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* 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
Nushell core libraries and plugins
These sub-crates form both the foundation for Nu and a set of plugins which extend Nu with additional functionality.
Foundational libraries are split into two kinds of crates:
- Core crates - those crates that work together to build the Nushell language engine
- Support crates - a set of crates that support the engine with additional features like JSON support, ANSI support, and more.
Plugins are likewise also split into two types:
- Core plugins - plugins that provide part of the default experience of Nu, including access to the system properties, processes, and web-connectivity features.
- Extra plugins - these plugins run a wide range of differnt capabilities like working with different file types, charting, viewing binary data, and more.