[wleeaf]

A link destination may contain parentheses only if they are escaped or part of a balanced pair. LinkScanner.scanLinkDestinationWithBalancedParens checks the balance when it sees ), but returns success at a space, a control character (including the line ending) or the end of the input without checking that all opened parentheses were closed. For inline links the following ) check catches this. For link reference definitions it does not, so invalid definitions are accepted and their text disappears:

Markdown	cmark / commonmark.js	commonmark-java
[foo]: (	<p>[foo]: (</p>	(nothing)
[foo]: (\nbar	<p>[foo]: (\nbar</p>	<p>bar</p>
[foo]: a(b\n\n[foo]	<p>[foo]: a(b</p>\n<p>[foo]</p>	<p><a href="a(b">foo</a></p>

The three exits now also require parens == 0. Valid destinations such as a(b) and inline links are unaffected.

Added SpecialInputTest.linkReferenceDefinitionWithUnbalancedParens; it fails before the change and passes after. mvn test passes, except that PathologicalTest.paragraphOfLinesThatTryBlockStarts hit its 3 s timeout once on a heavily loaded machine. That test is unrelated and passes when run on its own, on main as well as on this branch. spotless:check is clean.

Found by differential testing against cmark.

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