(byte-compile--first-symbol-with-pos): Fix bug#58601

* lisp/emacs-lisp/bytecomp.el: Require `subr-x`.
(byte-compile--first-symbol-with-pos): Avoid inf-loops on circular data.

1 files changed, 17 insertions, 21 deletions

diff --git a/lisp/emacs-lisp/bytecomp.el b/lisp/emacs-lisp/bytecomp.el
index 692a87f6d57..f0265682172 100644
--- a/lisp/emacs-lisp/bytecomp.el
+++ b/lisp/emacs-lisp/bytecomp.el
@@ -129,6 +129,7 @@
 ;; us from emitting warnings when compiling files which use cl-lib without
 ;; requiring it! (bug#30635)
 (eval-when-compile (require 'cl-lib))
+(eval-when-compile (require 'subr-x))
 
 ;; The feature of compiling in a specific target Emacs version
 ;; has been turned off because compile time options are a bad idea.
@@ -1185,27 +1186,22 @@ message buffer `default-directory'."
 (defun byte-compile--first-symbol-with-pos (form)
   "Return the first symbol with position in form, or nil if none.
 Order is by depth-first search."
-  (cond
-   ((symbol-with-pos-p form) form)
-   ((consp form)
-    (or (byte-compile--first-symbol-with-pos (car form))
-        (let ((sym nil))
-          (setq form (cdr form))
-          (while (and (consp form)
-                      (not (setq sym (byte-compile--first-symbol-with-pos
-                                      (car form)))))
-            (setq form (cdr form)))
-          (or sym
-              (and form (byte-compile--first-symbol-with-pos form))))))
-   ((or (vectorp form) (recordp form))
-    (let ((len (length form))
-          (i 0)
-          (sym nil))
-      (while (and (< i len)
-                  (not (setq sym (byte-compile--first-symbol-with-pos
-                                  (aref form i)))))
-        (setq i (1+ i)))
-      sym))))
+  (named-let loop ((form form)
+                   (depth 10))          ;Arbitrary limit.
+    (cond
+     ((<= depth 0) nil)                 ;Avoid cycles (bug#58601).
+     ((symbol-with-pos-p form) form)
+     ((consp form)
+      (or (loop (car form) (1- depth))
+          (loop (cdr form) (1- depth))))
+     ((or (vectorp form) (recordp form))
+      (let ((len (length form))
+            (i 0)
+            (sym nil))
+        (while (and (< i len)
+                    (not (setq sym (loop (aref form i) (1- depth)))))
+          (setq i (1+ i)))
+        sym)))))
 
 (defun byte-compile--warning-source-offset ()
   "Return a source offset from `byte-compile-form-stack' or nil if none."