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🐛 fix(convert): css_to_xpath empty value with i flag - #1086
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`css_to_xpath` translated `[att|="" i]`, and `p[lang|=""]` through HTML's [case-insensitive attribute list](https://html.spec.whatwg.org/multipage/semantics-other.html#case-sensitivity-of-selectors), into `translate(@att, ...) = '' or starts-with(...)`. [`string()` of an empty node-set](https://www.w3.org/TR/1999/REC-xpath-19991116/#function-string) is the empty string, so the expression also matched elements without the attribute, while [Selectors 4](https://www.w3.org/TR/selectors-4/#attribute-representation) matches `[att|=val]` only on elements that have `att`. The translation now requires the attribute before comparing its folded empty value, the guard #1086 added for `=`. A non-empty `|=` value never matches an empty string, and `^=`, `$=`, `*=` and `~=` already translate an empty value to `false()`, so the other cases keep their output. On `<div><p id=none></p><p id=empty d=""></p><p id=dash d="-x"></p></div>`, the XPath for `[d|="" i]` on lxml 6.1.3 now selects `empty` and `dash`, the same elements as `select()`. [cssselect 1.5.0](https://github.com/scrapy/cssselect/blob/v1.5.0/cssselect/xpath.py#L794-L804) wraps every `|=` match in the same presence guard, and it rejects the `i` flag with a syntax error. closes #1109
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css_to_xpathtranslated an attribute selector with an empty value and theiflag, such as[d="" i], intotranslate(@d, ...) = '', which also matches elements without the attribute becausetranslate()of an absent attribute is the empty string.The translation now requires the attribute before comparing its folded value, since XPath 1.0 turns an empty node-set into the empty string that
translate()then returns, while Selectors 4 matches[att=val]only on elements that haveatt, and itsiflag changes only how the value compares. It now selects the same elements asselect().Neither cssselect 1.5.0 nor css-to-xpath 0.1.0 parses the
iflag; both raise a syntax error on[d="" i].closes #1040