From: mame@...
Date: 2020-04-10T17:20:24+00:00
Subject: [ruby-core:97815] [Ruby master Bug#16776] Regression in coverage	library

Issue #16776 has been updated by mame (Yusuke Endoh).


Thank you for your report.  The reason why the method execution is missed is because:

* coverage measurement is based on TracePoint mechanism (since 2.6), and
* no TracePoint event is fired during the execution of TracePoint hooks (to avoid infinite chain of hooks).

So, this is a limitation of TracePoint.  Currently, the combination of multiple TracePoint hooks works not so great; they are completely exclusive.

This issue may be solved by improving TracePoint mechanism, but it is expensive to implement and @ko1 is negative.  How severe is this issue for you? 

----------------------------------------
Bug #16776: Regression in coverage library
https://bugs.ruby-lang.org/issues/16776#change-85033

* Author: deivid (David Rodr�guez)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
----------------------------------------
Hi!

I noticed a regression in the coverage library. I tried to write a minimal program to show it, hopefully it gives some clues or where the issue might lie.

In ruby 2.5.8 and earlier, the following program would print `{:lines=>[1, 1, nil]}`, showing that the body of the "foo" method was run once. However, on newer rubies, it prints `{:lines=>[1, 0, nil]}`, which is incorrect because the "foo" method body has actually been run once.

This is the repro script:

```ruby
# frozen_string_literal: true

require "coverage"
Coverage.start(lines: true)

code = <<~RUBY
  def foo
    "LOL"
  end
RUBY

File.open("foo.rb", "w") { |f| f.write(code) }

require_relative "foo"

TracePoint.new(:line) do |_tp|
  foo
end.enable do
  sleep 0
end

res = Coverage.result
puts res[File.expand_path("foo.rb")]
```




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