Re: [PATCH] Accept more :tangle-mode specification forms

[Tom Gillespie <tgbugs@gmail.com>]

> I'd like to understand these objections better. Aren't you overstating
what is at issue?

Yes, after hitting send I realized I overstated my position a bit.
In the meantime the comments in this thread are encouraging,
however I have finally figured out what I was really trying to say.

tl;dr file permission modes are not universal and should thus not
be part of the Org implementation, Org itself knows nothing about
files or permissions, it is the system that Org is running in/on.
Therefore, so long as we make it abundantly clear that the
value for :tangle-mode is not expected to be portable and that
it is always up to the user to ensure correct behavior, then we
are ok. I'm not happy about this conclusion from a security
perspective, but it isn't really worse than the situation we have
right now.


As many have pointed out, the grammar itself will not be affected.
However, other parts of the spec will. In general my objective is to
try to reduce the number of special cases that an org implementation
has to know about and delegate them to something else.

However in this case it is a bit tricky because of the security implications
and due to the fact that octal modes for file permissions are NOT universal
and should not be expected to be universal!

I actually think that my gut reaction was correct, but was expressed
in the wrong way.

Unix file modes are not universal and should thus not be encoded as
part of a portable document format. This means that it is up to the
user to know what representation is suitable.

Right now that representation is delegated to Emacs, because Emacs
handles file permissions for Org, and Emac's language for modes is
octal.

There are some octal modes that do not translate on Windows, and cannot
be correctly set. There will (hopefully) be some happy day in the future
where there is an operating system that will run Org babel where octal
file modes do not exist at all!

Therefore I suggest that we do not enshrine a particularly obscure way
of expressing file modes into Org itself. Right now Org is confined to
Emacs' representations, which in a sense protects Org from becoming
too ossified by bad designs of the past --- Emacs can keep all that
for us!

If we want a more user friendly syntax for this I would suggest that we do
something like what has been done for Org babel :results, i.e. like
:tangle-mode read write execute, unfortunately that does not compose
well at all with user, group, and other and becomes exceedingly verbose.


Final conclusion, after all that rambling, is that I'd actually be ok with
any of the solutions proposed, so long as it is clear that :tangle-mode
will always be implementation dependent, and may or may not be
meaningful depending on which operating system you are using.
Unfortunate for security, but I don't see any way around tha. The
best we could do for security would be for implementations to
test the file modes after tangling to ensure that they match,
which is more important I think.

That said, reducing the number of forms as Eric suggests would
be a happy medium.

Best!
Tom