<p><code>List of <a href="../build-ref.html#labels">labels</a>; optional</code></p>

<p>
A list of
<code><a href="platform.html#constraint_value">constraint_values</a></code>
that must be present in the execution platform for this target. This is in
addition to any constraints already set by the rule type. Constraints are used
to restrict the list of available execution platforms, see the description of
<a href="../toolchains.html#toolchain-resolution">toolchain resolution</a> for
details.
</p>

<p>
This attribute is available only on <code><a href="general.html#genrule">genrule</a></code>,
<a href="shell.html">shell rules</a>, and all test rules (*_test).
</p>