From f1b8a955cac6712623ff9704de8e0f29b1365756 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Felipe=20Corr=C3=AAa=20da=20Silva=20Sanches?=
 <juca@members.fsf.org>
Date: Fri, 20 Oct 2023 17:24:11 +0100
Subject: [PATCH] New check: Arabic letter high hamza isn't classified as a
 mark.

Many fonts incorrectly treat ARABIC LETTER HIGH HAMZA (U+0675) as a variant of
ARABIC HAMZA ABOVE (U+0654) and make it a combining mark of the same size.

But U+0675 is a base letter and should be a variant of ARABIC LETTER HAMZA
(U+0621) but raised slightly above baseline.

Not doing so effectively makes the font useless for Jawi and
possibly Kazakh as well.

Added to the Universal Profile
com.google.fonts/check/arabic_high_hamza (experimental)
(issue #4290)
---
 CHANGELOG.md                         |  1 +
 Lib/fontbakery/profiles/universal.py | 48 +++++++++++++++++++++++++++-
 2 files changed, 48 insertions(+), 1 deletion(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 284b71c56f..edf29faabf 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -10,6 +10,7 @@ A more detailed list of changes is available in the corresponding milestones for
 ### New checks
 #### Added to the Universal Profile
   - **EXPERIMENTAL - [com.google.fonts/check/arabic_spacing_symbols]:** Check that Arabic spacing symbols U+FBB2–FBC1 aren't classified as marks. (issue #4295)
+  - **EXPERIMENTAL - [com.google.fonts/check/arabic_high_hamza]:** Check that glyph for U+0675 ARABIC LETTER HIGH HAMZA is not a mark. (issue #4290)
 
 ### Changes to existing checks
 #### On the Universal Profile
diff --git a/Lib/fontbakery/profiles/universal.py b/Lib/fontbakery/profiles/universal.py
index d76a649778..3d4993a4c3 100644
--- a/Lib/fontbakery/profiles/universal.py
+++ b/Lib/fontbakery/profiles/universal.py
@@ -71,6 +71,7 @@
         "com.google.fonts/check/STAT_in_statics",
         "com.google.fonts/check/alt_caron",
         "com.google.fonts/check/arabic_spacing_symbols",
+        "com.google.fonts/check/arabic_high_hamza",
     ]
 )
 
@@ -777,7 +778,7 @@ def com_google_fonts_check_legacy_accents(ttFont):
     experimental="Since 2023/Oct/20",
     severity=4,
 )
-def com_google_fonts_check_spacing_symbols(ttFont):
+def com_google_fonts_check_arabic_spacing_symbols(ttFont):
     """Check that Arabic spacing symbols U+FBB2–FBC1 aren't classified as marks."""
     import babelfont
 
@@ -819,6 +820,51 @@ def com_google_fonts_check_spacing_symbols(ttFont):
         yield PASS, "Looks good!"
 
 
+@check(
+    id="com.google.fonts/check/arabic_high_hamza",
+    proposal=[
+        "https://github.com/googlefonts/fontbakery/issues/4290",
+    ],
+    rationale="""
+        Many fonts incorrectly treat ARABIC LETTER HIGH HAMZA (U+0675) as a variant of
+        ARABIC HAMZA ABOVE (U+0654) and make it a combining mark of the same size.
+
+        But U+0675 is a base letter and should be a variant of ARABIC LETTER HAMZA
+        (U+0621) but raised slightly above baseline.
+
+        Not doing so effectively makes the font useless for Jawi and
+        possibly Kazakh as well.
+    """,
+    experimental="Since 2023/Oct/20",
+    severity=4,
+)
+def com_google_fonts_check_arabic_high_hamza(ttFont):
+    """Check that glyph for U+0675 ARABIC LETTER HIGH HAMZA is not a mark."""
+    import babelfont
+
+    ARABIC_LETTER_HIGH_HAMZA = 0x0675
+
+    passed = True
+    font = babelfont.load(ttFont.reader.file.name)
+
+    if "GDEF" in ttFont:
+        class_def = ttFont["GDEF"].table.GlyphClassDef.classDefs
+        for glyph in font.glyphs:
+            if ARABIC_LETTER_HIGH_HAMZA in set(glyph.codepoints):
+                if glyph.name in class_def and class_def[glyph.name] == 3:
+                    passed = False
+                    yield FAIL, Message(
+                        "mark-in-gdef",
+                        f'"{glyph.name}" is defined in GDEF as a mark (class 3).',
+                    )
+    # TODO: Should we also validate the bounding box of the glyph and compare
+    #       it to U+0621 expecting them to have roughly the same size?
+    #       (within a certain tolerance margin)
+
+    if passed:
+        yield PASS, "Looks good!"
+
+
 @check(
     id="com.google.fonts/check/required_tables",
     conditions=["ttFont"],