GS build with fontc raises OTS error + warning

[chrissimpkins]

fontc source commit GS source commit

Fonts compiled in the default GH Actions Linux runner environment with the current stable Rust toolchain

ERROR: avar: Axis count mismatch
ERROR: Table discarded
WARNING: STAT: Unexpected non-zero offsetToAxisValueOffsets
File sanitized successfully!

[anthrotype]

Thanks Chris. The avar axis miscount is more worrying, we should look into it. The STAT is kind of a known issue in that we don't populate any axis values but only build a stub, just like varLib does by default, without full support for DSv5 axis labels (norad I think still doesn't parse those so fontc doesn't read them yet).

We have in the CI a simple script that runs OTS on a simple font but maybe it's better to run it on a full blown font like GS to catch more real world errors

[rsheeter]

+1 to OTS the GS we build

[chrissimpkins]

Added OTS tests on the Roman and Italic files in https://github.com/googlefonts/fontc/pull/589

[chrissimpkins]

The current error and warning do not yield a non-zero exit status code so CI will pass. The tests show the same ERROR/WARNING report that is shown in the OP here.

[anthrotype]

reopening to investigate if we can get rid of the STAT warning as well

[anthrotype]

apparently OTS is complaining that we have a non-zero offsetToAxisValueOffsets despite the axisValueCount is 0:

  if (this->axisValueCount == 0) {
    if (this->offsetToAxisValueOffsets != 0) {
      Warning("Unexpected non-zero offsetToAxisValueOffsets");
      this->offsetToAxisValueOffsets = 0;
    }

https://github.com/khaledhosny/ots/blob/be9445820c57ee12e738bd45b56f65648509682d/src/stat.cc#L91-L95

the generated_stat.rs looks like this?

    /// Offset in bytes from the beginning of the STAT table to the
    /// start of the design axes value offsets array. If axisValueCount
    /// is zero, set to zero; if axisValueCount is greater than zero,
    /// must be greater than zero.
    pub offset_to_axis_values: OffsetMarker<Vec<OffsetMarker<AxisValue>>, WIDTH_32>,

https://github.com/googlefonts/fontations/blob/dec4e1b073ce28c82df32f7c132517f46781dcd5/write-fonts/generated/generated_stat.rs#L19-L23

Basically if the axis_values array is empty, we want the offset to be 0. Do we need to use a NullableOffsetMarker perhaps?