Line breaking gives up without errors for very long line

[muzimuzhi]

(initially raised in T-F-S/tcolorbox#304 (comment))

When the code line is so long that \FV@LineBox is wider than \maxdimen, a "Dimension too large" error is raised when comparing width of \FV@LineBox to some dimension

fvextra/fvextra/fvextra.dtx

Line 7039 in 25ac61f

\ifdim\wd\FV@LineBox>\FV@LineWidth

But if the code line is even longer, no error is raised and the line breaking mechanism just gives up.

\documentclass{article}
\usepackage{fvextra}

\begin{document}
\Huge
% this triggers "Dimension too large" error, but a 3x long code line doesn't
\begin{Verbatim}[breaklines, breakanywhere]
abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,
\end{Verbatim}
\end{document}

[muzimuzhi]

Oh, the width of box also overflows.

\documentclass{article}
\begin{document}
\setbox0=\hbox{\hskip\maxdimen}
\the\wd0 % 16383.99998pt

\setbox0=\hbox{\hskip\maxdimen\hskip\maxdimen}
\the\wd0 % 32767.99997pt

\setbox0=\hbox{\hskip\maxdimen\hskip\maxdimen\hskip1pt}
\the\wd0 % -32767.00003pt, overflows
\end{document}

Meanwhile, replacing \ifdim with latex3 floating-point conditional function, the error "Dimension too large" can be avoided and the line breaking mechanism can even work for the case when width of \FV@LineBox overflows.

Of course this doesn't break the limitation that a broken line cannot across multiple pages (see general description in sec. 7 "Line Breaking" and the doc of breaklines in sec. 7.1, in package doc, which were added by 52fe9fa).

\usepackage{xpatch}
\makeatletter
\xpatchcmd\FV@ListProcessLine@Break
  {\ifdim\wd\FV@LineBox>\FV@LineWidth}
  {%
    \ifnum
      \FV@iffp{\the\wd\FV@LineBox}>{\FV@LineWidth}{1}{0}%
      % in case the box width overflows
      \FV@iffp{\the\wd\FV@LineBox}<{-100pt}{1}{0}%
    >0\relax
  }
  {}{\PatchFailed}

\ExplSyntaxOn
% both \exp_args:NeNe and \fp_compare:nNnTF are fully expandable, so as \FV@iffp
\cs_new:Npn \FV@iffp
  {
    \exp_args:NeNe \fp_compare:nNnTF
  }
\exp_args_generate:n { eNe }
\ExplSyntaxOff
\makeatother

Full example

\documentclass{article}
\usepackage{fvextra}

\usepackage{xpatch}
\makeatletter
\xpatchcmd\FV@ListProcessLine@Break
  {\ifdim\wd\FV@LineBox>\FV@LineWidth}
  {%
    \ifnum
      \FV@iffp{\the\wd\FV@LineBox}>{\FV@LineWidth}{1}{0}%
      % in case the box width overflows
      \FV@iffp{\the\wd\FV@LineBox}<{-100pt}{1}{0}%
    >0\relax
  }
  {}{\PatchFailed}

\ExplSyntaxOn
% both \exp_args:NeNe and \fp_compare:nNnTF are fully expandable, so as \FV@iffp
% is expandable too
\cs_new:Npn \FV@iffp
  {
    \exp_args:NeNe \fp_compare:nNnTF
  }
\exp_args_generate:n { eNe }
\ExplSyntaxOff
\makeatother

\begin{document}
\Huge
% this triggers "Dimension too large" error, but a 3x long code line doesn't
\begin{Verbatim}[breaklines, breakanywhere]
abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,
\end{Verbatim}

\begin{Verbatim}[breaklines, breakanywhere]
abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,abcdefghijklmnopqrstuvwxyz,
\end{Verbatim}
\end{document}