<html>
<head>
<base href="https://bugs.llvm.org/">
</head>
<body><table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Bug ID</th>
<td><a class="bz_bug_link
bz_status_NEW "
title="NEW - Headers containing just #error harm __has_include"
href="https://bugs.llvm.org/show_bug.cgi?id=39749">39749</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>Headers containing just #error harm __has_include
</td>
</tr>
<tr>
<th>Product</th>
<td>libc++
</td>
</tr>
<tr>
<th>Version</th>
<td>unspecified
</td>
</tr>
<tr>
<th>Hardware</th>
<td>PC
</td>
</tr>
<tr>
<th>OS</th>
<td>Linux
</td>
</tr>
<tr>
<th>Status</th>
<td>NEW
</td>
</tr>
<tr>
<th>Severity</th>
<td>enhancement
</td>
</tr>
<tr>
<th>Priority</th>
<td>P
</td>
</tr>
<tr>
<th>Component</th>
<td>All Bugs
</td>
</tr>
<tr>
<th>Assignee</th>
<td>unassignedclangbugs@nondot.org
</td>
</tr>
<tr>
<th>Reporter</th>
<td>bmerry@gmail.com
</td>
</tr>
<tr>
<th>CC</th>
<td>llvm-bugs@lists.llvm.org, mclow.lists@gmail.com
</td>
</tr></table>
<p>
<div>
<pre>It looks like the latest version of <experimental/optional>
(<a href="https://llvm.org/svn/llvm-project/libcxx/trunk/include/experimental/optional">https://llvm.org/svn/llvm-project/libcxx/trunk/include/experimental/optional</a>)
consists only of a #error to tell the user that it isn't supported anymore.
While a helpful error, it will presumably(*) break any code that uses
__has_include to detect whether this header is supported (as recommended by
N4480).
The same applies to <experimental/string_view>, and I'm guessing others
although I haven't checked.
(*) I haven't yet got my own build of libc++ trunk to verify experimentally, so
if there is some compiler magic to know that __has_include should be 0 for
these special cases then I'm less worried.</pre>
</div>
</p>
<hr>
<span>You are receiving this mail because:</span>
<ul>
<li>You are on the CC list for the bug.</li>
</ul>
</body>
</html>