Allow string to copmpare with another string

[yukitomoda]

Description

Nushell parser now reject comparison operator with 2 strings (e.g. "abc" < "cba"). This pr fixes it.

before

~
❯ "abc" < "bca"
Error: nu::parser::unsupported_operation

  × less-than comparison is not supported on values of type string
   ╭─[entry #43:1:1]
 1 │ "abc" < "bca"
   · ──┬── ┬
   ·   │   ╰── doesn't support this value
   ·   ╰── string
   ╰────


~
❯ def foo []: nothing -> string { "abc" }

~
❯ (foo) < "bca"
Error: nu::parser::unsupported_operation

  × less-than comparison is not supported on values of type string
   ╭─[entry #53:1:1]
 1 │ (foo) < "bca"
   · ──┬── ┬
   ·   │   ╰── doesn't support this value
   ·   ╰── string
   ╰────

after

~
❯ "abc" < "bca"
true

~
❯ def foo []: nothing -> string { "abc" }

~
❯ (foo) < "bca"
true

User-Facing Changes

Following pattern will be allowed.

operator	type of lhs	type of rhs	result
<	string	string	bool
<=	string	string	bool
>	string	string	bool
>=	string	string	bool

Tests + Formatting

• cargo fmt --all -- --check to check standard code formatting (cargo fmt --all applies these changes)
• cargo clippy --workspace -- -D warnings -D clippy::unwrap_used to check that you're using the standard code style
• cargo test --workspace to check that all tests pass (on Windows make sure to enable developer mode)
• cargo run -- -c "use std testing; testing run-tests --path crates/nu-std" to run the tests for the standard library

After Submitting

[fdncred]

please forgive my ignorance but i've never really understood this. What does "abc" < "bca" even mean? What exactly is it comparing to say this is true?

[yukitomoda]

please forgive my ignorance but i've never really understood this. What does "abc" < "bca" even mean? What exactly is it comparing to say this is true?

"abc" and "bca" are compared by using std::string::String::partial_cmp internally. This compares the strings' UTF-8 representation as Vec<u8>.
This is the same behavior as comparing strings statically typed as any which was also allowed in Nushell up to now (e.g. (do { "abc" }) < "bca"). So I think it is consistent.

[fdncred]

ok, thanks for the explanation.