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soup: the attribute-operators empty-value rule has no test coverage #192
Description
What
The empty-value rule for the attribute operators is documented but has no test coverage. _attr_operator_matches states it:
The empty-value cases follow the CSS spec:
~=,^=,$=and*=never match an empty expected.
Removing the bool(expected) guard from any of the five operators leaves soup/test_soup_correctness.py green at 175 passed, checked one at a time. Nothing in the suite would notice.
Evidence
At 75d09b4 (the #182 merge; soup/soup.py is byte-identical to the reviewed 291042d), on
<p><b class="x" data-empty="">1</b><b class="x" data-v="a">2</b><b>3</b></p>| mutation | suite | selector | before | after | soupsieve 2.10 |
|---|---|---|---|---|---|
^=: drop bool(expected) and |
175 passed | b[class^=""] |
[] |
['1', '2'] |
[] |
$=: drop bool(expected) and |
175 passed | b[class$=""] |
[] |
['1', '2'] |
[] |
*=: drop bool(expected) and |
175 passed | b[class*=""] |
[] |
['1', '2'] |
[] |
~=: drop bool(expected) and |
175 passed | b[class~=""] |
[] |
[] |
[] |
|=: require a non-empty expected |
175 passed | b[data-empty|=""] |
['1'] |
[] |
['1'] |
The three substring operators are the ones that matter, and they fail in the direction #182 exists to prevent: with the guard gone, [class^=""] stops meaning "no match" and starts matching every element that carries the attribute. |= is load-bearing the other way, since its empty-value branch is what matches an empty attribute value, so that mutation under-matches instead. ~='s guard is inert either way, because "" in text.split() is already false.
Fix
Add the empty case to the operator matrix so it is compared against the reference like the rest of the matrix already is:
[attr~=""],[attr^=""],[attr$=""],[attr*=""]-> no match[attr|=""]-> matches an empty attribute value
Against an attribute that is present and empty and one present and non-empty, since the present-and-empty case is what makes the rule visible at all.
Behaviour today is correct: all 15 attribute/operator combinations agree with soupsieve 2.10. This is a coverage gap rather than a defect, which is why #182 merged with it.
Related: #187 (legacy case-insensitive attributes), #191 (a quoted comma in a selector list).
Activity
fix(soup): match the spec for |= with an empty expected
test(soup): cover the attribute-operator empty-value rule
fix(soup): match the spec for |= with an empty expected