nushell/devdocs/FAQ.md

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# Frequently asked question for developers
Let's collect some questions a lot of Nushell contributors have.
- How do I do....?
- Why do I need to do certain things a certain way?
Let's keep the answers concise and up to date (or general enough) to remain relevant
## How do I properly test my feature or bugfix?
TODO (Probably fork out into its own file)
## I want to report an error to the user
Approximate flow:
1. Are you reporting the error in the parser/static checking phase?
- Use `nu_protocol::ParseError` variants
- Follow the logic used in the context as we need to collect multiple errors for a good IDE experience
2. Pick the right `nu_protocol::ShellError` variant
- Does a matching existing variant fit your need? (go to references of the `ShellError` variant for inspiration)
- Check what context the [`miette`](https://docs.rs/miette) macros add during formatting! (go to definition of `ShellError`)
- If it is a one-of specific error, consider using a generic variant
- Else add a new class of errors
- add the necessary `Span` information
- general shared error text, to inform and point to a resolution
- dynamic information gathered from the error site
- Don't use a tuple enum variant, named structs going forward only!
3. Are you in a command?
- `return Err(ShellError::...)` and you're done in a `Command::run`
4. Do you want to report a warning but not stop execution?
- **NEVER** `println!`, we can write to stderr if necessary but...
- good practice: `nu_protocol::cli_error::report_error` or `report_error_new`
- depending on whether you have access to a `StateWorkingSet`
- if only relevant to in the field debugging: `log`-crate macros.
## How do I check an environment variable?
TODO
## WTF is `PipelineMetadata`?
TODO