X-Git-Url: http://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=dgit.git;a=blobdiff_plain;f=git-debrebase;h=a67008f7ed4039d083eb59fe522a5756a133d5f2;hp=3ac087c980034a3a4812b97ec6d8a5b21c4b1e07;hb=8c94cb4bc182dc63bd51adb430c1649dbb3da37e;hpb=612dca82a7f17f88835f495155fe3ff1502e336c

diff --git a/git-debrebase b/git-debrebase
index 3ac087c9..a67008f7 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -50,12 +50,13 @@ 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 $wrecknoteprefix = 'refs/debrebase/wreckage';
+our $merge_cache_ref = 'refs/debrebase/merge-resolutions';
 
 $|=1;
 
@@ -109,8 +110,8 @@ sub get_commit ($) {
 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 $playprefix = 'debrebase';
@@ -180,72 +181,158 @@ sub run_deferred_updates ($) {
     @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;
 
@@ -349,11 +436,65 @@ 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 ($$;$) {
+    my ($gdrlast, $newvalue, $oldvalue) = @_;
+    $oldvalue ||= $git_null_obj;
+    push @deferred_updates, "update $gdrlast $newvalue $oldvalue";
+}
+
+sub fail_unprocessable ($) {
+    my ($msg) = @_;
+    changedir $maindir;
+    my ($ffqs, $ffqm, $symref, $ffq_prev, $gdrlast) = ffq_prev_branchinfo();
+
+    my $mangled = <<END;
+Branch/history seems mangled - no longer in gdr format.
+See ILLEGAL OPERATIONS in git-debrebase(5).
+END
+    chomp $mangled;
+
+    if (defined $ffqm) {
+	fail <<END;
+$msg
+Is this meant to be a gdr branch?  $ffqm
+END
+    } elsif (git_get_ref $ffq_prev) {
+	fail <<END;
+$msg
+$mangled
+Consider git-debrebase scrap, to throw away your recent work.
+END
+    } elsif (!git_get_ref $gdrlast) {
+	fail <<END;
+$msg
+Branch does not seem to be meant to be a git-debrebase branch?
+Wrong branch, or maybe you needed git-debrebase convert-from-*.
+END
+    } elsif (is_fast_fwd $gdrlast, git_rev_parse 'HEAD') {
+	fail <<END;
+$msg
+$mangled
+END
+    } else {
+	fail <<END;
+$msg
+Branch/history mangled, and diverged since last git-debrebase.
+Maybe you reset to, or rebased from, somewhere inappropriate.
+END
+    }
+};
+
 sub gbp_pq_export ($$$) {
     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;
@@ -363,18 +504,13 @@ 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?
@@ -391,6 +527,9 @@ sub merge_failed ($$;@) {
 
     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";
@@ -414,6 +553,19 @@ sub mwrecknote ($$$) {
     $wrecknotes->{$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}
@@ -438,19 +590,11 @@ 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, @_); };
 
-    my $attempt_cmd = sub {
-	debugcmd '+', @_;
-	$!=0; $?=-1;
-	if (system @_) {
-	    merge_failed $wrecknotes,
-		failedcmd_waitstatus(),
-		"failed command: @_";
-	}
-    };
+    my $attempt_cmd = sub { &merge_attempt_cmd($wrecknotes, @_); };
 
     local $workarea;
     fresh_workarea "merge";
@@ -586,18 +730,32 @@ 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 @git, qw(checkout -q -b mergec), $merged_pq;
 
-	$attempt_cmd->(qw(gbp pq import));
+	merge_attempt_cmd($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";
@@ -611,7 +769,7 @@ sub merge_series ($$$;@) {
 	    $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;
 
@@ -621,7 +779,7 @@ 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 $result;
@@ -886,7 +1044,6 @@ sub classify ($) {
 
     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{^\[(git-debrebase|dgit)[: ].*\]$}m) {
@@ -896,7 +1053,7 @@ sub classify ($) {
 	return $unknown->("octopus merge");
     }
 
-    if (!$ENV{GIT_DEBREBASE_EXPERIMENTAL_MERGE}) {
+    if (!$opt_merges) {
 	return $unknown->("general two-parent merge");
     }
 
@@ -950,7 +1107,7 @@ sub keycommits ($;$$$$$) {
     my $clogonly;
     my $cl;
     my $found_pm;
-    $fatal //= sub { fail $_[1]; };
+    $fatal //= sub { fail_unprocessable $_[1]; };
     my $x = sub {
 	my ($cb, $tagsfx, $mainwhy, $xwhy) = @_;
 	my $why = $mainwhy.$xwhy;
@@ -1047,8 +1204,8 @@ sub walk ($;$$$) {
 	my ($prose, $info) = @_;
 	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 $rewrite_from_here = sub {
@@ -1075,7 +1232,7 @@ sub walk ($;$$$) {
 	if ($nogenerate) {
 	    return (undef,undef);
 	}
-	fail "found unprocessable commit, cannot cope".
+	fail_unprocessable "found unprocessable commit, cannot cope".
 	    (defined $cl->{Why} ? "; $cl->{Why}:": ':').
 	    " (commit $cur) (d.".
 	    (join ' ', map { sprintf "%#x", $_->{Differs} }
@@ -1129,7 +1286,7 @@ sub walk ($;$$$) {
 	} 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;
 	    };
 	    $queue->(\@brw_cl, "debian");
@@ -1182,12 +1339,12 @@ sub walk ($;$$$) {
 		push @brw_cl, {
 		    %$cl,
 		    SpecialMethod => 'DgitImportDebianUpdate',
-                    $xmsg->("convert dgit import: debian changes")
+                    $xmsg->("debian changes", 'convert dgit import')
 		}, {
 		    %$cl,
 		    SpecialMethod => 'DgitImportUpstreamUpdate',
                     $xmsg->("convert dgit import: upstream update",
-			    " anchor")
+			    "anchor")
 		};
 		$prline->(" Import");
 		$rewrite_from_here->(\@brw_cl);
@@ -1217,7 +1374,7 @@ sub walk ($;$$$) {
 	    # 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 $best_anchor;
@@ -1380,7 +1537,7 @@ sub walk ($;$$$) {
                 %$cl,
                 SpecialMethod => 'MergeCreateMergedBreakwaters',
                 $xmsg->('constructed from vanilla merge',
-			' merged-breakwater'),
+			'merged-breakwater'),
             };
 	    push @upp_cl, {
                 %$cl,
@@ -1405,11 +1562,6 @@ sub walk ($;$$$) {
 
     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 $committer_authline = calculate_committer_authline();
@@ -1421,7 +1573,12 @@ sub walk ($;$$$) {
     in_workarea sub {
 	mkdir $rd or $!==EEXIST or die $!;
 	my $current_method;
-	runcmd @git, qw(read-tree), $build;
+	my $want_debian = $build;
+	my $want_upstream = $build;
+
+	my $read_tree_upstream = sub { ($want_upstream) = @_; };
+	my $read_tree_debian = sub { ($want_debian) = @_; };
+
 	foreach my $cl (qw(Debian), (reverse @brw_cl),
 			{ SpecialMethod => 'RecordBreakwaterTip' },
 			qw(Upstream), (reverse @upp_cl)) {
@@ -1435,7 +1592,7 @@ sub walk ($;$$$) {
 	    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 ($method eq 'StartRewrite') {
@@ -1445,7 +1602,7 @@ sub walk ($;$$$) {
 		$breakwater = $build;
 		next;
 	    } elsif ($method eq 'DgitImportDebianUpdate') {
-		read_tree_debian($cltree);
+		$read_tree_debian->($cltree);
 	    } elsif ($method eq 'DgitImportUpstreamUpdate') {
  		confess unless $rewriting;
 		my $differs = (get_differs $build, $cltree);
@@ -1456,15 +1613,23 @@ sub walk ($;$$$) {
 		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:
@@ -1501,27 +1666,46 @@ 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 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;
+	    } else {
+		$build = $cl->{CommitId};
+		trees_diff_walk "$want_upstream:", "$build:", sub {
+		    my ($n) = @_;
+		    no warnings qw(exiting);
+		    next if $n eq 'debian/';
+		    confess "mismatch @_ ?";
+		};
+		trees_diff_walk "$want_debian:debian", "$build:debian", sub {
+		    confess "mismatch @_ ?";
+		};
+		my @old_parents = map { $_->{CommitId} } @{ $cl->{Parents} };
+		confess "mismatch @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;
             }
@@ -1556,7 +1740,7 @@ sub update_head_checkout ($$$) {
 
 sub update_head_postlaunder ($$$) {
     my ($old, $tip, $reflogmsg) = @_;
-    return if $tip eq $old;
+    return if $tip eq $old && !@deferred_updates;
     print "git-debrebase: laundered (head was $old)\n";
     update_head $old, $tip, $reflogmsg;
     # no tree changes except debian/patches
@@ -1615,11 +1799,6 @@ sub cmd_analyse () {
     STDOUT->error and die $!;
 }
 
-sub ffq_prev_branchinfo () {
-    my $current = git_get_symref();
-    return gdr_ffq_prev_branchinfo($current);
-}
-
 sub ffq_check ($;$$) {
     # calls $ff and/or $notff zero or more times
     # then returns either (status,message) where status is
@@ -1761,8 +1940,7 @@ sub stitch ($$$$$) {
 	    # ffq-prev is ahead of us, and the only tree changes it has
 	    # are possibly addition of things in debian/patches/.
 	    # Just wind forwards rather than making a pointless pseudomerge.
-	    push @deferred_updates,
-		"update $gdrlast $ffq_prev_commitish $git_null_obj";
+	    record_gdrlast $gdrlast, $ffq_prev_commitish;
 	    update_head_checkout $old_head, $ffq_prev_commitish,
 		"stitch (fast forward)";
 	    return;
@@ -1775,7 +1953,7 @@ sub stitch ($$$$$) {
 	'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";
 }
 
@@ -2023,7 +2201,7 @@ END
 	# 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]",
             ];
     };
 
@@ -2159,7 +2337,10 @@ sub cmd_stitch () {
     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;
@@ -2183,19 +2364,32 @@ sub cmd_conclude () {
 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) {
+    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 ($) {
@@ -2204,9 +2398,11 @@ sub make_patches_staged ($) {
     # 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 ($) {
@@ -2220,7 +2416,7 @@ sub make_patches ($) {
 	read_tree_subdir 'debian/patches', $ptree;
 	$out = make_commit [$head], [
             'Commit patch queue (exported by git-debrebase)',
-            '[git-debrebase: export and commit patches]',
+            '[git-debrebase make-patches: export and commit patches]',
         ];
     };
     return $out;
@@ -2251,6 +2447,54 @@ sub cmd_make_patches () {
     }
 }
 
+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',
+		"$seriesfn contains comments, which will be discarded"
+		unless $comments_snagged++;
+	    next;
+	}
+	fail "patch $f repeated in $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', "Unused patch file $f will be discarded";
+    }
+}
+
+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"
 	unless @ARGV<=1;
@@ -2265,7 +2509,7 @@ 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) {
@@ -2298,6 +2542,8 @@ END
 	    "upstream ($upstream) contains debian/ directory";
     }
 
+    check_series_has_all_patches $old_head;
+
     my $previous_dgit_view = eval {
 	my @clogcmd = qw(dpkg-parsechangelog --format rfc822 -n2);
 	my ($lvsn, $suite);
@@ -2318,19 +2564,25 @@ END
 	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{/};
+	    unless $mtag =~ m{/};
 	is_fast_fwd $mtag, 'HEAD' or
 	    die "HEAD is not FF from maintainer tag $mtag!";
 	my $dtag = "archive/$mtag";
+	git_get_ref "refs/tags/$dtag" or
+	    die "dgit view tag $dtag not found\n";
 	is_fast_fwd $mtag, $dtag or
-	    die "dgit view tag $dtag is not FF from maintainer tag $mtag";
+	    die "dgit view tag $dtag is not FF from maintainer tag $mtag\n";
 	print "will stitch in dgit view, $dtag\n";
 	git_rev_parse $dtag;
     };
     if (!$previous_dgit_view) {
 	$@ =~ s/^\n+//;
 	chomp $@;
-	print STDERR "cannot stitch in dgit view: $@\n";
+	print STDERR <<END;
+Cannot confirm dgit view: $@
+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();
@@ -2371,24 +2623,30 @@ 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 <<END or die $!;
+git-debrebase: 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";
@@ -2430,7 +2688,7 @@ sub cmd_convert_from_dgit_view () {
 			 };
     }
 
-    my $head = get_head();
+    my ($head, $gdrlastinfo) = begin_convert_from();
 
     if (!$always) {
 	my $troubles = 0;
@@ -2448,6 +2706,8 @@ END
 	}
     }
 
+    check_series_has_all_patches $head;
+
     snags_maybe_bail_early();
 
     my $version = upstreamversion $clogp->{Version};
@@ -2500,7 +2760,7 @@ 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,
@@ -2534,7 +2794,7 @@ 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} ], [
@@ -2584,12 +2844,62 @@ END
 
     printf STDERR "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 "Not suitable for recording git-debrebaseness anyway: $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;
@@ -2647,6 +2957,7 @@ getoptions_main
 	   '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"