Configuration
Rustup has a TOML settings file at
${RUSTUP_HOME}/settings.toml (which defaults to ~/.rustup or
%USERPROFILE%/.rustup). The schema for this file is not part of the public
interface for rustup - the rustup CLI should be used to query and set settings.
On Unix operating systems a fallback settings file is consulted for some
settings. This fallback file is located at /etc/rustup/settings.toml and
currently can define only default_toolchain.