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<title>Issue 2625: [filesys.ts] [PDTS] Copying equivalent paths effects not specified</title>
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<p><em>This page is a snapshot from the LWG issues list, see the <a href="lwg-active.html">Library Active Issues List</a> for more information and the meaning of <a href="lwg-active.html#TS">TS</a> status.</em></p>
<h3 id="2625"><a href="lwg-defects.html#2625">2625</a>. [filesys.ts] [PDTS] Copying equivalent paths effects not specified</h3>
<p><b>Section:</b> 15.4 [filesys.ts::fs.op.copy_file] <b>Status:</b> <a href="lwg-active.html#TS">TS</a>
 <b>Submitter:</b> CH-15 <b>Opened:</b> 2014-01-20 <b>Last modified:</b> 2017-07-30</p>
<p><b>Priority: </b>Not Prioritized
</p>
<p><b>View all issues with</b> <a href="lwg-status.html#TS">TS</a> status.</p>
<p><b>Discussion:</b></p>
<p><b>Addresses: filesys.ts</b></p>
<p>Even if <code>to</code> and <code>from</code> are different paths, they may be equivalent.</p>

<p>Specify what happens if <code>(options &amp; copy_options::overwrite_existing)</code> but <code>from</code> and <code>to</code>
resolve to the same file.</p>

  <p><i>[2014-02-09, Beman Dawes: Need advice on this issue:]</i></p>


  <p/>What do existing implentations do?

  <p/>Possible resolutions:
  <ol>
    <li>Treat it as an error.</li>
    <li>Once equivalence is determined, take no further action and return true? false?</li>
    <li>Don't bother to detect a file overwriting itself. This will likely result in an error, anyhow.</li>
  </ol>
  <p><i>[2014-02-13 LWG/SG-3 Issaquah: LWG/SG-3 decided to treat equivalence in this case as an error.
  Beman to provide wording.]</i></p>


  <p><i>[2014-04-09 Beman provided wording as requested. The Effects were rewritten to increase
  clarity. Behavior remains unchanged except for treating equivalence as an error.]</i></p>


  <p><i>[17 Jun 2014 Rapperswil LWG moves to Immediate. Jonathan Wakely will provide editorial
  changes to improve the presentation of bitmask values.]</i></p>




<p id="res-2625"><b>Proposed resolution:</b></p>
  <p/>
  <i>Change 15.4 [fs.op.copy_file]:</i>

  <blockquote>
    <p>
      <i>Precondition:</i> At most one constant from each <code>copy_options</code>
      option group ([enum.copy_options]) is present
      in <code>options</code>.
    </p>

    <p>
      <i>Effects:</i>
    </p>
    <blockquote>
      
        <p><del>
          If&nbsp; <code>exists(to) &amp;&amp;</code> <code>
            !(options &amp; (copy_options::skip_existing
            | copy_options::overwrite_existing | copy_options::update_existing))
          </code> report a
          file already exists error as specified in Error reporting (7).
        </del></p>
      
      
        <p><del>
          If <code>
            !exists(to) || (options &amp; copy_options::overwrite_existing) || ((options &amp; copy_options::update_existing)
            &amp;&amp; last_write_time(from) &gt; last_write_time(to)) || !(options &amp; (copy_options::skip_existing
            | copy_options::overwrite_existing | copy_options::update_existing))
          </code> copy the contents and attributes of the file <code>from</code>
          resolves to  the file <code>to</code> resolves to.
        </del></p>
      
    </blockquote>
    <blockquote>
      
        <p>
          <ins>
            Report a file already exists error as specified in
            Error reporting (7)
            if:
          </ins>
        </p>
        <ul>
          <li><ins>
              <ins><code>exists(to)</code> and <code>equivalent(from, to)</code>,
              or</ins>
          </ins></li>
          <li><ins>
              <code>exists(to)</code> and <code>
                (options &amp; (copy_options::skip_existing
                | copy_options::overwrite_existing | copy_options::update_existing)) == copy_options::none.
              </code>
          </ins></li>
        </ul>
        <p><ins>
          Otherwise copy the contents and attributes of the file <code>from</code>
          resolves to to the file <code>to</code> resolves to if:
          </ins></p>
        <ul>
          <li><ins>
              <code>!exists(to)</code>, or
          </ins></li>
          <li><ins>
            <code>exists(to)</code> and <code>
              (options &amp;
              copy_options::overwrite_existing) != copy_options::none
            </code>, or
          </ins></li>
          <li><ins>
            <code>exists(to)</code> and <code>
              (options &amp;
              copy_options::update_existing) != copy_options::none
            </code> and <code>from</code> is more
            recent than <code>to</code>, determined as if by use of the <code>
              last_write_time
            </code> function.
          </ins></li>
        </ul>
        <p><ins>Otherwise no effects.</ins></p>
      
    </blockquote>

    <p>
      <i>Returns</i>: <code>true</code> if the <code>from</code> file
      was copied, otherwise <code>false</code>. The signature with argument <code>ec</code> return
      <code>false</code> if an error occurs.
    </p>
    <p>
      <i>Throws:</i> As specified in Error reporting (7).
    </p>
    <p>
      <i>Complexity:</i> At most one direct or indirect invocation of <code>
        status(to)</code>.
    </p>
  </blockquote>
  





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