[metapost] Question: [MPLib, MetaFun, ConTeXt, LuaTeX] metapost logging and message primitive?

[Aditya Mahajan]

On Mon, 18 Feb 2013, Colin Fraizer wrote:

> I have a METAPOST program that works fine with mpost, but fails when I try
> to run it inline in ConTeXt. In order to debug it, I would like to see the
> usual METAPOST logging and/or to use the METAPOST "message" primitive.
>
> However, whenever I add "loggingall;" or a message statement to my ConTeXt
> file, I encounter errors like this
>
> %------
> metapost        > initializing instance 'metafun' using format 'metafun'
> metapost        > loading 'metafun':
> D:/texlive/2012/texmf-dist/metapost/context/base/metafun.mpiv
> ! terminal:
> %-------

You can get rid of the error message by setting

\disabledirectives[mplib.texerrors]

but that results in an equally useless:

~~~~
metapost        > terminal:

metapost        > error: unknown, no error, terminal or log messages
~~~

The logic in metapost.reporterror(...) function in mlib-run.lua is a bit 
weird. It assumes that metapost.texerrors is always set to false!

> What is the appropriate way to debug problems with inline METAPOST code in
> ConTeXt?

I think that it is better to redefine metapost.reporterror as follows:

\startluacode

local report_metapost = logs.reporter("metapost")
local texerrormessage = logs.texerrormessage

-- metapost.showlog = true

function metapost.reporterror(result)
     if not result then
         report_metapost("error: no result object returned")
     elseif result.status > 0 then
         local t, e, l = result.term, result.error, result.log
         if t and t ~= "" and metapost.showlog then
             report_metapost("terminal: %s",t)
         end
         if e then
             (metapost.texerrors and texerrormessage or 
report_metapost)("error: %s",(e=="" and "?") or e)
         elseif l then
             if metapost.showlog then
                 metapost.lastlog = metapost.lastlog .. "\n" .. l
                 report_metapost("log: %s",l)
             end
         else
             report_metapost("error: unknown, no error, terminal or log 
messages")
         end
     else
         return false
     end
     return true
end
\stopluacode


That way, when you enable metapost.showlog and set loggingall at the 
metapost end, the logging messages will be shown on the terminal as 
well in the log file.

Aditya