git-debrebase: Actually avoid read-tree in walk when not rewriting

See
   git-debrebase: Prep for avoid read-tree in walk when not rewriting
for the motivation.

Here we try to check that the commit we would make, if we were
actually calling read-tree, write-tree and hash-object, would be
identical to the one we are reusing.

In particular, we check that the upstream files, and the debian/
directory, have the contents we would feed to read-tree.  And we check
that the parent list is the same.

With these checks this new algorithm is, I think, safe enough to just
use always.   So set $opt_careful to 0.  We will abolish this
variable in a moment.

Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

1 files changed, 13 insertions, 1 deletions

diff --git a/git-debrebase b/git-debrebase
index d04f2a3..c240d88 100755
--- a/git-debrebase
+++ b/git-debrebase
@@ -53,7 +53,7 @@ END
 our ($opt_force, $opt_careful, $opt_noop_ok, @opt_anchors);
 our ($opt_defaultcmd_interactive);
 
-$opt_careful = 1;
+$opt_careful = 0;
 
 our $us = qw(git-debrebase);
 
@@ -1612,6 +1612,18 @@ sub walk ($;$$$) {
 		$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";
 	    }
             if (grep { $method eq $_ } qw(DgitImportUpstreamUpdate)) {
                 $last_anchor = $cur;