($n eq 'series' && $plain->($ix) && $plain->($iy)) {
+		    my $x_s = (git_cat_file "$xp/series", 'blob');
+		    my $y_s = (git_cat_file "$yp/series", 'blob');
+		    chomp $x_s;  $x_s .= "\n";
+		    $ok = $x_s eq substr($y_s, 0, length $x_s);
+		} else {
+		    # nope
+		}
+		$differs |= $ok ? D_PAT_ADD : D_PAT_OTH;
+	    };    
+	};
+    };
 
     printdebug sprintf "get_differs %s %s = %#x\n", $x, $y, $differs;
 
@@ -295,10 +398,10 @@ sub snag ($$;@) {
     my ($tag,$msg) = @_; # ignores extra args, for benefit of keycommits
     if (grep { $_ eq $tag } @snag_force_opts) {
 	$snags_forced++;
-	print STDERR "git-debrebase: snag ignored (-f$tag): $msg\n";
+	print STDERR f_ "%s: snag ignored (-f%s): %s\n", $us, $tag, $msg;
     } else {
 	$snags_tripped++;
-	print STDERR "git-debrebase: snag detected (-f$tag): $msg\n";
+	print STDERR f_ "%s: snag detected (-f%s): %s\n", $us, $tag, $msg;
     }
 }
 
@@ -310,17 +413,17 @@ sub snag ($$;@) {
 sub snags_maybe_bail () {
     return if all_snags_summarised();
     if ($snags_forced) {
-	printf STDERR
+	print STDERR f_
 	    "%s: snags: %d overriden by individual -f options\n",
 	    $us, $snags_forced;
     }
     if ($snags_tripped) {
 	if ($opt_force) {
-	    printf STDERR
+	    print STDERR f_
 		"%s: snags: %d overriden by global --force\n",
 		$us, $snags_tripped;
 	} else {
-	    fail sprintf
+	    fail f_
   "%s: snags: %d blocker(s) (you could -f<tag>, or --force)",
 		$us, $snags_tripped;
 	}
@@ -336,11 +439,65 @@ sub any_snags () {
     return $snags_forced || $snags_tripped;
 }
 
+sub ffq_prev_branchinfo () {
+    my $current = git_get_symref();
+    return gdr_ffq_prev_branchinfo($current);
+}
+
+sub record_gdrlast ($$;$) {
+    my ($gdrlast, $newvalue, $oldvalue) = @_;
+    $oldvalue ||= $git_null_obj;
+    push @deferred_updates, "update $gdrlast $newvalue $oldvalue";
+}
+
+sub fail_unprocessable ($) {
+    my ($msg) = @_;
+    changedir $maindir;
+    my ($ffqs, $ffqm, $symref, $ffq_prev, $gdrlast) = ffq_prev_branchinfo();
+
+    my $mangled = __ <<END;
+Branch/history seems mangled - no longer in gdr format.
+See ILLEGAL OPERATIONS in git-debrebase(5).
+END
+    chomp $mangled;
+
+    if (defined $ffqm) {
+	fail f_ <<END, $msg, $ffqm;
+%s
+Is this meant to be a gdr branch?  %s
+END
+    } elsif (git_get_ref $ffq_prev) {
+	fail f_ <<END, $msg, $mangled;
+%s
+%s
+Consider git-debrebase scrap, to throw away your recent work.
+END
+    } elsif (!git_get_ref $gdrlast) {
+	fail f_ <<END, $msg;
+%s
+Branch does not seem to be meant to be a git-debrebase branch?
+Wrong branch, or maybe you needed git-debrebase convert-from-*.
+END
+    } elsif (is_fast_fwd $gdrlast, git_rev_parse 'HEAD') {
+	fail <<END;
+$msg
+$mangled
+END
+    } else {
+	fail f_ <<END, $msg;
+%s
+Branch/history mangled, and diverged since last git-debrebase.
+Maybe you reset to, or rebased from, somewhere inappropriate.
+END
+    }
+};
+
 sub gbp_pq_export ($$$) {
     my ($bname, $base, $tip) = @_;
     # must be run in a workarea.  $bname and patch-queue/$bname
     # ought not to exist.  Leaves you on patch-queue/$bname with
     # the patches staged but not committed.
+    # returns 1 if there were any patches
     printdebug "gbp_pq_export $bname $base $tip\n";
     runcmd @git, qw(checkout -q -b), $bname, $base;
     runcmd @git, qw(checkout -q -b), "patch-queue/$bname", $tip;
@@ -350,29 +507,68 @@ sub gbp_pq_export ($$$) {
 	{ local ($!,$?); copy('../gbp-pq-err', \*STDERR); }
 	failedcmd @gbp_cmd;
     }
-    runcmd @git, qw(add -f debian/patches) if stat_exists 'debian/patches';
+    return 0 unless stat_exists 'debian/patches';
+    runcmd @git, qw(add -f debian/patches);
+    return 1;
 }
 
 
-# xxx allow merge resolution separately from laundering, before git merge
-#
-# xxx general gdr docs highlight forbidden things
-# xxx general gdr docs list allowable things ?
-# xxx general gdr docs explicitly forbid some rebase
-#
-# xxx provide a way for the user to help
-# xxx (eg, provide wreckage provide way to continue)
+# MERGE-TODO allow merge resolution separately from laundering, before git merge
 
 # later/rework?
 #  use git-format-patch?
 #  our own patch identification algorithm?
 #  this is an alternative strategy
 
+sub merge_failed ($$;@) {
+    my ($wrecknotes, $emsg, @xmsgs) = @_;
+    my @m;
+    push @m, "Merge resolution failed: $emsg";
+    push @m, @xmsgs;
+
+    changedir $maindir;
+
+    my @updates;
+    merge_wreckage_cleaning \@updates;
+    run_ref_updates_now "merge failed", \@updates;
+
+    @updates = ();
+    keys %$wrecknotes;
+    while (my ($k,$v) = each %$wrecknotes) {
+	push @updates, "create $wrecknoteprefix/$k $v";
+    }
+    run_ref_updates_now "merge failed", \@updates;
+    push @m, "Wreckage left in $wrecknoteprefix/*.";
+
+    push @m, "See git-debrebase(1) section FAILED MERGES for suggestions.";
+
+    # use finish rather than fail, in case we are within an eval
+    # (that can happen inside walk!)
+    print STDERR "\n";
+    print STDERR "$us: $_\n" foreach @m;
+    finish 15;
+}
+
 sub mwrecknote ($$$) {
     my ($wrecknotes, $reftail, $commitish) = @_;
+    confess unless defined $commitish;
+    printdebug "mwrecknote $reftail $commitish\n";
     $wrecknotes->{$reftail} = $commitish;
 }
 
+sub merge_attempt_cmd {
+    my $wrecknotes = shift @_;
+    debugcmd '+', @_;
+    $!=0; $?=-1;
+    if (system @_) {
+	merge_failed $wrecknotes,
+	    failedcmd_waitstatus(),
+	    "failed command: @_";
+    }
+}
+
+sub merge_series_patchqueue_convert ($$$);
+
 sub merge_series ($$$;@) {
     my ($newbase, $wrecknotes, $base_q, @input_qs) = @_;
     # $base_q{SeriesBase}  $input_qs[]{SeriesBase}
@@ -397,32 +593,34 @@ sub merge_series ($$$;@) {
     # $prereq{<patch filename>}{<possible prereq}  exists or not (later)
     # $prereq{<patch filename>}               exists or not (even later)
 
-    my $result;
+    my $merged_pq;
 
     my $mwrecknote = sub { &mwrecknote($wrecknotes, @_); };
 
-    local $workarea = fresh_playground "$playprefix/merge";
+    my $attempt_cmd = sub { &merge_attempt_cmd($wrecknotes, @_); };
+
+    local $workarea;
+    fresh_workarea "merge";
     my $seriesfile = "debian/patches/series";
     in_workarea sub {
 	playtree_setup();
 	foreach my $q ($base_q, reverse @input_qs) {
 	    my $s = $q->{MR}{S};
-	    gbp_pq_export "p-$s", $q->{SeriesBase}, $q->{SeriesTip};
+	    my $any = gbp_pq_export "p-$s", $q->{SeriesBase}, $q->{SeriesTip};
 	    my @earlier;
-	    if (open S, $seriesfile) {
+	    if ($any) {
+		open S, $seriesfile or confess "$seriesfile $!";
 		while (my $patch = <S>) {
-		    chomp $patch or die $!;
+		    chomp $patch or confess $!;
 		    $prereq{$patch} //= {};
 		    foreach my $earlier (@earlier) {
-			$prereq{$patch}{$earlier}{$s}++ and die;
+			$prereq{$patch}{$earlier}{$s}++ and confess;
 		    }
 		    push @earlier, $patch;
-		    stat "debian/patches/$patch" or die "$patch ?";
+		    stat "debian/patches/$patch" or confess "$patch ?";
 		}
-		S->error and die "$seriesfile $!";
+		S->error and confess "$seriesfile $!";
 		close S;
-	    } else {
-		die "$seriesfile $!" unless $!==ENOENT;
 	    }
 	    read_tree_upstream $newbase, 1;
 	    my $pec = make_commit [ grep { defined } $base_q->{MR}{PEC} ], [
@@ -454,17 +652,14 @@ sub merge_series ($$$;@) {
 	    printdebug "pec' $pec\n";
             runcmd @git, qw(reset -q --hard), $pec;
 	    $q->{MR}{PEC} = $pec;
-	    $mwrecknote->("$q->{LeftRight}-patchqueue");
+	    $mwrecknote->("$q->{LeftRight}-patchqueue", $pec);
 	}
 	# now, because of reverse, we are on $input_q->{MR}{OQC}
 	runcmd @git, qw(checkout -q -b merge);
 	printdebug "merge_series merging...\n";
 	my @mergecmd = (@git, qw(merge --quiet --no-edit), "p-1");
-	debugcmd '+', @mergecmd;
-	$!=0; $?=-1;
-	if (system @mergecmd) {
-	    failedcmd @mergecmd;
-	}
+
+	$attempt_cmd->(@mergecmd);
 
 	printdebug "merge_series merge ok, series...\n";
 	# We need to construct a new series file
@@ -503,7 +698,7 @@ sub merge_series ($$$;@) {
 	my $authordate = sub {
 	    my ($f) = @_;
 	    $authordate{$f} //= do {
-		open PF, "<", "debian/patches/$f" or die "$f $!";
+		open PF, "<", "debian/patches/$f" or confess "$f $!";
 		while (<PF>) {
 		    return $nodate if m/^$/;
 		    last if s{^Date: }{};
@@ -513,7 +708,7 @@ sub merge_series ($$$;@) {
 	    };
 	};
 
-	open NS, '>', $seriesfile or die $!;
+	open NS, '>', $seriesfile or confess $!;
 
 	while (keys %prereq) {
 	    my $best;
@@ -528,7 +723,7 @@ sub merge_series ($$$;@) {
 		$best = $try;
 	    }
 	    printdebug "merge_series series next $best\n";
-	    print NS "$best\n" or die $!;
+	    print NS "$best\n" or confess $!;
 	    delete $prereq{$best};
 	    foreach my $gp (values %prereq) {
 		delete $gp->{$best};
@@ -537,17 +732,32 @@ sub merge_series ($$$;@) {
 
 	runcmd @git, qw(add), $seriesfile;
 	runcmd @git, qw(commit --quiet -m), 'Merged patch queue form';
-	$mwrecknote->('merged-patchqueue', git_rev_parse 'HEAD');
+	$merged_pq = git_rev_parse 'HEAD';
+	$mwrecknote->('merged-patchqueue', $merged_pq);
+    };
+    return merge_series_patchqueue_convert
+	    $wrecknotes, $newbase, $merged_pq;
+}
+
+sub merge_series_patchqueue_convert ($$$) {
+    my ($wrecknotes, $newbase, $merged_pq) = @_;
 
+    my $result;
+    in_workarea sub {
+	playtree_setup();
 	printdebug "merge_series series gbp pq import\n";
-	runcmd qw(gbp pq import);
+	runcmd @git, qw(checkout -q -b mergec), $merged_pq;
+
+	merge_attempt_cmd($wrecknotes, qw(gbp pq import));
+	# MERGE-TODO consider git-format-patch etc. instead,
+	# since gbp pq doesn't always round-trip :-/
 
 	# OK now we are on patch-queue/merge, and we need to rebase
 	# onto the intended parent and drop the patches from each one
 
 	printdebug "merge_series series ok, building...\n";
 	my $build = $newbase;
-	my @lcmd = (@git, qw(rev-list --reverse merge..patch-queue/merge));
+	my @lcmd = (@git, qw(rev-list --reverse mergec..patch-queue/mergec));
 	foreach my $c (grep /./, split /\n/, cmdoutput @lcmd) {
 	    my $commit = git_cat_file $c, 'commit';
 	    printdebug "merge_series series ok, building $c\n";
@@ -555,13 +765,13 @@ sub merge_series ($$$;@) {
 	    my $tree = cmdoutput @git, qw(write-tree);
 	    $commit =~ s{^parent (\S+)$}{parent $build}m or confess;
 	    $commit =~ s{^tree (\S+)$}{tree $tree}m      or confess;
-	    open C, ">", "../mcommit" or die $!;
-	    print C $commit or die $!;
-	    close C or die $!;
+	    open C, ">", "../mcommit" or confess $!;
+	    print C $commit or confess $!;
+	    close C or confess $!;
 	    $build = cmdoutput @git, qw(hash-object -w -t commit ../mcommit);
 	}
 	$result = $build;
-	$mwrecknote->('merged-result', $result);
+	mwrecknote($wrecknotes, 'merged-result', $result);
 
 	runcmd @git, qw(update-ref refs/heads/result), $result;
 
@@ -571,7 +781,7 @@ sub merge_series ($$$;@) {
 	runcmd @git, qw(commit --allow-empty -q -m M-WORKTREE);
 	my $mdebug = git_rev_parse 'HEAD';
 	printdebug sprintf "merge_series done debug=%s\n", $mdebug;
-	$mwrecknote->('merged-debug', $mdebug);
+	mwrecknote($wrecknotes, 'merged-debug', $mdebug);
     };
     printdebug "merge_series returns $result\n";
     return $result;
@@ -628,11 +838,11 @@ sub parsecommit ($;$) {
     #    $p_ref, if provided, must be [] and is used as a base for Parents
 
     $p_ref //= [];
-    die if @$p_ref;
+    confess if @$p_ref;
 
     my ($h,$m) = get_commit $objid;
 
-    my ($t) = $h =~ m/^tree (\w+)$/m or die $objid;
+    my ($t) = $h =~ m/^tree (\w+)$/m or confess $objid;
     my (@ph) = $h =~ m/^parent (\w+)$/mg;
 
     my $r = {
@@ -721,9 +931,11 @@ sub classify ($) {
 	# reject it here then we avoid making the pseudomerge which
 	# would be needed to push it.
 
-	my $badanchor = sub { $unknown->("git-debrebase \`anchor' but @_"); };
-	@p == 2 or return $badanchor->("has other than two parents");
-	$haspatches and return $badanchor->("contains debian/patches");
+	my $badanchor = sub {
+	    $unknown->(f_ "git-debrebase \`anchor' but %s", "@_");
+	};
+	@p == 2 or return $badanchor->(__ "has other than two parents");
+	$haspatches and return $badanchor->(__ "contains debian/patches");
 
 	# How to decide about l/r ordering of anchors ?  git
 	# --topo-order prefers to expand 2nd parent first.  There's
@@ -749,11 +961,11 @@ sub classify ($) {
 	# parents from left to right, in order, so it's easy to see
 	# which way round a pseudomerge is.
 
-	$p[0]{IsOrigin} and $badanchor->("is an origin commit");
+	$p[0]{IsOrigin} and $badanchor->(__ "is an origin commit");
 	$p[1]{Differs} & ~DS_DEB and
-	    $badanchor->("upstream files differ from left parent");
+	    $badanchor->(__ "upstream files differ from left parent");
 	$p[0]{Differs} & ~D_UPS and
-	    $badanchor->("debian/ differs from right parent");
+	    $badanchor->(__ "debian/ differs from right parent");
 
 	return $classify->(qw(Anchor),
 			   OrigParents => [ $p[1] ]);
@@ -764,7 +976,7 @@ sub classify ($) {
 	if ($d == D_PAT_ADD) {
 	    return $classify->(qw(AddPatches));
 	} elsif ($d & (D_PAT_ADD|D_PAT_OTH)) {
-	    return $unknown->("edits debian/patches");
+	    return $unknown->(__ "edits debian/patches");
 	} elsif ($d & DS_DEB and !($d & ~DS_DEB)) {
 	    my ($ty,$dummy) = git_cat_file "$p[0]{CommitId}:debian";
 	    if ($ty eq 'tree') {
@@ -776,20 +988,20 @@ sub classify ($) {
 	    } elsif ($ty eq 'missing') {
 		return $classify->(qw(BreakwaterStart));
 	    } else {
-		return $unknown->("parent's debian is not a directory");
+		return $unknown->(__ "parent's debian is not a directory");
 	    }
 	} elsif ($d == D_UPS) {
 	    return $classify->(qw(Upstream));
 	} elsif ($d & DS_DEB and $d & D_UPS and !($d & ~(DS_DEB|D_UPS))) {
 	    return $classify->(qw(Mixed));
 	} elsif ($d == 0) {
-	    return $unknown->("no changes");
+	    return $unknown->(__ "no changes");
 	} else {
 	    confess "internal error $objid ?";
 	}
     }
     if (!@p) {
-	return $unknown->("origin commit");
+	return $unknown->(__ "origin commit");
     }
 
     if (@p == 2 && @identical == 1) {
@@ -802,7 +1014,8 @@ sub classify ($) {
     if (@p == 2 && @identical == 2) {
 	my $get_t = sub {
 	    my ($ph,$pm) = get_commit $_[0]{CommitId};
-	    $ph =~ m/^committer .* (\d+) [-+]\d+$/m or die "$_->{CommitId} ?";
+	    $ph =~ m/^committer .* (\d+) [-+]\d+$/m
+		or confess "$_->{CommitId} ?";
 	    $1;
 	};
 	my @bytime = @p;
@@ -836,18 +1049,17 @@ sub classify ($) {
 
     if (@p == 2 and
 	$r->{Msg} =~ m{^\[git-debrebase merged-breakwater.*\]$}m) {
-	# xxx ^ metadata tag needs adding to (5)
 	return $classify->("MergedBreakwaters");
     }
     if ($r->{Msg} =~ m{^\[(git-debrebase|dgit)[: ].*\]$}m) {
-	return $unknown->("unknown kind of merge from $1");
+	return $unknown->(f_ "unknown kind of merge from %s", $1);
     }
     if (@p > 2) {
-	return $unknown->("octopus merge");
+	return $unknown->(__ "octopus merge");
     }
 
-    if (!$ENV{GIT_DEBREBASE_EXPERIMENTAL_MERGE}) {
-	return $unknown->("general two-parent merge");
+    if (!$opt_merges) {
+	return $unknown->(__ "general two-parent merge");
     }
 
     return $classify->("VanillaMerge");
@@ -864,7 +1076,8 @@ sub mergedbreakwaters_anchor ($) {
 	$best_anchor = $panchor
 	    if !defined $best_anchor
 	    or is_fast_fwd $best_anchor, $panchor;
-	fail "inconsistent anchors in merged-breakwaters $p->{CommitId}"
+	fail f_ "inconsistent anchors in merged-breakwaters %s",
+	    $p->{CommitId}
 	    unless is_fast_fwd $panchor, $best_anchor;
     }
     return $best_anchor;
@@ -874,9 +1087,8 @@ sub keycommits ($;$$$$$) {
     my ($head, $furniture, $unclean, $trouble, $fatal, $claimed_bw) = @_;
     # => ($anchor, $breakwater)
 
-    # $unclean->("unclean-$tagsfx", $msg, $cl)
     # $furniture->("unclean-$tagsfx", $msg, $cl)
-    # $dgitimport->("unclean-$tagsfx", $msg, $cl))
+    # $unclean->("unclean-$tagsfx", $msg, $cl)
     #   is callled for each situation or commit that
     #   wouldn't be found in a laundered branch
     # $furniture is for furniture commits such as might be found on an
@@ -900,11 +1112,11 @@ sub keycommits ($;$$$$$) {
     my $clogonly;
     my $cl;
     my $found_pm;
-    $fatal //= sub { fail $_[1]; };
+    $fatal //= sub { fail_unprocessable $_[1]; };
     my $x = sub {
 	my ($cb, $tagsfx, $mainwhy, $xwhy) = @_;
 	my $why = $mainwhy.$xwhy;
-	my $m = "branch needs laundering (run git-debrebase): $why";
+	my $m = f_ "branch needs laundering (run git-debrebase): %s", $why;
 	fail $m unless defined $cb;
 	return unless $cb;
 	$cb->("unclean-$tagsfx", $why, $cl, $mainwhy);
@@ -932,41 +1144,47 @@ sub keycommits ($;$$$$$) {
 	    $found_anchor->($head);
 	} elsif ($ty eq 'Upstream') {
 	    $x->($unclean, 'ordering',
- "packaging change ($breakwater) follows upstream change"," (eg $head)")
+ (f_ "packaging change (%s) follows upstream change", $breakwater),
+		 (f_ " (eg %s)", $head))
 		if defined $breakwater;
 	    $clogonly = undef;
 	    $breakwater = undef;
 	} elsif ($ty eq 'Mixed') {
 	    $x->($unclean, 'mixed',
-		 "found mixed upstream/packaging commit"," ($head)");
+		 (__ "found mixed upstream/packaging commit"),
+		 (f_ " (%s)", $head));
 	    $clogonly = undef;
 	    $breakwater = undef;
 	} elsif ($ty eq 'Pseudomerge' or
 		 $ty eq 'AddPatches') {
 	    my $found_pm = 1;
 	    $x->($furniture, (lc $ty),
-		 "found interchange bureaucracy commit ($ty)"," ($head)");
+		 (f_ "found interchange bureaucracy commit (%s)", $ty),
+		 (f_ " (%s)", $head));
 	} elsif ($ty eq 'DgitImportUnpatched') {
 	    if ($found_pm) {
 		$x->($trouble, 'dgitimport',
-		     "found dgit dsc import"," ($head)");
+		     (__ "found dgit dsc import"),
+		     (f_ " (%s)", $head));
 		return (undef,undef);
 	    } else {
 		$x->($fatal, 'unprocessable',
-		     "found bare dgit dsc import with no prior history",
-		     " ($head)");
+		     (__ "found bare dgit dsc import with no prior history"),
+		     (f_ " (%s)", $head));
 		return (undef,undef);
 	    }
 	} elsif ($ty eq 'VanillaMerge') {
 	    $x->($trouble, 'vanillamerge',
-		 "found vanilla merge"," ($head)");
+		 (__ "found vanilla merge"),
+		 (f_ " (%s)", $head));
 	    return (undef,undef);
 	} elsif ($ty eq 'MergedBreakwaters') {
 	    $found_anchor->(mergedbreakwaters_anchor $cl);
 	} else {
 	    $x->($fatal, 'unprocessable',
-		 "found unprocessable commit, cannot cope: $cl->{Why}",
-		 " ($head)");
+		 (f_ "found unprocessable commit, cannot cope: %s",
+		     $cl->{Why}),
+		 (f_ " (%s)", $head));
 	    return (undef,undef);
 	}
 	$head = $cl->{Parents}[0]{CommitId};
@@ -995,10 +1213,12 @@ sub walk ($;$$$) {
     my $cl;
     my $xmsg = sub {
 	my ($prose, $info) = @_;
+	# We deliberately do not translate $prose, since this mostly
+	# appears in commits in Debian and they should be in English.
 	my $ms = $cl->{Msg};
 	chomp $ms;
-	$info //= '';
-	$ms .= "\n\n[git-debrebase$info: $prose]\n";
+	confess unless defined $info;
+	$ms .= "\n\n[git-debrebase $info: $prose]\n";
 	return (Msg => $ms);
     };
     my $rewrite_from_here = sub {
@@ -1025,12 +1245,14 @@ sub walk ($;$$$) {
 	if ($nogenerate) {
 	    return (undef,undef);
 	}
-	fail "found unprocessable commit, cannot cope".
-	    (defined $cl->{Why} ? "; $cl->{Why}:": ':').
-	    " (commit $cur) (d.".
-	    (join ' ', map { sprintf "%#x", $_->{Differs} }
-	     @{ $cl->{Parents} }).
-		 ")";
+	my $d =
+	    join ' ',
+	    map { sprintf "%#x", $_->{Differs} }
+	    @{ $cl->{Parents} };
+	fail_unprocessable f_ +(defined $cl->{Why}
+ ? i_ 'found unprocessable commit, cannot cope; %3$s: (commit %1$s) (d.%2$s)'
+ : i_ 'found unprocessable commit, cannot cope: (commit %1$s) (d.%2$s)'),
+                                   $cur, $d, $cl->{Why};
     };
 
     my $build;
@@ -1044,7 +1266,8 @@ sub walk ($;$$$) {
     };
 
     my $nomerge = sub {
-	fail "something useful about failed merge attempt @_ xxx".Dumper($cl);
+	my ($emsg) = @_;
+	merge_failed $cl->{MergeWreckNotes}, $emsg;
     };
 
     my $mwrecknote = sub { &mwrecknote($cl->{MergeWreckNotes}, @_); };
@@ -1053,6 +1276,7 @@ sub walk ($;$$$) {
 
     for (;;) {
 	$cl = classify $cur;
+	$cl->{MergeWreckNotes} //= {};
 	my $ty = $cl->{Type};
 	my $st = $cl->{SubType};
 	$prline->("$cl->{CommitId} $cl->{Type}");
@@ -1077,7 +1301,7 @@ sub walk ($;$$$) {
 	} elsif ($ty eq 'Mixed') {
 	    my $queue = sub {
 		my ($q, $wh) = @_;
-		my $cls = { %$cl, $xmsg->("split mixed commit: $wh part") };
+		my $cls = { %$cl, $xmsg->("mixed commit: $wh part",'split') };
 		push @$q, $cls;
 	    };
 	    $queue->(\@brw_cl, "debian");
@@ -1130,12 +1354,12 @@ sub walk ($;$$$) {
 		push @brw_cl, {
 		    %$cl,
 		    SpecialMethod => 'DgitImportDebianUpdate',
-                    $xmsg->("convert dgit import: debian changes")
+                    $xmsg->("debian changes", 'convert dgit import')
 		}, {
 		    %$cl,
 		    SpecialMethod => 'DgitImportUpstreamUpdate',
                     $xmsg->("convert dgit import: upstream update",
-			    " anchor")
+			    "anchor")
 		};
 		$prline->(" Import");
 		$rewrite_from_here->(\@brw_cl);
@@ -1148,10 +1372,10 @@ sub walk ($;$$$) {
 		# patches as commits.  Unfortunately it contains
 		# debian/patches/.
 		printdebug "*** WALK BOMB bare dgit import\n";
-		$cl->{Why} = "bare dgit dsc import";
+		$cl->{Why} = __ "bare dgit dsc import";
 		return $bomb->();
 	    }
-	    die "$ty ?";
+	    confess "$ty ?";
 	} elsif ($ty eq 'MergedBreakwaters') {
 	    $last_anchor = mergedbreakwaters_anchor $cl;
 	    $build_start->(' MergedBreakwaters', $cur);
@@ -1165,7 +1389,7 @@ sub walk ($;$$$) {
 	    # which was reachable via ffq-prev is no longer findable.
 	    # This is suboptimal, but if it all works we'll have done
 	    # the right thing.
-	    # xxx we should warn the user in the docs about this
+	    # MERGE-TODO we should warn the user in the docs about this
 
 	    my $ok=1;
 	    my $best_anchor;
@@ -1297,8 +1521,9 @@ sub walk ($;$$$) {
 	    my ($btip, $bbw, $banchor) = eval {
 		walk $ib, 0, $report, $report_lprefix.'  ';
 	    };
-	    $nomerge->("walking interchange branch merge base ($ibleaf): ".
-		       $@) if length $@;
+	    $nomerge->("walking interchange branch merge base ($ibleaf):\n".
+		       $@)
+		if length $@;
 
 	    $mwrecknote->("mergebase-laundered", $btip);
 	    $mwrecknote->("mergebase-breakwater", $bbw);
@@ -1327,7 +1552,7 @@ sub walk ($;$$$) {
                 %$cl,
                 SpecialMethod => 'MergeCreateMergedBreakwaters',
                 $xmsg->('constructed from vanilla merge',
-			' merged-breakwater'),
+			'merged-breakwater'),
             };
 	    push @upp_cl, {
                 %$cl,
@@ -1352,23 +1577,23 @@ sub walk ($;$$$) {
 
     my $rewriting = 0;
 
-    my $read_tree_upstream = sub {
-	my ($treeish) = @_;
-	read_tree_upstream $treeish, 0, $build;
-    };
-
     $#upp_cl = $upp_limit if defined $upp_limit;
  
     my $committer_authline = calculate_committer_authline();
 
     printdebug "WALK REBUILD $build ".(scalar @processed)."\n";
 
-    confess "internal error" unless $build eq (pop @processed)->{CommitId};
+    confess __ "internal error" unless $build eq (pop @processed)->{CommitId};
 
     in_workarea sub {
-	mkdir $rd or $!==EEXIST or die $!;
+	mkdir $rd or $!==EEXIST or confess $!;
 	my $current_method;
-	runcmd @git, qw(read-tree), $build;
+	my $want_debian = $build;
+	my $want_upstream = $build;
+
+	my $read_tree_upstream = sub { ($want_upstream) = @_; };
+	my $read_tree_debian = sub { ($want_debian) = @_; };
+
 	foreach my $cl (qw(Debian), (reverse @brw_cl),
 			{ SpecialMethod => 'RecordBreakwaterTip' },
 			qw(Upstream), (reverse @upp_cl)) {
@@ -1382,7 +1607,7 @@ sub walk ($;$$$) {
 	    printdebug "WALK BUILD ".($cltree//'undef').
 		" $method (rewriting=$rewriting)\n";
 	    if ($method eq 'Debian') {
-		read_tree_debian($cltree);
+		$read_tree_debian->($cltree);
 	    } elsif ($method eq 'Upstream') {
 		$read_tree_upstream->($cltree);
 	    } elsif ($method eq 'StartRewrite') {
@@ -1392,7 +1617,7 @@ sub walk ($;$$$) {
 		$breakwater = $build;
 		next;
 	    } elsif ($method eq 'DgitImportDebianUpdate') {
-		read_tree_debian($cltree);
+		$read_tree_debian->($cltree);
 	    } elsif ($method eq 'DgitImportUpstreamUpdate') {
  		confess unless $rewriting;
 		my $differs = (get_differs $build, $cltree);
@@ -1403,15 +1628,23 @@ sub walk ($;$$$) {
 		print "Found a general merge, will try to tidy it up.\n";
 		$rewriting = 1;
 		$read_tree_upstream->($cl->{MergeBestAnchor});
-		$read_tree_upstream->($cl->{MergeBestAnchor});
-		read_tree_debian($cltree);
+		$read_tree_debian->($cltree);
 		@parents = map { $_->{Breakwater} } @{ $cl->{Parents} };
 	    } elsif ($method eq 'MergeMergeSeries') {
-		print "Running merge resolution for $cl->{CommitId}...\n";
-		$build = merge_series
-		    $build, $cl->{MergeWreckNotes},
-		    $cl->{MergeInterchangeBaseInfo},
-		    @{ $cl->{Parents} };
+		my $cachehit = reflog_cache_lookup
+		    $merge_cache_ref, "vanilla-merge $cl->{CommitId}";
+		if ($cachehit) {
+		    print "Using supplied resolution for $cl->{CommitId}...\n";
+		    $build = $cachehit;
+		    $mwrecknote->('cached-resolution', $build);
+		} else {
+		    print "Running merge resolution for $cl->{CommitId}...\n";
+		    $mwrecknote->('new-base', $build);
+		    $build = merge_series
+			$build, $cl->{MergeWreckNotes},
+			$cl->{MergeInterchangeBaseInfo},
+			@{ $cl->{Parents} };
+		}
 		$last_anchor = $cl->{MergeBestAnchor};
 
 		# Check for mismerges:
@@ -1448,27 +1681,46 @@ sub walk ($;$$$) {
 		    printdebug "WALK REWRITING NOW cl=$cl procd=$procd\n";
 		}
 	    }
-	    my $newtree = cmdoutput @git, qw(write-tree);
-	    my $ch = $cl->{Hdr};
-	    $ch =~ s{^tree .*}{tree $newtree}m or confess "$ch ?";
-	    $ch =~ s{^parent .*\n}{}mg;
-	    $ch =~ s{(?=^author)}{
-		join '', map { "parent $_\n" } @parents
-	    }me or confess "$ch ?";
 	    if ($rewriting) {
-		$ch =~ s{^committer .*$}{$committer_authline}m
-		    or confess "$ch ?";
+		read_tree_upstream $want_upstream, 0, $want_debian;
+
+		my $newtree = cmdoutput @git, qw(write-tree);
+		my $ch = $cl->{Hdr};
+		$ch =~ s{^tree .*}{tree $newtree}m or confess "$ch ?";
+		$ch =~ s{^parent .*\n}{}mg;
+		$ch =~ s{(?=^author)}{
+		    join '', map { "parent $_\n" } @parents
+		}me or confess "$ch ?";
+		if ($rewriting) {
+		    $ch =~ s{^committer .*$}{$committer_authline}m
+			or confess "$ch ?";
+		}
+		my $cf = "$rd/m$rewriting";
+		open CD, ">", $cf or confess $!;
+		print CD $ch, "\n", $cl->{Msg} or confess $!;
+		close CD or confess $!;
+		my @cmd = (@git, qw(hash-object));
+		push @cmd, qw(-w) if $rewriting;
+		push @cmd, qw(-t commit), $cf;
+		my $newcommit = cmdoutput @cmd;
+		confess "$ch ?" unless $rewriting
+		    or $newcommit eq $cl->{CommitId};
+		$build = $newcommit;
+	    } else {
+		$build = $cl->{CommitId};
+		trees_diff_walk "$want_upstream:", "$build:", sub {
+		    my ($n) = @_;
+		    no warnings qw(exiting);
+		    next if $n eq 'debian/';
+		    confess f_ "mismatch %s ?", "@_";
+		};
+		trees_diff_walk "$want_debian:debian", "$build:debian", sub {
+		    confess f_ "mismatch %s ?", "@_";
+		};
+		my @old_parents = map { $_->{CommitId} } @{ $cl->{Parents} };
+		confess f_ "mismatch %s != %s ?", "@parents", "@old_parents"
+		    unless "@parents" eq "@old_parents";
 	    }
-	    my $cf = "$rd/m$rewriting";
-	    open CD, ">", $cf or die $!;
-	    print CD $ch, "\n", $cl->{Msg} or die $!;
-	    close CD or die $!;
-	    my @cmd = (@git, qw(hash-object));
-	    push @cmd, qw(-w) if $rewriting;
-	    push @cmd, qw(-t commit), $cf;
-	    my $newcommit = cmdoutput @cmd;
-	    confess "$ch ?" unless $rewriting or $newcommit eq $cl->{CommitId};
-	    $build = $newcommit;
             if (grep { $method eq $_ } qw(DgitImportUpstreamUpdate)) {
                 $last_anchor = $cur;
             }
@@ -1476,7 +1728,7 @@ sub walk ($;$$$) {
     };
 
     my $final_check = get_differs $build, $input;
-    die sprintf "internal error %#x %s %s", $final_check, $input, $build
+    confess f_ "internal error %#x %s %s", $final_check, $input, $build
 	if $final_check & ~D_PAT_ADD;
 
     my @r = ($build, $breakwater, $last_anchor);
@@ -1503,8 +1755,8 @@ sub update_head_checkout ($$$) {
 
 sub update_head_postlaunder ($$$) {
     my ($old, $tip, $reflogmsg) = @_;
-    return if $tip eq $old;
-    print "git-debrebase: laundered (head was $old)\n";
+    return if $tip eq $old && !@deferred_updates;
+    print f_ "%s: laundered (head was %s)\n", $us, $old;
     update_head $old, $tip, $reflogmsg;
     # no tree changes except debian/patches
     runcmd @git, qw(rm --quiet --ignore-unmatch -rf debian/patches);
@@ -1518,7 +1770,7 @@ sub currently_rebasing() {
 }
 
 sub bail_if_rebasing() {
-    fail "you are in the middle of a git-rebase already"
+    fail __ "you are in the middle of a git-rebase already"
 	if currently_rebasing();
 }
 
@@ -1544,14 +1796,14 @@ sub cmd_launder_v0 () {
 
 sub defaultcmd_rebase () {
     push @ARGV, @{ $opt_defaultcmd_interactive // [] };
-    my ($tip,$breakwater) = do_launder_head 'launder for rebase';
+    my ($tip,$breakwater) = do_launder_head __ 'launder for rebase';
     runcmd @git, qw(rebase), @ARGV, $breakwater if @ARGV;
 }
 
 sub cmd_analyse () {
-    badusage "analyse does not support any options"
+    badusage __ "analyse does not support any options"
 	if @ARGV and $ARGV[0] =~ m/^-/;
-    badusage "too many arguments to analyse" if @ARGV>1;
+    badusage __ "too many arguments to analyse" if @ARGV>1;
     my ($old) = @ARGV;
     if (defined $old) {
 	$old = git_rev_parse $old;
@@ -1559,12 +1811,7 @@ sub cmd_analyse () {
 	$old = git_rev_parse 'HEAD';
     }
     my ($dummy,$breakwater) = walk $old, 1,*STDOUT;
-    STDOUT->error and die $!;
-}
-
-sub ffq_prev_branchinfo () {
-    my $current = git_get_symref();
-    return gdr_ffq_prev_branchinfo($current);
+    STDOUT->error and confess $!;
 }
 
 sub ffq_check ($;$$) {
@@ -1581,7 +1828,7 @@ sub ffq_check ($;$$) {
     # normally $currentval should be HEAD
     my ($currentval, $ff, $notff) =@_;
 
-    $ff //= sub { print $_[0] or die $!; };
+    $ff //= sub { print $_[0] or confess $!; };
     $notff //= \&snag;
 
     my ($status, $message, $current, $ffq_prev, $gdrlast)
@@ -1589,9 +1836,9 @@ sub ffq_check ($;$$) {
     return ($status, $message) unless $status eq 'branch';
 
     my $exists = git_get_ref $ffq_prev;
-    return ('exists',"$ffq_prev already exists") if $exists;
+    return ('exists', f_ "%s already exists", $ffq_prev) if $exists;
 
-    return ('not-branch', 'HEAD symref is not to refs/heads/')
+    return ('not-branch', __ 'HEAD symref is not to refs/heads/')
 	unless $current =~ m{^refs/heads/};
     my $branch = $';
 
@@ -1614,14 +1861,15 @@ sub ffq_check ($;$$) {
 	return unless length $lrval;
 
 	if (is_fast_fwd $lrval, $currentval) {
-	    $ff->("OK, you are ahead of $lrref\n");
+	    $ff->(f_ "OK, you are ahead of %s\n", $lrref);
 	    $checked{$lrref} = 1;
 	} elsif (is_fast_fwd $currentval, $lrval) {
 	    $checked{$lrref} = -1;
-	    $notff->('behind', "you are behind $lrref, divergence risk");
+	    $notff->('behind', f_ "you are behind %s, divergence risk",
+		                  $lrref);
 	} else {
 	    $checked{$lrref} = -1;
-	    $notff->('diverged', "you have diverged from $lrref");
+	    $notff->('diverged', f_ "you have diverged from %s", $lrref);
 	}
     };
 
@@ -1642,9 +1890,11 @@ sub ffq_check ($;$$) {
 			'remote push branch');
     }
     if ($branch =~ m{^dgit/}) {
-	$check->("refs/remotes/dgit/$branch", 'remote dgit branch');
+	$check->("refs/remotes/dgit/$branch",
+		 __ 'remote dgit branch');
     } elsif ($branch =~ m{^master$}) {
-	$check->("refs/remotes/dgit/dgit/sid", 'remote dgit branch for sid');
+	$check->("refs/remotes/dgit/dgit/sid",
+		 __ 'remote dgit branch for sid');
     }
     return (undef, undef, $ffq_prev, $gdrlast);
 }
@@ -1671,7 +1921,8 @@ sub record_ffq_prev_deferred () {
 
     push @deferred_updates, "update $ffq_prev $currentval $git_null_obj";
     push @deferred_updates, "delete $gdrlast";
-    push @deferred_update_messages, "Recorded previous head for preservation";
+    push @deferred_update_messages,
+	__ "Recorded previous head for preservation";
     return ('deferred', undef);
 }
 
@@ -1679,7 +1930,7 @@ sub record_ffq_auto () {
     my ($status, $message) = record_ffq_prev_deferred();
     if ($status eq 'deferred' || $status eq 'exists') {
     } else {
-	snag $status, "could not record ffq-prev: $message";
+	snag $status, f_ "could not record ffq-prev: %s", $message;
 	snags_maybe_bail();
     }
 }
@@ -1690,7 +1941,7 @@ sub ffq_prev_info () {
     my ($status, $message, $current, $ffq_prev, $gdrlast)
 	= ffq_prev_branchinfo();
     if ($status ne 'branch') {
-	snag $status, "could not check ffq-prev: $message";
+	snag $status, f_ "could not check ffq-prev: %s", $message;
 	snags_maybe_bail();
     }
     my $ffq_prev_commitish = $ffq_prev && git_get_ref $ffq_prev;
@@ -1708,10 +1959,9 @@ sub stitch ($$$$$) {
 	    # ffq-prev is ahead of us, and the only tree changes it has
 	    # are possibly addition of things in debian/patches/.
 	    # Just wind forwards rather than making a pointless pseudomerge.
-	    push @deferred_updates,
-		"update $gdrlast $ffq_prev_commitish $git_null_obj";
+	    record_gdrlast $gdrlast, $ffq_prev_commitish;
 	    update_head_checkout $old_head, $ffq_prev_commitish,
-		"stitch (fast forward)";
+		sprintf "stitch (%s)", __ 'fast forward';
 	    return;
 	}
     }
@@ -1719,10 +1969,12 @@ sub stitch ($$$$$) {
     # We make pseudomerges with L as the contributing parent.
     # This makes git rev-list --first-parent work properly.
     my $new_head = make_commit [ $old_head, $ffq_prev ], [
-	'Declare fast forward / record previous work',
+        # we translate this against the time when this same code is
+        # used outside Debian, for downstreams and users
+	(__ 'Declare fast forward / record previous work'),
         "[git-debrebase pseudomerge: $prose]",
     ];
-    push @deferred_updates, "update $gdrlast $new_head $git_null_obj";
+    record_gdrlast $gdrlast, $new_head;
     update_head $old_head, $new_head, "stitch: $prose";
 }
 
@@ -1731,7 +1983,7 @@ sub do_stitch ($;$) {
 
     my ($ffq_prev, $gdrlast, $ffq_prev_commitish) = ffq_prev_info();
     if (!$ffq_prev_commitish) {
-	fail "No ffq-prev to stitch." unless $opt_noop_ok;
+	fail __ "No ffq-prev to stitch." unless $opt_noop_ok;
 	return;
     }
     my $dangling_head = get_head();
@@ -1760,9 +2012,11 @@ sub resolve_upstream_version ($$) {
 	my @tried;
 	$new_upstream = upstream_commitish_search $upstream_version, \@tried;
 	if (!length $new_upstream) {
-	    fail "Could not determine appropriate upstream commitish.\n".
-		" (Tried these tags: @tried)\n".
-		" Check version, and specify upstream commitish explicitly.";
+	    fail f_
+		"Could not determine appropriate upstream commitish.\n".
+		" (Tried these tags: %s)\n".
+		" Check version, and specify upstream commitish explicitly.",
+		"@tried";
 	}
     }
     $new_upstream = git_rev_parse $new_upstream;
@@ -1776,12 +2030,13 @@ sub cmd_new_upstream () {
 
     my %pieces;
 
-    badusage "need NEW-VERSION [UPS-COMMITTISH]" unless @ARGV >= 1;
+    badusage __ "need NEW-VERSION [UPS-COMMITTISH]" unless @ARGV >= 1;
 
     # parse args - low commitment
     my $spec_version = shift @ARGV;
     my $new_version = (new Dpkg::Version $spec_version, check => 1);
-    fail "bad version number \`$spec_version'" unless defined $new_version;
+    fail f_ "bad version number \`%s'", $spec_version
+	unless defined $new_version;
     if ($new_version->is_native()) {
 	$new_version = (new Dpkg::Version "$spec_version-1", check => 1);
     }
@@ -1797,7 +2052,8 @@ sub cmd_new_upstream () {
         my ($n, @x) = @_; # may be ''
         my $pc = $pieces{$n} //= {
     	    Name => $n,
-	    Desc => ($n ? "upstream piece \`$n'" : "upstream (main piece"),
+	    Desc => ($n ? (f_ "upstream piece \`%s'", $n)
+		        : (__ "upstream (main piece")),
 	};
 	while (my $k = shift @x) { $pc->{$k} = shift @x; }
         $pc;
@@ -1817,11 +2073,11 @@ sub cmd_new_upstream () {
     while (@ARGV && $ARGV[0] !~ m{^-}) {
 	my $n = shift @ARGV;
 
-        badusage "for each EXTRA-UPS-NAME need EXTRA-UPS-COMMITISH"
+        badusage __ "for each EXTRA-UPS-NAME need EXTRA-UPS-COMMITISH"
             unless @ARGV && $ARGV[0] !~ m{^-};
 
 	my $c = git_rev_parse shift @ARGV;
-	die unless $n =~ m/^$extra_orig_namepart_re$/;
+	confess unless $n =~ m/^$extra_orig_namepart_re$/;
 	$newpiece->($n, New => $c);
     }
 
@@ -1835,7 +2091,7 @@ sub cmd_new_upstream () {
     my $old_upstream;
     if (!$old_anchor_cl->{OrigParents}) {
 	snag 'anchor-treated',
-	    'old anchor is recognised due to --anchor, cannot check upstream';
+ __ 'old anchor is recognised due to --anchor, cannot check upstream';
     } else {
 	$old_upstream = parsecommit
 	    $old_anchor_cl->{OrigParents}[0]{CommitId};
@@ -1850,7 +2106,7 @@ sub cmd_new_upstream () {
 	    my $old_n_parents = scalar @{ $old_upstream->{Parents} };
 	    if ($old_n_parents != @oldpieces &&
 		$old_n_parents != @oldpieces + 1) {
-		snag 'upstream-confusing', sprintf
+		snag 'upstream-confusing', f_
 		    "previous upstream combine %s".
 		    " mentions %d pieces (each implying one parent)".
 		    " but has %d parents".
@@ -1859,7 +2115,7 @@ sub cmd_new_upstream () {
 		    (scalar @oldpieces),
 		    $old_n_parents;
 	    } elsif ($oldpieces[0] ne '.') {
-		snag 'upstream-confusing', sprintf
+		snag 'upstream-confusing', f_
 		    "previous upstream combine %s".
 		    " first piece is not \`.'",
 		    $oldpieces[0];
@@ -1872,9 +2128,10 @@ sub cmd_new_upstream () {
 		}
 	    }
 	} else {
-	    snag 'upstream-confusing',
-		"previous upstream $old_upstream->{CommitId} is from".
-               " git-debrebase but not an \`upstream-combine' commit";
+	    snag 'upstream-confusing', f_
+		"previous upstream %s is from".
+               " git-debrebase but not an \`upstream-combine' commit",
+	       $old_upstream->{CommitId};
 	}
     }
 
@@ -1883,13 +2140,14 @@ sub cmd_new_upstream () {
 	    # we have complained already
 	} elsif (!$pc->{Old}) {
 	    snag 'upstream-new-piece',
-		"introducing upstream piece \`$pc->{Name}'";
+		f_ "introducing upstream piece \`%s'", $pc->{Name};
 	} elsif (!$pc->{New}) {
 	    snag 'upstream-rm-piece',
-		"dropping upstream piece \`$pc->{Name}'";
+		f_ "dropping upstream piece \`%s'", $pc->{Name};
 	} elsif (!is_fast_fwd $pc->{Old}, $pc->{New}) {
 	    snag 'upstream-not-ff',
-		"not fast forward: $pc->{Name} $pc->{Old}..$pc->{New}";
+		f_ "not fast forward: %s %s",
+		   $pc->{Name}, "$pc->{Old}..$pc->{New}";
 	}
     }
 
@@ -1941,36 +2199,43 @@ sub cmd_new_upstream () {
  "[git-debrebase anchor: new upstream $new_upstream_version, merge]",
             ];
 
-	my $clogsignoff = cmdoutput qw(git show),
-	    '--pretty=format:%an <%ae>  %aD',
-	    $new_bw;
-
 	# Now we have to add a changelog stanza so the Debian version
-	# is right.
-	die if unlink "debian";
-	die $! unless $!==ENOENT or $!==ENOTEMPTY;
-	unlink "debian/changelog" or $!==ENOENT or die $!;
-        mkdir "debian" or die $!;
-	open CN, ">", "debian/changelog" or die $!;
-	my $oldclog = git_cat_file ":debian/changelog";
-	$oldclog =~ m/^($package_re) \(\S+\) / or
-	    fail "cannot parse old changelog to get package name";
-	my $p = $1;
-	print CN <<END, $oldclog or die $!;
-$p ($new_version) UNRELEASED; urgency=medium
-
-  * Update to new upstream version $new_upstream_version.
-
- -- $clogsignoff
-
-END
-	close CN or die $!;
+	# is right.  We use debchange to do this.  Invoking debchange
+	# here is a bit fiddly because it has a lot of optional
+	# exciting behaviours, some of which will break stuff, and
+	# some of which won't work in a playtree.
+
+	# Make debchange use git's idea of the user's identity.
+	# That way, if the user never uses debchange et al, configuring
+	# git is enough.
+	my $usetup = sub {
+	    my ($e, $k) = @_;
+	    my $v = cfg $k, 1;
+	    defined $v or return;
+	    $ENV{$e} = $v;
+	};
+	$usetup->('DEBEMAIL',    'user.email');
+	$usetup->('DEBFULLNAME', 'user.name');
+
+	my @dch = (qw(debchange
+		      --allow-lower-version .*
+		      --no-auto-nmu
+		      --preserve
+		      --vendor=Unknown-Vendor
+		      --changelog debian/changelog
+		      --check-dirname-level 0
+		      --release-heuristic=changelog
+		      -v), $new_version,
+		   "Update to new upstream version $new_upstream_version.");
+
+	runcmd @git, qw(checkout -q debian/changelog);
+	runcmd @dch;
 	runcmd @git, qw(update-index --add --replace), 'debian/changelog';
 
 	# Now we have the final new breakwater branch in the index
         $new_bw = make_commit [ $new_bw ],
             [ "Update changelog for new upstream $new_upstream_version",
-              "[git-debrebase: new upstream $new_upstream_version, changelog]",
+              "[git-debrebase changelog: new upstream $new_upstream_version]",
             ];
     };
 
@@ -1992,28 +2257,28 @@ sub cmd_record_ffq_prev () {
     badusage "no arguments allowed" if @ARGV;
     my ($status, $msg) = record_ffq_prev_deferred();
     if ($status eq 'exists' && $opt_noop_ok) {
-	print "Previous head already recorded\n" or die $!;
+	print __ "Previous head already recorded\n" or confess $!;
     } elsif ($status eq 'deferred') {
 	run_deferred_updates 'record-ffq-prev';
     } else {
-	fail "Could not preserve: $msg";
+	fail f_ "Could not preserve: %s", $msg;
     }
 }
 
 sub cmd_anchor () {
-    badusage "no arguments allowed" if @ARGV;
+    badusage __ "no arguments allowed" if @ARGV;
     my ($anchor, $bw) = keycommits +(git_rev_parse 'HEAD'), 0,0;
-    print "$bw\n" or die $!;
+    print "$anchor\n" or confess $!;
 }
 
 sub cmd_breakwater () {
-    badusage "no arguments allowed" if @ARGV;
+    badusage __ "no arguments allowed" if @ARGV;
     my ($anchor, $bw) = keycommits +(git_rev_parse 'HEAD'), 0,0;
-    print "$bw\n" or die $!;
+    print "$bw\n" or confess $!;
 }
 
 sub cmd_status () {
-    badusage "no arguments allowed" if @ARGV;
+    badusage __ "no arguments allowed" if @ARGV;
 
     # todo: gdr status should print divergence info
     # todo: gdr status should print upstream component(s) info
@@ -2035,22 +2300,22 @@ sub cmd_status () {
 	$newest //= $oldest;
     };
     my ($anchor, $bw) = keycommits +(git_rev_parse 'HEAD'),
-	sub { $note->(1, 'branch contains furniture (not laundered)', @_); },
-	sub { $note->(2, 'branch is unlaundered', @_); },
-	sub { $note->(3, 'branch needs laundering', @_); },
-	sub { $note->(4, 'branch not in git-debrebase form', @_); };
+	sub { $note->(1, __ 'branch contains furniture (not laundered)',@_); },
+	sub { $note->(2, __ 'branch is unlaundered', @_); },
+	sub { $note->(3, __ 'branch needs laundering', @_); },
+	sub { $note->(4, __ 'branch not in git-debrebase form', @_); };
 
     my $prcommitinfo = sub {
 	my ($cid) = @_;
-	flush STDOUT or die $!;
+	flush STDOUT or confess $!;
 	runcmd @git, qw(--no-pager log -n1),
 	    '--pretty=format:    %h %s%n',
 	    $cid;
     };
 
-    print "current branch contents, in git-debrebase terms:\n";
+    print __ "current branch contents, in git-debrebase terms:\n";
     if (!$oldest->{Badness}) {
-	print "  branch is laundered\n";
+	print __ "  branch is laundered\n";
     } else {
 	print "  $oldest->{OurMsg}\n";
 	my $printed = '';
@@ -2066,83 +2331,99 @@ sub cmd_status () {
     my $prab = sub {
 	my ($cid, $what) = @_;
 	if (!defined $cid) {
-	    print "  $what is not well-defined\n";
+	    print f_ "  %s is not well-defined\n", $what;
 	} else {
 	    print "  $what\n";
 	    $prcommitinfo->($cid);
 	}
     };
-    print "key git-debrebase commits:\n";
-    $prab->($anchor, 'anchor');
-    $prab->($bw, 'breakwater');
+    print __ "key git-debrebase commits:\n";
+    $prab->($anchor, __ 'anchor');
+    $prab->($bw, __ 'breakwater');
 
     my ($ffqstatus, $ffq_msg, $current, $ffq_prev, $gdrlast) =
 	ffq_prev_branchinfo();
 
-    print "branch and ref status, in git-debrebase terms:\n";
+    print __ "branch and ref status, in git-debrebase terms:\n";
     if ($ffq_msg) {
 	print "  $ffq_msg\n";
     } else {
 	$ffq_prev = git_get_ref $ffq_prev;
 	$gdrlast = git_get_ref $gdrlast;
 	if ($ffq_prev) {
-	    print "  unstitched; previous tip was:\n";
+	    print __ "  unstitched; previous tip was:\n";
 	    $prcommitinfo->($ffq_prev);
 	} elsif (!$gdrlast) {
-	    print "  stitched? (no record of git-debrebase work)\n";
+	    print __ "  stitched? (no record of git-debrebase work)\n";
 	} elsif (is_fast_fwd $gdrlast, 'HEAD') {
-	    print "  stitched\n";
+	    print __ "  stitched\n";
 	} else {
-	    print "  not git-debrebase (diverged since last stitch)\n"
+	    print __ "  not git-debrebase (diverged since last stitch)\n"
 	}
     }
-    print "you are currently rebasing\n" if currently_rebasing();
+    print __ "you are currently rebasing\n" if currently_rebasing();
 }
 
 sub cmd_stitch () {
     my $prose = 'stitch';
     getoptions("stitch",
 	       'prose=s', \$prose);
-    badusage "no arguments allowed" if @ARGV;
+    badusage __ "no arguments allowed" if @ARGV;
     do_stitch $prose, 0;
 }
-sub cmd_prepush () { cmd_stitch(); }
+sub cmd_prepush () {
+    $opt_noop_ok = 1;
+    cmd_stitch();
+}
 
 sub cmd_quick () {
-    badusage "no arguments allowed" if @ARGV;
-    do_launder_head 'launder for git-debrebase quick';
+    badusage __ "no arguments allowed" if @ARGV;
+    do_launder_head __ 'launder for git-debrebase quick';
     do_stitch 'quick';
 }
 
 sub cmd_conclude () {
     my ($ffq_prev, $gdrlast, $ffq_prev_commitish) = ffq_prev_info();
     if (!$ffq_prev_commitish) {
-	fail "No ongoing git-debrebase session." unless $opt_noop_ok;
+	fail __ "No ongoing git-debrebase session." unless $opt_noop_ok;
 	return;
     }
     my $dangling_head = get_head();
     
     badusage "no arguments allowed" if @ARGV;
-    do_launder_head 'launder for git-debrebase quick';
+    do_launder_head __ 'launder for git-debrebase quick';
     do_stitch 'quick';
 }
 
 sub cmd_scrap () {
     if (currently_rebasing()) {
 	runcmd @git, qw(rebase --abort);
+	push @deferred_updates, 'verify HEAD HEAD';
+	# noop, but stops us complaining that scrap was a noop
     }
+    badusage __ "no arguments allowed" if @ARGV;
     my ($ffq_prev, $gdrlast, $ffq_prev_commitish) = ffq_prev_info();
-    if (!$ffq_prev_commitish) {
-	fail "No ongoing git-debrebase session." unless $opt_noop_ok;
+    my $scrapping_head;
+    if ($ffq_prev_commitish) {
+	$scrapping_head = get_head();
+	push @deferred_updates,
+	    "update $gdrlast $ffq_prev_commitish $git_null_obj",
+	    "update $ffq_prev $git_null_obj $ffq_prev_commitish";
+    }
+    if (git_get_ref $merge_cache_ref) {
+	push @deferred_updates,
+	    "delete $merge_cache_ref";
+    }
+    if (!@deferred_updates) {
+	fail __ "No ongoing git-debrebase session." unless $opt_noop_ok;
 	finish 0;
     }
-    my $scrapping_head = get_head();
-    badusage "no arguments allowed" if @ARGV;
-    push @deferred_updates,
-	"update $gdrlast $ffq_prev_commitish $git_null_obj",
-	"update $ffq_prev $git_null_obj $ffq_prev_commitish";
     snags_maybe_bail();
-    update_head_checkout $scrapping_head, $ffq_prev_commitish, "scrap";
+    if ($scrapping_head) {
+	update_head_checkout $scrapping_head, $ffq_prev_commitish, "scrap";
+    } else {
+	run_deferred_updates "scrap";
+    }
 }
 
 sub make_patches_staged ($) {
@@ -2151,23 +2432,30 @@ sub make_patches_staged ($) {
     # laundered.
     my ($secret_head, $secret_bw, $last_anchor) = walk $head;
     fresh_workarea();
+    my $any;
     in_workarea sub {
-	gbp_pq_export 'bw', $secret_bw, $secret_head;
+	$any = gbp_pq_export 'bw', $secret_bw, $secret_head;
     };
+    return $any;
 }
 
 sub make_patches ($) {
     my ($head) = @_;
     keycommits $head, 0, \&snag;
-    make_patches_staged $head;
+    my $any = make_patches_staged $head;
     my $out;
     in_workarea sub {
-	my $ptree = cmdoutput @git, qw(write-tree --prefix=debian/patches/);
+	my $ptree = !$any ? undef :
+	    cmdoutput @git, qw(write-tree --prefix=debian/patches/);
 	runcmd @git, qw(read-tree), $head;
-	read_tree_subdir 'debian/patches', $ptree;
+	if ($ptree) {
+	    read_tree_subdir 'debian/patches', $ptree;
+	} else {
+	    rm_subdir_cached 'debian/patches';
+	}
 	$out = make_commit [$head], [
-            'Commit patch queue (exported by git-debrebase)',
-            '[git-debrebase: export and commit patches]',
+            (__ 'Commit patch queue (exported by git-debrebase)'),
+            '[git-debrebase make-patches: export and commit patches]',
         ];
     };
     return $out;
@@ -2177,34 +2465,85 @@ sub cmd_make_patches () {
     my $opt_quiet_would_amend;
     getoptions("make-patches",
 	       'quiet-would-amend!', \$opt_quiet_would_amend);
-    badusage "no arguments allowed" if @ARGV;
+    badusage __ "no arguments allowed" if @ARGV;
     bail_if_rebasing();
     my $old_head = get_head();
     my $new = make_patches $old_head;
     my $d = get_differs $old_head, $new;
     if ($d == 0) {
-	fail "No (more) patches to export." unless $opt_noop_ok;
+	fail __ "No (more) patches to export." unless $opt_noop_ok;
 	return;
     } elsif ($d == D_PAT_ADD) {
 	snags_maybe_bail();
 	update_head_checkout $old_head, $new, 'make-patches';
     } else {
-	print STDERR failmsg
+	print STDERR failmsg f_
 	    "Patch export produced patch amendments".
-	    " (abandoned output commit $new).".
-	    "  Try laundering first."
+	    " (abandoned output commit %s).".
+	    "  Try laundering first.",
+	    $new
 	    unless $opt_quiet_would_amend;
 	finish 7;
     }
 }
 
+sub check_series_has_all_patches ($) {
+    my ($head) = @_;
+    my $seriesfn = 'debian/patches/series';
+    my ($dummy, $series) = git_cat_file "$head:$seriesfn",
+	[qw(blob missing)];
+    $series //= '';
+    my %series;
+    our $comments_snagged;
+    foreach my $f (grep /\S/, grep {!m/^\s\#/} split /\n/, $series) {
+	if ($f =~ m/^\s*\#/) {
+	    snag 'series-comments', f_
+		"%s contains comments, which will be discarded",
+		$seriesfn
+		unless $comments_snagged++;
+	    next;
+	}
+	fail f_ "patch %s repeated in %s !", $f, $seriesfn if $series{$f}++;
+    }
+    foreach my $patchfile (get_tree "$head:debian/patches", 1,1) {
+	my ($f,$i) = @$patchfile;
+	next if $series{$f};
+	next if $f eq 'series';
+	snag 'unused-patches', f_
+	    "Unused patch file %s will be discarded", $f;
+    }
+}
+
+sub begin_convert_from () {
+    my $head = get_head();
+    my ($ffqs, $ffqm, $symref, $ffq_prev, $gdrlast) = ffq_prev_branchinfo();
+
+    fail __ "ffq-prev exists, this is already managed by git-debrebase!"
+	if $ffq_prev && git_get_ref $ffq_prev;
+
+    my $gdrlast_obj = $gdrlast && git_get_ref $gdrlast;
+    snag 'already-converted', __
+	"ahead of debrebase-last, this is already managed by git-debrebase!"
+	if $gdrlast_obj && is_fast_fwd $gdrlast_obj, $head;
+    return ($head, { LastRef => $gdrlast, LastObj => $gdrlast_obj });
+}
+
+sub complete_convert_from ($$$$) {
+    my ($old_head, $new_head, $gi, $mrest) = @_;
+    ffq_check $new_head;
+    record_gdrlast $gi->{LastRef}, $new_head, $gi->{LastObj}
+	if $gi->{LastRef};
+    snags_maybe_bail();
+    update_head_checkout $old_head, $new_head, $mrest;
+}
+
 sub cmd_convert_from_gbp () {
-    badusage "want only 1 optional argument, the upstream git commitish"
+    badusage __ "want only 1 optional argument, the upstream git commitish"
 	unless @ARGV<=1;
 
     my $clogp = parsechangelog();
     my $version = $clogp->{'Version'}
-	// die "missing Version from changelog";
+	// fail __ "missing Version from changelog\n";
 
     my ($upstream_spec) = @ARGV;
 
@@ -2212,39 +2551,43 @@ sub cmd_convert_from_gbp () {
     my $upstream =
 	resolve_upstream_version($upstream_spec, $upstream_version);
 
-    my $old_head = get_head();
+    my ($old_head, $gdrlastinfo) = begin_convert_from();
 
     my $upsdiff = get_differs $upstream, $old_head;
     if ($upsdiff & D_UPS) {
 	runcmd @git, qw(--no-pager diff --stat),
 	    $upstream, $old_head,
 	    qw( -- :!/debian :/);
-	fail <<END;
-upstream ($upstream_spec) and HEAD are not
+	fail f_ <<END, $upstream_spec, $upstream_spec;
+upstream (%s) and HEAD are not
 identical in upstream files.  See diffstat above, or run
-  git diff $upstream_spec HEAD -- :!/debian :/
+  git diff %s HEAD -- :!/debian :/
 END
     }
 
     if (!is_fast_fwd $upstream, $old_head) {
 	snag 'upstream-not-ancestor',
-	    "upstream ($upstream) is not an ancestor of HEAD";
+	    f_ "upstream (%s) is not an ancestor of HEAD", $upstream;
     } else {
 	my $wrong = cmdoutput
 	    (@git, qw(rev-list --ancestry-path), "$upstream..HEAD",
 	     qw(-- :/ :!/debian));
 	if (length $wrong) {
-	    snag 'unexpected-upstream-changes',
-		"history between upstream ($upstream) and HEAD contains direct changes to upstream files - are you sure this is a gbp (patches-unapplied) branch?";
-	    print STDERR "list expected changes with:  git log --stat --ancestry-path $upstream_spec..HEAD -- :/ ':!/debian'\n";
+	    snag 'unexpected-upstream-changes', f_
+		"history between upstream (%s) and HEAD contains direct changes to upstream files - are you sure this is a gbp (patches-unapplied) branch?",
+		$upstream;
+	    print STDERR f_ "list expected changes with:  %s\n", 
+ "git log --stat --ancestry-path $upstream_spec..HEAD -- :/ ':!/debian'";
 	}
     }
 
     if ((git_cat_file "$upstream:debian")[0] ne 'missing') {
 	snag 'upstream-has-debian',
-	    "upstream ($upstream) contains debian/ directory";
+	    f_ "upstream (%s) contains debian/ directory", $upstream;
     }
 
+    check_series_has_all_patches $old_head;
+
     my $previous_dgit_view = eval {
 	my @clogcmd = qw(dpkg-parsechangelog --format rfc822 -n2);
 	my ($lvsn, $suite);
@@ -2258,26 +2601,33 @@ END
 	    $suite = $stz->{Distribution};
 	    last;
 	};
-	die "neither of the first two changelog entries are released\n"
+	die __ "neither of the first two changelog entries are released\n"
 	    unless defined $lvsn;
 	print "last finished-looking changelog entry: ($lvsn) $suite\n";
 	my $mtag_pat = debiantag_maintview $lvsn, '*';
 	my $mtag = cmdoutput @git, qw(describe --always --abbrev=0 --match),
 	    $mtag_pat;
-	die "could not find suitable maintainer view tag $mtag_pat\n"
-	    unless $mtag_pat =~ m{/};
+	die f_ "could not find suitable maintainer view tag %s\n", $mtag_pat
+	    unless $mtag =~ m{/};
 	is_fast_fwd $mtag, 'HEAD' or
-	    die "HEAD is not FF from maintainer tag $mtag!";
+	    die f_ "HEAD is not FF from maintainer tag %s!", $mtag;
 	my $dtag = "archive/$mtag";
+	git_get_ref "refs/tags/$dtag" or
+	    die f_ "dgit view tag %s not found\n", $dtag;
 	is_fast_fwd $mtag, $dtag or
-	    die "dgit view tag $dtag is not FF from maintainer tag $mtag";
-	print "will stitch in dgit view, $dtag\n";
+	    die f_ "dgit view tag %s is not FF from maintainer tag %s\n",
+	           $dtag, $mtag;
+	print f_ "will stitch in dgit view, %s\n", $dtag;
 	git_rev_parse $dtag;
     };
     if (!$previous_dgit_view) {
 	$@ =~ s/^\n+//;
 	chomp $@;
-	print STDERR "cannot stitch in dgit view: $@\n";
+	print STDERR f_ <<END, "$@";
+Cannot confirm dgit view: %s
+Failed to stitch in dgit view (see messages above).
+dgit --overwrite will be needed on the first dgit push after conversion.
+END
     }
 
     snags_maybe_bail_early();
@@ -2318,34 +2668,40 @@ END
 	}
     };
 
-    ffq_check $work;
-    snags_maybe_bail();
-    update_head_checkout $old_head, $work, 'convert-from-gbp';
+    complete_convert_from $old_head, $work, $gdrlastinfo, 'convert-from-gbp';
+    print f_ <<END, $us or confess $!;
+%s: converted from patched-unapplied (gbp) branch format, OK
+END
 }
 
 sub cmd_convert_to_gbp () {
     badusage "no arguments allowed" if @ARGV;
     my $head = get_head();
     my (undef, undef, undef, $ffq, $gdrlast) = ffq_prev_branchinfo();
-    keycommits $head, 0;
-    my $out;
-    make_patches_staged $head;
-    in_workarea sub {
-	$out = make_commit ['HEAD'], [
-            'Commit patch queue (converted from git-debrebase format)',
-            '[git-debrebase convert-to-gbp: commit patches]',
-        ];
-    };
+    my ($anchor, $breakwater) = keycommits $head, 0;
+    my $out = $breakwater;
+    my $any = make_patches_staged $head;
+    if ($any) {
+	in_workarea sub {
+	    $out = make_commit [$out], [
+		'Commit patch queue (converted from git-debrebase format)',
+		'[git-debrebase convert-to-gbp: commit patches]',
+	    ];
+	};
+    } else {
+	# in this case, it can be fast forward
+	$out = $head;
+    }
     if (defined $ffq) {
 	push @deferred_updates, "delete $ffq";
 	push @deferred_updates, "delete $gdrlast";
     }
     snags_maybe_bail();
     update_head_checkout $head, $out, "convert to gbp (v0)";
-    print <<END or die $!;
-git-debrebase: converted to git-buildpackage branch format
-git-debrebase: WARNING: do not now run "git-debrebase" any more
-git-debrebase: WARNING: doing so would drop all upstream patches!
+    print f_ <<END, $us,$us,$us or confess $!;
+%s: converted to git-buildpackage branch format
+%s: WARNING: do not now run "git-debrebase" any more
+%s: WARNING: doing so would drop all upstream patches!
 END
 }
 
@@ -2364,7 +2720,7 @@ sub cmd_convert_from_dgit_view () {
 	       'origs!', \$do_origs,
 	       'tags!', \$do_tags,
 	       'always-convert-anyway!', \$always);
-    fail "takes 1 optional argument, the upstream commitish" if @ARGV>1;
+    fail __ "takes 1 optional argument, the upstream commitish" if @ARGV>1;
 
     my @upstreams;
 
@@ -2372,12 +2728,12 @@ sub cmd_convert_from_dgit_view () {
 	my $spec = shift @ARGV;
 	my $commit = git_rev_parse "$spec^{commit}";
 	push @upstreams, { Commit => $commit,
-			   Source => "$ARGV[0], from command line",
+			   Source => (f_ "%s, from command line", $ARGV[0]),
 			   Only => 1,
 			 };
     }
 
-    my $head = get_head();
+    my ($head, $gdrlastinfo) = begin_convert_from();
 
     if (!$always) {
 	my $troubles = 0;
@@ -2385,32 +2741,36 @@ sub cmd_convert_from_dgit_view () {
 	keycommits $head, sub{}, sub{}, $trouble, $trouble;
 	printdebug "troubles=$troubles\n";
 	if (!$troubles) {
-	    print STDERR <<END;
-$us: Branch already seems to be in git-debrebase format!
-$us: --always-convert-anyway would do the conversion operation anyway
-$us: but is probably a bad idea.  Probably, you wanted to do nothing.
+	    print STDERR f_ <<END, $us,$us,$us;
+%s: Branch already seems to be in git-debrebase format!
+%s: --always-convert-anyway would do the conversion operation anyway
+%s: but is probably a bad idea.  Probably, you wanted to do nothing.
 END
-	    fail "Branch already in git-debrebase format." unless $opt_noop_ok;
+	    fail __ "Branch already in git-debrebase format."
+		unless $opt_noop_ok;
 	    finish 0;
 	}
     }
 
+    check_series_has_all_patches $head;
+
     snags_maybe_bail_early();
 
     my $version = upstreamversion $clogp->{Version};
-    print STDERR "Considering possible commits corresponding to upstream:\n";
+    print STDERR __
+	"Considering possible commits corresponding to upstream:\n";
 
     if (!@upstreams) {
 	if ($do_tags) {
 	    my @tried;
 	    my $ups_tag = upstream_commitish_search $version, \@tried;
 	    if ($ups_tag) {
-		my $this = "git tag $tried[-1]";
+		my $this = f_ "git tag %s", $tried[-1];
 		push @upstreams, { Commit => $ups_tag,
 				   Source => $this,
 				 };
 	    } else {
-		printf STDERR
+		print STDERR f_
 		    " git tag: no suitable tag found (tried %s)\n",
 		    "@tried";
 	    }
@@ -2420,17 +2780,18 @@ END
 	    # we do a quick check to see if there are plausible origs
 	    my $something=0;
 	    if (!opendir BPD, $bpd) {
-		die "$bpd: opendir: $!" unless $!==ENOENT;
+		die f_ "opendir build-products-dir %s: %s", $bpd, $!
+		    unless $!==ENOENT;
 	    } else {
 		while ($!=0, my $f = readdir BPD) {
 		    next unless is_orig_file_of_p_v $f, $p, $version;
-		    printf STDERR
+		    print STDERR f_
 			" orig: found what looks like a .orig, %s\n",
 			"$bpd/$f";
 		    $something=1;
 		    last;
 		}
-		die "read $bpd: $!" if $!;
+		confess "read $bpd: $!" if $!;
 		closedir BPD;
 	    }
 	    if ($something) {
@@ -2447,7 +2808,7 @@ Import effective orig tree for upstream version $version
 END
 This includes the contents of the .orig(s), minus any debian/ directory.
 
-[git-debrebase import-from-dgit-view upstream-import-convert: $version]
+[git-debrebase convert-from-dgit-view upstream-import-convert: $version]
 END
 						    ];
 		    push @upstreams, { Commit => $ups_synth,
@@ -2455,7 +2816,7 @@ END
 				     };
 		}
 	    } else {
-		printf STDERR
+		print STDERR f_
 		    " orig: no suitable origs found (looked for %s in %s)\n",
 		    "${p}_".(stripeoch $version)."...", $bpd;
 	    }
@@ -2464,7 +2825,8 @@ END
 
     my $some_patches = stat_exists 'debian/patches/series';
 
-    print STDERR "Evaluating possible commits corresponding to upstream:\n";
+    print STDERR __
+	"Evaluating possible commits corresponding to upstream:\n";
 
     my $result;
     foreach my $u (@upstreams) {
@@ -2481,7 +2843,7 @@ END
  'git-debrebase convert-from-dgit-view: drop upstream changes from breakwater',
  "Drop upstream changes, and delete debian/patches, as part of converting\n".
  "to git-debrebase format.  Upstream changes will appear as commits.",
- '[git-debrebase convert-from-dgit-view: drop patches from tree]'
+ '[git-debrebase convert-from-dgit-view drop-patches]'
 					   ];
 	    }
 	    $work = make_commit [ $work, $u->{Commit} ], [
@@ -2500,7 +2862,7 @@ END
 		}
 		my $r = system @gbp_cmd;
 		if ($r) {
-		    printf STDERR
+		    print STDERR f_
 			" %s: couldn't apply patches: gbp pq %s",
 			$u->{Source}, waitstatusmsg();
 		    return;
@@ -2509,8 +2871,9 @@ END
 	    my $work = git_rev_parse qw(HEAD);
 	    my $diffout = cmdoutput @git, qw(diff-tree --stat HEAD), $work;
 	    if (length $diffout) {
-		print STDERR
-		    " $u->{Source}: applying patches gives different tree\n";
+		print STDERR f_
+		    " %s: applying patches gives different tree\n",
+		    $u->{Source};
 		print STDERR $diffout if $diagnose;
 		return;
 	    }
@@ -2522,21 +2885,73 @@ END
     }
 
     if (!$result) {
-	fail <<END;
+	fail __ <<END;
 Could not find or construct a suitable upstream commit.
 Rerun adding --diagnose after convert-from-dgit-view, or pass a
 upstream commmit explicitly or provide suitable origs.
 END
     }
 
-    printf STDERR "Yes, will base new branch on %s\n", $result->{Source};
+    print STDERR f_ "Yes, will base new branch on %s\n", $result->{Source};
 
-    ffq_check $result->{Result};
-    snags_maybe_bail();
-    update_head_checkout $head, $result->{Result},
+    complete_convert_from $head, $result->{Result}, $gdrlastinfo,
 	'convert-from-dgit-view';
 }
 
+sub cmd_forget_was_ever_debrebase () {
+    badusage __ "forget-was-ever-debrebase takes no further arguments"
+	if @ARGV;
+    my ($ffqstatus, $ffq_msg, $current, $ffq_prev, $gdrlast) =
+	ffq_prev_branchinfo();
+    fail f_ "Not suitable for recording git-debrebaseness anyway: %s",
+	    $ffq_msg
+	if defined $ffq_msg;
+    push @deferred_updates, "delete $ffq_prev";
+    push @deferred_updates, "delete $gdrlast";
+    snags_maybe_bail();
+    run_deferred_updates "forget-was-ever-debrebase";
+}
+
+sub cmd_record_resolved_merge () {
+    badusage "record-resolved-merge takes no further arguments" if @ARGV;
+    # MERGE-TODO needs documentation
+    my $new = get_head();
+    my $method;
+
+    print "Checking how you have resolved the merge problem\n";
+    my $nope = sub { print "Not $method: @_"; 0; };
+
+    my $maybe = sub { print "Seems to be $method.\n"; };
+    my $yes = sub {
+	my ($key, $ref) = @_;
+	reflog_cache_insert $merge_cache_ref, $key, $ref;
+	print "OK.  You can switch branches and try git-debrebase again.\n";
+	1;
+    };
+
+    fresh_workarea 'merge';
+    sub {
+	$method = 'vanilla-merge patchqueue';
+	my $vanilla = git_get_ref "$wrecknoteprefix/vanilla-merge";
+	$vanilla or return $nope->("wreckage was not of vanilla-merge");
+	foreach my $lr (qw(left right)) {
+	    my $n = "$wrecknoteprefix/$lr-patchqueue";
+	    my $lrpq = git_get_ref $n;
+	    $lrpq or return $nope->("wreckage did not contain patchqueues");
+	    is_fast_fwd $lrpq, $new or return $nope->("HEAD not ff of $n");
+	}
+	$maybe->();
+	my $newbase = git_get_ref "$wrecknoteprefix/new-base"
+	    or die "wreckage element $wrecknoteprefix/new-base missing";
+	my $result = merge_series_patchqueue_convert
+	    {}, $newbase, $new;
+	$yes->("vanilla-merge $vanilla", $result);
+	1;
+    }->() or sub {
+	fail "No resolved merge method seems applicable.\n";
+    }->();
+}
+
 sub cmd_downstream_rebase_launder_v0 () {
     badusage "needs 1 argument, the baseline" unless @ARGV==1;
     my ($base) = @ARGV;
@@ -2586,19 +3001,23 @@ sub cmd_downstream_rebase_launder_v0 () {
     }
 }
 
+setlocale(LC_MESSAGES, "");
+textdomain("git-debrebase");
+
 getoptions_main
-          ("bad options\n",
+          (__ "bad options\n",
 	   "D+" => \$debuglevel,
 	   'noop-ok', => \$opt_noop_ok,
 	   'f=s' => \@snag_force_opts,
 	   'anchor=s' => \@opt_anchors,
 	   '--dgit=s' => \($dgit[0]),
 	   'force!',
+	   'experimental-merge-resolution!', \$opt_merges,
 	   '-i:s' => sub {
 	       my ($opt,$val) = @_;
-	       badusage "git-debrebase: no cuddling to -i for git-rebase"
+	       badusage f_ "%s: no cuddling to -i for git-rebase", $us
 		   if length $val;
-	       die if $opt_defaultcmd_interactive; # should not happen
+	       confess if $opt_defaultcmd_interactive; # should not happen
 	       $opt_defaultcmd_interactive = [ qw(-i) ];
 	       # This access to @ARGV is excessive familiarity with
 	       # Getopt::Long, but there isn't another sensible
@@ -2606,14 +3025,13 @@ getoptions_main
 	       push @$opt_defaultcmd_interactive, @ARGV;
 	       @ARGV=();
 	   },
-	   'help' => sub { print $usage_message or die $!; finish 0; },
+	   'help' => sub { print __ $usage_message or confess $!; finish 0; },
 	   );
 
 initdebug('git-debrebase ');
 enabledebug if $debuglevel;
 
-my $toplevel = cmdoutput @git, qw(rev-parse --show-toplevel);
-chdir $toplevel or die "chdir $toplevel: $!";
+changedir_git_toplevel();
 
 $rd = fresh_playground "$playprefix/misc";
 
@@ -2627,7 +3045,7 @@ if (!@ARGV || $opt_defaultcmd_interactive || $ARGV[0] =~ m{^-}) {
     $cmdfn =~ y/-/_/;
     $cmdfn = ${*::}{"cmd_$cmdfn"};
 
-    $cmdfn or badusage "unknown git-debrebase sub-operation $cmd";
+    $cmdfn or badusage f_ "unknown git-debrebase sub-operation %s", $cmd;
     $cmdfn->();
 }