Cloning repo with depth 1 on installation

[Quantalabs]

Provide a detailed description of the proposed feature

Instead of cloning the homebrew repo as:

git clone https://github.com/Homebrew/brew

or the core repo, cloning with depth 1 will make the installation quicker:

git clone https://github.com/Homebrew/brew --depth=1

What is the motivation for the feature?

After installing homebrew 2 times, I've been frustrated by the long time it takes to install, the longest of which was the cloning of the homebrew/core repo.

How will the feature be relevant to at least 90% of Homebrew users?

It will be very relevant as new users will have a quick installation, and updates for existing users will be faster and easier.

What alternatives to the feature have been considered?

Manually installing, perhaps? However when I tried this homebrew updated, and took forever to update while cloning the homebrew/core repo.

[Rylan12]

We intentionally do not support shallow clones per a request from GitHub. While shallow clones are faster for the initial clone step, each fetch (i.e. brew update run) will take much longer and be much more computationally expensive for GitHub's servers.

If you must have a shallow clone, manual installation is the only option (and you'll need to manually clone the homebrew/core repo). Also, if you choose to do this, brew update will not be able to update Homebrew and its taps; you'll need to manually update them using git. Note, though, that we are in the process of removing the need to have the homebrew/core (and, eventually, homebrew/cask) repo(s) downloaded locally which will speed up the installation process and future brew update runs.

See #7050 and #10557, among others. You may also find these GitHub blog posts to be helpful in understanding why this is the case: Get up to speed with partial clone and shallow clone and Git clone: a data-driven study on cloning behaviors