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This fixes an issue brought up by nihilander in
[Discord](https://discord.com/channels/601130461678272522/614593951969574961/1201594105986285649).
# Description
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Nushell panics when the spread operator is used like this (the
`...$rest` shouldn't actually be parsed as a spread operator at all):
```nu
$ def foo [...rest: string] {...$rest}
$ foo bar baz
thread 'main' panicked at /root/.cargo/registry/src/index.crates.io-6f17d22bba15001f/nu-protocol-0.89.0/src/signature.rs:650:9:
Internal error: can't run a predeclaration without a body
stack backtrace:
0: rust_begin_unwind
1: core::panicking::panic_fmt
2: <nu_protocol::signature::Predeclaration as nu_protocol::engine::command::Command>::run
3: nu_engine::eval::eval_call
4: nu_engine::eval::eval_expression_with_input
5: nu_engine::eval::eval_element_with_input
6: nu_engine::eval::eval_block
7: nu_cli::util::eval_source
8: nu_cli::repl::evaluate_repl
9: nu::run::run_repl
10: nu::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.
```
The problem was that whenever the parser saw something like `{...$`,
`{...(`, or `{...[`, it would treat that as a record with a spread
expression, ignoring the syntax shape of the block it was parsing. This
should now be fixed, and the snippet above instead gives the following
error:
```nu
Error: nu:🐚:external_command
× External command failed
╭─[entry #1:1:1]
1 │ def foo [...rest] {...$rest}
· ────┬───
· ╰── executable was not found
╰────
help: No such file or directory (os error 2)
```
# User-Facing Changes
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Stuff like `do { ...$rest }` will now try to run a command `...$rest`
rather than complaining that variable `$rest` doesn't exist.
# Tests + Formatting
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crates/nu-std"` to run the tests for the standard library
> **Note**
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# After Submitting
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Sorry about the issue, I am not touching the parser again for a long
time :)
c08f46f836