How to shallow clone a local git repository with a relative path?

Question

Shallow clones of local directories require file:// as explained at: git clone: warning: --depth is ignored in local clones; use file:// instead

But how

Answer 1

You should try without the file:// prefix:

git clone --depth 1 ./mymodule mymodule2

Answer 2

But how to use relative paths with that?

This is not supported; file:// expects only absolute paths. There are e.g. RFC1738 and RFC8089 which describe this kind of URIs.

A file URL takes the form:

   file://<host>/<path>

where is the fully qualified domain name of the system on
which the is accessible, and is a hierarchical
directory path of the form //.../.

When you write file://mymodule, the mymodule can be interpreted as a hostname.

Answer 3

It's neither necessary nor beneficial to shallow clone a local repo. Just git clone ./relative/path and you are good to go.

I assume you want to shallow copy because you want to save the disk space and save time, but

1. It doesn't save disk space in local cloning.

From Git 2.24.1 manual:

For local repositories, also supported by Git natively, the following syntaxes may be used:

• /path/to/repo.git/

• file:///path/to/repo.git/

These two syntaxes are mostly equivalent, except the former implies --local option.

and

-l, --local

When the repository to clone from is on a local machine, this flag bypasses the normal "Git aware" transport mechanism and clones the repository by making a copy of HEAD and everything under objects and refs directories. The files under .git/objects/ directory are hardlinked to save space when possible.

So a shallow copy with file:///path/to/repo.git/ syntax should consume more disk space than a full copy with /path/to/repo.git/ syntax because the former has real copies of objects instead of hard links.

(And I believe that hard-linking is the reason why --depth get ignored when --local is set.)

2. It doesn't save time either.

Still, Git 2.24.1 manual:

-l, --local

When the repository to clone from is on a local machine, this flag bypasses the normal "Git aware" transport mechanism and clones the repository by making a copy of HEAD and everything under objects and refs directories. The files under .git/objects/ directory are hardlinked to save space when possible.

"Git aware" transport mechanism is time-consuming even when the URI is file://... because it includes object compressing:

$ time git clone --depth 1 --local --shallow-submodules file://$(pwd)/../linux
Cloning into 'linux'...
warning: --local is ignored
remote: Enumerating objects: 65607, done.
remote: Counting objects: 100% (65607/65607), done.
remote: Compressing objects: 100% (61137/61137), done.
remote: Total 65607 (delta 4886), reused 39965 (delta 3556)
Receiving objects: 100% (65607/65607), 176.65 MiB | 10.81 MiB/s, done.
Resolving deltas: 100% (4886/4886), done.
Updating files: 100% (61793/61793), done.
git clone --depth 1 --local --shallow-submodules  73.55s user 4.97s system 245% cpu 31.976 total

(I don't know why the receiving speed is 10.81 MiB/s on my NVMe SSD)

And cloning with --local flag is much quicker:

$ time git clone ../linux
Cloning into 'linux'...
done.
Updating files: 100% (61793/61793), done.
git clone ../linux  4.16s user 1.71s system 100% cpu 5.857 total