org-latex-preview: Use appropriate TeX compiler

* lisp/org-latex-preview.el (org-latex-preview--tex-compile-async,
org-latex-preview-process-alist): Introduce %l and %L placeholders for
the LaTeX compiler.
(org-latex-preview-precompile): Record the LaTeX compiler in the
preamble hash, and add %l/%L to the `org-compile-file' format spec.
(org-latex-preview-compiler-command-map): Introduce a new variable to
map each LaTeX compiler name to the command and arguments needed.

Note that due to idiosyncrasies in how the various TeX compilers behave,
pdfLaTeX will likely continue to provide a smoother experience.  In the
future, some work can be done to improve this situation.

lisp/org-latex-preview.el

@@ -132,8 +132,8 @@ All available processes and theirs documents can be found in
      :image-input-type "dvi"
      :image-output-type "png"
      :image-size-adjust (1.4 . 1.2)
-     :latex-compiler ("latex -interaction nonstopmode -output-directory %o %f")
-     :latex-precompiler ("latex -output-directory %o -ini -jobname=%b \"&latex\" mylatexformat.ltx %f")
+     :latex-compiler ("%l -interaction nonstopmode -output-directory %o %f")
+     :latex-precompiler ("%l -output-directory %o -ini -jobname=%b \"&%L\" mylatexformat.ltx %f")
      :image-converter ("dvipng --follow -D %D -T tight --depth --height -o %B-%%09d.png %f")
      :transparent-image-converter
      ("dvipng --follow -D %D -T tight -bg Transparent --depth --height -o %B-%%09d.png %f"))
@@ -144,8 +144,8 @@ All available processes and theirs documents can be found in
      :image-input-type "dvi"
      :image-output-type "svg"
      :image-size-adjust (1.4 . 1.2)
-     :latex-compiler ("latex -interaction nonstopmode -output-directory %o %f")
-     :latex-precompiler ("latex -output-directory %o -ini -jobname=%b \"&latex\" mylatexformat.ltx %f")
+     :latex-compiler ("%l -interaction nonstopmode -output-directory %o %f")
+     :latex-precompiler ("%l -output-directory %o -ini -jobname=%b \"&%L\" mylatexformat.ltx %f")
      ;; With dvisvgm the --bbox=preview flag is needed to emit the preview.sty-provided
      ;; height+width+depth information. The --optimise, --clipjoin, and --relative flags
      ;; cause dvisvgm do do some extra work to tidy up the SVG output, but barely add to
@@ -200,13 +200,19 @@ PROPERTIES accepts the following attributes:
 If set, :transparent-image-converter is used instead of :image-converter to
 convert an image when the background color is nil or \"Transparent\".
 
-Place-holders used by `:image-converter' and `:latex-compiler':
+Place-holders used by `:image-converter', `:latex-precompiler',
+and `:latex-compiler':
 
   %f    input file name
   %b    base name of input file
   %o    base directory of input file
   %O    absolute output file name
 
+Place-holders only used by `:latex-precompiler' and `:latex-compiler':
+
+  %l   LaTeX compiler command string
+  %L   LaTeX compiler command name
+
 Place-holders only used by `:image-converter':
 
   %D    dpi, which is used to adjust image size by some processing commands.
@@ -217,6 +223,22 @@ Place-holders only used by `:image-converter':
   :type '(alist :tag "LaTeX to image backends"
           :value-type (plist)))
 
+(defcustom org-latex-preview-compiler-command-map
+  '(("pdflatex" . "latex")
+    ("xelatex" . "xelatex -no-pdf")
+    ("lualatex" . "dvilualatex"))
+  "An alist mapping from each of `org-latex-compilers' to command strings.
+Each key is a LaTeX compiler name, for each compiler in
+`org-latex-compilers', and the value the command that should be used
+when producing a preview (optionally including flags).
+
+This should only ever be changed in the event that PDF, not DVI output
+is required."
+  :group 'org-latex-preview
+  :package-version '(Org . "9.7")
+  :type '(alist :tag "Compiler"
+          :value-type (string :type "command")))
+
 (defcustom org-preview-latex-image-directory "ltximg/"
   "Path to store latex preview images.
 A relative path here creates many directories relative to the
@@ -1181,7 +1203,7 @@ NUMBER is the equation number that should be used, if applicable."
                       (goto-char (org-element-property :begin datum))
                       (org-element-context)))))))))
 
-(defun org-latex-preview-create-image-async (processing-type fragments-info)
+(defun org-latex-preview-create-image-async (processing-type fragments-info &optional latex-processor)
   "Preview PREVIEW-STRINGS asynchronously with method PROCESSING-TYPE.
 
 FRAGMENTS-INFO is a list of plists, each of which provides
@@ -1194,13 +1216,29 @@ where
 - fragment-hash is a string that uniquely identifies the fragment
 
 It is worth noting the FRAGMENTS-INFO plists will be modified
-during processing to hold more information on the fragments."
+during processing to hold more information on the fragments.
+
+LATEX-PROCESSOR is a member of `org-latex-compilers' which is guessed if unset."
   (let* ((processing-type
           (or processing-type org-latex-preview-default-process))
+         (latex-processor
+          (or latex-processor
+              (and (derived-mode-p 'org-mode)
+                   (cdr (assoc "LATEX_COMPILER"
+                               (org-collect-keywords
+                                '("LATEX_COMPILER") '("LATEX_COMPILER")))))
+              org-latex-compiler))
          (processing-info
-          (alist-get processing-type org-latex-preview-process-alist))
+          (nconc (list :latex-processor latex-processor)
+                 (alist-get processing-type org-latex-preview-process-alist)))
          (programs (plist-get processing-info :programs))
          (error-message (or (plist-get processing-info :message) "")))
+    ;; xelatex produces .xdv (eXtended dvi) files, not .dvi, so as a special
+    ;; case we check for xelatex + dvi and if so switch the file extension to xdv.
+    (when (and (equal latex-processor "xelatex")
+               (equal (plist-get processing-info :image-input-type) "dvi"))
+      (setq processing-info
+            (plist-put (copy-sequence processing-info) :image-input-type "xdv")))
     (dolist (program programs)
       (org-check-external-command program error-message))
     (when org-latex-preview-processing-indicator
@@ -1374,7 +1412,7 @@ The path of the created LaTeX file is returned."
               (get-buffer-create org-latex-preview--latex-log)
             (erase-buffer)
             (current-buffer)))
-         (tex-compile-command
+         (tex-compile-command-fmt
           (pcase (plist-get extended-info :latex-compiler)
             ((and (pred stringp) cmd) cmd)
             ((and (pred consp) cmds)
@@ -1383,13 +1421,22 @@ The path of the created LaTeX file is returned."
                      (cdr cmds)))
              (car cmds))))
          (texfile (plist-get extended-info :texfile))
+         (org-tex-compiler
+          (cdr (assoc (plist-get extended-info :latex-processor)
+                      org-latex-preview-compiler-command-map)))
          (tex-command-spec
           `((?o . ,(shell-quote-argument temporary-file-directory))
             (?b . ,(shell-quote-argument (file-name-base texfile)))
-            (?f . ,(shell-quote-argument texfile))))
+            (?f . ,(shell-quote-argument texfile))
+            (?l . ,org-tex-compiler)
+            (?L . ,(car (split-string org-tex-compiler)))))
          (tex-formatted-command
           (split-string-shell-command
-           (format-spec tex-compile-command tex-command-spec))))
+           (format-spec tex-compile-command-fmt tex-command-spec))))
+    (unless org-tex-compiler
+      (user-error "No `org-latex-preview-compiler-command-map' entry found for LaTeX processor %S, it should be a member of `org-latex-compilers' %S"
+                  (plist-get extended-info :latex-processor)
+                  org-latex-compilers))
     (list 'org-async-task
           tex-formatted-command
           :buffer tex-process-buffer
@@ -1909,6 +1956,7 @@ process."
             (concat
              (prin1-to-string
               (car (plist-get processing-info :programs)))
+             (plist-get processing-info :latex-processor)
              (and (string-match-p "\\(?:\\\\input{\\|\\\\include{\\)"
                                   header)
                   default-directory))
@@ -1931,7 +1979,12 @@ process."
       (condition-case file
           (org-compile-file
            header-file (plist-get processing-info :latex-precompiler)
-           "fmt" nil precompile-buffer)
+           "fmt" nil precompile-buffer
+           (let ((org-tex-compiler
+                  (cdr (assoc (plist-get processing-info :latex-processor)
+                              org-latex-preview-compiler-command-map))))
+             `((?l . ,org-tex-compiler)
+               (?L . ,(car (split-string org-tex-compiler))))))
         (:success
          (kill-buffer precompile-buffer)
          (delete-file header-file)