Add indentation style setting for c-ts-mode in .dir-locals.el

* lisp/progmodes/c-ts-mode.el (c-ts-indent-style-safep): New
predicate.
(c-ts-mode-indent-style): Use it to test the value for being safe.

* .dir-locals.el (c-ts-mode): Set 'c-ts-mode-indent-style' to 'gnu'.

2 files changed, 7 insertions, 1 deletions

diff --git a/.dir-locals.el b/.dir-locals.el
index 6733b5326a6..0bcded4b5d1 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -21,7 +21,8 @@
                (electric-quote-comment . nil)
                (electric-quote-string . nil)
                (mode . bug-reference-prog)))
- (c-ts-mode . ((indent-tabs-mode . t)
+ (c-ts-mode . ((c-ts-mode-indent-style . gnu)
+               (indent-tabs-mode . t)
                (mode . bug-reference-prog)))
  (log-edit-mode . ((log-edit-font-lock-gnu-style . t)
                    (log-edit-setup-add-author . t)
diff --git a/lisp/progmodes/c-ts-mode.el b/lisp/progmodes/c-ts-mode.el
index 166399f922d..6100f00e3ba 100644
--- a/lisp/progmodes/c-ts-mode.el
+++ b/lisp/progmodes/c-ts-mode.el
@@ -136,6 +136,10 @@ symbol."
               (loop (append res (list buffer)) (cdr buffers))
             (loop res (cdr buffers))))))))
 
+(defun c-ts-indent-style-safep (style)
+  "Non-nil if STYLE's value is safe for file-local variables."
+  (and (symbolp style) (not (functionp style))))
+
 (defcustom c-ts-mode-indent-style 'gnu
   "Style used for indentation.
 
@@ -150,6 +154,7 @@ follows the form of `treesit-simple-indent-rules'."
                  (symbol :tag "BSD" bsd)
                  (function :tag "A function for user customized style" ignore))
   :set #'c-ts-mode--indent-style-setter
+  :safe 'c-ts-indent-style-safep
   :group 'c)
 
 (defun c-ts-mode--get-indent-style (mode)