dgit: quilt fixup: Don't use dpkg-source --commit, but git diff

There are many things that dpkg-source can successfully extract, but
which it can't create.  (This is because dpkg-source largely delegates
application to diff(1), and diff can do many more things nowadays.)

Most real packages were made with git-format-patch or equivalent
nowadays, so use of these features is common.  (Hence #949675
and #995056, where even glibc has patches that dpkg-source cannot make.)

Right now the practical consequences are:

 * Creating an executable file is fixed.  This actually completes
   the work for #949675.

 * Creating a symlink has a regression in the error handling.
   Previously, dpkg-source --commit failed during quilt fixup.
   Now, we happily git diff which generates a patch that dpkg-source
   can't apply.  We're going to fix this soon by aligning the
   representable change checking with reality.

 * It's faster and less complicated.

Closes: #1018143
Signed-off-by: Ian Jackson <ijackson@chiark.greenend.org.uk>

2 files changed, 18 insertions, 44 deletions

diff --git a/dgit b/dgit
index 0468ac1..5cf5fec 100755
--- a/dgit
+++ b/dgit
@@ -5389,8 +5389,9 @@ sub quiltify_make_dpkg_patch ($$$$$;$) {
     $xinfo //= '';
 
     mkpath '.git/dgit'; # we are in playtree
-    my $descfn = ".git/dgit/quilt-description.tmp";
-    open O, '>', $descfn or confess "$descfn: $!";
+    my $patchfn = "debian/patches/$patchname";
+    ensuredir dirname $patchfn;
+    open O, '>', $patchfn or confess "$patchfn: $!";
     $msg =~ s/\n+/\n\n/;
     print O <<END or confess "$!";
 From: $author
@@ -5400,12 +5401,14 @@ ${xinfo}Subject: $msg
 END
     close O or confess "$!";
 
-    {
-	local $ENV{'EDITOR'} = cmdoutput qw(realpath --), $0;
-	local $ENV{'VISUAL'} = $ENV{'EDITOR'};
-	local $ENV{$fakeeditorenv} = cmdoutput qw(realpath --), $descfn;
-	runcmd @dpkgsource, qw(--commit --include-removal .), $patchname;
-    }
+    my @diffcmd = (@git, qw(diff --no-ext-diff), $oldtreeish, $newtreeish,
+		   '--', ':!/debian', ':!/.pc');
+    runcmd qw(sh -ec), 'exec >>"$1"; shift; exec "$@"', 'x', $patchfn,
+      @diffcmd;
+
+    open S, ">> debian/patches/series" or confess "$!";
+    print S "$patchname\n" or confess "$!";
+    close S or confess "$!";
 }
 
 sub quiltify_trees_differ ($$;$$$) {
@@ -5891,13 +5894,6 @@ sub quiltify ($$$$) {
 	$!==ENOENT or confess "$patchname$index $!";
 
 	runcmd @git, qw(checkout -q), $cc;
-
-	# We use the tip's changelog so that dpkg-source doesn't
-	# produce complaining messages from dpkg-parsechangelog.  None
-	# of the information dpkg-source gets from the changelog is
-	# actually relevant - it gets put into the original message
-	# which dpkg-source provides our stunt editor, and then
-	# overwritten.
 	runcmd @git, qw(checkout -q), $target, qw(debian/changelog);
 
 	quiltify_make_dpkg_patch
@@ -6239,44 +6235,22 @@ sub quilt_fixup_multipatch ($$$) {
     #  - determine the git commit corresponding to the tip of
     #    the patch stack (if there is one)
     #  - if there is such a git commit, convert each subsequent
-    #    git commit into a quilt patch with dpkg-source --commit
+    #    git commit into a quilt patch, simulating dpkg-source --commit
     #  - otherwise convert all the differences in the tree into
     #    a single git commit
     #
     # To do this we:
 
-    # Our git tree doesn't necessarily contain .pc.  (Some versions of
-    # dgit would include the .pc in the git tree.)  If there isn't
-    # one, we need to generate one by unpacking the patches that we
-    # have.
-    #
-    # We first look for a .pc in the git tree.  If there is one, we
-    # will use it.  (This is not the normal case.)
-    #
-    # Otherwise need to regenerate .pc so that dpkg-source --commit
-    # can work.  We do this as follows:
+    # So we need to find out what the tree for the tip of the patch
+    # stack is.
     #     1. Collect all relevant .orig from parent directory
     #     2. Generate a debian.tar.gz out of
     #         debian/{patches,rules,source/format,source/options}
     #     3. Generate a fake .dsc containing just these fields:
     #          Format Source Version Files
     #     4. Extract the fake .dsc
-    #        Now the fake .dsc has a .pc directory.
-    # (In fact we do this in every case, because in future we will
-    # want to search for a good base commit for generating patches.)
     #
-    # Then we can actually do the dpkg-source --commit
-    #     1. Make a new working tree with the same object
-    #        store as our main tree and check out the main
-    #        tree's HEAD.
-    #     2. Copy .pc from the fake's extraction, if necessary
-    #     3. Run dpkg-source --commit
-    #     4. If the result has changes to debian/, then
-    #          - git add them them
-    #          - git add .pc if we had a .pc in-tree
-    #          - git commit
-    #     5. If we had a .pc in-tree, delete it, and git commit
-    #     6. Back in the main tree, fast forward to the new HEAD
+    # Then we can actually do the fake dpkg-source --commit.
 
     # Another situation we may have to cope with is gbp-style
     # patches-unapplied trees.
@@ -6359,7 +6333,7 @@ END
     my $mustdeletepc=0;
     if (stat_exists ".pc") {
         -d _ or die;
-	progress __ "Tree already contains .pc - will use it then delete it.";
+	progress __ "Tree already contains .pc - will delete it.";
         $mustdeletepc=1;
     } else {
         rename '../fake/.pc','.pc' or confess "$!";
diff --git a/tests/tests/unrepresentable b/tests/tests/unrepresentable
index c9ba11c..fa1f985 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 'new version is symlink' 'new version is symlink'
+finish BUILD:'modifies file work/new through a symlink' 'new version is symlink'
 
 start src.c
 	git rm src.c
@@ -138,7 +138,7 @@ start newx
 	echo hi >newx
 	chmod 755 newx
 	git add newx
-finish BUILD:'differs .* debian/patches' LATE-EP:'Mode change from 644 to 755'
+finish GOOD:add-755 LATE-EP:'Mode change from 644 to 755'
 
 start nothing
 finish NOTHING NOTHING