lang/latex: replace viewer flags with variable

The +zathura, +skim, +okular and +pdf-tools module flags have been
removed in favor of +latex-viewers, which takes a list of symbols. Its
order determines the priority. The first viewer found on your system is
used.

If none of these viewers are found, it will fall back to
latex-preview-pane.

modules/lang/latex/+preview-pane.el

@@ -1,16 +0,0 @@
-;;; lang/latex/+preview-pane.el -*- lexical-binding: t; -*-
-;;;###if (featurep! +preview-pane)
-
-(def-package! latex-preview-pane
-  :when (featurep! +preview-pane)
-  :hook (LaTeX-mode . latex-preview-pane-enable)
-  :commands latex-preview-pane-mode
-  :init
-  (setq latex-preview-pane-multifile-mode 'auctex)
-  :config
-  (add-to-list 'TeX-view-program-list '("preview-pane" latex-preview-pane-mode))
-  (add-to-list 'TeX-view-program-selection '(output-pdf "preview-pane"))
-  (define-key! doc-view-mode-map
-    (kbd "ESC") #'delete-window
-    "q" #'delete-window
-    "k" (λ! (quit-window) (delete-window))))

modules/lang/latex/+viewers.el

@@ -1,22 +1,43 @@
 ;;; lang/latex/+viewers.el -*- lexical-binding: t; -*-
 
-(when (featurep! +okular)
-  ;; Configure Okular as viewer. Including a bug fix
-  ;; (https://bugs.kde.org/show_bug.cgi?id=373855)
-  (add-to-list 'TeX-view-program-list '("Okular" ("okular --unique file:%o" (mode-io-correlate "#src:%n%a"))))
-  (add-to-list 'TeX-view-program-selection '(output-pdf "Okular")))
+(cl-block nil
+  (dolist (viewer (reverse +latex-viewers))
+    (if (pcase viewer
+          (`skim
+           (when (and IS-MAC
+                      (file-exists-p! (or "/Applications/Skim.app"
+                                          "~/Applications/Skim.app")))
+             (add-to-list 'TeX-view-program-selection '(output-pdf "Skim"))))
 
-;; Or Skim
-(when (featurep! +skim)
-  (add-to-list 'TeX-view-program-selection 'output-pdf '("Skim")))
+          (`okular
+           (when (executable-find "okular")
+             ;; Configure Okular as viewer. Including a bug fix
+             ;; (https://bugs.kde.org/show_bug.cgi?id=373855)
+             (add-to-list 'TeX-view-program-list '("Okular" ("okular --unique file:%o" (mode-io-correlate "#src:%n%a"))))
+             (add-to-list 'TeX-view-program-selection '(output-pdf "Okular"))))
 
-;; Or Zathura
-(when (featurep! +zathura)
-  (add-to-list 'TeX-view-program-selection '(output-pdf "Zathura")))
+          (`zathura
+           (when (executable-find "zathura")
+             (add-to-list 'TeX-view-program-selection '(output-pdf "Zathura"))))
+
+          (`pdf-tools
+           (when (featurep! :tools pdf)
+             (add-to-list 'TeX-view-program-selection '(output-pdf "PDF Tools"))
+             ;; Update PDF buffers after successful LaTeX runs
+             (add-hook 'TeX-after-compilation-finished-function #'TeX-revert-document-buffer))))
+
+        (cl-return t)))
+
+  ;; fall back to latex-preview-pane
+  (add-to-list 'TeX-view-program-list '("preview-pane" latex-preview-pane-mode))
+  (add-to-list 'TeX-view-program-selection '(output-pdf "preview-pane")))
+
+
+(after! latex-preview-pane
+  (setq latex-preview-pane-multifile-mode 'auctex)
+
+  (define-key! doc-view-mode-map
+    (kbd "ESC") #'delete-window
+    "q" #'delete-window
+    "k" (λ! (quit-window) (delete-window))))
 
-;; Or PDF-tools, but only if the module is also loaded
-(when (and (featurep! :tools pdf)
-           (featurep! +pdf-tools))
-  (add-to-list 'TeX-view-program-selection '(output-pdf "PDF Tools"))
-  ;; Update PDF buffers after successful LaTeX runs
-  (add-hook 'TeX-after-compilation-finished-function #'TeX-revert-document-buffer))

modules/lang/latex/config.el

@@ -11,6 +11,13 @@
 enabling unicode symbols in math regions. This requires the unicode-math latex
 package to be installed.")
 
+(defconst +latex-viewers `(skim zathura okular pdf-tools)
+  "A list of enabled latex viewers to use, in this order. If they don't exist,
+they will be ignored. Recognized viewers are skim, zathura, okular and
+pdf-tools.
+
+If no viewers are found, `latex-preview-pane' is used.")
+
 ;;
 (defvar +latex--company-backends nil)