rustc has a test for annotating ano-break space near the start of a line with whitespace following it.annotate-snippets currently fails this test because it usesstd::char::is_whitespace for calculatingwhitespace_left, which treatsno-break space as whitespace, leadingwhitespace_left to be larger thanlabel_right, which causes a subtract with overflow panic.rustc gets around this by usingrustc_parse::is_whitespace, which does not treat a no-break space as whitespace. That solution only masks the problem, as it would still panic when annotating whitespace chars with more whitespace following them. Instead, this PR fixes theMargin calculations to allow annotating whitespace before more whitespace.