[ruby-core:113897] [Ruby master Bug#19715] Coverage oneshot_lines mode is not working after result clear

Issue #19715 has been updated by ngan (Ngan Pham).


mame (Yusuke Endoh) wrote in #note-1:
> `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.

Ah yes, we were looking to use oneshot_lines to determine which tests run which production files. Using `lines` is slow so I figured oneshot_lines was usable for this. We do need to clear and reset the markers after each test though. I might switch to use TracePoint since the `lines` is really slow.

----------------------------------------
Bug #19715: Coverage oneshot_lines mode is not working after result clear
https://bugs.ruby-lang.org/issues/19715#change-103549

* 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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