Re: [PATCH v3 2/5] clone: add a --no-tags option to clone without tags

> Add a --no-tags option to clone without fetching any tags.
>
> Without this change there's no easy way to clone a repository without
> also fetching its tags.
>
> When supplying --single-branch the primary remote branch will be
> cloned, but in addition tags will be followed & retrieved. Now
> --no-tags can be added --single-branch to clone a repository without
> tags, and which only tracks a single upstream branch.
>
> This option works without --single-branch as well, and will do a
> normal clone but not fetch any tags.
>
> Many git commands pay some fixed overhead as a function of the number
> of references. E.g. creating ~40k tags in linux.git will cause a
> command like `git log -1 >/dev/null` to run in over a second instead
> of in a matter of milliseconds, in addition numerous other things will
> slow down, e.g. "git log <TAB>" with the bash completion will slowly
> show ~40k references instead of 1.
>
> The user might want to avoid all of that overhead to simply use a
> repository like that to browse the "master" branch, or something like
> a CI tool might want to keep that one branch up-to-date without caring
> about any other references.
>
> Without this change the only way of accomplishing this was either by
> manually tweaking the config in a fresh repository:
>
>     git init git &&
>     cat >git/.git/config <<EOF &&
>     [remote "origin"]
>         url = git@github.com:git/git.git
>         tagOpt = --no-tags
>         fetch = +refs/heads/master:refs/remotes/origin/master
>     [branch "master"]
>         remote = origin
>         merge = refs/heads/master
>     EOF
>     cd git &&
>     git pull
>
> Which requires hardcoding the "master" name, which may not be the main
> --single-branch would have retrieved, or alternatively by setting
> tagOpt=--no-tags right after cloning & deleting any existing tags:
>
>     git clone --single-branch git@github.com:git/git.git &&
>     cd git &&
>     git config remote.origin.tagOpt --no-tags &&
>     git tag -l | xargs git tag -d
>
> Which of course was also subtly buggy if --branch was pointed at a
> tag, leaving the user in a detached head:
>
>     git clone --single-branch --branch v2.12.0 git@github.com:git/git.git &&
>     cd git &&
>     git config remote.origin.tagOpt --no-tags &&
>     git tag -l | xargs git tag -d
>
> Now all this complexity becomes the much simpler:
>
>     git clone --single-branch --no-tags git@github.com:git/git.git
>
> Or in the case of cloning a single tag "branch":
>
>     git clone --single-branch --branch v2.12.0 --no-tags git@github.com:git/git.git
>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>

> +--no-tags::
> +       Don't clone any tags, and set
> +       `remote.<remote>.tagOpt=--no-tags` in the config, ensuring
> +       that future `git pull` and `git fetch` operations won't follow
> +       any tags. Subsequent explicit tag fetches will still work,
> +       (see linkgit:git-fetch[1]).
> ++
> +Can be used in conjunction with `--single-branch` to clone and
> +maintain a branch with no references other than a single cloned
> +branch. This is useful e.g. to maintain minimal clones of the default
> +branch of some repository for search indexing.

> @@ -652,7 +655,7 @@ static void update_remote_refs(const struct ref *refs,
>
>         if (refs) {
>                 write_remote_refs(mapped_refs);
> -               if (option_single_branch)
> +               if (option_single_branch && !option_no_tags)