Error on using math in section name with hyperref

[navdeeprana]

Description

I get the following error

Package hyperref Warning: Token not allowed in a PDF string (Unicode): removing `math shift'
Package hyperref Warning: Token not allowed in a PDF string (Unicode): removing `math shift'
Error: Improper alphabetic constant.
Error: Fatal error occurred, no output PDF file produced!

when I compile the following code

\documentclass[a4,12pt]{report}                                                                                                
\usepackage{fontspec}      
\usepackage{libertine}                                                                                                         
\usepackage{unicode-math}                                                                                                      
\usepackage[unicode=true]{hyperref}                                                                                            
\begin{document}                                                                                                               
\section{$\lambda = 1$}                                                                                                              
\end{document}    

Add info or delete as appropriate:

• Relevant for XeTeX
• Relevant for LuaTeX

#530 says something similar, but there it's a warning.

[navdeeprana]

Some digging in stackoverflow yields the following solution

\usepackage[unicode=true,psdextra]{hyperref}

Is this the correct way to resolve the issue?

[davidcarlisle]

I would guess this is more of a hyperref issue unicode. actually two issues

• probably psdextra probably ought to be set by default for luatex and xetex

and

• for the actual error itself that is already logged as
  problems with commands let to a char. hyperref#63

although that does leave the remaining unicode-math issue over whether \let is the best definition form to use here (as opposed to say \def or \Umathchardef )

[ArchangeGabriel]

Oh, I always \texorpdfstring{}{}’ed those assuming math in PDF toc wasn’t supported. Now I’ll have to try psdextra. :)