Discourage DSIG table presence

[khaledhosny]

Observed behaviour

fontbakery issues a FAIL message for fonts without DSIG table (com.google.fonts/check/dsig).

Expected behaviour

Do nothing, don’t even issue a WARN or INFO, DSIG table is unused; MS Office used to require it to enable OpenType features for so-called simple scripts but does not do any more and not everyone is building such fonts.

Resources and exact process needed to replicate

Any font produced in the last millennium that did not add DSIG table to make fontbackery FAIL go away.

[simoncozens]

I remember rumours that MS Office Mac still does?

[chrissimpkins]

#1845 (comment)

[davelab6]

Any font produced in the last millennium that did not add DSIG table to make fontbackery FAIL go away.

LOL

In fact, I think we should flip the check to WARN people if a DSIG is found at all, and tell them to remove it.

[davelab6]

This is relatively high severity because it is so annoying :)

[felipesanches]

The rationale in this check currently says:

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Microsoft Office 2013 and below products expect fonts to have a digital signature declared in a DSIG table in order to implement OpenType features. The EOL date for Microsoft Office 2013 products is 4/11/2023. This issue does not impact Microsoft Office 2016 and above products.

This checks verifies that this signature is available in the font.

A fake signature is enough to address this issue. If needed, a dummy table can be added to the font with the gftools fix-dsig script available at https://github.com/googlefonts/gftools

---

I'm OK with changing the check to reflect a new policy of removing the table from all fonts even if there's still ~1,5 year until the EOL date for Office 2013. Sounds like a reasonable time to do so now.

[felipesanches]

For now, a WARN, but by November 2023 we should finally make this a FAIL.