install-script: support custom install location via common environment variables

[practicalli-johnny]

Describe the improvement

The install script for Linux has a fixed install location for the Cargo binary to $HOME/.cargo/bin directory. If another directory is used then the install fails.

Consider extending the script to support CARGO_HOME from Rustup tool and the XDG_CONFIG_HOME from xfreedesktop.org.

I suggest first checking in this order

1. CARGO_HOME - installing in $CARGO_HOME/bin
2. XDG_CONFIG_HOME - installing in XDG_CONFIG_HOME/cargo/bin
3. If none of the above set, install in $HOME/.cargo/bin

NOTE: a quick fix was to create a $HOME/.cargo symbolic link pointing to $CARGO_HOME`

Rustup and custom locations

Rustup tool can be installed using custom locations, using the RUSTUP_HOME and CARGO_HOME environment variables. If these are set in the shell resource config (.bashrc / .zshrc) then the rustup install will use their custom locations.

# ----------------------------------------
# Rust Lang Development tools - rustup
export RUSTUP_HOME="${RUSTUP_HOME:=$HOME/.config/rust/rustup}"
export CARGO_HOME="${CARGO_HOME:=$HOME/.config/rust/cargo}"
# ----------------------------------------

Using XDG_CONFIG_HOME

A popular standard for user configuration files under one directory, e.g. $HOME/.config which also simplifies version control for those configuration files.

The xfreedesktop.org Base Directory specification defines the XDG_CONFIG_HOME environment variable that sets the base directory for all user account configurations.

This location is typically $HOME/.config and contains a (non-hidden) directory name for each configuration, e.g. for Cargo: $HOME/.config/cargo

# ----------------------------------------
# Set XDG_CONFIG_HOME for clean management of configuration files
export XDG_CONFIG_HOME="${XDG_CONFIG_HOME:=$HOME/.config}"
export XDG_DATA_HOME="${XDG_DATA_HOME:=$HOME/.local/share}"
export XDG_STATE_HOME="${XDG_STATE_HOME:=$HOME/.local/state}"
export XDG_CACHE_HOME="${XDG_CACHE_HOME:=$HOME/.cache}"
export ZDOTDIR="${ZDOTDIR:=$XDG_CONFIG_HOME/zsh}"
# ----------------------------------------

Duplicate declaration

• I have searched the issues and this improvement has not been requested before.

[jonaro00]

Thanks for the detailed description!

Respecting CARGO_HOME sounds like a good idea.

Is it conventional to install binaries in the XDG_CONFIG_HOME ("config") directory?
Does rustup check or other tools like cargo-binstall respect this variable?

Would be good if we can follow the conventions of rustup/cargo/cargo-binstall as closely as possible :)

[practicalli-johnny]

Supporting CARGO_HOME would be to most valuable (and easiest) approach at present.

Changes to rustup and cargo would seem the best place to support the xfreedesktop.org as a first step.

There seems an amount of work for rustup and cargo in order to support the xfreedesktop.org. There have been discussions since 2015, so perhaps not priorities for those projects. I will review and see if there is something I can add to help.

• Consider moving to platform-specific configuration directories rust-lang/rustup#247
• Make Cargo obey platform-specific directory standards rust-lang/cargo#2127

Looking at the contents of my RUSTUP_HOME and CARGO_HOME directories there are files that would be placed in XDG cache, data and perhaps even runtime locations. So not a simple change and would need co-ordination across the rust community.

Thanks for considering these ideas.