it is somehow a special variable in closure (since 0.92)

[wdv4758h]

Describe the bug

See more info in discussion link.

Discussed in #12440

^{Originally posted by wdv4758h April 7, 2024}
With 0.92, it seems that it is treated differently.

This print 42 in 0.91, but gets error in 0.92.

let tmp = {
  let it = 42
  print $it
}

do -c $tmp

errors in 0.92:

  × Missing parameter: $it.
   ╭─[example.nu:6:1]
 5 │ 
 6 │ do -c $tmp
   · ─┬
   ·  ╰── missing parameter: $it
   ╰────

This print 42 in both 0.91 and 0.92.

let tmp = {
  let x = 42
  print $x
}

do -c $tmp

How to reproduce

See above code.

Expected behavior

Works without error.

Screenshots

No response

Configuration

key	value
version	0.92.3
major	0
minor	92
patch	3
branch	nightly
commit_hash	24ecb84
build_os	linux-x86_64
build_target	x86_64-unknown-linux-gnu
rust_version	rustc 1.77.2 (25ef9e3d8 2024-04-09)
rust_channel	1.77.2-x86_64-unknown-linux-gnu
cargo_version	cargo 1.77.2 (e52e36006 2024-03-26)
build_time	2024-04-28 01:44:34 +00:00
build_rust_channel	release
allocator	mimalloc
features	dataframe, default, sqlite, static-link-openssl, system-clipboard, trash, which
installed_plugins	query

Additional context

No response

[dedebenui]

In do_.rs in the nu-cmd-lang crate, we get a reference to the do block with the following line (l. 78 I think):

let block = engine_state.get_block(block.block_id);

With a debug print, we see that somehow, the block has a positional argument in its signature when $it is declared and referenced inside. If I add a positional parameter like so

do {|x| print $x; let $it = 2; print $it} 5

it works as expected (it prints 5, then 2) and the block only has one positional argument x

This behavior seems to come parser.rs:4451 in nu-parser. If a signature already exists (like the |x| above), it takes it, but if not, it creates one if $it is in the block, not sure why. Could we get rid of the else block there?

[WindSoilder]

@dedebenui Excellent hack! I think nushell once allowed such syntax before(yeah version 0.44):

let x = { echo $it };

In this way we need to run do $x with additional argument. But it's not allowed anymore, so I think we can get rid of else block there.