Merge branch 'jk/squelch-missing-link-warning-for-unreachable' into maint

Recent "git prune" traverses young unreachable objects to safekeep
old objects in the reachability chain from them, which sometimes
caused error messages that are unnecessarily alarming.

* jk/squelch-missing-link-warning-for-unreachable:
  suppress errors on missing UNINTERESTING links
  silence broken link warnings with revs->ignore_missing_links
  add quieter versions of parse_{tree,commit}

commit.c

@@ -353,7 +353,7 @@ int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long s
 	return 0;
 }
 
-int parse_commit(struct commit *item)
+int parse_commit_gently(struct commit *item, int quiet_on_missing)
 {
 	enum object_type type;
 	void *buffer;
@@ -366,7 +366,8 @@ int parse_commit(struct commit *item)
 		return 0;
 	buffer = read_sha1_file(item->object.sha1, &type, &size);
 	if (!buffer)
-		return error("Could not read %s",
+		return quiet_on_missing ? -1 :
+			error("Could not read %s",
 			     sha1_to_hex(item->object.sha1));
 	if (type != OBJ_COMMIT) {
 		free(buffer);

commit.h

@@ -59,7 +59,11 @@ struct commit *lookup_commit_reference_by_name(const char *name);
 struct commit *lookup_commit_or_die(const unsigned char *sha1, const char *ref_name);
 
 int parse_commit_buffer(struct commit *item, const void *buffer, unsigned long size);
-int parse_commit(struct commit *item);
+int parse_commit_gently(struct commit *item, int quiet_on_missing);
+static inline int parse_commit(struct commit *item)
+{
+	return parse_commit_gently(item, 0);
+}
 void parse_commit_or_die(struct commit *item);
 
 /*

list-objects.c

@@ -81,7 +81,7 @@ static void process_tree(struct rev_info *revs,
 		die("bad tree object");
 	if (obj->flags & (UNINTERESTING | SEEN))
 		return;
-	if (parse_tree(tree) < 0) {
+	if (parse_tree_gently(tree, revs->ignore_missing_links) < 0) {
 		if (revs->ignore_missing_links)
 			return;
 		die("bad tree object %s", sha1_to_hex(obj->sha1));

revision.c

@@ -817,7 +817,7 @@ static int add_parents_to_list(struct rev_info *revs, struct commit *commit,
 			parent = parent->next;
 			if (p)
 				p->object.flags |= UNINTERESTING;
-			if (parse_commit(p) < 0)
+			if (parse_commit_gently(p, 1) < 0)
 				continue;
 			if (p->parents)
 				mark_parents_uninteresting(p);
@@ -844,7 +844,7 @@ static int add_parents_to_list(struct rev_info *revs, struct commit *commit,
 	for (parent = commit->parents; parent; parent = parent->next) {
 		struct commit *p = parent->item;
 
-		if (parse_commit(p) < 0)
+		if (parse_commit_gently(p, revs->ignore_missing_links) < 0)
 			return -1;
 		if (revs->show_source && !p->util)
 			p->util = commit->util;

t/t6501-freshen-objects.sh

@@ -129,4 +129,19 @@ for repack in '' true; do
 	'
 done
 
+test_expect_success 'do not complain about existing broken links' '
+	cat >broken-commit <<-\EOF &&
+	tree 0000000000000000000000000000000000000001
+	parent 0000000000000000000000000000000000000002
+	author whatever <whatever@example.com> 1234 -0000
+	committer whatever <whatever@example.com> 1234 -0000
+
+	some message
+	EOF
+	commit=$(git hash-object -t commit -w broken-commit) &&
+	git gc 2>stderr &&
+	verbose git cat-file -e $commit &&
+	test_must_be_empty stderr
+'
+
 test_done

tree.c

@@ -204,7 +204,7 @@ int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size)
 	return 0;
 }
 
-int parse_tree(struct tree *item)
+int parse_tree_gently(struct tree *item, int quiet_on_missing)
 {
 	 enum object_type type;
 	 void *buffer;
@@ -214,7 +214,8 @@ int parse_tree(struct tree *item)
 		return 0;
 	buffer = read_sha1_file(item->object.sha1, &type, &size);
 	if (!buffer)
-		return error("Could not read %s",
+		return quiet_on_missing ? -1 :
+			error("Could not read %s",
 			     sha1_to_hex(item->object.sha1));
 	if (type != OBJ_TREE) {
 		free(buffer);

tree.h

@@ -16,7 +16,11 @@ struct tree *lookup_tree(const unsigned char *sha1);
 
 int parse_tree_buffer(struct tree *item, void *buffer, unsigned long size);
 
-int parse_tree(struct tree *tree);
+int parse_tree_gently(struct tree *tree, int quiet_on_missing);
+static inline int parse_tree(struct tree *tree)
+{
+	return parse_tree_gently(tree, 0);
+}
 void free_tree_buffer(struct tree *tree);
 
 /* Parses and returns the tree in the given ent, chasing tags and commits. */