He is talking about the whole sidebar, hence a region, not a block.
hook_block() will not help here.
In the past we have done it by setting the visibility PHP code for each
block
in a given region, and that would make the entire sidebar invisible if
the
conditions are met. It is a pain if you have more than a few blocks in
that
region (right side bar for example).
You said you don't want it in the theme, but it would be a simple
change in
page.tpl.php
<?php if ($right): ?>
<?php if (
!custom_visibility_function()) ?>
<div id="sidebar-right" class="sidebar">
<?php print $right ?>
</div>
<?php endif; ?>
<?php endif; ?>
The other option is to use preprocess_block(). Perhaps something like
this in
template.php
<?php
function phptemplate_preprocess_block(&$variables) {
if ($variables['block']->region = 'right') {
if (!custom_visibility_function()) {
unset($variables['block'];
}
}
}
?>
Still in the theme though.