iftex.sty: incomplete \ifx

[olsak]

Minimal example:

\newif \ifpdftex
\input iftex.sty
\end

Process it by "pdftex test" (no LaTeX).
The rerror: ! Incomplete \ifx; all text was ignored after line 243.
Version of iftex.sty: the last from TeXlive 2019, begins with:

%% iftex TeX engine tests
%% LaTeX3 Project
...
\ProvidesPackage{iftex}[2019/11/07 v1.0c TeX engine tests]

Why I need to use this file when I am using plain TeX only: Tikz for plain TeX uses it, unfortunately.
The reason of this bug:
The line 112 does \let\ifIFTEX@savedpdftex=\ifpdftex.
The lines 243--246 includes the control sequence \ifIFTEX@savedpdftex in nested \ifx...\fi. The meaning of this control sequence is \ifpdftex=\iffalse (or \iftrue) and skipping over nested \if..\fi fails.

[davidcarlisle]

@olsak er yes,

I think this works correctly but I may see if I can re-organise it to avoid so many \expandafter and \csname

% special compat for scrbase
\ifx\scr@ifpdftex\@undefined\else\expandafter\ifx\csname ifIFTEX@savedpdftex\endcsname\relax\else
\relax
\IFTEX@let{pdftex}{IFTEX@savedpdftex}
\IFTEX@protected\edef\RequirePDFTeX{\noexpand\IFTEX@Require\expandafter\noexpand\csname ifPDFTeX\endcsname{pdfTeX}\expandafter\noexpand\csname fi\endcsname}
\fi\fi
\ifx\scr@ifVTeX\@undefined\else\expandafter\ifx\csname ifIFTEX@savedVTeX\endcsname\relax\else
 \IFTEX@let{VTeX}{IFTEX@savedVTeX}
\fi\fi

The whole block could possibly be deleted as the koma-script package code changed to avoid the issue that this is protecting against, but I'd like to keep it for compatibility with older releases for a while. It is supposed to work in plain though......

[davidcarlisle]

1.0d gone to CTAN thanks for the report.