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    <head>
      <base href="https://llvm.org/bugs/" />
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    <body><table border="1" cellspacing="0" cellpadding="8">
        <tr>
          <th>Bug ID</th>
          <td><a class="bz_bug_link 
          bz_status_NEW " title="NEW --- - preprocessor should warn on #include_next with a filename different from the including name" href="https://urldefense.proofpoint.com/v2/url?u=https-3A__llvm.org_bugs_show-5Fbug.cgi-3Fid-3D23750&d=AwMBaQ&c=8hUWFZcy2Z-Za5rBPlktOQ&r=pF93YEPyB-J_PERP4DUZOJDzFVX5ZQ57vQk33wu0vio&m=z9a5jae6zzVuEA2m-jHlnHQWCQf42J9GeLcVXVOW6a4&s=l1EsniSR9K3Utsc7DUjKOxZXwtr2jGfBjGhKmYfxkq8&e=">23750</a>
          </td>
        </tr>

        <tr>
          <th>Summary</th>
          <td>preprocessor should warn on #include_next with a filename different from the including name
          </td>
        </tr>

        <tr>
          <th>Product</th>
          <td>clang
          </td>
        </tr>

        <tr>
          <th>Version</th>
          <td>trunk
          </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>normal
          </td>
        </tr>

        <tr>
          <th>Priority</th>
          <td>P
          </td>
        </tr>

        <tr>
          <th>Component</th>
          <td>Frontend
          </td>
        </tr>

        <tr>
          <th>Assignee</th>
          <td>unassignedclangbugs@nondot.org
          </td>
        </tr>

        <tr>
          <th>Reporter</th>
          <td>richard-llvm@metafoo.co.uk
          </td>
        </tr>

        <tr>
          <th>CC</th>
          <td>llvmbugs@cs.uiuc.edu
          </td>
        </tr>

        <tr>
          <th>Classification</th>
          <td>Unclassified
          </td>
        </tr></table>
      <p>
        <div>
        <pre>Suppose:

main.cpp:
#include "foo/bar.h"

foo/bar.h:
#pragma once // or an include guard
#include_next "bar.h"

baz/bar.h:
extern int n;


... and we compile main.cpp with -Ifoo -Ibaz:

  main.cpp includes foo/bar.h
  foo/bar.h includes *itself*

Note that baz/bar.h is never included, and confusion reigns.

We should issue a warning if a file issues a #include_once with a name that
would not have found that same file in the starting search directory for the
#include_next search (that is, if the includer used the wrong name for the
file).</pre>
        </div>
      </p>
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