Re: org-babel-load-languages usability issue

[Ihor Radchenko <yantar92@gmail.com>]

Tim Cross <theophilusx@gmail.com> writes:

>> We have [[info:org#Languages]] linking to
>> https://orgmode.org/worg/org-contrib/babel/languages/index.html
>> I guess we can simply add the manual link to the docstring. Would it be
>> sufficient?
>>
>
> Yes, I think so. That was what I was thinking would be reasonable and
> would avoid maintenance issues for the doc string when languages are
> added/removed.

Done.
https://git.savannah.gnu.org/cgit/emacs/org-mode.git/commit/?id=7c20552ed636d6c058d6be649e19d3d5edc0f62a

>>> Would it load them if the default values for all the languages which
>>> have bundleed modes in Emacs were set to nil rather than t?
>>
>> I am not sure if it is a good idea.
>> I am now looking at the usage of org-babel-load-languages in the code,
>> and I am seeing `org-lint-wrong-header-argument',
>> `org-babel-demarcate-block' ignoring difference between (lang . nil) and
>> (lang .t).
>
> OK, so if I understand you correctly, not all of org code honours the
> enabled/disabled setting so adding all bundled languages, but setting
> them to nil, would result in unexpected or additional processing for
> those languages despite them being disabled?

Yes, though I am not 100% sure if the impact is significant enough for
us to care.

> If that is the case, you right and adding them would be
> problematic. However, I would also argue this is probably a
> bug. Essentially, it means that the value associated with the language
> symbol key is sometimes interpreted and sometimes ignored. I think this
> is an inconsistency which can potentially cause confusion and could
> contribute to subtle bugs.

Agree. 

> One thing I do wonder though wrt the two examples you cited. Could this
> be deliberate/intentional for these functions?
>
> I wondering about the scenario where you want to include blocks for a
> certain language, but you do not need to evaluate them, so no need for
> babel support. Might this be a case where you would set the language to
> nil, but be fine with lint and other checks verifying the block
> structure? Provided this isn't also resulting in loading of language
> specific babel code, it may not be an issue?

I do not think that your example is a valid use-case.
(lang . nil), when set during startup, means that (require 'ob-lang) has
never been executed (or, at least, we cannot guarantee it).
When (lang . nil) is changed from (lang . t) at some point,
(require 'ob-lang) is executed, but org-babel-do-load-languages
explicitly unloads the babel function that executes the LANG blocks.

In general, we cannot assume that any of the ob-lang functions are
loaded when there is (lang . nil). No LANG-specific info is available.

Also, (lang . nil) is supposed to deny loading LANG. It should be no
different compared to not listing LANG at all.

-- 
Ihor Radchenko,
Org mode contributor,
Learn more about Org mode at https://orgmode.org/.
Support Org development at https://liberapay.com/org-mode,
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