Here's what happens when you run 'show' with a toolchain that is not installed:
brian@DESKTOP-CODN6ST MINGW64 /c/Users/brian/Documents/dev/rustup.rs
$ rustup override set beta
info: using existing install for 'beta-x86_64-pc-windows-msvc'
info: override toolchain for 'C:\Users\brian\Documents\dev\rustup.rs' set to 'beta-x86_64-pc-windows-msvc'
beta-x86_64-pc-windows-msvc unchanged - rustc 1.19.0-beta.1 (a87984118 2017-06-06)
brian@DESKTOP-CODN6ST MINGW64 /c/Users/brian/Documents/dev/rustup.rs
$ rustup toolchain remove beta
info: uninstalling toolchain 'beta-x86_64-pc-windows-msvc'
info: toolchain 'beta-x86_64-pc-windows-msvc' uninstalled
brian@DESKTOP-CODN6ST MINGW64 /c/Users/brian/Documents/dev/rustup.rs
$ rustup show
Default host: x86_64-pc-windows-msvc
error: override toolchain 'beta-x86_64-pc-windows-msvc' is not installed
Instead of displaying various information about installed toolchains it immediately errors.
It should instead do something like:
brian@DESKTOP-CODN6ST MINGW64 /c/Users/brian/Documents/dev/rustup.rs
$ rustup override remove
info: override toolchain for 'C:\Users\brian\Documents\dev\rustup.rs' removed
brian@DESKTOP-CODN6ST MINGW64 /c/Users/brian/Documents/dev/rustup.rs
$ rustup show
Default host: x86_64-pc-windows-msvc
installed toolchains
--------------------
stable-x86_64-pc-windows-msvc
nightly-x86_64-pc-windows-msvc (default)
active toolchain
----------------
beta-x86_64-pc-windows-msvc (override set by blah blah blah)
(error: override toolchain 'beta-x86_64-pc-windows-msvc' is not installed)
Fix will be in rustup_cli::rustup_mode::show. Instead of returning the error, print it into the show output.