make else if generate helpful error when condition have an issue

[WindSoilder]

Description

Fixes: #7575

User-Facing Changes

Previously:

if❯ if false { "aaa" } else if $a { 'a' }
Error: nu::parser::parse_mismatch

  × Parse mismatch during operation.
   ╭─[entry #10:1:1]
 1 │ if false { "aaa" } else if $a { 'a' }
   ·                         ─┬
   ·                          ╰── expected block, closure or record
   ╰────

After:

❯ if false { "aaa" } else if $a { 'a' }
Error: nu::parser::variable_not_found

  × Variable not found.
   ╭─[entry #1:1:1]
 1 │ if false { "aaa" } else if $a { 'a' }
   ·                            ─┬
   ·                             ╰── variable not found
   ╰────

Tests + Formatting

Don't forget to add tests that cover your changes.

Make sure you've run and fixed any issues with these commands:

• cargo fmt --all -- --check to check standard code formatting (cargo fmt --all applies these changes)
• cargo clippy --workspace -- -D warnings -D clippy::unwrap_used -A clippy::needless_collect to check that you're using the standard code style
• cargo test --workspace to check that all tests pass

After Submitting

If your PR had any user-facing changes, update the documentation after the PR is merged, if necessary. This will help us keep the docs up to date.

[WindSoilder]

It breaks the following mut usage:

stderr: Error: nu::parser::expected_keyword

  × Capture of mutable variable.
   ╭─[/tmp/.tmpaaj31c:1:1]
 1 │ mut x = 100; if 2 > 3 { $x = 200 } else { $x = 300 }; $x 
   ·                                           ─┬
   ·                                            ╰── capture of mutable variable
   ╰────

Because { $x = 300 } is parsed as a closure, and it doesn't allowed to capture mutable variable, a solution would be restrict closure syntax to not mess up with block syntax

[fdncred]

Because { $x = 300 } is parsed as a closure, and it doesn't allowed to capture mutable variable, a solution would be restrict closure syntax to not mess up with block syntax

ahhhh, that makes sense now. I've been having problems with else if for weeks now. We definitely need to fix that.

[sholderbach]

How can we resolve the remaining issues here? Do we need the block/closure separation to land?

[WindSoilder]

Yeah, #8290 needs to be mreged first(block by pr on virtualenv..), or else I have to try another solution, I'd prefer to merge #8290 first(when it's ok)

[WindSoilder]

I've re-implement it and the implementation doesn't rely on #8273

[codecov]

Codecov Report

Merging #8274 (b882f47) into main (03e688e) will increase coverage by 0.01%.
The diff coverage is 70.58%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #8274      +/-   ##
==========================================
+ Coverage   68.49%   68.51%   +0.01%     
==========================================
  Files         620      620              
  Lines       99472    99488      +16     
==========================================
+ Hits        68133    68160      +27     
+ Misses      31339    31328      -11     

Impacted Files	Coverage Δ
crates/nu-parser/src/parser.rs	82.52% <70.58%> (+0.03%)	⬆️
crates/nu-cli/src/util.rs	67.47% <0.00%> (-1.04%)	⬇️
crates/nu-protocol/src/ty.rs	87.14% <0.00%> (+0.71%)	⬆️
src/config_files.rs	25.88% <0.00%> (+1.17%)	⬆️
crates/nu-parser/src/lex.rs	91.39% <0.00%> (+3.56%)	⬆️

[fdncred]

Are we ready to break things with this? LOL

[WindSoilder]

Yeah, I think we can land it