nushell/crates/nu-command
132ikl d69e131450
Rely on display_output hook for formatting values from evaluations (#14361)
# Description

I was reading through the documentation yesterday, when I stumbled upon
[this
section](https://www.nushell.sh/book/pipelines.html#behind-the-scenes)
explaining how command output is formatted using the `table` command. I
was surprised that this section didn't mention the `display_output`
hook, so I took a look in the code and was shocked to discovered that
the documentation was correct, and the `table` command _is_
automatically applied to printed pipelines.

This auto-tabling has two ramifications for the `display_output` hook:

1. The `table` command is called on the output of a pipeline after the
`display_output` has run, even if `display_output` contains the table
command. This means each pipeline output is roughly equivalent to the
following (using `ls` as an example):
    ```nushell
    ls | do $config.hooks.display_output | table
    ```
2. If `display_output` returns structured data, it will _still_ be
formatted through the table command.

This PR removes the auto-table when the `display_output` hook is set.
The auto-table made sense before `display_output` was introduced, but to
me, it now seems like unnecessary "automagic" which can be accomplished
using existing Nushell features.

This means that you can now pull back the curtain a bit, and replace
your `display_output` hook with an empty closure
(`$env.config.hooks.display_output = {||}`, setting it to null retains
the previous behavior) to see the values printed normally without the
table formatting. I think this is a good thing, and makes it easier to
understand Nushell fundamentals.

It is important to note that this PR does not change how `print` and
other commands (well, specifically only `watch`) print out values. They
continue to use `table` with no arguments, so changing your
config/`display_output` hook won't affect what `print`ing a value does.

Rel: [Discord
discussion](https://discord.com/channels/601130461678272522/615329862395101194/1307102690848931904)
(cc @dcarosone)

# User-Facing Changes

Pipelines are no longer automatically formatted using the `table`
command. Instead, the `display_output` hook is used to format pipeline
output. Most users should see no impact, as the default `display_output`
hook already uses the `table` command.

# Tests + Formatting

- 🟢 `toolkit fmt`
- 🟢 `toolkit clippy`
- 🟢 `toolkit test`
- 🟢 `toolkit test stdlib`

# After Submitting


Will update mentioned docs page to call out `display_output` hook.
2024-11-19 21:04:29 +08:00
..
src Rely on display_output hook for formatting values from evaluations (#14361) 2024-11-19 21:04:29 +08:00
tests update uutils crates (#14371) 2024-11-17 19:31:36 -06:00
Cargo.toml Add utouch command from uutils/coreutils (#11817) 2024-11-17 18:03:21 -06:00
LICENSE Fix rest of license year ranges (#8727) 2023-04-04 09:03:29 +12:00
README.md Add top-level crate documentation/READMEs (#12907) 2024-07-14 10:10:41 +02:00

This crate contains the majority of our commands

We allow ourselves to move some of the commands in nu-command to nu-cmd-* crates as needed.

Internal Nushell crate

This crate implements components of Nushell and is not designed to support plugin authors or other users directly.