Mrthfx

Today, the generation of one of my dtx files stopped with the error:

! Undefined control sequence.

UseTextAccent ...up @firstofone let @curr@enc

                                              cf@encoding @use@text@en...

As I have not changed the files for more than two months now, but updated my MiKTeX last week (and listened carefully to @Ulrike Fischer reporting on kernel changes at the last DANTE meeting), I gladly found out rather quickly, that the new LaTeX kernel (2018/04/01) is responsible for that.
Using pdflatex 'UseRawInputEncoding input{FILENAME.dtx}' as stated in the LaTeX news document, everything runs smoothly.

I then started preparing a MWE, which led to newunicodechar from the same called package causing the problem:

% iffalse meta-comment

%<*internal>

iffalse

%</internal>

%<*internal>

fi

defnameofplainTeX{plain}

ifxfmtnamenameofplainTeXelse

  expandafterbegingroup

fi

%</internal>

%<*install>

input docstrip.tex

keepsilent

askforoverwritefalse

generate{

  file{jobname.cls}{from{jobname.dtx}{class}}

}

%</install>

%<install>endbatchfile

%<*internal>

generate{

  file{jobname.ins}{from{jobname.dtx}{install}}

}

ifxfmtnamenameofplainTeX

  expandafterendbatchfile

else

  expandafterendgroup

fi

%</internal>

% fi

%

% iffalse

%<*driver>

ProvidesFile{testclass.dtx}

%</driver>

%<class>NeedsTeXFormat{LaTeX2e}[1999/12/01]

%<class>ProvidesClass{testclass}

%<*class>

    [2018/04/16 v1.0 A LaTeX class]

%</class>

%<*driver>

documentclass{ltxdoc}

RequirePackage[utf8]{inputenc}

RequirePackage[T1]{fontenc}

RequirePackage[ngerman]{babel}

EnableCrossrefs

CodelineIndex

RecordChanges

begin{document}

  DocInput{jobname.dtx}

end{document}

%</driver>

% fi

%

% CheckSum{0}

%

% CharacterTable

%  {Upper-case    ABCDEFGHIJKLMNOPQRSTUVWXYZ

%   Lower-case    abcdefghijklmnopqrstuvwxyz

%   Digits        123456789

%   Exclamation   !     Double quote  "     Hash (number) #

%   Dollar        $     Percent       %     Ampersand     &

%   Acute accent  '     Left paren    (     Right paren   )

%   Asterisk      *     Plus          +     Comma         ,

%   Minus         -     Point         .     Solidus       /

%   Colon         :     Semicolon     ;     Less than     <

%   Equals        =     Greater than  >     Question mark ?

%   Commercial at @     Left bracket  [     Backslash     \

%   Right bracket ]     Circumflex    ^     Underscore    _

%   Grave accent  `     Left brace    {     Vertical bar  |

    %   Right brace   }     Tilde         ~}

% GetFileInfo{jobname.dtx}

% DoNotIndex{newcommand,newenvironment}

%

% title{A test class}

% author{Martin Sievers}

%

% maketitle

%

% StopEventually{^^A

%  PrintChanges

% }

%

% section{Implementation}

%    begin{macrocode}

%<*class>

%    end{macrocode}

%    begin{macrocode}

LoadClass{minimal}

%    end{macrocode}

%    begin{macrocode}

RequirePackage[utf8]{inputenc}

RequirePackage[T1]{fontenc}

RequirePackage[english]{babel}

RequirePackage{newunicodechar}

newunicodechar{⸗}{hyphen}

%    end{macrocode}

%    begin{macrocode}

%</class>

%    end{macrocode}

% Finale

endinput

However, putting everything into a simple LaTeX file does not result in the same error. So, there must be more about it ...

Is this a foreseeable problem caused by the change to UTF8 as the new standard encoding of files? The dtx file is encoded as UTF8 and as you can see there is always an inputenc entry using the utf8 option as well.

With current (2018,2019) releases

The posted code produces the error

! Package inputenc Error: Unicode char ⸗ (U+2E17)

(inputenc)                not set up for use with LaTeX.

The problem is that the newunicodechar package is loaded and used to declare this character in the generated class file, but the typeset documentation is not using this class and so latex can not typeset this line:

newunicodechar{⸗}{hyphen}

You can declare a setting for this character in the typeset document, the standard fonts don't really have a suitable character so I just used - here.

This is as posted in the question, with the addition of

DeclareUnicodeCharacter{2E17}{-}

% iffalse meta-comment

%<*internal>

iffalse

%</internal>

%<*internal>

fi

defnameofplainTeX{plain}

ifxfmtnamenameofplainTeXelse

  expandafterbegingroup

fi

%</internal>

%<*install>

input docstrip.tex

keepsilent

askforoverwritefalse

generate{

  file{jobname.cls}{from{jobname.dtx}{class}}

}

%</install>

%<install>endbatchfile

%<*internal>

generate{

  file{jobname.ins}{from{jobname.dtx}{install}}

}

ifxfmtnamenameofplainTeX

  expandafterendbatchfile

else

  expandafterendgroup

fi

%</internal>

% fi

%

% iffalse

%<*driver>

ProvidesFile{testclass.dtx}

%</driver>

%<class>NeedsTeXFormat{LaTeX2e}[1999/12/01]

%<class>ProvidesClass{testclass}

%<*class>

    [2018/04/16 v1.0 A LaTeX class]

%</class>

%<*driver>

documentclass{ltxdoc}

RequirePackage[utf8]{inputenc}

DeclareUnicodeCharacter{2E17}{-}

RequirePackage[T1]{fontenc}

RequirePackage[ngerman]{babel}

EnableCrossrefs

CodelineIndex

RecordChanges

begin{document}

  DocInput{jobname.dtx}

end{document}

%</driver>

% fi

%

% CheckSum{0}

%

% CharacterTable

%  {Upper-case    ABCDEFGHIJKLMNOPQRSTUVWXYZ

%   Lower-case    abcdefghijklmnopqrstuvwxyz

%   Digits        123456789

%   Exclamation   !     Double quote  "     Hash (number) #

%   Dollar        $     Percent       %     Ampersand     &

%   Acute accent  '     Left paren    (     Right paren   )

%   Asterisk      *     Plus          +     Comma         ,

%   Minus         -     Point         .     Solidus       /

%   Colon         :     Semicolon     ;     Less than     <

%   Equals        =     Greater than  >     Question mark ?

%   Commercial at @     Left bracket  [     Backslash     \

%   Right bracket ]     Circumflex    ^     Underscore    _

%   Grave accent  `     Left brace    {     Vertical bar  |

    %   Right brace   }     Tilde         ~}

% GetFileInfo{jobname.dtx}

% DoNotIndex{newcommand,newenvironment}

%

% title{A test class}

% author{Martin Sievers}

%

% maketitle

%

% StopEventually{^^A

%  PrintChanges

% }

%

% section{Implementation}

%    begin{macrocode}

%<*class>

%    end{macrocode}

%    begin{macrocode}

LoadClass{minimal}

%    end{macrocode}

%    begin{macrocode}

RequirePackage[utf8]{inputenc}

RequirePackage[T1]{fontenc}

RequirePackage[english]{babel}

RequirePackage{newunicodechar}

newunicodechar{⸗}{hyphen}

%    end{macrocode}

%    begin{macrocode}

%</class>

%    end{macrocode}

% Finale

endinput