org-html-src-block: Treat code blocks without LANG equally

* lisp/ox-html.el (org-html-src-block): Do not treat src blocks
without LANG as example blocks.  Instead, export them using "nil"
language.  This way, such src blocks will get captions, unlike example
blocks.

The new behavior is consistent with ox-latex and ox-ascii.

Reported-by: Johan Bolmsjö <org-mode@johan.bitmaster.se>
Link: https://orgmode.org/list/87zgb90win.fsf@localhost

lisp/ox-html.el

@@ -3616,32 +3616,32 @@ contextual information."
 	   (klipsify  (and  (plist-get info :html-klipsify-src)
                             (member lang '("javascript" "js"
 					   "ruby" "scheme" "clojure" "php" "html")))))
-      (if (not lang) (format "<pre class=\"example\"%s>\n%s</pre>" label code)
+      (format "<div class=\"org-src-container\">\n%s%s\n</div>"
-	(format "<div class=\"org-src-container\">\n%s%s\n</div>"
+	      ;; Build caption.
-		;; Build caption.
+	      (let ((caption (org-export-get-caption src-block)))
-		(let ((caption (org-export-get-caption src-block)))
+		(if (not caption) ""
-		  (if (not caption) ""
+		  (let ((listing-number
-		    (let ((listing-number
+			 (format
-			   (format
+			  "<span class=\"listing-number\">%s </span>"
-			    "<span class=\"listing-number\">%s </span>"
+			  (format
-			    (format
+			   (org-html--translate "Listing %d:" info)
-			     (org-html--translate "Listing %d:" info)
+			   (org-export-get-ordinal
-			     (org-export-get-ordinal
+			    src-block info nil #'org-html--has-caption-p)))))
-			      src-block info nil #'org-html--has-caption-p)))))
+		    (format "<label class=\"org-src-name\">%s%s</label>"
-		      (format "<label class=\"org-src-name\">%s%s</label>"
+			    listing-number
-			      listing-number
+			    (org-trim (org-export-data caption info))))))
-			      (org-trim (org-export-data caption info))))))
+	      ;; Contents.
-		;; Contents.
+	      (if klipsify
-		(if klipsify
+		  (format "<pre><code class=\"src src-%s\"%s%s>%s</code></pre>"
-		    (format "<pre><code class=\"src src-%s\"%s%s>%s</code></pre>"
+			  lang ; lang being nil is OK.
-			    lang
+			  label
-			    label
+			  (if (string= lang "html")
-			    (if (string= lang "html")
+			      " data-editor-type=\"html\""
-				" data-editor-type=\"html\""
+			    "")
-			      "")
+			  code)
-			    code)
+		(format "<pre class=\"src src-%s\"%s>%s</pre>"
-		  (format "<pre class=\"src src-%s\"%s>%s</pre>"
+                        ;; Lang being nil is OK.
-                          lang label code)))))))
+                        lang label code))))))
 
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