Bug #15674: Regression: ObjectSpace.allocation_sourceline produces the wrong location for allocations, it shows the end of the method instead of the line where the object was created

• Status: Open
• Priority: Normal
• Assignee: -
• Target version: -
• ruby -v: 2.6.2
• Backport: 2.4: UNKNOWN, 2.5: UNKNOWN, 2.6: UNKNOWN

[schneems (Richard Schneeman)]

Originally I opened this up as an issue in memory profiler https://github.com/SamSaffron/memory_profiler/issues/67, however I was able to isolate the issue to just Ruby 2.6.

ObjectSpace.allocation_sourceline is reporting the line where a method ends rather than the line where the object was actually allocated.

Here's the script. You would expect that object space would tell me the allocation happens on line 2 but instead it gets reported as line 3:

def my_concat(a, b)
  return a + b # <====================
end

require 'fileutils'
require 'objspace'
FileUtils.mkdir_p("tmp")

def run
  ObjectSpace.trace_object_allocations do
    10.times do
      my_concat("hello".freeze, "world".freeze)
    end

    10.times do
      my_concat("hello".freeze, "world".freeze)
    end
  end

  ObjectSpace.each_object do |obj|
    file = ObjectSpace.allocation_sourcefile(obj)
    line = ObjectSpace.allocation_sourceline(obj)
    next unless file && line
    puts "#{file}:#{line}"
  end
end

run

If you add space to the method body it keeps incrementing the line number of the output. For example, changing the method body to this, should not change the allocation location:

def my_concat(a, b)
  return a + b # <====================





end

However, it is reported as a different line:

script.rb:8

I tested with Ruby 2.3, 2.4, and 2.5 and all those versions produce a correct result, this regression is limited to only 2.6.