ox: Make export errors more prominent

* lisp/ox-html.el (org-html-fontify-code):
* lisp/ox-latex.el (org-latex-generate-engraved-preamble):
(org-latex-inline-src-block):
(org-latex-src-block):
(org-latex-src--engrave-code):
* lisp/ox-odt.el:
(org-odt--table):
(org-odt--translate-latex-fragments):
(org-odt--export-wrap): Use `warn' instead of `message' when external
dependency/tool is missing/fails.

lisp/ox-html.el

@@ -2326,9 +2326,9 @@ is the language used for CODE, as a string, or nil."
      ((not org-html-htmlize-output-type) (org-html-encode-plain-text code))
      ;; No htmlize library or an inferior version of htmlize.
      ((not (progn (require 'htmlize nil t)
-		  (fboundp 'htmlize-region-for-paste)))
+		(fboundp 'htmlize-region-for-paste)))
       ;; Emit a warning.
-      (message "Cannot fontify source block (htmlize.el >= 1.34 required)")
+      (warn "Cannot fontify source block (htmlize.el >= 1.34 required)")
       (org-html-encode-plain-text code))
      (t
       ;; Map language

lisp/ox-latex.el

@@ -1374,7 +1374,7 @@ which are given by `org-latex-engraved-preamble' and
                         "\n"))
                (t (funcall gen-theme-spec engraved-theme))))
            (funcall gen-theme-spec engraved-theme))
-       (message "Cannot engrave source blocks. Consider installing `engrave-faces'.")
+       (warn "Cannot engrave source blocks. Consider installing `engrave-faces'.")
        "% WARNING syntax highlighting unavailable as engrave-faces-latex was missing.\n")
      "\n")))
 
@@ -2423,8 +2423,8 @@ contextual information."
       (`engraved (org-latex-inline-src-block--engraved info code lang))
       (`listings (org-latex-inline-src-block--listings info code lang))
       (oldval
-       (message "Please update the LaTeX src-block-backend to %s"
-                (if oldval "listings" "verbatim"))
+       (warn "Please update the LaTeX src-block-backend to %s"
+             (if oldval "listings" "verbatim"))
        (if oldval
            (org-latex-inline-src-block--listings info code lang)
          (org-latex--text-markup code 'code info))))))
@@ -3321,8 +3321,8 @@ contextual information."
          (`listings #'org-latex-src-block--listings)
          ((guard custom-env) #'org-latex-src-block--custom)
          (oldval
-          (message "Please update the LaTeX src-block-backend to %s"
-                   (if oldval "listings" "verbatim"))
+          (warn "Please update the LaTeX src-block-backend to %s"
+                (if oldval "listings" "verbatim"))
           (if oldval
               #'org-latex-src-block--listings
             #'org-latex-src-block--verbatim)))
@@ -3498,8 +3498,8 @@ to the Verbatim environment or Verb command."
                 (when lang-mode
                   (if (functionp lang-mode)
                       (funcall lang-mode)
-                    (message "Cannot engrave code as %s. %s is undefined."
-                             lang lang-mode)))
+                    (warn "Cannot engrave code as %s. %s is undefined."
+                          lang lang-mode)))
                 (engrave-faces-latex-buffer)))
              (engraved-code
               (with-current-buffer engraved-buffer

lisp/ox-odt.el

@@ -1009,7 +1009,7 @@ See `org-odt--build-date-styles' for implementation details."
 	      (setq exit-code (archive-zip-extract archive member))
 	      (buffer-string)))
       (unless (zerop exit-code)
-	(message command-output)
+	(warn command-output)
 	(error "Extraction failed")))))
 
 ;;;; Target
@@ -3413,7 +3413,7 @@ contextual information."
     ;; such tables from export.
     (table.el
      (prog1 nil
-       (message
+       (warn
 	(concat
 	 "(ox-odt): Found table.el-type table in the source Org file."
 	 "  table.el doesn't support export to ODT format."
@@ -3720,16 +3720,16 @@ contextual information."
        (if (and (fboundp 'org-format-latex-mathml-available-p)
 		(org-format-latex-mathml-available-p))
 	   (setq processing-type 'mathml)
-	 (message "LaTeX to MathML converter not available.")
+	 (warn "LaTeX to MathML converter not available.  Falling back to verbatim.")
 	 (setq processing-type 'verbatim)))
       ((dvipng imagemagick)
        (unless (and (org-check-external-command "latex" "" t)
 		    (org-check-external-command
 		     (if (eq processing-type 'dvipng) "dvipng" "convert") "" t))
-	 (message "LaTeX to PNG converter not available.")
+	 (warn "LaTeX to PNG converter not available.  Falling back to verbatim.")
 	 (setq processing-type 'verbatim)))
       (otherwise
-       (message "Unknown LaTeX option.  Forcing verbatim.")
+       (warn "Unknown LaTeX option.  Forcing verbatim.")
        (setq processing-type 'verbatim)))
 
     ;; Store normalized value for later use.
@@ -4089,8 +4089,8 @@ contextual information."
        (error
 	;; Cleanup work directory and work files.
 	(funcall --cleanup-xml-buffers)
-	(message "OpenDocument export failed: %s"
-		 (error-message-string err))))))
+	(warn "OpenDocument export failed: %s"
+	      (error-message-string err))))))
 
 
 ;;;; Export to OpenDocument formula