Bug: org-babel-expand-src-block expands sh blocks independent of shell defined by src block [9.0.5 (9.0.5-elpaplus @ ~/.emacs.d/elpa/org-plus-contrib-20170210/)]

[Derek Feichtinger <derek.feichtinger@psi.ch>]

Hi

When using =org-babel-expand-src-block= with a shell src block one 
always gets the same code expansion (in my case bash) independent of the 
shell that is used while the execution of the shell block uses the 
correct expansion.


I define the following table to illustrate the problem:

#+NAME: tbltest
| col1 | col2 | col3 |
|   11 |   12 |   13 |
|   21 |   22 |   23 |
|   31 |   32 |   33 |

Now for the example source block where I read in the table

#+BEGIN_SRC sh :results value  :exports both :var tbl=tbltest :colnames yes
   echo $tbl
#+END_SRC

When expanding the sh source block above with 
=org-babel-expand-src-block= it is wrongly expanded to the
bash expansion and not to the sh expansion that is used when the block 
is executed. So, instead of the
sh expansion,

  tbl='11    12    13
  21    22    23
  31    32    33'


I see the following bash related expansion in the opened buffer:

#+BEGIN_EXAMPLE
    unset tbl
    declare -A tbl
    tbl['11']='12
    13'
    tbl['21']='22
    23'
    tbl['31']='32
    33'
    echo $tbl
#+END_EXAMPLE

Reason:

The case distinction in =org-babel-variable-assignments:shell= is
made based on the shell-file-name which is a standard emacs
variable set by emacs in C code. This is pointing to "/bin/bash"
for my installation.

#+BEGIN_SRC elisp :exports source
    (defun org-babel-variable-assignments:shell (params)
     "Return list of shell statements assigning the block's variables."
     (let ((sep (cdr (assq :separator params)))
       (hline (when (string= "yes" (cdr (assq :hlines params)))
            (or (cdr (assq :hline-string params))
            "hline"))))
       (mapcar
        (lambda (pair)
      (if (string-suffix-p "bash" shell-file-name)
          (org-babel--variable-assignments:bash
               (car pair) (cdr pair) sep hline)
            (org-babel--variable-assignments:sh-generic
         (car pair) (cdr pair) sep hline)))
        (org-babel--get-vars params))))
#+END_SRC

Looking at the calls stack for the case where we execute the source 
block and where we just expand it, we see
the following call stack for execution

#+BEGIN_EXAMPLE
     org-babel-variable-assignments:shell
     org-babel-execute:shell
     org-babel-execute:sh
     org-babel-execute-src-block
#+END_EXAMPLE

while in the case of just expanding the source block we have

#+BEGIN_EXAMPLE
    org-babel-variable-assignments:sh
    org-babel-expand-src-block
#+END_EXAMPLE

Note that =org-babel-variable-assignments:sh= is an alias for
=org-babel-variable-assignments:shell=.

A bit of investigation shows that for all shell languages there
are aliases defined that finally call
=org-babel-execute:shell=. This is set up in the
=org-babel-shell-initialize= function. And it is set up in a way
that =shell-file-name= is overridden by the name of the
particular shell, and this then leads to the correct case
distinction using =shell-file-name= in
=org-babel-variable-assignments:shell=.

#+BEGIN_SRC elisp :exports source
    (defun org-babel-shell-initialize ()
     "Define execution functions associated to shell names.
    This function has to be called whenever `org-babel-shell-names'
    is modified outside the Customize interface."
     (interactive)
     (dolist (name org-babel-shell-names)
       (eval `(defun ,(intern (concat "org-babel-execute:" name))
          (body params)
        ,(format "Execute a block of %s commands with Babel." name)
        (let ((shell-file-name ,name))
          (org-babel-execute:shell body params))))
       (eval `(defalias ',(intern (concat 
"org-babel-variable-assignments:" name))
        'org-babel-variable-assignments:shell
        ,(format "Return list of %s statements assigning to the block's \
    variables."
             name)))))
#+END_SRC

The same kind of overriding would have to be in place when
=org-babel-expand-src-block= calls
=org-babel-variable-assignments:shell= in the simple code expansion 
case. But that
would be a bit hacky since the generic =org-babel-expand-src-block= 
function should
not override variables needed in just one subclass of backends. It would be
cleaner to have different functions =org-babel-variable-assignments:XXX= 
for the
different shells.



Emacs  : GNU Emacs 25.2.3 (x86_64-pc-linux-gnu, GTK+ Version 3.18.9)
  of 2017-04-25
Package: Org mode version 9.0.5 (9.0.5-elpaplus @ 
~/.emacs.d/elpa/org-plus-contrib-20170210/)


-- 
Paul Scherrer Institut
Dr. Derek Feichtinger                   Phone:   +41 56 310 47 33
Section Head Science-IT                 Email: derek.feichtinger@psi.ch
Building/Room No. WHGA/U126
CH-5232 Villigen PSI