Subject: Re: [PATCH v2 2/8] fast-import: fix handling of deleted tags

From: René Scharfe <[email-masked]>
Date: Thu, 3 Oct 2019 13:53:23 +0200

Am 30.09.19 um 23:10 schrieb Elijah Newren:
> If our input stream includes a tag which is later deleted, we were not
> properly deleting it.  We did have a step which would delete it, but we
> left a tag in the tag list noting that it needed to be updated, and the
> updating of annotated tags occurred AFTER ref deletion.  So, when we
> record that a tag needs to be deleted, also remove it from the list of
> annotated tags to update.
>
> While this has likely been something that has not happened in practice,
> it will come up more in order to support nested tags.  For nested tags,
> we either need to give temporary names to the intermediate tags and then
> delete them, or else we need to use the final name for the intermediate
> tags.  If we use the final name for the intermediate tags, then in order
> to keep the sanity check that someone doesn't try to update the same tag
> twice, we need to delete the ref after creating the intermediate tag.
> So, either way nested tags imply the need to delete temporary inner tag
> references.
>
> Signed-off-by: Elijah Newren <[email-masked]>
> ---
>  fast-import.c          | 29 +++++++++++++++++++++++++++++
>  t/t9300-fast-import.sh | 13 +++++++++++++
>  2 files changed, 42 insertions(+)
>
> diff --git a/fast-import.c b/fast-import.c
> index b44d6a467e..546da3a938 100644
> --- a/fast-import.c
> +++ b/fast-import.c
> @@ -2793,6 +2793,35 @@ static void parse_reset_branch(const char *arg)
>  		b = new_branch(arg);
>  	read_next_command();
>  	parse_from(b);
> +	if (b->delete && !strncmp(b->name, "refs/tags/", 10)) {

b->name is a NUL-terminated string; starts_with() could be used to avoid
the magic number 10.

> +		/*
> +		 * Elsewhere, we call dump_branches() before dump_tags(),
> +		 * and dump_branches() will handle ref deletions first, so
> +		 * in order to make sure the deletion actually takes effect,
> +		 * we need to remove the tag from our list of tags to update.
> +		 *
> +		 * NEEDSWORK: replace list of tags with hashmap for faster
> +		 * deletion?
> +		 */
> +		struct strbuf tag_name = STRBUF_INIT;

This adds a small memory leak.

> +		struct tag *t, *prev = NULL;
> +		for (t = first_tag; t; t = t->next_tag) {
> +			strbuf_reset(&tag_name);
> +			strbuf_addf(&tag_name, "refs/tags/%s", t->name);
> +			if (!strcmp(b->name, tag_name.buf))

So the strbuf is used to prefix t->name with "refs/tags/", which we know
b->name starts with, and to compare the result with b->name.  Removing
the "refs/tags/" prefix from b->name using skip_prefix() and comparing
the result with t->name would be easier.

> +				break;
> +			prev = t;
> +		}
> +		if (t) {
> +			if (prev)
> +				prev->next_tag = t->next_tag;
> +			else
> +				first_tag = t->next_tag;
> +			if (!t->next_tag)
> +				last_tag = prev;
> +			/* There is no mem_pool_free(t) function to call. */
> +		}
> +	}
>  	if (command_buf.len > 0)
>  		unread_command_buf = 1;
>  }

Here's a squashable patch for that:

---
 fast-import.c | 8 +++-----
 1 file changed, 3 insertions(+), 5 deletions(-)

diff --git a/fast-import.c b/fast-import.c
index 70cd3f0ff4..a109591406 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -2779,6 +2779,7 @@ static void parse_new_tag(const char *arg)
 static void parse_reset_branch(const char *arg)
 {
 	struct branch *b;
+	const char *tag_name;

 	b = lookup_branch(arg);
 	if (b) {
@@ -2794,7 +2795,7 @@ static void parse_reset_branch(const char *arg)
 		b = new_branch(arg);
 	read_next_command();
 	parse_from(b);
-	if (b->delete && !strncmp(b->name, "refs/tags/", 10)) {
+	if (b->delete && skip_prefix(b->name, "refs/tags/", &tag_name)) {
 		/*
 		 * Elsewhere, we call dump_branches() before dump_tags(),
 		 * and dump_branches() will handle ref deletions first, so
@@ -2804,12 +2805,9 @@ static void parse_reset_branch(const char *arg)
 		 * NEEDSWORK: replace list of tags with hashmap for faster
 		 * deletion?
 		 */
-		struct strbuf tag_name = STRBUF_INIT;
 		struct tag *t, *prev = NULL;
 		for (t = first_tag; t; t = t->next_tag) {
-			strbuf_reset(&tag_name);
-			strbuf_addf(&tag_name, "refs/tags/%s", t->name);
-			if (!strcmp(b->name, tag_name.buf))
+			if (!strcmp(t->name, tag_name))
 				break;
 			prev = t;
 		}
--
2.23.0