Face::set_variation change in behaviour

[alexheretic]

I noticed Face::set_variation now returns Some(()) even when the face does not have the axis since v0.20.0.

If this is intended the docs should be amended.

Returns None when face is not variable or doesn't have such axis.

Reproduce

// [dependencies]
// ttf-parser19 = { version = "0.19", package = "ttf-parser" }
// ttf-parser = "0.20"

const VAR_FONT: &[u8] = include_bytes!("../Cantarell-VF.otf");

fn main() {
    let mut face = ttf_parser19::Face::parse(VAR_FONT, 0).unwrap();
    dbg!(face.set_variation(ttf_parser19::Tag::from_bytes(b"wght"), 600.0)); // Some(())
    dbg!(face.set_variation(ttf_parser19::Tag::from_bytes(b"foob"), 200.0)); // None
    dbg!(face.set_variation(ttf_parser19::Tag::from_bytes(b"barr"), 200.0)); // None

    let mut face = ttf_parser::Face::parse(VAR_FONT, 0).unwrap();
    dbg!(face.set_variation(ttf_parser::Tag::from_bytes(b"wght"), 600.0)); // Some(())
    dbg!(face.set_variation(ttf_parser::Tag::from_bytes(b"foob"), 200.0)); // Some(())
    dbg!(face.set_variation(ttf_parser::Tag::from_bytes(b"barr"), 200.0)); // Some(())
}

Using Cantarell-VF.otf.

[RazrFalcon]

Yes, my bad. It should not return anything now. You have to use face.variation_axes() to check for available tags beforehand.

This mimics the harfbuzz API: https://github.com/harfbuzz/harfbuzz/blob/b0150ffd05523c7cef9b3c91a8d6050177fceda3/src/hb-font.cc#L2658-L2676