Respecting the `CARGO_HOME` environment variable after `rustup` was installed

Problem you are trying to solve

I downloaded rustup via the command provided on the official website:

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

and then followed the on-screen instructions to install it. I then added
the CARGO_HOME environment variable to my shell initialization script (.zshrc in my case):

export CARGO_HOME="$HOME/.rust/cargo"

only to find out that the line added to .profile or .zshenv is already
using the default location for cargo:

. $HOME/.cargo/env

and also the env script was adding the default bin to my PATH:

export PATH="$HOME/.cargo/bin:$PATH"

and so my CARGO_HOME environment variable was effectively doing nothing.

Solution you'd like

I fixed the problem by modifying the line in my shell initialization script to
look like below:

. "$CARGO_HOME/env"

And also modified the $CARGO_HOME/env script:

export PATH="${CARGO_HOME}/bin:$PATH"

I think this would make a nice addition to the project: a cleaner
rustup install management.

Notes

Since this was a simple enough fix and I've been looking for a way to
start contributing to open-source projects, I thought this might be a
good first contribution for me. I searched through this repository
and the rustup-init.sh file so that I could maybe find the relevant lines
of code and fix them--with no success.

If possible, I would like a little bit of guidance on which files to edit
so that I can contribute this fix myself.

Start by inspecting rustup-init.sh and the shell initialization references mentioned in the issue, including .profile, .zshenv, and $CARGO_HOME/env. Trace how CARGO_HOME and PATH are written during installation, then verify that the generated setup uses the configured Cargo location rather than the default; the payload names no existing test to run.