Re: c-ts-mode: How to set indent-style in dir-locals

(describe-variable 'c-ts-mode-indent-style)

c-ts-mode-indent-style is a variable defined in ‘c-ts-mode.el’.

Its value is ‘gnu’

Style used for indentation.

The selected style could be one of GNU, K&R, LINUX or BSD.  If the
supplied styles don’t suffice, the value could be a function instead.
This function takes no arguments and is expected to return a list of
indent RULEs as described in ‘treesit-simple-indent-rules’.  Note that
the list of RULEs doesn’t need to contain the language symbol.

   This variable is safe as a file local variable if its value
   satisfies the predicate ‘c-ts-indent-style-safep’.
   This variable was introduced, or its default value was changed, in
   version 29.1 of Emacs.
   You can customize this variable.
   Setting this variable directly with ‘setq’ may not take effect;
   use either customize or ‘setopt’, or call 
‘c-ts-mode--indent-style-setter’.

[back]

You can see the key clue right there in the documentation:

"Setting this variable directly with ‘setq’ may not take effect; use 
either customize or ‘setopt’, or call ‘c-ts-mode--indent-style-setter’."

(describe-function 'c-ts-mode--indent-style-setter)

c-ts-mode--indent-style-setter is a native-comp-function in
‘c-ts-mode.el’.

(c-ts-mode--indent-style-setter SYM VAL)

Inferred type: (function (t t) null)

Custom setter for ‘c-ts-mode-set-style’.

Apart from setting the default value of SYM to VAL, also change
the value of SYM in ‘c-ts-mode’ and ‘c++-ts-mode’ buffers to VAL.

SYM should be ‘c-ts-mode-indent-style’, and VAL should be a style
symbol.

[back]

;; This may work (what you need to do)
(c-ts-mode--indent-style-setter 'c-ts-mode-indent-style 'bsd)
;; Or better:
(c-ts-mode-set-style 'bsd)


-- 
Jean Louis