org-latex-preview: Improve preview creation msg

* lisp/org-latex-preview.el: (org-latex-preview,
org-latex-preview-create-image-async): `org-latex-preview' starts an
async process, and so it can only inform the user of the start of the
process. Information about the completion (to success or failure) is
provided by the relevant process sentinels instead.
(org-latex-preview--latex-log, org-latex-preview--image-log,
org-latex-preview--precompile-log): Log buffer names for preview latex
processing.
(org-latex-preview--tex-compile-async,
org-latex-preview--image-extract-async, org-latex-preview-precompile,
org-latex-preview-create-image): Use the newly created log buffer name
variables.

lisp/org-latex-preview.el

@@ -226,6 +226,13 @@ images at the same place."
   "Face applied to LaTeX fragments for which a preview is being generated."
   :group 'org-faces)
 
+(defconst org-latex-preview--image-log "*Org Preview Convert Output*"
+  "Buffer name for Preview image conversion output.")
+(defconst org-latex-preview--latex-log "*Org Preview LaTeX Output*"
+  "Buffer name for Preview LaTeX output.")
+(defconst org-latex-preview--precompile-log "*Org Preview Preamble Precompilation*"
+  "Buffer name for Preview LaTeX output.")
+
 (defun org-format-latex-mathml-available-p ()
   "Return t if `org-latex-to-mathml-convert-command' is usable."
   (save-match-data
@@ -643,8 +650,7 @@ fragments in the buffer."
    ;; Preview whole buffer.
    ((equal arg '(16))
     (message "Creating LaTeX previews in buffer...")
-    (org-latex-preview--preview-region (point-min) (point-max))
-    (message "Creating LaTeX previews in buffer... done."))
+    (org-latex-preview--preview-region (point-min) (point-max)))
    ;; Clear current section.
    ((equal arg '(4))
     (org-latex-preview-clear-overlays
@@ -658,8 +664,7 @@ fragments in the buffer."
        (org-with-limited-levels (org-entry-end-position)))))
    ((use-region-p)
     (message "Creating LaTeX previews in region...")
-    (org-latex-preview--preview-region (region-beginning) (region-end))
-    (message "Creating LaTeX previews in region... done."))
+    (org-latex-preview--preview-region (region-beginning) (region-end)))
    ;; Toggle preview on LaTeX code at point.
    ((let ((datum (org-element-context)))
       (and (memq (org-element-type datum) '(latex-environment latex-fragment))
@@ -668,8 +673,7 @@ fragments in the buffer."
              (if (org-latex-preview-clear-overlays beg end)
                  (message "LaTeX preview removed")
                (message "Creating LaTeX preview...")
-               (org-latex-preview--preview-region beg end)
-               (message "Creating LaTeX preview... done."))
+               (org-latex-preview--preview-region beg end))
              t))))
    ;; Preview current section.
    (t
@@ -678,8 +682,7 @@ fragments in the buffer."
                    (org-with-limited-levels (org-back-to-heading t) (point)))))
           (end (org-with-limited-levels (org-entry-end-position))))
       (message "Creating LaTeX previews in section...")
-      (org-latex-preview--preview-region beg end)
-      (message "Creating LaTeX previews in section... done.")))))
+      (org-latex-preview--preview-region beg end)))))
 
 (defun org-latex-preview-collect-fragments (&optional beg end)
   "Collect all LaTeX maths fragments/environments between BEG and END."
@@ -841,10 +844,11 @@ Some of the options can be changed using the variable
                         :key hash)
                   fragment-info))
           (setq prev-fg fg prev-bg bg))))
-    (when fragment-info
-      (org-latex-preview-create-image-async
-       processing-type
-       (nreverse fragment-info)))))
+    (if fragment-info
+        (org-latex-preview-create-image-async
+         processing-type
+         (nreverse fragment-info))
+      (message "Creating LaTeX previews... done."))))
 
 (defun org-latex-preview--colors-at (pos)
   "Find colors for LaTeX previews to be inserted at POS."
@@ -947,9 +951,13 @@ during processing to hold more information on the fragments."
       (plist-put (cddr img-extract-async) :success
                  (list ; The order is important here.
                   #'org-latex-preview--check-all-fragments-produced
-                  #'org-latex-preview--cleanup-callback))
+                  #'org-latex-preview--cleanup-callback
+                  "Creating LaTeX previews... done."))
       (plist-put (cddr img-extract-async) :failure
-                 #'org-latex-preview--failure-callback)
+                 (list
+                  #'org-latex-preview--failure-callback
+                  (format "Creating LaTeX previews... failed. Please see %s for details"
+                          (propertize org-latex-preview--image-log 'face 'warning))))
       (pcase processing-type
         ('dvipng
          (plist-put (cddr img-extract-async) :filter
@@ -1034,7 +1042,7 @@ The path of the created LaTeX file is returned."
   "Create an `org-async-call' spec to compile the texfile in EXTENDED-INFO."
   (let* ((tex-process-buffer
           (with-current-buffer
-              (get-buffer-create "*Org Preview LaTeX Output*")
+              (get-buffer-create org-latex-preview--latex-log)
             (erase-buffer)
             (current-buffer)))
          (tex-compile-command
@@ -1066,7 +1074,7 @@ The path of the created LaTeX file is returned."
   "Create an `org-async-call' spec to extract images according to EXTENDED-INFO."
   (let* ((img-process-buffer
           (with-current-buffer
-              (get-buffer-create "*Org Preview Convert Output*")
+              (get-buffer-create org-latex-preview--image-log)
             (erase-buffer)
             (current-buffer)))
          (img-extract-command
@@ -1505,7 +1513,7 @@ process."
          (header-file (concat header-base-file ".tex"))
          (precompile-buffer
           (with-current-buffer
-              (get-buffer-create "*Org Preview Preamble Precompilation*")
+              (get-buffer-create org-latex-preview--precompile-log)
             (erase-buffer)
             (current-buffer))))
     (if (file-exists-p dump-file)
@@ -1780,7 +1788,7 @@ a HTML file."
           (or (and (string= bg "Transparent")
                    (plist-get processing-info :transparent-image-converter))
               (plist-get processing-info :image-converter)))
-         (log-buf (get-buffer-create "*Org Preview LaTeX Output*"))
+         (log-buf (get-buffer-create org-latex-preview--latex-log))
          (resize-mini-windows nil)) ;Fix Emacs flicker when creating image.
     (dolist (program programs)
       (org-check-external-command program error-message))