ob-emacs-lisp: Set `lexical-binding' in edit buffers

* lisp/ob-emacs-lisp.el (org-babel-execute:emacs-lisp,
  org-babel-emacs-lisp-lexical): Factor out the conversion of the
  :lexical source block argument to a form that is appropriate for
  `lexical-binding' and the LEXICAL argument to `eval'.

* lisp/ob-emacs-lisp.el (org-babel-edit-prep:emacs-lisp): Set
  `lexical-binding'.

* lisp/ob-emacs-lisp.el (org-babel-default-header-args:emacs-lisp):
  Update docstring.

etc/ORG-NEWS

@@ -96,6 +96,10 @@ You can add dynamic block into ~org-dynamic-block-alist~ with function
 ~org-dynamic-block-insert-dblock~ command.
 
 *** Babel
+**** ob-emacs-lisp sets ~lexical-binding~ in Org edit buffers
+When editing an Elisp src block, the editing buffer's
+~lexical-binding~ is set according to the src block's =:lexical=
+parameter.
 **** Add LaTeX output support in PlantUML
 *** New minor mode to display headline numbering
 

lisp/ob-emacs-lisp.el

@@ -42,8 +42,9 @@
 
 A value of \"yes\" or t causes source blocks to be eval'd using
 lexical scoping.  It can also be an alist mapping symbols to
-their value.  It is used as the optional LEXICAL argument to
-`eval', which see.")
+their value.  It is used both as the optional LEXICAL argument to
+`eval', and as the value for `lexical-binding' in buffers created
+by `org-edit-src-code'.")
 
 (defun org-babel-expand-body:emacs-lisp (body params)
   "Expand BODY according to PARAMS, return the expanded body."
@@ -71,9 +72,7 @@ their value.  It is used as the optional LEXICAL argument to
 				       (member "pp" result-params))
 				   (concat "(pp " body ")")
 				 body))
-			 (if (listp lexical)
-			     lexical
-			   (member lexical '("yes" "t"))))))
+			 (org-babel-emacs-lisp-lexical lexical))))
       (org-babel-result-cond result-params
 	(let ((print-level nil)
               (print-length nil))
@@ -88,6 +87,23 @@ their value.  It is used as the optional LEXICAL argument to
          (org-babel-pick-name (cdr (assq :rowname-names params))
                               (cdr (assq :rownames params))))))))
 
+(defun org-babel-emacs-lisp-lexical (lexical)
+  "Interpret :lexical source block argument.
+Convert LEXICAL into the form appropriate for `lexical-binding'
+and the LEXICAL argument to `eval'."
+  (if (listp lexical)
+      lexical
+    (not (null (member lexical '("yes" "t"))))))
+
+(defun org-babel-edit-prep:emacs-lisp (info)
+  "Set `lexical-binding' in Org edit buffer.
+Set `lexical-binding' in Org edit buffer according to the
+corresponding :lexical source block argument."
+  (setq lexical-binding
+        (org-babel-emacs-lisp-lexical
+         (org-babel-read
+          (cdr (assq :lexical (nth 2 info)))))))
+
 (org-babel-make-language-alias "elisp" "emacs-lisp")
 
 (provide 'ob-emacs-lisp)