Check for buffer liveness when accessing tree-sitter node (bug#71012)

* src/treesit.h (treesit_node_buffer_live_p): Declare function.
* src/print.c (print_vectorlike): Print node without position if
buffer is killed.
* src/treesit.c (treesit_node_buffer_live_p): New function.
(treesit_check_node): Add buffer liveness check.
(syms_of_treesit): New error treesit-node-buffer-killed.

src/print.c

@@ -2029,6 +2029,11 @@ print_vectorlike (Lisp_Object obj, Lisp_Object printcharfun, bool escapeflag,
 	  print_c_string ("-outdated>", printcharfun);
 	  break;
 	}
+      if (!treesit_node_buffer_live_p (obj))
+	{
+	  print_c_string ("-in-killed-buffer>", printcharfun);
+	  break;
+	}
       printchar (' ', printcharfun);
       /* Now the node must be up-to-date, and calling functions like
 	 Ftreesit_node_start will not signal.  */

src/treesit.c

@@ -1786,6 +1786,13 @@ treesit_check_node (Lisp_Object obj)
   CHECK_TS_NODE (obj);
   if (!treesit_node_uptodate_p (obj))
     xsignal1 (Qtreesit_node_outdated, obj);
+
+  /* Technically a lot of node functions can work without the
+     associated buffer being alive, but I doubt there're any real
+     use-cases for that; OTOH putting the buffer-liveness check here is
+     simple, clean, and safe.  */
+  if (!treesit_node_buffer_live_p (obj))
+    xsignal1 (Qtreesit_node_buffer_killed, obj);
 }
 
 /* Checks that OBJ is a positive integer and it is within the visible
@@ -1806,6 +1813,14 @@ treesit_node_uptodate_p (Lisp_Object obj)
   return XTS_NODE (obj)->timestamp == XTS_PARSER (lisp_parser)->timestamp;
 }
 
+bool
+treesit_node_buffer_live_p (Lisp_Object obj)
+{
+  struct buffer *buffer
+    = XBUFFER (XTS_PARSER (XTS_NODE (obj)->parser)->buffer);
+  return BUFFER_LIVE_P (buffer);
+}
+
 DEFUN ("treesit-node-type",
        Ftreesit_node_type, Streesit_node_type, 1, 1, 0,
        doc: /* Return the NODE's type as a string.
@@ -3549,6 +3564,8 @@ syms_of_treesit (void)
 	  "treesit-load-language-error");
   DEFSYM (Qtreesit_node_outdated,
 	  "treesit-node-outdated");
+  DEFSYM (Qtreesit_node_buffer_killed,
+	  "treesit-node-buffer-killed");
   DEFSYM (Quser_emacs_directory,
 	  "user-emacs-directory");
   DEFSYM (Qtreesit_parser_deleted, "treesit-parser-deleted");
@@ -3577,6 +3594,9 @@ syms_of_treesit (void)
   define_error (Qtreesit_node_outdated,
 		"This node is outdated, please retrieve a new one",
 		Qtreesit_error);
+  define_error (Qtreesit_node_buffer_killed,
+		"The buffer associated with this node is killed",
+		Qtreesit_error);
   define_error (Qtreesit_parser_deleted,
 		"This parser is deleted and cannot be used",
 		Qtreesit_error);

src/treesit.h

@@ -189,6 +189,7 @@ extern Lisp_Object make_treesit_parser (Lisp_Object, TSParser *, TSTree *,
 extern Lisp_Object make_treesit_node (Lisp_Object, TSNode);
 
 extern bool treesit_node_uptodate_p (Lisp_Object);
+extern bool treesit_node_buffer_live_p (Lisp_Object);
 
 extern void treesit_delete_parser (struct Lisp_TS_Parser *);
 extern void treesit_delete_query (struct Lisp_TS_Query *);