repack: respect --keep-pack with geometric repack

Update 'repack' to ignore packs named on the command line with the
'--keep-pack' option. Specifically, modify 'init_pack_geometry()' to treat
command line-kept packs the same way it treats packs with an on-disk '.keep'
file (that is, skip the pack and do not include it in the 'geometry'
structure).

Without this handling, a '--keep-pack' pack would be included in the
'geometry' structure. If the pack is *before* the geometry split line (with
at least one other pack and/or loose objects present), 'repack' assumes the
pack's contents are "rolled up" into another pack via 'pack-objects'.
However, because the internally-invoked 'pack-objects' properly excludes
'--keep-pack' objects, any new pack it creates will not contain the kept
objects. Finally, 'repack' deletes the '--keep-pack' as "redundant" (since
it assumes 'pack-objects' created a new pack with its contents), resulting
in possible object loss and repository corruption.

Add a test ensuring that '--keep-pack' packs are now appropriately handled.

Co-authored-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Victoria Dye <vdye@github.com>
Signed-off-by: Taylor Blau <me@ttaylorr.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/repack.c

@@ -137,6 +137,8 @@ static void collect_pack_filenames(struct string_list *fname_nonkept_list,
 			string_list_append_nodup(fname_nonkept_list, fname);
 	}
 	closedir(dir);
+
+	string_list_sort(fname_kept_list);
 }
 
 static void remove_redundant_pack(const char *dir_name, const char *base_name)
@@ -332,17 +334,38 @@ static int geometry_cmp(const void *va, const void *vb)
 	return 0;
 }
 
-static void init_pack_geometry(struct pack_geometry **geometry_p)
+static void init_pack_geometry(struct pack_geometry **geometry_p,
+			       struct string_list *existing_kept_packs)
 {
 	struct packed_git *p;
 	struct pack_geometry *geometry;
+	struct strbuf buf = STRBUF_INIT;
 
 	*geometry_p = xcalloc(1, sizeof(struct pack_geometry));
 	geometry = *geometry_p;
 
 	for (p = get_all_packs(the_repository); p; p = p->next) {
-		if (!pack_kept_objects && p->pack_keep)
+		if (!pack_kept_objects) {
-			continue;
+			/*
+			 * Any pack that has its pack_keep bit set will appear
+			 * in existing_kept_packs below, but this saves us from
+			 * doing a more expensive check.
+			 */
+			if (p->pack_keep)
+				continue;
+
+			/*
+			 * The pack may be kept via the --keep-pack option;
+			 * check 'existing_kept_packs' to determine whether to
+			 * ignore it.
+			 */
+			strbuf_reset(&buf);
+			strbuf_addstr(&buf, pack_basename(p));
+			strbuf_strip_suffix(&buf, ".pack");
+
+			if (string_list_has_string(existing_kept_packs, buf.buf))
+				continue;
+		}
 
 		ALLOC_GROW(geometry->pack,
 			   geometry->pack_nr + 1,
@@ -353,6 +376,7 @@ static void init_pack_geometry(struct pack_geometry **geometry_p)
 	}
 
 	QSORT(geometry->pack, geometry->pack_nr, geometry_cmp);
+	strbuf_release(&buf);
 }
 
 static void split_pack_geometry(struct pack_geometry *geometry, int factor)
@@ -714,17 +738,20 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 		strbuf_release(&path);
 	}
 
-	if (geometric_factor) {
-		if (pack_everything)
-			die(_("options '%s' and '%s' cannot be used together"), "--geometric", "-A/-a");
-		init_pack_geometry(&geometry);
-		split_pack_geometry(geometry, geometric_factor);
-	}
-
 	packdir = mkpathdup("%s/pack", get_object_directory());
 	packtmp_name = xstrfmt(".tmp-%d-pack", (int)getpid());
 	packtmp = mkpathdup("%s/%s", packdir, packtmp_name);
 
+	collect_pack_filenames(&existing_nonkept_packs, &existing_kept_packs,
+			       &keep_pack_list);
+
+	if (geometric_factor) {
+		if (pack_everything)
+			die(_("options '%s' and '%s' cannot be used together"), "--geometric", "-A/-a");
+		init_pack_geometry(&geometry, &existing_kept_packs);
+		split_pack_geometry(geometry, geometric_factor);
+	}
+
 	sigchain_push_common(remove_pack_on_signal);
 
 	prepare_pack_objects(&cmd, &po_args);
@@ -764,9 +791,6 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	if (use_delta_islands)
 		strvec_push(&cmd.args, "--delta-islands");
 
-	collect_pack_filenames(&existing_nonkept_packs, &existing_kept_packs,
-			       &keep_pack_list);
-
 	if (pack_everything & ALL_INTO_ONE) {
 		repack_promisor_objects(&po_args, &names);
 

t/t7703-repack-geometric.sh

@@ -180,6 +180,34 @@ test_expect_success '--geometric ignores kept packs' '
 	)
 '
 
+test_expect_success '--geometric ignores --keep-pack packs' '
+	git init geometric &&
+	test_when_finished "rm -fr geometric" &&
+	(
+		cd geometric &&
+
+		# Create two equal-sized packs
+		test_commit kept && # 3 objects
+		git repack -d &&
+		test_commit pack && # 3 objects
+		git repack -d &&
+
+		find $objdir/pack -type f -name "*.pack" | sort >packs.before &&
+		git repack --geometric 2 -dm \
+			--keep-pack="$(basename "$(head -n 1 packs.before)")" >out &&
+		find $objdir/pack -type f -name "*.pack" | sort >packs.after &&
+
+		# Packs should not have changed (only one non-kept pack, no
+		# loose objects), but $midx should now exist.
+		grep "Nothing new to pack" out &&
+		test_path_is_file $midx &&
+
+		test_cmp packs.before packs.after &&
+
+		git fsck
+	)
+'
+
 test_expect_success '--geometric chooses largest MIDX preferred pack' '
 	git init geometric &&
 	test_when_finished "rm -fr geometric" &&