This code has the same symptoms. Removing the second begin/rescue, the method, or the return statement makes the code work (reports SyntaxError, without crashing).

#!/usr/bin/env ruby

def test
  begin
    break
  rescue
    # NOOP
  end

  return if true

  begin
    # Test
  rescue
    # NOOP
  end
end

Error:

[BUG] iseq_set_sequence: adjust bug -1 < 0)

On versions:

• ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-darwin16]
• ruby 2.3.1p112 (2016-04-26 revision 54768) [x86_64-darwin16]

Rubies 2.2.4 and earlier also warn about invalid break, before crashing.

• ruby 2.2.4p230 (2015-12-16 revision 53155) [x86_64-darwin16]
• ruby 2.1.6p336 (2015-04-13 revision 50298) [x86_64-darwin16.0]
• ruby 2.0.0p648 (2015-12-16 revision 53162) [x86_64-darwin16.3.0]

./break_fail.rb:5: Invalid break
./break_fail.rb: [BUG] iseq_set_sequence: adjust bug

Applied in changeset r57300.

compile.c: check compile

• compile.c (iseq_compile_each): check if sub nodes succeeded.
  [ruby-core:76531] [Bug ]

r57368 would be better, to backport at least.

ruby_2_3 r57572 merged revision(s) 57368.

ruby_2_4 r57854 merged revision(s) 57300,57368.

ruby_2_2 r58090 merged revision(s) 57368.