Bug #21933: Ruby::Box: named capture local variable can become nil after non-matching lines

• Status: Open
• Assignee: -
• Target version: -
• ruby -v: 4.0.1
• Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN, 4.0: UNKNOWN

[katsyoshi (Katsuyoshi MATSUMOTO)]

Environment:

• Ruby 4.0.1
• RUBY_BOX=1
• OS: Linux x86_64

Summary:
With Ruby::Box enabled, a named capture local variable from =~ may become nil,
even when the regexp matches. This happens after iterating over non-matching lines first.

Reproducer:

sample.rb

text = <<~ASM
  .intel_syntax noprefix
  .globl main
main:
  nop
ASM

cur=nil
text.each_line do |line|
  if /^(?<label>[_A-Za-z.]\w*):/ =~ line
    p [:matched, line.inspect, label.inspect]
    cur = label
    break
  end
end
p [:cur, cur.inspect]

Expected:

[:matched, "\"main:\\n\"", "\"main\""]
[:cur, "\"main\""]

Actual (with RUBY_BOX=1):

[:matched, "\"main:\\n\"", "nil"]
[:cur, "nil"]

Control:
Without RUBY_BOX=1, the same script returns "main" as expected.

[katsyoshi (Katsuyoshi MATSUMOTO)]

• Description updated (diff)

[tompng (tomoya ishida)]

Shorter reproduction code

/(?<a>foo)/ =~ 'bar'
/(?<b>baz)/ =~ 'baz'
p b # should be present, got nil with RUBY_BOX=1

/foo/ =~ 'bar'
$~
/baz/ =~ 'baz'
p $~ # should be MatchData, got nil with RUBY_BOX=1