new check: arabic_spacing_symbols

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

src/checks/arabic_spacing_symbols.rs

@@ -0,0 +1,61 @@
+use crate::{
+    check::{return_result, Status, StatusList},
+    Check, TestFont,
+};
+
+fn arabic_spacing_symbols(f: &TestFont) -> StatusList {
+    // code-points
+    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
+    ];
+
+    let mut problems: Vec<Status> = vec![];
+    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 ARABIC_SPACING_SYMBOLS_CHECK: 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: Some("
+        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: Some("https://github.com/googlefonts/fontbakery/issues/4295"),
+    check_one: Some(&arabic_spacing_symbols),
+    check_all: None
+};

src/checks/mod.rs

@@ -1,7 +1,9 @@
+mod arabic_spacing_symbols;
 mod bold_italic_unique;
 mod name_trailing_spaces;
 mod unwanted_tables;
 mod required_tables;
+pub use arabic_spacing_symbols::ARABIC_SPACING_SYMBOLS_CHECK;
 pub use bold_italic_unique::BOLD_ITALIC_UNIQUE_CHECK;
 pub use name_trailing_spaces::NAME_TRAILING_SPACES_CHECK;
 pub use unwanted_tables::UNWANTED_TABLES_CHECK;

src/font.rs

@@ -1,5 +1,10 @@
 use crate::constants::RIBBI_STYLE_NAMES;
-use read_fonts::{tables::os2::SelectionFlags, TableProvider};
+use read_fonts::{
+    tables::cmap::Cmap,
+    tables::gdef::ClassDef,
+    tables::os2::SelectionFlags,
+    TableProvider,
+};
 use skrifa::{
     font::FontRef,
     string::{LocalizedStrings, StringId},
@@ -37,6 +42,16 @@ impl TestFont {
         Ok(os2.fs_selection())
     }
 
+    pub(crate) fn get_gdef_glyph_class_def(&self) -> Result<ClassDef, Box<dyn Error>> {
+        let gdef = self.font().gdef()?;
+        Ok(gdef.glyph_class_def().unwrap()?)
+    }
+
+    pub(crate) 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)
     }

src/universal.rs

@@ -1,7 +1,8 @@
 use crate::checks::*;
 use crate::Check;
 
-pub const UNIVERSAL_PROFILE: [Check<'_>; 4] = [
+pub const UNIVERSAL_PROFILE: [Check<'_>; 5] = [
+    ARABIC_SPACING_SYMBOLS_CHECK,
     BOLD_ITALIC_UNIQUE_CHECK,
     NAME_TRAILING_SPACES_CHECK,
     UNWANTED_TABLES_CHECK,