updates let-env signature to remove required params

[fdncred]

Description

This PR changes the signature of the deprecated command let-env so that it does not mislead people when invoking it without parameters.

Before

> let-env
Error: nu::parser::missing_positional

  × Missing required positional argument.
   ╭─[entry #2:1:1]
 1 │ let-env
   ╰────
  help: Usage: let-env <var_name> = <initial_value>

After

❯ let-env
Error: nu::shell::deprecated_command

  × Deprecated command let-env
   ╭─[entry #1:1:1]
 1 │ let-env
   · ───┬───
   ·    ╰── 'let-env' is deprecated. Please use '$env.<environment variable> = ...' instead.
   ╰────

User-Facing Changes

Tests + Formatting

After Submitting

[amtoine]

but now we get

> let-env FOO = "foo"
Error: nu::parser::extra_positional

  × Extra positional argument.
   ╭─[entry #1:1:1]
 1 │ let-env FOO = "foo"
   ·         ─┬─
   ·          ╰── extra positional argument
   ╰────
  help: Usage: let-env

instead of

> let-env FOO = "foo"
Error: nu::shell::deprecated_command

  × Deprecated command let-env
   ╭─[entry #18:1:1]
 1 │ let-env FOO = "foo"
   · ───┬───
   ·    ╰── 'let-env' is deprecated. Please use '$env.<environment variable> = ...' instead.
   ╰────

🤔

[fdncred]

Apparently, we have to "pick our poison". At least it's not telling you to use an old syntax and when you're typing let-env FOO = blah everything after let-env is red, at least in my theme, indicating it's invalid. I think I'd land this PR because it's better than the previous error.

[sophiajt]

As mentioned in discord, I believe this will work if you make the params optional rather than required (or removed).

[fdncred]

updated to optional, seems to be working as expected now.