[ruby-core:97859] [Ruby master Bug#16776] Regression in coverage library

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


IMO, TracePoint hooks should have a priority.  A TracePoint hook that is first enabled should monitor a hook code that is second enabled:

```ruby
1: TracePoint.new(:line) do |tp|
2:   p [:parent, tp]
3: end.enable do
4:   TracePoint.new(:line) do |tp|
5:     p [:child, tp]
6:   end.enable do
7:     p :main
8:   end
9: end
```

```
$ ruby t.rb
[:parent, #<TracePoint:[e-mail]:4>]
[:parent, #<TracePoint:line@<internal:trace_point>:96 in `new'>]
[:parent, #<TracePoint:line@<internal:trace_point>:196 in `enable'>]
[:child, #<TracePoint:[e-mail]:7>]
[:parent, #<TracePoint:[e-mail]:7>]
:main
```

I expect `[:parent, #<TracePoint:[e-mail]:5>]` before `[:child, #<TracePoint:[e-mail]:7>]`.  @ko1, what do you think?

----------------------------------------
Bug #16776: Regression in coverage library
https://bugs.ruby-lang.org/issues/16776#change-85084

* Author: deivid (David Rodr刕uez)
* 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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