Re: [BUG] obscure error for invalid :exports

[Ihor Radchenko]

Max Nikulin <manikulin@gmail.com> writes:

> Trying to export (to HTML buffer)
>
>      src_elisp[:exports source]{a}
>
> I have got an obscure error
>
>      org-export-as: Wrong type argument: char-or-string-p, nil
>
> I believe, some meaningful error should be signaled.
>
> I was quite surprised since the following is exported with no error
>
>      #+begin_src elisp :exports source
>        a
>      #+end_src

Confirmed.

The behavior on unknown value of :exports header arg is undefined.
We may, however, show a warning in such scenario and avoid throwing
cryptic error.
See the attached tentative patch.

>From 8fcf787ca739008118f9834720ee56d6e190401d Mon Sep 17 00:00:00 2001
Message-ID: 
<8fcf787ca739008118f9834720ee56d6e190401d.1709891167.git.yantar92@posteo.net>
From: Ihor Radchenko <yantar92@posteo.net>
Date: Fri, 8 Mar 2024 12:42:33 +0300
Subject: [PATCH] org-export: Display a warning when the value of :exports
 header arg is invalid

* lisp/ob-exp.el (org-babel-exp-do-export): Display warning when
:exports value is not known.  Document nil return value.
(org-babel-exp-process-buffer): Do not remove code block when
`org-babel-exp-do-export' returns nil.

Reported-by: Max Nikulin <manikulin@gmail.com>
Link: https://orgmode.org/list/usc9jn$g2r$1@ciao.gmane.io
---
 lisp/ob-exp.el | 70 +++++++++++++++++++++++++++++++-------------------
 1 file changed, 43 insertions(+), 27 deletions(-)

diff --git a/lisp/ob-exp.el b/lisp/ob-exp.el
index aa6091924..af726dc2c 100644
--- a/lisp/ob-exp.el
+++ b/lisp/ob-exp.el
@@ -218,22 +218,27 @@ (defun org-babel-exp-process-buffer ()
                         (goto-char begin)
                         (let ((replacement
                                (org-babel-exp-do-export info 'inline)))
-                          (if (equal replacement "")
-                              ;; Replacement code is empty: remove
-                              ;; inline source block, including extra
-                              ;; white space that might have been
-                              ;; created when inserting results.
-                              (delete-region begin
-                                             (progn (goto-char end)
-                                                    (skip-chars-forward " \t")
-                                                    (point)))
-                            ;; Otherwise: remove inline source block
-                            ;; but preserve following white spaces.
-                            ;; Then insert value.
-                            (unless (string= replacement
-                                             (buffer-substring begin end))
-                              (delete-region begin end)
-                              (insert replacement))))))
+                          (cond
+                            ((equal replacement "")
+                            ;; Replacement code is empty: remove
+                            ;; inline source block, including extra
+                            ;; white space that might have been
+                            ;; created when inserting results.
+                            (delete-region begin
+                                           (progn (goto-char end)
+                                                  (skip-chars-forward " \t")
+                                                  (point))))
+                            ((not replacement)
+                             ;; Replacement code cannot be determined.
+                             ;; Leave the code block as is.
+                             (goto-char end))
+                           ;; Otherwise: remove inline source block
+                           ;; but preserve following white spaces.
+                           ;; Then insert value.
+                            ((not (string= replacement
+                                        (buffer-substring begin end)))
+                            (delete-region begin end)
+                            (insert replacement))))))
                      ((or `babel-call `inline-babel-call)
                       (org-babel-exp-do-export
                        (or (org-babel-lob-get-info element)
@@ -249,21 +254,27 @@ (defun org-babel-exp-process-buffer ()
                         ;; the object/element, including any extra
                         ;; white space that might have been created
                         ;; when including results.
-                        (if (equal rep "")
-                            (delete-region
-                             begin
-                             (progn (goto-char end)
-                                    (if (not (eq type 'babel-call))
-                                        (progn (skip-chars-forward " \t")
-                                               (point))
-                                      (skip-chars-forward " \r\t\n")
-                                      (line-beginning-position))))
+                        (cond
+                          ((equal rep "")
+                          (delete-region
+                           begin
+                           (progn (goto-char end)
+                                  (if (not (eq type 'babel-call))
+                                      (progn (skip-chars-forward " \t")
+                                             (point))
+                                    (skip-chars-forward " \r\t\n")
+                                    (line-beginning-position)))))
+                          ((not rep)
+                           ;; Replacement code cannot be determined.
+                           ;; Leave the code block as is.
+                           (goto-char end))
+                          (t
                           ;; Otherwise, preserve trailing
                           ;; spaces/newlines and then, insert
                           ;; replacement string.
                           (goto-char begin)
                           (delete-region begin end)
-                          (insert rep))))
+                          (insert rep)))))
                      (`src-block
                       (let ((match-start (copy-marker (match-beginning 0)))
                             (ind (org-current-text-indentation)))
@@ -335,6 +346,8 @@ (defun org-babel-exp-do-export (info type &optional hash)
 TYPE is the code block type: `block', `inline', or `lob'.  HASH is the
 result hash.
 
+Return nil when exported content cannot be determined.
+
 The function respects the value of the :exports header argument."
   (let ((silently (lambda () (let ((session (cdr (assq :session (nth 2 
info)))))
                          (unless (equal "none" session)
@@ -348,7 +361,10 @@ (defun org-babel-exp-do-export (info type &optional hash)
       ("results" (org-babel-exp-results info type nil hash) "")
       ("both"
        (org-babel-exp-results info type nil hash)
-       (org-babel-exp-code info type)))))
+       (org-babel-exp-code info type))
+      (unknown-value
+       (warn "Unknown value of src block parameter :exports %S" unknown-value)
+       nil))))
 
 (defcustom org-babel-exp-code-template
   "#+begin_src %lang%switches%flags\n%body\n#+end_src"
-- 
2.43.0

-- 
Ihor Radchenko // yantar92,
Org mode contributor,
Learn more about Org mode at <https://orgmode.org/>.
Support Org development at <https://liberapay.com/org-mode>,
or support my work at <https://liberapay.com/yantar92>