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# Description
This PR makes the span of a pipeline accessible through `metadata`,
meaning it's possible to get the span of a pipeline without collecting
it.
Examples:
```nushell
ls | metadata
# => ╭────────┬────────────────────╮
# => │ │ ╭───────┬────────╮ │
# => │ span │ │ start │ 170218 │ │
# => │ │ │ end │ 170220 │ │
# => │ │ ╰───────┴────────╯ │
# => │ source │ ls │
# => ╰────────┴────────────────────╯
```
```nushell
ls | metadata access {|meta|
error make {msg: "error", label: {text: "here", span: $meta.span}}
}
# => Error: × error
# => ╭─[entry #7:1:1]
# => 1 │ ls | metadata access {|meta|
# => · ─┬
# => · ╰── here
# => 2 │ error make {msg: "error", label: {text: "here", span: $meta.span}}
# => ╰────
```
Here's an example that wouldn't be possible before, since you would have
to use `metadata $in` to get the span, collecting the (infinite) stream
```nushell
generate {|x=0| {out: 0, next: 0} } | metadata access {|meta|
# do whatever with stream
error make {msg: "error", label: {text: "here", span: $meta.span}}
}
# => Error: × error
# => ╭─[entry #16:1:1]
# => 1 │ generate {|x=0| {out: 0, next: 0} } | metadata access {|meta|
# => · ────┬───
# => · ╰── here
# => 2 │ # do whatever with stream
# => ╰────
```
I haven't done the tests or anything yet since I'm not sure how we feel
about having this as part of the normal metadata, rather than a new
command like `metadata span` or something. We could also have a
`metadata access` like functionality for that with an optional closure
argument potentially.
# User-Facing Changes
* The span of a pipeline is now available through `metadata` and
`metadata access` without collecting a stream.
# Tests + Formatting
TODO
# After Submitting
N/A
Nushell core libraries and plugins
These sub-crates form both the foundation for Nu and a set of plugins which extend Nu with additional functionality.
Foundational libraries are split into two kinds of crates:
- Core crates - those crates that work together to build the Nushell language engine
- Support crates - a set of crates that support the engine with additional features like JSON support, ANSI support, and more.
Plugins are likewise also split into two types:
- Core plugins - plugins that provide part of the default experience of Nu, including access to the system properties, processes, and web-connectivity features.
- Extra plugins - these plugins run a wide range of different capabilities like working with different file types, charting, viewing binary data, and more.