diff --git a/lisp/treesit.el b/lisp/treesit.el
index b120ca68c5..651898e948 100644
--- a/lisp/treesit.el
+++ b/lisp/treesit.el
@@ -99,6 +99,15 @@ treesit
   :group 'tools
   :version "29.1")
 
+(defcustom treesit-enabled-modes nil
+  "List of modes to enable tree-sitter support if available.
+When initialising a major mode with potential tree-sitter
+support, this variable is consulted.  The special value t will
+enable tree-sitter support whenever possible."
+  :type '(choice (const :tag "Whenever possible" t)
+                 (repeat :tag "Specific modes" function))
+  :version "29.1")
+
 (defcustom treesit-max-buffer-size
   (let ((mb (* 1024 1024)))
     ;; 40MB for 64-bit systems, 15 for 32-bit.
@@ -2690,20 +2699,19 @@ treesit--install-language-grammar-1
 For LANG, URL, SOURCE-DIR, GRAMMAR-DIR, CC, C++, see
 `treesit-language-source-alist'.  If anything goes wrong, this
 function signals an error."
-  (let* ((lang (symbol-name lang))
-         (default-directory "/tmp")
-         (workdir (expand-file-name "treesit-workdir-00893133134"))
+  (let* ((default-directory (make-temp-file "treesit-workdir" t))
+         (workdir (expand-file-name "repo"))
          (source-dir (expand-file-name (or source-dir "src") workdir))
          (grammar-dir (expand-file-name (or grammar-dir "") workdir))
-         (cc (or cc "cc"))
-         (c++ (or c++ "c++"))
+         (cc (or cc (seq-find #'executable-find '("cc" "gcc" "c99"))
+                 (error "No C compiler found")))
+         (c++ (or c++ (seq-find #'executable-find '("c++" "g++"))))
          (soext (pcase system-type
                   ('darwin "dylib")
                   ((or 'ms-dos 'cywin 'windows-nt) "dll")
                   (_ "so")))
          (out-dir (or (and out-dir (expand-file-name out-dir))
-                      (expand-file-name
-                       "tree-sitter" user-emacs-directory)))
+                      (locate-user-emacs-file "tree-sitter")))
          (lib-name (format "libtree-sitter-%s.%s" lang soext)))
     (unwind-protect
         (with-temp-buffer
@@ -2713,8 +2721,8 @@ treesit--install-language-grammar-1
            "git" nil t nil "clone" url "--depth" "1" "--quiet"
            workdir)
           ;; cp "${grammardir}"/grammar.js "${sourcedir}"
-          (copy-file (concat grammar-dir "/grammar.js")
-                     (concat source-dir "/grammar.js"))
+          (copy-file (file-name-concat grammar-dir "grammar.js")
+                     (file-name-concat source-dir "grammar.js"))
           ;; cd "${sourcedir}"
           (setq default-directory source-dir)
           (message "Compiling library")
@@ -2723,6 +2731,7 @@ treesit--install-language-grammar-1
            cc nil t nil "-fPIC" "-c" "-I." "parser.c")
           ;; cc -fPIC -c -I. scanner.c
           (when (file-exists-p "scanner.c")
+            (unless c++ (error "No C++ compiler found"))
             (treesit--call-process-signal
              cc nil t nil "-fPIC" "-c" "-I." "scanner.c"))
           ;; c++ -fPIC -I. -c scanner.cc
@@ -2739,7 +2748,7 @@ treesit--install-language-grammar-1
                       (rx bos (+ anychar) ".o" eos))
                    "-o" ,lib-name))
           ;; Copy out.
-          (copy-file lib-name (concat out-dir "/") t)
+          (copy-file lib-name (file-name-as-directory out-dir) t)
           (message "Library installed to %s/%s" out-dir lib-name))
       (when (file-exists-p workdir)
         (delete-directory workdir t)))))