From 09ae95332f34791c68c841f8ad41b3f3ff9e8609 Mon Sep 17 00:00:00 2001
From: Randy Stauner <randy@r4s6.net>
Date: Tue, 10 Feb 2026 10:48:17 -0700
Subject: ZJIT: Avoid runtime exceptions from RubyVM::ZJIT.stats_string
 (#16134)

Before this it would raise if zjit wasn't enabled
and raise a different exception if zjit was but extended stats were
not (_some_ stats are available).
---
 test/ruby/test_zjit.rb | 12 ++++++++++++
 zjit.rb                |  6 +++---
 2 files changed, 15 insertions(+), 3 deletions(-)

diff --git a/test/ruby/test_zjit.rb b/test/ruby/test_zjit.rb
index 333e34e927..ff7c167327 100644
--- a/test/ruby/test_zjit.rb
+++ b/test/ruby/test_zjit.rb
@@ -27,6 +27,18 @@ class TestZJIT < Test::Unit::TestCase
     RUBY
   end
 
+  def test_stats_string_no_zjit
+    assert_runs 'nil', <<~RUBY, zjit: false
+      RubyVM::ZJIT.stats_string
+    RUBY
+    assert_runs 'true', <<~RUBY, stats: false
+      RubyVM::ZJIT.stats_string.is_a?(String)
+    RUBY
+    assert_runs 'true', <<~RUBY, stats: true
+      RubyVM::ZJIT.stats_string.is_a?(String)
+    RUBY
+  end
+
   def test_stats_quiet
     # Test that --zjit-stats-quiet collects stats but doesn't print them
     script = <<~RUBY
diff --git a/zjit.rb b/zjit.rb
index 0cc9ca8261..f73ef12a63 100644
--- a/zjit.rb
+++ b/zjit.rb
@@ -165,13 +165,13 @@ class << RubyVM::ZJIT
 
   # Get the summary of ZJIT statistics as a String
   def stats_string
+    return unless stats = self.stats
     buf = +"***ZJIT: Printing ZJIT statistics on exit***\n"
-    stats = self.stats
 
-    if stats[:guard_type_count].nonzero?
+    if stats[:guard_type_count]&.nonzero?
       stats[:guard_type_exit_ratio] = stats[:exit_guard_type_failure].to_f / stats[:guard_type_count] * 100
     end
-    if stats[:guard_shape_count].nonzero?
+    if stats[:guard_shape_count]&.nonzero?
       stats[:guard_shape_exit_ratio] = stats[:exit_guard_shape_failure].to_f / stats[:guard_shape_count] * 100
     end
 
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