Bug #14191: Coverage decreased between 2.4.3 and 2.5.0rc1

• Status: Closed
• Assignee: mame (Yusuke Endoh)
• Target version: 2.5
• ruby -v: 2.5.0rc1
• Backport: 2.3: UNKNOWN, 2.4: UNKNOWN

[kddnewton (Kevin Newton)]

Just ran the test suite on my Rails app on the new rc and noticed that the coverage dropped by a full 3%. After some investigation discovered a lot of lines aren't being reported as covered anymore even though they clearly are. Here are all of the instances that I found that don't report coverage when they should:

# test.rb
require 'coverage'
Coverage.start

require_relative './file.rb'
p Coverage.result

# file.rb
FOO = [
  { foo: 'bar' },
  { bar: 'baz' }
]

'some string'.split
             .map(&:length)

some =
  'value'

Struct.new(
  :foo,
  :bar
).new

class Test
  def foo(bar)
    {
      foo: bar
    }
  end
end

Test.new.foo(Object.new)

In this case we're not getting coverage on the constant assignment, on the second method of the string manipulation, on the multi-line assignment, on the instantiation of the struct, or on the return value of the Test#foo method.

[mame (Yusuke Endoh)]

• Status changed from Open to Assigned
• Assignee set to mame (Yusuke Endoh)
• Target version set to 2.5

Thank you for the report!

I found that #14104 changed TracePoint's lineno, which broke coverage.so. I'll fix it with ko1.

[mame (Yusuke Endoh)]

• Status changed from Assigned to Closed

Applied in changeset trunk|r61313.

---

iseq.c (finish_iseq_build): fix coverage leakage [Bug #14191]

Before this change, coverage.so had failed to measure some multiple-line
code fragments. This is because removing trace instructions (#14104)
changed TracePoint's lineno (new lineno), and coverage counter array was
based on old lineno.
This change initializes coverage counter array based on new lineno.

[mame (Yusuke Endoh)]

I have just fixed the issue. I'd appreciate if you could try r61313 and tell me if the coverage is measured correctly.

Your report was really helpful. Thank you very much!

[mame (Yusuke Endoh)]

Sangyong Sim told me that 2.5's line coverage measurement was slower than 2.4 because of some reasons. I talked with ko1, and decided to revert the changes of line coverage (2.4 and 2.5 use a special event and special instruction for line coverage). I committed r61350. This change also means that line numbers are back to 2.4. In short, everything about 2.5's line coverage should be the same as 2.4.