Issue #13838 has been reported by yui-knk (Kaneko Yuichiro).

----------------------------------------
Bug #13838: Add the ability to detect Coverage status
https://bugs.ruby-lang.org/issues/13838

* Author: yui-knk (Kaneko Yuichiro)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: 
* Backport: 2.2: UNKNOWN, 2.3: UNKNOWN, 2.4: UNKNOWN
----------------------------------------
## Description

I want to detect current status of Coverage, which is enabled or not.
Now we can detect status only trying `Coverage.peek_result` or `Coverage.result` and catch RuntimeError.
Attached patch enable us to detect status without any exceptions.

## Why

My daily work is developing a web application with Ruby.

I am using `Coverage.peek_result` to record coverage information on a per-request basis.

When recording coverage information, I want to start Coverage on a part of production servers,
because Coverage tool may have some overhead.

In this case, the code of my program looks like

```ruby
# Implement as Rack middleware
class CoverageMiddleware
  def initialize(app)
    @app = app
  end 

  def call(env)
    # To ensure return response, rescue exceptions
    before = Coverage.peek_result rescue nil
    res = @app.call(env)
    after = Coverage.peek_result rescue nil

    if (before && after)
      write_file(diff(before, after))
    end

    return res
  end
end
```

## Example

By using `Coverage.enabled?, I can

```ruby
class CoverageMiddleware
  def initialize(app)
    @app = app
  end 

  def call(env)
    if Coverage.enabled?
      before = Coverage.peek_result
      res = @app.call(env)
      after = Coverage.peek_result

      write_file(diff(before, after))
    else
      res = @app.call(env)
    end

    return res
  end
end
```



---Files--------------------------------
Coverage.patch (1.47 KB)


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