When evaluating the following elisp snippet in the *scratch* buffer,

    (treesit-install-language-grammar 'bash)

I expected treesit.el to download and compile the grammar for the bash
language.

Instead, I got

⛔ Warning (treesit): The installed language grammar for bash cannot be
located or has problems (not-found): (libtree-sitter-bash.so
libtree-sitter-bash.so.0 libtree-sitter-bash.so.0.0
libtree-sitter-bash.dylib libtree-sitter-bash.dylib.0
libtree-sitter-bash.dylib.0.0) No such file or directory

The ~/.emacs.d/tree-sitter directory doesn't even get created,
indicating that there was in fact no attempt to build or download the
library.

Upon digging down with the debugger, the bug appears to be in
https://git.savannah.gnu.org/cgit/emacs.git/tree/lisp/treesit.el#n3073
which should read

                  default-out-dir)))

instead of

                  out-dir)))

Fixing that line as indicated and re-loading the function, fixes the
problem described above.
--
 Dominique Quatravaux
 dominique@quatravaux.org