Multiple noweb-ref

[Théo Maxime Tyburn]

Hi,

I have several code blocks that I label using `:noweb-ref label`. I set
them for all blocks under a subtree by setting the org property
`header-args+` of the root of the subtree to `:noweb-ref label`.

Now with this approach, I can't accumulate `noweb-ref` like I could do for
tags. I would like all blocks under a subtree A to have the
reference "foo" and all the blocks under a subtree B of subtree A to
have the reference "bar", while also having the reference "foo".

What I would like to have, when I expand `<<bar>>` is to get all the blocks
under A, and when I expand `<<foo>>` I get all the blocks under B. For
now when I expand `<<foo>>` I only get the blocks under A that are not under B.

Is there a way to do this with the current features of org-babel?

Anyway I tried to hack my way trough it. It seems there are two things
to do :
1) Enable noweb-ref to contain multiple references.
2) Accumulate references when using header-args+ or use tags to set the
value of noweb-ref

I came up with a quick patch for 1):
modified   lisp/ob-core.el
@@ -2910,8 +2910,11 @@ block but are passed literally to the \"example-block\"."
                        (if (org-in-commented-heading-p)
                            (org-forward-heading-same-level nil t)
                          (let* ((info (org-babel-get-src-block-info t))
-                                (ref (cdr (assq :noweb-ref (nth 2 info)))))
-                           (push info (gethash ref cache))))))
+                                (refs (cdr (assq :noweb-ref (nth 2 info)))))
+                            (if refs
+                                (dolist (ref (s-split "+" refs))
+                                 (push info (gethash ref cache)))
+                              (push info (gethash refs cache)))))))
                     (funcall expand-references id cache)))))
             ;; Interpose PREFIX between every line.
             (mapconcat #'identity

With this I already get interesting results. A noweb-ref "foo+bar" gets
expanded by <<foo>> by and <<bar>>. For example if I define references like
this

#+BEGIN_SRC emacs-lisp :noweb-ref one
aaa
#+END_SRC
#+BEGIN_SRC emacs-lisp :noweb-ref two
bbb
#+END_SRC
#+BEGIN_SRC emacs-lisp :noweb-ref one+two
ababab
#+END_SRC

and tangle them like this

#+BEGIN_SRC emacs-lisp :tangle one.el :noweb yes
<<one>>
#+END_SRC
#+BEGIN_SRC emacs-lisp :tangle two.el :noweb yes
<<two>>
#+END_SRC

I get two files
one.el:
aaa
ababab

and two.el:
bbb
ababab

This is already nice!
Feedback on the code is of course very welcome. Not sure if using a plus
sign as a delimiter is clever. Also not sure if using `s-split` is a
good idea, what would be the builtin alternative?

For 2) I didn't check in detail how one could achieve this. I have the
impression it would be easier to use tags. One could define a
new variable `org-babel-set-noweb-refs-from-tags` that would be used in
`org-babel-get-src-block-info` to generate the value of noweb-ref we
would like to have depending on the tags of the headline of the
block. I'll try this soonish.

Best,

Théo