bug#30063: 26.0.90; Silent fail with `rst-compile-pdf-preview'

["Simen Heggestøyl" <simenheg@gmail.com>]

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How about something like the attached patch?

-- Simen

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From 11bb53e567588539c92a520db321a5a9b746df58 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Simen=20Heggest=C3=B8yl?= <simenheg@gmail.com>
Date: Sat, 27 Jan 2018 12:18:40 +0100
Subject: [PATCH] Warn about missing executables in RST PDF preview

* lisp/textmodes/rst.el (rst-compile-pdf-preview): Warn about missing
executables when attempting to compile and preview an RST file as PDF.
(Bug#30218)
---
 lisp/textmodes/rst.el | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/lisp/textmodes/rst.el b/lisp/textmodes/rst.el
index c93e4e474c..a16d5bca3a 100644
--- a/lisp/textmodes/rst.el
+++ b/lisp/textmodes/rst.el
@@ -4382,10 +4382,15 @@ rst-compile-pdf-preview
   "Convert the document to a PDF file and launch a preview program."
   (interactive)
   (let* ((tmp-filename (make-temp-file "rst_el" nil ".pdf"))
+         (pdf-compile-program (cadr (assq 'pdf rst-compile-toolsets)))
 	 (command (format "%s %s %s && %s %s ; rm %s"
-			  (cadr (assq 'pdf rst-compile-toolsets))
+			  pdf-compile-program
 			  buffer-file-name tmp-filename
 			  rst-pdf-program tmp-filename tmp-filename)))
+    (unless (executable-find pdf-compile-program)
+      (error "Cannot find executable `%s'" pdf-compile-program))
+    (unless (executable-find rst-pdf-program)
+      (error "Cannot find executable `%s'" rst-pdf-program))
     (start-process-shell-command "rst-pdf-preview" nil command)
     ;; Note: you could also use (compile command) to view the compilation
     ;; output.
-- 
2.15.1