Problem with alignat

[ahaselbacher]

I've run into a problem running latexdiff on files containing alignat. With this file, called temp-old.tex

\documentclass{article}
\begin{document}
Hello this was a test.
\end{document} 

and temp.tex

\documentclass{article}
\usepackage{amsmath}
\begin{document}
Hello this is a test.
\begin{alignat}{3}
  a& = b &\quad & \text{if} & \quad & x\ne y\\
  c& = d &      & \text{if} &       & x = y
\end{alignat}    
\end{document}

and running

latexdiff temp-old.tex temp.tex > diff.tex
pdflatex diff.tex

I get the error

! Missing number, treated as zero.
<to be read again> 
                   {
l.46 \DIFaddbegin \begin{alignat}{\DIFadd{3}}

This is not surprising because diff.tex contains

\DIFaddbegin \begin{alignat}{\DIFadd{3}}
  \DIFadd{a}& \DIFadd{= b }&\DIFadd{\quad }& \DIFadd{\text{if} }& \DIFadd{\quad }& \DIFadd{x\ne y}\\
  \DIFadd{c}& \DIFadd{= d }&      & \DIFadd{\text{if} }&       & \DIFadd{x = y
}\end{alignat}

When changed to

\DIFaddbegin \begin{alignat}{3}
  \DIFadd{a}& \DIFadd{= b }&\DIFadd{\quad }& \DIFadd{\text{if} }& \DIFadd{\quad }& \DIFadd{x\ne y}\\
  \DIFadd{c}& \DIFadd{= d }&      & \DIFadd{\text{if} }&       & \DIFadd{x = y
}\end{alignat}

everything works.

[ahaselbacher]

Btw, I'm running This is LATEXDIFF 1.3.1.1 (Algorithm::Diff 1.15 so, Perl v5.30.2) on Mac OS 11.6 with LaTeX2e <2021-06-01> patch level 1

[ftilmann]

Running this with --mathmode=FINE worked for me but might cause other problems. In any case it should be fixed properly with commit 5d7ebb4 . Thanks for reporting.