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 735 <body class="article">
 736 <div id="header">
 737 <h1>Error reporting in git</h1>
 738 <span id="revdate">2024-04-15</span>
 739 </div>
 740 <div id="content">
 741 <div id="preamble">
 742 <div class="sectionbody">
 743 <div class="paragraph"><p><code>BUG</code>, <code>bug</code>, <code>die</code>, <code>usage</code>, <code>error</code>, and <code>warning</code> report errors of
 744 various kinds.</p></div>
 745 <div class="ulist"><ul>
 746 <li>
 747 <p>
 748 <code>BUG</code> is for failed internal assertions that should never happen,
 749   i.e. a bug in git itself.
 750 </p>
 751 </li>
 752 <li>
 753 <p>
 754 <code>bug</code> (lower-case, not <code>BUG</code>) is supposed to be used like <code>BUG</code> but
 755   prints a "BUG" message instead of calling <code>abort()</code>.
 756 </p>
 757 <div class="paragraph"><p>A call to <code>bug()</code> will then result in a "real" call to the <code>BUG()</code>
 758 function, either explicitly by invoking <code>BUG_if_bug()</code> after call(s)
 759 to <code>bug()</code>, or implicitly at <code>exit()</code> time where we&#8217;ll check if we
 760 encountered any outstanding <code>bug()</code> invocations.</p></div>
 761 <div class="paragraph"><p>If there were no prior calls to <code>bug()</code> before invoking <code>BUG_if_bug()</code>
 762 the latter is a NOOP. The <code>BUG_if_bug()</code> function takes the same
 763 arguments as <code>BUG()</code> itself. Calling <code>BUG_if_bug()</code> explicitly isn&#8217;t
 764 necessary, but ensures that we die as soon as possible.</p></div>
 765 <div class="paragraph"><p>If you know you had prior calls to <code>bug()</code> then calling <code>BUG()</code> itself
 766 is equivalent to calling <code>BUG_if_bug()</code>, the latter being a wrapper
 767 calling <code>BUG()</code> if we&#8217;ve set a flag indicating that we&#8217;ve called
 768 <code>bug()</code>.</p></div>
 769 <div class="paragraph"><p>This is for the convenience of APIs who&#8217;d like to potentially report
 770 more than one "bug", such as the optbug() validation in
 771 parse-options.c.</p></div>
 772 </li>
 773 <li>
 774 <p>
 775 <code>die</code> is for fatal application errors.  It prints a message to
 776   the user and exits with status 128.
 777 </p>
 778 </li>
 779 <li>
 780 <p>
 781 <code>usage</code> is for errors in command line usage.  After printing its
 782   message, it exits with status 129.  (See also <code>usage_with_options</code>
 783   in the <a href="api-parse-options.html">parse-options API</a>.)
 784 </p>
 785 </li>
 786 <li>
 787 <p>
 788 <code>error</code> is for non-fatal library errors.  It prints a message
 789   to the user and returns -1 for convenience in signaling the error
 790   to the caller.
 791 </p>
 792 </li>
 793 <li>
 794 <p>
 795 <code>warning</code> is for reporting situations that probably should not
 796   occur but which the user (and Git) can continue to work around
 797   without running into too many problems.  Like <code>error</code>, it
 798   returns -1 after reporting the situation to the caller.
 799 </p>
 800 </li>
 801 </ul></div>
 802 <div class="paragraph"><p>These reports will be logged via the trace2 facility. See the "error"
 803 event in <a href="api-trace2.html">trace2 API</a>.</p></div>
 804 </div>
 805 </div>
 806 <div class="sect1">
 807 <h2 id="_customizable_error_handlers">Customizable error handlers</h2>
 808 <div class="sectionbody">
 809 <div class="paragraph"><p>The default behavior of <code>die</code> and <code>error</code> is to write a message to
 810 stderr and then exit or return as appropriate.  This behavior can be
 811 overridden using <code>set_die_routine</code> and <code>set_error_routine</code>.  For
 812 example, "git daemon" uses set_die_routine to write the reason <code>die</code>
 813 was called to syslog before exiting.</p></div>
 814 </div>
 815 </div>
 816 <div class="sect1">
 817 <h2 id="_library_errors">Library errors</h2>
 818 <div class="sectionbody">
 819 <div class="paragraph"><p>Functions return a negative integer on error.  Details beyond that
 820 vary from function to function:</p></div>
 821 <div class="ulist"><ul>
 822 <li>
 823 <p>
 824 Some functions return -1 for all errors.  Others return a more
 825   specific value depending on how the caller might want to react
 826   to the error.
 827 </p>
 828 </li>
 829 <li>
 830 <p>
 831 Some functions report the error to stderr with <code>error</code>,
 832   while others leave that for the caller to do.
 833 </p>
 834 </li>
 835 <li>
 836 <p>
 837 errno is not meaningful on return from most functions (except
 838   for thin wrappers for system calls).
 839 </p>
 840 </li>
 841 </ul></div>
 842 <div class="paragraph"><p>Check the function&#8217;s API documentation to be sure.</p></div>
 843 </div>
 844 </div>
 845 <div class="sect1">
 846 <h2 id="_caller_handled_errors">Caller-handled errors</h2>
 847 <div class="sectionbody">
 848 <div class="paragraph"><p>An increasing number of functions take a parameter <em>struct strbuf *err</em>.
 849 On error, such functions append a message about what went wrong to the
 850 <em>err</em> strbuf.  The message is meant to be complete enough to be passed
 851 to <code>die</code> or <code>error</code> as-is.  For example:</p></div>
 852 <div class="literalblock">
 853 <div class="content">
 854 <pre><code>if (ref_transaction_commit(transaction, &amp;err))
 855         die("%s", err.buf);</code></pre>
 856 </div></div>
 857 <div class="paragraph"><p>The <em>err</em> parameter will be untouched if no error occurred, so multiple
 858 function calls can be chained:</p></div>
 859 <div class="literalblock">
 860 <div class="content">
 861 <pre><code>t = ref_transaction_begin(&amp;err);
 862 if (!t ||
 863     ref_transaction_update(t, "HEAD", ..., &amp;err) ||
 864     ret_transaction_commit(t, &amp;err))
 865         die("%s", err.buf);</code></pre>
 866 </div></div>
 867 <div class="paragraph"><p>The <em>err</em> parameter must be a pointer to a valid strbuf.  To silence
 868 a message, pass a strbuf that is explicitly ignored:</p></div>
 869 <div class="literalblock">
 870 <div class="content">
 871 <pre><code>if (thing_that_can_fail_in_an_ignorable_way(..., &amp;err))
 872         /* This failure is okay. */
 873         strbuf_reset(&amp;err);</code></pre>
 874 </div></div>
 875 </div>
 876 </div>
 877 </div>
 878 <div id="footnotes"><hr /></div>
 879 <div id="footer">
 880 <div id="footer-text">
 881 Last updated
 882  2022-09-21 15:44:34 PDT
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