Thursday, October 16, 2008

Fixing bug in hyperref's autoref: amsmath-type equations under items get "item" label

Earlier this year, in a comp.text.tex posting, I discussed a bug I found in hyperref. That bug was then fixed in hyperref 6.77a, but there are still plenty of old packages hanging around that have this bug (for example, the hyperref from TeXLive 2007 on my system that I still haven't upgraded to TeXLive 2008).

The problem happens when
  • amsmath (or mathtools) is loaded.
  • An equation (or any other type of displayed-math environment) environment with labels occurs INSIDE an enumerated item.
  • You try to use \autoref to generate a reference to one of those equation labels later.
The \autoref macro will not properly return an "Equation" label (e.g., "Equation 1"). Instead, it will return an "item" label (e.g., "item 1").

To fix this problem, I use these lines of code just after I load hyperref in my preamble:
    \expandafter\let\csname old#1\expandafter\endcsname%
        \csname #1\endcsname%
    \expandafter\renewcommand\csname #1\endcsname{%
        \@hyper@itemfalse\csname old#1\endcsname}}
The \AMShreffix (i.e., AMS-href-fix) macro "fixes" the displayed-math environment that you pass it. This example fixes equation, align, and gather. If you want to fix alignat too, add a \AMShreffix{alignat} at the end of those lines. Make similar changes for your other displayed-math environments (e.g., flalign and multline too).

That fix changes all of the improper "item" labels back into proper "Equation" labels.

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