On Tue, 14 Nov 2017 16:30:43 -0800
Stefan Beller <sbeller@xxxxxxxxxx> wrote:
> The walking is performed in reverse order to show the introduction of a
> blob rather than its last occurrence.
The code as implemented here does not do this - it instead shows the last
occurrence.
> NAME
> ----
> -git-describe - Describe a commit using the most recent tag reachable from it
> +git-describe - Describe a commit or blob using the graph relations
I would write "Describe a commit or blob using a tag reachable from it".
> +If the given object refers to a blob, it will be described
> +as `<commit-ish>:<path>`, such that the blob can be found
> +at `<path>` in the `<commit-ish>`. Note, that the commit is likely
> +not the commit that introduced the blob, but the one that was found
> +first; to find the commit that introduced the blob, you need to find
> +the commit that last touched the path, e.g.
> +`git log <commit-description> -- <path>`.
> +As blobs do not point at the commits they are contained in,
> +describing blobs is slow as we have to walk the whole graph.
I think some of this needs to be updated?
> +static void process_object(struct object *obj, const char *path, void *data)
> +{
> + struct process_commit_data *pcd = data;
> +
> + if (!oidcmp(&pcd->looking_for, &obj->oid) && !pcd->dst->len) {
> + reset_revision_walk();
> + describe_commit(&pcd->current_commit, pcd->dst);
> + strbuf_addf(pcd->dst, ":%s", path);
> + pcd->revs->max_count = 0;
> + }
> +}
Setting max_count to 0 does not work when reverse is used, because the
commits are first buffered into revs->commits (see get_revision() in
revision.c). There doesn't seem to be a convenient way to terminate the
traversal immediately - I think setting revs->commits to NULL should
work (but I didn't check). Remember to free revs->commits (using
free_commit_list) first.
> +test_expect_success 'describe a blob at a tag' '
> + echo "make it a unique blob" >file &&
> + git add file && git commit -m "content in file" &&
> + git tag -a -m "latest annotated tag" unique-file &&
> + git describe HEAD:file >actual &&
> + echo "unique-file:file" >expect &&
> + test_cmp expect actual
> +'
This is probably better named "describe a blob at a directly tagged
commit". (Should we also test the case where a blob is directly
tagged?)
> +test_expect_success 'describe a blob with its last introduction' '
> + git commit --allow-empty -m "empty commit" &&
> + git rm file &&
> + git commit -m "delete blob" &&
> + git revert HEAD &&
> + git commit --allow-empty -m "empty commit" &&
> + git describe HEAD:file >actual &&
> + grep unique-file-3-g actual
> +'
The description is not true: firstly, this shows the last occurrence,
not the last introduction (you can verify this by adding another commit
and noticing that the contents of "actual" changes), and what we want is
not the last introduction anyway, but the first one.
