Variables Declared In () Or [] context produce unhelpful error message

[lace-wing]

Describe the bug

As title says, mut variables declared in () or [] closures are not accessible even right in the same closure.

How to reproduce

# create a () or [] clousure
(
    # declare a mutable variable
    mut m = ""
    # try accessing the variable
    $m # Variable not found!
)

Expected behavior

Mutable variable should be accessible just as they are in non-()[] environments:

mut m = ""
$m = "Yes!"

Screenshots

Configuration

key	value
version	0.93.0
major	0
minor	93
patch	0
branch
commit_hash
build_os	macos-aarch64
build_target	aarch64-apple-darwin
rust_version	rustc 1.77.2 (25ef9e3d8 2024-04-09) (Homebrew)
cargo_version	cargo 1.77.2
build_time	2024-04-30 22:51:13 +00:00
build_rust_channel	release
allocator	mimalloc
features	dataframe, default, sqlite, system-clipboard, trash, which
installed_plugins	gstat

Additional context

No response

[sholderbach]

To clarify () declares a subexpression and you can use a variable declared inside if the statements are sepearated with ;:

(
  let x = 10;
  $x
)  
# returns: 10

Worth diving in if we can infer that the ; is not needed here after a line break.

[] is declaring a list.
Each of the entries of the list is its own expression (with restrictions on what is allowed without parens, as our lists permit whitespace as a separator). So to me it would be surprising or a deliberate design choice if the scope of a previous expression would be valid for the next entry.

No closures involved. That term is reserved for anonymous functions that are permitted to capture values from the outside scope as their own (close over them). In Nushell their syntax is { code }/{ || code}/{ | args | code }

[sholderbach]

I think the takeaway for this issue is that we should make the parsing rules of let/mut binding/assignment stricter so they produce a helpful error:

• when placed inside a list: here the assignment expression doesn't return a useful value to be added to the list
• When extra tokens are supplied after the complete right hand side expression of the assignment (let x = 10 extra) so we could provide a "did you forget a ;" in subexpression.