Check that Arabic spacing symbols U+FBB2–FBC1 aren't classified as marks.

Unicode has a few spacing symbols representing Arabic dots and other marks,
but they are purposefully not classified as marks.

Many fonts mistakenly classify them as marks, making them unsuitable
for their original purpose as stand-alone symbols to used in pedagogical
contexts discussing Arabic consonantal marks.

com.google.fonts/check/arabic_spacing_symbols
Added to Universal profile.

(Ported from fonttools/fontbakery#4295)

Author: felipesanches

fontspector-checkapi/src/font.rs

@@ -1,5 +1,10 @@
 use crate::{constants::RIBBI_STYLE_NAMES, filetype::FileTypeConvert, FileType, Testable};
-use read_fonts::{tables::os2::SelectionFlags, TableProvider};
+use read_fonts::{
+    tables::cmap::Cmap,
+    tables::gdef::ClassDef,
+    tables::os2::SelectionFlags,
+    TableProvider,
+};
 use skrifa::{
     charmap::Charmap,
     font::FontRef,
@@ -68,6 +73,16 @@ impl TestFont {
         Ok(os2.fs_selection())
     }
 
+    pub fn get_gdef_glyph_class_def(&self) -> Result<ClassDef, Box<dyn Error>> {
+        let gdef = self.font().gdef()?;
+        Ok(gdef.glyph_class_def().unwrap()?)
+    }
+
+    pub fn get_cmap(&self) -> Result<Cmap, Box<dyn Error>> {
+        let cmap = self.font().cmap()?;
+        Ok(cmap)
+    }
+
     pub fn get_name_entry_strings(&self, name_id: StringId) -> LocalizedStrings {
         self.font().localized_strings(name_id)
     }

profile-universal/src/checks/arabic_spacing_symbols.rs

@@ -0,0 +1,61 @@
+use fontspector_checkapi::{prelude::*, FileTypeConvert};
+
+const ARABIC_SPACING_SYMBOLS: [u16; 17] = [
+    0xFBB2,  // Dot Above
+    0xFBB3,  // Dot Below
+    0xFBB4,  // Two Dots Above
+    0xFBB5,  // Two Dots Below
+    0xFBB6,  // Three Dots Above
+    0xFBB7,  // Three Dots Below
+    0xFBB8,  // Three Dots Pointing Downwards Above
+    0xFBB9,  // Three Dots Pointing Downwards Below
+    0xFBBA,  // Four Dots Above
+    0xFBBB,  // Four Dots Below
+    0xFBBC,  // Double Vertical Bar Below
+    0xFBBD,  // Two Dots Vertically Above
+    0xFBBE,  // Two Dots Vertically Below
+    0xFBBF,  // Ring
+    0xFBC0,  // Small Tah Above
+    0xFBC1,  // Small Tah Below
+    0xFBC2,  // Wasla Above
+];
+
+fn arabic_spacing_symbols(t: &Testable) -> StatusList {
+    let mut problems: Vec<Status> = vec![];
+    let f = TTF.from_testable(t).expect("Not a TTF file");
+    let cmap = f.get_cmap().unwrap();
+    let class_def = f.get_gdef_glyph_class_def().unwrap();
+
+    for codepoint in ARABIC_SPACING_SYMBOLS {
+        let gid = cmap.map_codepoint(codepoint);
+        if gid.is_some() && class_def.get(gid.unwrap()) == 3 {
+            problems.push(Status::fail(&format!(
+                "U+{:04X} is defined in GDEF as a mark (class 3).", codepoint)));
+        }
+    }
+
+    if problems.is_empty() {
+        Status::just_one_pass()
+    } else {
+        return_result(problems)
+    }
+}
+
+pub const CHECK_ARABIC_SPACING_SYMBOLS: Check = Check {
+    id: "com.google.fonts/check/arabic_spacing_symbols",
+    title: "Check that Arabic spacing symbols U+FBB2–FBC1 aren't classified as marks.",
+    rationale: "
+        Unicode has a few spacing symbols representing Arabic dots and other marks,
+        but they are purposefully not classified as marks.
+
+        Many fonts mistakenly classify them as marks, making them unsuitable
+        for their original purpose as stand-alone symbols to used in pedagogical
+        contexts discussing Arabic consonantal marks.
+    ",
+    proposal: "https://github.com/googlefonts/fontbakery/issues/4295",
+    check_one: Some(&arabic_spacing_symbols),
+    check_all: None,
+    applies_to: "TTF",
+    hotfix: None,
+    fix_source: None,
+};

profile-universal/src/checks/mod.rs

@@ -1,7 +1,9 @@
+mod arabic_spacing_symbols;
 mod bold_italic_unique;
 mod name_trailing_spaces;
 mod required_tables;
 mod unwanted_tables;
+pub use arabic_spacing_symbols::CHECK_ARABIC_SPACING_SYMBOLS;
 // pub use bold_italic_unique::CHECK_BOLD_ITALIC_UNIQUE;
 pub use name_trailing_spaces::CHECK_NAME_TRAILING_SPACES;
 pub use required_tables::CHECK_REQUIRED_TABLES;

profile-universal/src/lib.rs

@@ -5,6 +5,7 @@ pub struct Universal;
 
 impl fontspector_checkapi::Plugin for Universal {
     fn register(&self, cr: &mut Registry) -> Result<(), String> {
+        cr.register_check(checks::CHECK_ARABIC_SPACING_SYMBOLS);
         cr.register_check(checks::CHECK_NAME_TRAILING_SPACES);
         cr.register_check(checks::CHECK_UNWANTED_TABLES);
         cr.register_check(checks::CHECK_REQUIRED_TABLES);
@@ -14,6 +15,7 @@ impl fontspector_checkapi::Plugin for Universal {
                 r#"
 [sections]
 "Universal Profile Checks" = [
+    "com.google.fonts/check/arabic_spacing_symbols",
     "com.google.fonts/check/name/trailing_spaces",
     "com.google.fonts/check/unwanted_tables",
     "com.google.fonts/check/required_tables",