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LibWeb: Correct handling of negative step values in nth-foo() selectors
This should be 1% on Acid3. :^) Added the `-5n+3` case to all `nth-of-whatever()` selector test pages, so we can easily check that it works.
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5 changed files with 123 additions and 18 deletions
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@ -179,13 +179,21 @@ static inline bool matches_pseudo_class(CSS::Selector::SimpleSelector::PseudoCla
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VERIFY_NOT_REACHED();
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}
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if (step_size < 0) {
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// When "step_size" is negative, selector represents first "offset" elements in document tree.
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// When "step_size == -1", selector represents first "offset" elements in document tree.
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if (step_size == -1)
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return !(offset <= 0 || index > offset);
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} else if (step_size == 1) {
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// When "step_size == 1", selector represents last "offset" elements in document tree.
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// When "step_size == 1", selector represents last "offset" elements in document tree.
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if (step_size == 1)
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return !(offset < 0 || index < offset);
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}
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// When "step_size == 0", selector picks only the "offset" element.
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if (step_size == 0)
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return index == offset;
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// If both are negative, nothing can match.
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if (step_size < 0 && offset < 0)
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return false;
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// Like "a % b", but handles negative integers correctly.
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auto const canonical_modulo = [](int a, int b) -> int {
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@ -196,15 +204,12 @@ static inline bool matches_pseudo_class(CSS::Selector::SimpleSelector::PseudoCla
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return c;
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};
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if (step_size == 0) {
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// Avoid divide by zero.
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if (index != offset) {
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return false;
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}
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} else if (canonical_modulo(index - offset, step_size) != 0) {
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return false;
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}
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return true;
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// When "step_size < 0", we start at "offset" and count backwards.
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if (step_size < 0)
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return index <= offset && canonical_modulo(index - offset, -step_size) == 0;
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// Otherwise, we start at "offset" and count forwards.
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return index >= offset && canonical_modulo(index - offset, step_size) == 0;
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}
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return false;
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