[ruby-core:113847] [Ruby master Bug#19715] Coverage oneshot_lines mode is not working after result clear

Issue #19715 has been updated by mame (Yusuke Endoh).

Status changed from Open to Rejected

Hi @ngan 

The documentation may not be clear, but this is by design. (Document improvements are welcome!)

`oneshot_lines` is a mode that reports execution at most once for each line. The record is not reset even by `clear: true`. Currently, we do not provide a way to reset the record.

The supposed use case for `oneshot_lines` is to get information for removing unnecessary codes. By periodically calling `Coverage.result(stop: false, clear: true)` on a long-running server, you can collect code line numbers that are executed. Conversely, this information will reveal the code that is most likely no longer being used.
In this use case, if duplicate line executions are reported before and after `clear: true`, it will bring unneeded overhead.

Do you want such a reset feature? If so, please let me know the use case for that.

----------------------------------------
Bug #19715: Coverage oneshot_lines mode is not working after result clear
https://bugs.ruby-lang.org/issues/19715#change-103496

* Author: ngan (Ngan Pham)
* Status: Rejected
* Priority: Normal
* Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN
----------------------------------------
Given a simple Ruby file (`foo.rb`):
```ruby
def hello
  puts "hello"
end
```

If I do the following in `irb`, I get unexpected results:
```
irb(main):001:0> require 'coverage'
irb(main):002:0> Coverage.setup(oneshot_lines: true)
=> nil
irb(main):003:0> require_relative 'foo'
=> true
irb(main):004:0> Coverage.resume
=> nil
irb(main):005:0> hello
hello
=> nil
irb(main):006:0> Coverage.suspend
=> nil
irb(main):007:0> Coverage.result(stop: false, clear: true)
=> {"/project/foo.rb"=>{:oneshot_lines=>[2]}}
irb(main):008:0> Coverage.resume
=> nil
irb(main):009:0> Coverage.suspend
=> nil
irb(main):010:0> Coverage.result(stop: false, clear: true)
=> {"/project/foo.rb"=>{:oneshot_lines=>[]}}
irb(main):011:0> Coverage.resume
=> nil
irb(main):012:0> hello
hello
=> nil
irb(main):013:0> Coverage.suspend
=> nil
irb(main):014:0> Coverage.result(stop: false, clear: true)
=> {"/project/foo.rb"=>{:oneshot_lines=>[]}}
```

You can see that in the third `Coverage.result` call, oneshot_lines did not populate despite me executing `hello`.

If I use `lines`, then it works the way I'd expect it to:
```
irb(main):001:0> require 'coverage'
irb(main):002:0> Coverage.setup(lines: true)
=> nil
irb(main):003:0> require_relative 'foo'
=> true
irb(main):004:0> Coverage.resume
=> nil
irb(main):005:0> hello
hello
=> nil
irb(main):006:0> Coverage.suspend
irb(main):007:0> Coverage.result(stop: false, clear: true)
=> {"/project/foo.rb"=>{:lines=>[0, 1, nil]}}
irb(main):008:0> Coverage.resume
=> nil
irb(main):009:0> Coverage.suspend
irb(main):010:0> Coverage.result(stop: false, clear: true)
=> {"/project/foo.rb"=>{:lines=>[0, 0, nil]}}
irb(main):011:0> Coverage.resume
=> nil
irb(main):012:0> hello
hello
=> nil
irb(main):013:0> Coverage.suspend
irb(main):014:0> Coverage.result(stop: false, clear: true)
=> {"/project/foo.rb"=>{:lines=>[0, 1, nil]}}
```

I get that `oneshot_lines` is only suppose to count the line once, but I'd expect that upon a reset/clear, it should remark the line as executed. I wasn't sure if this is expected behavior or a bug.



-- 
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