Re: [PATCH] [GSoC] remove_subtree(): reimplement using iterators

[Stefan Beller <sbeller@google.com>]

Welcome to the Git community!

On Thu, Mar 23, 2017 at 9:07 PM, Daniel Ferreira <bnmvco@gmail.com> wrote:
> Uses dir_iterator to traverse through remove_subtree()'s directory tree,
> avoiding the need for recursive calls to readdir() and simplifying code.

Please use a more imperative style. (e.g. s/Uses/Use/ ...
s/and simplfying/which simplifies/)

>
> Suggested in the GSoC microproject list, as well as:
> https://public-inbox.org/git/xmqqk27m4h3h.fsf@gitster.mtv.corp.google.com/

Thanks for this link. It gives good context for reviewing the change,
but it will not be good context to record as a commit message.
(When someone looks at a commit message later on, they are usually trying
to figure out what the author was thinking; if there were any special cases to
be thought about. Was performance on the authors mind? etc)

So I propose to put the link into the more informal section if a
reroll is needed.
I cc'd Duy, who came up with this Microproject.

> A conversion similar in purpose was previously done at 46d092a
> ("for_each_reflog(): reimplement using iterators", 2016-05-21).

Thanks for pointing at another conversion.

>
> Signed-off-by: Daniel Ferreira <bnmvco@gmail.com>
> ---
>
> Hey there! This is my microproject for Google Summer of Code on git.
> It has passed on Travis CI (https://travis-ci.org/theiostream/git),
> although I would appreciate any suggestion to improve test coverage
> for the affected function.

This function is deep down in the worktree update mechanism, so any run
of "git reset", "git checkout", git cherry-pick" (and all the others), which
remove a directory (possibly recursive) covers the functionality.

If I were to search for test coverage for this function in particular, I'd
start by looking at "(cd t && ls t1*)".


> This is, to my knowledge, one of the few microprojects that have not
> yet been started by someone on this list, but please let me know if
> someone else is already on it.

cool. :)

> --- a/entry.c
> +++ b/entry.c
> @@ -2,6 +2,8 @@
>  #include "blob.h"
>  #include "dir.h"
>  #include "streaming.h"
> +#include "iterator.h"
> +#include "dir-iterator.h"
>
>  static void create_directories(const char *path, int path_len,
>                                const struct checkout *state)
> @@ -46,29 +48,17 @@ static void create_directories(const char *path, int path_len,
>
>  static void remove_subtree(struct strbuf *path)
>  {
> -       DIR *dir = opendir(path->buf);
> -       struct dirent *de;
> +       struct dir_iterator *diter = dir_iterator_begin(path->buf);
>         int origlen = path->len;
>
> -       if (!dir)
> -               die_errno("cannot opendir '%s'", path->buf);
> -       while ((de = readdir(dir)) != NULL) {
> -               struct stat st;
> -
> -               if (is_dot_or_dotdot(de->d_name))
> -                       continue;
> -
> +       while (dir_iterator_advance(diter) == ITER_OK) {
>                 strbuf_addch(path, '/');
> -               strbuf_addstr(path, de->d_name);
> -               if (lstat(path->buf, &st))
> -                       die_errno("cannot lstat '%s'", path->buf);
> -               if (S_ISDIR(st.st_mode))
> -                       remove_subtree(path);
> -               else if (unlink(path->buf))
> +               strbuf_addstr(path, diter->relative_path);
> +               if (unlink(path->buf))
>                         die_errno("cannot unlink '%s'", path->buf);
>                 strbuf_setlen(path, origlen);

Instead of constructing the path again here based on relative path
and the path parameter, I wonder if we could use

    if (unlink(diter->path))
        ..

here? Then we would not need the strbuf at all?
Also we'd need to handle (empty) directories differently for removal?
Do we need to check the return code of dir_iterator_advance
for ITER_ERROR as well?

>         }
> -       closedir(dir);
> +
>         if (rmdir(path->buf))
>                 die_errno("cannot rmdir '%s'", path->buf);

This would remove the "top level" directory as given by path.
When reading the dir-iterator code, I am not sure if this is
also part of the yield in dir_iterator_advance.

Thanks for working on this micro project!
Stefan