str: Implement str::trim_newline

[ijackson]

This function was contemplated here rust-lang/rfcs#3196 (comment)

It seems like a good idea to me. I chose to call it trim_newline rather than trim_end_newline since trimming newlines anywhere else would be weird, so end felt redundant.

I have not provided a method on String as contemplated in that issue. We don't have any other mutating versions of str trimming methods, so everyone who wants that has to write s.truncate(s.trim_wombat().len()). I think that's OK since it is more idiomatic to work with slices.

[rust-highfive]

r? @joshtriplett

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[ijackson]

Obviously, if the basic idea seems good I will open the tracking issue and update the MR branch.

[klensy]

This test will fail:

assert_eq!("Text", "Text\n\r".trim_newline());

Ahh,

    /// 'Newline' is precisely a newline character (`0xA`), perhaps
    /// preceded by a carriage return (`0xD`).  I.e., `'\r\n'` or
    /// `'\n'`.  (This is the same definition as used by [`str::lines`]

ok then.

[ijackson]

This test will fail:

assert_eq!("Text", "Text\n\r".trim_newline());

Ahh,

    /// 'Newline' is precisely a newline character (`0xA`), perhaps
    /// preceded by a carriage return (`0xD`).  I.e., `'\r\n'` or
    /// `'\n'`.  (This is the same definition as used by [`str::lines`]

Indeed. Your response seems to me to demonstrate that the docs needed improving :-). I have added the actual handling of this, with a note, to the example.

lines() treats "Text\n\r" as two lines, "Text" and "": https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=648cd55ce2178e7c3228e9f75d9b531b . Arguably the 2nd line should be "\r" since there was no LF but it is surely too late to change that now.

[JohnCSimon]

Ping from triage:
@ijackson Can you post your status on this PR? thanks

[Dylan-DPC]

Closing this as inactive