ob-exp: Preserve header arguments in source block after processing

* lisp/ob-exp.el (org-babel-exp-process-buffer): Fix infinite loop
when the inline src block replacement is the same as the existing src
block.
(org-babel-exp-code): Support new placeholder %header-args for
non-default header arguments.
(org-babel-exp-inline-code-template):
(org-babel-exp-code-template): Change the templates to include header
arguments.
* testing/lisp/test-ob-exp.el (ob-exp/exports-inline-code):
(ob-exp/exports-inline-code-double-eval-exports-both):
(ob-export/export-with-results-before-block): Adjust tests.
* etc/ORG-NEWS (=ox-org= preserves header non-default arguments in src
blocks): Document the breaking change.

This change fixes ox-org export for src blocks.  Previously src blocks
did not preserve their header arguments.  Now, non-default header
arguments are preserved.

Link: https://github.com/emacsorphanage/ox-pandoc/issues/37

etc/ORG-NEWS

@@ -83,6 +83,11 @@ transcoders.
 
 Users can disable citations processors by customizing new
 ~org-export-process-citations~ option.
+*** =ox-org= preserves header non-default arguments in src blocks
+
+Previously, all the header arguments where stripped from src blocks
+during export.  Now, header arguments are preserved as long as their
+values are not equal to the default header argument values.
 
 *** =ox-org= disables citation processors by default
 

lisp/ob-exp.el

@@ -238,7 +238,10 @@ this template."
                             ((not (string= replacement
 					 (buffer-substring begin end)))
 			     (delete-region begin end)
-			     (insert replacement))))))
+			     (insert replacement))
+                            ;; Replacement is the same as the source
+                            ;; block.  Continue onwards.
+                            (t (goto-char end))))))
 		      ((or `babel-call `inline-babel-call)
 		       (org-babel-exp-do-export
 			(or (org-babel-lob-get-info element)
@@ -367,7 +370,7 @@ The function respects the value of the :exports header argument."
        nil))))
 
 (defcustom org-babel-exp-code-template
-  "#+begin_src %lang%switches%flags\n%body\n#+end_src"
+  "#+begin_src %lang%switches%flags%header-args\n%body\n#+end_src"
   "Template used to export the body of code blocks.
 This template may be customized to include additional information
 such as the code block name, or the values of particular header
@@ -379,6 +382,7 @@ and the following %keys may be used.
  body ------ the body of the code block
  switches -- the switches associated to the code block
  flags ----- the flags passed to the code block
+ header-args the non-default header arguments of the code block
 
 In addition to the keys mentioned above, every header argument
 defined for the code block may be used as a key and will be
@@ -388,7 +392,7 @@ replaced with its value."
   :package-version '(Org . "9.6"))
 
 (defcustom org-babel-exp-inline-code-template
-  "src_%lang[%switches%flags]{%body}"
+  "src_%lang[%switches%flags%header-args]{%body}"
   "Template used to export the body of inline code blocks.
 This template may be customized to include additional information
 such as the code block name, or the values of particular header
@@ -400,6 +404,7 @@ and the following %keys may be used.
  body ------ the body of the code block
  switches -- the switches associated to the code block
  flags ----- the flags passed to the code block
+ header-args the non-default header arguments of the code block
 
 In addition to the keys mentioned above, every header argument
 defined for the code block may be used as a key and will be
@@ -432,6 +437,41 @@ replaced with its value."
 		      (and (org-string-nw-p f) (concat " " f))))
      ("flags" . ,(let ((f (assq :flags (nth 2 info))))
 		   (and f (concat " " (cdr f)))))
+     ("header-args"
+      .
+      ,(let* ((header-args
+               (mapcar
+                (lambda (pair)
+                  ;; Do no include special parameters, parameters with
+                  ;; their values equal to defaults.
+                  (unless (or
+                           ;; Special parameters that are not real header
+                           ;; arguments.
+                           (memq (car pair)
+                                 '( :result-params :result-type
+                                    ;; This is an obsolete parameter still
+                                    ;; used in some tests.
+                                    :flags))
+                           ;; Global defaults.
+                           (equal (cdr pair)
+                                  (alist-get
+                                   (car pair)
+                                   (if (eq type 'inline) org-babel-default-inline-header-args
+			             org-babel-default-header-args)))
+                           ;; Per-language defaults.
+                           (let ((lang-headers
+                                  (intern
+			           (concat "org-babel-default-header-args:"
+                                           (nth 0 info)))))
+                             (and (boundp lang-headers)
+                                  (equal (cdr pair)
+                                         (alist-get (car pair)
+                                                    (eval lang-headers t))))))
+                    (format "%s %s" (car pair) (cdr pair))))
+                (nth 2 info)))
+              (header-arg-string
+               (mapconcat #'identity (delq nil header-args) " ")))
+         (unless (seq-empty-p header-arg-string) (concat " " header-arg-string))))
      ,@(mapcar (lambda (pair)
 		 (cons (substring (symbol-name (car pair)) 1)
 		       (format "%S" (cdr pair))))

testing/lisp/test-ob-exp.el

@@ -205,14 +205,14 @@ Here is one at the end of a line. {{{results(=2=)}}}
 
 (ert-deftest ob-exp/exports-inline-code ()
   (should
-   (equal "src_emacs-lisp[]{(+ 1 1)}"
+   (equal "src_emacs-lisp[ :exports code]{(+ 1 1)}"
 	  (org-test-with-temp-text "src_emacs-lisp[:exports code]{(+ 1 1)}"
 	    (let ((org-babel-inline-result-wrap "=%s=")
 		  (org-export-use-babel t))
 	      (org-babel-exp-process-buffer))
 	    (buffer-string))))
   (should
-   (equal "src_emacs-lisp[]{(+ 1 1)}"
+   (equal "src_emacs-lisp[ :exports code]{(+ 1 1)}"
 	  (org-test-with-temp-text "src_emacs-lisp[ :exports code ]{(+ 1 1)}"
 	    (let ((org-babel-inline-result-wrap "=%s=")
 		  (org-export-use-babel t))
@@ -220,14 +220,14 @@ Here is one at the end of a line. {{{results(=2=)}}}
 	    (buffer-string))))
   ;; Do not escape characters in inline source blocks.
   (should
-   (equal "src_c[]{*a}"
+   (equal "src_c[ :exports code]{*a}"
 	  (org-test-with-temp-text "src_c[ :exports code ]{*a}"
 	    (let ((org-babel-inline-result-wrap "=%s=")
 		  (org-export-use-babel t))
 	      (org-babel-exp-process-buffer))
 	    (buffer-string))))
   (should
-   (equal "src_emacs-lisp[]{(+ 1 1)} {{{results(=2=)}}}"
+   (equal "src_emacs-lisp[ :exports both]{(+ 1 1)} {{{results(=2=)}}}"
 	  (org-test-with-temp-text "src_emacs-lisp[:exports both]{(+ 1 1)}"
 	    (let ((org-babel-inline-result-wrap "=%s=")
 		  (org-export-use-babel t))
@@ -262,10 +262,10 @@ Here is one at the end of a line. {{{results(=2=)}}}
    (string-match
     (replace-regexp-in-string
      "\\\\\\[]{" "\\(?:\\[]\\)?{" ;accept both src_sh[]{...} or src_sh{...}
-     (regexp-quote "Here is one in the middle src_sh[]{echo 1} of a line.
+     (regexp-quote "Here is one in the middle src_sh[ :exports code]{echo 1} of a line.
-Here is one at the end of a line. src_sh[]{echo 2}
+Here is one at the end of a line. src_sh[ :exports code]{echo 2}
-src_sh[]{echo 3} Here is one at the beginning of a line.
+src_sh[ :exports code]{echo 3} Here is one at the beginning of a line.
-Here is one that is also evaluated: src_sh[]{echo 4} {{{results(=4=)}}}")
+Here is one that is also evaluated: src_sh[ :exports both]{echo 4} {{{results(=4=)}}}")
      nil t)
     (org-test-at-id "cd54fc88-1b6b-45b6-8511-4d8fa7fc8076"
       (org-narrow-to-subtree)
@@ -301,7 +301,7 @@ be evaluated."
 (ert-deftest ob-exp/exports-inline-code-double-eval-exports-both ()
   (let ((org-export-use-babel t))
     (should
-     (string-match (concat "\\`src_emacs-lisp\\(?:\\[]\\)?{(\\+ 1 1)} "
+     (string-match (concat "\\`src_emacs-lisp\\(?:\\[.+?]\\)?{(\\+ 1 1)} "
 			   "{{{results(src_emacs-lisp\\[ :exports code\\]{2})}}}$")
 		   (org-test-with-temp-text
 		       (concat "src_emacs-lisp[:exports both :results code "
@@ -403,7 +403,7 @@ be evaluated."
 : 2
 
 #+NAME: src1
-#+begin_src emacs-lisp
+#+begin_src emacs-lisp :exports both
 \(+ 1 1)
 #+end_src"
       (org-test-with-temp-text