<ctype.h> functions for AsciiExt

[zackw]

As discussed at https://internals.rust-lang.org/t/improvements-to-asciiext/4689 I have added is_ascii_* equivalents of most (not quite all) of C's ctype.h's isxxx functions to the AsciiExt trait.

The new functions are

• is_ascii_alphabetic
• is_ascii_uppercase
• is_ascii_lowercase
• is_ascii_alphanumeric
• is_ascii_digit
• is_ascii_hexdigit
• is_ascii_punctuation
• is_ascii_graphic
• is_ascii_whitespace (matches the Infra Standard definition of ASCII whitespace, not POSIX)
• is_ascii_control

They are implemented for char, u8, str, and [u8], and, for backward compatibility with external trait implementations, have default implementations that call unimplemented!().

PR to follow, but I needed to file this bug in order to get an issue number to put in the stability annotations.

[SimonSapin]

Stabilize?

I just wrote if let b'A' ... b'Z' = b {, it’s not too bad but might have looked nicer as if b.is_ascii_uppercase() {

[zackw]

There was a request over in #39659 to deprecate AsciiExt and convert all the methods to intrinsics on str, [u8], etc. but I never got around to it and don't have time in the near future either. I dunno how a plan to do that would affect the stabilization schedule.

[LukasKalbertodt]

What's the status here? Could I try to "deprecate AsciiExt and convert all the methods to intrinsics on str, [u8]", create a PR and it might be accepted? Or are there other plans? If there is nothing except "lack of time" blocking this, I might be able to help.

[zackw]

From my end it's just lack of time. I think the team would be glad to at least look at a patch if you made one.