[ruby-core:114650] [Ruby master Bug#19857] Eval coverage is reset after each `eval`.

Issue #19857 has been updated by ioquatix (Samuel Williams).


> Thanks. In your case of ERB.new, the test function does not actually use its arguments.

I'm not sure what you mean. Depending on the argument, different coverage is generated. Can you explain why you think "the test function does not actually use its arguments"?

> In this case, if we ever pass a multi-line string to test, automatic merging of the coverage results would bring trouble.

```
ERB.new(File.read(path).gsub("VALUE") { value || "default" })
```

I understand your concern, and I have never seen such a code in the real world. Can you share the real world risk?

----------------------------------------
Bug #19857: Eval coverage is reset after each `eval`.
https://bugs.ruby-lang.org/issues/19857#change-104479

* Author: ioquatix (Samuel Williams)
* Status: Open
* Priority: Normal
* Assignee: ioquatix (Samuel Williams)
* Backport: 3.0: DONTNEED, 3.1: DONTNEED, 3.2: REQUIRED
----------------------------------------
It seems like `eval` based coverage is reset every time eval is invoked.

```ruby
#!/usr/bin/env ruby

require 'coverage'

def measure(flag)
  c = Class.new
  c.class_eval(<<~RUBY, "foo.rb", 1)
    def foo(flag)
      if flag
        puts "foo"
      else
        puts "bar"
      end
    end
  RUBY
  
  return c.new.foo(flag)
end

Coverage.start(lines: true, eval: true)

# Depending on the order of these two operations, different coverage is calculated, because the evaluation of the code is considered different, even if the content/path is the same.
measure(false)
measure(true)

p Coverage.result
```

Further investigation is required.



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