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Replace #8824: CONTRIBUTING.md for standard library (#8894)

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# Description
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Replaces #8824, which was languishing in review limbo and becoming
increasingly difficult to keep current with upstream changes.

In addition to all the edits, this PR includes updated documentation for
running unit tests via `std run-tests`.

# User-Facing Changes
<!-- List of all changes that impact the user experience here. This
helps us keep track of breaking changes. -->
A CONTRIBUTING.md documenting guidelines and getting started info for
potential stdlib contributors.
# 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 -A
clippy::needless_collect` to check that you're using the standard code
style
- `cargo test --workspace` to check that all tests pass
- `cargo run -- crates/nu-std/tests/run.nu` 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
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# Contributing
Welcome to the Nushell standard library and thank you for considering contributing!
## Ideas for the standard library
If you've got a great idea, or just want to contribute to open source
by working on the Nushell standard library,
we invite you to talk to the team before you start coding.
You'll find we're friendly, passionate about Nushell and always open to new ideas!
You'll generally find the team members on
[Discord standard-library channel](https://discord.com/channels/601130461678272522/1075541668922658868),
and can have preliminary discussions there to clarify the issues involved.
You can open a [Github issue](https://github.com/nushell/nushell/issues/new/choose)
to have a more focused discussion of your idea.
Generally, we think the standard library should contain items that are
relevant to most/all Nushell users regardless of the application space they're working in.
If your idea isn't quite so broadly applicable,
consider publishing it in [nu_scripts](https://github.com/nushell/nu_scripts).
Preliminary discussions should focus on the *user benefit* your idea would provide.
How many users will be affected by your idea, how much would it help them solve a problem or work more productively?
Given consensus on the user benefit, the team will be motivated to
help you create, deploy and maintain a solution long term.
## Lifecycle of a change
1. Verify the team thinks your idea is potentially relevant and useful, as above.
1. If it's more than a simple bug fix, open a placeholder PR
as soon as you get started and [set it to draft status][github_draft_pr].
This will alert other contributors that you're working in this area and let you
advertise roughly what scope of changes you're thinking of.
See [below](#the_pr) for details.
1. Get things working in your local development environment.
If you have questions along the way, you can post a question in your PR
or have a more casual discussion with Nushell fans on
[Discord implementation-chat channel](https://discord.com/channels/601130461678272522/615962413203718156)
1. When you get to an appropriate state of doneness, push your changes to the PR and remove the draft status.
2. Team members and other contributors will then review your PR.
Respond to any review comments they raise and address them one way or another.
(Not all comments demand you make a change!)
1. When you and the team are comfortable with the PR,
a team member will merge it into the repo and you can delete your working branch.
2. If you've added a whole new command or made a breaking change,
(strongly) consider writing it up for the release notes.
Currently, release notes are maintained in a different repo, [nushell.github.io](https://github.com/nushell/nushell.github.io).
Make your change in a local clone of that repo and submit a PR to the release notes repo to get it integrated.
## Developing
(All paths below shown relative to the root folder of the git repository containing the standard library.)
### Setup
0. Install the Rust toolchain and Nushell build tools. See [nushell CONTRIBUTING](https://github.com/nushell/nushell/blob/main/CONTRIBUTING.md) for details.
The standard library is tightly coupled to a particular version of Nushell interpreter,
you need to be running that version to test your changes
(unlike a "normal" script module library).
1. Clone the Nushell repo containing the standard library and create a feature branch for your development work.
Currently, that's the [Nushell interpreter source repo](https://github.com/nushell/nushell).
Once you set your working directory to the root of this repository, you'll generally leave it there throughout the session.
```
git clone https://github.com/nushell/nushell
cd nushell
git checkout -b <featureBranch>
```
1. In your IDE, open the folder within the repository containing the standard library.
The folder is currently `./crates/nu-std`, and it is a Rust crate, containing a `Cargo.toml`
and subfolders:
* `src/` (which contains the Rust code to load the standard library modules into memory for efficiency),
* `lib` (which contains all the script module sources for the standard library),
* `tests/` (unit tests for lib).
### The PR
Assuming you've already validated the need with other Nushell contributors, you're focusing on design and implementation
at this point. Share your thinking all along the way!
You can open a [draft][github_draft_pr] pull request based on a small, placeholder code change
and use the PR comments to outline your design and user interface. You'll get feedback from
other contributors that may lead to a more robust and perhaps more idomatic solution.
The threads in the PR can be a convenient reference for you when writing release notes and
for others on the team when researching issues.
Note that the PR will not get final code review or be merged until you remove the draft status.
### Design considerations
The standard library consists of Nushell custom commands and their associated environment variables, packaged in script modules underneath module `std`. For background on scripts, custom commands and modules, see
[Modules chapter of the Nushell book](https://www.nushell.sh/book/modules.html).
To add a completely new module, for example, a `foo` command and some `foo subcommand`s,
you will be dealing with 2 new source files: the module source itself (`./crates/nu-std/lib/foo.nu`) and a unit tests file (`./crates/nu-std/tests/test_foo`); and will be modifying 1 or 2 existing files (`./crates/nu-std/lib/mod.nu` and possibly `./crates/nu-std/src/lib.rs`). This is described below:
1. Source for a custom command `foo` should go in `./crates/nu-std/lib/foo.nu`.
* A source file will typically implement multiple subcommands and possibly a main command as well.
Use `export def` to make these names public to your users.
* If your command is updating environment variables, you must use `export def-env` (instead of `export def`)
to define the subcommand, `export-env {}` to initialize the environment variables and `let-env` to update them.
For an example of a custom command which modifies environment variables,
see: `./crates/nu-std/lib/dirs.nu`.
For an example of a custom command which does *not* modify environment variables, see: `./crates/nu-std/lib/assert.nu`.
* If your standard library module wishes to use a utility from another module of the standard library,
for example `log info`,
you need to import it directly from its module in the `use` statement.
```shell
... your foo.nu ...
export def mycommand [] {
use log "log info"
. . .
log info "info level log message"
. . .
}
```
This is `use log "log info"` rather than `use std "log info"` (which is the usual way commands are imported
from the standard library) because your `foo` module is also a child module under `std`.
1. Unit tests for `foo` should go in `./crates/nu-std/tests/test_foo.nu`. Thou shalt provide unit tests to cover your changes.
* Unit tests should use one of the `assert` commands to check a condition and report the failure in a standard format.
* To import `assert` commands for use in your test, import them via `use std` (unlike the `use log` for your source code; the tests are not modules under `std`). For example:
```shell
... your test_foo.nu ...
def test1 [] {
use std
. . .
std assert greater $l $r
. . .
std assert $predicate
}
def test2 [] {
use std ['assert greater' assert]
. . .
assert greater $l $r
. . .
assert $predicate
}
```
The choice of import style is up to you.
2. A `foo` command will be exposed to the user as `std foo` (at a minimum).
To enable this, update file `./crates/nu-std/lib/mod.nu` and add this code:
```
export use foo * # command doesn't update environment
export-env {
use bar * # command *does* update environment
}
```
The `use *` hoists the public definitions in `foo.nu` into `mod.nu` and thus into the `std` namespace.
1. Some commands from the standard library are also preloaded, so user can invoke them without explicit
import via `use std ...`.
A command implemented as `std foo`, can be preloaded as a bare `foo`:
* modify `./crates/nu-std/src/lib.rs`,
* find the initialization of the "prelude" at line 90 or thereabouts
* add `("foo", "foo")`
* or, to be preloaded as `std foo`, add `("std foo", "foo")`.
(This code may be restructured soon: if you can't find it, check with the team on Discord.)
Note that you will need to recompile the Nushell interpreter to test this change,
see [Nushell CONTRIBUTING#Setup](https://github.com/nushell/nushell/blob/main/CONTRIBUTING.md#setup).
More design guidelines:
1. Ensure your custom command provides useful help.
This is done with comments before the `def` for the custom command.
1. Use `error make` to report can't-proceed errors to user, not `log error`.
2. Use `log info` to provide verbose progress messages that the user can optionally enable for troubleshooting.
e.g:
```shell
NU_LOG_LEVEL=INFO foo # verbose messages from command foo
```
1. Use `assert` in unit tests to check for and report failures.
### Useful Commands
- Run all unit tests for the standard library:
```shell
cargo run -- -c 'use std; NU_LOG_LEVEL=ERROR std run-tests'
```
Note that this uses the debug version of NU interpreter from the same repo, which is the usual development scenario.
Log level 'ERROR' shows only failures (meaning no output is the desired outcome).
Log level 'INFO' shows progress by module and 'DEBUG' show each individual test.
- Run all tests for a specific test module, e.g, `crates/nu-std/tests/test_foo.nu`
```shell
cargo run -- -c 'use std; NU_LOG_LEVEL=INFO std run-tests --module test_foo'
```
- Run a custom command with additional logging (assuming you have instrumented
the command with `log <level>`, as we recommend.)
```shell
NU_LOG_LEVEL=INFO std foo bar bas # verbose
NU_LOG_LEVEL=DEBUG std foo bar bas # very verbose
```
- Build and run Nushell (e.g, if you modify the prelude):
```shell
cargo run
```
## Git commit and repo conventions
The standard library project uses the same protocols and conventions
for squashing git commits and handling github PRs as the core Nushell project.
Please see [nushell CONTRIBUTING#git_etiquette](https://github.com/nushell/nushell/blob/main/CONTRIBUTING.md#git-etiquette) for details.
[github_draft_pr]:(https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/proposing-changes-to-your-work-with-pull-requests/changing-the-stage-of-a-pull-request)

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<img src="https://media.giphy.com/media/hvRJCLFzcasrR4ia7z/giphy.gif" width="28"></img> <img src="https://media.giphy.com/media/hvRJCLFzcasrR4ia7z/giphy.gif" width="28"></img>
</h1> </h1>
The standard library is a pure-`nushell` collection of commands to allow anyone to build The standard library is a pure-`nushell` collection of custom commands which
complex applications using standardized tools gathered incrementally. provide interactive utilities and building blocks for users writing casual scripts or complex applications.
In this library, you might find `rust`-like `assert` commands to write tests, tools to To see what's here:
manipulate paths and strings, etc, etc, ...
## :toolbox: use the standard library in the REPL or in scripts
in order to "import" the standard library to either the interactive [*REPL*][REPL] of
`nushell` or inside some `.nu` script, you might want to use the
[`use`](https://nushell.sh/commands/docs/use.html) command!
```bash
use std
``` ```
〉use std
〉help commands | select name usage | where name =~ "std "
╭────┬─────────────────────────────┬────────────────────────────────────────────────────────────────╮
│ # │ name │ usage │
│ 0 │ std assert │ Universal assert command │
│ 1 │ std assert equal │ Assert $left == $right │
. . .
│ 11 │ std clip │ put the end of a pipe into the system clipboard. │
│ 12 │ std dirs add │ Add one or more directories to the list. │
. . .
├────┼─────────────────────────────┼────────────────────────────────────────────────────────────────┤
│ # │ name │ usage │
╰────┴─────────────────────────────┴────────────────────────────────────────────────────────────────╯
```
## :toolbox: Using the standard library in the REPL or in scripts
All commands in the standard library must be "imported" into the running environment
(the interactive read-execute-print-loop (REPL) or a `.nu` script) using the
[`use`](https://nushell.sh/commands/docs/use.html) command.
You can choose to import the whole module, but then must refer to individual commands with a `std` prefix, e.g:
```
use std
. . .
std log debug "Running now"
std assert (1 == 2)
```
Or you can enumerate the specific commands you want to import and invoke them without the `std` prefix.
```
use std ["log debug" assert]
. . .
log debug "Running again"
assert (2 == 1)
```
This is probably the form of import you'll want to add to your `env.nu` for interactive use.
## :pencil2: contribute to the standard library ## :pencil2: contribute to the standard library
- all the commands of the standard_library are located in [`std.nu`](std.nu) You're invited to contribute to the standard library!
- the tests are located in files that have a name starting with "test_", e.g. [`test_std.nu`](test_std.nu) See [CONTRIBUTING.md]([./CONTRIBUTING.md](https://github.com/nushell/nushell/blob/main/crates/nu-std/CONTRIBUTING.md))
- a test runner, at [`tests.nu`](tests.nu), allows to run all the tests automatically for details
### :wrench: add new commands
- add new standard commands by appending to [`std.nu`](std.nu)
- add associated tests to [`test_std.nu`](tests_std.nu) or preferably to `test_<submodule>.nu`.
- define a new exported (!) `test_<feature>` command
- import the `assert` functions you need at the top of the functions, e.g. `use std.nu "assert eq"`
### :test_tube: run the tests
the following call should return no errors
```bash
NU_LOG_LEVEL=DEBUG cargo run -- -c "use std; std run-tests --path crates/nu-std"
```
> **Warning**
> the `cargo run --` part of this command is important to ensure the version of `nushell` and the version of the library are the same.

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@ -79,6 +79,13 @@ pub fn load_standard_library(
("xml", include_str!("../lib/xml.nu")), ("xml", include_str!("../lib/xml.nu")),
]; ];
// Define commands to be preloaded into the default (top level, unprefixed) namespace.
// User can invoke these without having to `use std` beforehand.
// Entries are: (name to add to default namespace, path under std to find implementation)
//
// Conventionally, for a command implemented as `std foo`, the name added
// is either `std foo` or bare `foo`, not some arbitrary rename.
let prelude = vec![ let prelude = vec![
("std help", "help"), ("std help", "help"),
("std help commands", "help commands"), ("std help commands", "help commands"),