Re: [PATCH] fast-import: disallow empty branches as parents
Hi Dmitry,
Dmitry Ivankov wrote:
> Empty branches (either new or reset-ed) have null_sha1 in fast-import
> internals. These null_sha1 heads can slip to the real commit objects.
[... nice explanation snipped ...]
Very nice, thanks much for this.
Would it be possible to split this into multiple independent fixes? See [*] below for one way.
Show 10 quoted lines
> --- a/fast-import.c
> +++ b/fast-import.c
> @@ -2540,7 +2540,8 @@ static void file_change_deleteall(struct branch *b)
> b->num_notes = 0;
> }
>
> -static void parse_from_commit(struct branch *b, char *buf, unsigned long size)
> +static void parse_from_commit(struct branch *b, unsigned char *sha1,
> + char *buf, unsigned long size)
> {What is happening here? The new argument doesn't seem to be used.
[...]
Show 19 quoted lines
> @@ -2551,29 +2552,31 @@ static void parse_from_commit(struct branch *b, char *buf, unsigned long size)
> b->branch_tree.versions[1].sha1);
> }
>
> -static void parse_from_existing(struct branch *b)
> +static void parse_from_existing(struct branch *b, unsigned char *sha1)
> {
> - if (is_null_sha1(b->sha1)) {
> + if (is_null_sha1(sha1)) {
> hashclr(b->branch_tree.versions[0].sha1);
> hashclr(b->branch_tree.versions[1].sha1);
> } else {
> unsigned long size;
> char *buf;
>
> - buf = read_object_with_reference(b->sha1,
> - commit_type, &size, b->sha1);
> + buf = read_object_with_reference(sha1,
> + commit_type, &size, sha1);This seems to be about delaying the effect of "from" so it doesn't interfere with a "merge" command referring to the same commit.
[...]
Show 11 quoted lines
> -static int parse_from(struct branch *b)
> +static int parse_from(struct branch *b, unsigned char *sha1out)
> {
> const char *from;
> struct branch *s;
>
> - if (prefixcmp(command_buf.buf, "from "))
> + if (prefixcmp(command_buf.buf, "from ")) {
> + hashclr(sha1out);
> return 0;
> + }This code path handles the case where there is no "from" after a "reset" or "commit" command. We clear sha1out to make the calling convention simple --- sha1out is always written to, and the caller does not have to worry about initializing it in advance.
I guess this is part of the change that delays the effect of "from"?
[...]
Show 7 quoted lines
> @@ -2586,7 +2589,10 @@ static int parse_from(struct branch *b)
> die("Can't create a branch from itself: %s", b->name);
> else if (s) {
> unsigned char *t = s->branch_tree.versions[1].sha1;
> + if (is_null_sha1(s->sha1))
> + die("Can't create a branch from an empty branch:"
> + " %s from %s", b->name, s->name);This seems to be about protecting against "from" with an unborn branch.
> - hashcpy(b->sha1, s->sha1);
> + hashcpy(sha1out, s->sha1);
Delaying the effect of "from", maybe.
[...]
Show 6 quoted lines
> @@ -2594,16 +2600,16 @@ static int parse_from(struct branch *b)
> struct object_entry *oe = find_mark(idnum);
> if (oe->type != OBJ_COMMIT)
> die("Mark :%" PRIuMAX " not a commit", idnum);
> - hashcpy(b->sha1, oe->idx.sha1);
> + hashcpy(sha1out, oe->idx.sha1);Show 5 quoted lines
> if (oe->pack_id != MAX_PACK_ID) {
> unsigned long size;
> char *buf = gfi_unpack_entry(oe, &size);
> - parse_from_commit(b, buf, size);
> + parse_from_commit(b, sha1out, buf, size);Show 8 quoted lines
> free(buf);
> } else
> - parse_from_existing(b);
> + parse_from_existing(b, sha1out);
> - } else if (!get_sha1(from, b->sha1))
> + } else if (!get_sha1(from, sha1out))
> - parse_from_existing(b);
> + parse_from_existing(b, sha1out);
Show 14 quoted lines
> else
> die("Invalid ref name or SHA1 expression: %s", from);
>
> @@ -2622,9 +2628,11 @@ static struct hash_list *parse_merge(unsigned int *count)
> from = strchr(command_buf.buf, ' ') + 1;
> n = xmalloc(sizeof(*n));
> s = lookup_branch(from);
> - if (s)
> + if (s) {
> + if (is_null_sha1(s->sha1))
> + die("Can't merge empty branch: %s", s->name);
> hashcpy(n->sha1, s->sha1);
> - else if (*from == ':') {
> + } else if (*from == ':') {Protecting against "merge" with unknown branch.
[...]
Show 14 quoted lines
> @@ -2656,6 +2664,7 @@ static void parse_new_commit(void)
> {
> static struct strbuf msg = STRBUF_INIT;
> struct branch *b;
> + unsigned char sha1[20];
> char *sp;
> char *author = NULL;
> char *committer = NULL;
> @@ -2683,7 +2692,7 @@ static void parse_new_commit(void)
> die("Expected committer but didn't get one");
> parse_data(&msg, 0, NULL);
> read_next_command();
> - parse_from(b);
> + parse_from(b, sha1);Delayed "from" effect?
[...]
Show 9 quoted lines
> @@ -2730,7 +2739,9 @@ static void parse_new_commit(void)
> strbuf_reset(&new_data);
> strbuf_addf(&new_data, "tree %s\n",
> sha1_to_hex(b->branch_tree.versions[1].sha1));
> - if (!is_null_sha1(b->sha1))
> + if (!is_null_sha1(sha1))
> + strbuf_addf(&new_data, "parent %s\n", sha1_to_hex(sha1));
> + else if (!is_null_sha1(b->sha1))
> strbuf_addf(&new_data, "parent %s\n", sha1_to_hex(b->sha1));
Show 6 quoted lines
> @@ -2855,7 +2866,7 @@ static void parse_reset_branch(void)
> else
> b = new_branch(sp);
> read_next_command();
> - parse_from(b);
> + parse_from(b, b->sha1);
Likewise?
[*] So it looks like this would be easier to read as three patches:
1. protecting against "from" of unborn branch
2. protecting against "merge" of unborn branch
3. delaying the effect of "from" to avoid it confusingly changing
the effect of a "merge" in the same commit(1) and (2) would be no-brainers, while (3) seems more subtle --- maybe it should be documented to help importers for other version control systems to know to make the same change?
[...]
Show 17 quoted lines
> --- a/t/t9300-fast-import.sh
> +++ b/t/t9300-fast-import.sh
> @@ -2895,6 +2895,54 @@ test_expect_success 'S: merge with garbage after mark must fail' '
> test_i18ngrep "after mark" err
> '
>
> +test_expect_success 'S: empty branch as merge parent must fail' '
> + test_must_fail git fast-import <<-EOF 2>err &&
> + commit refs/heads/chicken
> + committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
> + data <<COMMIT
> + I am the chicken.
> + COMMIT
> + merge refs/heads/chicken
> + EOF
> + cat err &&
> + test_must_fail git rev-parse --verify refs/heads/chicken^
There would be no "chicken" branch after this import at all, right?
[...]
Show 18 quoted lines
> +test_expect_success 'S: empty branch as merge parent must fail (2)' '
> + test_must_fail git fast-import <<-EOF 2>err &&
> + commit refs/heads/egg1
> + committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
> + data <<COMMIT
> + I am the egg N1.
> + COMMIT
> +
> + commit refs/heads/egg2
> + committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
> + data <<COMMIT
> + I am the egg N2.
> + COMMIT
> + from refs/heads/egg1
> + merge refs/heads/egg2
> + EOF
> + cat err &&
> + test_must_fail git rev-parse --verify refs/heads/egg2^2
Show 13 quoted lines
> +test_expect_success 'S: empty branch as a parent must fail ' '
> + test_must_fail git fast-import <<-EOF 2>err &&
> + reset refs/heads/egg3
> +
> + commit refs/heads/egg4
> + committer $GIT_COMMITTER_NAME <$GIT_COMMITTER_EMAIL> $GIT_COMMITTER_DATE
> + data <<COMMIT
> + I am the egg N4.
> + COMMIT
> + from refs/heads/egg3
> + EOF
> + cat err &&
> + test_must_fail git rev-parse --verify refs/heads/egg4^2
Likewise for egg4.
If this were split up as described above, I imagine it would be much easier to read and most of it would move into the "obviously good" category (I'm still uncertain about some details of the "delayed from" implementation and haven't checked carefully whether it misses any spots). What do you think?
Thanks for a pleasant read, and hope that helps, Jonathan
Dmitry Ivankov