* lisp/cus-start.el: Make 'treesit-extra-load-path' customizable.

* lisp/treesit.el (treesit-auto-install-grammar): Add the value 'ask-dir'.
(treesit-ensure-installed): When 'treesit-auto-install-grammar' is
'ask' or 'ask-dir', ask for the directory to install the grammar library
using the first writable directory of 'treesit-extra-load-path' as default.
Also add the provided directory to 'treesit-extra-load-path' afterwards.

* src/treesit.c (treesit-extra-load-path): In the docstring
mention the fact that the first directory is special (bug#79862).

1 files changed, 3 insertions, 1 deletions

diff --git a/src/treesit.c b/src/treesit.c
index 3230d0a50a1..d3b6f36ec81 100644
--- a/src/treesit.c
+++ b/src/treesit.c
@@ -5273,7 +5273,9 @@ The value should be a list of directories.
 When trying to load a tree-sitter language definition,
 Emacs first looks in the directories mentioned in this variable,
 then in the `tree-sitter' subdirectory of `user-emacs-directory', and
-then in the system default locations for dynamic libraries, in that order.  */);
+then in the system default locations for dynamic libraries, in that order.
+The first writeable directory in the list is special: it's used as the
+default directory when automatically installing the language grammar.  */);
   Vtreesit_extra_load_path = Qnil;
 
   DEFVAR_LISP ("treesit-thing-settings",