Jeff King <p...@peff.net> writes:

> The get_ref_cache code was designed to scale to the actual number of
> submodules. I do not mind seeing it become a hash if people really do
> have a large number of submodules, but that is not what is happening
> here.
> ...
> So git-clean speculatively asks "what is HEAD in this maybe-submodule?". The
> right solution is probably one of:
>
>   1. In remove_dirs, find out if we have an actual submodule before calling
>      resolve_gitlink_ref.
>
>   2. Teach get_ref_cache a "read-only" mode that will not auto-vivify the 
> cache
>      if it does not already exist.
>
> Of the two, I think (1) is probably cleaner (I think the way the ref
> code is structured, we have to create the submodule ref_cache in order
> to start looking things up in it).

Thanks for a great analysis.  I too wondered if we should be growing
the per-submodule ref-cache when we are only probing.

> It looks like we don't even really care about the value of HEAD. We just
> want to know "is it a git directory?". I think in other places (like
> "git add"), we just do an existence check for "$dir/.git". That would
> not catch a bare repository, but I do not think the current check does
> either (it is looking for submodules, which always have a .git).

If we wanted to be consistent, perhaps we should be reusing the "is
this a git repository?" check used by the auto-discovery codepath
(setup.c:is_git_directory(), perhaps?), but the idea looks simple
enough and sounds sensible.

> Maybe something like (largely untested):
>
> diff --git a/builtin/clean.c b/builtin/clean.c
> index 98c103f..e2cc47b 100644
> --- a/builtin/clean.c
> +++ b/builtin/clean.c
> @@ -148,6 +148,32 @@ static int exclude_cb(const struct option *opt, const 
> char *arg, int unset)
>       return 0;
>  }
>  
> +static int dir_is_repo(struct strbuf *path)
> +{
> +     size_t orig = path->len;
> +     int ret;
> +
> +     strbuf_addstr(path, "/.git");
> +     if (!access(path->buf, F_OK))
> +             ret = 1; /* definitely */
> +     else if (errno == ENOENT)
> +             ret = 0; /* definitely not */
> +     else {
> +             /*
> +              * We couldn't tell. It would probably be safer to err
> +              * on the side of saying "yes" here, because we are
> +              * deciding what to delete, and are more likely to keep
> +              * a sub-repo. But it would probably also create annoying
> +              * false positives, where a directory we do not have
> +              * permission to read would say something misleading
> +              * like "not deleting sub-repo foo..."
> +              */
> +             ret = 0;
> +     }
> +     strbuf_setlen(path, orig);
> +     return ret;
> +}
> +
>  static int remove_dirs(struct strbuf *path, const char *prefix, int 
> force_flag,
>               int dry_run, int quiet, int *dir_gone)
>  {
> @@ -155,13 +181,11 @@ static int remove_dirs(struct strbuf *path, const char 
> *prefix, int force_flag,
>       struct strbuf quoted = STRBUF_INIT;
>       struct dirent *e;
>       int res = 0, ret = 0, gone = 1, original_len = path->len, len;
> -     unsigned char submodule_head[20];
>       struct string_list dels = STRING_LIST_INIT_DUP;
>  
>       *dir_gone = 1;
>  
> -     if ((force_flag & REMOVE_DIR_KEEP_NESTED_GIT) &&
> -                     !resolve_gitlink_ref(path->buf, "HEAD", 
> submodule_head)) {
> +     if ((force_flag & REMOVE_DIR_KEEP_NESTED_GIT) && dir_is_repo(path)) {
>               if (!quiet) {
>                       quote_path_relative(path->buf, prefix, &quoted);
>                       printf(dry_run ?  _(msg_would_skip_git_dir) : 
> _(msg_skip_git_dir),
--
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