tex4ht: conflict between `wrapfig` and `caption` packages

Question

MWE:

\documentclass[12pt]{book}

\usepackage{caption}
\usepackage{wrapfig}

\begin{document}
\begin{wrapfigure}{o}{1.25in}
\end{wrapfigure}
\end{document}

If I compile it with tex4ebook, or htlatex, then I come up with an error:

! Undefined control sequence.
\b:wrapfloat ->\endWrap 

l.8 \end{wrapfigure}

Note that there is no error while we compile with pdflatex, and that if I change the order of including caption and wrapfig packages, then there won't be any errors.

I hope an improvement in these .4ht files.

(By the way, do anybody know how to configure tex4ebook so that it will pause compiling at errors, instead of ignoring them quietly, as before?)

Edit: As michal-h21 points out, in newer versions of tex4ebook, running with parameter -a debug suffices.

A sample code with caption:

\documentclass[12pt]{book}

\usepackage[labelformat=empty]{caption}
\usepackage{wrapfig}

\begin{document}
\begin{wrapfigure}{o}{1.25in}
\caption{Test}
\end{wrapfigure}
\end{document}

Answer 1

It seems that the Caption package redefines lot of other packages commands. It does that after TeX4ht already patched commands from these packages, which results in lose of the inserted TeX4ht configurations. I think the only safe solution is to prevent Caption from patching of all these commands. Try this version of usepackage.4ht:

% usepackage.4ht (2019-12-13-14:32), generated from tex4ht-4ht.tex
% Copyright 2003-2009 Eitan M. Gurari
% Copyright 2009-2019 TeX Users Group
%
% This work may be distributed and/or modified under the
% conditions of the LaTeX Project Public License, either
% version 1.3c of this license or (at your option) any
% later version. The latest version of this license is in
%   http://www.latex-project.org/lppl.txt
% and version 1.3c or later is part of all distributions
% of LaTeX version 2005/12/01 or later.
%
% This work has the LPPL maintenance status "maintained".
%
% The Current Maintainer of this work
% is the TeX4ht Project <http://tug.org/tex4ht>.
%
% If you modify this program, changing the
% version identification would be appreciated.
\immediate\write-1{version 2019-12-13-14:32}

   \def\:temp{tex4ht}\ifx \:temp\@currname
   \:warning{\string\usepackage{tex4ht} again?}
   \def\:temp#1htex4ht.def,tex4ht.sty#2!*?: {\def\:temp{#2}}
\expandafter\:temp \@filelist htex4ht.def,tex4ht.sty!*?: %
\ifx \:temp\empty  \else
   \:warning{if
    \string\RequirePackage[tex4ht]{hyperref} or
    \string\usepackage[tex4ht]{hyperref} was
    used try instead, repectively,
    \string\RequirePackage{hyperref} or
    \string\usepackage{hyperref}}
\fi

\fi
\gdef\a:usepackage{\use:package xr,xr-hyper,eso-pic,expl3,savetrees,biblatex,xeCJK,polyglossia,fontspec,tikz,pdfbase,graphics,xcolor,imakeidx,minted,fancyhdr,caption,,!*?: }
\gdef\use:package#1,{%
   \if :#1:\def\:temp##1!*?: {}\else
      \def\:temp{#1}\ifx \@currname\:temp
             \def\:temp##1!*?: {\input usepackage.4ht  }%
      \else \let\:temp=\use:package \fi
   \fi \:temp}
\def\:temp{xr}\ifx \@currname\:temp
   \AtEndOfPackage{\let\XR:\XR@
   \def\XR@[#1]#2{%
    \Configure{AtBeginDocument}{\XR:[#1]{#2}}{}}%
}

\fi
\def\:temp{xr-hyper}\ifx \@currname\:temp
   \AtEndOfPackage{\let\XR:\XR@
    \def\XR@[#1][#2]#3{%
      \AtBeginDocument{\XR:[#1][#2]{#3}}
    }%
}

\fi
\def\:temp{eso-pic}\ifx \@currname\:temp
\:dontusepackage{eso-pic}
\newcommand\AddToShipoutPicture{\@ifstar{}{}}
\let\AddToShipoutPictureBG\AddToShipoutPicture
\let\AddToShipoutPictureFG\AddToShipoutPicture
\fi
\def\:temp{expl3}\ifx \@currname\:temp
\ifdefined\XeTeXversion%
\xenunidelblock{Latin-expl3}%
\AtEndOfPackage{\xeuniuseblock{Latin-expl3}}
\fi
\fi
\def\:temp{savetrees}\ifx \@currname\:temp
\:dontusepackage{savetrees}
\fi
\def\:temp{biblatex}\ifx \@currname\:temp
\AtEndOfPackage{%
  \def\blx@mknoautolang{%
    \blx@lbxinput{\blx@languagename}%
    {}{}%
  }%
  \def\blx@lbxinput@iii#1#2{%
  \global\csundef{blx@lng@#2}%
  \:IfFileExists{#1.lbx}
    {\blx@lbxinput@iv{#2}{#1}{language '#2' -> '#1'}}
    {\ifcsdef{blx@suffmaptried@#2}
      {}
      {\blx@warning@noline{%
          File '#1.lbx' not found!\MessageBreak
          Ignoring mapping '#2' -> '#1'}%
       \global\cslet{blx@suffmaptried@#2}\@empty}%
     \blx@lbxinput@iv{#2}{#2}{language '#2'}}}

}
\fi
\def\:temp{xeCJK}\ifx \@currname\:temp
\:dontusepackage{xeCJK}
\AtEndOfPackage{%
  \RequirePackage{fontspec}
}
\DeclareDocumentCommand\setCJKmainfont{o m o}{}
\let\setCJKsansfont\setCJKmainfont
\let\setCJKmonofont\setCJKmainfont

\DeclareDocumentCommand\setCJKfamilyfont {m o m }{}
\DeclareDocumentCommand\newCJKfontfamily {o m o m}{\expandafter\gdef\csname #2\endcsname{\relax}}

\DeclareDocumentCommand\xeCJKsetup{m}{}
% }
\AtBeginDocument{%
  \xeuniuseblock{CJK}
}
\fi
\def\:temp{polyglossia}\ifx \@currname\:temp
\ExplSyntaxOn
\AtEndOfPackage{

\cs_set_eq:NN\orig_polyglossia@keys_define_lang:n\polyglossia@keys_define_lang:n
\cs_set_protected:Npn \polyglossia@keys_define_lang:n #1 {
  \orig_polyglossia@keys_define_lang:n{#1}
  \keys_define:nn {polyglossia}{
    #1 / direction
    .  code:n = {}
  }
}
\def\RequireBidi{}%
}
\ExplSyntaxOff
\fi
\def\:temp{fontspec}\ifx \@currname\:temp
  \ifdefined\fontspec
    \:dontusepackage{fontspec}
  \else
    \input usepackage-fontspec.4ht
  \fi
\fi
\def\:temp{tikz}\ifx \@currname\:temp
\AtEndOfPackage{%
\let\use:tikzlibrary\usetikzlibrary
\def\find:externalize#1external#2\@nil{%
\if\relax#2\relax\else
  \let\tikz:externalize\tikzexternalize
  \renewcommand\tikzexternalize[1][]{\tikz:externalize[##1,mode=only graphics]}
    \tikzset{%
      tex4ht inc/.style={%
        /pgf/images/include external/.code={%
          \includegraphics[]{####1.pdf}%
        }%
      }
    }
    \tikzset{tex4ht inc}
  \fi
}
\renewcommand\usetikzlibrary[1]{%
  \use:tikzlibrary{#1}%
  \find:externalize#1external\@nil%
}
}
\fi
\def\:temp{pdfbase}\ifx\@currname\:temp
\AtEndOfPackage{%
  \let\old:outputpage\@outputpage
  \def\@outputpage{\old:outputpage{}}
}
\fi
\def\:temp{graphics}\ifx\@currname\:temp
  \ifdefined\XeTeXversion
    \PassOptionsToPackage{dvips}{graphics}
  \fi
\fi
\def\:temp{xcolor}\ifx\@currname\:temp
  \ifdefined\XeTeXversion
    \PassOptionsToPackage{dvips}{xcolor}
  \fi
\fi
\def\:temp{imakeidx}\ifx\@currname\:temp
  \PassOptionsToPackage{noautomatic}{imakeidx}
\fi
\def\:temp{minted}\ifx\@currname\:temp
  \AtEndOfPackage{%
    \define@booleankey{minted@opt@g}{breaklines}{}{}{}%
  }
\fi
\def\:temp{fancyhdr}\ifx\@currname\:temp
  \AtEndOfPackage{%
  \def\ps@fancy{}%
  }
\fi

\def\:temp{caption}\ifx\@currname\:temp
\AtEndOfPackage{%
\long\def\caption@If@Package@Loaded#1[#2]#3#4{}
}
\fi

\endinput

The important part is this:

\def\:temp{caption}\ifx\@currname\:temp
\AtEndOfPackage{%
\long\def\caption@If@Package@Loaded#1[#2]#3#4{}
}
\fi

This code is inserted when Caption is loaded using \usepackage the \AtEndOfPackage executes code after the package code is loaded. It redefines the command responsible for package patching to do nothing.

This is the resulting HTML from your sample:

<body>
   <div class='wrapfig-o'>                       </div>

</body>