This is a way to shrink call spans that doesn't involve mixing different spans,
and avoids overlap with argument spans.
This patch also removes some low-value comments that were causing rustfmt to
ignore the match arms.
For coverage tests, splitting code across multiple lines often makes the
resulting coverage report easier to interpret, so we force rustfmt to retain
line breaks by adding dummy line comments with `//`.
These tests deliberately use non-standard formatting, so that the line
execution counts reported by `llvm-cov` reveal additional information about
where code regions begin and end.
