# Description
This PR adds a directory to the `$nu` constant that shows where the
system level autoload directory is located at. This folder is modifiable
at compile time with environment variables.
```rust
// Create a system level directory for nushell scripts, modules, completions, etc
// that can be changed by setting the NU_VENDOR_AUTOLOAD_DIR env var on any platform
// before nushell is compiled OR if NU_VENDOR_AUTOLOAD_DIR is not set for non-windows
// systems, the PREFIX env var can be set before compile and used as PREFIX/nushell/vendor/autoload
// pseudo code
// if env var NU_VENDOR_AUTOLOAD_DIR is set, in any platform, use it
// if not, if windows, use ALLUSERPROFILE\nushell\vendor\autoload
// if not, if non-windows, if env var PREFIX is set, use PREFIX/share/nushell/vendor/autoload
// if not, use the default /usr/share/nushell/vendor/autoload
```
### Windows default
```nushell
❯ $nu.vendor-autoload-dir
C:\ProgramData\nushell\vendor\autoload
```
### Non-Windows default
```nushell
❯ $nu.vendor-autoload-dir
/usr/local/share/nushell/vendor/autoload
```
### Non-Windows with PREFIX set
```nushell
❯ PREFIX=/usr/bob cargo r
❯ $nu.vendor-autoload-dir
/usr/bob/share/nushell/vendor/autoload
```
### Non-Windows with NU_VENDOR_AUTOLOAD_DIR set
```nushell
❯ NU_VENDOR_AUTOLOAD_DIR=/some/other/path/nushell/stuff cargo r
❯ $nu.vendor-autoload-dir
/some/other/path/nushell/stuff
```
> [!IMPORTANT]
To be clear, this PR does not do the auto-loading, it just sets up the
folder to support that functionality that can be added in a later PR.
The PR also does not create the folder defined. It's just setting the
$nu constant.
# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
# Tests + Formatting
<!--
Don't forget to add tests that cover your changes.
Make sure you've run and fixed any issues with these commands:
- `cargo fmt --all -- --check` to check standard code formatting (`cargo
fmt --all` applies these changes)
- `cargo clippy --workspace -- -D warnings -D clippy::unwrap_used` to
check that you're using the standard code style
- `cargo test --workspace` to check that all tests pass (on Windows make
sure to [enable developer
mode](https://learn.microsoft.com/en-us/windows/apps/get-started/developer-mode-features-and-debugging))
- `cargo run -- -c "use toolkit.nu; toolkit test stdlib"` to run the
tests for the standard library
> **Note**
> from `nushell` you can also use the `toolkit` as follows
> ```bash
> use toolkit.nu # or use an `env_change` hook to activate it
automatically
> toolkit check pr
> ```
-->
# After Submitting
<!-- If your PR had any user-facing changes, update [the
documentation](https://github.com/nushell/nushell.github.io) after the
PR is merged, if necessary. This will help us keep the docs up to date.
-->
c09a8a5ec9