"TRUE" does not parse into boolean

[djensen1997]

Summary of the issue

When taking input into my program, I ran into a situation where the user would pass "TRUE" into a field that I was attempting to use the .parse() method into a boolean:

fn input(value: &str) -> Result<(), MyErrorType> {
  let new_val: bool = value.parse().map_err(|_| MyErrorType{})?;
  Ok(())
}

when I split this specific line of code into a fresh rust project:

fn main() {
    let x: bool = "TRUE".parse().expect("NOPE");
}

I got the output:
thread 'main' panicked at 'NOPE: ParseBoolError', src/main.rs:20:34

What I expect to happen

I would expect rust to see the string value "TRUE" and read that as a boolean with the value true

What actually happens

I am getting an error return with MyErrorType

[CollinEMac]

It looks like Rust properly parses "true" and "false" in lowercase to a boolean but not the capitalized "TRUE" or "FALSE".

This is documented here:
https://doc.rust-lang.org/std/primitive.bool.html#method.from_str

[Noratrieb]

It's not clearly documented what exactly is and is not supposed to be parsed, but I think that the current behaviour of only parsing true and false is the best solution here, and changing the behaviour of functions like this is generally a breaking change.

For comparison, here's what a few other languages do:

• Java: ignores case
• Swift: only true and false
• Javascript (JSON.parse): only true and false
• Go: accepts 1, t, T, TRUE, true, True, 0, f, F, FALSE, false, False.

[GuillaumeGomez]

I opened #102094 which should fix this issue.