[ruby/irb] Suppress crash when bignum is set to SAVE_HISTORY

ruby/irb@5044eb2730

lib/irb/ext/save-history.rb

@@ -109,7 +109,12 @@ def save_history
 
         open(history_file, "w:#{IRB.conf[:LC_MESSAGES].encoding}", 0600) do |f|
           hist = history.map{ |l| l.split("\n").join("\\\n") }
-          f.puts(hist[-num..-1] || hist)
+          begin
+            hist = hist.last(num) if hist.size > num
+          rescue RangeError # bignum too big to convert into `long'
+            # Do nothing because the bignum should be treated as inifinity
+          end
+          f.puts(hist)
         end
       end
     end

test/irb/test_history.rb

@@ -52,6 +52,29 @@ def test_history_save_100
       HISTORY_FILE
     end
 
+    def test_history_save_bignum
+      result_output, result_history_file = launch_irb_with_irbrc_and_irb_history(<<~IRBRC, <<~IRB_HISTORY) do |stdin|
+        IRB.conf[:USE_READLINE] = true
+        IRB.conf[:SAVE_HISTORY] = 10 ** 19
+      IRBRC
+        1
+        2
+        3
+        4
+      IRB_HISTORY
+        stdin.write("5\nexit\n")
+      end
+
+      assert_equal(<<~HISTORY_FILE, result_history_file)
+        1
+        2
+        3
+        4
+        5
+        exit
+      HISTORY_FILE
+    end
+
     private
 
     def launch_irb_with_irbrc_and_irb_history(irbrc, irb_history)