* Allow environment variables to be hidden
This change allows environment variables in Nushell to have a value of
`Nothing`, which can be set by the user by passing `$nothing` to
`let-env` and friends.
Environment variables with a value of Nothing behave as if they are not
set at all. This allows a user to shadow the value of an environment
variable in a parent scope, effectively removing it from their current
scope. This was not possible before, because a scope can not affect its
parent scopes.
This is a workaround for issues like #3920.
Additionally, this allows a user to simultaneously set, change and
remove multiple environment variables via `load-env`. Any environment
variables set to $nothing will be hidden and thus act as if they are
removed. This simplifies working with virtual environments, which rely
on setting multiple environment variables, including PATH, to specific
values, and remove/change them on deactivation.
One surprising behavior is that an environment variable set to $nothing
will act as if it is not set when querying it (via $nu.env.X), but it is
still possible to remove it entirely via `unlet-env`. If the same
environment variable is present in the parent scope, the value in the
parent scope will be visible to the user. This might be surprising
behavior to users who are not familiar with the implementation details.
An additional corner case is the the shorthand form of `with-env` does
not work with this feature. Using `X=$nothing` will set $nu.env.X to the
string "$nothing". The long-form works as expected: `with-env [X
$nothing] {...}`.
* Remove unused import
* Allow all primitives to be convert to strings
* move commands, futures.rs, script.rs, utils
* move over maybe_print_errors
* add nu_command crate references to nu_cli
* in commands.rs open up to pub mod from pub(crate)
* nu-cli, nu-command, and nu tests are now passing
* cargo fmt
* clean up nu-cli/src/prelude.rs
* code cleanup
* for some reason lex.rs was not formatted, may be causing my error
* remove mod completion from lib.rs which was not being used along with quickcheck macros
* add in allow unused imports
* comment out one failing external test; comment out one failing internal test
* revert commenting out failing tests; something else might be going on; someone with a windows machine should check and see what is going on with these failing windows tests
* Update Cargo.toml
Extend the optional features to nu-command
Co-authored-by: Jonathan Turner <jonathandturner@users.noreply.github.com>
