master b70c71dc318 1/2: Improve 'describe-theme' (bug#65468)

[Eli Zaretskii]

branch: master
commit b70c71dc318bdae6de397521f76c518b210aab9b
Author: Thierry Volpiatto <thievol@posteo.net>
Commit: Eli Zaretskii <eliz@gnu.org>

    Improve 'describe-theme' (bug#65468)
    
    * lisp/cus-theme.el (describe-theme-from-file): New function.
---
 lisp/cus-theme.el | 34 +++++++++++++++++++++++++---------
 1 file changed, 25 insertions(+), 9 deletions(-)

diff --git a/lisp/cus-theme.el b/lisp/cus-theme.el
index 5d3f2585976..c6c9d9c892b 100644
--- a/lisp/cus-theme.el
+++ b/lisp/cus-theme.el
@@ -490,6 +490,29 @@ It includes all faces in list FACES."
     (with-current-buffer standard-output
       (describe-theme-1 theme))))
 
+(defun describe-theme-from-file (&optional file short)
+  "Describe theme from its file FILE without loading it.
+
+If FILE is nil try to find the file from the theme name in
+`custom-theme-load-path'.
+If SHORT is non nil show only the first line of documentation."
+    (let ((file (or file
+                  (locate-file (concat (symbol-name theme) "-theme.el")
+                              (custom-theme--load-path)
+                              '("" "c")))))
+      (with-temp-buffer
+        (insert-file-contents file)
+        (catch 'found
+          (let (sexp)
+            (while (setq sexp (let ((read-circle nil))
+                               (condition-case nil
+                                   (read (current-buffer))
+                                 (end-of-file nil))))
+              (when (eq (car-safe sexp) 'deftheme)
+               (throw 'found (if short
+                                  (car (split-string (nth 2 sexp) "\n"))
+                                (nth 2 sexp))))))))))
+
 (defun describe-theme-1 (theme)
   (prin1 theme)
   (princ " is a custom theme")
@@ -510,16 +533,9 @@ It includes all faces in list FACES."
            (princ "It is loaded but disabled."))
          (setq doc (get theme 'theme-documentation)))
       (princ "It is not loaded.")
-      ;; Attempt to grab the theme documentation
+      ;; Attempt to grab the theme documentation from file.
       (when fn
-       (with-temp-buffer
-         (insert-file-contents fn)
-         (let ((sexp (let ((read-circle nil))
-                       (condition-case nil
-                           (read (current-buffer))
-                         (end-of-file nil)))))
-            (and (eq (car-safe sexp) 'deftheme)
-                (setq doc (nth 2 sexp)))))))
+       (setq doc (describe-theme-from-file fn))))
     (princ "\n\nDocumentation:\n")
     (princ (if (stringp doc)
               (substitute-command-keys doc)