ob-core.el: Add :noweb-prefix babel header argument

* lisp/ob-core.el (org-babel-expand-noweb-references): Add support for
`noweb-prefix' header argument, to not repeat the prefix characters
when expanding a noweb reference.
(org-babel-common-header-args-w-values):
(org-babel-safe-header-args): Add `noweb-prefix' value.
* doc/org-manual.org: Document `noweb-prefix' babel header argument.
* etc/ORG-NEWS: Document `:noweb-prefix'.

Author: sebmiq

doc/org-manual.org

@@ -18760,6 +18760,23 @@ else:
     print('do things when false')
 #+end_example
 
+This prefix behavior can be turned off in a block by setting the
+=noweb-prefix= header argument to =no=, as in:
+
+#+begin_example
+,#+BEGIN_SRC elisp :noweb-prefix no
+  (setq example-data "<<example>>")
+,#+END_SRC
+#+end_example
+
+#+texinfo: @noindent
+which expands to:
+
+#+begin_example
+(setq example-data "this is the
+multi-line body of example")
+#+end_example
+
 When in doubt about the outcome of a source code block expansion, you
 can preview the results with the following command:
 

etc/ORG-NEWS

@@ -150,7 +150,7 @@ The entry points are ~org-persist-register~, ~org-persist-unregister~,
 ~org-persist-read~, and ~org-persist-read-all~.  Storing circular
 structures is supported.  Storing references between different
 variables is also supported (see =:inherit= key in
-~org-persist-register~).  
+~org-persist-register~).
 
 The library permits storing buffer-local variables.  Such variables
 are linked to the buffer text, file =inode=, and file path.
@@ -175,6 +175,10 @@ the =compact-itemx= export option, or globally using the
 Items in a description list that begin with =Function:=, =Variable:=
 or certain related prefixes are converted using Texinfo definition
 commands.
+*** New =:noweb-prefix= babel header argument
+
+=:noweb-prefix= can be set to =no= to prevent the prefix characters
+from being repeated when expanding a multiline noweb reference.
 
 ** New functions and changes in function arguments
 

lisp/ob-core.el

@@ -413,6 +413,7 @@ then run `org-babel-switch-to-session'."
     (noweb	. ((yes no tangle no-export strip-export)))
     (noweb-ref	. :any)
     (noweb-sep  . :any)
+    (noweb-prefix . ((no yes)))
     (output-dir . :any)
     (padline	. ((yes no)))
     (post       . :any)
@@ -438,8 +439,8 @@ specific header arguments as well.")
 
 (defconst org-babel-safe-header-args
   '(:cache :colnames :comments :exports :epilogue :hlines :noeval
-	   :noweb :noweb-ref :noweb-sep :padline :prologue :rownames
-	   :sep :session :tangle :wrap
+	   :noweb :noweb-ref :noweb-sep :noweb-prefix :padline
+           :prologue :rownames :sep :session :tangle :wrap
 	   (:eval . ("never" "query"))
 	   (:results . (lambda (str) (not (string-match "file" str)))))
   "A list of safe header arguments for babel source blocks.
@@ -2827,6 +2828,10 @@ block but are passed literally to the \"example-block\"."
          (lang (nth 0 info))
          (body (nth 1 info))
 	 (comment (string= "noweb" (cdr (assq :comments (nth 2 info)))))
+         (noweb-prefix (let ((v (assq :noweb-prefix (nth 2 info))))
+                         (or (not v)
+                             (and (org-not-nil (cdr v))
+                                  (not (equal (cdr v) "no"))))))
 	 (noweb-re (format "\\(.*?\\)\\(%s\\)"
 			   (with-current-buffer parent-buffer
 			     (org-babel-noweb-wrap))))
@@ -2923,9 +2928,11 @@ block but are passed literally to the \"example-block\"."
 			    (push info (gethash ref cache))))))
 		     (funcall expand-references id cache)))))
 	     ;; Interpose PREFIX between every line.
-	     (mapconcat #'identity
-			(split-string expansion "[\n\r]")
-			(concat "\n" prefix))))))
+	     (if noweb-prefix
+                 (mapconcat #'identity
+			    (split-string expansion "[\n\r]")
+			    (concat "\n" prefix))
+               expansion)))))
      body t t 2)))
 
 (defun org-babel--script-escape-inner (str)