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Stefan Holderbach 1be4eaeae3
Revert #8395 "Treat empty pipelines as pass-through" (#9472) 
In my view we should revert nushell/nushell#8395 for now

## Potentially inconsistent application of semantic change
#8395 (1d5e7b441b) was loosening the type
coercion rules significantly, to let missing data / void returns that
were either expressed by `PipelineData::Empty` or the `Value::nothing`
be accept by specifically those commands/operations that made use of
`PipelineData::into_iter_strict()`. This could apply the new rules
inconsistently.

## Turning explicit failures into silent continuations
Furthermore the effect of this breaking change to the missing data
semantics could make previous errors into silent failures.
This could either just reduce the effectiveness of teaching error
messages in interactive use:

### Contrived example before
```bash
> cd . | where blah
Error: nu:🐚:only_supports_this_input_type

  × Input type not supported.
   ╭─[entry #13:1:1]
 1 │ cd . | where blah
   ·        ──┬──┬
   ·          │  ╰── input type: null
   ·          ╰── only list, binary, raw data or range input data is supported
   ╰────
```
### ...after, with #8395
```bash
> cd . | where blah
╭────────────╮
│ empty list │
╰────────────╯
```

In rare cases people could already try to rely on catching an error of a
downstream command to actually deal with the missing data, so it would
be a breaking change for their existing code.

## Problem with `PipelineData::into_iter_strict()`

Maybe this makes `_strict` a bit of a misnomer for this particular
iterator construction.
Further we did not actively test the `PipelineData::empty` branch before

![grafik](https://github.com/nushell/nushell/assets/15833959/c377bf1d-d47c-4c25-a342-9a348539f242)

## Parsimonious solution exists

For the motivating issue https://github.com/nushell/nushell/issues/8393
there already exists a fix that makes `ls` more consistent with the type
system by returning an empty `Value::List`
https://github.com/nushell/nushell/pull/8439
2023-06-20 20:27:18 +12:00
..
src Revert #8395 "Treat empty pipelines as pass-through" (#9472) 2023-06-20 20:27:18 +12:00
tests Type mismatch span fix #7288 (#8271) 2023-02-28 21:12:53 -08:00
Cargo.toml revert: move to ahash (#9464) 2023-06-18 15:27:57 +12:00
LICENSE Fix rest of license year ranges (#8727) 2023-04-04 09:03:29 +12:00
README.md Add nu-protocol 2021-09-02 13:29:43 +12:00

README.md

nu-protocol

The nu-protocol crate holds the definitions of structs/traits that are used throughout Nushell. This gives us one way to expose them to many other crates, as well as make these definitions available to each other, without causing mutually recursive dependencies.