another texinfo.tex bug in \scanmacro

[Norbert Preining <preining@logic.at>]

Hi Gavin, dear all,

(please keep cc)

Another problem with 6.1 has popped up, not being really
Debian specific. It is in the sources of sbcl (common lisp
interpreter).

I reduced the problem to the following minimal not-working
example:

>>>>>>>>>>>>>>>>
\input texinfo   @c -*-texinfo-*-

@iftex
@tex
\newif\ifdash
\long\def\dashp#1{\expandafter\setnext#1-\dashphelper}
\long\def\setnext#1-{\futurelet\next\dashphelper}
\long\def\dashphelper#1\dashphelper{
  \ifx\dashphelper\next\dashfalse\else\dashtrue\fi
}
\def\lw#1{\leavevmode\dashp{#1}\ifdash#1\else\hbox{#1}\fi}
@end tex
@end iftex

@macro lw{word}
@tex
\\lw{\word\}%
@end tex
@end macro

@code{@lw{aaa}}

@bye
>>>>>>>>>>>>>>>>>>>>>>>>>>>

and the error message is
/mnwe.texinfo:21: TeX capacity exceeded, sorry [text input levels=15].
\scanmacro ...atspaces }\scantokens {#1\texinfoc }
                                                  \aftermacro 
l.2 \lw{aaa}
            %
\scanmacro ...atspaces }\scantokens {#1\texinfoc }
                                                  \aftermacro 
l.2 \lw{aaa}
            %
\scanmacro ...atspaces }\scantokens {#1\texinfoc }
                                                  \aftermacro 
l.2 \lw{aaa}
            %
...
l.21 @code{@lw{aaa}}
                    
No pages of output.
>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>

I did run the test with the version in Debian, as well as with the
latest code in svn (texinfo [version 2016-03-06.18]).

I also confirmed that with the version from 6.0 it works:
>>>>>>>>>>>>>>>>>>>>>>
This is pdfTeX, Version 3.14159265-2.6-1.40.16 (TeX Live 2015/Debian) (preloaded format=etex)
 restricted \write18 enabled.
entering extended mode
(./mnwe.texinfo (/home/norbert/ti/texinfo.tex
Loading texinfo [version 2015-06-24.23]: pdf, fonts, markup, glyphs,
page headings, tables, conditionals, indexing, sectioning, toc, environments,
defuns, macros, cross references, insertions,
(/usr/share/texlive/texmf-dist/tex/generic/epsf/epsf.tex
This is `epsf.tex' v2.7.4 <14 February 2011>
) localization, formatting, and turning on texinfo input format.) [1] )
Output written on mnwe.dvi (1 page, 200 bytes).
Transcript written on mnwe.log.
>>>>>>>>>>>>>>>>>>>>>>

All the best

Norbert

------------------------------------------------------------------------
PREINING, Norbert                               http://www.preining.info
JAIST, Japan                                 TeX Live & Debian Developer
GPG: 0x860CDC13   fp: F7D8 A928 26E3 16A1 9FA0  ACF0 6CAC A448 860C DC13
------------------------------------------------------------------------