[Buildroot] genmanual: generates kconfiglib.pyc in Buildroot source tree

[Yann E. MORIN <yann.morin.1998@free.fr>]

Samuel, All,

On 2013-12-05 19:04 +0100, Samuel Martin spake thusly:
> 2013/12/5 Yann E. MORIN <yann.morin.1998@free.fr>
> 
> > Arnout, All,
> >
> > On 2013-12-05 09:00 +0100, Arnout Vandecappelle spake thusly:
> > > On 04/12/13 23:52, Yann E. MORIN wrote:
> > > >Samuel, All,
> > > >
> > > >When one runs 'make manual', python will create:
> > > >     support/scripts/kconfiglib.pyc
> > > >in the Buildroot source tree.
> > > >
> > > >Python will happily run, even if it is not able to generate that file
> > > >(eg. because the source tree is read-only).
> > > >
> > > >However, the file is not cleaned on 'make clean'. I'm a bit reluctant at
> > > >adding it since it would try to remove a file outside of $(O), which
> > > >could break parallel builds in multiple $(O) at the same time... Not
> > > >sure what to do here.
> > > >
> > > >Since we do not really care about speed, would it be possible to tell
> > > >python not to generate it at all?
> > >
> > >  I do 'man python', and the first thing I see is
> > >
> > > -B     Don't write .py[co] files on import. See also
> > PYTHONDONTWRITEBYTECODE.
> >
> > Hey! I read the manpage, but only greped for '\.pyc' not for this.
> > Thanks for pointing it to me.
> >
> > >  I'd say, go for it! Unfortunately, you can't add it directly in the #!
> > line
> > > of the script because all the arguments are concatenated together. So I
> > > guess the PYTHONDONTWRITEBYTECODE environment variable should be set when
> > > calling the script.
> >
> But, in manual.mk, you can explicitly call:
> python -B $(TOPDIR)/support/scripts/gen-manual-lists.py

But currently, gen-manual-lists.py is using this sha-bang:
    #!/usr/bin/env python

And the way the sha-bang is interpreted is that:
  - #!    <- the sha-bang
  - an optional space
  - the path to the interpreter

If there is a space after the interpreter, then whatever follows that
space until the end of the line is passed as argv[1] to the interpreter.
So, we can pass only one argument to the interpreter.

'python' is the first arg to 'env', and we can't pass any arg to python.

We could use "#!/usr/bin/python" but I don't want to change that.
And passing PYTHONDONTWRITEBYTECODE is easy enough, and works (just
tested it).

Regards,
Yann E. MORIN.

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