ox-latex: Allow percent sign in 'src-block' caption

* lisp/ox-latex.el (org-latex-src-block): Prevent leak of percent sign
from caption to `format' first argument causing export failure due to
insufficient argument number.  The fix covers only the case of verbatim
environment.
* testing/lisp/test-ox.el
(test-org-export/latex-src-block-verbatim-caption): New test for src
block LaTeX export with cases of various formatting of caption and
verbatim environment.  Check that percent signs in caption and source
block body do not lead to errors.

Reported-by: Charest, Luc <charest.luc@hydroquebec.com>
<https://lists.gnu.org/archive/html/emacs-orgmode/2021-08/msg00017.html>

lisp/ox-latex.el

@@ -2942,22 +2942,20 @@ contextual information."
       (cond
        ;; Case 1.  No source fontification.
        ((or (not lang) (not listings))
-	(let* ((caption-str (org-latex--caption/label-string src-block info))
-	       (float-env
-		(cond ((string= "multicolumn" float)
-		       (format "\\begin{figure*}[%s]\n%s%%s\n%s\\end{figure*}"
-			       (plist-get info :latex-default-figure-position)
-			       (if caption-above-p caption-str "")
-			       (if caption-above-p "" caption-str)))
-		      (caption (concat
-				(if caption-above-p caption-str "")
-				"%s"
-				(if caption-above-p "" (concat "\n" caption-str))))
-		      (t "%s"))))
-	  (format
-	   float-env
-	   (concat (format "\\begin{verbatim}\n%s\\end{verbatim}"
-			   (org-export-format-code-default src-block info))))))
+	(let ((caption-str (org-latex--caption/label-string src-block info))
+              (verbatim (format "\\begin{verbatim}\n%s\\end{verbatim}"
+                                (org-export-format-code-default src-block info))))
+          (cond ((string= "multicolumn" float)
+                 (format "\\begin{figure*}[%s]\n%s%s\n%s\\end{figure*}"
+                         (plist-get info :latex-default-figure-position)
+                         (if caption-above-p caption-str "")
+                         verbatim
+                         (if caption-above-p "" caption-str)))
+                (caption (concat
+                          (if caption-above-p caption-str "")
+                          verbatim
+                          (if caption-above-p "" (concat "\n" caption-str))))
+                (t verbatim))))
        ;; Case 2.  Custom environment.
        (custom-env
 	(let ((caption-str (org-latex--caption/label-string src-block info))

testing/lisp/test-ox.el

@@ -3896,6 +3896,103 @@ Another text. (ref:text)
 	      (org-export-format-code-default
 	       (org-element-map tree 'src-block #'identity info t) info))))))
 
+(ert-deftest test-org-export/latex-src-block-verbatim-caption ()
+  "Test `org-latex-src-block' caption for verbatim environment.
+Check that percent sign does not become a part of format.
+This test does not cover listings and custom environments."
+  (let ((export
+	 (lambda (buffer-text)
+	   (org-test-with-parsed-data
+	       buffer-text
+	     (let* ((backend (org-export-get-backend 'latex))
+		    (info (org-combine-plists
+			   (org-export--get-export-attributes backend)
+			   (org-export-get-environment backend)))
+		    (result (org-latex-src-block
+			     (org-element-map tree 'src-block #'identity info t)
+			     t info)))
+	       ;; Remove properties to make failure reports more clear.
+	       (set-text-properties 0 (length result) nil result)
+	       result)))))
+
+    (should (equal
+	     "\
+\\begin{verbatim}
+\"No float, no listings, 20%S\"
+\\end{verbatim}
+\\captionof{figure}{Caption of verbatim is below, 20\\%s}
+"
+	     (funcall export
+		      "\
+#+CAPTION: Caption of verbatim is below, 20%s
+#+BEGIN_SRC emacs-lisp
+  \"No float, no listings, 20%S\"
+#+END_SRC")))
+
+    ;; `org-latex-caption-above' has no associated property or keyword.
+    (should (equal
+	     "\
+\\captionof{figure}{Caption of verbatim is above, 40\\%s}
+\\begin{verbatim}
+\"No float, no listings, 40%S\"
+\\end{verbatim}"
+	     (let ((org-latex-caption-above t))
+	       (funcall export
+			"\
+#+CAPTION: Caption of verbatim is above, 40%s
+#+BEGIN_SRC emacs-lisp
+  \"No float, no listings, 40%S\"
+#+END_SRC"))))
+
+    (should (equal
+	     "\
+\\begin{figure*}[tp]
+\\caption{Caption is above, 60\\%s}
+\\begin{verbatim}
+\"Float, no listings, 60%S\"
+\\end{verbatim}
+\\end{figure*}"
+	     (let ((org-latex-caption-above t)
+		   (org-latex-default-figure-position "tp"))
+	       (funcall export
+			"\
+#+CAPTION: Caption is above, 60%s
+#+ATTR_LATEX: :float multicolumn
+#+BEGIN_SRC emacs-lisp
+  \"Float, no listings, 60%S\"
+#+END_SRC"))))
+
+    (should (equal
+	     "\
+\\begin{figure*}[tp]
+\\begin{verbatim}
+\"Float, no lang, listings, 80%S\"
+\\end{verbatim}
+\\caption{Caption is below, 60\\%s}
+\\end{figure*}"
+	     (let ((org-latex-listings 'minted) ; inactive due to missing lang
+		   (org-latex-default-figure-position "tp"))
+	       ;; Namely "multicolumn" value to get just figure environment
+	       ;; looks like a bug.
+	       (funcall export
+			"\
+#+CAPTION: Caption is below, 60%s
+#+ATTR_LATEX: :float multicolumn
+#+BEGIN_SRC
+  \"Float, no lang, listings, 80%S\"
+#+END_SRC"))))
+
+    (should (equal
+	     "\
+\\begin{verbatim}
+\"No caption, no float, no listings, 100%S\"
+\\end{verbatim}"
+	     (funcall export
+		      "\
+#+BEGIN_SRC emacs-lisp
+  \"No caption, no float, no listings, 100%S\"
+#+END_SRC")))))
+
 
 
 ;;; Smart Quotes