[GR-19220] Fix IRB readline history handling when moving past bounds

PullRequest: truffleruby/3743

Author: andrykonchin

CHANGELOG.md

@@ -131,6 +131,7 @@ Performance:
 * `Process.pid` is now cached per process like `$$` (#2882, @horakivo)
 * Use the system `libyaml` for `psych` to improve warmup when parsing YAML (#2089, @eregon).
 * Fixed repeated deoptimizations for methods building an `Array` which is growing over multiple calls at a given call site (@eregon).
+* Fixed errors in IRB when attempting to navigate beyond bounds in singleline mode (@rwstauner).
 
 Changes:
 

spec/tags/truffle/irb/history_tags.txt

@@ -0,0 +1 @@
+slow:IRB ignores key sequences that would move past history in singleline mode

spec/truffle/irb/history_spec.rb

@@ -0,0 +1,29 @@
+# Copyright (c) 2019, 2023 Oracle and/or its affiliates. All rights reserved. This
+# code is released under a tri EPL/GPL/LGPL license. You can use it,
+# redistribute it and/or modify it under the terms of the:
+#
+# Eclipse Public License version 2.0, or
+# GNU General Public License version 2, or
+# GNU Lesser General Public License version 2.1.
+
+require_relative '../../ruby/spec_helper'
+
+describe "IRB" do
+  it "ignores key sequences that would move past history in singleline mode" do
+    # --readline is needed otherwise Readline is not used when stdin is not a TTY.
+    IO.popen([*ruby_exe, "-S", "irb", "-f", "--prompt=simple", "--readline", "--singleline"], "r+") do |io|
+      io.gets.should == "Switch to inspect mode.\n"
+
+      io.puts "\C-n" # next-history (none)
+      io.gets.should == ">> \n"
+
+      # Prove that the session is still valid.
+      io.puts "1+1"
+      io.gets.should == ">> 1+1\n"
+      io.gets.should == "=> 2\n"
+
+      io.puts "exit"
+      io.gets.should == ">> exit\n"
+    end
+  end
+end

src/main/java/org/truffleruby/stdlib/readline/MemoryHistory.java

@@ -148,6 +148,9 @@ protected boolean matchPatterns(String patterns, String line) {
 
     @Override
     public String current() {
+        if (index >= size()) {
+            return "";
+        }
         return entries.get(index).line();
     }