nushell/crates/nu-std/CONTRIBUTING.md

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, and can have preliminary discussions there to clarify the issues involved.

You can open a Github issue 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.

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.
2. 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.
   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 for details.
3. 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
4. When you get to an appropriate state of doneness, push your changes to the PR and remove the draft status.
5. 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!)
6. 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.
7. 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. 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 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.
   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>
   

2. 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 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.

To add a completely new module, for example, a foo command and some foo subcommands, 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.

     ... 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.

2. 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:

     ... 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.

3. 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.

4. 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.

More design guidelines:

1. Ensure your custom command provides useful help.
   This is done with comments before the def for the custom command.
2. Use error make to report can't-proceed errors to user, not log error.
3. Use log info to provide verbose progress messages that the user can optionally enable for troubleshooting. e.g:

   NU_LOG_LEVEL=INFO foo # verbose messages from command foo
   

4. Use assert in unit tests to check for and report failures.

Useful Commands

• Run all unit tests for the standard library:

  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

  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.)

  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):

  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 for details.