From 217b38398bfa523c48f630b06b21427974d93e1d Mon Sep 17 00:00:00 2001
From: Wilfred Hughes <me@wilfred.me.uk>
Date: Fri, 10 Dec 2021 21:38:58 -0800
Subject: Rewrite helpful--tree-any-p as a loop

Fixes #279
---
 CHANGELOG.md              |  2 ++
 helpful.el                | 18 +++++++++++-------
 test/helpful-unit-test.el |  4 ++++
 3 files changed, 17 insertions(+), 7 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 5c0d1d4..8d757f2 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -8,6 +8,8 @@ Fixed issue with displaying circular data structures.
 Fixed a crash in `helpful-variable` in files that weren't
 syntactically valid lisp.
 
+Fixed stack overflow in macroexpanding large s-expressions (#279).
+
 # v0.18
 
 Show the original value for custom variables whose value has changed.
diff --git a/helpful.el b/helpful.el
index b811811..3e064d7 100644
--- a/helpful.el
+++ b/helpful.el
@@ -1317,13 +1317,17 @@ If it fails, attempt to partially macroexpand FORM."
 (defun helpful--tree-any-p (pred tree)
   "Walk TREE, applying PRED to every subtree.
 Return t if PRED ever returns t."
-  (cond
-   ((null tree) nil)
-   ((funcall pred tree) t)
-   ((not (consp tree)) nil)
-   (t (or
-       (helpful--tree-any-p pred (car tree))
-       (helpful--tree-any-p pred (cdr tree))))))
+  (catch 'found
+    (let ((stack (list tree)))
+      (while stack
+        (let ((next (pop stack)))
+          (cond
+           ((funcall pred next)
+            (throw 'found t))
+           ((consp next)
+            (push (car next) stack)
+            (push (cdr next) stack))))))
+    nil))
 
 (defun helpful--find-by-macroexpanding (buf sym callable-p)
   "Search BUF for the definition of SYM by macroexpanding
diff --git a/test/helpful-unit-test.el b/test/helpful-unit-test.el
index 1fbf87c..510396c 100644
--- a/test/helpful-unit-test.el
+++ b/test/helpful-unit-test.el
@@ -1072,3 +1072,7 @@ find the source code."
   "Ensure that we can describe an autoloaded function
 that has advice attached before it is loadedl."
   (helpful-function 'ruby-mode))
+
+(ert-deftest helpful--tree-any-p ()
+  (should (helpful--tree-any-p (lambda (x) (eq x 1)) '((((1))))))
+  (should (helpful--tree-any-p (lambda (x) (eq x 1)) (cons 2 1))))
-- 
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