[ruby-core:97858] [Ruby master Bug#16776] Regression in coverage library

Issue #16776 has been updated by Eregon (Benoit Daloze).


I'm surprised too the coverage stdlib gets hit by this issue.

Maybe coverage could use a second type of internal tracepoint to fix this issue (internal coverage handlers are likely pure C and so don't emit any extra event)?

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Bug #16776: Regression in coverage library
https://bugs.ruby-lang.org/issues/16776#change-85083

* Author: deivid (David Rodr刕uez)
* Status: Open
* Priority: Normal
* Backport: 2.5: UNKNOWN, 2.6: UNKNOWN, 2.7: UNKNOWN
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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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