new check: 'opentype/dsig'

"The font should not need a DSIG table anymore."
Added to the OpenType profile.

ported from https://github.com/fonttools/fontbakery/blob/33632eba19c5b8a9f75f4ce268db7dd7f987e44c/Lib/fontbakery/checks/opentype/dsig.py#L6-L39

(original proposal: fonttools/fontbakery#3398)

Author: felipesanches

profile-universal/src/checks/dsig.rs

@@ -0,0 +1,40 @@
+use fontspector_checkapi::{prelude::*, testfont, FileTypeConvert};
+use read_fonts::TableProvider;
+use skrifa::Tag;
+
+#[check(
+    id = "opentype/dsig",
+    title = "The font should not need a DSIG table anymore.",
+    rationale = "
+        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 was 4/11/2023.
+
+        This issue does not impact Microsoft Office 2016 and above products. It is now considered better to completely remove the table.
+
+        But if you still want your font to support OpenType features on Office 2013,
+        then you may find it handy to add a fake signature on a placeholder DSIG table
+        by running one of the helper scripts provided at
+        https://github.com/googlefonts/gftools
+
+        Reference: https://github.com/fonttools/fontbakery/issues/1845
+    ",
+    proposal = "https://github.com/fonttools/fontbakery/issues/3398"
+)]
+fn dsig(t: &Testable, _context: &Context) -> CheckFnResult {
+    let f = testfont!(t);
+    let dsig_data = f.font().expect_data_for_tag(Tag::new(b"DSIG"));
+    if dsig_data.is_ok() {
+        Ok(Status::just_one_warn(
+            "found-DSIG",
+            "This font has a digital signature (DSIG table) which \
+             is only required - even if only a placeholder \
+             - on old programs like MS Office 2013 in order to \
+             work properly.\n\
+             The current recommendation is to completely \
+             remove the DSIG table."
+        ))
+    } else {
+        Ok(Status::just_one_pass())
+    }
+}

profile-universal/src/checks/mod.rs

@@ -1,6 +1,7 @@
 pub mod arabic_spacing_symbols;
 pub mod bold_italic_unique;
 pub mod code_pages;
+pub mod dsig;
 pub mod fvar;
 pub mod glyphnames;
 pub mod hhea;

profile-universal/src/lib.rs

@@ -8,6 +8,7 @@ impl fontspector_checkapi::Plugin for Universal {
     fn register(&self, cr: &mut Registry) -> Result<(), String> {
         cr.register_check(checks::arabic_spacing_symbols::arabic_spacing_symbols);
         cr.register_check(checks::code_pages::code_pages);
+        cr.register_check(checks::dsig::dsig);
         cr.register_check(checks::fvar::axis_ranges_correct);
         cr.register_check(checks::fvar::regular_coords_correct);
         cr.register_check(checks::glyphnames::valid_glyphnames);