Support CSS Nesting

docs/first_steps.rst

@@ -14,7 +14,7 @@ WeasyPrint |version| depends on:
 * pydyf_ ≥ 0.8.0
 * CFFI_ ≥ 0.6
 * html5lib_ ≥ 1.1
-* tinycss2_ ≥ 1.0.0
+* tinycss2_ ≥ 1.3.0
 * cssselect2_ ≥ 0.1
 * Pyphen_ ≥ 0.9.1
 * Pillow_ ≥ 9.1.0

pyproject.toml

@@ -15,7 +15,7 @@ dependencies = [
   'pydyf >=0.8.0',
   'cffi >=0.6',
   'html5lib >=1.1',
-  'tinycss2 >=1.0.0',
+  'tinycss2 >=1.3.0',
   'cssselect2 >=0.1',
   'Pyphen >=0.9.1',
   'Pillow >=9.1.0',

tests/css/test_descriptors.py

@@ -19,7 +19,7 @@ def test_font_face_1():
     assert at_rule.at_keyword == 'font-face'
     font_family, src = list(preprocess_descriptors(
         'font-face', 'https://weasyprint.org/foo/',
-        tinycss2.parse_declaration_list(at_rule.content)))
+        tinycss2.parse_blocks_contents(at_rule.content)))
     assert font_family == ('font_family', 'Gentium Hard')
     assert src == (
         'src', (('external', 'https://example.com/fonts/Gentium.woff'),))
@@ -40,7 +40,7 @@ def test_font_face_2():
     font_family, src, font_style, font_weight, font_stretch = list(
         preprocess_descriptors(
             'font-face', 'https://weasyprint.org/foo/',
-            tinycss2.parse_declaration_list(at_rule.content)))
+            tinycss2.parse_blocks_contents(at_rule.content)))
     assert font_family == ('font_family', 'Fonty Smiley')
     assert src == (
         'src', (('external', 'https://weasyprint.org/foo/Fonty-Smiley.woff'),))
@@ -60,7 +60,7 @@ def test_font_face_3():
     assert at_rule.at_keyword == 'font-face'
     font_family, src = list(preprocess_descriptors(
         'font-face', 'https://weasyprint.org/foo/',
-        tinycss2.parse_declaration_list(at_rule.content)))
+        tinycss2.parse_blocks_contents(at_rule.content)))
     assert font_family == ('font_family', 'Gentium Hard')
     assert src == ('src', (('local', None),))
 
@@ -77,7 +77,7 @@ def test_font_face_4():
     assert at_rule.at_keyword == 'font-face'
     font_family, src = list(preprocess_descriptors(
         'font-face', 'https://weasyprint.org/foo/',
-        tinycss2.parse_declaration_list(at_rule.content)))
+        tinycss2.parse_blocks_contents(at_rule.content)))
     assert font_family == ('font_family', 'Gentium Hard')
     assert src == ('src', (('local', 'Gentium Hard'),))
 
@@ -96,7 +96,7 @@ def test_font_face_5():
     with capture_logs() as logs:
         font_family, src = list(preprocess_descriptors(
             'font-face', 'https://weasyprint.org/foo/',
-            tinycss2.parse_declaration_list(at_rule.content)))
+            tinycss2.parse_blocks_contents(at_rule.content)))
     assert font_family == ('font_family', 'Gentium Hard')
     assert src == ('src', (('local', 'Gentium Hard'),))
     assert len(logs) == 1
@@ -119,7 +119,7 @@ def test_font_face_bad_1():
         font_family, src, font_stretch = list(
             preprocess_descriptors(
                 'font-face', 'https://weasyprint.org/foo/',
-                tinycss2.parse_declaration_list(at_rule.content)))
+                tinycss2.parse_blocks_contents(at_rule.content)))
     assert font_family == ('font_family', 'Bad Font')
     assert src == (
         'src', (('external', 'https://weasyprint.org/foo/BadFont.woff'),))

tests/css/test_expanders.py

@@ -12,7 +12,7 @@
 
 def expand_to_dict(css, expected_error=None):
     """Helper to test shorthand properties expander functions."""
-    declarations = tinycss2.parse_declaration_list(css)
+    declarations = tinycss2.parse_blocks_contents(css)
 
     with capture_logs() as logs:
         base_url = 'https://weasyprint.org/foo/'

tests/css/test_nesting.py

@@ -0,0 +1,27 @@
+"""Test CSS nesting."""
+
+import pytest
+
+from ..testing_utils import assert_no_logs, render_pages
+
+
+@assert_no_logs
+@pytest.mark.parametrize('style', (
+    'div { p { width: 10px } }',
+    'p { div & { width: 10px } }',
+    'p { width: 20px; div & { width: 10px } }',
+    'p { div & { width: 10px } width: 20px }',
+    'div { & { & { p { & { width: 10px } } } } }',
+    '@media print { div { p { width: 10px } } }',
+))
+def test_nesting_block(style):
+    page, = render_pages('''
+      <style>%s</style>
+      <div><p></p></div><p></p>
+    ''' % style)
+    html, = page.children
+    body, = html.children
+    div, p = body.children
+    div_p, = div.children
+    assert div_p.width == 10
+    assert p.width != 10

tests/css/test_validation.py

@@ -12,7 +12,7 @@
 
 
 def get_value(css, expected_error=None):
-    declarations = tinycss2.parse_declaration_list(css)
+    declarations = tinycss2.parse_blocks_contents(css)
 
     with capture_logs() as logs:
         base_url = 'https://weasyprint.org/foo/'

weasyprint/css/__init__.py

@@ -13,6 +13,7 @@
 """
 
 from collections import namedtuple
+from itertools import groupby
 from logging import DEBUG, WARNING
 
 import cssselect2
@@ -297,7 +298,7 @@ def find_style_attributes(tree, presentational_hints=False, base_url=None):
 
     """
     def check_style_attribute(element, style_attribute):
-        declarations = tinycss2.parse_declaration_list(style_attribute)
+        declarations = tinycss2.parse_blocks_contents(style_attribute)
         return element, declarations, base_url
 
     for element in tree.iter():
@@ -919,33 +920,42 @@ def preprocess_stylesheet(device_media_type, base_url, stylesheet_rules,
             continue
 
         if rule.type == 'qualified-rule':
-            declarations = list(preprocess_declarations(
-                base_url, tinycss2.parse_declaration_list(rule.content)))
-            if declarations:
+            try:
                 logger_level = WARNING
-                try:
-                    selectors = cssselect2.compile_selector_list(rule.prelude)
-                    for selector in selectors:
-                        matcher.add_selector(selector, declarations)
-                        if selector.pseudo_element not in PSEUDO_ELEMENTS:
-                            if selector.pseudo_element.startswith('-'):
-                                logger_level = DEBUG
-                                raise cssselect2.SelectorError(
-                                    'ignored prefixed pseudo-element: '
-                                    f'{selector.pseudo_element}')
-                            else:
-                                raise cssselect2.SelectorError(
-                                    'unknown pseudo-element: '
-                                    f'{selector.pseudo_element}')
+                selectors_declarations = list(
+                    preprocess_declarations(
+                        base_url, tinycss2.parse_blocks_contents(rule.content),
+                        rule.prelude))
+
+                if selectors_declarations:
+                    selectors_declarations = groupby(
+                        selectors_declarations, key=lambda x: x[0])
+                    for selectors, declarations in selectors_declarations:
+                        declarations = [
+                            declaration[1] for declaration in declarations]
+                        for selector in selectors:
+                            matcher.add_selector(selector, declarations)
+                            if selector.pseudo_element not in PSEUDO_ELEMENTS:
+                                prelude = tinycss2.serialize(rule.prelude)
+                                if selector.pseudo_element.startswith('-'):
+                                    logger_level = DEBUG
+                                    raise cssselect2.SelectorError(
+                                        f"'{prelude}', "
+                                        'ignored prefixed pseudo-element: '
+                                        f'{selector.pseudo_element}')
+                                else:
+                                    raise cssselect2.SelectorError(
+                                        f"'{prelude}', "
+                                        'unknown pseudo-element: '
+                                        f'{selector.pseudo_element}')
+                        ignore_imports = True
+                else:
                     ignore_imports = True
-                except cssselect2.SelectorError as exc:
-                    LOGGER.log(
-                        logger_level,
-                        "Invalid or unsupported selector '%s', %s",
-                        tinycss2.serialize(rule.prelude), exc)
-                    continue
-            else:
-                ignore_imports = True
+            except cssselect2.SelectorError as exc:
+                LOGGER.log(
+                    logger_level,
+                    "Invalid or unsupported selector, %s", exc)
+                continue
 
         elif rule.type == 'at-rule' and rule.lower_at_keyword == 'import':
             if ignore_imports:
@@ -1026,7 +1036,7 @@ def preprocess_stylesheet(device_media_type, base_url, stylesheet_rules,
             for page_type in data:
                 specificity = page_type.pop('specificity')
                 page_type = PageType(**page_type)
-                content = tinycss2.parse_declaration_list(rule.content)
+                content = tinycss2.parse_blocks_contents(rule.content)
                 declarations = list(preprocess_declarations(base_url, content))
 
                 if declarations:
@@ -1039,7 +1049,7 @@ def preprocess_stylesheet(device_media_type, base_url, stylesheet_rules,
                         continue
                     declarations = list(preprocess_declarations(
                         base_url,
-                        tinycss2.parse_declaration_list(margin_rule.content)))
+                        tinycss2.parse_blocks_contents(margin_rule.content)))
                     if declarations:
                         selector_list = [(
                             specificity, f'@{margin_rule.lower_at_keyword}',
@@ -1049,7 +1059,7 @@ def preprocess_stylesheet(device_media_type, base_url, stylesheet_rules,
 
         elif rule.type == 'at-rule' and rule.lower_at_keyword == 'font-face':
             ignore_imports = True
-            content = tinycss2.parse_declaration_list(rule.content)
+            content = tinycss2.parse_blocks_contents(rule.content)
             rule_descriptors = dict(
                 preprocess_descriptors('font-face', base_url, content))
             for key in ('src', 'font_family'):
@@ -1076,7 +1086,7 @@ def preprocess_stylesheet(device_media_type, base_url, stylesheet_rules,
                 continue
 
             ignore_imports = True
-            content = tinycss2.parse_declaration_list(rule.content)
+            content = tinycss2.parse_blocks_contents(rule.content)
             counter = {
                 'system': None,
                 'negative': None,

weasyprint/css/validation/__init__.py

@@ -1,7 +1,10 @@
 """Validate properties, expanders and descriptors."""
 
 
-from tinycss2 import serialize
+from cssselect2 import SelectorError, compile_selector_list
+from tinycss2 import parse_blocks_contents, serialize
+from tinycss2.ast import (
+    FunctionBlock, IdentToken, LiteralToken, WhitespaceToken)
 
 from ... import LOGGER
 from ..utils import InvalidValues, remove_whitespace
@@ -104,23 +107,69 @@
     'scrollbar-gutter',
     'scrollbar-width',
 }
+NESTING_SELECTOR = LiteralToken(1, 1, '&')
+ROOT_TOKEN = LiteralToken(1, 1, ':'), IdentToken(1, 1, 'root')
 
 
-def preprocess_declarations(base_url, declarations):
+def preprocess_declarations(base_url, declarations, prelude=None):
     """Expand shorthand properties, filter unsupported properties and values.
 
     Log a warning for every ignored declaration.
 
     Return a iterable of ``(name, value, important)`` tuples.
 
     """
+    # Compile list of selectors.
+    if prelude is not None:
+        try:
+            if NESTING_SELECTOR in prelude:
+                # Handle & selector in non-nested rule. MDN explains that & is
+                # then equivalent to :scope, and :scope is equivalent to :root
+                # as we don’t support :scope yet.
+                original_prelude, prelude = prelude, []
+                for token in original_prelude:
+                    if token == NESTING_SELECTOR:
+                        prelude.extend(ROOT_TOKEN)
+                    else:
+                        prelude.append(token)
+            selectors = compile_selector_list(prelude)
+        except SelectorError:
+            raise SelectorError(f"'{serialize(prelude)}'")
+
+    # Yield declarations.
+    is_token = LiteralToken(1, 1, ':'), FunctionBlock(1, 1, 'is', prelude)
     for declaration in declarations:
         if declaration.type == 'error':
             LOGGER.warning(
                 'Error: %s at %d:%d.',
                 declaration.message,
                 declaration.source_line, declaration.source_column)
 
+        if declaration.type == 'qualified-rule':
+            # Nested rule.
+            if prelude is None:
+                continue
+            declaration_prelude = declaration.prelude
+            if NESTING_SELECTOR in declaration.prelude:
+                # Replace & selector by parent.
+                declaration_prelude = []
+                for token in declaration.prelude:
+                    if token == NESTING_SELECTOR:
+                        declaration_prelude.extend(is_token)
+                    else:
+                        declaration_prelude.append(token)
+            else:
+                # No & selector, prepend parent.
+                is_token = (
+                    LiteralToken(1, 1, ':'),
+                    FunctionBlock(1, 1, 'is', prelude))
+                declaration_prelude = [
+                    *is_token, WhitespaceToken(1, 1, ' '),
+                    *declaration.prelude]
+            yield from preprocess_declarations(
+                base_url, parse_blocks_contents(declaration.content),
+                declaration_prelude)
+
         if declaration.type != 'declaration':
             continue
 
@@ -183,4 +232,8 @@ def validation_error(level, reason):
 
         important = declaration.important
         for long_name, value in result:
-            yield long_name.replace('-', '_'), value, important
+            if prelude is not None:
+                declaration = (long_name.replace('-', '_'), value, important)
+                yield selectors, declaration
+            else:
+                yield long_name.replace('-', '_'), value, important

weasyprint/svg/css.py

@@ -35,7 +35,7 @@ def parse_declarations(input):
     """Parse declarations in a given rule content."""
     normal_declarations = []
     important_declarations = []
-    for declaration in tinycss2.parse_declaration_list(input):
+    for declaration in tinycss2.parse_blocks_contents(input):
         # TODO: warn on error
         # if declaration.type == 'error':
         if (declaration.type == 'declaration' and