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.

3 files changed, 26 insertions, 0 deletions

diff --git a/src/print.c b/src/print.c
index d52d98ad371..8ee5a3616eb 100644
--- a/src/print.c
+++ b/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           print_c_string ("-outdated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.  */
diff --git a/src/treesit.c b/src/treesit.c
index 21c61a35e70..45efa429f9a 100644
--- a/src/treesit.c
+++ b/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           "treesit-node-outdated");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);
diff --git a/src/treesit.h b/src/treesit.h
index f5c8c67395d..dcb19648a37 100644
--- a/src/treesit.h
+++ b/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 *);