Re: [Orgmode] Problems with buffer-local variables

[Dan Davison]

Carsten Dominik <address@hidden> writes:

> On Dec 22, 2010, at 3:51 PM, Dan Davison wrote:
>
>> There's recently been some advocacy of using buffer-local variables
>> for
>> Org-mode configuration. It seems like a good idea to me. However, I
>> think that it raises a problem: there are at least two situations in
>> which Org internally spawns a buffer that is supposed to be a sort of
>> "copy" of another Org buffer: these situations are export and org-src
>> edit buffer. The problem is that the "copy" buffer doesn't inherit
>> local
>> variables from the parent buffer.
>>
>> It seems that either we should propagate all local variables in these
>> cases (but I suspect that is inappropriate for some variables), or we
>> have to have a rule for identifying the subset of local variables
>> which
>> need to be propagated.
>>
>> Below is one example which I think demonstrates a problem. If you
>> evaluate the elisp block and then export to HTML, the noweb does not
>> get
>> expanded, because the configuration variable is buffer-local (behind
>> the
>> scenes, Org creates a buffer copy just before exporting a buffer).
>>
>> --8<---------------cut here---------------start------------->8---
>> #+title: Local variables issues?
>>
>> Evaluate this block, then do C-c C-e h
>> #+begin_src emacs-lisp :results silent :exports none
>>  (set-default 'org-babel-default-header-args:sh
>>          nil)
>>  (set (make-local-variable 'org-babel-default-header-args:sh)
>>       '((:noweb . "yes")))
>> #+end_src
>>
>> #+begin_src sh :exports both
>> <<foo>>
>> #+end_src
>>
>> #+source: foo
>> #+begin_src sh :exports none
>> echo hello
>> #+end_src
>> --8<---------------cut here---------------end--------------->8---
>>
>> It's also a problem when spawning the org-src edit buffer. There is a
>> patch in the pipeline that tries to identify all the necessary local
>> variables and transmit them to the edit buffer:
>>
>> http://patchwork.newartisans.com/patch/438/
>>
>> That's a bit messy, but in the export case it seems even harder to
>> identify all variables that might need to be transmitted.
>>
>> What is a good solution?
>
>
> Hi Dan,
>
> I see only two possibilities.  Either use a list of variables that
> should be transported, or copy all local variables, or all local
> variables that match a pattern.  An example for doing something like
> this can be found in org-get-local-variables which is, for example,
> used by `org-run-like-in-org-mode'.

Here's a patch. It clones into the pre-export buffer all buffer-local
variables that match a regexp (currently "^\\(org-\\|orgtbl-\\)"). We
might want to watch out for unanticipated side effects.

This should mean that we can use buffer-local variables to set export
related variables on a per-buffer basis[1].

On reflection I think that the src edit buffer case should be dealt with
as it is currently (by ad-hoc transporting of variables in the org-src
code). I still stand by my pending patch 438, which tidies up the
local-variables stuff in org-edit-src-code.

http://patchwork.newartisans.com/patch/438/

Dan

Footnotes:
[1] Also, we can use the 'local argument to add-hook to set the various
export hooks.


    Ensure that buffer-local variables have their effects during export.
    
    * lisp/org.el (org-clone-local-variables): New function to copy local
    variables from another buffer.
    * lisp/org-exp.el (org-export-preprocess-string): Clone local
    variables from source org buffer into temporary export preprocessing
    buffer.

#+begin_src diff
diff --git a/lisp/org-exp.el b/lisp/org-exp.el
index 97f17e5..6b333a7 100644
--- a/lisp/org-exp.el
+++ b/lisp/org-exp.el
@@ -1028,6 +1028,7 @@ on this string to produce the exported version."
         (inhibit-read-only t)
         (drawers org-drawers)
         (outline-regexp "\\*+ ")
+        (source-buffer (current-buffer))
         target-alist rtn)
 
     (setq org-export-target-aliases nil
@@ -1051,6 +1052,7 @@ on this string to produce the exported version."
 
       (let ((org-inhibit-startup t)) (org-mode))
       (setq case-fold-search t)
+      (org-clone-local-variables source-buffer "^\\(org-\\|orgtbl-\\)")
       (org-install-letbind)
 
       ;; Call the hook
diff --git a/lisp/org.el b/lisp/org.el
index 808c9ed..dda97d9 100644
--- a/lisp/org.el
+++ b/lisp/org.el
@@ -8127,6 +8127,18 @@ Possible values in the list of contexts are `table', 
`headline', and `item'."
                 x nil))
           varlist))))
 
+(defun org-clone-local-variables (from-buffer &optional regexp)
+  "Clone local variables from FROM-BUFFER.
+Optional argument REGEXP selects variables to clone."
+  (mapc
+   (lambda (pair)
+     (and (symbolp (car pair))
+         (or (null regexp)
+             (string-match regexp (symbol-name (car pair))))
+         (set (make-local-variable (car pair))
+              (cdr pair))))
+   (buffer-local-variables from-buffer)))
+
 ;;;###autoload
 (defun org-run-like-in-org-mode (cmd)
   "Run a command, pretending that the current buffer is in Org-mode.
#+end_src

>
> - Carsten