Merge branch 'jc/resolve-undo' into maint

The resolve-undo information in the index was not protected against
GC, which has been corrected.
source: <xmqq35f7kzad.fsf@gitster.g>

* jc/resolve-undo:
  fsck: do not dereference NULL while checking resolve-undo data
  revision: mark blobs needed for resolve-undo as reachable

builtin/fsck.c

@@ -19,6 +19,7 @@
 #include "decorate.h"
 #include "packfile.h"
 #include "object-store.h"
+#include "resolve-undo.h"
 #include "run-command.h"
 #include "worktree.h"
 
@@ -757,6 +758,43 @@ static int fsck_cache_tree(struct cache_tree *it)
 	return err;
 }
 
+static int fsck_resolve_undo(struct index_state *istate)
+{
+	struct string_list_item *item;
+	struct string_list *resolve_undo = istate->resolve_undo;
+
+	if (!resolve_undo)
+		return 0;
+
+	for_each_string_list_item(item, resolve_undo) {
+		const char *path = item->string;
+		struct resolve_undo_info *ru = item->util;
+		int i;
+
+		if (!ru)
+			continue;
+		for (i = 0; i < 3; i++) {
+			struct object *obj;
+
+			if (!ru->mode[i] || !S_ISREG(ru->mode[i]))
+				continue;
+
+			obj = parse_object(the_repository, &ru->oid[i]);
+			if (!obj) {
+				error(_("%s: invalid sha1 pointer in resolve-undo"),
+				      oid_to_hex(&ru->oid[i]));
+				errors_found |= ERROR_REFS;
+				continue;
+			}
+			obj->flags |= USED;
+			fsck_put_object_name(&fsck_walk_options, &ru->oid[i],
+					     ":(%d):%s", i, path);
+			mark_object_reachable(obj);
+		}
+	}
+	return 0;
+}
+
 static void mark_object_for_connectivity(const struct object_id *oid)
 {
 	struct object *obj = lookup_unknown_object(the_repository, oid);
@@ -938,6 +976,7 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		}
 		if (active_cache_tree)
 			fsck_cache_tree(active_cache_tree);
+		fsck_resolve_undo(&the_index);
 	}
 
 	check_connectivity();

revision.c

@@ -33,6 +33,7 @@
 #include "bloom.h"
 #include "json-writer.h"
 #include "list-objects-filter-options.h"
+#include "resolve-undo.h"
 
 volatile show_early_output_fn_t show_early_output;
 
@@ -1696,6 +1697,39 @@ static void add_cache_tree(struct cache_tree *it, struct rev_info *revs,
 
 }
 
+static void add_resolve_undo_to_pending(struct index_state *istate, struct rev_info *revs)
+{
+	struct string_list_item *item;
+	struct string_list *resolve_undo = istate->resolve_undo;
+
+	if (!resolve_undo)
+		return;
+
+	for_each_string_list_item(item, resolve_undo) {
+		const char *path = item->string;
+		struct resolve_undo_info *ru = item->util;
+		int i;
+
+		if (!ru)
+			continue;
+		for (i = 0; i < 3; i++) {
+			struct blob *blob;
+
+			if (!ru->mode[i] || !S_ISREG(ru->mode[i]))
+				continue;
+
+			blob = lookup_blob(revs->repo, &ru->oid[i]);
+			if (!blob) {
+				warning(_("resolve-undo records `%s` which is missing"),
+					oid_to_hex(&ru->oid[i]));
+				continue;
+			}
+			add_pending_object_with_path(revs, &blob->object, "",
+						     ru->mode[i], path);
+		}
+	}
+}
+
 static void do_add_index_objects_to_pending(struct rev_info *revs,
 					    struct index_state *istate,
 					    unsigned int flags)
@@ -1724,6 +1758,8 @@ static void do_add_index_objects_to_pending(struct rev_info *revs,
 		add_cache_tree(istate->cache_tree, revs, &path, flags);
 		strbuf_release(&path);
 	}
+
+	add_resolve_undo_to_pending(istate, revs);
 }
 
 void add_index_objects_to_pending(struct rev_info *revs, unsigned int flags)

t/t2030-unresolve-info.sh

@@ -194,4 +194,75 @@ test_expect_success 'rerere forget (add-add conflict)' '
 	test_i18ngrep "no remembered" actual
 '
 
+test_expect_success 'resolve-undo keeps blobs from gc' '
+	git checkout -f main &&
+
+	# First make sure we do not have any cruft left in the object store
+	git repack -a -d &&
+	git prune --expire=now &&
+	git prune-packed &&
+	git gc --prune=now &&
+	git fsck --unreachable >cruft &&
+	test_must_be_empty cruft &&
+
+	# Now add three otherwise unreferenced blob objects to the index
+	git reset --hard &&
+	B1=$(echo "resolve undo test data 1" | git hash-object -w --stdin) &&
+	B2=$(echo "resolve undo test data 2" | git hash-object -w --stdin) &&
+	B3=$(echo "resolve undo test data 3" | git hash-object -w --stdin) &&
+	git update-index --add --index-info <<-EOF &&
+	100644 $B1 1	frotz
+	100644 $B2 2	frotz
+	100644 $B3 3	frotz
+	EOF
+
+	# These three blob objects are reachable (only) from the index
+	git fsck --unreachable >cruft &&
+	test_must_be_empty cruft &&
+	# and they should be protected from GC
+	git gc --prune=now &&
+	git cat-file -e $B1 &&
+	git cat-file -e $B2 &&
+	git cat-file -e $B3 &&
+
+	# Now resolve the conflicted path
+	B0=$(echo "resolve undo test data 0" | git hash-object -w --stdin) &&
+	git update-index --add --cacheinfo 100644,$B0,frotz &&
+
+	# These three blob objects are now reachable only from the resolve-undo
+	git fsck --unreachable >cruft &&
+	test_must_be_empty cruft &&
+
+	# and they should survive GC
+	git gc --prune=now &&
+	git cat-file -e $B0 &&
+	git cat-file -e $B1 &&
+	git cat-file -e $B2 &&
+	git cat-file -e $B3 &&
+
+	# Now we switch away, which nukes resolve-undo, and
+	# blobs B0..B3 would become dangling.  fsck should
+	# notice that they are now unreachable.
+	git checkout -f side &&
+	git fsck --unreachable >cruft &&
+	sort cruft >actual &&
+	sort <<-EOF >expect &&
+	unreachable blob $B0
+	unreachable blob $B1
+	unreachable blob $B2
+	unreachable blob $B3
+	EOF
+	test_cmp expect actual &&
+
+	# And they should go away when gc runs.
+	git gc --prune=now &&
+	git fsck --unreachable >cruft &&
+	test_must_be_empty cruft &&
+
+	test_must_fail git cat-file -e $B0 &&
+	test_must_fail git cat-file -e $B1 &&
+	test_must_fail git cat-file -e $B2 &&
+	test_must_fail git cat-file -e $B3
+'
+
 test_done