new check: com.google.fonts/check/glyf_nested_components

"Check that components do not reference glyphs which are themselves compontents"
(issue #2961)

Author: simoncozens

CHANGELOG.md

@@ -14,6 +14,7 @@ A more detailed list of changes is available in the corresponding milestones for
   - **[com.google.fonts/check/metadata/gf-axisregistry_valid_tags]:** VF axis tags are registered on GF Axis Registry (issue #3010)
   - **[com.google.fonts/check/metadata/gf-axisregistry_bounds]:** VF axes have ranges compliant to the bounds specified on the GF Axis Registry (issue #3022)
   - **[com.google.fonts/check/STAT/gf-axisregistry]:** Check that particle names and values on STAT table match the fallback names in each axis registry at the Google Fonts Axis Registry (issue #3022)
+  - **[com.google.fonts/check/glyf_nested_components]:** Check that components do not reference glyphs which are themselves compontents (issue #2961)
 
 ### Changes to existing checks
   - **[com.google.fonts/check/family/win_ascent_and_descent]**: Skip if font is cjk

Lib/fontbakery/profiles/glyf.py

@@ -127,3 +127,34 @@ def com_google_fonts_check_glyf_non_transformed_duplicate_components(ttFont):
     else:
         yield PASS, ("Glyphs do not contain duplicate components which have"
                      " the same x,y coordinates.")
+
+@check(
+    id = 'com.google.fonts/check/glyf_nested_components',
+    rationale = "There have been bugs rendering variable fonts with nested components. Additionally, some static fonts with nested components have been reported to have rendering and printing issues. (See googlefonts/fontbakery#2961 and arrowtype/recursive#412.)",
+    conditions = ['is_ttf'],
+    misc_metadata = {
+        'request': 'https://github.com/googlefonts/fontbakery/issues/2961'
+    }
+)
+def com_google_fonts_check_glyf_nested_components(ttFont):
+    """Check glyphs do not have components which are themselves components."""
+    from fontbakery.utils import pretty_print_list
+    failed = []
+    for glyph_name in ttFont['glyf'].keys():
+        glyph = ttFont['glyf'][glyph_name]
+        if not glyph.isComposite():
+            continue
+        for comp in glyph.components:
+            if ttFont['glyf'][comp.glyphName].isComposite():
+                failed.append(glyph_name)
+    if failed:
+        formatted_list = "\t* " + pretty_print_list(failed,
+                                                    shorten=10,
+                                                    sep="\n\t* ")
+        yield FAIL, \
+              Message('found-nested-components',
+                      f"The following glyphs have components which"
+                      f" themselves are component glyphs:\n"
+                      f"{formatted_list}")
+    else:
+        yield PASS, ("Glyphs do not contain nested components.")

Lib/fontbakery/profiles/opentype.py

@@ -72,6 +72,7 @@
     'com.google.fonts/check/maxadvancewidth',
     'com.google.fonts/check/points_out_of_bounds',
     'com.google.fonts/check/glyf_non_transformed_duplicate_components',
+    'com.google.fonts/check/glyf_nested_components',
     'com.google.fonts/check/all_glyphs_have_codepoints',
     'com.google.fonts/check/code_pages',
 ]

tests/profiles/glyf_test.py

@@ -70,3 +70,18 @@ def test_check_glyf_non_transformed_duplicate_components():
     assert_results_contain(check(ttFont),
                            FAIL, 'found-duplicates')
 
+
+def test_check_glyf_nested_components():
+    """Check glyphs do not have nested components."""
+    check = CheckTester(opentype_profile,
+                        "com.google.fonts/check/glyf_nested_components")
+
+    ttFont = TTFont(TEST_FILE("nunito/Nunito-Regular.ttf"))
+    assert_PASS(check(ttFont))
+
+    # We need to create a nested component. "second" has components, so setting
+    # one of "quotedbl"'s components to "second" should do it.
+    ttFont['glyf']['quotedbl'].components[0].glyphName = "second"
+
+    assert_results_contain(check(ttFont),
+                           FAIL, 'found-nested-components')