Error: Unable to create cache directory

[James-Mart]

Description

I build my repository in CI/CD by checking out the repository, and then mounting it into a docker container in which I execute the build using CMake/Make.
The image for the container used to have cargo-component v0.15.0, and everything worked fine.
I am in the process of trying to upgrade my build image to use cargo-component v0.21.1, and I suddenly started getting the following error:

[ 50%] Performing build step for 'MyComponent'
cd /home/.../src/MyComponent-build && cargo component build -r --target wasm32-unknown-unknown --manifest-path /home/.../my-component/Cargo.toml --target-dir /home/.../build/MyComponent
Error: Unable to create cache directory

Caused by:
    Permission denied (os error 13) 

Root cause

Presumably this is because I am running the build as a non-root user within the docker container and code was added that attempts to create a cache directory in a permissioned space.

Workaround

For anyone else experiencing this issue, I've found the following workaround:
Manually set a value for the CARGO_COMPONENT_CACHE_DIR environment variable. e.g. export CARGO_COMPONENT_CACHE_DIR=.cargo-component-cache