dgit: unrepresentable check: Don't tolerate symlink creation

git diff can represent changes to symlinks, but dpkg-source uses
diff(1) to apply changes, and git diff cannot.  The result if we
permit them is that we end up making source packages that can't be
built, or aren't treesame to our HEAD.

Reject this early.  This resolves the error handling regression in
  dgit: quilt fixup: Don't use dpkg-source --commit, but git diff

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

2 files changed, 4 insertions, 5 deletions

diff --git a/dgit b/dgit
index 9079ef3..f95e246 100755
--- a/dgit
+++ b/dgit
@@ -5447,7 +5447,7 @@ sub quiltify_trees_differ ($$;$$$) {
 
 	if ($unrepres) {
 	    eval {
-		die __ "not a plain file or symlink\n"
+		die __ "not a plain file\n"
 		    unless $newmode =~ m/^(?:10|12)\d{4}$/ ||
 		           $oldmode =~ m/^(?:10|12)\d{4}$/;
 		if ($oldmode =~ m/[^0]/ &&
@@ -5463,10 +5463,9 @@ sub quiltify_trees_differ ($$;$$$) {
 			unless $oldmode =~ m/^10/;
 		} else {
 		    # creation
-		    die __ "creation with non-default mode\n"
+		    die __ "creation with non-default mode, or symlink\n"
 			unless $newmode =~ m/^100644$/ or
-			       $newmode =~ m/^100755$/ or
-			       $newmode =~ m/^120000$/;
+			       $newmode =~ m/^100755$/;
 		}
 	    };
 	    if ($@) {
diff --git a/tests/tests/unrepresentable b/tests/tests/unrepresentable
index 70f7f78..490b8f7 100755
--- a/tests/tests/unrepresentable
+++ b/tests/tests/unrepresentable
@@ -115,7 +115,7 @@ finish EP:'deletion of symlink' LATE-EP:'Mode change from 20000 to 000000'
 start new
 	ln -s hi new
 	git add new
-finish BUILD:'modifies file work/new through a symlink' 'new version is symlink'
+finish EP:'creation .* symlink' 'new version is symlink'
 
 start src.c
 	git rm src.c