Re: how to not break cross-building

[Olaf Till]

On Thu, Apr 28, 2016 at 02:51:16PM -0400, John W. Eaton wrote:
> On 04/28/2016 02:12 PM, Mike Miller wrote:
> >On Thu, Apr 28, 2016 at 13:24:23 +0200, Olaf Till wrote:
> >>In building package documentation, when the package is not yet
> >>installed, the cleanest way for extracting help strings from C++ code
> >>seems to be to compile a (minimalistic) binary which outputs this help
> >>string. In this way, all special characters in the C-string are
> >>treated as they should be.
> >>
> >>This certainly will break cross-building if the cross-compiler is used
> >>to compile the minimalistic binary. But any native C-compiler would
> >>serve, it only has to evaluate the C-string correctly and call
> >>'printf'. I have no practical experience with cross-building, I only
> >>care for it because I know others want to do it with packages. Is
> >>there a way to specifiy, in the Makefile, that for a certain step a
> >>native compiler should be used, not the cross-compiler?
> >
> >I am actually not familiar with the minimalistic binary approach.

It's not necessarily a general approach, I just preliminarily
implemented it this way.

> >In Octave's build system, the C++ preprocessor is used to extract the
> >docstrings from all source files, which are then inserted into the
> >manual and used to build the doc-cache file. I think that a
> >cross-preprocessor would be just as effective as a native preprocessor.
> 
> Yes, the .df files are generated using the preprocessor and sed (sed script
> is in libinterp/mkdefs).  The .df files still have \n and \" in them.  Those
> are handled by the libinterp/gendoc.pl script.  I think it is better to do
> this job with a perl script instead of compiling a program that includes the
> docstrings.

Originally I used sed for \n , forgetting \" . It would have been easy
to use sed for \" and \\ also when I noticed the mistake, but what is
with escaped octal and hexadecimal numbers?  Are they supposed never
to be used?  Though I daresay a perl script could probably deal with
them somehow ...

> Rik and I had some plans to change the way docstrings are handled in the
> Octave sources so that instead of writing
> 
>   DEFUN (fcn, args, nargout,
>          "-*- texinfo -*-\n\
>   @deftypefn ...
>   ...
>   ...)
> 
> you would write something like this:
> 
>   DEFUN (fcn, args, nargout,
>          doc: /* -*- texinfo -*-
>   @deftypefn ...
>   ...
>   ...)
> 
> This is what is done in the Emacs sources now (and Emacs is where I got the
> idea for the DEFUN macro).
> 
> If we switch to this method, the docstring in the C++ sources would be
> easier to edit because they would just need to be valid C comments instead
> of having to follow the rules for C strings.

This sounds good.

> Either way, I think we could eliminate the need for the preprocessor just
> having a perl script search for DEFUN and extract the docstrings.

The preprocessor is not fooled by a DEFUN which occurs in a comment or
in a string, while a perl script needs a special effort for this ...

> But it
> would be simpler to not have to deal with escape sequences.

Yes.

Olaf

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