Add test script for sanity of font fallback chain

Various tests have been added:

1. Availability of hyphens: Make sure that every font used for
rendering a language that is automatically hyphenated includes either
of Unicode hyphen characters U+2010 HYPHEN or U+002D HYPHEN-MINUS.

2. Range of values: Make sure that styles, weights, and styles belong
to certain limited sets.

Bug: 26187231
Bug: 21570828
Bug: 21815394
Change-Id: Ia63d63cc8da4f2d6bc81fe5619ccac6cfcd9a54e

1 files changed, 157 insertions, 0 deletions

diff --git a/tools/fonts/fontchain_lint.py b/tools/fonts/fontchain_lint.py
new file mode 100755
index 000000000000..fb2213cdad57
--- /dev/null
+++ b/tools/fonts/fontchain_lint.py
@@ -0,0 +1,157 @@
+#!/usr/bin/env python
+
+import collections
+import glob
+from os import path
+import sys
+from xml.etree import ElementTree
+
+from fontTools import ttLib
+
+LANG_TO_SCRIPT = {
+    'de': 'Latn',
+    'en': 'Latn',
+    'es': 'Latn',
+    'eu': 'Latn',
+    'ja': 'Jpan',
+    'ko': 'Kore',
+    'hu': 'Latn',
+    'hy': 'Armn',
+    'nb': 'Latn',
+    'nn': 'Latn',
+    'pt': 'Latn',
+}
+
+def lang_to_script(lang_code):
+    lang = lang_code.lower()
+    while lang not in LANG_TO_SCRIPT:
+        hyphen_idx = lang.rfind('-')
+        assert hyphen_idx != -1, (
+            'We do not know what script the "%s" language is written in.'
+            % lang_code)
+        assumed_script = lang[hyphen_idx+1:]
+        if len(assumed_script) == 4 and assumed_script.isalpha():
+            # This is actually the script
+            return assumed_script.title()
+        lang = lang[:hyphen_idx]
+    return LANG_TO_SCRIPT[lang]
+
+
+def get_best_cmap(font):
+    font_file, index = font
+    font_path = path.join(_fonts_dir, font_file)
+    if index is not None:
+        ttfont = ttLib.TTFont(font_path, fontNumber=index)
+    else:
+        ttfont = ttLib.TTFont(font_path)
+    all_unicode_cmap = None
+    bmp_cmap = None
+    for cmap in ttfont['cmap'].tables:
+        specifier = (cmap.format, cmap.platformID, cmap.platEncID)
+        if specifier == (4, 3, 1):
+            assert bmp_cmap is None, 'More than one BMP cmap in %s' % (font, )
+            bmp_cmap = cmap
+        elif specifier == (12, 3, 10):
+            assert all_unicode_cmap is None, (
+                'More than one UCS-4 cmap in %s' % (font, ))
+            all_unicode_cmap = cmap
+
+    return all_unicode_cmap.cmap if all_unicode_cmap else bmp_cmap.cmap
+
+
+def assert_font_supports_any_of_chars(font, chars):
+    best_cmap = get_best_cmap(font)
+    for char in chars:
+        if char in best_cmap:
+            return
+    sys.exit('None of characters in %s were found in %s' % (chars, font))
+
+
+def check_hyphens(hyphens_dir):
+    # Find all the scripts that need automatic hyphenation
+    scripts = set()
+    for hyb_file in glob.iglob(path.join(hyphens_dir, '*.hyb')):
+        hyb_file = path.basename(hyb_file)
+        assert hyb_file.startswith('hyph-'), (
+            'Unknown hyphenation file %s' % hyb_file)
+        lang_code = hyb_file[hyb_file.index('-')+1:hyb_file.index('.')]
+        scripts.add(lang_to_script(lang_code))
+
+    HYPHENS = {0x002D, 0x2010}
+    for script in scripts:
+        fonts = _script_to_font_map[script]
+        assert fonts, 'No fonts found for the "%s" script' % script
+        for font in fonts:
+            assert_font_supports_any_of_chars(font, HYPHENS)
+
+
+def parse_fonts_xml(fonts_xml_path):
+    global _script_to_font_map, _fallback_chain
+    _script_to_font_map = collections.defaultdict(set)
+    _fallback_chain = []
+    tree = ElementTree.parse(fonts_xml_path)
+    for family in tree.findall('family'):
+        name = family.get('name')
+        variant = family.get('variant')
+        langs = family.get('lang')
+        if name:
+            assert variant is None, (
+                'No variant expected for LGC font %s.' % name)
+            assert langs is None, (
+                'No language expected for LGC fonts %s.' % name)
+        else:
+            assert variant in {None, 'elegant', 'compact'}, (
+                'Unexpected value for variant: %s' % variant)
+
+        if langs:
+            langs = langs.split()
+            scripts = {lang_to_script(lang) for lang in langs}
+        else:
+            scripts = set()
+
+        for child in family:
+            assert child.tag == 'font', (
+                'Unknown tag <%s>' % child.tag)
+            font_file = child.text
+            weight = int(child.get('weight'))
+            assert weight % 100 == 0, (
+                'Font weight "%d" is not a multiple of 100.' % weight)
+
+            style = child.get('style')
+            assert style in {'normal', 'italic'}, (
+                'Unknown style "%s"' % style)
+
+            index = child.get('index')
+            if index:
+                index = int(index)
+
+            _fallback_chain.append((
+                name,
+                frozenset(scripts),
+                variant,
+                weight,
+                style,
+                (font_file, index)))
+
+            if name: # non-empty names are used for default LGC fonts
+                map_scripts = {'Latn', 'Grek', 'Cyrl'}
+            else:
+                map_scripts = scripts
+            for script in map_scripts:
+                _script_to_font_map[script].add((font_file, index))
+
+
+def main():
+    target_out = sys.argv[1]
+    global _fonts_dir
+    _fonts_dir = path.join(target_out, 'fonts')
+
+    fonts_xml_path = path.join(target_out, 'etc', 'fonts.xml')
+    parse_fonts_xml(fonts_xml_path)
+
+    hyphens_dir = path.join(target_out, 'usr', 'hyphen-data')
+    check_hyphens(hyphens_dir)
+
+
+if __name__ == '__main__':
+    main()